M20J or GLIDER?

[cnoe]

The weather turned nice here today with clearing skies, calm winds, and warm temps. So I went flying. Don't tell my wife. Okay, go ahead; she already knows.

As I like to try new things and learn more about my baby (27 months mine) today's flight was to see first-hand how far I could glide in a power out situation. And boy was I surprised!

I've always been told and used 10-1 for a glide ratio calculation so anytime I'm cruising I figure I can glide about 1.6 nm for every 1,000' AGL in calm air. Looking at my POH it's a bit more optimistic showing a glide ratio of over 11-1. But in today's test flight I beat that easily, achieving a glide ratio of 13.8 - 1. Needless to say I was gleefully surprised!

I set this up by departing my home base to the south climbing to 10,000 AGL about 20nm from the airport. I turned east and reduced power to slowly stabilize the temps as low as possible (to minimize the possibility of shock cooling) before turning back north towards the airport. When I was 16nm from the airport (GPS distance) I pulled the power to idle and the prop control all the way back keeping the airframe in a clean configuration. I then trimmed for an airspeed of ~100ias and started the glide. It was weird seeing the prop turning so slowly (<1,000 rpm) and the engine was making virtually no power. I couldn't hear the engine running and before too long the EGTs on my JPI830 went completely off-scale (low). I occasionally advanced the throttle just a bit to make sure it would power up, but for only a half-second or so (not long enough to affect the results I believe).

As I approached the airport I couldn't believe how HIGH I still was; I had expected to be set up for an approach after starting 16nm out at 10,000AGL. Instead I decided to go ahead and milk the glide as far as I could (down to 1,000AGL). When I crossed the threshold my altitude was still 2,900AGL! So, I continued to the 0nm point at the airport's center before turning west. From that point I glided another 4.5nm before finally dropping down to 1,000AGL at which point I eased in some throttle and prop to arrest the descent. I babied it back in to the runway on a long base-to-final to avoid heating it back up too quickly after the long descent at no power.

I had glided 20.5nm or approximately 124,500' while only giving up 9,000' of altitude! This is much better performance than I expected.

I will qualify by stating that I was at a weight of 2,300#; not gross. But I also was a bit faster than the book speed for best glide which is stated as 98ias (105ias @ 2,740#). I don't know how much another 440# would affect the glide but my POH only has the one graph for this calculation and it doesn't state which weight is shown. I suspect it's for gross.

In any case, from now on while cruising I won't necessarily rule out those airports 20nm-22nm away while in the 10,000AGL range. In fact, for most of my flights I believe that a glide ratio of 13-1 is fairly conservative based on today's test flight.

Any comments, questions, suggestions? I'd love to know if anybody else has done this and what their results were.

CNOE

[kortopates]

How did you account for winds aloft?

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[bonal]

14 minutes ago, kortopates said:

How did you account for winds aloft?

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Yes that was my thought what were the winds at the time of your long glide working for or against you regardless pretty impressive 

[FlyDave]

The heavier you are the faster your best glide speed is - a bit counter intuitive but that's the way it is.

Many high performance sailplanes have water ballast tanks in the wings. On days when an abundance of lift is forecast, pilots of these ships fill the water tanks and increase their best glide speed by as much as 20% from pilot only weights. If you watch youtube videos of sailplane races, when the ships cross the finish line they are dumping the water ballast. It almost looks like they have a smoke system.

[carusoam]

Nice collection of data.  Thanks for sharing it.

Best regards,

-a-

[flyntgr1]

I wouldn't think that the extra weight would effect your glide ratio to much.  It would just increase the speed at which max L/D is achived.  On good soaring days, the high performace sailplane pilots load their wing tanks up with water to make them heavier.  Doesn't effect their L/D just the speed that they achieve it.  This allows them to complete the coarse in a faster time during compititions.  I would think the same principle applys to you.

[carusoam]

Expect the AOA to change a small amount to account for the increased weight.  The cost of the increased AOA will be an increase of lift induced drag.

I would expect the O to be a bit draggier for the same basic reasoning.

I am only a PP.  My largest concern is always going to be an engine out situation.

Best regards,

-a-

[cnoe]

How did you account for winds aloft?

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To be honest I didn't. But I believe they were working against me. It was essentially calm on the ground.

