Before the Robinson, what percentage of training ships ... er, strike that, ships used in training had low-inertia rotor systems? (People will buy what they want Lu, no one has forced those training facilities to buy a Robbie. Indeed you should be asking yourself why they do, even at increased insurance rates ... Market driven economy here, they want it 'cause they like it)

I ask because it stands to reason that all who were flying higher inertia systems came to the robbie, and without the proper training to respond in a timely manner to certain flight conditions, were killing themselves.

Sure, the Robbie requires one to be sharp, the arguement possibly being that you have to be sharper than in something else (arguement in JH about the Hughes 300) to stay on top of it.

Yxcapt, if one is trained properly, the bird is plenty of fun! I'm sorry to hear that perhaps you were not with some who might have been.

[ 26 December 2001: Message edited by: RW-1 ]</p>

Frank Robinson once told me he had conceived the R22 over a period in which the US was training tens of thousands of helicopter pilots for Vietnam, and his attempts to interest his various employers in the small personal helicopter had been driven by the expectation that these people would need personal helicopters when they were demobilised.
The big manufacturers, however, had been bitten that way before. Sikorsky, Piasecki, Hiller and Bell all expected a "helicopter in every garage" scenario to develop after the Second World War, only to be sadly disillusioned.
Some people have claimed that Robinson only makes this claim to forestall potential liability; I think, however, that there is truth in it.
As to the claim that Robinson didn't put tipweights in his early machines because he "never thought of it," believe it if you want. He spent every waking moment thinking about the helicopter from 1957 to the day it flew; he previously worked for Beoing-Vertol who (as Piasecki) started putting tip weights in blades in the 1940s.

Here are some recommendations the FAA made in 1995 for the R-22... The complete text of this document can be found at:

<a href="http://www.opspecs.com/AFSData/FSBRs/Final/R22FSBR1.TXT" target="_blank">http://www.opspecs.com/AFSData/FSBRs/Final/R22FSBR1.TXT</a>

13. MISCELLANEOUS

13.1 The following recommendations of the FSB pertain to the
certification of the aircraft and suggested design changes to certain
systems as improvements deemed necessary for ensuring safe operations
of the R-22.

13.1.1 Carburetor air temperature system should
incorporate a relocated probe for accuracy of readings of real time
carburetor air temperatures. Application of carburetor heat should
be initiated at all low power settings (approaches and autorotations)
regardless of atmospheric conditions to preclude engine stoppage due
to carburetor ice and reinforce pilot training.

13.1.2 Improved rotor speed governor system for the R-22
to reduce the possibility of rotor speed decay due to pilot
inattention.

13.1.3 Longitudinal and lateral dampers in parallel with
the R-22 cyclic controls to impede abrupt movement of the cyclic.

13.1.4 Low rotor RPM warning system horn should be made
more audible. Wiring through the headphone (ICS) system or audio
panel may increase pilot awareness.

13.1.5 Redesign of cyclic system to include incorporation of
dual cyclic controls as opposed to single teetering control system so
as to increase pilot accessibility at each station.

13.1.6 Modification of Rotor/Engine RPM monitoring system
(tachometer) to increase visible marking range for usable rotor RPM
range (e.g.; 50% to 116%)

13.1.7 Increase inertia of main rotor system

13.1.8 Revise FAR Part 27 to consider main rotor system
inertia in single engine helicopters.

To: Tain't natural

I believe the primary reason for adding the tip weights was to establish the mass balance of the blade. On early Sikorsky blades they used lead shot which was fixed into the tubular spar of the blade. With the advent of the metal blades they used metal weights to establish the spanwise mass balance and the weights could be moved chordwise to neutralize the tendency for the blade to climb or dive. I think the same basic principle applied to all helicopters at that time. Of course the addition of the tip weights added a higher moment of inertia to keep the blades moving in the event of a power loss.

