Glide Ratios

Morne

Morne

Line Up and Wait
Joined
Sep 18, 2011
Messages
699
Display Name
Display name:
Morne
Is there somewhere a list of common GA aircraft and their glide ratios? Just sort of curious. What2fly.com doesn't include glide ratio with all of their other (very cool) information.
 
average spam cans seem to be right around 8 or 9:1. I don't know of a list.
 
tonycondon said:
average spam cans seem to be right around 8 or 9:1. I don't know of a list.
Click to expand...
Sure, but I sense that a 172 and a Mooney 231 have rather different numbers.
 
Morne said:
Sure, but I sense that a 172 and a Mooney 231 have rather different numbers.
Click to expand...
Probably closer than you think. Airplanes fly on excess power, not grace, not engineering.
 
ClimbnSink said:
Probably closer than you think. Airplanes fly on excess power, not grace, not engineering.
Click to expand...

A car that has alot of horsepower is 300+

a spam can with a lot of horsepower is 180-200


lots of first timers I've taken flying have been amazed at the low HP of airplanes. No one expects an air cooled 160hp with a carb.
 
Last edited:
dell30rb said:
lots of first timers I've taken flying have been amazed at the low HP of airplanes. No one expects an air cooled 160hp with a carb.
Click to expand...
This describes me. Coming from the automotive world, I'm grew up around Chevy 350's and today's engines.

My first flight lesson, I did a walk around on a 1970 Cherokee 140 and marveled at how physically small the engine was. I remember thinking, "That little thing is gonna haul us and the airplane off the ground?"
 
Meanwhile the airplane was looking at you and having similar thoughts?

AggieMike88 said:
This describes me. Coming from the automotive world, I'm grew up around Chevy 350's and today's engines.

My first flight lesson, I did a walk around on a 1970 Cherokee 140 and marveled at how physically small the engine was. I remember thinking, "That little thing is gonna haul us and the airplane off the ground?"
Click to expand...
 
Arrow, gear up = sheet of plywood.

Arrow, gear down = rock
 
Satchmo10th said:
R22, Between 2:1 and 4:1
Click to expand...
:eek:

For the record, qualitative descriptions are not what I am looking for. One man's "glides like a pregnant brick" is another's "floats to the next county".:idea:

I have an engineering degree. I like numbers.
 
Then why do you want a twin?

Morne said:
:eek:

For the record, qualitative descriptions are not what I am looking for. One man's "glides like a pregnant brick" is another's "floats to the next county".:idea:

I have an engineering degree. I like numbers.
Click to expand...
 
Sac Arrow said:
Arrow, gear up = sheet of plywood.

Arrow, gear down = rock
Click to expand...

Agree, especially if you mean the hershey bar variety.

On my commercial checkride, the DPE wanted me to put the gear down on the downwind leg in preparation for the power off 180. I made it but just barely.

It's 8:1, so it's not too bad...but you get that at 100-110 knots. Therefore, compared to a 172, the glide ratio is only slightly worse but at a 50% higher forward speed and a 50% higher sinkrate.

I believe the 172 is 9:1 and the 182 is 10:1. If you have a controllable pitch propeller, you can increase that by about 10%, and if you stop the prop, it increases about 20% (Barry Schiff, Proficient Pilot).
 
wabower said:
Then why do you want a twin?
Click to expand...
Do you live to crap in threads or what?

If you wish to make some sort of pursuasive argument then post up some horrid examples of glide ratios for twins. I'll bet there are some out there.

This thread is not about "single vs twin". If you'd care to discuss that, go start your own thread.
 
dmspilot said:
I believe the 172 is 9:1 and the 182 is 10:1.
Click to expand...

Meh... The real-world measurements I've done with our 182 resulted in a 7.04:1 glide ratio. (Probably similar to the "pregnant brick" mentioned earlier.)

The DA40 can do about 11:1 at lower altitudes, and gets better the higher you go (true of any airplane, due to higher TAS at altitude maintaining Vg IAS). One glide I did from 7500' down to the surface at ~800 MSL resulted in an 11.54 glide ratio.
 
Morne said:
If you wish to make some sort of pursuasive argument then post up some horrid examples of glide ratios for twins. I'll bet there are some out there.
Click to expand...

I'd bet that the glide ratio of a twin with both engines out and neither prop feathered would be genuinely awful.

But, it's not something that people normally discuss, since the theory is that you shouldn't have a double engine failure. Typically, that is correct.
 
twins are probably in the same range for engine out L/D i.e. 8-10:1. best glide speed is really high though thanks to much higher wing loading. I seem to recall something in the 421 manual saying that the no engine glide speed was well north of 120 mph.
 
dmspilot said:
Agree, especially if you mean the hershey bar variety.

