Engine Out Glide Ratio

[Acenels]

How far can your RV glide with the engine out?

So I surfed around all kinds of places. I read the Cafe testing of an RV6A (what I fly). And I gotta tell ya, people who have a glide ratio over 9:1, I think it's wrong. Mayyyybe the RV9 is way different, but not a 6. Its much less.

In fact, in my "POH" that was created for my plane, which I have modified, it is listed as 11.4:1, and that is WAY over what I found through testing.

Would love to hear any other thoughts here. My methodology explained in the video.

 

[ArlingtonRV]

Nice video, thanks for putting that together. That is really good information. I have been using 8.5:1, but that is not based on my own testing. I may go do the same thing just to see what I get.

 

[wcalvert]

Didn't catch it in the video ... prop stopped or turning? Made a big difference on my tests.

Good stuff, keep it up!

Cheers

 

[Dan 57]

Thanks for that Ace.
Yep, looking into SkyDemon (European NavData tool) I found the glide ratio set at 12… by myself, a few years ago, no testing

The -6 has, if only the bits sticking out of the fuselage are considered, the shortest wings of the fleet (but for the -3?).

Again, thanks for your time testing and publishing. I’ve downed my ratio to 8 for now.

 

[Acenels]

Didn't catch it in the video ... prop stopped or turning? Made a big difference on my tests.

Good stuff, keep it up!

Cheers

Kept spinning. I did (on other runs) get down into the 60s and the prop stayed spinning.

I am (of course!) tempted to pitch up, stop the prop, and see if that makes a meaningful difference. I know some others have done that on other types of planes, but my curiosity on the RV is (of course) peaked to try it out.

 

[edclee]

Glide Ratio

I have tested my RV-9A at various speeds and with just me and full fuel, that is below max gross, I get just over 10. I use a simple formula in my mind for it at 2 miles per 1000 ft of altitude above ground. 100 mph at that weight. Faster if you are heavier. I instructed about 40 hours in a 6A and agree with you, no way is it even close to 10:1.
Ed

 

[Mike S]

As I recall, the CAFE test was on Steve Barnard's 6a and they had the plane rigged with a bunch of instrumentation----including a way to run the engine at the needed RPM to keep the thrust and prop drag down to zero for the testing.

 

[Desert Rat]

It will be fun to play with this once I'm flying and it would be a happy surprise to discover I'm wrong, but I'll be shocked if an RV7 has more than about a 7:1 glide ratio with the prop windmilling.

A 172 has basically the same wing loading and a much higher aspect ratio, yet it's only around 9:1.

 

[MacCool]

As I recall, the CAFE test was on Steve Barnard's 6a and they had the plane rigged with a bunch of instrumentation----including a way to run the engine at the needed RPM to keep the thrust and prop drag down to zero for the testing.

CAFE Foundation similarly tested N129RV, which is/was owned by Van's, apparently an early quick-build RV-9A (9A was introduced a couple of years before the conventional gear version IIUC). I have the PDF of their very comprehensive report, but I don't know if it's online anywhere. They indicated a 12:1 glide ratio, which seems optimistic for that model, based on my experiece and casual testing. I use 10:1

 

[agent4573]

It will be fun to play with this once I'm flying and it would be a happy surprise to discover I'm wrong, but I'll be shocked if an RV7 has more than about a 7:1 glide ratio with the prop windmilling.

A 172 has basically the same wing loading and a much higher aspect ratio, yet it's only around 9:1.

We've got 8:1 programmed in for our 7 and it seems to fit the "rule of thumb" I've seen on the board that if the airport is under your wing you can glide there.

I've also seen people say 90kias is best guide, and for us a 90kias glide with the prop forward is a 30 degrees nose down dive bomb at the ground giving us roughly a 3:1 glide. So make sure to back up any number given to you with your own tests.

 

[Ralph Inkster]

To me- glide ratio is a 'feel good number'

Effectively, after you process the fact that you don't have a reliable engine... look down & anything within a 45 degree visual cone below you is your realistic glide distance.

