Question on CSP when engine quits

[piperboy84]

Does the windmilling effect at best glide speed during engine failure with a CSP (on a single engine airplane) provide enough RPM (with throttle full open) to create the oil pressure needed by the governor to move the prop to full course? Anyone actually been in this situation and were the results of shifting to course noticeable in enhancing the glide?

Edit to add: And if so, does this apply from both the engine failing in the cruise configuration with the RPM provided by windmilling being enough to maintain the course pitch and also in takeoff allowing to move from fine to course?

[john_tullamarine]

In years long passed, I flew various jump ships, generally an old C182A. SOP on descent was to pull full coarse and then use the prop control as an drag modifier during the descent. Worked a treat and makes a BIG difference to gradient.

[9 lives]

If your engine has stopped for a reason other than oil pressure failure/internal mechanical failure, you should expect that a windmilling engine will provide enough oil pressure to move the pitch to coarse, if it is that type of propeller. Note that if the engine is allowed to windmill to a stop, you may no longer be able to select coarse or feather pitch, due to fine pitch blade latches.

Selecting coarse pitch will have favourable affect on gliding. For one of my planes, this is vital, as the power off (engine running or not) fine pitch glide is very steep, and selecting full coarse completely changes the glide characteristics to be entirely fine.

Note that in the case of a failed engine which is windmilling, throttle position will not affect how the engine operates if it is not creating any power.

[piperboy84]

Note that in the case of a failed engine which is windmilling, throttle position will not affect how the engine operates if it is not creating any power.

I thought throttle being fully open would create less of a vacuum in the intake manifold allowing the engine to turn easier and hopefully giving sufficient RPM to work the governor?

[ShyTorque]

I thought throttle being fully open would create less of a vacuum in the intake manifold allowing the engine to turn easier and hopefully giving sufficient RPM to work the governor?

But with the throttle fully open the pistons have to compress a full charge of air on every compression stroke.

[piperboy84]

Quote:
I thought throttle being fully open would create less of a vacuum in the intake manifold allowing the engine to turn easier and hopefully giving sufficient RPM to work the governor?
But with the throttle fully open the pistons have to compress a full charge of air on every compression stroke.

So its "6 and a half dozen" then if you leave the throttle open the compression stroke using more energy to compress, close the throttle and the intake stroke takes more energy due to the vacuum?

[oggers]

Does the windmilling effect at best glide speed during engine failure with a CSP (on a single engine airplane) provide enough RPM (with throttle full open) to create the oil pressure needed by the governor to move the prop to full course?

It stands to reason that supply pressure to the governor would be adequate due to the requirement for the engine driven pump to provide sufficient pressure for lubrication even at idle speed, whilst having to be limited by a pressure relief valve at higher revs.

I understand that in the case of a full feathering prop (so not usually fitted to a single), the feed to the governor from the oil tank must be lower than the feed to the engine pump to provide an oil reserve for feathering in case of a leak. That would further suggest that a windmilling prop and governor pressure alone are sufficient.

But with the throttle fully open the pistons have to compress a full charge of air on every compression stroke.

Ah, but you get most of that effort back on the 'power stroke' (even without combustion). So in theory the net position is the engine will windmill quicker with the throttle open, not that I've seen it recommended anywhere....

[horizon flyer]

ShyTorque you are correct about the compression but think of it as a spring once over TDC the gas pressure pushes the piston down and on the intake stroke it does not pull a vacuum so less drag. On old carbed cars if flooded the technique was to gently floor the accelerator and spin the engine to the rich mixture out, it always turns faster take your foot of and it slows down. This works on aero engines as well.

[sycamore]

pB84,suggest you go up to about 4000 ft,overhead an airfield/strip ,and shut down the engine;then try pulling back to coarse whilst opening /closing the throttle,and noting the differences in ROD in each case....repeat as necessary,and let us know the results.........

[dirkdj]

May I suggest you have a look at the book written by Nate Jaros. He is an F16 instructor and Bonanza owner. The title is Engine Out Survival Tactics.

[TheOddOne]

Thank you. Just bought that for Kindle - only £4.99. A little light bed-time reading!

