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  #1  
Old 11-16-2019, 11:14 PM
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skylor skylor is offline
 
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Default High Key/Low Key Testing an RV-8

****THIS THREAD IS NOT ABOUT ENGINE OUT TURN-BACKS ON TAKEOFF. PLEASE DON'T BRING IT UP!****

This evening I went up to find the High Key and Low Key numbers for my RV-8.

Previous discussions about this subject here:

Rocket Glider

And here:

High Key approach in a -10

Admittedly this is something I should have done many years ago. Somehow I never seemed to remember to do it or find the time for this. Recent reflections of a fatal accident of an acquaintance (not in an RV) that occured about a year and a half ago finally convinced me to go do this.

For the test, I climbed to 4500’ msl (4400 all) above my home field, entered the “upwind,” pulled the mixture to idle cutoff and established stabilized best glide (95 - 100 kias) straight ahead until 4000’ and then entered a 45 degree banked turn. I maintained the turn at the same speed through 360 degrees, noting altitude at the 180 and 360 degree points. At these conditions, the altitude loss at 360 degrees ( high key) was ~ 1150’ and ~ 550’ at 180 degrees (low key). I repeated this 4 times and the results were very consistent. I ran an additional attempt (actually, my first one) at 30 degrees bank and the numbers were ~ 1450’ and 750’ for high key/Low key respectively.

My RV-8 is equipped with a stock IO30-A1B6 (angle valve) and 74” Hartzell blended airfoil constant speed propellor. I ran all tests with the mixture at idle cutoff, the throttle fully retarded, and the prop control full forward.

I recommend testing this yourself in your own aircraft.

Skylor


****THIS THREAD IS NOT ABOUT ENGINE OUT TURN-BACKS ON TAKEOFF. PLEASE DON'T BRING IT UP!****

Last edited by skylor : 11-17-2019 at 01:12 PM.
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  #2  
Old 11-17-2019, 12:18 AM
scsmith scsmith is offline
 
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I really should do this too. I would have no qualms about doing it at idle. Idle cut-off seems kinda scary, even though I'm a glider pilot. When you finished the 360 and pushed the mixure knob forward, I assume you got power back immediately?
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  #3  
Old 11-17-2019, 06:09 AM
Desert Rat Desert Rat is offline
 
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Default

I've done this on a bunch of single engine airplanes over the years, (with power back to idle, not ico) and your results are consistent with what I've found, regarding the steep vs. shallow bank.

Almost without fail, the minimum altitude loss in a turn back to the airport scenario is pitch for best glide and then crank in as much bank as the plane can handle without stalling at that airspeed.

One something like a c172 I can do a power off 180 entered from a Vy climb with about a 300' altitude loss, but thats when I know it's coming ahead of time, and with the stall horn is going off the whole time. Validates what we were all taught; i.e. if you have a power failure on the upwind, it's probably best to crash straight ahead wings level rather that try to turn back and either cartwheel or spin it in trying to stretch a glide.

Good that you figured out those numbers for your own airplane, so you can make that decision for yourself ahead of time, instead of guessing in the heat of the moment.
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  #4  
Old 11-17-2019, 11:29 AM
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skylor skylor is offline
 
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Default Turn Back?

Quote:
Originally Posted by Desert Rat View Post
I've done this on a bunch of single engine airplanes over the years, (with power back to idle, not ico) and your results are consistent with what I've found, regarding the steep vs. shallow bank.

Almost without fail, the minimum altitude loss in a turn back to the airport scenario is pitch for best glide and then crank in as much bank as the plane can handle without stalling at that airspeed.

One something like a c172 I can do a power off 180 entered from a Vy climb with about a 300' altitude loss, but thats when I know it's coming ahead of time, and with the stall horn is going off the whole time. Validates what we were all taught; i.e. if you have a power failure on the upwind, it's probably best to crash straight ahead wings level rather that try to turn back and either cartwheel or spin it in trying to stretch a glide.

Good that you figured out those numbers for your own airplane, so you can make that decision for yourself ahead of time, instead of guessing in the heat of the moment.
Please note that my intent for determining High-Key/Low-Key numbers is not for the impossible turn/takeoff turn back scenario. These values are used to establish a safe power off overhead approach in a scenario where you have an engine failure at sufficient altitude to safely glide to an airport, such as from cruise flight.

Skylor
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  #5  
Old 11-17-2019, 11:57 AM
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skylor skylor is offline
 
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Default ICO

Quote:
Originally Posted by scsmith View Post
I really should do this too. I would have no qualms about doing it at idle. Idle cut-off seems kinda scary, even though I'm a glider pilot. When you finished the 360 and pushed the mixure knob forward, I assume you got power back immediately?
Pulling the mixture to ICO in flight while at idle is a complete non-issue for an airworthy engine as long as you don’t stop the prop, which is pretty difficult to do. This is not a whole lot different than normal use of the mixture control during flight.

In my case I could not hear or feel any difference when I pulled the mixture lever back and the only way I could tell the engine was “off” was the “0” fuel flow reading. I even continued to get warm air from the cabin heater due to residual exhaust pipe heat. When I pushed the mixture back in and advanced the throttle, the engine never missed a beat!

This is not the first time that I’ve “shut the engine off” in my plane. During Phase 1 testing in 2010, I did this nearly 2 dozen times to collect power off glide performance data (straight ahead). Again, a non-issue. Also note that I always do this type of thing at safe altitude above an airport!

Skylor
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  #6  
Old 11-17-2019, 01:05 PM
Papa Papa is offline
 
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For the record: I can do a “Split S” starting at 85 KIAS and idle power in 6 to 7 hundred feet. But I wouldn’t recommend it as an engine out technique!
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  #7  
Old 11-17-2019, 01:10 PM
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skylor skylor is offline
 
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Default Not a "Turnback" Discussion!

Quote:
Originally Posted by Papa View Post
For the record: I can do a “Split S” starting at 85 KIAS and idle power in 6 to 7 hundred feet. But I wouldn’t recommend it as an engine out technique!
Please don't try to make this a "turnback" discussion. That's not what this thread is about.

Skylor
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  #8  
Old 11-17-2019, 01:19 PM
rocketman1988 rocketman1988 is offline
 
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Default Really?

"...When I pushed the mixture back in and advanced the throttle, the engine never missed a beat!..."

It works fine until it doesn't...
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  #9  
Old 11-17-2019, 01:43 PM
flyinga flyinga is offline
 
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Quote:
Originally Posted by rocketman1988 View Post
"...When I pushed the mixture back in and advanced the throttle, the engine never missed a beat!..."

It works fine until it doesn't...
Just like pushing the throttle up after an extended glide with throttle at idle.
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  #10  
Old 11-17-2019, 05:49 PM
rocketman1988 rocketman1988 is offline
 
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Default Yeah, right

So you are comparing an idling engine to one that has been intentionally stopped. Not a good comparison, IMO.

Hypothetically, imagine the NTSB report from an accident resulting from intentionally stopping an engine in flight even if it is over an airport...any guesses what it would say?

I can give you a hint if you want...
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Aerospace Engineer '88

RV-10
Structure - 90% Done
Cabin Top - Aaarrghhh...
EFII System 32 - Done
297 HP Barrett Hung
ShowPlanes Cowl with Skybolts Fitted - Beautiful
Wiring...

Dues+ Paid 2019,...Thanks DR+
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