Making Sense of Best Glide and Glide Ratio

[Max Clark]

I'm updating procedures and my checklist after new avionics.

Every checklist (and Foreflight) I've bought has a different Vg and Glide Ratio listed. Section III of the POH lists 85 KIAS (flaps up) for engine failure after takeoff. Then there's the actual POH/AFM entries that list different Vg based on weight, and a super helpful glide distance chart.

Foreflight has 89 KIAS and 11.5:1. I didn't dig into this or question it before - lesson learned. This makes sense assuming max gross takeoff and ~2.5 hours of fuel burn, which is likely not where I'll be most of the time. Worse my prop AFMS has a note that "it decreases glide distance approximately 7%

What number have you burned into your brain for Vg? What do you use for Glide Ratio?

[Ibra]

Best glide ratio does not change with weight, it's pure geometry: the B747, PC12, P51 have some nice glide ratios yet they are "pretty heavy" 

The propeller has lot of effect, I would say between 1:10-1:13 in M20J, however, I am damn sure it will not work if an engine fails unless I forgot to put Avgas 

Best glide speed Vbg increase with weight (like stall speed increment but one need to whole polar curve) and headwinds (decrease with tailwind), in thoery, one should calculate vertical speed (fpm) to ground speed (kts), then find indicated airspeed that maximise the ratio. I have done hundreds of hours optimising glides in Astir and Discus, none of that was relevant when engine quit in C172, I just glanced at iPad for my options, put it at 80kts and started looking outside.

It's mostly about having a speed I  mind and doing some planning, what matters is where your aiming point or selected field moves with respect to the horizon and the aircraft, if it goes up you won't make it, if it goes down you will make it, this applies irrespective of calculations 

In M20J, I plan to fly 90kias and plan 1:10 to arrive at 2000ft overhead my landing spot

On a side note, I wonder what numbers go into "smart glide" by  GTN? 

Edited February 16 by Ibra

[PT20J]

15 minutes ago, Ibra said:

On a side note, I wonder what numbers go into "smart glide" by  GTN? 

Glide ratio and one glide speed are entered in config mode. There is no adjustment for weight. But after Smart Glide activates the GFC 500 in IAS mode, you can adjust the airspeed up or down with the thumbwheel.

[PT20J]

2 hours ago, Max Clark said:

I'm updating procedures and my checklist after new avionics.

Every checklist (and Foreflight) I've bought has a different Vg and Glide Ratio listed. Section III of the POH lists 85 KIAS (flaps up) for engine failure after takeoff. Then there's the actual POH/AFM entries that list different Vg based on weight, and a super helpful glide distance chart.

Foreflight has 89 KIAS and 11.5:1. I didn't dig into this or question it before - lesson learned. This makes sense assuming max gross takeoff and ~2.5 hours of fuel burn, which is likely not where I'll be most of the time. Worse my prop AFMS has a note that "it decreases glide distance approximately 7%

What number have you burned into your brain for Vg? What do you use for Glide Ratio?

You should use the speeds in Section III of the POH/AFM for your airplane. Best glide occurs at a specific angle of attack, so the airspeed will vary with weight. This is because lift = weight and if the angle of attack is constant then CL is constant so the airspeed has to be variable. The heavier you are, the faster you need to fly and the faster will be your descent, but the glide angle will not chsnge.

[Max Clark]

Foreflight has the glide ratio of 11.5:1. I've seen numbers of 11.4/11.46:1 so quasi consistent.

The Hartzell 3 blade reduces distance by 7%, which takes me to 10.6:1.

Should I just shorten this to 10:1 and have confidence I'd reach anything inside of the ring ignoring everything outside of it?

[MikeOH]

49 minutes ago, Ibra said:

In M20J, I plan to fly 90kias and plan 1:10 to arrive at 2000ft overhead my landing spot\

^^^. THIS. ^^^

I figure both back pockets are going to be touching each other if I have an engine failure...No way I'm risking any more of a helmet fire by trying to optimize glide speed based on exact weight and trying to figure out wind speed and direction at several altitudes below me.  I've got Foreflight set to 10:1.  My biggest fear is going for an airport close to the edge of the glide ring vs. accepting a for-certain makeable off-field site.

[midlifeflyer]

12 hours ago, MikeOH said:

 

I figure both back pockets are going to be touching each other if I have an engine failure...No way I'm risking any more of a helmet fire by trying to optimize glide speed based on exact weight and trying to figure out wind speed and direction at several altitudes below me.  I've got Foreflight set to 10:1.  My biggest fear is going for an airport close to the edge of the glide ring vs. accepting a for-certain makeable off-field site.

THIS for me as well.

