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High Key/Low Key Testing an RV-8

skylor

Well Known Member
****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!****
 
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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?
 
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.
 
Turn Back?

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
 
ICO

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
 
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! :)
 
Not a "Turnback" Discussion!

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
 
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...:rolleyes:
 
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...
 
Please don't try to make this a "turnback" discussion. That's not what this thread is about.

Skylor

Skylor my friend...my post was tongue-in-cheek, that?s why I put a smiley face in it. I certainly don?t advocate using a split-s to return to the runway! But on a more serious note, if you?re trying to work out high and low key numbers as targets for an engine out approach, I would advise bumping them up a bit and giving yourself a long enough final so that you can kill any extra altitude with a slip or gentle s turns. You can fix being a little high (within reason), but if you error on the low side, there isn?t a lot you can do to fix it!

Papa
 
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 know what it'll say, he'll never admit he did it on purpose, he'll just say the engine quit on its own.
 
Safety Margin

Skylor my friend...my post was tongue-in-cheek, that?s why I put a smiley face in it. I certainly don?t advocate using a split-s to return to the runway! But on a more serious note, if you?re trying to work out high and low key numbers as targets for an engine out approach, I would advise bumping them up a bit and giving yourself a long enough final so that you can kill any extra altitude with a slip or gentle s turns. You can fix being a little high (within reason), but if you error on the low side, there isn?t a lot you can do to fix it!

Papa

Yes, I?m aware of the need to add a bit of margin to these numbers. I actually rounded the altitude losses up slightly from the raw values and one needs a bit of margin to allow for wind effects and pilot performance variation. Thank you.

Skylor
 
...and

"...As for the negative replies, remember - no good deed goes unpunished. Certain people just like to hear themselves type!..."

Well you ought to be able to hear the typing when that engine doesn't start...:D
 
SFO Practice

Skylor,

Excellent data and great idea for a thread.

I regularly practice SFO (simulated flame-out patterns). One of the things you noted was that you lost less altitude in a 45-degree banked turn than a 30 degree banked turn, which is a bit counter-intuitive; but physics isn't always intuitive! The most important thing is to have parameters for your airplane (altitude lost in a 180 and 360-degree descending turn, power off and airspeed and/or AOA references for L/Dmax and ONSPEED). One of the biggest factors is the type of propeller fitted. A light-weight, composite fixed pitch propeller may quickly stop in an actual engine failure as you slow to L/Dmax, which reduces drag. A metal prop will usually continue to windmill (unless power loss was the result of an oil system failure) unless the pilot wishes to intentionally stop it. A good ROT is to not bother with attempting to stop the prop at altitudes below 3-4K AGL unless you are very familiar with the technique to do so in your airplane. If the propeller is controllable, the pitch selected has a big impact on glide performance. And residual thrust factors in, practicing in IDLE is not the same as a true power condition; but it is certainly worthwhile practice nonetheless.

Another thing that may seem counter-intuitive is that it may be easier to consistently maneuver an airplane with a lower glide ratio--going down and slowing down simultaneously isn't as difficult and there is less time aloft reducing exposure to wind effects over time. The light weight, motor glider that I fly (160 HP fixed pitch RV-4) just doesn't want to quit flying, which means I have to apply malice of forethought any time I want to go down or, god forbid, go down AND slow down--wind is always a factor, even when it's light.

I find it's actually more challenging from an energy management perspective to fly an "A" pattern, because of the shallow bank angles involved and the need to compensate for winds aloft during descent:

https://youtu.be/vTJotyoBQWM

Although steeper bank angles and some G's are involved, I find the "B" pattern easier to fly consistently well since it reliably drops me off at a standard low key for my airplane. This pattern is just a 1080 steep spiral to 180 power off approach:

https://youtu.be/u4qKhgi32C8

I'm a fan of accurate AOA references, since the key performance AOA's I care about aren't affected by bank angle/G, weight or density altitude. It simplifies energy management. All I have to do is maintain desired AOA and make the sight picture look right--which is about as much cockpit math as my unfrozen fighter pilot brain can handle. You don't need specific bank angle parameters, just "more, less" or "whatever it takes." I'm also a fan of flying every approach (traffic permitting) as an idle 180 so I've got lot's of practice in a power off turn to 10-12" stable final, on parameters.

This, of course, is all technique, not procedure. The only requirements are to maintain sufficient energy and not lose control of the airplane--best to practice regularly using whatever technique suits you to develop consistent hoops to fly thru and sight pictures.

Great discussion.

v/r,

Vac
 
Good specific subject matter Skylor, thanks for sharing.

Love the videos VAC, very useful and your time in making them is apprecuated. I like your pattern B depiction. I'm also a glider pilot. I didn't train on gliders until I was already flying 747's, and it was a great antidote for over exposure to excessive resources in aviation. Learning these types of techniques and thinking proper energy management down low while targeting tight landing fields is thankfully something that comes easy to any "ready to learn" pilot with enough thoughtful (safe) introduction, exposure and practice. In an RV, SFO practice is great for fun and getting better at techniques involved. It's also highly beneficial to keep commonly used procedures anchored to real world needs. We may have to deal with a "SFO" weather we like it or not, when we are least ready to do so and with the least amount of excess mental capacity to come up with something not recently worked on. Having a few good anchor numbers to work with is an outstanding start to executing a real SFO when needed. I also use an old pilotage visual reference SA rule of thumb where my wingtip crossing an object on the ground dictates a safe "fly direct to" no wind glide distance, subject to energy bleed off when turning toward and using speed to make the turn, pulling to glide AOA, etc. Obviously a real SFO overhead arrival procedure can't be to a "direct to" chosen field but in any situation, there is a spectrum of useful techniques one is proficient in that get partially or fully employed along the way to arrive at a successful solution.
 
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