were any big radials reliable

[sludge]

If you have a good maintenance program and pilots who aren't complete idiots, radials do just fine. My exp. with the 1830 and 1820 is that they are solid, predictable, reliable engines. Sure I had a few failures, thats part of flying. You may blow a jug or main bearing, but its still running and making torque - get outta the woods and deal with it. No worries.

[Feather #3]

I must thoroughly endorse what Sludge says; maintenance and handling.

The -1830 and -2800 are the standouts among the large engines.

In its later models, the R-3350-EA series, Curtiss-Wright's finest became a good engine once it got past 25hrs after overhaul. It's progress to quite high TBO's [depending on the operator; different organisations set different times] was assured if it was looked after.

We've operated our L1049 since 1996 with no failures and only 3 precautionary shutdowns; one for an oil leak and the others associated with props. That's not a bad record although we're only putting low hours on the a/c and compares very favourably with other users in this day and age.

G'day

[bobw]

Hi....flew a Convair 440 with the PW R2800 water injection, reliable to a tee. Occasionly when switching to "high blower" abover 16000' the clutch may crap out.
Also flew the PBY- Canso water bombers.....PW 1830, reliable but underpowered for the aircraft and its useage....the Super Canso had the Wright R2600's....lots more power but very tempermental and prone to carb icing. Seem to me the PW were more reliable than the Wrights as a general rule.

[Big Pistons Forever]

Hard to beat the R280. We used the DC6 for firebombing and were brutally hard on the engine. One day on short turn fire we did 11 wet max gross takeoffs in 1.1 airtime. Right after takeoff we were at the fire, back to 25 MP and then back to METO to climb away from the drop

But unlike modern t/prop and jet engines... the engine life of a big radial is directly proportional to the skill of the flight crew.

Bottom line: There is no better sound in aviation than a 4 big radial engines at cruise RPM leaned out and sync'd up.

[DC-ATE]

Well, this topic has pretty much been beat to death, but I might as well add my thoughts. The 3350 [Turbo and Straight] were nearly as good as the R-2800.....IF.....you took care of them and operated according to Wright's Specs. Some airlines in order to "compete" tried to operate them at higher power settings and consequently, the R-3350 got a bad name. I only flew the 3350 for six months [EAL Shuttle], but never shut one down. As everyone has said the R-2800 is perhaps the best of the 'big round' engines. Flew those [DC-6] for five years and only feathered ONE prop. Oil leak of some kind. Sure do miss the sounds of both the 2800s and the 3350s.

[LeadSled]

Folks,
As the old story goes: What is the difference between a DC-6 and a DC-7??
One is a four engine aeroplane with three blade props, the other a three engine aeroplane with four blade props.

The story of the R-2800 is very interesting, in the development/early production days, there were severe harmonic vibration problems, but some very smart people got to the bottom of the problems --- and the engine in service developed the good reputation mentioned here. For anybody of an engineering bent, the development story, and harmonics never observed before, and their cure, is a fascinating story.

In one day in the QF history, every Connie was on the ground somewhere with an engine failure. Mum and Dad spent almost a week, living in the "old" terminal ( a single story brick building) in Bahrain, waiting while an engine was sourced and changed on a 1049G. Qantas variously used a Lanc. and Liberator as full time engine carriers.

The reason you don't hear much about "transport" Merlins was their very low overhaul lives, and general unreliability. 500 TBO targets were rarely achieved --- when Wright R1820 and P&W R1830 regularly made 2600h. In the Qantas Lancastrians (which had to be use on "colonial routes", because US built aircraft were not permitted, in those days) an engine surviving two round trips to London from Sydney was usually about "it".

The Argonaut, a DC-4 re-engined with Merlins, was a dog of an aeroplane.

As for the pom sleeve valve engines ---- the answer to why there are none in service, but still plenty of P&W and quite a few Wright ought to be obvious. Darwinian selection!

Tootle pip!!

PS: Feather 3,
A big increase in the PRT turbine clearances doesn't hurt, and having hydraulic props. is definitely a "good thing" compared to electric props.

[Chris Scott]

So, according to you experts, the winners are: the P&W 1830 and 2800?

What a fascinating thread. LeadSled, that triggered my best laugh today!

Have only handled the 1830, serviced in the UK by Fields in the late 'Sixties. "Lost" only one in 500 hours. Not everyone was that fortunate. But will never forget sitting next to a 2800 (in the No.3 nacelle of a 6B) for 13 hours as a boy, mainly at night, en-route from Brazzaville to Nice. An occasional sight of the white-hot exhaust stack, as the gills opened, and the steady throb... Watching the often protracted procedure of firing up 4 big radials in the dusk in Africa is what first got me hooked.

BTW, no one has specifically mentioned the (sleeve-valved?) Hercules yet?

[galaxy flyer]

LeadSled

Historical question, why weren't US-built planes not permitted on those routes?

GF

BTW, fascinating thread.

[barit1]

Qantas variously used a Lanc. and Liberator as full time engine carriers.

TWA used a Fairchild C-82 N9701F (R-2800's) for like duty in/around Europe. It "grew" a J34 turbine atop the center section for duty in the sandpit.

[barit1]

Historical question, why weren't US-built planes (not) permitted on those routes?

It was a matter of UK industrial policy dating back to at least the late 20s.

I once attended an excellent presentation by Dr. Douglas H. Robinson on early transatlantic flying boat days. In essence, the specs for British-built aircraft were determined within Britain, with little consideration to potential foreign customers.

One of Robinson's illustrations was head-on views of the slender Pan Am S-42 vs BOAC's lumbering boats; given the engines of the day, the Sikorsky was much faster. Flight magazine of the day remarked how efficient the US ship was "despite its great speed"; a failure to recognize that speed was directly linked to productivity and efficient utilization.

In any event, the British continued to protect their domestic manufacturers from foreign competition, instead of developing aircraft for a global market; An object lesson for protectionist governments everywhere.

[privateer01]

R2800's were my favorite from a pilot and mechanic standpoint.

I've never so much as blown a jug on the 2800....course some of that has to be luck of the draw. We also never had the two speed blowers.

Now the 1830....I've shut down 8 engines for various reasons (blown jugs etc) all ran again without removal from the airframe.

The 1820-80.....well 16 shutdowns over the years....none of which ever ran again without overhaul. There aways seemed to be a disproportionate chance the master rod would get lunched during the ensuing carnage.

1820-80B, and -86 had scavage oil filtering and were a bit better in this regard.

In fairness....2 of the 1820 failures were the same engine and were traced to overhaul shops failure to assemble the crankcase and accessory housing and line bore the supercharger bearing area before bearing installation. Result was a busted blower shaft and no boost....


I'd love to rehash the extremes some operations went to to increase engine longetivity........Snake oil, voodoo, virgin sacrifice, Magneto retardation, etc... all tried....some successfully some not.

