Is your ACTUAL glide ratio wrong?
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- Опубліковано 24 сер 2023
- Engine out glide is hotly debated. I tested my plane with the engine OFF to get my real-world performance numbers. Your glide ratio is critical if you have a real-world engine failure, in particular if you are using something like glide advisor in foreflight. My results were WAY off the 10, 11, or even 12 to one some people reported they were using for a vans RV aircraft.
👍Nice post. I tested this in my RV-7A also.
There are two scenarios for an engine failure: Fuel starvation=wind-milling prop... and engine seizure=prop stopped.
Wind-milling produces more drag than stopped.
I tested mine both ways and found slightly better glide performance with the prop stopped.
To get my Hartzell constant speed two bladed prop to stop (after engine shutdown), the airspeed had to be decreased to just above stall speed. Eventually, it flops to a stop.
Your test results are reasonable for a side-by-side nose-dragger. I'm sure a taildragger tandem seat RV would have way LESS aerodynamic drag than mine... and better glide performance.
Another useful number to determine is Minimum Sink speed....assuming you've glided to overhead a landing field and have lots of altitude remaining to work your problem.
Well... A lot of this is splitting hairs with the glide performance numbers. HOW you fly your airplane in the first minutes of a sudden engine failure is more crucial.
Obviously, turning immediately toward the nearest airport or landing area is important. I always have NRST airport displayed on my RNAV unit even on local flights.
Energy conservation: If you're cruising at 130 knots when the engine quits, the best technique is to pitch up, trading speed for altitude until reaching best glide speed (80 kts) & THEN TRIM to stay there. That will stretch your overall glide distance much better than staying at altitude and bleeding energy due to drag.
Practicing "Power Off 180's" in the pattern is also great practice for energy management. That is the most failed item on a Commercial Pilot checkride. Another tool is mastering the "Forward Slip to Landing".... That takes practice.
Thanks for a great post, Flying Aardvark...
Waldo
I took a Cessna 172B over on my airplane channel - and heavily modified the wings: STOL cuff, VGs, and wing extensions of 3 extra feet in length. I know my glide ratio changed, and I've been testing it but I haven't yet got a solid number. So I've kept a very conservative stock 172 ratio in Foreflight until I can finish testing.
Nice Q-1 shirt.
Interesting video but you neglected a very important factor - the windmilling propeller. There are two basic types of engine failures with two different glide ratios. Let's call the first, Type 1 - Engine isn't producing power but prop is windmilling. Type 2 - Engine seizes, prop stops. Type 2 has a significantly better glide ratio. You might consider a re-do where you pull the mixture then pull the nose up enough to stop the prop. If you do, I think you'll be amazed at the difference. I've tried it in a Citabria, huge difference, felt like I was in an early, low performance sailplane, gobs of time to glide to the ground. Thanks for the video but please address this important variable. John McClanahan, Atlanta
Sounds like a good “part 2.” Will give it a try and see how different it is.
Great video, honestly made me reconsider my glide performance settings in FF. I’m sure this will help a lot of pilots, thx!!
Thanks, and it sure was an eye opener for me!
One more piece to the puzzle... The prop is still spinning during the engine-out descent. This is causing additional drag that would bring different numbers if you were able to get it to stop.
I would think that at idle, the engine isn't producing "thrust" as much as it is assisting overcoming some of the drag that is created with the windmill pumping losses...
Would be interesting to see how much it improves the results, with the prop stopped.
A part II?!?!?!
When I did my, I got around 7.5. That was a lot less than I though it would be in a RV7a. Great vid Ace.
Great video. Looking forward to the follow up with a stopped propeller.
Thanks for the info. I’ve also noticed that some of the glide ratios posted elsewhere in the interwebs seemed a bit optimistic. As a 6A owner I appreciate your test. I’d prefer to err on the side of caution running 7.5:1 as you did.
I wasn’t going to kill the engine in flight as you did to find out so thanks for that too!
Thank you for this! Awesome job. Companies should be forced to provide "correct glide ratios", It may matter to the extent of life or death!
Guys and Gals... this deserves a thumbs up!
Thanks, Robert!
I haven't stopped the prop yet, but I have a SLSA with an absurdly conservative number in the POH. I did a series of tests, using autopilot to reduce the human factor, and I also tested reflex (negative) flap settings and zero. It's hard to test with winds though! I guess I'll have to go up when there's either a perfect crosswind in my test valley or find a time when the wind is near zero. I feel like I'm missing an obvious correction for wind speed so my numbers are still valid, I have the wind data since I'm pulling logs out of my panel anyhow.
Reflex? Wow--What are you flying?
@@flyingaardvarks1133 nothing exotic, just a Flight Design LSA. I know Pipistrels and Maules have reflex, RV10 does, and something like the Columbia or Lancair does as well.
Maybe I missed it but do you run a constant speed prop? My RV-7A got similar glide results but when I pulled the prop control the glide ratio went way up! I too did it with engine off. Nice work
Yup-CS prop. Going to test it in also (next) with the prop way back. But I will still keep my glide ration at 7.5 so I know “worst case” ie no pitch control.
You're obviously also assuming a straight line glide. Having to make a turn would affect your 'safe gliding distance'-no?
It would for sure
Glide "radio"? Really? At least proofread the title..
Ha-thanks. Fixed it.