Do You Pitch Up First For Best Glide?

Maintain altitude until Vbg, then trim. And like Mark said, all the time looking for a place to land.
 
Found a math error :rolleyes:
For the 172-like model there is a slight advantage to climbing at some reasonable rate to max range glide, which seems intuitive. I didn't go this far, but I expect there is a crossover with climb angle even if you could pushover instantaneously to max range glide.

That being said, reduced workload will also probably give you better results, so not horsing the airplane around might be the best option.

HornetDriver said:
If you're faster than max glide then by definition parasitic drag is greater than induced drag. The relationship between induced drag and AOA is proportional; parasitic drag rises exponentially with velocity. You get twice the payoff from trading parasitic drag for the induced drag, plus the extra altitude.
Click to expand...
I might take issue with the wording but we're mostly in agreement here. Don't forget the additional deceleration term due to gravity in a climb. Otherwise this simplification will tell you that best results are with a min drag climb, which is zero lift and a vertical climb, to best glide.

HornetDriver said:
In a GA aircraft practically speaking it probably doesn't matter very much due to the limited airspeed differential. When you add in the human component a level decel may be just as good or better. But the math is the math.
Click to expand...
Absolutely agreed.

HornetDriver said:
The engineers who get paid to come up with the right answer appear to be correct
Click to expand...
There might even be a few of them here ;)

Nauga,
who knows 'trust but verify' works for both nukes and NATOPS.
 
This past week I have done some testing on the "roll the Trim Back tactic".
I tried it in a C-172XP with 2 people a front, a C-152 with 2 people and a C-172N with 3 people on board.
Rolling trim all the way back with 10 degrees of flaps or less after a power failure resulted in reasonably close to the best glide speed. I guess this is what the proponents of this method actually say this does. This works ok until you either add power for a recovery from practicing or after resolving the cause of the power loss or you add more flaps. The 172's with full flaps and the the trim full back produced about a 50kt glide, this Ok until you go to flare for your landing and you have no energy to stop the descent. You will need to either re-trim for landing or push the nose down to gain some speed for the flare.
I also found it takes a lot of turns of the trim to go to full up trim. I found this distracting and takes a fair amount of time that I could be using for either attempting a restart or setting up for my approach.

Brian
CFIIG/ASEL
 
FastEddieB said:
As others have said, probably not enough difference to worry about.
Click to expand...
Depends greatly on airplane and speed differential. A 172 might not see a big gain but try it in a faster airplane and you can easily gain 1,000' getting to Vg. And that might be the difference between making a rwy or landing out.

I've done it before, just as a test. Try it out with your own airplane when you get a chance. It is a great exercise, it helps being prepared. And I like suggesting to be prepared. It increases your chances in a true emergency.
 
BigBadLou said:
I've done it before, just as a test. Try it out with your own airplane when you get a chance. It is a great exercise, it helps being prepared. And I like suggesting to be prepared. It increases your chances in a true emergency.
Click to expand...

I plan on doing that. May even take the GoPro along.
 
Just as important...pull the prop to full coarse pitch. That's like getting kicked in the butt. It significantly reduces drag.
 
timwinters said:
Just as important...pull the prop to full coarse pitch. That's like getting kicked in the butt. It significantly reduces drag.
Click to expand...
Just a minuscule detail people often overlook: if you lose your engine for real and are out of oil pressure, you are SOL with coarse prop pitch.
But if you just lost, let's say, fuel supply or mags and your engine is still windmilling and building oil pressure, coarse pitch will work. :thumbsup:
 
Barring a problem specifically with the oil supply, will you have oil pressure whenever the prop is windmilling?
 
timwinters said:
Why in the world would you add flaps when trimming for best glide?
Click to expand...

Obviously you wouldn't add flaps for best glide, but the point that most people recommending using the roll the trim back method forget to mention is you probably aren't going to land in that configuration. In fact if done well you should be either slipping or using flaps to get down to you chosen landing spot just because you planned it so there was no change of getting to low.

My concern is I have seen pilots trained to just do this after a power outage and then they don't reconfigure when they setup for landing, which is where I see them get "scary slow".

My analysis is that it works ok if you absolutely need best glide. But in most cases you are not going to need your best glide speed and your energy is better spent just making sure you don't stall, restarting the engine, or making as normal of a landing as possible. So it is kind of a neat trick to be aware of, but probably not the best procedure to use as a rote engine failure procedure.

