182 down by Smithers

[photofly]

I think that you may have come to a conclusion and are now coming up with complicated ideas to back up the conclusion. I suggest testing it out on an appropriate aircraft and then get back to us with the results.

Even NTS and Beta Follow-up are designed to coarsen blades to reduce drag on certain turboprop engines. The coarser the prop, the less the drag.

I agree with that. (There’s nothing really very complicated about looking at the aerodynamic forces on a propeller blade).

So you agree that selecting full coarse on the blades on a windmilling prop will increase the glide distance.

I agree that the drag goes down when the blades are coarser. It’s certainly true for a stopped prop, and a reasonable proposition for one that’s windmilling. I have to go and see if in a piston single with the throttle closed the prop control still affects the blade angle. I don’t know if it will come off the full fine stop at such a low rpm. But I’ll take ahramin’s word for it, until I get a chance to try it.

Nevertheless, a rotating prop should not be thought of as generating force by “flat plate area”: look at the braking effect of a “discing” prop due to negative blade AoA. The rotation of the blade makes a big difference when compared to the drag generated by a stationary one. I would not trust reasoning based on “flat plate area” even if the conclusion is correct.

Even with a stationary blade, airplane drag is not due to “flat plate area” but due to the blade being stalled (with the opposite sign of AoA to when it is turning and producing thrust, but it’s still stalled.) As the stationary blade turns coarse, its AoA decreases, and it unstalls, decreasing drag. A feathered prop is one with zero AoA: least drag.

I’m not sure about the throttle position: intuition says opening the throttle will decrease the resistance to turning the prop, increasing the windmilling speed and absorbing more energy from the aircraft, which is not what you want. My intuition is usually pretty good, so if you have reason to understand the opposite, I’d like to hear it. It’s a harder experiment to carry out, because with a functioning engine opening the throttle will provide power. I guess one could experiment with the magnetos shut off.

[pelmet]

I agree with that. (There’s nothing really very complicated about looking at the aerodynamic forces on a propeller blade).

So you agree that selecting full coarse on the blades on a windmilling prop will increase the glide distance.

I agree that the drag goes down when the blades are coarser. It’s certainly true for a stopped prop, and a reasonable proposition for one that’s windmilling. I have to go and see if in a piston single with the throttle closed the prop control still affects the blade angle. But I’ll take ahramin’s word for it, until I get a chance to try it.

It makes perfect sense that Ahramin had an rpm decrease due to coarsening. No need to test for yourself as you have no doubt already witnessed the same thing many times already. One can see it on a PT-6 and PW100(both of which I have operated) on the ground when the engine is started in feather and then the props are moved out of feather and vice versa in terms of rpm. There is a huge difference in rpm due to the change in drag. probably no different than when we used to note the drag while holding one's palm outside the car window a 60 mph with palm facing wind and palm 90° to wind.

Watch the blade angle change and see the rpm increase...........
https://www.youtube.com/watch?v=JdjIsEJsUY4

Watch the blade angle change and see the rpm decrease(followed by a separate shutdown)......
https://www.youtube.com/watch?v=Y_m44Q-ti4Y

[photofly]

So you agree that selecting full coarse on the blades on a windmilling prop will increase the glide distance.

I agree that the drag goes down when the blades are coarser. It’s certainly true for a stopped prop, and a reasonable proposition for one that’s windmilling. I have to go and see if in a piston single with the throttle closed the prop control still affects the blade angle. But I’ll take ahramin’s word for it, until I get a chance to try it.

It makes perfect sense that Ahramin had an rpm decrease due to coarsening. No need to test for yourself as you have no doubt already witnessed the same thing many times already. One can see it on a PT-6 and PW100(both of which I have operated) on the ground when the engine is started in feather and then the props are moved out of feather and vice versa in terms of rpm. There is a huge difference in rpm due to the change in drag. probably no different than when we used to note the drag while holding one's palm outside the car window a 60 mph with palm facing wind and palm 90° to wind.

Watch the blade angle change and see the rpm increase...........
https://www.youtube.com/watch?v=JdjIsEJsUY4

Watch the blade angle change and see the rpm decrease(followed by a separate shutdown)......
https://www.youtube.com/watch?v=Y_m44Q-ti4Y

The question being discussed is specifically about a 182:

Wouldn't a 182 glide further with the prop in full coarse?