I determined & had to confirmed that fact a couple times...

 

[Bill Boyd]

If I remember my trig correctly, that 45 degree cone is the same as an assumed 1:1 glide ratio. Sounds pretty conservative to me.

 

[jrs14855]

Prop

"prop forward" in post number 10 is only mention of the significant difference between fixed pitch and constant speed props as well as the difference between various props, both fixed pitch and constant speed.
An important part of emergency procedure is prop control all the way back for most but not all constant speeds.
Another consideration is what percentage of wing area is behind the prop. The RV9 would be expected to perform better in that regard because of the smaller percentage of wing area behind the prop.

 

[rocketman1988]

Nice to know

Glide ratio is is nice to know, still air, theoretical number. In reality, though, it is not nearly as impressive or useful...

 

[RV8iator]

Actual experience

I had an engine failure on my 8 several years ago. I was at 6500 MSL, 5800 AGL cruising along and it went silent. Didn’t take long to figure out it was real. Did all the pilot stuff and was established at my best glide speed say within 500 feet.
Went back and looked at all my EFIS data and time from loss of power to touchdown was just over 4 and a half minutes. Prop was windmilling for about a minute until I stopped it. My descent rate worked out about 1200 FPM.
Be prepared is good advice. When it happens, it happens pretty quick. And a glide ratio of somewhere around 8:1 is pretty steep. Flying high is good insurance too.
The low spot in the far treeline was my approach path and the bottom pic shows where I turned around on roll out because of the house up front.



The good news was not a scratch to either me or plane. This was second one of these in my career. I hooe that’s it. But, it can happen!

Got the tee shirt..

 

[Roadjunkie1]

Engine failure.....

I had an engine failure on my 8 several years ago.....

Nice job of saving yourself and your airplane!

What did you find was the cause of your engine failure?

 

[Ralph Inkster]

Yes, first time I was high enough to glide 5 miles to the nearest runway.
Second time I was 1000 agl & that gives you just time to lock in best glide speed & look down where you are going to plant it, which turned out to be a remote road that was prepped to be paved the next day..

So test for best glide speed, give it a very conservative considered glide ratio & factor in maneuvering time in that glide.

 

[RV8iator]

Nice job of saving yourself and your airplane!

What did you find was the cause of your engine failure?

46 hours on a brand new ECI. I had just installed an inverted oil system. Was on the way to KAND to get in the aerobatic box and play and thought I’d just do some inverted check on the way. I rolled inverted and within just a second or two it stopped cold. Did all the normal “oh crap” items, pump, mixture, ignition blah blah cussed a bit..
but it just popped and windmilled. Zero oil pressure.
It turned out there must have been FOD in the case that was dislodged with the negative Gs because when they opened it up it has teeth missing on a couple gears in the accessory case. Enough that the cam was not spinning at all.
It was DOA. I should’ve boight a lottery ticket that day!

 

[Roadjunkie1]

Practice practice practice....

Make sure to back up any number given to you with your own tests.

Knowing what your best glide speed is and the glide ratio are good things to know. Going out and practicing your emergency procedures is KEY to putting that knowledge to good use. You need to have your emergency checklist in your head as well as on your knee. When the Music Stops, things suddenly start to happen very quickly. The first thing that happens is the delay between the Stop and your understanding that it is really happening! Probably at least 5 seconds or so. Being raised on Cubs, I've had several engine outs and, having practiced the Emergency Check List, am happy when I remember all of the key points and disappointed when I forget something.

I have no Foreflight to look at in the Cub and have established where things line up on the airplane with the ground that tells me I can make it to that point on the ground. Same with SuzieQ: I know where on the airplane those places are on the ground that line up and tell me yes, I can make it to that point. I'm checking the airspeed with frequent glances to make sure the airplane is doing what it is telling me it is doing. But I have likely already have a place in mind to put the airplane. And am going through the Emergency Checklist in my mind, with back up on my kneeboard. That way almost ALL of my attention is OUTSIDE the airplane.