TOO

[terry holloway]

The best advice is to read the POH for the particular aeroplane and nail the correct speed. If you are really high there is a good chance of reaching the nearest airfield, but if not the priority must be to select a decent field and landing in it - having gone through the re start drills. Charles Church died because he tried to nurse a failing engine home. He crashed in a small one having flown past some really good ones.
I've only had one proper failure and that was in a twin ( a Dove ), and it's true what they say: "it takes a little longer to get to the scene of the crash in a twin"! I just made it into Dauville in a gradual descent ft from 5,000ft with the good engine on max continuous, which made it start to fail!

[9 lives]

read the POH for the particular aeroplane and nail the correct speed.

Well, a hot button topic for me: Which correct speed? The POH will state a speed for "best glide" (it's a certification requirement). That speed is the speed to fly for the least altitude loss per distance traveled. This is of course very important if you're over the water trying to make it to the coast.

However, another speed which you should consider will be the faster speed, probably not stated in the POH, from which you can execute a nice flare, and have a little reserve of energy in case you misjudged. The alternative may be a crunch, if you use your little energy reserve (stored only as airspeed) in an imprecise flare.

A place to look in the POH will be the speed stated for climb after a normal takeoff (not Vx). That speed (faster than Vx, and maybe best glide speed) will be the speed which has been demonstrated will allow you to make a gliding landing straight ahead following an engine failure (another design requirement).

If you're keen, practice a full power off landing from circuit altitude at the "best glide speed". It can be done, but you're flare best be very well timed! Too early, and you'll crunch, as the aircraft, though pitched up, will not have arrested the descent. Too late, and crunch, because you did not arrest the descent.

I did this testing in a Cessna Grand Caravan, and it was very scary, the runway sure comes at you fast! However, to support the original theme, selecting coarse pitch, and further feathering the prop (which can be done with the engine running in the Caravan) made a terrific difference in the glide, and the POH so directs for that type.

All of this is definitely a practiced skill, just remember the factors associated with shock cooling an engine, if you're going to glide.

[piperboy84]

The POH does list a speed for best glide however that was based on the stock prop a 76" Hartzell, I got a FAA field approval to install a 198cm 3 blade MT prop (that is 20 lbs lighter), the effect on approach when moved to full fine for landing is like throwing a chute out the back. The reason for the original question is I'm trying to get some off my glide capability back if I have an engine failure as this new props air braking effect is significant.

[terry holloway]

I would advocate the POH best glide speed. That provides time and distance. Im not familiar with the Caravan, but in the C182 it's 75 Kts flapless and 70 with them down. Both speeds in that aircraft are more than adequate for a proper flare with the engine out.

[9 lives]

I got a FAA field approval to install a 198cm 3 blade MT prop (that is 20 lbs lighter), the effect on approach when moved to full fine for landing is like throwing a chute out the back

Ah ha! Piperboy, that's a whole different situation! All bets are off for POH speeds and procedures having done that! We commend the FAA for giving that field approval, but a number of design requirements for certification were overlooked when that approval was issued (a fundamental flaw in the FAA field approval system). Email Martin Albrecht at MT, and review the situation, he may have some suggestions about adjusting the pitch stops to improve things, you simply do not need that braking affect for your flying.

In the mean time, if you have had an engine failure, do the following: Best glide speed*, prop selected to full coarse, select your forced landing place (closer being better), cause check (altitude permitting), and if you cannot get the engine running again at that time, mixture to ICO, and mags off then. Doing so forces you to follow through on a decent forced landing, rather than the engine spurting back to life, and luring you into passing up a decent forced landing opportunity for a worse/rushed one later and lower altitude, when it quits a second time.

I would advocate the POH best glide speed. That provides time and distance.

Yes, certainly. If you need the time and distance for you glide, fly at best glide speed. *However, if you can make a suitable landing area sooner/closer, do that and carry the extra speed to assure yourself a margin of reserve for a decent approach and landing. If you arrive to midway back final with too much speed/height, more flaps or sideslip, because you don't have airbrakes as the sailplane pilots do. Piperboy could select full fine again though!

I train this a lot when I'm doing advanced type training, and I regularly see really poor skills in terms of simply putting the plane back on the ground with a reserve of safety - pilots regularly overestimate their glide ability. Ultimately, if you're going to get it wrong as you cross the fence, you would much rather be too fast than too slow, and go off the far end at a few knots, than not cross the fence, and slam into whatever it is at flying speed!