Piston singles in general have and the 182 in particular has a very different constant speed units to piston twins and turboprops. As you will know, single engine CSUs default (via a heavy spring) to full fine pitch and use a rise in oil pressure to turn the blade coarse when the RPM rises above a threshold set by the prop lever. Since there is no operational advantage to governing a prop in the typical range of a windmilling blade I’m not confident the CSU is designed to govern as low as 1200-1400 rpm on a 182. Hence my doubt that moving the prop lever of a 182 in a glide changes the blade angle at all. If it doesn’t, then the answer to Joe’s question, as posed, is “no”. But that bit is easy for me to test, since I own one.

Regarding the videos: I don’t think conclusions from engines under power apply to drag from windmilling props.

There is a huge difference in rpm due to the change in drag

I believe we are using the word drag differently - both correct, but in different contexts. I was referring to airframe drag retarding the forward speed of the aircraft. For maximum glide range, that is the force that must be reduced. I’m unable to connect rpm changes (with pitch) of an engine under power to the quantity of interest.

Gyrocopter pilots might be able to add to the conversation: the rotor of a gyrocopter is always under autorotation like a windmilling prop blade.

[pelmet]

I agree that the drag goes down when the blades are coarser. It’s certainly true for a stopped prop, and a reasonable proposition for one that’s windmilling. I have to go and see if in a piston single with the throttle closed the prop control still affects the blade angle. But I’ll take ahramin’s word for it, until I get a chance to try it.

It makes perfect sense that Ahramin had an rpm decrease due to coarsening. No need to test for yourself as you have no doubt already witnessed the same thing many times already. One can see it on a PT-6 and PW100(both of which I have operated) on the ground when the engine is started in feather and then the props are moved out of feather and vice versa in terms of rpm. There is a huge difference in rpm due to the change in drag. probably no different than when we used to note the drag while holding one's palm outside the car window a 60 mph with palm facing wind and palm 90° to wind.

Watch the blade angle change and see the rpm increase...........
https://www.youtube.com/watch?v=JdjIsEJsUY4

Watch the blade angle change and see the rpm decrease(followed by a separate shutdown)......
https://www.youtube.com/watch?v=Y_m44Q-ti4Y

The question being discussed is specifically about a 182:

Wouldn't a 182 glide further with the prop in full coarse?

Piston singles in general have and the 182 in particular has a very different constant speed units to piston twins and turboprops. As you will know, single engine CSUs default (via a heavy spring) to full fine pitch and use a rise in oil pressure to turn the blade coarse when the RPM rises above a threshold set by the prop lever. Since there is no operational advantage to governing a prop in the typical range of a windmilling blade I’m not confident the CSU is designed to govern as low as 1200-1400 rpm on a 182. But it’s easily tested: I own one.

Regarding the videos: I don’t think conclusions from engines under power apply to drag from windmilling props.

There is a huge difference in rpm due to the change in drag

I believe we are using the word drag differently - both correct, but in different contexts. I was referring to airframe drag retarding the forward speed of the aircraft. For maximum glide range, that is the force that must be reduced. I can’t connect rpm changes (with pitch) of an engine under power to that.

Gyrocopter pilots might be able to add to the conversation: the rotor of a gyrocopter is always under autorotation like a windmilling prop blade.

I believe that the rpm changes on the propeller are due to changes in air resistance(which some might call drag). This explains the change in rpm that Ahramin experienced.

Then there is the the drag on the aircraft which affects the glide range. Coarser pitch means less drag on the aircraft which is why the propeller blades are feathered if possible to reduce drag.

Therefore, greater drag to propeller blade rpm means less drag on the aircraft forward motion.

The intent of the videos is to show the effect of propeller aerodynamics. Coarsen the blades and look at what happens. Of course This can be overcome by increased power(ie fuel flow) but that is not the intent of the PW100 on shutdown so there is not an fuel flow increase.

However, one need only look at the Allisons on this Electra to see the coarsening being used differently for more power. The engines are operating at 100% as it taxies out to the runway(which is why it is so damn loud during taxi). One might ask how the engines can be operating at 100% while taxiing. The blade angle is at high pitch with not too much forward thrust. Then the power is added for takeoff but the rpm remains at 100%. What happens is the blades coarsen significantly. This means much more drag(air resistance to rpm) but also increased thrust due to higher propeller pitch. Increased fuel flow is required to maintain the 100% rpm that is creating more thrust with higher blade AOA. A lot more fuel is required with the blade angle continuing to coarsen to the takeoff setting.

https://www.youtube.com/watch?v=JRd4iuC ... =emb_title

Of course, for the engine out scenarios we were discussing, it is with an engine that has lost power where the propeller is driving the engine instead of the normal opposite situation.