Portion of article on AVweb.
For complete article see: <a href="http://www.avweb.com/articles/rotorrpm.html" target="_blank">http://www.avweb.com/articles/rotorrpm.html</a>

&gt;"Helicopters with low-inertia rotor systems are extremely unforgiving of low-rotor rpm. Actually, all rotor systems are unforgiving of low rpm, but a low-inertia system loses rpm faster, which requires the pilot to react quicker to prevent low-rotor rpm from reaching the critical stage.

At this point, many helicopter pilots ask "why not just add some blade tip weights to, say, a Robinson R22 helicopter, to make it into a high-inertia system?"

"It's not as easy as that," says Frank Robinson, the R22's designer. "Rotor blade tip speeds are similar for all helicopters regardless of the size of the machine, because they are all limited by the speed of sound in air. The stored energy of a tip weight is only dependent on tip speed, therefore, a one-pound tip weight added to the 50-foot diameter rotor of a large helicopter would store the same energy as a one-pound tip weight added to the 25-foot diameter R22 rotor. However, the centrifugal force produced by a tip weight is inversely proportional to the rotor diameter, so the one-pound tip weight would produce twice as much centrifugal force in the R22 rotor as it would in the larger helicopter rotor, even though it would not store any more energy. The increased centrifugal loads carried by the blades, the pitch change bearings, and by the rotor hub would all be twice as great. Clearly it is very difficult to engineer a small helicopter with a high-inertia rotor." "&lt;

_________________

Frank Robinson's statements about the same amount of energy in both rotors and about the centrifugal ratio of 2:1 between the rotors are correct.

I believe that his position breaks down when he does not consider that the large rotor has four times the area of the small rotor. If both rotors have the same disk loading then the small helicopter is one quarter the weight of the large helicopter. In other word; the small helicopter actually has an increase of 4-times the relative energy of the large helicopter.

It appears, if my calculations are correct, that for the same increase in centrifugal effect the smaller helicopter actually has twice the increase in relative energy.

He also mentions that "Clearly it is very difficult to engineer a small helicopter with a high-inertia rotor" and yet it is claimed that the very small (ultralight) UltraSport helicopter has enough inertia to land, takeoff and re-land in autorotation.

_____________

There is no intent to find fault with the R-22 helicopter, merely clarify facts and features.

heedm, or others may wish to recheck the physics.

[ 28 December 2001: Message edited by: Dave Jackson ]</p>

It would seem to me that on larger helicopters, where the “tip weights” are added to establish the mass balance of the rotor blade, the engineers have taken into consideration the fact that the weights will have to be added and the manufacturing tolerances of the blades being quite close the tip weights will fall into a fixed range. Knowing this they can calculate the loads of the blade on the rotorhead and allow a sufficient safety factor. It should also be noted that the high inertia rotor systems are not made that way by the addition of tip weights but by the weight of the blades themselves. If this were the case then Frank Robinson could have calculated the amount of weight addition necessary to provide a higher moment of inertia to his blades. Another point is that in AD 95-26-04, which dictated, the addition of cautions in the R-22 and R-44 POHs also stated that it was recommended that Robinson do something to increase the moment of inertia. If he had not calculated the centrifugal loads in the initial design then it would seem that in order to do so at this time he would have to completely redesign the rotorhead and the blades to take the additional loads.

This in MHO makes his statement about the difficulty of designing a high inertia rotor system in a small helicopter a bit self serving.

[ 28 December 2001: Message edited by: Lu Zuckerman ]</p>

I do believe that in the early Sikorsky craft like the R4 only static balancing was done - if they weighed the same they were deemed to be a match. As a result some of those machines would shake the fillings out of your teeth. (I'm open to correction here, it's just what I've heard.) Frank Piasecki would weigh his blades, then hang three of them up and swing them. On the one that swung slowest, he would move a balance weight closer to the hub. The one that swung fastest, he'd move the weight towards the tip. Voila - three dynamically balanced blades.

