Windmilling propellers
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An aside to this discussion is how to practice/demonstrate forced approaches in a high perf single. As one doesn't actually stop the prop in a practice forced approach shouldn't one move the pitch control to lowest RPM to most accurately simulate a "dead stick" condition? I know I did and when questioned by the check pilot I gave the reason mentioned above. He said "Hmm, I hadn't thought of that."
After an excellent landing you can use the airplane again!
After an excellent landing you can use the airplane again!
In a single (no feather) you move the pitch control to full coarse in order to reduce drag and give you the best glide distance.
It used to be a demonstration as part of the Constant Speed Unit endorsement (it's a separate endorsement in Australia) to set up a glide, and then pull the pitch control back to point out the surge of extra speed.
Only if the engine has failed because you have run out of fuel. 
It used to be a demonstration as part of the Constant Speed Unit endorsement (it's a separate endorsement in Australia) to set up a glide, and then pull the pitch control back to point out the surge of extra speed.
Lack of fuel flow, assuming a flow gauge is fitted, would be the major indictaor.
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Thanks CB, that piece of knowledge wasn't current when I checked out. Constant speed wasn't an endorsement then here and I don't know if it is now!
After an excellent landing etc...
After an excellent landing etc...
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that piece of knowledge wasn't current when I checked out
Worth playing with the CSU on a single. On parachute ops years ago, we did the whole descent control on the pitch lever through to flare - with a fairly (low) constant throttle setting so that we didn't have to worry too much about engine temps.
Worth playing with the CSU on a single. On parachute ops years ago, we did the whole descent control on the pitch lever through to flare - with a fairly (low) constant throttle setting so that we didn't have to worry too much about engine temps.
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I cannot convince a non-aircrew colleague of mine that on large supercharged piston engines with constant-speed-propellers, if you lost an engine during cruise due to fuel starvation, it would continue to windmill at the selected rpm with accompanying boost (manifold pressure) and oil pressure. The only indication of the engine failure -if you missed the initial hiccup of parameters - would be the falling cylinder-head or coolant temperature and yaw and decay of airspeed.
Several posters have touched on correct principles, and some have been fairly misguided by partial facts.
A propeller governor, especially for a Hamilton Standard Hydromatic and other types of propeller systems found on large radial piston engines, doesn't work on torque, but strictly on RPM. The amount of torque produced by the engine will determine the pitch commanded by the propeller governor, in it's attempt to maintain a particular RPM...but it won't determine the RPM.
Until the propeller reaches it's high or low pitch stops, the propeller and engine will maintain a constant RPM (assuming no governor or stephead malfunctions). Once the propeller comes to rest on the low pitch stops, it's in an underspeed condition and it's RPM is a function of airspeed (assuming no engine power, or in other words, assuming no torque). If the propeller is resting on the high pitch stops, then it's reached an overspeed condition and it's RPM is a function of both airspeed and torque...engine power.
Whether the RPM gauge will indicate an engine failure is largely a function of the engine RPM at the time of the engine failure. It may, or may not show a loss of RPM. At a low airspeed, a loss of engine power may result in an RPM decay, because if the propeller is already resting on the low pitch stops or reaches them in an effort to maintain RPM via the governor, nothing can be done to keep RPM up once airspeed is no longer sufficient to drive the propeller at it's scheduled RPM. Therefore, at lower airspeeds, one may see a loss of RPM following an engine failure or power loss. At higher airspeeds, quite likely no loss will be seen.
Oil pressure often remains constant following power loss, particularly if the only change has been cessation of fuel flow. If the engine continues to turn at the same RPM, then oil pressure remains constant.
Whereas the original poster said nothing about a BMEP (Brake Manifold Effective Pressure) gauge, it need not be addressed here. It will show a power loss, but as it hasn't been included in the instrumentation stipulated in the original post, it's irrelevant.
Manifold pressure is a more complex subject, and may or may not show a decrease. The subject powerplant in the original post was equipped with a supercharger, which is geared to the engine and has an output based on throttle position and engine RPM. Whether one sees a manifold pressure drop following a power loss depends on where the manifold pressure was to begin with. One may or may not see a drop. I've experienced engine failures involving disintegration of the supercharger clutch, for example, in a R2600, in which the manifold pressure merely reduced to ambient, or barometric. I've experienced other types of power loss or failures, especially at lower power settings, in which the manifold pressure indication remained the same.