Many years ago, I did a C172 checkout for a 20,000 hour retired airline pilot. When we got to the simulated engine failure, he was at best glide and heading toward a landing spot within 6 seconds. Once I realized what he was doing, I started to test it out with other airplanes. 

All he did was look out the window and pitch for the most familiar attitude - level cruise. Turned out that a level cruise attitude resulted in a speed close enough to best glide that the difference was inconsequential. So inconsequential that trying to be perfect has a negative impact. Even seems to account for weight. I’ve been using and teaching it ever since. I used that technique recently in an “impossible turn” demo. It wasn’t in a Mooney, but I’m linking it below anyway.  

Tweak if you need to with a touch of trim. If your autopilot has an IAS mode, use it.  But  only once underway to your landing area.

 

[A64Pilot]

It’s called “Attitude flying” something I learned in helicopters and it works for everything.

Basically it’s learning what attitude correlates for what airspeed.

If your example you learn the 90 kt attitude and if the engine quits you adjust to that attitude the aircraft will end up at 90 kts allowing you to do other things like looking out for a place to land as opposed to chasing airspeed.

It is also more efficient as in you will lose less altitude pitching to the correct angle of attack and staying there than if you pull the nose up to slow to 90 kts then drop the nose to stay there.

We had “bucket” airspeeds on the helicopter and I’m sure we do too on an airplane. basically if you graph the lift vs drag on a chart it will be bucket shaped and not a perfect one lowest point, on the helicopter 64 kts was lowest rate of descent in an autorotation and 94 kts gave max range in autorotation.

Get slow though and you don’t have the extra energy speed gives you to swap for a low rate of descent for touchdown, and you won’t have the altitude to recover the speed, so don’t get slow until your sure you have the landing area made, it takes discipline to maintain that 90 kts, when the ground is coming up, but you need to.

Long way of saying I guess that it’s better to be a little fast than a little slow

 

Edited February 21 by A64Pilot

[Falcon Man]

Two different Fedex instructors (they also train regular CA pilots) taught me to  trim for full down elevator and that is your best glide for the operating conditions at the time of your engine failure. Also, the FedEX company philosophy is "TLAR" - "Than Looks About Right". In their analysis a pilots absolute adherence to perfect scenario (eg. holding course tracking perfectly in IFR), leads to more pilot errors.

[PT20J]

16 minutes ago, Falcon Man said:

Two different Fedex instructors (they also train regular CA pilots) taught me to  trim for full down elevator and that is your best glide for the operating conditions at the time of your engine failure. Also, the FedEX company philosophy is "TLAR" - "Than Looks About Right". In their analysis a pilots absolute adherence to perfect scenario (eg. holding course tracking perfectly in IFR), leads to more pilot errors.

Did you mean full UP trim? I once did a trim runaway experiment in my M20J and going full down trim at cruise speed required in excess of 40lbs pull (measured with a spring scale) to avoid extreme nose down attitude.

[201Mooniac]

Barry Schiff once wrote an article (in AOPA I think) that said he tried the full nose up trim in several types and found it is typically about right for approximating best glide.  I haven't tried it in my M20J but maybe I will this weekend.

[Max Clark]

Full trim up is interesting - will have to try this.

[AJ88V]

My attitude is that if you're NEEDING best glide speed, you're better off just learning/picking a/sticking with a "best glide speed" and putting your focus on where you will put down.  In my case, that's 90mph.  Sure, it may be more optimal at some other speed, but that advantage is small, whereas picking where you're putting down and how you manage the final approach to that spot is way more important than the maybe 500 - 1000 ft in distance you might gain by optimizing best glide. 

Said another way, your brain is gonna be all kinds of busy, so pick a speed and focus on all the other stuff like maintaining attitude, looking for obstructions, shutting off fuel, making a last radio call and shutting off  electrics and popping the door and maybe making a gear up/gear down decision.  And if all that works out well, you'll likely end up too high at the end and need to slip her in to land at your chosen best/optimal spot.

YMMV.

[Falcon Man]

Yes I stand corrected its full nose up.  Just like landing a Mooney on final by trimming nose up to reduce the pressure on the yoke!

[Z W]

I was also taught full nose up as a way to approximate best glide in the 172 trainer I learned in. It works pretty good in the Mooney too. Maybe a little slow, so slightly less than full nose up trim is ideal, but full nose up gets you close and then you can trim after that to exactly where you want it.

The idea is the plane will naturally want to hold proper speed that way while you're looking out the window to pick your landing spot, running the engine restart checklist, making your mayday call, turning on your ELT, securing the cabin, and otherwise preparing for an emergency landing. So step 1 is full (or nearly full) nose up trim. It does however make it to where it requires less backpressure to stall the aircraft on short final, so you still have to watch your airspeed and not try to stretch your glide.