[photofly]

Of course, for the engine out scenarios we were discussing, it is with an engine that has lot power where the propeller is driving the engine instead of the normal opposite situation.

I don’t think you can dismiss the difference in a throwaway line at the end of a post, as though it’s a minor detail.

Why do you recommend opening the throttle?

[pelmet]

Why do you recommend opening the throttle?

Best explained in this article here with no clear answer as to why......

https://books.google.ca/books?id=1bkFXh ... ce&f=false

[ahramin]

I had a closer look at the data and the average increase when going to full fine was 141 RPM. This is a minimum though as I never waited for it to stabilize before adding power. This was at speeds from 70 to 80 knots. Another interesting point is that the RPM slowly but consistently decreases during the descent, maybe because of engine cooling.

Test Card 8.jpg (997.71 KiB) Viewed 1330 times

[pelmet]

According to Peter Garrison(who some on this forum have indicated is well respected).....

"The most important thing to remember, in airplanes with separate prop and throttle controls, is throttle forward, prop back. Glide at your approach speed, with the throttle open and the prop in coarse pitch — that is, low rotations per minute."

https://www.flyingmag.com/glide-sail-so ... can-do-it/

From another article by someone experimenting with a C210......

"Part of the best-glide procedure should be to clean up the airplane: flaps and landing gear retracted, cowl flaps closed, rudder trimmed. With a variable-pitch prop, pull back the prop to as slow a speed as possible. Years ago, as part of establishing power settings in typical configurations and generally getting to know our then-newly-purchased Cessna 210, we discovered that, with the aircraft clean, at idle, and best-glide speed, pulling back the prop reduced drag so we could trim up, lowering the descent rate from 2000 to 900 fpm, a difference of 1100 fpm.

Years later when we replaced the prop with a shorter, modern prop with less drag, the difference was only 750 fpm, but still significant. We also learned the big gear doors act as excellent speed brakes, increasing the descent 1200 fpm. Try this prop exercise yourself (another great excuse to go flying) at a safe altitude, and assuming the engine has cooled and the airspace is clear. You can also use this time to determine an approximate descent rate for your plane, to help determine gliding range should an aircraft engine failure happen to you."

https://disciplesofflight.com/dealing-w ... in-flight/

I personally, have never experimented with this idea. It is interesting in the difference created by different sized props.

[marlin]

Something I feel is worth mentioning - it very much depends on what kind of propeller you have on your airplane. Most piston singles don't roll out with a feathering propeller.

http://www.sq44.cawgcap.org/uploads/ngr ... cerpts.pdf

Page 2-5 shows the high and low ranges of motion in a factory standard Cessna 182R. The range of motion between low and high pitch is 14.4 degrees (between 15 and 29.4 degrees) between low and high stops.

https://desertflying.club/wp-content/up ... ec-POH.pdf

Conversely, Page 2-2 of this Aztec manual gives you 65.5 degrees of prop pitch (14.5 to 80 degrees at full feather).

Regardless of whether you're even able to control prop pitch effectively after an engine failure, you aren't reducing nearly as much drag in a piston single with a non-feathering prop. I'd personally just focus on following the applicable emergency checklists to the letter - lots of other important things to do, and efficiently using the time you've already got is at least as worthwhile as trying to gain a handful of extra seconds.

[pelmet]

Regardless of whether you're even able to control prop pitch effectively after an engine failure, you aren't reducing nearly as much drag in a piston single with a non-feathering prop. I'd personally just focus on following the applicable emergency checklists to the letter - lots of other important things to do, and efficiently using the time you've already got is at least as worthwhile as trying to gain a handful of extra seconds.

According to the first article by Peter Garrison, he was able to increase his gliding distance by 30% in a variable pitch single engine aircraft. Considering that the actions to do that take less than two seconds and may save your life, it is well worth considering.

[marlin]

Fair enough, certainly worth keeping in mind - the caveat is that this was demonstrated with a healthy engine at idle power.

If I'm not mistaken, most governor mechanisms for piston singles (with non-feathering propellers) require oil pressure to maintain that high pitch and reduced drag. If your damaged engine stops windmilling or producing idle power to run the governor pump, or if you run out of oil, the risk is that you could revert back to low pitch and increased drag - if you were relying on that performance increase to make a field, you might suddenly be SOL! I guess it depends on how confident the pilot is in the nature of the failure, and their knowledge of their airplane's specific systems.

