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Engine failure - glide tests


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On 9/15/2022 at 10:04 AM, T. Peterson said:

I don’t mind the hijacking. What really bugs me is that the threads all get hijacked to electric cars or sailboats - never to Goldwing motorcycles. I think I am suffering from all y’all’s micro-aggression. Calling my Psychiatrist right now!!

Oooohhhh, micro aggressions. Now *thats* a potential thread hijack :-)

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On 8/22/2022 at 8:36 PM, GeeBee said:

Actually you have to get going fairly fast to windmill after a stop. On my PA-18 you had to go well into the yellow arc. Constant speed prop may be less, but also many times higher compression ratio engine.

 

Same experience in an old champ. We had to go way faster than that plane would’ve ever attained in level flight.

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On 8/23/2022 at 7:15 AM, M20Doc said:

I wonder what the effect of opening the throttle fully would have on glide performance with the engine shut down?  

Prop would turn faster for a given input.

More air for higher compression is a near a net wash because of the rebound from the compressed air ATDC

choking (throttle) the system will slow the prop.

On 8/23/2022 at 7:23 AM, ArtVandelay said:


I’d expect more air in the cylinders means more compression resistance, hence a slower turning prop? Maybe slightly better glide.

Your initial thought was correct.

On 8/23/2022 at 6:06 PM, A64Pilot said:

It will decrease glide distance, the engine being driven is essentially an air compressor, more air you let in the greater the drag.

Engines that shut down cylinders to achieve greater fuel efficiency, shut down the exhaust valve, then the air in the cylinder is essentially a spring, takes energy to compress it, but you get most back on the downstroke. Called cylinder deactivation if you want to look it up.

A compression release is another example, “Jake brakes” are used to slow trucks down so they don’t get any energy back on what is normally the power stroke of a four stroke motor.

I believe this is the opposite of what happens. Opening the throttle will allow the engine turn easier, not harder.
 

The reason a “Jake brake” works is because it opens the exhaust valves at the top of the comp stroke releasing the stored energy (compressed air) so it doesn’t transfer energy back to the piston ATDC.

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5 hours ago, Will.iam said:

Yea i think the goldwing is more of a cessna type of bike. Nice and roomy but not as fast as the others. 
i think A Ducati motorcycle is more inline like a mooney fast hand built maybe? 

Bite your tongue Mon Ami! GW like a Cessna??? Negative on your declarative! GW is more like the Bonanza.

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1 hour ago, Shadrach said:

Prop would turn faster for a given input.

More air for higher compression is a near a net wash because of the rebound from the compressed air ATDC

choking (throttle) the system will slow the prop.

Your initial thought was correct.

I believe this is the opposite of what happens. Opening the throttle will allow the engine turn easier, not harder.
 

The reason a “Jake brake” works is because it opens the exhaust valves at the top of the comp stroke releasing the stored energy (compressed air) so it doesn’t transfer energy back to the piston ATDC.

Easiest answer is to go out and try it, or put an inductive amp meter on an air compressor, read amp draw, then block off the intake with something substantial, not your hand and watch, the amp draw will drop. It requires energy to compress that air, remove the airflow and the energy draw is less.

Jusr exactly like the engines that deactivate cylinders

 

Put you hand on a compressor or Diesel intake and it’s likely you’ll be hurt, so use a piece of wood or metal.

But maybe you should leave the throttle open and mags hot if an engine quit, who knows maybe it was a blocked fuel line and it could clear? Unlikely, but possible?

With the throttle open and mags left hot the engine would come back, but with the throttle closed you may not notice it running.

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1 hour ago, Shadrach said:

The reason a “Jake brake” works is because it opens the exhaust valves at the top of the comp stroke releasing the stored energy (compressed air) so it doesn’t transfer energy back to the piston ATDC.

Turns it into noise instead.  ;)

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2 hours ago, EricJ said:

Turns it into noise instead.  ;)

Bloody awful noise. It’s a good indicator of driving skill. I live about 10 miles from a quarry. There’s a curve at the top of a hill not far from my house.  The good drivers manage energy well and don’t “Jake Brake” uphill.