Aviate. Navigate. Communicate: Aviate: FLY THE AIRPLANE. Navigate: FLY THE AIRPLANE to that piece of space I need to be in, both in the air and on the ground. Communicate: if necessary, which means pushing the radio 121.9 key. Pushing the ELT ON key. Keying the mic and telling anyone who might be listening that things might be going awry. That might be further down the checklist.....

On to the checklist. The thing I forget the most: fuel off. I think it is a mental thing: if you turn the fuel off, you are committed to landing where you are going. That has become less frequent with practice. Muscle memory is a wonderful thing!

Practice practice practice......

 

[wcalvert]

Michael, good advice. I always approach these potential situations knowing that my brain will be operating at about 50% and an un-memorized checklist will be useless. BIG picture will be your method of operation with half speed flying skills thrown in. Inside the wingtip for possible glide distance, have a speed in mind, and just to add some fun, assume your instruments will be unavailable.

The last comment may sound strange, but heading into OSH last summer my Dynon decided to start showing my big red X's instead of useful info. I had a tablet that showed GPS altitude and airspeed, and the tight pattern and landing was done with that. No boasting, just a reminder that stuff does happen and all your planning will be mute when you sustain combat damage.

So go fly more, test some scenarios and learn some stuff about your plane!

Cheers

 

[BobTurner]

And don’t forget: best glide speed - defined as best distance covered over the ground per foot of altitude loss - depends on the wind. With a headwind (always desirable for an off airport touchdown) max distance speed will be higher than no-wind max glide. There are so many variables (prop spinning or stalled, CS at max angle attack, weight, as well as wind) that for any real emergency best glide is where to start, then quickly adjust depending on the actual conditions.

 

[Scott Hersha]

"prop forward" in post number 10 is only mention of the significant difference between fixed pitch and constant speed props as well as the difference between various props, both fixed pitch and constant speed.
An important part of emergency procedure is prop control all the way back for most but not all constant speeds.
Another consideration is what percentage of wing area is behind the prop. The RV9 would be expected to perform better in that regard because of the smaller percentage of wing area behind the prop.

My thoughts are the same. My current airplane is an RV6 with a GA fixed pitch prop, and it sure is a lot different in terms glide range than my prior RV’s with constant speed props. With the CS propped airplanes in the landing pattern, if I wanted an idle power approach/landing, when on the perch at 135 KIAS and pulling the throttle to idle, I needed to turn base and final right away or I would have to add power to make the runway. With my current fixed pitch RV6, I need to be at about 100KIAS at mid field downwind with the throttle at idle, or I’ll end up with a long (2-3 mile) final. I feel that my estimated 10:1 ratio in my current airplane is a safe conservative ratio. On my CS RV’s I assumed a 6:1, and maybe it was not that conservative.
Question I have - pulling the prop lever all the way back to coarse pitch makes a difference in glide ratio with the engine still running at idle - but what if the engine wasn’t running, and you had no oil pressure? Wouldn’t the prop drive to fine pitch with no oil pressure? In the landing pattern, when my airspeed got down to 80-90K, moving the prop lever either way had no effect at all - on all three of my CS RV’s. I assume I was outside of the prop governing range. I know that on preflight run up I needed more than 1800 RPM to cycle the prop. I don’t need to worry about that anymore with my fixed pitch RV6 - which I like (most of the time) - but it always made me wonder if I would actually be able to stretch my glide with my CS prop set to full low RPM.

 

[Jpm757]

Best L/D is easy for those using AOA, 2 green bars on my AFS/Dynon.

 

[PhatRV]

I am prepping for the phase 1 testing using the EAA flight test manual.

The manual says to test the best glide speed for specific airplane configuration, and use the three reference speeds: Vy-10kts, Vy, Vy+10kts. At each speed, set the airplane for the least amount drag configuration, test by gliding your airplane at idle and to find the distance travelled after a loss of 3000 ft. Climb and do the same gliding speed at the reciprocal direction to cancel out the effects of wind. Repeat using the other two speeds. The manual also says to test the light weight configuration and the heavy weight configuration because the best glide speed differs based on the airplane weight. This makes sense based on my experience with gliders

Plot the speeds tested and distance travels for each speed. The speed that has the longest distance is a best glide speed. There are few new RVs in local area and I know some never performed this test.

