Radial Engines
 

I think I am right in saying that Radial Engines always had an odd number of cylinders.

If so, can somebody please explain why ?

Thanks,
Mr G.

At the risk that fading brain cells have dropped some vital details, I recall that the firing order would be to the next cylinder after 180 degrees.

With an even number of cylinders, the engine might get confused as to which way to turn.

A firing order to adjacent cylinders would generate some interesting stresses on the mount:D

The total number of cylinders in a radial could be even, by arranging them in separate rows. The Pratt & Whitney series (and probably others) indicated the number of cylinders by the designation - an R2800 had 28 (4 rows of 7 cyls), R3600 (4 x 9) and so on.

Not quite so.
 

R XXXX does not indicate the number of cylinders. It designates the cubic displacement or close to it. The R-2800 has two rows of nine cylinders. The R-1830 has two rows of nine cylinders where the R-2600 has two rows of nine cylinders. The individual banks have an uneven number of cylinders as postulated in the first post.

All of this through the fog of time.

:cool:

radials
 

Paper Tiger
Sorry to disillusion you but US engines are designated by capacity and type
P& W R-985- is a Pratt&Whitney Radial of 985 cu.ins capacity. It is also a single - row 9 cylinder.
A Wright R3350 is an 18 cylinder Radial of 3350 cu.ins capacity.double -row(2 x 9).
A Packard V-1650 is a licence built Merlin.
A P&W R-4360 IS A 28 CYL, 4- row radial( 4x7).
The USA system for designating engines is based around capacity,whereas our system is more HP based,and capacity in litres.(conversion factor for cu.ins - ltrs = x16.38)
As a guess you can probably guesstimate the number of cylinders by dividing capacity by 110 for small engines and 140-155 for larger one s.
Lu Z will probably to put me straight if i`m talking bO*****S.

:) :)

I think it is to do with having two pistons changing direction at the same time. With an even number of cylinders, they do, which would produce a more severe vibration. With pistons as large as the ones they used, this would have been a significant factor. This is the principle behind five cylinder car engines (Volvo et. al.).

The direction of rotation is governed by the inlet and outlet valve and ignition timing, and the starter usually gives the engine a clue;)

I should have figured it couldn't be that simple, sycamore.

In case it's not yet clear...
 

Suppose you built a single-row eight-cylinder radial (a four-stroke-cycle radial, which I assume the well-known radials were). All the cylinders connect to the same crank-- right? So the #1 piston starts its downstroke, then the #2, then the #3... but as you go around the circle you'd like power strokes to alternate with intake strokes. So if #1 fires, then #2 does its intake, #3 fires, and so on around to #7 fires, #8 intakes... and then #1 is scheduled for an intake. So now what?

But with an odd number of cylinders that problem doesn't arise.

A typo in the previous post: the R-1830 has two rows of seven cylinders, of course.

Round engines are over square.
 

I’m straining my brain on this one. I attended mechanic school in 1949. What is quoted above is quite possibly the reason but the internal geometry of the engine may also come into play. On a radial engine the connecting rods are not quite the same as on a conventional internal combustion engine. On an auto engine the crank throw passes through a 360-degree path and the connecting rods pass through the same path. On a radial engine there is what is called a master rod and this is attached to the crankshaft which is similar to that of an auto engine. The center of the master rod passes through a 360-degree path. The other rods are called articulating rods and they are attached to the master rod at the periphery of the master rod and as such when the master rod passes through a circular path the articulating rods pass through an elliptical path. I believe this type of set-up can not accommodate an odd number of articulating rods. (The master and the articulating rods total up to an uneven number).

Because the articulating rods pass through an elliptical path the firing of the spark plugs must be altered so that when the engine passes through two revolutions all of the plugs fire at the same position of the piston. This is accomplished by the use of a compensated cam on the magnetos, which is profiled to cause the points on the mags to open at the correct time. The cam rings on the engine are profiled so that the valves open and close at the same time to compensate for the uneven movement of the pistons.

At least I think this is correct.

Check this out: http://www.howstuffworks.com/radial-engine2.htm


:D

And then we have the most advanced radial of 'em all, the Curtis-Wright R3350- DA/EA series, eighteen fuel injected cylinders and three power recovery turbines pumping out (largest version) 3,400 HP. SFC 'round about 0.36 pounds fuel/HP/Hr.

However, in order for them to churn out all that HP, 115/145 fuel was required.

Worked good....provided you didn't run short of oil...1.5 gal/hr as I recall.:eek:

Check out http://www.enginehistory.org/
It's the Aviation Engine Historical Society site. Great stuff. In the gallery section, one member has done some CAD images of the R3350TC, including the PRT's.
There's also an article on the development of the R2800, and the problems they encountered with crank shaft torsional flexing.

Set a record.
 

