Glide Ratios

[Txbyker]

After my BFR this morning my instructor and I performed some glide manuevers to determine best speeds and configurations of my J should I need to glide from altitude for any reason.  I am always pressing NRST to determine closet airport when I change tanks or lose site of towns, etc.  I felt it would be nice to know my glide configuration that is best for me, not just what is in the POH.

Normal pilot, one passenger, full fuel.

We glided from 6000 feet to 1000 feet with full prop and zero throttle into a 10 knot wind.  Glide at 90 knots and see 600-700 foot per minute descent.  

Glided with the wind, 90 knots, and see similar 600-700 ft per minute descent.  So a good average number is about 2 miles per 1000 feet should something happen to have to glide to land.  Pulling the prop all the way back changed to about 400-500 ft per minute descent.

This exercise was good for me.  I can see that if you are calm and have some altitude there is plenty of time to plan, communicate, and navigate.

Did the same drill in the pattern similating engine failure and glide to land.  All in all an impactful lesson for me.

Does anyone else have any comments or personal formulas for no-power glides?

[Jeff_S]

Yes, you're going to see the same descent ration either into or with the wind because your airplane doesn't know it's in the wind! Of course, your ground speed is what matters, so did you factor that into your 2 miles/1000' calculation? That does sound about right for no-wind...I always felt the M20J had a roughly 11:1 glide ratio as a rule of thumb. I also got the lesson in my transition training about the difference between having the prop in or out...it makes a big difference! Any type of engine out landing I think would merit pulling the prop out immediately to reduce drag and give you more options. Coming from a fixed-pitch airplane this was an eye opener.

[231flyer]

I can confirm the 2 miles per 1000 ft glide at 85 knots and bears out close to the book values.  85 knots turns out to be the best speed in my 231 and translates to 500 ft/min decent provided the prop is stopped, flat,  and positioned parallel to the wings.  The decent required is sharper (~650 ft/min) if the prop is allowed to windmill.

I too highly recommend power off practice landings because most of us fail to realize the feel of the airplane with the power completely off.  The only addition I would suggest is to go practice a full no power (cut your engine) landing next time you get a calm no wind day.  Line up at 3000 ft AGL over your field and stop the engine. You will probably get 2/2.5 circuits over the field before you are ready to line up for your base to final transition.  Make sure you are proficient with your full slip landings incase you are a little high or fast before touch down.  Cork-screw landings are fun and a great way to keep your flying skills sharp. As always its best to have a safety pilot in the right seat.

I had an emergency landing without power (engine fire) at KLIT several years ago.  I learned to fly in gliders and those skills definitely saved my butt.

[Shadrach]

When you say cut your engine, are you suggesting mags off, prop stopped?

[231flyer]

The preferred method is to bring the throttle back to flight idle and then cut-off the mixture.  It is crucial you are proficient in your stalls/slips etc before you go out and attempt a complete engine off landing but yes, I do mean engine stoppped! The actual prop stopping is, I believe, a function of airspeed, pitch, lunar phase, wind, and solar flares;).  The only instance of my prop comming to a complete stop was accomplished in a take-off configuration with full onset of a stall.  I think the airspeed was below 60 Knots when I killed the engine.  My prop (2 blade McCauley) always windmills in my power off practice landings.  The difference between actual power off and flight idle is quite acute.  We have all been trained to do power off landings with the engine pulled to flight idle.  Having survived an actual engine off, dead stick landing I can personally attest the experience is completely different.  With gear out and 5 degrees flaps the Mooney drops like a rock. If you practice the cork-screw, the base turn is essentially abeam the numbers and the landing roll is basically non existent. I think an actual power-off landing should be part of our initial and recurrent training. This sort of training is also useful if your engine quits on takeoff.  Many accomplished single-engine pilots end up stalling their planes after an engine out on takeoff because we never actually experience the plane without power. Sounds scary but a good instructor can be invaluable, else go get some glider time!!!!

[jetdriven]

2 miles per 1000 ft it slightly better than the book says, which is 19 miles (zero wind).   Pulling the prop back in a 201 with the McCauley C212 prop doesnt change anything, the RPM is already stabilized at ~1700. At least in ours it doesnt.   Im not sure how it lowered your descent rate 20%. At lower weights than gross, Vg is less as well, but glide distance remains the same.