To: T'aint natural

When I was first exposed to Sikorsky helicopters we worked on HOS-1s and R-4s but at the level of instruction we never got into the mass balancing of the fabric blades and wooden tail rotors. The S-51s that I maintained had just been converted to having hydraulic boost and the fabric blades had been replaced by metal blades. Our helicopters still had a three blade tail rotor made from wood. These too would eventually be replaced by a two blade tail rotor made of metal.

When I went to work for Sikorsky I was involved in a long term training program that included class room instruction and working in the shop to include building blades, mass balancing blades and whirl testing of blades to establish aerodynamic properties and to establish neutral climb and or dive tendencies.

The blades were balanced on a knife edge balance beam that had a fixed weight on one end. The weight was held in a neutral position with a mechanical lock. When the blade was attached the lock was released and the weight would move down and the blade would move up. A machined metal weight was attached in a neutral spot on the blade tip. The tip cap and the attaching screws were weighed and then set aside. Smaller weights and attaching hardware were placed on the blade outboard end until the blade was in perfect balance. Then the weight of the tip cap and screws were removed and the tip cap attached which kept the blade in balance. The tolerance was ¼ inch ounce.

The blade CG was calculated and this information was stenciled on the underside of the blade.

The blade was then sent to the whirl stand. Two brand new blades would then be installed on the whirl stand rotor head and a third master blade would also be installed. The master blade had built into it all of the desirable aerodynamic and aeromechanical characteristics. The pitch link for each blade had a proof ring (strain gage) to measure the feedback forces from each of the three blades. First the blades were spun up and measurements taken along with a blade track using a canvas strip. The trailing edges of the two blades under test were bent up or down to bring the blades into track. On the second spin up they would check the feedback forces on the two test blades cross checking them against the master blade. Other adjustments were made until the forces on all three blades were the same. Then the blades were checked for a tendency to climb or dive when cyclic and collective pitch were input into the system. If the blade wanted to climb the tip cap on that blade was removed and the balance weights were moved forward. If the blade wanted to dive the opposite movement of the weight would be made. Then the tip cap was replaced and the whirl test would then verify that the two test blades had the same characteristics of the master blade.

Hopefully I didn’t leave anything out or get the sequence mixed up. This all happened in 1955-56.

There has been some concern about the amount of rotor inertia in the R-22.

I just calculated the time to fully dissipate the energy in the rotors of both the Robinson R-22 and the Schweizer/Hughes 300C. The data used for the helicopters' moments of inertia, tip speeds and horsepowers etc. came from Prouty's 'Helicopter Performance, Stability and Control'.

It is interesting to note that both helicopters appear to have almost identical rotor decay rates; at least from a theoretical perspective

Has anyone done autorotations in both helicopters and can comment from a practical perspective?

R22 shut down procedure
 

Hi all,. .been chatting to a mustering pilot (r22) in Oz here and here told me standard practise for shutdowns was to turn off the mags. He had actually been told company policy was not to pull the mixture/cutout as cable breaks in the outback were too problematic(?).

Having thought this through a wee tad..................well a little fuel in the pots of a warm/hot engine will vaporise quick smart so shouldn't be a problem.

Initial reaction was "you what" (yrs of being told/shuting down meself the standard way) but really nothing wrong here...........or is there

Opinions Please (horror stories due to ......gratefully accepted)

Cheers & fly safe. .Hone

Im not totally sure but I have often wondered the same thing, I mean isnt that how one shuts off his car? Although being young I have never dealt with a car with mixture control.