[A64Pilot]

I try to tell this whenever it comes up, but try going rapidly to full power on short final with the trim full up, if you have the strength and are comfortable with the excess pressure required to keep from stalling, fine.

Maybe it should be done at altitude.

If nothing else I think it should be done so pilots see just how much pressure is required, if you don’t expect it, it could catch you off guard.

Ray Maule used to teach an approach in a Maule trimmed full nose up, I did a go around once and that was the last time I landed trimmed full up, it took both hands to hold the nose down, obviously I didn’t die, Mooney especially a 4 cyl one ought to be more forgiving

Edited February 23 by A64Pilot

[M20F]

I hold 104.937472727 MPH but I have a really supple wrist.  

[Hank]

20 minutes ago, M20F said:

I hold 104.937472727 MPH but I have a really supple wrist.  

Wow! Glad I dont fly an F! Why so fast?

In my C, short final is a max of 85 mph, down to 70-75 just before pavement, and on go arounds I aim around 85 initially   (seriously), unless I'm still a couple hundred feet high, then I just maintain standard pattern speed of 90 mph.

Then again, not much arm strength is required with only 180 hp. Good thing, too. 

I also don't use full nose-up trim, usually landing somewhere around the Takeoff mark. Trim is just another flight control to use to hit my intended point of landing, just like rudder, elevator and ailerons (which I also rarely move to their travel limits while landing); I just trim away the yoke force. Flaring is done by pulling gently on the yoke, and that close to the ground, I'm not letting go of the yoke to reach down for the trim wheel. 

[Max Clark]

1 hour ago, A64Pilot said:

I try to tell this whenever it comes up, but try going rapidly to full power on short final with the trim full up, if you have the strength and are comfortable with the excess pressure required to keep from stalling, fine.

Maybe it should be done at altitude.

If nothing else I think it should be done so pilots see just how much pressure is required, if you don’t expect it, it could catch you off guard.

Ray Maule used to teach an approach in a Maule trimmed full nose up, I did a go around once and that was the last time I landed trimmed full up, it took both hands to hold the nose down, obviously I didn’t die, Mooney especially a 4 cyl one ought to be more forgiving

This was beat into me by my transition instructor. Yoke trim doesn’t move nearly fast enough you’ve got to get on the wheel aggressively. 

[Z W]

To clarify - the full nose up trim I described above is for an engine out situation. I do not use it for regular landings. I don't want it in that configuration if a go-around may be required.

[A64Pilot]

5 minutes ago, Max Clark said:

This was beat into me by my transition instructor. Yoke trim doesn’t move nearly fast enough you’ve got to get on the wheel aggressively. 

Or just don’t trim full, personally my trim ends up where it is at takeoff, and you should plan on electric trim not working, because it’s some kind of rule, when you need anything the most is when it won’t be available, even when trimmed for takeoff, it takes quite a lot of pressure and trim when I raise flaps

[PeteMc]

On 2/16/2025 at 1:10 PM, Max Clark said:

What number have you burned into your brain for Vg? What do you use for Glide Ratio?

 After I upgraded my panel I now have an Airspeed Bug that I don't really use.  So I tagged the Gross Vbg speed and I just leave it there.  So if something happens there's no reading the numbers, doubting myself that I'm remember the correct speed, etc.  Push and go for the Bug.  But once I'm there, assuming I'm up higher, I can think about how loaded I am and drop the speed a bit if I think I need the extra glide time.  

And I also have the ~11kt range, which may be true of all Mooneys.  But I doubt I'd ever want to really guess how slow I could really go.  So I'd probably only slow up a few knots, maybe 5 at the most even if I knew I was very light. 

As for FF or any other App that may be asking for Vbg.  Your best bet is to put in the speed for Gross Weight. 

[Pinecone]

Do some reading about glider flying.  They ALWAYS fly engine out.

There are two speeds used.  Best Glide and Minimum Sink.

Best glide is used for maximum distance traveled for the altitude loss.  So used if you want to get somewhere.

Minimum sink is lowest vertical speed.  So it gives you the most time before running out of altitude.

Low altitude, min sink may be a better choice to give you more time to try a restart and get ready for the off field landing.  You aren't going very far anyway.

 

[cliffy]

If the engine goes cold you won't have the time or the inclination to be fumbling with an iPad trying to find your speed

Have one number in your head and just fly the airplane and look out the window.

The ground will be there a lot quicker than you think right now.

  

 

 

[M20F]

16 hours ago, Hank said:

Wow! Glad I dont fly an F! Why so fast?

Son I don’t fly a Piper.