Lets hear yoru favorite.

[GotTheTshirt]

Worked on 1340, 1830 and 2800
We were never short on work and plenty of O/T

Why is it only US radials get lots of mention ? I guess because anyone who worked on them has lots of stories to tell.

The BEST radial engine in civvi use was the Bristol Centaurus with the Hercules in close place.

The UK ARB ( CAA ) TBO on the 1830 was 1200 hours and many did not make it.
In all fairness the problem we had in UK and SA ( both Fields O/H shops) was lack of spares.Many pistons and cylinders were run 4 and 5 lives and reused.

The Centaurus was 2200 TBO and we trialed to 2400.
In over 5 years with 6 engines operating some 80,000+ hours we had 1 ( ONE) failure and ONE cylinder change ( due to sheared plug on maintence.)
Maintenance on the Centaurus was oil and plug changes not like 1830 with cylinder changes, mag changes and jolly old routine valve clearance checks
3 guys half a day and knuckles bleeding

On the 1830's cylinder changes were routine and generally easy except the bottom ones. The mags were a pain until we cut the access panels in the firewall.
Leaking push rods were also a pain ( Not fitted on Centaurus ) especially as in UK we had to wirelock the gland nuts

[privateer01]

"In all fairness the problem we had in UK and SA ( both Fields O/H shops) was lack of spares.Many pistons and cylinders were run 4 and 5 lives and reused."

+1.

As supplies got harder to find....that became alot of places including the USA

[LeadSled]

Folks,
I should have been a little more precise in my phraseology. I referred to "colonial routes", I should have said "Imperial" route, as dictated by the UK Colonial Office ( and maybe that should be the Colonial and Commonwealth Office -- don't take me to task, I am not a historian).

Of course, at the time, many Commonwealth Governments looked down their nose at US airlines, being private, as opposed to nationalized industries, much the political preference of the day. This was the period when the remaining public shares in Qantas were purchased by the Commonwealth.

Not entirely thread drift, but all non-UK manufactured aircraft brought into Australia were subject to a 7.5% British Preferential Tariff ----- the pommy manufacturer only had to state they "could" build a competitive aircraft (which they always did say) for the tariff to be applied. This nonsense lasted into B727 days, and would you believe, even applied to military aircraft. DoD or whatever it was called at the time had to pay Customs and Excise 7.5% on all the Neptunes and early Hercules --- what a nonsense exercise --- a transfer from one Can'tberra set of books to another.

Re. the UK manufacturers not building for the market, the honorable exception was the BAC-111, which was built to a specification from a (Gasp!! Horror!! off with their heads) private enterprise organization, British United Airlines, and good old Freddy Laker.

At one stage, unions were refusing to build Viscounts for "private orders", ie: Eagle and BUA.

Tootle pip!!

[A37575]

We don't seem to hear the same stories about the linear engines like the Rolls-Roce Merlin that you do about the radials. Did the Merlin really have a better reliability record ?

I had two tours involving 3000 hours on the Lincoln Mk 31 based at Townsville, Australia in the Fifties. Engines were RR Merlin 85 and 102's. During that time I experienced 30 engine failures - these were called blow-backs usually at high power. Each required an engine change. Other pilots on the squadron also had engine failures so from that I can say with some certainty the RR Merlin in Lincolns wasn't that reliable.

[bcgallacher]

About 1953 as a boy I flew from Singapore to London in a BOAC Argonaut, on 3 occasions we turned back with an engine feathered - once out of Singapore and twice out of Karachi.We also had a departure delayed as the cowlings fell off an engine when the aircraft was ferrying from Kallang airport to Changi military airport - the runway at Kallang was too short for a high weight takeoff.When we finally got out of Singapore the journey took a week!I believe there were 3 engine changes.I think this was about par for the course as nobody seemed to think this flight was unusual in any way.

[WHBM]

Originally Posted by barit1

TWA used a Fairchild C-82 N9701F (R-2800's) for like duty in/around Europe.

BOAC, once they had got rid of their old WW2-derived fleet of freighters, used Avro Yorks chartered in from various UK independent operators during this period. It was pretty much a full time operation for at least one, sometimes two, such aircraft with whoever had the contract in a particular year, and the aircraft were just based directly at the BOAC maintenance HQ at Heathrow.

[Brian Abraham]

I thought I'd post the following excerpt from Graham Whites book on the R-2800, so that the younger generation raised on the revolting stench of kerosene, might understand the breed of aviators who took to the air with the aphrodisiac smell of high octane in their nostrils, and did battle with the elements, while tending with skill and care to these mechanical marvels of propulsion.

Operating, Service Difficulties

Sitting behind the power of one, two, or four R-2800s can be an intimidating and yet exhilarating experience. The pilot/flight engineer needs the dexterity and skill of an organ player as throttles, mixture controls, propeller controls, cowl flaps, magneto switches, boost pumps, and oil cooler flaps are manipulated in a mechanical ballet of flying arms and fingers. At the same time, the condition of the engine(s) is/are monitored via the oil pressure, cylinder head temperature, oil temperature, fuel pressure, tachometer, and BMEP meter. All R-2800s being operated now use direct crank electric starters. Engaging the starter emits that sweet sounding high pitched whine that could only come from straight-cut, precision reduction gearing. Bringing an R-2800 to life is like awakening a giant dinosaur: somewhat reluctant, but once in motion you have a tiger by the tall. Normal procedure is to motor the engine over on the starter for about four revolutions of the propeller, then energize the magnetos. During the initial cranking, a judicious amount of prime in the form of raw gasoline is injected into the intake system. This is where a skilled pilot/flight engineer can show his worth by judging what amount of prime is required based on ambient temperature and how long it has been since the engine was last shut down. As soon as the mag switches are energized, providing the correct amount of prime has been administered and the engine is in reasonably good mechanical condition, the cowl will shudder as the first couple of cylinders realize that a highly volatile and combustible mixture is trapped inside and a source of ignition has just been provided. Blue smoke from entrapped oil burning with the fuel/air mixture starts to emit from the exhaust stacks. As cranking continues, more cylinders come on line announced by further clouds of dense blue smoke. When all eighteen cylinders are hitting-some better than others, the blue smoke starts to diminish. Even so, it takes several minutes for the lower cylinders, the ones that are more vulnerable to oil build-up, to clear. This is evidenced by characteristic puffs of blue smoke from individual cylinders blowing out of the exhaust stacks, almost like smoke signals. Warm-up is then commenced at 800 to 1000 rpm. Anything less will not ensure adequate oil flow to the bearings and anything greater imposes too much thermal stress and loading on the engine.

Following is an operating procedure issued by Pratt & Whitney during the 1950s for CB engines. This procedure has been paraphrased and abbreviated by the author. Even so, it gives an idea of what it takes to operate an R-2800.