. .Although I would still stick to the factory recomended procedure. <img src="wink.gif" border="0">

[ 23 January 2002: Message edited by: baranfin ]</p>

This is based on what I learned over fifty years ago (52 to be exact). If you shut the engine down by turning the mags off and the twist grip is in the secured position the vacuum behind the butterfly will cause a very significant increase in the suction (I was told that there is no such word it is a differential of pressure). This will draw in a large amount of fuel from the idle jets and possibly the main jets depending on which side of the butterfly they are located. This raw fuel will be ingested into the hot cylinder and it may as stated above vaporize but it is still highly combustible. If there is a hot spot in the cylinder the fuel will ignite and the resultant firing of an individual cylinder could develop sufficient force to crack the crankshaft.

later model cars are turned off by the computer(fuel and spark together) a lot of later carbyed cars used to have devices that turned the fuel off when the ignition was switched off(fuel cut off soliniods) to provent run on from a hot engine. older cars had less compression and diddnt suffer from running on so much.. .i dont know about cracking the crank lu and i dont see how there could be more vacuum when the engine slows down but the best way to shut an engine down in a plane would be to take away the fuel so a flick from the magneto wont start the prop when your having a bit of a look at it.. .helicopters its harder to accidently turn the engine and cause any unwanted spark so it probably doesnt matter so much.

if you dont use the mixture cutoff, how do you know its servicable? <img src="confused.gif" border="0">

R22 maggie check 75%
 

i think the magie check should be done at 104% insted of 75%. its much easier to tell a crook plug. i wonder why they changed it?? <img src="mad.gif" border="0">

noise abatement ?

Have heard the cooling fan is subject to cracking due rough running at that speed.

Here in the UK we have some very cold and damp days, especially at this time of year, I feel that if you didn't run the fuel out of the system before earthing your mags it could store a problem for the next time the craft was started up, with the possibility existing that the previouse or next pilot could/be a student who left the throttle open enough to cause some initial start up possibility of an overspeed, also excess fuel could drain into the oil and create an explosive possibility in the crankcase!. .but why not follow the manufacture's route, and when was the last time anyone was stuck for a wire breakage on the fuel cut off?. . <img src="eek.gif" border="0">

Sorry, I seem to have posted this answer on the wrong thread, should be on Mags shutdown R22, many apologys

[ 24 January 2002: Message edited by: Vfrpilotpb ]</p>

To: vorticey

On opposed engines used on a helicopter you do not have the flywheel effect of a propeller but you do have a flywheel which has a relatively high moment of inertia. When you shut down by turning off the mags the engine will continue for several revolutions creating a high vacuum behind the closed butterfly drawing in fuel from the jets. As I had indicated if this fuel is drawn into a cylinder that has a hot spot (carbon build up on the valves or on the cylinder or plug the fuel can ignite. Under normal start-up of the engine the starter is providing the motive power and all cylinders should start firing in sequence after the initial firing of a single cylinder. However, at shut down there might be only one cylinder that fires and it must rotate the crank along with the resistance of the other cylinders and the weight of the rotating mass. This can put a localized torsional stress on the crank and if sufficiently strong can cause the crank to crack. The US Army had a lot of problems on their engines used on the H-13s and the H-23s suffering cracked cranks. Although not from improper shut down but it illustrates that certain conditions can cause the crankshaft to break.

Another problem is fuel entering a cylinder and being ignited by a hot spot while the intake valve is open resulting in a backfire against a closed butterfly valve on the carb.

[ 23 January 2002: Message edited by: Lu Zuckerman ]

[ 23 January 2002: Message edited by: Lu Zuckerman ]</p>

Same here. We were told that the check was to be done at 75% to prevent cooling fan cracks and excessive stresses.

Also something to do with vibration alterations when you do get a duff-un.

"Some days you are the pigeon, some days you are the statue!"

MY THEORY IS THAT CUTTING THE IGNITION SOURCE ALLOWS UNBURNT FUEL MIXTURE TO WASH LUBRICANT FROM CYLINDER BORES CAUSING DAMAGING FRICTION UPON STARTUP,IF THIS OCCURS REGULARY THE RESULT. .WOULD BE PREMATURE WEAR AND LOSS OF VALUBLE COMPRESSION.KEPT IT AS SHORT AS I COULD (COULD HAVE GONE ON & ON ETC).