Brian
 
For the planes I usually fly, best glide is at or just above normal final approach speed.
 
I have no idea which way is mathematically better, but I’m betting the best way to do it is not to worry about it. We are likely talking 10 feet of glide here, but a mile if we get distracted with minutia.
 
I don't worry, I just do it the way I was taught.
 
Palmpilot said:
I don't worry, I just do it the way I was taught.
Click to expand...
I never worried either By the time you realize what’s happening you’re almost there.

It’s truly splitting hairs.
 
Palmpilot said:
I don't worry, I just do it the way I was taught.
Click to expand...
So I have had two instructors. First one holds until best glide, the other pitches up - both quite adamant.

This topic is like strapping a open face peanut butter sandwich to the back of a cat and dropping them. Who hits the ground?

What about a plane with a excellent glide ratio (MD-80?) traveling pretty fast up at cruising altitude...do they pitch up?

Also curious since they were fairly low, did Sullenberger pitch up right away or just hold altitude until their best glide?
 
Sinistar said:
Also curious since they were fairly low, did Sullenberger pitch up right away or just hold altitude until their best glide?
Click to expand...

Since they were climbing out I believe they were at or below best glide already.
 
Sinistar said:
So I have had two instructors. First one holds until best glide, the other pitches up - both quite adamant....
Click to expand...
I've only had one instructor who taught me engine out procedure in a single, so I don't have that problem. And I've learned the hard way that if I'm going to deviate from what I was taught, I need a good reason.
 
kgruber said:
I'm typed in several jets and never have seen a "best glide" speed published.
Click to expand...
But they surely have a glide ratio which must be somehow tied to a certain config (clean?) and pitch angle which I would think would then have a speed?
 
Sinistar said:
But they surely have a glide ratio which must be somehow tied to a certain config (clean?) and pitch angle which I would think would then have a speed?
Click to expand...

It would be a certain angle of attack.

Aircraft with low parasite drag have high best glide speeds. I am pretty sure that the average passenger jet has a best glide speed somewhere in the 200s.
 
Some pilots seem to think that the longer they glide, the safer the off field landing will be. Thats possible, but its only one scenario. The tendency is to overshoot.

I pull the power and glide on in, almost every landing. Makes every landing an "engine out" drill. Do it all the time, you get good at it.
 
timwinters said:
Just as important...pull the prop to full coarse pitch. That's like getting kicked in the butt. It significantly reduces drag.
Click to expand...

BigBadLou said:
Just a minuscule detail people often overlook: if you lose your engine for real and are out of oil pressure, you are SOL with coarse prop pitch.
But if you just lost, let's say, fuel supply or mags and your engine is still windmilling and building oil pressure, coarse pitch will work. :thumbsup:
Click to expand...

Tim's right on this one. MT and others make electric adjustable props. So perhaps the only modification to his statement would be "if you can."
 
High wing or low wing?
 
Palmpilot said:
High wing or low wing?
Click to expand...

Neither.

4821.jpg
 
Winner!

(But don't you mean "both"?)
 
kgruber said:
I'm typed in several jets and never have seen a "best glide" speed published.
Click to expand...
I have. The citations have a chart.
Not sure if Airbus actually publishes a speed, but you can fly “green dot”. Green dot is a marker on the airspeed tape depicting L/D max.
 
FastEddieB said:
I think the nod goes to staying level. Pulling up into a climb increases the induced drag as a result of the increased angle of attack. I would think that given identical planes under identical conditions, the one that climbed would come up just a tad shorter than the one that stayed level.
Click to expand...

You get a tiny bit of extra drag with the higher AoA initiating the climb, but only for a second or less... And then the lower speed makes up for it.

Mtns2Skies said:
I'd actually argue the other side of that. Drag is exponentially increased with speed. Therefore the sooner you can bleed off that extra speed(i.e, re-purposing that energy into altitude), the less overall energy you are wasting.
Click to expand...

This.

EDIT: The reality is though that the difference in cruise speed and best glide speed for most GA airplanes is so small that it really won't make much difference either way.
Click to expand...

Speak for yourself. The Mooney has a 50-70 knot difference (depending on altitude) between cruise and best glide.
 
flyingcheesehead said:
Speak for yourself. The Mooney has a 50-70 knot difference (depending on altitude) between cruise and best glide.
Click to expand...
Even a 172 has a 45 - 55 knot difference, depending on the horsepower.
 
You must log in or register to reply here.
Back
Top