[Guillaume]

Quote: jetdriven

2 miles per 1000 ft it slightly better than the book says, which is 19 miles (zero wind).   Pulling the prop back in a 201 with the McCauley C212 prop doesnt change anything, the RPM is already stabilized at ~1700. At least in ours it doesnt.   Im not sure how it lowered your descent rate 20%. At lower weights than gross, Vg is less as well, but glide distance remains the same.

[danb35]

I tested my F a few years ago--climbed to 10k, shut down the engine with mixture, trimmed for best glide, and timed the descent from 9k to 6k with the prop windmilling.  I did two tests, one with the prop full forward, the second with it all the way back.  Unlike in Byron's J, there was a significant difference in RPM for me, and the glide was about 20% better with the prop back (low RPM).  Overall was a little better than 12:1--I'll have to see if I can find my original write-up.

[Alan Fox]

During my initial training with a C/S prop the instructor pulled the prop lever back when doing a simulated emercency landing , and it felt like releasing the parking brake on a car....Big difference...

[Ned Gravel]

During my initial training with a C/S prop the instructor pulled the prop lever back when doing a simulated emercency landing , and it felt like releasing the parking brake on a car....Big difference...

 

That is a good example of why having the prop control all the way forward on approaches (like near the FAF) can sometimes act like a speedbrake. 

[carusoam]

I'm looking forward to Jim's iPhone findings.

Old iEquipment bought at a nicely discounted price, improving situational awareness.

Do we have an app that measures glide ratio in real time? WingX or something from the glider world?

Best regards,

-a-

[bd32322]

Pulling the prop back should work if you have oil pressure, which you may not have in an engine failure ... I think.

Another thing an AOPA article recommended is to get the aircraft close to stall speed. That stops the prop from windmilling and you end up with the prop in a feathered condition. Even though you later increase speed to best glide, the prop will not windmill. Recommended only if you absolutely have to stretch the glide. Never tried it because I have never knowingly turned off the fan.

[bumper]

Pulling the prop back should work if you have oil pressure, which you may not have in an engine failure ... I think.

Another thing an AOPA article recommended is to get the aircraft close to stall speed. That stops the prop from windmilling and you end up with the prop in a feathered condition. Even though you later increase speed to best glide, the prop will not windmill. Recommended only if you absolutely have to stretch the glide. Never tried it because I have never knowingly turned off the fan.

 

There are some Mooney conversions (Missle, Rocket) with feathering props (blades go full feather with loss of oil pressure), but I think factory stuff goes to flat pitch stops with loss of oil pressure.

 

If a prop is windmilling, the swept area is pretty much like flat plate drag. Going course pitch helps some. Stopping the prop reduces drag much more, as you and others state. If you have far to glide or if "final glide" (glider speak) is in doubt, stopping the prop makes sense, as does leaving the draggy stuff up and tucked away until the runway is made (just don't forget in your exuberance in having arrived at the airport with altitude to spare). In my one instance of engine failure I put the wheels down on short final . . . nice that even the Mooney electric gear is quick. Glider experience is most reassuring!

 

I have not stopped the prop on my Mooney.  I have done so with my Husky (O-360). Nose up to almost stall to get it to stop, then the Husky was still climbing at over 1,000 fpm in our resident Sierra mountain wave. I didn't leave it off long as I was afraid of cold soaking the engine in the 20'ish OAT. Nosed over to windmill start and promptly decided that was not a great idea with the ASI rapidly approached VNe and the prop not showing any inclination to move. Used the starter instead.

[WardHolbrook]

... had an emergency landing without power (engine fire) at KLIT several years ago.  I learned to fly in gliders and those skills definitely saved my butt.

 

Amen to that. I had an engine failure in a C172 several years back and drawing upon my glider experience saved my bacon that day as well.

 

Pulling the prop back cuts the drag significantly, but if the engine has failed you're going to want to stop the prop from windmilling as well for maximum drag reduction.

[bd32322]

Amen to that. I had an engine failure in a C172 several years back and drawing upon my glider experience saved my bacon that day as well.

 

Pulling the prop back cuts the drag significantly, but if the engine has failed you're going to want to stop the prop from windmilling as well for maximum drag reduction.