I will research the reported winds and report back. A quick look at Foreflight shows a ~20kt headwind between 3,000 and 9,000 4 hours post-flight. The airport is KLBX and the flight time was 2200Z if anybody wants to check the winds themselves. My heading inbound was ~360.

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[201er]

Now try it with the power completely off and you will probably find that it actually is closer to 11:1. With power off, the windmilling prop and engine make nothing but drag. The idling engine at minimum overcomes its own drag and maybe even gives you a little thrust.

[Immelman]

You're getting a fair amount of power from the engine at idle... I did some experiments on the subject and found the POH numbers were pretty spot on. Stopping the prop makes a significant difference but chews up a bit of altitude to slow to MCA and then recover to a glide:

 

 

Speed was adjusted for actual weight. This was an E model.

 

[carusoam]

Anyone have a glide ratio display on any instrument or app?  I was thinking one of my GPS devices has it somewhere.

If I were gliding, I would be doing things with 10:1 in mind.  It would be comforting to know that the wind was staying at my back or not..,

Best regards,

-a-

[cnoe]

1 hour ago, 201er said:

Now try it with the power completely off and you will probably find that it actually is closer to 11:1. With power off, the windmilling prop and engine make nothing but drag. The idling engine at minimum overcomes its own drag and maybe even gives you a little thrust.

 

Now that I have a better idea of what it can do I'm thinking that pulling the mixture to ICO is the next step. I'm still thinking that 10:1 is erroneous and 12:1+ might be feasible. Thank you for the input.

 

1 hour ago, Immelman said:

You're getting a fair amount of power from the engine at idle... I did some experiments on the subject and found the POH numbers were pretty spot on. Stopping the prop makes a significant difference but chews up a bit of altitude to slow to MCA and then recover to a glide:

 

 

Speed was adjusted for actual weight. This was an E model.

 

And this is the type input I'm seeking. Great info Immelman! As stated above I may compare my results to those of pulling mixture to ICO  (in the airport vicinity) as shown in your table. My question is... how long did you continue your descent at ICO? Over an entire 9K-10K foot descent the results should be informative.

In any case I believe my 10:1 ratio was overly-conservative and I'm going to start looking at possible landing areas 25%-30% further out than previously considered in the case of an engine out.

 

[Hank]

Don't you have a page like this? Your J is heavier than my C, but should be aerodynamically cleaner and glide better. Pulling the prop back is the key to reaching these numbers, and you've already figured that part out. I've made simulated engine out landings at Class D, pulling the power midfield downwind, flying my normal pattern at normal speeds, dropping flaps and gear at the normal spots.

I took a Piper pilot flying, cause he was shopping and had never been in a Mooney. Coming in to land, I pulled the throttle to idle ~60' over the treestops, call it 1/4 mile from the displaced threshold. His head snapped over to me, then back out the window Then made a normal landing. As we were taxiing clear of the runway, he said, "if I'd done that in the Cherokee, we'd of been in the trees, but your plane didn't do anything . . . " with big, round eyes.

Gotta love these planes! Al did everything right, without even a calculator much less a computer, CAD package, wind tunnel, etc.

 

Edited March 4, 2016 by Hank
Picture didn't load the first time

[cnoe]

Here's all the '78 J POH offers for glide...

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[Bob - S50]

10 hours ago, Immelman said:

You're getting a fair amount of power from the engine at idle... I did some experiments on the subject and found the POH numbers were pretty spot on. Stopping the prop makes a significant difference but chews up a bit of altitude to slow to MCA and then recover to a glide:

 

 

Speed was adjusted for actual weight. This was an E model.

 

Immelman,

Great data!  Based on your findings it appears that with the engine at idle, leaving the prop full forward does a good job of simulating an engine failure with the prop pulled all the way out.  Gives me more confidence that I'll be getting realistic practice for the real thing.

[PTK]

Very nice job and fun experiment and great data! I'm looking forward to see your winds aloft analysis! 

[Gone]

For my E model I ran a similar test about 7 years ago and got this result.  The "prop stopped" data came from another source.

Best Glide Prop Windmilling, (12.7:1 glide ratio), 875 fpm descent rate, 105 mph IAS,  91 kts IAS

Best Glide Prop Stopped, (10.3:1 glide ratio), 670 fpm descent rate, 100 mph IAS, 87 kts IAS.