This is extra important in drag changed planes, like floatplanes, skiplanes and float amphibians.

This should be practiced a lot. Every pilot I train and practice with seems to have an eye opener when we do this, so I'm thinking that other pilots could benefit from more practice too. That practice has most value only if it includes a touchdown - go arounds at 50 feet really don't show you that you could have landed and stopped.

Piperboy, I have installed an MT reversing propeller on my flying boat, and found the same characteristics you describe - a forced landing in fine pitch would be very challenging. I found similar, though less dramatic characteristics when I tested the MT reversing prop on the 182 amphibian. I have also flown the MT props during testing on 182, Lake Amphibians, Twin Comanche, and DA-42-L360. I really like them, but they're different, and sometime these differences are not well understood. Talk to Martin.

[n5296s]

If you're keen, practice a full power off landing from circuit altitude at the "best glide speed". It can be done, but you're flare best be very well timed! Too early, and you'll crunch, as the aircraft, though pitched up, will not have arrested the descent. Too late, and crunch, because you did not arrest the descent.


I'm surprised by this. Best glide speed in my TR182 (clean) is 75, empirically determined, 78 iirc in the POH. There's no documented dirty best glide speed (because why would you be doing this) but empirically it's about 65. That's exactly my normal over-the-threshold speed which has plenty of energy to flare and even float a little.

Of course this is type dependent so maybe the Caravan is especially bad in this regard.

[mary meagher]

A few years back, undergoing a checkride in the Supercub with an instructor of renown, he presented me with not a dead engine, but a sick one, at 3,000' over Banbury... 7 nautical miles to our home airfield at Shenington (formerly Edgehill).

I figured I had enough height to get back to the airfield even with a sick engine,
but just to be sure, decided NOT to attempt any sort of circuit (or pattern) and as the wind was not strong, about 8 knots, set up a downwind landing which worked nicely. Plenty of height for a straight in approach.

Surprised the instructor, he had expected me to attempt a circuit and run out of height.

Of course a sick engine is more likely to tempt one into a poor decision. A dead engine can present you with no choice at all.

[RatherBeFlying]

If whatever you are flying has lots of drag available, such as fine pitch, big flaps or good spoilers as in newer gliders, you can point your nose at your chosen landing spot and allow the airspeed to come up - most preferably on an approach slope steeper than best glide speed will give you.

With windshear you have some airspeed you can give up, or decrease drag.

On round out, the drag will reduce airspeed quickly; so don't round out too high:=

This will get you over the near fence. As before noted it won't hurt as much to get intimate with the far fence.

Of course when the landing surface is water, minimum sink will be the best splash down speed.

[piperboy84]

Does anyone have an idea at what MAP when reducing Power that the prop will go "off the governor" (underspeed) and move to fine pitch on your average 235hp c182 or Cherokee6 on approach? I know I'm asking a lot of wired questions, just trying to get the concept clear in my wee heed.

[The Ancient Geek]

It depends on the RPM that you have set on the prop lever.
If the engine is not producing enough horses to turn the prop at that speed the prop will reduce pitch to keep up.
In practice you always set the prop to max RPM on approach.

[piperboy84]

It depends on the RPM that you have set on the prop lever.
If the engine is not producing enough horses to turn the prop at that speed the prop will reduce pitch to keep up.
In practice you always set the prop to max RPM on approach.


Ok, so does the bottom of the green arc on the MAP gauge signify (normally about 15 inches) that below this the prop is going to fine pitch automarpticakky if it ain't there already ?

[The Ancient Geek]

No, it is irrelevant. It just tells you the manifold pressure on a turbocharged engine and therefore the power being produced..
The prop knows nothing about MAP, it just understands RPM.

[India Four Two]

In practice you always set the prop to max RPM on approach

OK. I'm setting myself up as a target, but not me!

In the 182 towplane I fly, after takeoff, I bring the RPM back to 2300 rpm for noise abatement and leave it like that for the remainder of the flight, including the landing, again for noise considerations.

Now if I had to go around in an emergency, of course I would go to full fine, but I have determined (at altitude) that going around without changing the rpm and with those lovely barn-door (40 degree) flaps down, the rate of climb is more than adequate, even at DAs of 5000-6000'. I should confess at this point, that I am flying behind a P Ponk engine - 265 HP.