The R 3350 Turbo compound was the first A/C recip engine to develop more horsepower than its' cubic displacemnent. I remember long ago reading a US Navy publication that they had the first TC R-3350 to exceed 1000 hours installed on the wing. In that article it stated 3500 horsepower.

:cool:

And of course they sound good. :D

Cat Driver

I notice all the radials referred to are of US origin :p :p
Its like Mr P & W had a patent on them
Having worked many hours ( and nights ) on Mr Pratts fine products I'm afraid they could not hold a candle to the Bristol Beauties. :D :D

When we were getting between 800 and 1,000 hours on the wing from Pratt we were getting 2000 hours + on Centaurus.

We never changed a cylinder in anger on a Centaurus. Bit different from Pratts ! On the 1830 we got plenty of practice and you just hoped it wasn't a bottom cylinder on your shift.

Incidentally for the uninitiated the Bristols were sleeved valved
:p :p

(tongue firmly in cheek here)

The reason the English engines lasted longer is because they'd NEVER rust at all, not with the amount of oil that comes out of them! :)

The only radial I've had anything to do with is the Alvis Leonides, in the Twin Pioneer.

18 wheeler,

Alvis are Ok but you cant beat a pair of Bristols;) ;)

Hey, I've got that on a T-shirt!! :D

A pair of what?
 

Are you referring to the engine or something else?

:D

bristols
 

Lu
Seems like we on this side of the pond need to keep edificatin` you N.Americans.
Bristols-- large , round and firm,--- usually found on the front of girls. Depends upon age( of subject), but usually ,Jupiter,Mercury,Hercules, or Centaurus, in ascending order of capacity---- or size of hand for measuring..;) ;)

Sycamore trees have monkey balls
 

Thats what I was alluding to when I said engines or something else.

I believe it comes from Cockney rhyming slang.

:D

You are quite correct Lu.

The full cockney rhyming slang is Bristol City, plural . . .Cities. I am sure I don't need to elaborate.

To return to the topic, I was also very fond of the Bristol Hercules, as fitted to the Varsity on which I did my advance training.

A bit confused
 

I have maintained R-985s, R-1300s, R-1340s, R-1820s, R-1830s, R-2800s and R-2600s and I can’t for the life of me figure how the valve trains on British engines operate. Is there some source on the internet that explains it?

:confused: :confused: :confused: :confused: :confused: :confused:

Mr_Grubby's initial question has probably been answered by now, especially thanks to Lu's excellent link to the "howstuffworks" site - I shall enjoy browsing that!

However, I couldn't let pass GotTheTshirt's earlier comment about Beautiful Bristols and the predominance of PW, especially in view of Lu's latest post. I can't instantly recall how the valve drive worked (after 32 years!) but I am sure someone here can.

Meanwhile, here is a nice pic of the Bristol Hercules layout and a cylinder cutaway of its Sleeve Valve. For Eng Hist buffs, this comes from a short bio of Sir Harry Ricardo FRS who was the genious responsible for introducing this highly reliable valve design to British aero engines (courtesy of Cambridge University Eng Dept).

Through pigboat's link to the "enginehistory" site you can also find detailed colour pics of Brizzle aero engines at Midland Air Museum, Coventry. Clicking on the cutaways will produce a hi-res detail of a sleeve-valve cylinder. Hope this is of interest.

Now, where did I store my course notes . . . . :(

Speaking of Bristols, I remember the Bristol Freighter and those wonderful Bristol Hercules… Hard to imagine that the same engine had powered the Sea Fury.

On the subject of big round engines, is there anyone out there who could give a brief exposition on the workings of a rotary engine (not the 1970’s motor car version, but rotary engines as used in the Sopwith Camel and other WW1 fighters)?

I know that much of the engine (the cylinder block?) actually spun around, hence the name, but know little more than that about them. With all that spinning metal, the torque and gyroscopic precession must have been tremendous with large power changes and any rapid turns – I understand that it was faster to turn the Camel ‘the long way around’ in one direction (left or right? forget which), in what I imagine was a Derry Turn manoeuvre, making use of the precession to assist the turn, rather than in the ‘correct’ sense, where the pilot would be fighting against it. I understand that this was used to great effect in air to air tactics, where it not only got the aircraft to where the pilot wanted it faster, but foxed the opposition when the aircraft appeared to be turning in the opposite direction to the way it was actually turning.

I look forward to hearing all the accurate details from someone who knows.

Wiley

there is an active thread on rotary engines in Tech Log

http://www.pprune.org/forums/showthr...threadid=77079

A picture is worth a thousand words or, is it 1000 questions?
 

OK, I looked at the pictures of the sleeve valve cutaway and the engine minus the inlet tubes and the exhaust pipes. Regarding the sleeve valve does it move up and down to align the correct port with the correct inlet/outlet (inlet tubes/exhaust pipes? Or, does it rotate to do the same thing?

