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15/18m Construction and Performance?



 
 
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  #1  
Old December 14th 16, 02:53 AM posted to rec.aviation.soaring
Casey[_2_]
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Posts: 188
Default 15/18m Construction and Performance?

An owner of a 15m with 18m tips told me his glider was designed as 18m and the manufacture cut the tips to make removable and that it did not fly well as a 15m.

My question is this common or glider specific? How do manufactures design a 15/18m? Do they start with design of 15m and add 3m and then test performance or design 18m and cut down? Or do different manufactures have different technics? Can a 15/18m have equally performance or does one configuration suffer and that's the price one pays?
  #2  
Old December 14th 16, 06:09 AM posted to rec.aviation.soaring
Steve Leonard[_2_]
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Posts: 1,076
Default 15/18m Construction and Performance?

ASG-29 has won 15 and 18 meter titles. It does not have to suffer at one span to be good at another.

Steve Leonard
  #3  
Old December 14th 16, 07:15 AM posted to rec.aviation.soaring
Tim Taylor
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Posts: 751
Default 15/18m Construction and Performance?

Most modern 18m were optimized for 18m, but but can fly well as 15m. The only weakness of the 18m in 15m is they are heavy. Most are 100 to 150 pounds heavier than a pure 15m glider. The 29 does well in locations with stronger conditions, but suffers on very weak days. The motor versions are at a significant disadvantage in lighter lift. On the other side they do better in very strong conditions with significant cloud streets.

It will be interesting to see the next generation of 18m and 15m gliders.

I still prefer a true 15m glider with empty weights at 520 to 560 pounds over the much heavier wings of the 18/15m gliders.
  #4  
Old December 14th 16, 10:24 AM posted to rec.aviation.soaring
Jim White[_3_]
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Posts: 286
Default 15/18m Construction and Performance?

At 06:15 14 December 2016, Tim Taylor wrote:
Most modern 18m were optimized for 18m, but but can fly well as 15m. The
on=
ly weakness of the 18m in 15m is they are heavy. Most are 100 to 150
pounds=
heavier than a pure 15m glider. The 29 does well in locations with
strong=
er conditions, but suffers on very weak days. The motor versions are at

a
=
significant disadvantage in lighter lift. On the other side they do
bette=
r in very strong conditions with significant cloud streets. =20

It will be interesting to see the next generation of 18m and 15m gliders.


=
=20

I still prefer a true 15m glider with empty weights at 520 to 560 pounds
ov=
er the much heavier wings of the 18/15m gliders.

Interesting observations Tim. I too fly a 27 against 29s at 15M
competitions and would say that turbo-less 29 versions are at least the
same if not better than the 27 in weak conditions because of the lower wing
loading. Tim Scott's 29 is only a few kilos heavier than my 27 in 15M
configuration.

However the 29 can achieve a greater weight and wing loading than the 27
for good conditions but has a greater wetted area which probably makes then
equal at high speed.

  #5  
Old December 14th 16, 12:41 PM posted to rec.aviation.soaring
krasw
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Posts: 668
Default 15/18m Construction and Performance?

On Wednesday, 14 December 2016 03:53:34 UTC+2, Casey wrote:
An owner of a 15m with 18m tips told me his glider was designed as 18m and the manufacture cut the tips to make removable and that it did not fly well as a 15m.

My question is this common or glider specific? How do manufactures design a 15/18m? Do they start with design of 15m and add 3m and then test performance or design 18m and cut down? Or do different manufactures have different technics? Can a 15/18m have equally performance or does one configuration suffer and that's the price one pays?


Glider that have wing parting well inboard of 15m tips are usually quite well optimised for two classes. Such gliders are ASW 28/ASG 29/ASH 31, Ventus-2c/Discus-2c and LS10 (?). Downsize is that you are paying 20k euros for set of 15m tips (large section of wing) instead of 2,5 k euros (just short tips with winglets).

Most if not all 18m gliders come with engine, and they are usually too heavy for serious comp. pilots, at least in Europe. ASG29E-15 wingloading is easily 45kg/m2 without water. Try to thermal in 0,2 m/s with that...

Older generation of glider usually were optimized for 15m and then span was increased with narrow wing section, LS6/LS8/Ventus c, for example. You can also do a not-very-well-optimized smaller span glider by cutting wings shorter (Mini-LAK).
  #6  
Old December 14th 16, 03:47 PM posted to rec.aviation.soaring
Luke Szczepaniak
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Posts: 177
Default 15/18m Construction and Performance?

On 12/14/2016 4:24 AM, Jim White wrote:
At 06:15 14 December 2016, Tim Taylor wrote:
Most modern 18m were optimized for 18m, but but can fly well as 15m. The
on=
ly weakness of the 18m in 15m is they are heavy. Most are 100 to 150
pounds=
heavier than a pure 15m glider. The 29 does well in locations with
strong=
er conditions, but suffers on very weak days. The motor versions are at

a
=
significant disadvantage in lighter lift. On the other side they do
bette=
r in very strong conditions with significant cloud streets. =20

It will be interesting to see the next generation of 18m and 15m gliders.


=
=20

I still prefer a true 15m glider with empty weights at 520 to 560 pounds
ov=
er the much heavier wings of the 18/15m gliders.