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Funny thing is that a jake brake can be ducted back into the exhaust before the muffler, those you don’t even really hear.

https://www.jacobsvehiclesystems.com/sites/default/files/2018-08/Jacobs Vehicle Systems Engine Brake Noise Brochure_0.pdf

Then there is the type used on Cummins engines like the Dodge PU that close off the exhaust after the turbo. I don’t know how high they let the pressure in the exhaust go, but think it must be considerable. I think those are silent too.

https://www.dieselpowerproducts.com/pacbrake-prxb-exhaust-brake-67l-ram

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A lot of theoretical discussion here, which is good… but I question the practical value of the debate. 
 

As every EngineOut checklist says, your first priority is to trim and fly for best glide speed, and your second is to look for a place you can safely land.  GA fatality statistics suggest that far too many pilots try to extend their glide farther than the aerodynamics of their aircraft can achieve.  

When I had my emergency off-airport landing on 9/30/21–which I posted an account of here last year—I discovered that the ground comes up on you much quicker with no power than it does when you are at idle power. I thought I could extend my glide to reach a gravel road in my line of sight, but nope, I had to land in a pasture well short of that. (My prop wasn’t turning, so prop pitch wasn’t a factor.) But rather than focusing on where I wanted to land, I kept an eye on my airspeed and landed “by the numbers” and safely. Training for an engine-off landing at idle power, which I had done at my BFR only 3  months earlier, does NOT realistically approximate your speed of descent with NO power. 

I had extensive after-action discussions with the FAA investigator and my Savvy rep. They informed me that too many pilots try to extend their glide to reach an airport, etc, and in doing so fail to keep up their airspeed, and they stall on short final. The result of a stall at 100’ AGL is predictable, and generally fatal. 

Looking for ways to extend your glide in a power-off emergency may set you up for a dangerous mindset, one that increases the risk of failing to maintain airspeed and control all the way to a controlled off-airport landing. 

Instead of trying to reach a landing spot at the limit of your airplane’s glide capability (which I guarantee is less than you think it is!) I strongly suggest you look for the best place to land that is well within your best glide slope and land there. I doubt you will find many CFI’s, or many pilots who have survived such an emergency, who will argue otherwise. 

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2 hours ago, CoffeeCan said:

A lot of theoretical discussion here, which is good… but I question the practical value of the debate. 
 

As every EngineOut checklist says, your first priority is to trim and fly for best glide speed, and your second is to look for a place you can safely land.  GA fatality statistics suggest that far too many pilots try to extend their glide farther than the aerodynamics of their aircraft can achieve.  

When I had my emergency off-airport landing on 9/30/21–which I posted an account of here last year—I discovered that the ground comes up on you much quicker with no power than it does when you are at idle power. I thought I could extend my glide to reach a gravel road in my line of sight, but nope, I had to land in a pasture well short of that. (My prop wasn’t turning, so prop pitch wasn’t a factor.) But rather than focusing on where I wanted to land, I kept an eye on my airspeed and landed “by the numbers” and safely. Training for an engine-off landing at idle power, which I had done at my BFR only 3  months earlier, does NOT realistically approximate your speed of descent with NO power. 

I had extensive after-action discussions with the FAA investigator and my Savvy rep. They informed me that too many pilots try to extend their glide to reach an airport, etc, and in doing so fail to keep up their airspeed, and they stall on short final. The result of a stall at 100’ AGL is predictable, and generally fatal. 

Looking for ways to extend your glide in a power-off emergency may set you up for a dangerous mindset, one that increases the risk of failing to maintain airspeed and control all the way to a controlled off-airport landing. 

Instead of trying to reach a landing spot at the limit of your airplane’s glide capability (which I guarantee is less than you think it is!) I strongly suggest you look for the best place to land that is well within your best glide slope and land there. I doubt you will find many CFI’s, or many pilots who have survived such an emergency, who will argue otherwise. 

All good points. Appreciate your take on the situation and your experience. This discussion is about how to configure the plane for max glide performance. The points you bring up are worthy of discussion, but I think it’s a slightly different discussion.

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On 8/22/2022 at 7:11 AM, toto said:

Minor threadjack..

There's an interesting - and pretty comprehensive - book on GA engine out tactics by Nate Jaros.  Definitely worth a read.

https://www.amazon.com/Engine-Out-Survival-Tactics-Emergencies/dp/1483594556

Nate is @Buster1 here on MS.

 

 

Thanks for the heads-up on this book.  I downloaded it last evening and I’m halfway through it. Excellent book, it should be in every GA pilot’s aviation library. 

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