On my commercial checkride, the DPE wanted me to put the gear down on the downwind leg in preparation for the power off 180. I made it but just barely.
Click to expand...

Yikes!!! When I was getting my complex endorsement (Hershey bar wing Arrow) we did a power off 180 and I didn't drop the gear until very short final. And we turned for the runway as soon as the power was pulled. Not sure the plane would have made it to the runway if the gear had already been down.

midlifeflyer said:
Arrow is famous for a safe glide ratio - glides like a safe.
Click to expand...

Precisely the term my CFI used - safe mode glide. :D
 
a pretty decent policy in airplanes is that if you can see it over the nose there is good odds you can't make it there.
 
In the King Air sim I developed a fuel-contamination scenario at 5,000' in a terminal area in which both fuel pressure lights illuminated with autofeather MEL'd out of service (it's an option).

Use of boost pumps (per emer check list) wouldn't solve the problem and the windmilling props effectively eliminated any glide ratio other than down. When both props were feathered (manually) the glide ratio became quite good and the airplane would make it to the airport straight ahead. Upon reaching the airport, however, the reduced drag from both feathered resulted in difficulty slowing the airplane and increased landing distance compared to pilot's expectation.

The excercise/demo was the last landing of the sim session, so we didn't waste time with restart and all that stuff.

Ted DuPuis said:
I'd bet that the glide ratio of a twin with both engines out and neither prop feathered would be genuinely awful.

But, it's not something that people normally discuss, since the theory is that you shouldn't have a double engine failure. Typically, that is correct.
Click to expand...
 
dell30rb said:
A car that has alot of horsepower is 300+

a spam can with a lot of horsepower is 180-200


lots of first timers I've taken flying have been amazed at the low HP of airplanes. No one expects an air cooled 160hp with a carb.
Click to expand...

Allow me to qualify your comment ...

AC engines aren't 'low HP'. They are rated at a lower horsepower because they turn at a lower RPM. The 300HP cars aren't generating that power at 2,700 RPM they're doing it at 6K-7K RPM or more depending on displacement.

Example: I had a 600cc (36 cu in) motorcycle that was rated for 110HP ... @ 10,000RPM! But at 2,700 RPM I doubt it would get 15HP.

Cars only need 20-40 HP to maintain highway speeds. Your Cessna needs 120HP (75%) to maintain it's rated cruise speed. Try to run your car at 75% power and see how long it lasts.
 
MadseasoN said:
Cars only need 20-40 HP to maintain highway speeds. Your Cessna needs 120HP (75%) to maintain it's rated cruise speed. Try to run your car at 75% power and see how long it lasts.
Click to expand...

At those speeds, longer than your driver's license.
 
tonycondon said:
twins are probably in the same range for engine out L/D i.e. 8-10:1. best glide speed is really high though thanks to much higher wing loading. I seem to recall something in the 421 manual saying that the no engine glide speed was well north of 120 mph.
Click to expand...

The 310 I recall saying a best glide speed of 110 mph with both props feathered and no drag.

wabower said:
In the King Air sim I developed a fuel-contamination scenario at 5,000' in a terminal area in which both fuel pressure lights illuminated with autofeather MEL'd out of service (it's an option).

Use of boost pumps (per emer check list) wouldn't solve the problem and the windmilling props effectively eliminated any glide ratio other than down. When both props were feathered (manually) the glide ratio became quite good and the airplane would make it to the airport straight ahead. Upon reaching the airport, however, the reduced drag from both feathered resulted in difficulty slowing the airplane and increased landing distance compared to pilot's expectation.

The excercise/demo was the last landing of the sim session, so we didn't waste time with restart and all that stuff.
Click to expand...

Good anecdotal information. I'd be interested to try in a 310 sim at some point.

As Tony, AdamZ, AdamB, and a few others can attest, the Aztec can be made to have a glide ratio resembling a Steinway. The 310, not having 50 degree flaps and also having less drag, I'd expect does better. But either way, I wouldn't want to be in a double engine out situation with any of the twins I fly.
 
ClimbnSink said:
Probably closer than you think. Airplanes fly on excess power, not grace, not engineering.
Click to expand...

They may fly on excess power, but when they glide they have a fixed power, usually zero. The best glide is based on the best L/D and is a fixed angle. Usually the more efficient airframes have a lower D and therefore a higher glide ratio.
 
flyingcheesehead said:
Meh... The real-world measurements I've done with our 182 resulted in a 7.04:1 glide ratio. (Probably similar to the "pregnant brick" mentioned earlier.)