[Cliff Jumper]

the caveat is that this was demonstrated with a healthy engine at idle power.

I'm confused. For all of these 'trials' people are conducting, are we talking an idling engine, or a non running engine? (Ahramin, others?)

It seems to me that this difference would create wildly different results.

I'm still interested in photofly's question. Without any power (engine not running at idle) will there be enough oil pressure to drive the prop to course pitch? what min rpm does the prop need to be windmilling at, to create enough oil pressure to drive it to course, and wouldn't slowing the prop make the oil pressure even lower, causing it to drift back towards fine pitch?

[photofly]

The articles referenced refer to an engine windmilling in the air with magnetos off and mixture at idle cutoff, so not producing power.

[ahramin]

I'm confused. For all of these 'trials' people are conducting, are we talking an idling engine, or a non running engine? (Ahramin, others?)

The data above was with the engine idling. I've done these tests with the mixture ICO and the results are very similar. Even though the engine is "off", it's still turning at idle speed, the governor and oil pumps are still spinning, and the propeller blade angle still changes measurably.

[ahramin]

When all else fails consult the manufacturer's POH for guidance.

CESSNA MODEL 182Q

ENGINE FAILURE DURING FLIGHT

1. Airspeed -- 70 KIAS.
2. Carburetor Heat -- ON.
3. Fuel Selector Valve -- BOTH
4. Mixture -- RICH.
5. Ignition Switch -- BOTH (or START if propeller is stopped).
6. Primer -- IN and LOCKED.

FORCED LANDINGS

EMERGENCY LANDING WITHOUT ENGINE POWER

1. Airspeed -- 70 KIAS (flaps UP).
65 KIAS (flaps DOWN).
2. Mixture -- IDLE CUT-OFF.
3. Fuel Selector Valve -- OFF.
4. Ignition Switch -- OFF.
5. Wing Flaps -- AS REQUIRED.(40° recommended).
6. Master Switch -- OFF.
7. Doors -- UNLATCH PRIOR TO TOUCHDOWN.
8. Touchdown -- SLIGHTLY TAIL LOW.
9. Brakes -- APPLY HEAVILY.

No mention of prop.

No mention of trim either, or for that matter moving the yoke. The checklist contains required items but is not a complete description of how to successfully deal with an engine failure under all conditions. In many cases there is no advantage to adjusting the propeller control.

However if you get to the point in your engine failure procedure where you are selecting your landing spot and there is any doubt about being able to glide there, it should be a normal part of your flying skills to minimize drag, including pulling the prop control out to the stop.

[cncpc]

Why do you recommend opening the throttle?

Best explained in this article here with no clear answer as to why......

https://books.google.ca/books?id=1bkFXh ... ce&f=false

I remember way back in the day when Raf Zur blew a tank on a 185 in the circuit in Langley, switched, got nothing, and continued to the flare with the throttle wide open. As he was about to touch down, the engine finally fired, at full throttle, and more or less twisted out of his hands enough to hook a wingtip and bend the thing.

[telex]

When all else fails consult the manufacturer's POH for guidance.

CESSNA MODEL 182Q

ENGINE FAILURE DURING FLIGHT

1. Airspeed -- 70 KIAS.
2. Carburetor Heat -- ON.
3. Fuel Selector Valve -- BOTH
4. Mixture -- RICH.
5. Ignition Switch -- BOTH (or START if propeller is stopped).
6. Primer -- IN and LOCKED.

FORCED LANDINGS

EMERGENCY LANDING WITHOUT ENGINE POWER

1. Airspeed -- 70 KIAS (flaps UP).
65 KIAS (flaps DOWN).
2. Mixture -- IDLE CUT-OFF.
3. Fuel Selector Valve -- OFF.
4. Ignition Switch -- OFF.
5. Wing Flaps -- AS REQUIRED.(40° recommended).
6. Master Switch -- OFF.
7. Doors -- UNLATCH PRIOR TO TOUCHDOWN.
8. Touchdown -- SLIGHTLY TAIL LOW.
9. Brakes -- APPLY HEAVILY.

No mention of prop.

No mention of trim either, or for that matter moving the yoke. The checklist contains required items but is not a complete description of how to successfully deal with an engine failure under all conditions. In many cases there is no advantage to adjusting the propeller control.

