How do you improve glide ratio in a design?

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I just watched a Youtube video in the "Experimental in Ethiopia" thread and it got me thinking and inspired this question:

How exactly do you improve the glide ratio of an existing design? Is it about weight? Aerodynamic properties? What's the physics? :dunno:
 
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Reduce the drag. One of the easiest ways to do it for big gains is using a high aspect ratio (long and skinny) thin wing, but it costs you top speed and load. Everything is a trade off.
 
Sportsman STOL increases the wing area 4sq. ft. and it decreases the impingement point at the leading edge of the wing for our 180.

It increases g/r from about 7:1 to a reported 13:1 but I have not calculated it in mine yet.

The kit is advertised as not just a leading edge kit, but a new designed airfoil. I'm not affiliated with them, I just like mine. :)
 
txflyer said:
Sportsman STOL increases the wing area 4sq. ft. and it decreases the impingement point at the leading edge of the wing for our 180.

It increases g/r from about 7:1 to a reported 13:1 but I have not calculated it in mine yet.

The kit is advertised as not just a leading edge kit, but a new designed airfoil. I'm not affiliated with them, I just like mine. :)
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I would like to see how well that works. STOL kits are high lift devices that typically add some drag which reduces power off glide range. Do you have that little Frito hook-dip in your leading edge cuff f the one you have? I always liked the looks of that.
 
Extend the wings, replace the cowl with a better design, improve fairings, replace rivets with flush rivets, replace window seals with flush seals, better wheel pants, etc. etc. etc.

How much money do you have?
 
Capt. Geoffrey Thorpe said:
Extend the wings, replace the cowl with a better design, improve fairings, replace rivets with flush rivets, replace window seals with flush seals, better wheel pants, etc. etc. etc.

How much money do you have?
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What's the basic figure, $1000 a knot?

However there is a big dent you can create for little money and that is gap seals. You can make and glue in fabric aileron and elevator gap seals for next to nothing, and flap gap seal can be done with a strip of sheet metal or plastic. That's probably the single biggest drag reduction you can buy yourself without structural changes to the wing, and you can do it all for <$100. BTW, sail repair tape is most excellent for gap seals.
 
Get rid of struts and wires. Raise the gear. Use a laminar flow airfoil. Flush rivets. Long wingspan. All of those things that are on my low drag, fast plane.
 
Make it look like this. How much do you want to spend and what are you willing to give up?
 

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Big airliners have surprisingly high glide ratios because even though they may come down like a brick it's a brick moving laterally at high speed.
 
Yes, do not confuse glide ratio with glide speed. As pointed out, the glide ratio is determined by lift and drag. The glide speed actually varies with weight (but the ratio doesn't for practical matters).
 
flyingron said:
Yes, do not confuse glide ratio with glide speed. As pointed out, the glide ratio is determined by lift and drag. The glide speed actually varies with weight (but the ratio doesn't for practical matters).
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That is why racing gliders often carry water ballast, weight doesn't affect the glide ratio hardly at all.
My glider has a 38:1 glide ratio at 50 knots.
I can carry 21 gallons (not a lot) of water which changes to 38:1 at about 60kts.

Some of the long wing gliders can get 60:1 glide ratio's, but the best glide speeds tend to get pretty low, (40kts?), without water ballast. This means on really good soaring days a glider with a lower glide ratio can often fly an averge course speed faster than the higher glide ratio glider.

Brian
CFIIG/ASEL
 
decrease wing loading
decrease drag
 
put a 747 or a 787wing on there....and your glide ratio will improve. :D
 
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brcase said:
That is why racing gliders often carry water ballast, weight doesn't affect the glide ratio hardly at all.
My glider has a 38:1 glide ratio at 50 knots.
I can carry 21 gallons (not a lot) of water which changes to 38:1 at about 60kts.

Some of the long wing gliders can get 60:1 glide ratio's, but the best glide speeds tend to get pretty low, (40kts?), without water ballast. This means on really good soaring days a glider with a lower glide ratio can often fly an averge course speed faster than the higher glide ratio glider.

Brian
CFIIG/ASEL
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What if you filled the wings and tail with helium balloons? :popcorn::lol:;)
 
Weight doesn't affect the glide ratio except in the extremes. It changes the speed at which the best glide ratio can be obtained and that is a key for the high performance glider types. Note that Brian said his best L/D went from 50 to 60 knots. This gets you more distance over the ground in the same amount of time and altitude. As the others noted getting rid of drag is the way to improve things....

Frank
 
So as long as the prop stows clean on a motor glider, the glide range is unaffected.
 
Henning said:
I would like to see how well that works. STOL kits are high lift devices that typically add some drag which reduces power off glide range. Do you have that little Frito hook-dip in your leading edge cuff f the one you have? I always liked the looks of that.
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sportsmanairfoil.gif



Sportsman leading edge is by far the largest of the kits. According to them, it isn't just a cuff as much as a redesign of the stock NACA 2412 airfoil.

I did my due diligence and went down the rabbit hole online before choosing Stene's STOL kit. The stock 2412 wing is a damn good wing to begin with but it lacks computer design techniques which were unavailable at that time.

Stall break went from "oh! I crapped my pants!" to "I pooted" with no loss of top end speed that I can tell, so it works. :)
 
asicer said:
That'll decrease the descent rate but not necessarily improve the glide ratio.
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But...and correct me if I'm wrong...at same best glide air speed (AS) a lower descent rate(DR) equals improved glide ratio(GR):

DR in (alt change)/time divided by AS in distance/time = GR in (alt change)/dist.

So if DR decreases, at same AS, GR decreases....:dunno:
 
It still messes with my head that weight does not have that much of an effect on engine out glide distance.

Two identical airplanes; one is at max gross, one is empty - seems like the heavy one should pay a penalty.
 
wrbix said:
But...and correct me if I'm wrong...at same best glide air speed (AS) a lower descent rate(DR) equals improved glide ratio(GR):

DR in (alt change)/time divided by AS in distance/time = GR in (alt change)/dist.

So if DR decreases, at same AS, GR decreases....:dunno:
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As previously noted, best glide AS changes with weight and hence, wing loading.
 
txflyer said:
sportsmanairfoil.gif



Sportsman leading edge is by far the largest of the kits. According to them, it isn't just a cuff as much as a redesign of the stock NACA 2412 airfoil.

I did my due diligence and went down the rabbit hole online before choosing Stene's STOL kit. The stock 2412 wing is a damn good wing to begin with but it lacks computer design techniques which were unavailable at that time.

Stall break went from "oh! I crapped my pants!" to "I pooted" with no loss of top end speed that I can tell, so it works. :)
Click to expand...

Looks like an interesting cuff, and it does have a bit of a vortex dip in it. I haven't flown the Sportsman (unless it's on the Katmai, I'm not sure what they use, but it's awesome.), and like the feel of the Horton better than the Robertson. The flapperons of the Robertson were nice on the 188 working hot in the summer though, they helped me over the fence more than once.
 
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