[carusoam]

Related question:

Anyone have a glide ratio display on any instrument or app?  I was thinking one of my GPS devices has it somewhere.

If I were gliding, I would be doing things with 10:1 in mind.  It would be comforting to know that the wind was staying at my back or not..,

Best regards,

-a-

[BDPetersen]

This would be the place to insert a copy of the Mooney ad from the 60's featuring the Mark 21, prop stopped, in formation with a glider. But the usual example of the ad is not showing on eBay today.

[chrisk]

13 hours ago, Hank said:

 

I took a Piper pilot flying, cause he was shopping and had never been in a Mooney. Coming in to land, I pulled the throttle to idle ~60' over the treestops, call it 1/4 mile from the displaced threshold. His head snapped over to me, then back out the window Then made a normal landing. As we were taxiing clear of the runway, he said, "if I'd done that in the Cherokee, we'd of been in the trees, but your plane didn't do anything . . . " with big, round eyes.

I did my commercial in a piper T tail Lance.  The glide ratio was about half of what the Mooney has.  Pulling the power abeam the landing spot for a power off 180 required an immediate diving turn to the runway.  You wouldn't make it if you didn't pull the prop back.  And this was for a really tight pattern. 

I love my Mooney and I have yet to find another plane I would prefer.  The Lance had more space, great climb performance, and landing gear that would soak up any hard landing, but you would be so screwed if the engine ever quit.  --And it was slower, used more gas, .....

[cnoe]

Here is the update I promised with more details including available winds aloft. All the data points were as published by the Cloud Ahoy flight tracking app. Time and altitude figures should be fairly accurate.

N201CK Glide Performance .pdf

As shown in the attached .pdf my time to descend 9,000' was 15.83 minutes giving an average rate of 569 fpm. As a general rule my rate of descent lessened as the air density increased (though I gave up a little extra altitude between 4,000' and 3,000' thinking I was going to land).
The average glide ratio (distance) was 2.28:1 over the entire 9,000' descent in spite of a consistent headwind. Regarding the headwind... the forecast/computed headwind component (from Cloud Ahoy) averaged 16.4 kts, but computing time and distance the average groundspeed was 77.7 kts (89.4 mph). With a target airspeed of 100 mias there was clearly a significant headwind throughout the descent. I did not calculate TAS at each level as I did not track temperature though the altimeter setting was 29.92 so indicated altitude was the same as pressure altitude.

I may work on this more to try and glean more information from it all. I haven't made specific calculations to see how much the winds aloft affected the glide distance. For now I need to do some actual work.

I appreciate any and all input and discussion.

[Hank]

I hope 2.28:1 is 2.28 nm per 1000'. Otherwise you're "gliding" like a rock. 

[cnoe]

Uhhhh, yes. Thanks for pointing that out. I was in a hurry.

That equates to a glide ratio of 13.85:1 which is 38% better than what I previously counted on. Considering I had winds working against me I believe that 13:1 might be a reasonable estimate of glide ratio.

I will post more in the future after completing true "engine off" tests.

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[kpaul]

4 hours ago, Hank said:

I hope 2.28:1 is 2.28 nm per 1000'. Otherwise you're "gliding" like a rock. 

 

34 minutes ago, cnoe said:

Uhhhh, yes. Thanks for pointing that out. I was in a hurry.

That equates to a glide ratio of 13.85:1 which is 38% better than what I previously counted on. Considering I had winds working against me I believe that 13:1 might be a reasonable estimate of glide ratio.

I will post more in the future after completing true "engine off" tests.

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using 2.28 to 1 is a much easier way for most people to think about range.  The math is much easier.  You can glide 22 miles for every 10k of altitude with nearly a 20 kt headwind in this case. 

In the PC-12, I plan for 2.5 to 1 although it's actually better than that no wind.  It makes the using the distances on the nearest page quick and easy.

[cnoe]

Kpaul said:

In the PC-12, I plan for 2.5 to 1 although it's actually better than that no wind.  It makes the using the distances on the nearest page quick and easy.

cnoe replied:

That's pretty awesome! With the pointy nose and fully feathering prop I bet there's very little drag up front.

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