The following engine operating recommendations are intended to promote the most successful aw efficient use of the Pratt & Whitney R-2800.

1. Ground Operation

A. Ground Considerations- Since the R-2800's engine cooling provisions are not primarily designed for ground operation, additional consideration is required, not only to the engine but also to the accessories. To assist in maintaining adequate heat dissipation throughout the engine during warm-up and to provide maximum cooling thereafter, cowl flaps are left wide open during all ground operation.

The fuel booster pump is switched on prior to starting the engine. Especially on installations equipped with one-position boost pumps, the initial surge of boost fuel pressure, sometimes referred to as “hammer effect," due to "hydraulic-locking," is often sufficient to unseat the carburetor's mixture control plate and introduce a variable quantity of fuel into the intake system. This variable quantity of fuel may be sufficiently large to confuse priming requirements. By actuating the boost pump prior to starting, however, any excess fuel is dissipated during cranking, thus maintaining priming requirements at a relatively constant level.

B. Starting-Like any piston engine, a rich mixture is required for starting. The standard priming system is designed to provide sufficient fuel to start a cold engine during cold weather operation. In very cold conditions it may be necessary to actuate the primer continuously to get the R-2800 fired up. Conversely, in more temperate or tropical conditions, it is found that the standard system has a tendency to flood unless used intermittently with considerable caution. Therefore, like many aspects of the R-2800, sense of "feel" is required. The standard primer fuel flow is 250 to 300 pounds per hour. However, for aircraft operated in warmer climes this flow rate is reduced to 100 to 15 0 pounds per hour.

Prior to starting, the throttle should be positioned to yield 800 to 1000 rpm after the engine starts. Mixture is set to idle/cutoff and the propeller is set to fine pitch or max. rpm. At this point the engine is motored with the starter and magnetos off to purge the cylinders of residual fuel. This also insures initial lubrication of the reduction gearing is adequate. Should any hesitation or stoppage of propeller motion be noted, cranking should be discontinued immediately and the cause removed. This would indicate a classic case of a "hydraulic-locked" cylinder due to excessive fuel and/or oil. The primer switch should be actuated as required at, or just prior to, fifteen blades (six blades if engine was shut down within one hour). It is more desirable to underprime than overprime and risk the effects of a blower fire. A blower fire is due to a lean mixture backfire that causes fuel inside the supercharger to ignite. They are typically fairly harmless and will quickly bum themselves out as all the fuel is consumed. At fifteen blades (or six blades with a warm engine) the magneto switch is positioned to "Both" and cranking continued until the engine fires. The initial rpm surge should not be permitted to exceed 1100 rpm. After the engine fires, hold continuous prime, adjust the throttle to 800 rpm and note a rise in oil pressure. At this point, as the engine burns off the prime, the mixture control is slowly moved to the auto-rich position and priming discontinued when approximately 100 rpm decrease is noted.

The throttle is then adjusted to 1000 rpm and warm-up is considered complete when the oil temperature reaches 40°C.

C. Idling -Correct idle mixture is extremely important in obtaining a combination of proper engine operation with the least tendency toward spark plug fouling. In the idle range, fuel flow varies with throttle opening. Idle mixture must be set to accommodate desired ground idle as well as windmilling (touchdown), acceleration (wave off), and reversing operational characteristics. To best satisfy these requirements and minimize spark plug fouling, idle mixture should be adjusted at the speed most commonly used for ground operation (800 to 1000 rpm).

Idle mixture is not automatically compensated for changes in altitude. Therefore, when operating from a sea level base to a field above 4000 feet, it may become necessary to lean with the mixture control at the higher elevation, i.e., the mixture lever is positioned between auto-lean and idle cut-off. Of course, a pilot/flight engineer would need to exercise caution, however, to preclude taking off with a leaned mixture that would result in a severely damaged engine due to detonation.

When extended ground operation is necessary, it is helpful in preventing spark plug fouling to open the throttle to field barometric pressure for one minute during each ten-minute period of idle. Ground maintenance and flight personnel should be cautioned against excessive ground power and/or excessively long periods of power application during ground burnout procedures. If the procedure used is going to take effect, it should do so in ten or fifteen seconds. Also, excessively high power or long periods of power application on the ground when engine cooling is least effective will probably result in oil leaks from "cooked out" seals, possible ignition harness or low tension coil failures, or engine rubber mount core distress from excessive heat.

Again, as a concession to the marginal cooling available during ground operations, using reverse thrust for reverse taxiing is to be avoided due to its adverse effect on engine cooling. The cooling system and cylinder head temperature (CHT) locations were not designed to accommodate reverse flow.

D. Engine Run Up-Scuffed pistons have resulted by pulling power too quickly after starting cold engines. This is due to the aluminum pistons expanding at a faster rate than the steel barrel. Pilots have to exercise care not to exceed 1000 rpm until the oil temperature has reached 40'C. When the oil has warmed to this temperature, the propeller check may be started. The propeller check is performed at 1600 rpm.

While still at 1600 rpm and if desired, the spark advance check may be accomplished by switching to the "Cruise" (25 degrees of advance) position and then back to the "Takeoff and Climb” (20 degrees of advance) position, noting a BMEP fluctuation each time the switch position is changed. Usually, a satisfactory shift prior to the last descent will suffice, however, a visual check should be made to assure that the switch is in the "Takeoff and Climb" position. A takeoff made with spark advance in the "Cruise" position may result in a complete engine failure. This foregoing procedure is now all but redundant for the R-2800 because most, if not every, R-2800 operating in the world has had this feature disabled.

Engine power output is checked at a manifold pressure equal to field barometric pressure, as indicated by the manifold pressure gage prior to starting. Revolutions per minute at this mani-fold pressure should be approximately 2050-2200 rpm, depending on the propeller low pitch stop setting, the accessory load on the engine, and relative wind, regardless of field elevation. BMEP and fuel flow will vary with local atmospheric conditions. Should the rpm not fall within the prescribed rpm limits for the particular installation, a check for improper low pitch propeller settings and/or engine malfunction may be the culprit.

The blower shift check, if desired, may be performed by switching from low to high blower at field barometric and noting a rise (approximately of 2 in. Hg) in manifold pressure, a decrease in BMEP, and a momentary drop in oil pressure. The blower is then shifted back to the low position which is indicated by a drop in manifold pressure to the original value, an increase in BMEP, and a momentary drop in oil pressure. Should erratic indications of a shift be observed the cycle may be repeated after first idling the engine at 1000 rpm to allow the clutches to cool for two minutes. For en route run-up, a switch position check is usually regarded as sufficient.

The magneto check is also performed at field barometric pressure. The normal drop on one magneto is 50-75 rpm (5-7 BMEP) and should not exceed 100 rpm (10 BMEP). The maximum spread between the drops of right and left magnetos should not exceed 40 rpm (4 BMEP).