 

[Mikeyb]

CS prop effect on glide

How much effect the prop pitch has on glide ratio depends on the prop and governor and of course if you have oil pressure.

https://vansairforce.net/community/showthread.php?t=212038

I tested mine at idle power. The difference is dramatic.

Hartzell Composite prop and PCU 5000X governor.
1440 lb solo
88 mph


Prop full forward
1700 RPM
1100 fpm average rate of decent.

Prop full aft
1000RPM
600 fpm average rate of decent.
Mike

 

[Acenels]

For the record (as I didn’t mention it on the video), I left the prop pitch where it was. My logic for the “number” to use is that I want to assume a worst case “best glide.” Having prop control is a luxury on a really bad day ��

But this does make me curious. I want to go retest in course pitch and also with the prop fully stopped.

My prediction is that having the prop stopped won’t make as large an impact as one might think, if any, but I’ve been wrong before so will report back.

I’m sure the CAFE folks are smarter than me, but figuring out the thrust to negate the prop seems…I don’t know…off. Sure, if the prop departs the airplane that’s perfect, but in a real world scenario the prop is still causing drag. Am I missing something obvious on that? Their number is on the list that looks pretty optimistic to me for the rv6.

Ace

 

[rv8ch]

I found the best glide curve to be very flat around 100kts for my RV-8, and that's an easy number to remember, so that's what I use.

I've got my EFB "glide ring" set to 8:1 and it looks pretty reasonable.

I test this from time to time when coming into my home field - I stay kind of high (3000 ft AGL) until the glide ring just touches the runway, then cut power and pull back the blue knob and trim for 100kts and see how it goes. It seems to generally work out.

If I can't get the prop to go to coarse pitch in a real emergency, then I'll try to get it stopped by slowing way down, if I can't find a landing place right under me. Assuming I can even think in that scenario.

When flying cross country, I frequently pretend I just had an engine failure, and check "nearest" to see where I would go. Trying to make the buttonology become instinctual.

We can all hope for as good an outcome that Widget had during an actual failure. Impressive!

 

[agent4573]

My thoughts are the same. My current airplane is an RV6 with a GA fixed pitch prop, and it sure is a lot different in terms glide range than my prior RV’s with constant speed props. With the CS propped airplanes in the landing pattern, if I wanted an idle power approach/landing, when on the perch at 135 KIAS and pulling the throttle to idle, I needed to turn base and final right away or I would have to add power to make the runway. With my current fixed pitch RV6, I need to be at about 100KIAS at mid field downwind with the throttle at idle, or I’ll end up with a long (2-3 mile) final. I feel that my estimated 10:1 ratio in my current airplane is a safe conservative ratio. On my CS RV’s I assumed a 6:1, and maybe it was not that conservative.
Question I have - pulling the prop lever all the way back to coarse pitch makes a difference in glide ratio with the engine still running at idle - but what if the engine wasn’t running, and you had no oil pressure? Wouldn’t the prop drive to fine pitch with no oil pressure? In the landing pattern, when my airspeed got down to 80-90K, moving the prop lever either way had no effect at all - on all three of my CS RV’s. I assume I was outside of the prop governing range. I know that on preflight run up I needed more than 1800 RPM to cycle the prop. I don’t need to worry about that anymore with my fixed pitch RV6 - which I like (most of the time) - but it always made me wonder if I would actually be able to stretch my glide with my CS prop set to full low RPM.

The assumption for most is that the engine issue isn't a catastrophic loss of oil pressure but some other reason. As long as the prop is windmilling, you'll have some oil pressure. In our setup, power off 180s still allow full control of the prop pitch. We can use our prop as an adjustable speed break and it works great. Results will vary with prop and engine, but it's something you should test for your setup.