Someone suggested that because the supercharger is geared to the engine, and because the supercharger is theoretically turning at the same speed as the engine, there will be no manifold pressure loss. This isn't true. Bear in mind that because of the use of a constant speed propeller, one can increase manifold pressure substantially above barometric, with the use of a supercharger, with no increase in RPM. RPM, therefore, is not the only determining factor regarding manifold pressure, when a supercharger is used.
I recall a P2V crash (using the R3850 motor) some years ago, involving not a power loss, but a governor failure. The governor couldn't regulate speed within limits. The crew could push the power up, but the propeller would overspeed, and power would have to be retarded. The airplane would descend. Power would be pushed up again, the airplane would accelerate, and the propeller would again overspeed. The power would be retarded, the airplane would sink...and this dance continued over the course of an hour or so until the airplane finally crashed on the high desert floor.
Had the crew realized what was happening, they could have flown slowly and still used engine power. The engine RPM was exceeding limits largely because it was being driven not only by engine torque, but by airspeed. Slow down, and while full power wouldn't be available, partial power would be...and the crew could have carried power on that engine, and used it to return to the airport and land.
EGT is an important indication, or other temperature indications to include CHT (not in all circumstances). Other indications such as an ignition analyzer may also prove useful, though on a large radial engine one usually is fully aware of the power loss by simple fact of assymetrical thrust, yaw, and the heavy rudder required to keep the airplane flying straight...as well as the change in sound, and fuel flow.
Fuel flow sometimes proves to be an excellent indication of engine health, especially in conjunction with EGT, but is particularly so in the case of the scenario presented by the original poster: fuel exhaustion.
Being able to look at the full picture and make a decision before attempting to mash a feather button is important, as it's easy to rush and feather the wrong engine...particularly on a piston-powered airplane.
In a single (no feather) you move the pitch control to full coarse in order to reduce drag and give you the best glide distance.
Only if the engine has failed because you have run out of fuel
if you lost an engine during cruise due to fuel starvation
Someone suggested that because the supercharger is geared to the engine, and because the supercharger is theoretically turning at the same speed as the engine, there will be no manifold pressure loss. This isn't true. Bear in mind that because of the use of a constant speed propeller, one can increase manifold pressure substantially above barometric, with the use of a supercharger, with no increase in RPM. RPM, therefore, is not the only determining factor regarding manifold pressure, when a supercharger is used.
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As long as the prop can provide the same torque to turn the engine at the same speed, the supercharger will rotate at the same speed, and if the throttle hasn't been changed, the boost will be the same. N'est pas?
The propeller doesn't provide torque to the engine. The engine provides torque to the propeller.
So long as as the engine continues to rotate at the same speed, the supercharger will continue to rotate at the same speed, as I previously stated. This does not mean that manifold pressure will remain constant, even if the throttle position remains untouched...because manifold pressure is not merely a function of throttle position and engine RPM.
At high boosted settings, such as takeoff power, without touching the throttle position, during a power loss one will see a manifold pressure loss. The supercharger, despite turning the same RPM (assuming airspeed is adequate to drive the engine via the propeller to maintain that RPM) and despite the throttle position remaining unchanged, will show a loss in manifold pressure (trending back toward barometric).
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Whereas the original poster said nothing about a BMEP (Brake Manifold Effective Pressure) gauge, it need not be addressed here. It will show a power loss, but as it hasn't been included in the instrumentation stipulated in the original post, it's irrelevant.
BMEP = Brake MEAN Effective Pressure - Is a theoretical pressure developed inside the combustion chamber that if maintained equally throughout the two or four stroke cycle will develop a set horsepower. It has ABSOLUTELY NOTHING to do with MANIFOLD PRESSURE!!
Someone suggested that because the supercharger is geared to the engine, and because the supercharger is theoretically turning at the same speed as the engine, there will be no manifold pressure loss. This isn't true. Bear in mind that because of the use of a constant speed propeller, one can increase manifold pressure substantially above barometric, with the use of a supercharger, with no increase in RPM. RPM, therefore, is not the only determining factor regarding manifold pressure, when a supercharger is used.
And boosting manifold pressure above barometric is the whole point of the thing!!!!!!!
Pedant mode off!
Last edited by one dot right; 27th Jun 2010 at 18:36.
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BMEP = Brake MEAN Effective Pressure - Is a theoretical pressure developed inside the combustion chamber that if maintained equally throughout the two or four stroke cycle will develop a set horsepower. It has ABSOLUTELY NOTHING to do with MANIFOLD PRESSURE!!