The ADI system is checked as follows, pump switch may be actuated at field barometric pres-sure and a partial system check made by noting the water pressure light, ADI pressure of approximately 26 or 30 psi (depending on installation), and a fuel derichment of approximately 100- 150 pph (pounds per hour) fuel flow. The ADI flow at lower powers is negligible and may be left on without appreciably depleting the ADI supply. In any event, it is desirable to switch on the AD1 at least several seconds prior to the application of takeoff power to purge the system of entrapped air. When ADI is needed, it is really needed!

II Flight Operation

A. Takeoff-Again, cooling is a prime consideration. A conscientious effort should be made to secure the lowest practicable cylinder head temperature immediately prior to the application of takeoff power for the following reasons: (1) the power available at 2800 rpm increases with decreasing CHT at an approximate rate of 30 bhp per 20 degrees Centigrade; (2) common types of spark plug deposits become more conductive with increasing temperature and their ground-ing tendencies can be reduced or eliminated through the control of peak CHTs; (3) since CHT will rise 40 to 60 degrees Centigrade during a normal takeoff, less cowl flap drag will be incurred in establishing the desired 190 to 200 degrees Centigrade CHT for climb; and (4) the tendency toward detonation and/or pre-ignition decreases with a cooler CHT. If a malfunction were to occur which could lead to possible detonation, operating at a cooler CHT would delay or prevent this detonation.

Minimum pre-takeoff CHTs may be attained: (1) through efficient use of the briefest possible engine run-up time necessary to ascertain normal functioning; (2) through use of minimum post run-up rpm commensurate with generator and ventilating system requirements; (3) by facing the aircraft directly into the wind when practicable; and (4) by delaying cowl flap closure to the takeoff setting until immediately prior to the application of takeoff power. Desired CHT before takeoff is on the order of 15 OOC. There is no minimum pre-takeoff CHT.

Although it is desirable that all types of aircraft are faced into the wind during run-up, this is particularly important for the Convair twins. In this case, a downwind component will not only reduce the cooling air flow over the engine, but it will also impede the efficient operation of the augmentor tubes, resulting in a further rise in CHT.

With a fixed throttle setting from the start of takeoff to the point at which the first power reduc-tion is affected, increasing airscoop ram pressure, resulting from the increase in airspeed, will cause a manifold pressure rise of from one to three depending on flight techniques. If lift-off is abrupt, a momentary decrease of one or two inches of manifold pressure will result due to the change in airscoop attitude. This situation is somewhat analogous to compressor stall with an axial flow gas turbine. These characteristics should be anticipated and the throttle monitored in an effort to maintain the desired manifold pressure.

During a wet takeoff, the ADI pressure, fuel flow, and BMEP are monitored to assure proper ADI operation. It is not uncommon to see the maximum "no flow" pressure limit (32 psi on Convair twins, 29 psi on DC-6s) when the ADI pump is first turned on. Although this condition is referred to as "no flow" it really means "no flow" to the engine. Actually a total flow of about 150 pph per engine is being pumped through the lines and returned to the ADI tank through the vapor vent line. As the throttles are opened beyond 36-38 in. Hg, a pressure drop (3 to 7 psi on Convairs, 1 to 4 psi on the DC-6), depending upon the particular engine installation, will occur, indicating that ADI is flowing to the engine. The desired AD1 pressure with flow is 22 to 25 psi. If at any time during a wet takeoff the ADI pressure drops below approximately 18 psi and the carburetor enriches to more than 1800 pph fuel flow, the rich mixture, resulting from both fuel and ADI flow, will probably cause a severe power loss which will be indicated on the BMEP gage. A slight throttle closure may reduce ADI flow requirements sufficiently to restore derichment pressure and result in a BMEP higher than that for dry operation.

In the event the foregoing procedure proved ineffective and conditions permitted a takeoff with dry power on the affected engine or engines, dry takeoff power is set and the ADI switch turned off.

Maximum flight safety dictates the use of full authorized power for every takeoff and retaining this power and takeoff flap setting until the gear is retracted and it is apparent that all obstacles will be cleared by a comfortable margin. The use of takeoff power is authorized for a period of two minutes and, subject to limiting cylinder head and oil temperatures, this authorization may be utilized when required by abnormal conditions. Normally however, takeoff power is used for much shorter periods that seldom exceed one minute even at maximum gross weight on a hot day. Of course, when this procedure was written, Corrosion Corner did not exist!

In the interest of preserving the supply of ADI fluid, ADI switches may be turned off at any time during the first power reduction when the manifold pressure is below the dry takeoff rating. An increase in fuel flow should be noted as the ADI is switched off. Approximately one to one and a half gallons of ADI are consumed per engine during a takeoff.

B. Climb-Climb power should be set with rpm and manifold pressure as selected from the appropriate climb chart for the existing carburetor air temperature and pressure attitude. Throttles should be adjusted to yield the same manifold pressure for all engines. By setting equal air flow or engine output in this manner, the resulting fuel flow may be more easily monitored. BMEP differences between engines with equal manifold pressure, rpm, carburetor air temperature, and fuel flow are due entirely to unequal accessory loads, engine condition, and/or instrument inaccuracy. Here it should be noted that on some installations cabin superchargers (pressurization systems) will absorb as much as 6-8 BMEP.

It is important that fuel flow be monitored throughout the climb to ascertain that it is within prescribed limits. The minimum fuel flow limit is not an engine limit at normal climb power. It is, however, a carburetor limit designed to obviate damage which might otherwise result at higher power, where the margin between a safe fuel flow and engine detonation is diminishing. At climb power, therefore, it is considered safe to continue operation when the fuel flow is at, or 50 pph below, the minimum fuel flow, providing CHT and CAT limits are observed. If the climb fuel flow falls more than 50 pph below published minimum, power should be reduced by increments of 100 bhp until the fuel flow is not more than 50 pph below the limit for that particular reduced power. CHT and CAT limits must still be monitored. Because fuel/air mixture strength versus air flow, schedules vary to accommodate individual aircraft airscoop and exhaust system characteristics, note that minimum climb fuel flows differ among aircraft and carburetor settings.

Power settings for each blower configuration are made with manifold pressure and rpm. Fuel flow is frequently checked to assure it is within limits. The carburetor knows what power the engine is pulling only by measuring the air flow that the engine pumps to produce this power. The carburetor then meters fuel according to the mass air flow it senses. In order to properly monitor fuel flow and evaluate engine performance, the engine should be kept on the pre-arranged schedule of air flow that can only be set by the proper rpm and manifold pressure for the existing CAT and pressure altitude. The fuel flow-limits given, therefore, are only valid at the prescribed rpm, MP, CAT, and pressure altitude schedule.