The DA40 can do about 11:1 at lower altitudes, and gets better the higher you go (true of any airplane, due to higher TAS at altitude maintaining Vg IAS). One glide I did from 7500' down to the surface at ~800 MSL resulted in an 11.54 glide ratio.
Click to expand...

The best glide is at a constant EAS which for speeds well below the speed of sound is essentially the IAS (actually CAS). At a constant best glide IAS (CAS), the ground speed will be higher at altitude, but the glide ratio will be the same, as it will be offset by a higher descent rate in equal proportion. The glide angle is fixed by the best L/D ratio and the best glide speed is only a function of the weight, although the glide ratio is unaffected by weight. So, there isn't better glide performance at altitude.
 
Last edited:
Ted DuPuis said:
I'd bet that the glide ratio of a twin with both engines out and neither prop feathered would be genuinely awful.

But, it's not something that people normally discuss, since the theory is that you shouldn't have a double engine failure. Typically, that is correct.
Click to expand...

Undoubtedly true. But the glide ratio with both feathered is often much better than one finds on a single engine aircraft. My Bonanza has a glide ratio close to 10, but its Baron big brother is 12 with both engines feathered.
 
tonycondon said:
a pretty decent policy in airplanes is that if you can see it over the nose there is good odds you can't make it there.
Click to expand...

Probably not a bad rule of thumb and it is about right for my Bonanza in the high drag configuration. However, for my Bonanza, if my wing covers it up, I can glide to it in the low drag configuration, assuming no wind. I have to project an arc around between the two wing tips to estimate how far I can glide. The position of the prop control is enormous in determining the glide, With the prop at the rear stop, I get 900 feet/minute. If it is even a half inch off the rear stop, the descent rate increases to 1400 feet per minute. If you lose oil pressure, then you can't set the prop at minimum RPM and the glide suffers accordingly. The only good news is that if you lose oil pressure you are likely to have the engine freeze up and the prop stop, which improves the glide ratio.
 
John Collins said:
The best glide is at a constant EAS which for speeds well below the speed of sound is essentially the IAS (actually CAS). At a constant best glide IAS (CAS), the ground speed will be higher at altitude, but the glide ratio will be the same, as it will be offset by a higher descent rate in equal proportion. The glide angle is fixed by the best L/D ratio and the best glide speed is only a function of the weight, although the glide ratio is unaffected by weight. So, there isn't better glide performance at altitude.
Click to expand...

It is a constant AoA right?

One thing not mentioned in the thread so far is that your glide speed increases with reduced drag and vice versa. So if your POH gives you a best glide of e.g. 90 knots assuming a windmilling propeller, your glide ratio will increase with a stopped prop but it will increase even more if you raise your airspeed to take advantage of the decreased drag. By how much, I don't know. :confused: It's probably better not to think about it in practice.

Of course minimum sink speed is a different thing all together, and unfortunately there is a mistake in the Airplane Flying Handbook confusing the two (page 3-17: "When descending at a speed below the best glide speed, induced drag increases...the rate of descent will increase").

Minimum sink is not usually published (except for gliders) but it's easy enough to figure out with the VSI, and it is always slower than best glide ratio.
 
dmspilot said:
Minimum sink is not usually published (except for gliders) but it's easy enough to figure out with the VSI, and it is always slower than best glide ratio.
Click to expand...

Barry Schiff says that min sink airspeed is "about halfway between stall and normal glide speed."
 
dell30rb said:
A car that has alot of horsepower is 300+

a spam can with a lot of horsepower is 180-200


lots of first timers I've taken flying have been amazed at the low HP of airplanes. No one expects an air cooled 160hp with a carb.
Click to expand...

I usally remind those people that the airplane only weighs 2000-2500lbs loaded and its all about power/weight ratio.

<---<^>--->
 
p1l0t said:
My [flying club's] M20J is about 13:1 a 172 is about 9:1

<---<^>--->
Click to expand...
13:1 with the prop stalled, MAYBE. 10-11:1 otherwise.
That's recollection from 1,000 hours of ownership of an M20J.

Ed will be along shortly!
 
bbchien said:
13:1 with the prop stalled, MAYBE. 10-11:1 otherwise.
That's recollection from 1,000 hours of ownership of an M20J.
Click to expand...

OK, but curious what 1,000 hrs has to do with it? It's a simple datapoint that must be measured (one time will do). Extent of experience would have no correlation with the accuracy of your "recollection"...not that I don't believe you of course.
 
You must log in or register to reply here.
Back
Top