However if you get to the point in your engine failure procedure where you are selecting your landing spot and there is any doubt about being able to glide there, it should be a normal part of your flying skills to minimize drag, including pulling the prop control out to the stop.

In what other situations would you advocate deviating from manufacturer published procedures?

[cncpc]

Quick question, I didn't see any more mention of this on the TSB report. Quote from 1.13

and the propeller control was fully in (full fine pitch).

Wouldn't a 182 glide further with the prop in full coarse?

Yes, but I don't think it's part of the Cessna emergency procedures.

The farthest glide will be achieved with the prop stopped.

Lower compression engines like the 172 require you to raise the nose to stop the prop when the engine is windmilling. I did that by accident in a rejected forced approach to land when a truck pulled into the section of the San Mateo landfill that I was on a 50 foot high final for. I had excess speed, and pulled up sharply as the ocean was the only choice left and I had to reset. The prop stopped and I lowered the nose to start the next glide. It stayed stopped

It all happened so fast, and I knew nothing about this debate now, but it is valid. In my instructing days, at certain airports, I would pull the mixture, and raise the nose to stop the prop in forced approach practice. We then continued to a deadstick landing, or at least far enough so the student would recognize that there is a significant increase in glide distance when the prop is stopped, as it would be in quite a few engine failure situations. It's glider quiet, and the "deck angle" is noticeably less than it is when you are trying to maintain glide speed with a windmilling prop. Done it dozens of times and it certainly works.

Once the prop is stopped, it stays stopped even when the speed picks up a bit. But if for some reason, I didn't like the way the approach was going and decided to restart, or if a restart was part of the drill from the beginning, I would set the engine up and ask the student to turn the key for the starter. It only needed a couple of blades for the windmilling to start again, and it would then fire up.

Not sure how the 182 would be, given a bit higher compression. But, from my experience, it would likely glide farther with reducing the speed to get the prop to stop, and increasing to glide speed again once it had stopped.

[ahramin]

When all else fails consult the manufacturer's POH for guidance.

CESSNA MODEL 182Q

ENGINE FAILURE DURING FLIGHT

1. Airspeed -- 70 KIAS.
2. Carburetor Heat -- ON.
3. Fuel Selector Valve -- BOTH
4. Mixture -- RICH.
5. Ignition Switch -- BOTH (or START if propeller is stopped).
6. Primer -- IN and LOCKED.

FORCED LANDINGS

EMERGENCY LANDING WITHOUT ENGINE POWER

1. Airspeed -- 70 KIAS (flaps UP).
65 KIAS (flaps DOWN).
2. Mixture -- IDLE CUT-OFF.
3. Fuel Selector Valve -- OFF.
4. Ignition Switch -- OFF.
5. Wing Flaps -- AS REQUIRED.(40° recommended).
6. Master Switch -- OFF.
7. Doors -- UNLATCH PRIOR TO TOUCHDOWN.
8. Touchdown -- SLIGHTLY TAIL LOW.
9. Brakes -- APPLY HEAVILY.

No mention of prop.

No mention of trim either, or for that matter moving the yoke. The checklist contains required items but is not a complete description of how to successfully deal with an engine failure under all conditions. In many cases there is no advantage to adjusting the propeller control.

However if you get to the point in your engine failure procedure where you are selecting your landing spot and there is any doubt about being able to glide there, it should be a normal part of your flying skills to minimize drag, including pulling the prop control out to the stop.

In what other situations would you advocate deviating from manufacturer published procedures?

Lol. If trimming for 70 kts, turning towards a landing spot and pulling the prop full coarse are deviations from the above procedure, what's your plan for getting it on the ground following the checklist?

[telex]

No mention of trim either, or for that matter moving the yoke. The checklist contains required items but is not a complete description of how to successfully deal with an engine failure under all conditions. In many cases there is no advantage to adjusting the propeller control.

However if you get to the point in your engine failure procedure where you are selecting your landing spot and there is any doubt about being able to glide there, it should be a normal part of your flying skills to minimize drag, including pulling the prop control out to the stop.

In what other situations would you advocate deviating from manufacturer published procedures?

Lol. If trimming for 70 kts, turning towards a landing spot and pulling the prop full coarse are deviations from the above procedure, what's your plan for getting it on the ground following the checklist?

I suspect the difference in glide between full fine and full coarse in a single engine piston prop with a dead engine is negligible.

There is a reason why it is not in the published procedure.

It doesn't make a difference. Most pilots can process information at 70 knots.

Follow the manufacturer's published procedure.