Blower Shifting-A blower shift may be accomplished as indicated on the climb chart even though low blower cruise is anticipated. This practice will eliminate one desludging shift during the subsequent cruise period. To shift from low to high blower, merely retard the throttle by three or four inches of manifold pressure, actuate the supercharger switch, and readjust the manifold pressure to that called for by the high blower climb chart.

Not surprisingly, during climb operation in hot weather the cooling air flow, required to main-tain desired CHT (190 to 200°C) is necessarily greater than in winter. Two choices are available to the pilot/flight engineer: (1) through higher airspeed, or (2) higher cowl flap opening. In general the former is preferable from the standpoint of total trip fuel and block speed. Larger cowl flap gap and maximum L/D (lift/drag) airspeed can only be Justified when a higher angle (as opposed to the high rate of climb) is required.

C. Cruise Operation-Upon reaching cruise altitude, climb power is maintained until the indicated airspeed slightly exceeds that anticipated for the particular altitude, gross weight, and cruise power to be used. This higher airspeed will afford a cushion so that the airspeed dissipation incurred during trim and power adjustments (blower shift, etc.) will not result in an airspeed at the start of cruise less than that anticipated for cruise.

From the cruise chart for the selected bhp find the appropriate manifold pressure for the existing pressure altitude and carburetor air temperature. This will be listed directly opposite the pres-sure altitude and under the carburetor air temperature. From this point move toward the right and downward staying within the parallel lines to find rpm, blower ratio, BMEP drop, fuel flow, and nominal BMEP. Cruise power will then be set in this sequence:

1. Set cruise rpm.

2. Shift blower, if required.

3. Set cowl flaps to the angle anticipated to yield 190 to 200'C cylinder head temperature when stabilized.

4. Adjust throttle to selected manifold pressure, allowing for any known gage error.

5. While carefully observing BMEP, lean mixtures individually until BMEP has been reduced from its maximum value (best power) by the amount of the prescribed BMEP drop. Since the transport carburetor has been specifically designed to facilitate manual leaning, a dis-tinct rise in BMEP should be seen during the initial leaning process. If this initial BMEP rise is not observed but instead an immediate decrease in BMEP is noted, the carburetor, even though in the auto-rich position, is at or slightly on the lean side of best power in the cruise range. In this case intermittent prime may be used to determine best power. Since the BMEP drop setting is based on a constant manifold pressure, it is essential that airspeed and altitude be held constant during this step. A change in airspeed at constant throttle affects ram and therefore manifold pressure and BMEP to the extent that an airspeed change of ten knots can result in as much as a five BMEP change. This gives an indication of the powerful power enhancing aspect of ram air induction.

6. Readjust cowl flaps to provide the desired CHT, 190 to 200'C. When stabilized, cross check engine instruments. With equal manifold pressure, rpm, carburetor air, and cylinder head temperatures, equal engine air flow is normally obtained. With identical BMEP drop settings, fuel/air ratio and therefore fuel flows will also be equal, regardless of the condition of the
ignition system. Any difference in fuel flow under these conditions must be due to instrument inaccuracy, either flowmeter or manifold pressure, or to a mechanical malfunction, such as a stuck valve or broken pushrod, which affects mixture flow. In summary, BMEP differences will be due entirely to unequal accessory loads, instrument inaccuracy, and/or mechanical discrepancies.

7. Once cruise power has been set and stabilized, the maximum difference in indicated BMEP, after allowing for that due to unequal accessory loading, should not exceed 10 BMEP. With discrepancies greater than 10 BMEP, the pilot/flight engineer would make a note of it to assist in troubleshooting.

Mixtures adjusted in this manner should remain substantially the same regardless of small throttle adjustments necessary to counteract small changes in airspeed, altitude, and/or CAT. Mixtures, however, should be periodically checked during cruise and adjusted as required particularly after appreciable changes in CAT, power, or altitude. Mixture strength or BMEP drop can be quickly checked by applying prime in varying amounts to determine best power or peak BMEP.

.

[Brian Abraham]

Note that throttles were first set according to manifold pressure and they were not moved. This procedure affords the simplest and quickest adjustment to cruise power since it involves the fewest control movements. Another advantage Is that by setting equal air flow (rpm, MP, CAT, and CHT) and fuel/air ratio (BMEP drop) on all engines, any discrepancies are in greater evidence and in-flight troubleshooting is facilitated.

it is recommended that blowers be momentarily shifted to the opposite ratio once during every two hours of cruise operation. This procedure is effective in purging the clutch chamber of sludge build-up, which in their advanced stages can render a blower shift impossible. The shock that usually accompanies a blower shift is not harmful to the engine, but may be objectionable to passengers. This shock can be minimized by reducing the pumping load on the supercharger through a manifold pressure reduction of approximately 4 inches while making the shift. No change in rpm is necessary. The use of auto-rich mixture during this procedure is beneficial for several reasons. Most important, the change in fuel/air ratio will alter the temperature pattern within the combustion chamber and cause undesirable deposits to flake off and be exhausted thus prolonging spark plug life.

D. BMEP Fluctuations-13MEP fluctuations associated with lean cruise mixtures (10 to 12 BMEP drop) are attributed to one or a combination of several phenomena characteristic of lean mixture operation depending on the specific circumstances of each individual case.

From the classical curve of BMEP response with mixture strength at fixed throttle and rpm, it should be remembered that at and around best power the manifold pressure response is relatively flat but becomes increasingly steep with leaner mixtures. Thus, while the effect of any fluctuation in engine input may not be visible on the torquemeter at richer mixtures, the effect of this same magnitude of input fluctuation becomes increasingly magnified on the torquemeter with the leaner mixtures. In addition, marginal ignition has a tendency to exacerbate this condition even further as do partially fouled plugs since the leaner mixture may cause partially fouled plugs to misfire, which would otherwise fire normally at the richer mixtures.

To further compound this situation, the cooler combustion temperatures of the leaner cruise mixtures are conducive to certain types of plug deposits not associated with the hotter richer mixtures. It is for this reason that P&W recommends the application of prime for 30 to 60 seconds should severe BMEP fluctuations develop after prolonged lean mixture operation. Under these circumstances when BMEP fluctuations develop with time and are indicative of incipient cold plug fouling, the severe combustion temperature change resulting from the use of prime is beneficial in causing undesirable plug deposits to flake off from thermal shock and be passed harmlessly through the exhaust system.

On the other hand, if severe BMEP fluctuations occur from the start of lean operation, the other engine instruments should be consulted to aid in determining the primary cause of the situation. If all other instruments are normal and steady, this could be an indication of an ignition or spark plug problem that has existed all along but remained unnoticed at the rich mixtures. The previously mentioned bum-out procedure might help if fouled plugs are the cause. Use of an ignition analyzer would also help at this time to check the remaining parts of the ignition system to determine any maintenance action that might be indicated.