Interesting observations Tim. I too fly a 27 against 29s at 15M
competitions and would say that turbo-less 29 versions are at least the
same if not better than the 27 in weak conditions because of the lower wing
loading. Tim Scott's 29 is only a few kilos heavier than my 27 in 15M
configuration.

However the 29 can achieve a greater weight and wing loading than the 27
for good conditions but has a greater wetted area which probably makes then
equal at high speed.


After flying my 27 vs 29's in 15m I would say that the two are virtually
identical. I agree with Jim's observations about weak weather, even
though the empty weight of the 29 is higher the extra wing area reduces
the wing loading. It probably has more to do with superior skill of the
pilots in the 29's but it makes me feel better to blame it on their
gliders ;-)

Luke Szczepaniak
  #7  
Old December 14th 16, 08:10 PM posted to rec.aviation.soaring
Bob Kuykendall
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Posts: 1,345
Default 15/18m Construction and Performance?

On Tuesday, December 13, 2016 at 5:53:34 PM UTC-8, Casey wrote:
An owner of a 15m with 18m tips told me his glider was designed as 18m and the manufacture cut the tips to make removable and that it did not fly well as a 15m.

My question is this common or glider specific? How do manufactures design a 15/18m? Do they start with design of 15m and add 3m and then test performance or design 18m and cut down? Or do different manufactures have different technics? Can a 15/18m have equally performance or does one configuration suffer and that's the price one pays?


A few semi-random points of perspective from one who has BTDT and has the many epoxy-stained T-shirts and carbon splinters to show for it:

* There is no one way to design a 15/18 glider. You can start with a 15m and stretch it, or you can start with an 18m and cut it. Neither is perfectly optimized for both spans, but in both cases the optimization is not really all that bad.

* Especially for motorgliders, wing area can be an issue. Carrying a self-launch engine and systems on the area you get with 15m tips can result in sink rates you don't want on a weak day.

* As another poster points out, there are structural penalties at issue. If you are going to have 18m tips, you must provision the wing to accommodate the extra bending moment. The difference can be pretty big; adding span at the tip makes a huge increase in the stresses at the inboard end of the wing. One side effect to this is you can end up with a glider that rides nice in 18m config, but beats you up with the 15m tips.

* One thing I observed from studying the wings of the ASG29 is that you can improve the area distribution optimization by moving the 15/18m separation joint inboard. That gives you a head start on matching the local taper to the lift distribution. But as another poster points out, it also increases the amount of glider you have to buy and schlep around. With the separation line around the 5.5m semispan as on the ASG29, the short tips are 2m each and the long tips are about 3.5m each. That means you are buying and carrying around in the trailer about 22m of wing for a glider that is at most 18m span.

* I designed the HP-24 as a non-serious racing machine, so its span optimization leans towards the 15m end, but there will still be a substantial performance gain from the optional 18m tips. It's not meant to run with the ASG29, but it still has flaps, winglets, autoconnecting controls, water ballast, front-hinged canopy, and other advanced features at a price about 1/3 that of the '29.

Thanks, Bob K.
https://www.facebook.com/HP-24-Sailp...t-200931354951
  #8  
Old December 19th 16, 02:31 PM posted to rec.aviation.soaring
Christopher Schrader
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Posts: 9
Default 15/18m Construction and Performance?

When you say you designed the HP24 as a non-serious racing machine and mention it can't run with the ASG29 by what degree do you mean? Is the drag coming from the airfoil rather than the fuselage or both? If so, could you design and sell a more competitive airfoil for 18m config? As a larger pilot I like the 304S because of the roomier cockpit (I haven't seen it in person but I'm told it has a roomier cockpit much like the older 304C).
/Chris
  #9  
Old December 19th 16, 05:44 PM posted to rec.aviation.soaring
Bob Kuykendall
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Posts: 1,345
Default 15/18m Construction and Performance?

On Monday, December 19, 2016 at 5:31:42 AM UTC-8, Christopher Schrader wrote:
When you say you designed the HP24 as a non-serious racing machine and mention it can't run with the ASG29 by what degree do you mean? Is the drag coming from the airfoil rather than the fuselage or both? If so, could you design and sell a more competitive airfoil for 18m config? As a larger pilot I like the 304S because of the roomier cockpit (I haven't seen it in person but I'm told it has a roomier cockpit much like the older 304C).
/Chris


I don't know how the HP-24 will compare with the ASG-29 in practice; all I know is that isn't really what I designed it for. Our primary objective was to make it a sweet flying glider with good stability and handling right out of the box, and we got that. We also wanted enough cockpit volume that it could be adapted to pilots in the mid to high 6' range, and we got that too. But both of those have penalties in trim drag and parasitic drag.

I could certainly put together a team to develop a competitive 18m contender. But I am a bit leery that I could do so as a profitable (or at least non-unprofitable) venture. I'd be worried that kit sales wouldn't amortize the development costs. But I have been collecting wing profiles to analyze for a potential 2nd gen HP-24 wing, and we'll just have to see what happens.

One thing I have proven is that it is possible to get a pretty wide range of fuselage sizes from our standard molded parts. Right now we have a fuselage I call "Slim" under construction in our shop; with only minor modifications of our standard parts we have narrowed the cockpit and substantially reduced both frontal and wetted area; it is now down around the range of the LS6 fuselage.

Thanks, Bob K.
 




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