Nope, RPM is not the only factor governing manifold pressure but it is the only factor that governs supercharger output and with a constant throttle position, which is supposedly what we're dealing with here, would be the only thing that would affect manifold pressure!
A supercharged engine developing 49" of manifold pressure during takeoff, for example, will not maintain 49" of manifold pressure, or the same supercharger output, after a power loss, even though the same propeller RPM remains.
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Guppy, a supercharger is a simple air pump ? Surely it doesn't matter whether it's being driven by an engine under power or windmilling..... if the supercharger rpm is maintained, assuming the throttle position is constant, why will the output (manifold pressure) change ?
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Please enlighten us all!
Or are you perhaps confusing Supercharging with Turbocharging which will indeed lose boost pressure after a failure due to no longer being driven by the exhaust gasses.
Or are you perhaps confusing Supercharging with Turbocharging which will indeed lose boost pressure after a failure due to no longer being driven by the exhaust gasses.
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A supercharged engine developing 49" of manifold pressure during takeoff, for example, will not maintain 49" of manifold pressure, or the same supercharger output, after a power loss, even though the same propeller RPM remains.
And yes, supercharged, not turbosupercharged.
The rest who think otherwise are sadly misinformed.
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The rest who think otherwise are sadly misinformed
Just because you say it loud enough doesn't make it so.
Last edited by one dot right; 30th Jun 2010 at 08:24.
A lot of people spouting on this thread are failing to RTFQ.
In his OP, Virgo specifically referred to a SUPERCHARGED engine in the CRUISE. Others have made the point that what he describes will indeed happen PROVIDED the pitch stop limits are not reached, and yet we are still being told what happens to turbocharged engines, and what happens on take off.
I only did 2,500 odd hours on Shackletons, which is not a lot compared to some people, but I recall only too well that on every check ride, an engine would be failed in the cruise (by the engineer cutting the fuel flow, on a signal from the checking Captain ) so that you had to go through the procedure I described in post #29.
May I suggest that before anyone else sounds off, they RTFQ, read the thread, and stick to answering the FQ.
In his OP, Virgo specifically referred to a SUPERCHARGED engine in the CRUISE. Others have made the point that what he describes will indeed happen PROVIDED the pitch stop limits are not reached, and yet we are still being told what happens to turbocharged engines, and what happens on take off.
I only did 2,500 odd hours on Shackletons, which is not a lot compared to some people, but I recall only too well that on every check ride, an engine would be failed in the cruise (by the engineer cutting the fuel flow, on a signal from the checking Captain ) so that you had to go through the procedure I described in post #29.
May I suggest that before anyone else sounds off, they RTFQ, read the thread, and stick to answering the FQ.
Last edited by oxenos; 30th Jun 2010 at 10:49.
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...will not explain to us how a functioning compressor at the same RPM as it was before the failure is somehow not compressing now!!!
No fuel, MP decreases, and depending on the throttle blade opening a little, or a lot.
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411A
oxenos is correct. The Rolls Royce Griffon was an exceptional engine, producing some 2,500 horsepower from a V12. Any more power would have resulted in torsional flexing of the crankshaft. Instead of the traditional butterfly, it had a 'Rolls Royce Coreless Valve' in the fuel injector. This is best described as a cylinder within a cylinder, such that at full throttle, there was absolutely no restriction to the flow in the inlet manifold.
The propellors were contra-rotating; the engine drove the front prop which was geared via a rack bolt to the rear prop. The CSU was so efficient that it took just one second to fully restore the RPM following a fuel cut.
oxenos is correct. The Rolls Royce Griffon was an exceptional engine, producing some 2,500 horsepower from a V12. Any more power would have resulted in torsional flexing of the crankshaft. Instead of the traditional butterfly, it had a 'Rolls Royce Coreless Valve' in the fuel injector. This is best described as a cylinder within a cylinder, such that at full throttle, there was absolutely no restriction to the flow in the inlet manifold.
The propellors were contra-rotating; the engine drove the front prop which was geared via a rack bolt to the rear prop. The CSU was so efficient that it took just one second to fully restore the RPM following a fuel cut.
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No need for you to know why, those of us whom have flown the engine types I specified previously, would know for sure,
We have examples cited from people who have flown supercharged Griffons on Shackletons that categorically state that once the status quo has been resumed,ie the prop is now driving the engine, there is no loss of manifold pressure.
In the absence of any information from your supposed font of knowledge I can only assume that the American engines that you rave about suffered excessive back pressure such as Werbil describes, and there lies the problem!
Usually when people puff and blow without any real substance to their argument It's due to lack of knowledge!!!!