Pressure pulsations, peculiar to some carburetor airscoop installations, may cause a fluctuating signal in air metering forces in the carburetor of sufficient magnitude as to be transmitted to the fuel metering section and result in a fluctuating fuel flow which may or may not be picked up by the flowmeter. This engine input phenomenon will not affect torquemeter stability at rich mixtures but will become visible at the leaner mixtures due to the steeper BMEP response at these lean mixtures. Carburetor heat door rigging should be checked for security in this case. In many instances of this nature the following heat door manipulation proved successful with the DC-6 type of installation. Move the carburetor heat lever out of full cold slowly until the CAT gage just starts to increase. Then return the lever back toward cold a small increment to obtain the same CAT that previously existed in full cold, making the last movement of the lever toward the full cold position. In essence, this leaves the heat door open the small amount necessary to bleed higher pressure air from behind the engine into a lower pressure turbulent region immediately downstream of the sharp bend in the induction system. The overall effect is to dampen the pressure pulsations created at the bend making for steadier fuel metering.

In some cases, engine vibration could cause pulsating impact pressure metering through the automatic mixture control that could indicate maintenance action on the automatic mixture control (AMC) unit. In other cases, engine excited vibrations could cause mixture control plate oscillations. In either of these instances any resulting fuel flow fluctuations would not affect torquemeter response at rich mixtures but could very well be visible at lean mixtures. Mixture control rigging should be secure and on occasion it has been found helpful to make the last mixture control adjustment toward the rich position to preset the linkage toward that direction.

It goes without saying that the use of lean mixtures indicates utilization of the so-called long range mixture control plate. This plate results in a flatter fuel flow response with mixture control lever travel in the leaner range.

E. Icing

Keeping in mind the old adage, "Prevention is better than cure," when icing conditions are anticipated, it is desirable to apply preventative carburetor heat rather than risk the possibility of having to employ the more drastic deicing procedures once icing has occurred. A carburetor air temperature of 15 to 20°C is usually sufficient to prevent severe power loss when entering icing condition if applied several minutes prior to entry into those conditions. The automatic mixture control requires three to five minutes to adjust to large temperature changes and may tend to overcompensate for temperatures appreciably above standard. It is desirable, therefore, to enrich the mixture prior to the application of carburetor heat and delay resetting the chart BMEP drop to allow the automatic mixture control time to stabilize. New power settings should then be made for the existing carburetor air temperature. For operators using 25 degrees spark advance in cruise, it should be noted here, that spark must be retarded to the normal 20 degrees position before applying carburetor heat. Again, it should be noted that when this procedure was written, most R-2800s still had the automatic spark advance installed and operational.

When preventative preheat is applied, the maximum carburetor air temperature limit in low blower is 38°C In high blower the maximum CAT is 15°C; however, this limit has been extended to as high as 30°C for some cruise power settings. It is mandatory that these higher CAT limits in high blower, along with the specified BHP, RPM, BMEP, and CHT limits, not be exceeded. If any of these limits are exceeded, the maximum CAT limit reverts to 15°C.

In connection with preheat application, it should be recognized that, with the carburetor heat control in a fixed position, CAT will fluctuate with changes in power, airspeed, cowl flap opening, and particularly changes in the moisture content of the air. It is necessary, therefore, to monitor CAT to assure that sufficient CAT for ice prevention is maintained and that the above mentioned limits are not exceeded.

The first indication of carburetor ice is normally a change in fuel flow and BMEP, which may or may not be accompanied by a decrease in manifold pressure. If ice forms in the air metering elements of the carburetor, a false decrease in air flow will be sensed and the carburetor will reduce fuel metering proportionally to the reduction in air flow indicated by this faulty sense. If this icing occurs during cruise when the mixture is already on the lean side of best power, it has the same effect as further leaning the mixture, thus effecting a further drop in BMEP. Another less common type of carburetor icing may be encountered when descending through a warm moist, region with cold-soaked fuel in the tanks. The fuel, acting as a refrigerant, may cause ice to form in the bleeds between the air chambers of the carburetor, thus increasing the metering suction differential and fuel flow. If the mixture is adjusted to the lean side of best power when bleed ice occurs, BMEP will initially increase. However, if allowed to progress, power will reach a peak and decrease as the mixture enriches further. Throttle ice, screen ice, or any induc-tion ice that restricts air flow would be indicated directly by a loss of manifold pressure and a decrease in fuel flow proportional to the reduction in air flow. This reduced air flow would also be indicated by a loss in BMEP, which in all probability would be the first sign noticed by the pilot.

In the event that carburetor ice occurs, accompanied by a decrease in fuel flow, normal correc-tive action is to: (i) select normal 20 degree (takeoff and climb) spark advance, (11) move the mixture control to auto-rich, and (Iii) apply full carburetor heat for 30 seconds. If icing has been allowed to reach an advanced state where engine power is greatly reduced, the preheat effective-ness of the engine will also be reduced. It may be necessary to apply full preheat for a longer period of time. The carburetor heat control should then be moved slowly toward the cold position and a cheek made of fuel flow and BMEP to assure that the ice has been removed. If determined that the carburetor is free of ice, the CAT should be readjusted to maintain a minimum of 15°C.

Should icing conditions progress far enough to seriously impair engine power, it may be found difficult to obtain enough preheat to deice the carburetor and engine induction system. In this condition the use of continuous primer may be found useful in restoring enough engine power to reestablish a heat source.

When the fuel temperature is known to be well below freezing and bleed-air ice is encountered, as evidenced by an increased fuel flow, the following delcing procedure should be used: Apply carburetor heat to maintain the maximum preheat permissible for that particular power combination. As much as five to fifteen minutes or longer at maximum preheat temperature may be necessary to restore normal operation. If the carburetor has enriched sufficiently to bring about a severe loss in power, the mixture should be manually leaned to restore the desired fuel flow and BMEP. This manual leaning, however, should be practiced only in the cruise or climb power range, with the exception of emergency conditions that may dictate this procedure at higher powers.

After manual leaning fuel flow and BMEP should be closely monitored be cause mixtures will tend to lean out rapidly as the ice is dispelled. With normal operation restored and the ice contributing condition still present, a carburetor air temperature of 15°C should be maintained.

Carburetor alcohol, in the opinion of a few operators, has been helpful in ice elimination, although heat is generally found to be the more effective remedy.


Wing and tail anti-icing for Convair twins is accomplished by routing heated air, taken from the engine augmentor muffs, through ducts in the leading edge structures. Occasionally, in extreme icing conditions, the desired climb and cruise CHT of 200°C has been found to be incapable of adequate heat to the anti -icing system. Under these conditions it is permissible to raise CHT as necessary to a maximum of 232°C provided the following procedure is followed:

1. Engine operation must be confined to normal 20 degree spark advance.

2. Place mixture control in auto-rich.

3. After CAT, CHT, and engine operation have stabilized, it is permissible to manually lean to a maximum of 2 BMEP drop.

F. Descent-If high spark advance was used during cruise, a recommended time for shifting to normal spark is just before starting descent while the mixtures are still leaned. A shift at this point will be evidenced by a positive indication on the BMEP gage whereas a shift during descent is not so apparent, especially if mixtures have been moved to a richer position. In all cases, however, the return to normal spark advance must be accomplished before the final approach and a positive indication of shift should be observed on the BMEP gage.