On the engine picture you can see that some of the ports are blocked and others are open or, partially opened, which naturally suggests that it is a timed operation. The porting is similar to a two-stroke diesel engine but in this case the ports are fixed and the piston moves in relation to the ports. The porting on the Bristol engine is profiled which suggests that the inlet and exhaust are controlled to time the fuel air mixture inlet in relation to piston movement as is the exhaust port.

If there is relative movement between the sleeve valve and the cylinder is it lubricated?

:confused:

Lu,

If you look again at the picture of the sleeve valve cylinder, down in the bottom left there are two gears visible. The upper one of these is the sleeve drive for the sectioned cylinder, and coming out of it on the right hand side is the crank which moves the sleeve on a balljoint. So, up and down and round and round.

Graham

Wiley,
The Bristol Frightener and the Varsity, Valletta, Viking all had Hercs but the Sea Fury had Centaurus ( same as the Ambassador - 2,650 Hp!!)

Lu, I dont know if the web site shows it but the sleeve describes an ellipse. Its driven by a crank pin from a gear wheel. I suppose after a conventional P&W the system seems a bit more complicated but in the real world it was much less trouble. No valve to burn out , no tappits to adjust every 200 hours, no push rod oil leaks etc etc! When I first got involved I could not believe that the very small crank pin that drive the sleeve would not fail every 50 hours but in over 8 years of the beasts ( Herc and Centaurus) never saw a pin fail. Also on the Centaurus as I mentioned earlier never changed a cylinder and had 1 premature removal ( super charger drive shaft seal failed and pumped all the engine oil through the supercharger)
We did over 50,000 engine hours
:) :)

The Reno Sea Fury had the Centaurus and I think they managed to get well over 3,000 HP:D :D

I loved flying behind the Vendeneyev M14P in the Yak 52. A superb piece of kit (9 cylinder supercahrged, geared, radial).

It only problem is the capability to get hydraulic locks in the lower cylindrs despite pulling through before start. You really need to drain the inlet pipes to be sure....

SSD

The Alvis Leonides required turning manually through nine blades for best results on starting. Don't know how, or if, they did that on the Twin Pioneer with the same engine.

The Bristol Freighter was the last [only?] British aircraft with the same manufacturer of airframe and engine, Not a lot of people know that!

Radials starting
 

Samuel,
All Twin-Pins carried a long pole fitted with a stiff rope loop on the end,to pull the props over b4 start to prevent "hydraulicing". Once saw a 209 crew start that way after they had run out of cartridges/ safety-discs/10c pieces in Borneo.
Another way was to get a long rope with a loop on one end, loop that over a blade,and wind the rope around the CSU dome.Then commandeer all the pax. to pull smartly on the rope as someone pulls the blade over with the "puller-over"!
Last-ditch as the Indians-sorry, Indons in this case were coming over the border!!;)

Starting Radials
 

From what I've gathered, both from personal experience and some discussions with others, there are two approaches to starting radials with respect to oil in the cylinders. On an R-2600 the engine needs to be pulled through 4 revolutions (I've done so myself many times!) to get rid of the oil in the cylinders. The reasoning behind this is that the flywheel in the starter will take no account of any hydraulic lock and will continue to try to turn the engine even with the hydraulic lock. On an engine with a directly driven starter (no flywheel/mesh system) you can pull the engine through several revolutions on the starter to clear the oil as in a hydraulic lock situation a shearpin in the starter system would break before the engine will (from what I've been told this is the situation on a DC-4 engine). I think that on a Yak-52 installation some similar system exists which disconnects the starter when it meets with too much resistance.

Anybody else with more info?

Hydraulic loch. A lake in Scotland
 

The description above alludes to getting rid of the oil in the cylinder in order to eliminate the possibility of a lock with this being done by pulling the prop through manually. This is not to say this could not be done. However when pulling the prop through and the prop won’t move beyond a certain point the only way to get rid of the oil is to pull the plugs and purge the oil out of the cylinder through the plug holes. It may be necessary to clean or replace the plugs.

In the method described above if an intake valve opens and the oil runs into the intake tube the next time that same valve opens the oil can run back into the cylinder. If there is sufficient oil present a hydraulic lock can occur when the engine is turned over by the starter. Depending on the energy imparted by the starter you can bend an articulating rod, damage a piston or blow the head off of the cylinder. In any case the engine is a candidate for heavy inspection and resultant tear down or complete overhaul and inspection.

:cool:

Having been involved in operating a few dozen Daks over the years the hydraulicing bogey man was drilled into you from cradle.
I never saw an engine hydraulic (apart from a slight hesitation on rotation)and we never pulled an engine for hydraulic damage. I know that technically it can happen but I just never saw it. Lucky I guess.