 

[BobTurner]

Best L/D is easy for those using AOA, 2 green bars on my AFS/Dynon.

Remember that the airspeed for best glide ratio relative to the ground is not always max L/D, it’s faster into a headwind, slower with a tailwind.

 

[sailvi767]

It’s easy in the Rocket with a big 3 blade to tell what airfields I can reach. I just roll to 90 degrees of bank and look straight down. If there is an airfield I am golden. If not I am going to owe a farmer something!

 

[plehrke]

Best L/D is easy for those using AOA, 2 green bars on my AFS/Dynon.

I thought the same thing but I think I will spend a few gallons of gas doing some glides and see where my AOA is saying max L/D is and what flight data says. It has been 16 years since phase 1 testing glide ratio. Should be fun.

 

[Acenels]

What would your test profile look like for that?

 

[Blw2]

So this morning while walking the dog, youtube thought that I should watch this video...so I did! Enjoyed it.

A couple questions came to mind so I came here in mind to start a thread...but searched and found this!

1) was the already asked thing about the prop....

2) I can't ever recall a time with an instructor...and I know I've never done it solo.... when an engine was shut down cold..... except I'm pretty sure we did it a time or two when I was working on my multi rating....
but
even when doing the engine out drills in that old Apache, I'm pretty sure that most of the time the "dead" engine would be set at some low RPM, to simulate 'zero' thrust. I don't recall the number that was used, but I'm pretty sure it was not just full idle.... it might have been 100 or 200 RPM above that (???)
Anyway
my question was wondering if anyone had ever done any testing to determine if such a power setting does indeed match a real dead engine.

3) I don't recall ever testing this, but I have read that full nose up trim will result in something at or very close to best glide (in the context of certified aircraft). Curious how many homebuilts are rigged that way.

 

[BobTurner]

For a twin, running the engine at idle with the prop not feathered results in more drag than the engine off but the prop feathered. So adding a small additional power, slightly above idle, results in drag about the same as with the prop feathered. For our singles - assuming no-one has a full feathering prop - you’ll have more drag engine out windmilling than with any power on scenario, unless you think you can stop the prop completely (often hard to do).
Edit. Yes, when I was a partner in a 182, full nose up trim with idle power resulted in close to best glide speed for the pattern with only people in the front (e.g., the lower than gross weight reduction in ‘best glide’ speed for the lower weight was typically canceled by the need for higher speed due to the headwind on final). But with an aft- heavy loading, less trim up was needed.

 

[Blw2]

ahh yes, feathering. I knew there was a variable this rusty pilot was not remembering in that context! thanks

 

[Mnemonics]

On my RV-7 I glide at 80kts losing 750ft/m, which is almost 11:1 (prop not feathered).
Since I'm not going to actually kill my engine and feather the prop I'm not sure what it would do in that config.

 

[swjohnsey]

Pulling the prop back to low rpm dramatically increases you glide ration if you have a CS prop.

 

[Taltruda]

Fixed pitch RV-4, I use 90 knots and have my glide ring on Foreflight set to 9:1. Seems pretty close as I can do idle at 3000 feet when the airport is just touching the ring. I should test with mixture at ICO one these days..

 

[RVDan]

On my RV-7 I glide at 80kts losing 750ft/m, which is almost 11:1 (prop not feathered).
Since I'm not going to actually kill my engine and feather the prop I'm not sure what it would do in that config.

Do you actually have a feathering prop? Never seen one on a single engine recip aircraft, not that it couldn’t be done. They would typically only be on twins.

 

[donaziza]

Do you actually have a feathering prop? Never seen one on a single engine recip aircraft, not that it couldn’t be done. They would typically only be on twins.

I saw an RV 7 with a full feathering prop about 2 weeks ago. It was electric and feathered slower than molasses, but it "did" full feather. Can't remember now, but I think the engine was one of those European UL engines.

 

[Acenels]

So this morning while walking the dog, youtube thought that I should watch this video...so I did! Enjoyed it.