With pressurized aircraft, the rate of descent is not normally restricted by passenger comfort considerations, and many operators have found it expedient to maintain cruise altitude until relatively close to destination before starting their descent. This procedure permits rapid passage (approximately 2000 feet per minute) through turbulent strata at a conservative airspeed which will impose the least passenger discomfort and likelihood of structural damage from turbulence.

With power combinations of high rpm and low manifold pressure the centrifugal loads of piston movement are no longer sufficiently cushioned by the combustion chamber gas charge and they are transmitted through the link rods to the master rod bearings. These power combinations are known to be detrimental to master rod bearings and if frequently used for prolonged periods of time can eventually lead to bearing distress, thus they should be avoided. In other words this condition is "reverse loading," further described in Chapter 3, under the subheading "Master Rod Bearings." A good rule of thumb for reduced power setting is that a minimum of one inch manifold pressure should be used for each 100 rpm.

Engine stability also dictates that when power is reduced it should be accomplished by a reduc-tion in both manifold pressure and rpm. While it is true that some difficulty may be encountered in maintaining desired cylinder head temperatures during descent at reduced power, these cooler CHTs and the resulting engine instability are largely due to reduced manifold pressure and intake port temperature. It is also true that a reduction in rpm will further cool CHTs, however, it will also facilitate more stable engine operation by allowing more time for the combustion cycle of the slower burning mixture.

It is a safe, although somewhat wasteful procedure, to place mixture controls in the auto-rich position when departing cruise altitude. To effect greater economy, especially on long descents, mixtures may remain manually leaned, however they should be closely monitored to eliminate any tendency toward instability or backfiring which could come about with appreciable changes in altitude, power, and carburetor air temperature. Engine prime may be used to check BMEP drop and mixtures adjusted as required. During a descent with lean mixtures, BMEP and MP must be limited to the maximum cruise values so they also must be monitored and power reduced accordingly.

Blowers may be shifted at any convenient time during descent that power requirement can be met in low blower.

G. Approach -During this period cockpit controls are positioned to prepare the aircraft and engines for the intended landing or possible go-around. If low blower ratio, auto-rich mixtures and takeoff and climb spark advance have not already been selected, they should be at this time. If carburetor heat was used during descent and is not required for a balked landing, it should be removed well in advance of anticipated touchdown to allow time for the automatic mixture control to adjust to the colder temperature and preclude excessive leaning should a go-around at high power be necessary.

it is recommended that approach rpm not be set until the landing gear is extended. This will minimize the detrimental effect associated with operation at high rpm and low manifold pres-sure. When employing this procedure, however, caution must be exercised not to carry low rpm too far into the approach pattern. Should a go-around be necessary or any situation arises where high power is required quickly, the engine is better prepared to provide this power when the rpm has already been advanced.

Whenever the use of full wet takeoff power is anticipated in the event of a rejected landing, ADI should be switched on in sufficient time to allow the system to bleed. At powers less than 1000 bhp or 123 BMEP ADI flow will be negligible and its use should not be postponed beyond the pre-landing check.

H. Landing-Propeller reversing provides more effective deceleration at higher airspeeds and should, therefore, be initiated as soon as possible after the nose wheel is touched down. In manipulating the throttles, it has been found generally desirable to pause momentarily at the reverse idle detent before applying appreciable reverse thrust. This will reduce the yaw tendency that would accompany differing rates of propeller blade actuation and engine power response.

Cowl flaps should be positioned full open as soon as reverse power is applied. The engine baffles, cowling, and CHT instrumentation are designed for fore-to-aft air flow, and are much less effective during reverse pitch operation at low airspeeds.

Propellers should normally be returned to forward.pitch before the airplane has decelerated to 40 knots. Below this speed severe flight control buffeting is usually encountered and exhaust fumes may enter the cabin ventilation system in an objectionable quantity. Nothing like poisoning the passengers with carbon monoxide! Throttles should be returned directly to 1300 rpm and then retarded as required for taxiing. At low airspeeds, reverse propeller wash tends to starve the carburetor scoops, richening the fuel/air ratio at low rpm to the point that backfiring or popping may occur, particularly with throttles in the reverse detent. If desired, positive return to forward pitch may be checked by momentarily depressing the feathering button and observing a decrease in rpm. Correct idle mixture adjustment is of utmost importance to consistent reversing and unreversing performance and also to smooth engine performance during final approach with windmilling propellers and partially closed throttles.

1. Taxi and Shutdown-As previously stated, cowl flaps should be full open for all ground opera-tions, even in cold weather, to prevent excessive temperatures which may not be reflected on CHT gages.

Preference should be given to the 800 to 1000 rpm range for which the optimum idle mixture has been set. This will extend spark plug life considerably. Of course, rpm consistent with genera-tor requirements will take precedence.

Shut down with the mixture control whenever the CHT has dropped to 200'C. It is suggested that throttles are positioned to 1000 rpm and tachometers observed as the mixture control is slowly moved to idle cutoff. A rise of 10 to 20 rpm before dying indicates a correct idle mixture.

If for any reason it is desired to close cowl flaps, this should be delayed until at least 15 minutes after shutdown to allow residual heat to escape. Without this precaution fried ignition harnesses and damaged seals may be the result.

[Brian Abraham]

Operating Difficulties

The foregoing abbreviated and paraphrased process gives the reader a good indication of what pilots/flight engineers from a bygone age had to contend with in order to safely transport passengers. With such a complex and idiosyncratic mechanical marvel, it was inevitable that operating difficulties would arise-and they did in spades. Like the skilled organ player alluded to above, the life expectancy of the R-2800 hinged on good operating practices. As with all large, high performance aircraft piston engines, it had its sensitivities. Even so, some problems could not be overcome even in the most skilled hands. Perhaps the most common difficulties experienced by commercial operators were spark plug fouling and top piston ring land failure. As we shall see they were both connected.

By the time the CB series of engines was being commercially operated it was what is known in industry as a "mature" product. Furthermore, it had been developed into a high performance engine and consequently shrinking margins of error. And yet commercial operators demanded ever increasing times between overhaul.

