Best glide with gear down

ejensen

ejensen

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Gone West
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Feb 23, 2005
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Eric Jensen
It's pretty clear that best glide speed decreases with increased parasitic drag. But is there a way to estimate how much. I'm working in the commercial and the instructor teaches power off 180s with the gear down. I'm flying a Mooney M20F, I've been using best glide of 105 mph at gross lowered to 95 for training weights. These are estimate since the 68 owners manual doesn't offer much info, not even best glide. How much more should I reduce for the gear or is there a way to figure best glide speed?
 
Absent a lot more aerodynamic design data than we are likely to find available, the only way to find out is experimentally.
 
According to the AFH the 180 degree landing is flown at 1.4 Vso. IOW, it isn't a best glide airspeed maneuver at all.
 
Ed's right -- you don't want best glide speed for the 180 degree power-off precision landing. If you were at best glide speed for your landing configuration, you could not vary your glide path anywhere but steeper, and if you came up even a touch below glide path at any point, you'd have no good way to extend it. 1.4 Vs0 almost certainly puts you well above best glide, so if you're a bit short, you can pitch up closer to best glide and extend the touchdown point.

That said, it would be good to know your best glide speed in the landing configuration so if you do find yourself coming up short in a real engine-out landing situation, you know when you have run out of better means to than to resort to desparate measures like retracting gear or flaps to make your landing zone.
 
Thanks and point taken on the 1.4. I'll talk it over with the school. BTW, 1.4 VSO is 90 mph or right about what I've been flying for best glide.

For you second point Ron, this training has gotten me thinking more about best glide in various configuration and flight regimes.
Best glide - gear down
Best glide - steep spiral - does load facter affect bg?

Heck, my best glide period. It's not in my owner's manual but I found 105 mph on several after market checklists. On Ed's advice I bought a 201 flight manual and it gives 105 for a 201 at max. Now being a slicker aircraft with a slightly longer wing you'd think they'd be different. With less parasitic drag would the 201 be a little slower than the M20F?
 
Ron Levy said:
Absent a lot more aerodynamic design data than we are likely to find available, the only way to find out is experimentally.
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Yeah, all the formulas I found had more variables than I have data for.
 
Ron Levy said:
That said, it would be good to know your best glide speed in the landing configuration so if you do find yourself coming up short in a real engine-out landing situation, you know when you have run out of better means to than to resort to desparate measures like retracting gear or flaps to make your landing zone.
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Retracting the gear in a Mooney in a last minute attempt to extend a glide would be a bad decision. The drag of the gear retracting is considerably more than down and locked. Can't speak for other types, but Mooney owners should not have this one in their playbook.
 
Lance F said:
Retracting the gear in a Mooney in a last minute attempt to extend a glide would be a bad decision. The drag of the gear retracting is considerably more than down and locked. Can't speak for other types, but Mooney owners should not have this one in their playbook.
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Agreed, not something I'd be messing with. Mine isn't quite as bad as your 201. No inner doors and quite a bit faster, 1-2 seconds depending on how my right arm feels. But you have to remember to put them back down. Not guaranteed in an emergency.
 
I would pull the prop to extend a glide. It's surprising how much drag that windmilling prop produces.
 
I teach going to best glide clean immediately, then determining at constant energy that you will make the mark. Then add drag incrementally, maintaining best glide airspeed- in case that you dirty it up too much, the cleanup doesn't then involve pitching to best glide as you are already there.

We only let the airspeed deteriorate when the mark is made - even maintain best glide pitch in a slip (whatever that speed really is !!??!!). The candidates do seem to pass the ride and CAN do the specs....
 
Ed Guthrie said:
According to the AFH the 180 degree landing is flown at 1.4 Vso. IOW, it isn't a best glide airspeed maneuver at all.
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Quoting from my copy of the AFH, FAA-H-8083-3A, page 8-23:

"...to the manufacturer's recommended glide speed, or 1.4Vso."

...uuumm, I say it is a "best glide speed maneuver". However, I also agree with the technique of using a slightly higher glide speed for the purpose of being able to pitch up to a longer glide path on final when it seems necessary. But this is part of the training necessary to appreciate and respect "best glide speed".
 
nosehair said:
Quoting from my copy of the AFH, FAA-H-8083-3A, page 8-23:

"...to the manufacturer's recommended glide speed, or 1.4Vso."
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Thanks for the catch. How the blazes I skipped past "...recommended glide speed..." and locked onto "1.4 Vso" I'll never know.
 
the manuever isnt about gliding maximum distance, its about touching down on a predetermined point. manage the speed (energy) however works for you.

ask any glider pilot what best glide speed is for their glider and most will have to think a while. I *think* mine is 45 mph but fact is that best glide speed is never the optimum speed to fly for max distance. head/tailwinds and rising/sinking air all have major effects on glide angle.
 
tonycondon said:
the manuever isnt about gliding maximum distance, its about touching down on a predetermined point. manage the speed (energy) however works for you.

ask any glider pilot what best glide speed is for their glider and most will have to think a while. I *think* mine is 45 mph but fact is that best glide speed is never the optimum speed to fly for max distance. head/tailwinds and rising/sinking air all have major effects on glide angle.
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Very good points about speed/distance/ and energy management. Knowing, and being able to "feel", best glide as a base line from which you deviate for proper energy management is what you should be learning to be able to execute a "180 Power-Off Approach" to a pre-determined touch-down point.

You cannot do this properly by flying a constant airspeed with pitch, except where necessary to obtain "best distance".

This should support the argument that you shouldn't be using the airspeed needle solely as a pitch instrument. You should point the nose to where you want it to go and control the airspeed with other tools, like slips and flaps. Or power when you have it available.

If you start out training to "pitch to the airspeed", solely, without regard for how it changes your glidepath, then it will be extremely difficult to *not* pitch up when the airspeed gets too high on final, thus resulting in being too high. If the initial reaction to increased airspeed is to *keep the nose pointed* at the landing target, and *throttle back*, or *slip*, or use some, or more, flap, then the student pilot will develop the ability to stay ahead of the airplane and anticipate the use of these tools to make precision approaches and landings, instead of the auto-robots that are produced by automatic rote responses of pitching up and down to an airspeed needle resulting in a glide path that roller coaster rides emulate.

End of rant.
 
Wish I had glider time. You guys really do learn energy management.

And I agree power off accuracy is energy management. I doing OK with that. Hope I didn't imply I was trying to hold best glide most of the way down. The school wants gear down and best glide at the start of the decent. I was just wondering that that might be.

BTW interesting screen name, is there a story behind it or do you just carry sissors?:)
 
In the 172RG I used for my commercial we would drop the gear at pattern altitude, get stablized then normal traffic pattern procedures from there. The precision 180 power-off landings were no different. The gear would already be down, when I reached the target point. From there, it was just a simple matter of adjusting for the wind & etc.

I liked to turn toward the runway relatively quickly. Once on final, I'd dump in flaps as necessary, slip if needed. Normal flare (with great flair, of course) and touch down within spec or less.

I really enjoyed doing these landings. I thought they were great fun. Good luck !
 
Yeah, they are fun. I'm actually making them most of the time. 200' isn't much. We're using the 1000' aim point. I believe the stripes are 150'. I haven't been using the prop but might start. There's not much with a Mooney to change. The flaps are wimps compared to Cessna and the gear is already down and speed is more critical. Slipping is works fine.
 
bah sell that mooney and you'll have tons of money to soar for years! ;)
 
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