A couple questions came to mind so I came here in mind to start a thread...but searched and found this!

1) was the already asked thing about the prop....

2) I can't ever recall a time with an instructor...and I know I've never done it solo.... when an engine was shut down cold..... except I'm pretty sure we did it a time or two when I was working on my multi rating....
but
even when doing the engine out drills in that old Apache, I'm pretty sure that most of the time the "dead" engine would be set at some low RPM, to simulate 'zero' thrust. I don't recall the number that was used, but I'm pretty sure it was not just full idle.... it might have been 100 or 200 RPM above that (???)
Anyway
my question was wondering if anyone had ever done any testing to determine if such a power setting does indeed match a real dead engine.

3) I don't recall ever testing this, but I have read that full nose up trim will result in something at or very close to best glide (in the context of certified aircraft). Curious how many homebuilts are rigged that way.

On number 2, even a little RPM definitely added to the glide in my case.

 

[ChiefPilot]

Do you actually have a feathering prop? Never seen one on a single engine recip aircraft, not that it couldn’t be done. They would typically only be on twins.

Quite common on aerobatic aircraft. I’m kind of surprised more RVs don’t have them actually, at least those in the comp. aerobatics circles.

 

[Mnemonics]

Do you actually have a feathering prop? Never seen one on a single engine recip aircraft, not that it couldn’t be done. They would typically only be on twins.

Yes, I installed a ULPower 520iSA 6 cyl. engine on my RV-7 and according to the factory they advised an Airmaster prop which has either a feather or reverse mode on the controller. In hind site reverse would be cool too backing up in the hangar

 

[Mel]

Yes, I installed a ULPower 520iSA 6 cyl. engine on my RV-7 and according to the factory they advised an Airmaster prop which has either a feather or reverse mode on the controller. In hind site reverse would be cool too backing up in the hangar

Backing into hangar might be kinda tricky.

 

[airguy]

Yes, I installed a ULPower 520iSA 6 cyl. engine on my RV-7 and according to the factory they advised an Airmaster prop which has either a feather or reverse mode on the controller. In hind site reverse would be cool too backing up in the hangar

Might be a little sporty, trying to back a tailwheel...

 

[Desert Rat]

Backing into hangar might be kinda tricky.

One of coolest things about flying the Caravan was the ability to back it into a parking spot, but I was never brave (stupid?) enough try to back one into a hangar

 

[Mel]

One of coolest things about flying the Caravan was the ability to back it into a parking spot, but I was never brave (stupid?) enough try to back one into a hangar

I once observed a Republic Seabee back into a parking space.

 

[sailvi767]

My son backing a slightly larger aircraft.

https://www.cbc.ca/player/play/2230969923836

 

[Norman CYYJ]

Use to taxi into the hangar and then back out with the Twin Otter.

 

[ronrapp]

I've got the Sensenich composite ground adjustable prop on my RV-6 and at idle power, the aircraft will almost accelerate on a 3 degree glidepath.

On the other hand, I've flown plenty of -6 and -7 constant speed aircraft which could make very short approaches due to the drag from the prop at high pitch.

I used to teach a bunch in the Pitts S-2 series, and one of my favorite things to do with an experienced Pitts pilot was to give them a simulated engine failure on downwind. As others have noted, aerobatic props are like the ones on multi-engine airplanes: a loss of oil pressure will cause the prop to go to high pitch (aka low RPM) to protect the engine. So on downwind I'd pull the prop slowly back to low RPM, and without exception, every single pilot would end up excessively high and fast on final.

They just weren't used to flying the airplane without all the drag from an MTV9 or Hartzell Claw or whatever they had.

I liked this demonstration because it always impressed upon them that most of the drag comes from the prop. If it feathers or stops, you'll be flying a much different airplane.

FWIW, I got the idea for this from Norm De Witt, who once had an engine failure in an Extra and ended up flying over multiple stands of trees before he could get the airplane slowed down sufficiently to land it in a field.

--Ron