I have toyed with gliders ... Time for me to get serious and get a license. Its probably orders of magnitude cheaper

[aaronk25]

Went out yesterday to 6000 feet and did some glides in a friends 201 at about 2,350lbs. We put engine at idle and pulled the blue knob and we needed to sacrifice about 650 Fpm to maintain. 85 kts and rpm was at 1200. I said this isn't right and pulled the blue knob a bit more of a stiff pull and it came out more. There was almost like a indent in the cable or something but rpms fell off to 700 and airplane accelerated so we trimmed up and were able to get 550fpm at 85kts as a glide ratio.

Was surprised how much difference there was in glide range just because of the prop only being pulled back approx 90% of the way vs 100%.

[WardHolbrook]

I have toyed with gliders ... Time for me to get serious and get a license. Its probably orders of magnitude cheaper

 

Back in the day when I was actively instructing in gliders, most guys could crank out a pvt add-on in a couple of days. It just isn't that difficult and many of the things you learn are directly transferable to any power flying you do. For me, it made the difference between having to ditch vs making an island in that 172 after the engine failed. It also got me dinner after the sim instructor failed all of the engines at 10,000' agl. He heard me talking with a couple of other glider guys and bet me I couldn't put the jet on a runway. On the way down, I asked him to select the runway and I put it on the numbers. He bought dinner that night. 

 

If any of you question your ability to actually handle an engine failure scenario, I would highly recommend a little glider time. It won't take much effort and most guys find it a lot of fun. Here's a link to find the nearest soaring site...

 

http://www.ssa.org/sport/wheretofly.asp   

[carusoam]

http://www.ssa.org/

The link above didn't work, but a note showed this link above.

http://www.ssa.org/FAST.asp. Offers $99 for .5 hrs classroom and .5 hrs of flying

Best regards,

-a-

[WardHolbrook]

Here's the link that works...

 

http://ssa.org/sport/wheretofly.asp

 

Sorry

[fantom]

Can't wait for photos of your set up once you get it right, Jim. After lots of practice with power off glides in my heavy MSE, two people, half or more fuel, clean, the 11:1 ratio is right on, and we definitely picked up 15+% pulling the prop all the way back to flat. Byron....you have a weird bird

[jetdriven]

Perhaps so.  I have shut the fuel off several times inflight in our plane, anywhere near glide speed the prop stabilizes at ~1700 RPM and the blue knob does nothing. It also wont do anything below ~1900 on the ground during a runup. It is a stock ('78 and up) McCauley C214 that has been in the shop 130 hours ago and checked out fine, and this is the second engine and second prop governor that is plugged into it.

 

I have also fooled around with super low speed cruise and the prop will only govern down to 1950 RPM, then the knob hits the rear stop.

[xftrplt]

After lots of practice with power off glides in my heavy MSE, two people, half or more fuel, clean, the 11:1 ratio is right on...

As I'm sure Gary knows (and positive Byron knows), aircraft weight has no significant bearing on Glide Ratio.

The heavier you are, the faster you fly to hold the AOA for Max L/D. You'll go faster and descend faster, but the ratio is the same.

[xftrplt]

Jim, as you probably know, the correction for GW is approximately 2Kts/100# for your difference from the book speed.

Correction = (actual weight / POH weight)^2 (POH speed).

[Seth]

There are some Mooney conversions (Missle, Rocket) with feathering props (blades go full feather with loss of oil pressure), but I think factory stuff goes to flat pitch stops with loss of oil pressure.

 

That is correct.  My Missile has a fully feathering prop, though I have never shut the engine down in flight to test it.  The glide ration according to Rocket Engineering is 16:1 with the prop feathered.  Personally, I'd plan 3 miles for every 1000 feet, but I'd want to test that first on my own to see if my plane was indeed capable of the STCed 16:1 ratio.

 

Have any Rocket or Missile owners on this board ever feathered their props in flight?

 

-Seth

[fantom]

As I'm sure Gary knows (and positive Byron knows), aircraft weight has no significant bearing on Glide Ratio.

The heavier you are, the faster you fly to hold the AOA for Max L/D. You'll go faster and descend faster, but the ratio is the same.

 

Copy that, Dick.

 

My 'heavy' comment was aimed at the 2740 pounders  who want to spend big $ for another 160 lbs.

 

BTW, I'm gliding at 90 kts. +/- a couple, and the actual ratio is closer to 12:1