Starting out with a simple spark problem, a chain of events could lead to catastrophic engine damage. At wet takeoff power, a CB engine is producing 2400 horsepower at 2800 rpm. This means 23 power events per second. Although the flight deck or cockpit is well instrumented, these instruments cannot instantly react to the aforementioned 23 power strokes per second. For instance, the CHT has a relatively slow response to temperature change. At the beginning of a takeoff roll and full takeoff power is applied, it takes approximately 15 to 20 seconds for peak temperatures to be reached. Clearly, at maximum power and minimum speed cooling is inadequate. This results in hot spots occurring, particularly at the rear of the cylinder heads. This situation is aggravated if hot heat-range spark plugs are installed in the rear position. These hot spots now induce pre-ignition which quickly degenerates to the point of top piston land overheating, broken spark plug nose ceramics, and loss of BMEP. This chain of events typically originates in the upper cylinders and yet ironically, the only cylinders instrumented for CHT are #8 and #9, both of which are located in the cooler running lower section of the engine. By the time over-temps are observed for CHT serious damage has already wreaked havoc inside the engine and the hot running upper cylinders are already well into pre-ignition. One preventive measure that some operators found to be successful was the practice of installing a colder heat range plug in the rear positions. With hot plugs installed in the rear position, some degree of pre-ignition would occur at each takeoff. With this kind of thermal and mechanical distress, the top ring land is softened. After many takeoffs, the top ring land opens up and allows an excessive clearance to develop. After hundreds of takeoffs, the top ring land is opened up to the point where it no longer gives adequate support for the ring. Under normal operating conditions, rings rotate in their groove. With a damaged top ring land, the ring gap eventually coincides with the widest part of the ring groove-typically during a takeoff when temperatures are at the maximum and probably aided by pre-ignition. The now-softened ring land now offers minimal support and V2 inch to 1/8 inch of the top ring breaks off due to fatigue failure. As takeoff power is reduced to cruise power, the piston land cools off and the piece of broken piston ring is trapped in the groove. As the flight continues or on subsequent flights, the piece of broken piston ring flutters until it finally hammers its way out and escapes into the combustion chamber. As this piece of piston ring bounces around inside the combustion chamber, it eventually peens over the spark plugs. If the operator is in luck, the offending piece of piston ring will pass harmlessly through the exhaust. The damaged piston, particularly around the area of the broken land, acts as a glow plug that quickly deteriorates into complete piston failure by burning down through the lands. This classic piston failure invariably occurs at the rear of the piston adjacent to the exhaust port area.

The foregoing describes the most common manifestation of piston failure and pre-ignition along with spark plug failure, i.e., nose ceramics. By far the most common form of piston failure is by excessive temperatures. This can lead to other types of mechanical failure. When operated in pre-ignition mode. pressures inside the cylinder are two to three times that of normal operation. This puts additional load and stress on the valve train. Remember, the R-2800 opens its exhaust valve 70 degrees before bottom dead center. With an engine that is operating normally, a significant amount of residual pressure still resides inside the cylinder at the point of exhaust valve opening. Initial opening of the exhaust valve imposes a heavy load on the cam ring, pushrods, rocker arm, and valve. When this residual pressure is increased two or threefold, the resulting excessive loads on the valve gear lead to accelerated wear and eventually failure, usually a scuffed cam ring lobe. By "tricking" the engine with colder heat range plugs in the rear positions, many of these failures can be headed off by postponing the onset of pre-ignition. However, a ham fisted pilot/flight engineer can still cause distress to the engine if takeoff power is applied too suddenly. For several reasons, power applications on the R-2800 need to be added slowly: (1) temperatures have more time to stabilize without developing hot spots and (11) many gear trains inside the engine are heavily loaded, especially the blower drive gears which need to spin up a supercharger impeller 7 to 8 times crank speed. With a sudden acceleration of the engine these gear loads are magnified.

The Ethyl Corporation, the world's largest supplier of tetraethyl lead when it was commonly used, issued a report in the 1950s. They found that lead deposits on spark plug nose cores reacted with each other. As temperatures increased, new compounds were formed of higher melting points and higher insulating value. This in turn caused the core nose insulating value to stay above the critical value at which spark plug misfire occurred. If the temperature rise was rapid, i.e., our ham fisted pilot/flight engineer slammed the throttles forward, the deposit would lower in insulation value. The critical point, or worse, could occur allowing the classic copper flow scenario whereby the plug is shorted by bridging the gap. Of course, at this point the plug is rendered useless. Again, good operating procedures could have alleviated some of these plug maladies.

Ground Fouling

Ground fouling of the spark plugs is a function of idle mixture strength and the temperature of the plug electrodes and nose ceramics. Since the plug temperatures at idle are essentially the same as the CHT, it follows that ground fouling tendencies are the same for all plug heat ranges. In other words it make no difference whether the plug heat range rating is hot or cold. If the idle mixture is too rich, ground fouling will occur. The plug heat range rating is only valid at maximum or takeoff power. When ground fouling occurs, it is due to excessive carbon deposits on the plugs which then cause misfiring. This, however, can be rectified by burn-out procedures.

Problems of Oil Viscosity at Start-Up

At low temperatures aircraft oil congeals and takes on the consistency of molasses. Highly viscous oil can wreak havoc with an aircraft engine lubrication system by causing excessively high oil pres-sure and little or no oil flow. 0il flow may be reduced to the point where metal to metal contact can occur resulting in local seizure. Abnormally high oil pressures are generated, both on the pressure side and the scavenge side. This leads to blown seals, burst oil coolers, and burst oil lines. Two methods of controlling this damage are at the disposal of the designer. One is the controversial "oil dilution" system. As its name suggests, the oil is diluted via the oil scavenge line. The pilot/flight engineer has the option to inject raw gasoline into the oil system, while the engine is still hot, prior to shutting the engine down. Even on a frosty morning, the oil will be considerably less viscous and consequently cause less harm to the engine on start-up. As the engine warms up, the gasoline evaporates off. However, there is a serious downside to oil dilution. Gasoline acts as an excellent solvent, especially inside the bowels of an engine. Sludge is that nasty looking black stuff resulting from the by products of combustion. Its make-up includes carbon, acids, and water. After a number of hours have accumulated on an engine, sludge builds up, particularly in those areas exposed to centrifugal force such as inside crank pins and propeller domes. After oil dilution, special maintenance procedures are usually called for such as cleaning oil screens and filters to remove the sludge broken loose due to the dilution process.

Another method of increasing the rate of oil temperature warm-up is the stand pipe. A typical oil system for an R-2800 may contain up to 30 or more gallons. Rather than circulate all 30 gallons, it is advantageous to only circulate the amount of oil necessary to accomplish lubrication requirements. This may be as little as a couple of gallons. Built into the de-aerator is a stand pipe that only allows its contents to be circulated. As the engine warms up, a valve inside the oil tank opens and allows the full contents of the tank to be circulated. Another key role of the stand pipe is that of ensuring an oil supply in the event the propeller needs to be feathered. This is especially important if the engine suffers a catastrophic failure that result in the contents of the oil tank being dumped overboard.