We had both inertial and direct drive starters on our machines. The beauty of the inertial starters was that you has a hand start crank. This was an operation to behold. If we had a starter failure on depature we would dispatch the aircraft on pax flights with an erk and a starting handle to get it round the houses..
You put the handle in and wound the inertia wheel until it was rotating quite smartly then you could either mesh from the ground with a pull handle or if the mesh circuit was ok the crew could mesh from the cockpit. This relates much easier than reality believe me!!

We had oil dilution on the cold weather ones ( probably the same as the Canadian ones Lu).;)

On the Vikings there was a leather boot with a rope that went over one of the prop blades and the theory was that you could start the engine by pulling the blade round with a gang of blokes:D :D Fortunately I was never lucky enough to be one of the chosen few:rolleyes:

We had Cheetahs on our Anson's and of course they never had staters so all starts were done by winding a crank on the side of the engine.
This of course took took two guys but the old boys (old when I was a lad:p ) would start them on their own by giving them a good prime and pull them over by hand a few times then they set the engine with a piston right after TDC, get in the cockpit and press the booster coil button and voila off she go !!

Some of the later Ansons had starter motors and we had an Anson ready to go on an overseas job ( magnetometer dragging!) when the starter failed. They ordered a new starter AOG from the guy in Blackpool ( ANT - Whyatt ???) paid up front and sure enough a starter handle arrived at great expence !:D :D

Samuel, wouldn't the Britannia take the prize as last aircraft to have engines (Bristol Proteus) and airframe built by the same manufacturer? Not that I actually know when the last Britannia and last Freighter were resepctively built, but I'd assume the Britannia was later!

Yes, you're correct! I had forgotten about the Britannia. It was built a long time after the last Freighter.

I believe an RNZAF Bristol Freighter Centaurus was once started by the lawn mower method of attaching a rope and pulling!

On the subject of the Leonides, as attached to the Pembroke, turning the props was the price one paid for going wherever the Station Flight aircraft was going at Eastleigh! Those flights were never dull ! That aircraft is still flying I believe.

For Lu, the motion of the sleeves, as driven by the sleeve driving cranks, via the ball joint, is a combination of reciprocating and articulating, thus rotating the sleeve as it rises and falls.
Kidney shaped ports in the sleeves became aligned with the inlet and exhaust ports in the cylinders.
From memory there were 2 inlet, 2 exhaust, and 1 common port per sleeve, but only 4 cylinder ports.
The sleeves were lubricated but cleanliness was absolutely vital in the oil supply.:)

hydraulic locks

I'm a bit confused with hydraulic locks, I can understand how you can get a lock in the bottom cylinder and how you clear it by pulling the engine through, and the oil is dissipated as the valves open.

But what happens if the engine stops with the lowest cylinder on the compression stroke? All the valves will be closed so when you turn the engine over next time, surely you will pushing the piston into the accumulated oil, which has nowhere to go - hence the lock. :(

Do you then feel the resistance through the prop and whip a plug out to allow the oil to drain free?

An explanation of how it works in practical terms would be appreciated.

I think that on a Yak-52 installation some similar system exists which disconnects the starter when it meets with too much resistance.

Not so. The Vendeneyef M14P in the Yak52 doesn't have an external starter motor. It starts by admitting compressed air into the cylinders via a pneumatic distributer to drive the engine round.

From the pilot's point of view, after priming you press the starter button with the mags off. There is a loud 'pop' as the air solenoid valve opens, followed by an asthmatic wheezing as the prop jerks slowly round. The button also activates the 'shower of sparks' magneto, so the engine eventually fires up on a couple of cylinders at least, wherupon amid clouds of smoke the mags are switched on and button is released. Vigourous pumping of the primer may be required before the engine becomes self-sustaining.

The particular problem with hydraulic locks is becuase the inlet pipes actually extend furher out from the engine than do the internal bores of the cylinders - they attach to the heads near the top of each head. So on the lower 3 cylinders the internal bore of the pipe is lower than the inside of the head, so oil can collect there. Because it is below the level of the heads, and therefore the exhaust valves, pulling through will not remove it. If the engine is started with oil in the pipes, the oil will be drawn into the cylindr and cause a destructive lock.

To overcome this, the inlet pipes of the 3 lower cylinders have drain plugs fitted at their lowest point. If the engine has not been run for a while, the cowlings should be removed and these plugs unscrewed to drain out any accumulated oil.

If a lock destroys a cylinder on start up, that is bad news. But far worse news is a 'partial lock' Here, there is a hydraukic lock which is just sufficient to bend the con rod. The engine will run OK for maybe many hours, but now contains a time bomb. At some point that con rod will fail, and may take the whole engine with it. That is *very* bad news, and is why, if you run an M14P, you must be very, very careful of hydraulic locks.

SSD

Thanks SSD, that makes sense.