# Issues and Solutions for kit- and plans-based sailplanes and motorgliders

Discussion in 'Soaring' started by TerryM76, Sep 3, 2019.

1. Sep 6, 2019

### proppastie

#### Well-Known Member

Joined:
Feb 19, 2012
Messages:
3,888
1,135
Location:
NJ
Question. ...many European glass ships were experimental in USA? .......is modifying one of those an option.?

2. Sep 6, 2019

### proppastie

#### Well-Known Member

Joined:
Feb 19, 2012
Messages:
3,888
1,135
Location:
NJ
I see a pop-up turbine in the HP-24 future.

3. Sep 6, 2019

### Jay Kempf

Joined:
Apr 13, 2009
Messages:
3,702
962
Location:
Warren, VT USA
There is virtually no way that this airplane gets 30:1 at 15M. In the performance specs on the website there is this ~26:1. With open cooling ducts behind a stopped prop no matter how faired or feathered this thing is 25:1 on a good day with fixed tail dragger if faired well. I didn't see mention of the 17M extensions on their website but they will give a little useful load and not much more performance other than a little bit of sink rate help. Almost every airplane in this category is the same. Fold the gear and figure a way to get that prop somewhere hidden and close all the cooling ducts and I could see 30:1 maybe. The nose motor is always going to be a big drag source, probably 50% of the total drag. Fixed gear about 10% probably. That is why the only real 40+:1 powered gliders out there fold and hide the motor in doors in the turbulent part of the fuselage and hide all the engine cooling. Then you just have weight penalty.

I hang around with airplane designers too much I guess, the powered type. They are always talking about L/D of powered designs which is a theoretical that comes out of calculating basic aero parameters. It has no real meaning on a powered plane with a stopped prop and the gear down.

4. Sep 6, 2019

### Jay Kempf

Joined:
Apr 13, 2009
Messages:
3,702
962
Location:
Warren, VT USA
Greg Cole is a very sharp fellow. He knows what he is doing. Notice there are no endurance claims on electric just amp drains at speeds. Also note that there are no L/D claims, just great performance which I am sure it has. The wing comes from the SparrowHawk basically so it is known. The low wing fairing looks well figured out so probably minimal drag at the most critical modes. What I have heard about this design and some others is the way to lose the drag of the prop is to not stop it. There is a tiny battery drain for just windmilling the prop enough to net out any drag it might have stopped. Does that create turbulence on the fuselage? Maybe, maybe not but it is a clever way to just eliminate the drag penalty of a stopped motor. Doesn't work for IC motors as well but kinda.

When I was learning to fly power planes they bored the heck out of me so I would idle the motor in clean air, set some sink rate equal to soaring flight and then go thermal a C152. Less boring way to build hours than just watching the instrument needles

Hey mods. 5 times while typing this my cursor was taken away by ads. Typing along and then off somewhere, have to grab the mouse and click back in the window to start up again. Is that normal <happened again> with this new platform. Are these advertisers so desperate for our attention that they don't want us to type a whole sentence? I type really fast... annoying.

5. Sep 6, 2019

### Hot Wings

#### Well-Known MemberHBA Supporter

Joined:
Nov 14, 2009
Messages:
6,456
2,363
Location:
Rocky Mountains
Yes, ultimately we should all be building/designing what we want. But.......... Based on my recent experience there may be more of a market than we all have surmised. Since I went down the AV-36 path I've had at least a dozen inquiries. All but one generated here on HBA came as the result of one small obscure post on a web site with my e-mail attached. All are interested in a powered version, not the glider.

Fortunately I too am interested in a powered version so the work needed to build one won't be all "work".

Topaz likes this.
6. Sep 6, 2019

### BJC

#### Well-Known MemberHBA Supporter

Joined:
Oct 7, 2013
Messages:
9,757
6,538
Location:
97FL, Florida, USA
C.A.F.E. measured the L/D of powered aircraft with a zero thrust power setting. They used a proximity sensor to adjust the throttle until the crankshaft floated in the thrust bearing. They validated it by towing a C150 or 152 aloft without a propeller for comparison.

BJC

7. Sep 6, 2019

### PiperCruisin

#### Well-Known Member

Joined:
Jan 18, 2017
Messages:
136
65
Location:
Idaho
For a single seat, self-launch glider, the electric Swift is very attractive. I quoted it once. It was in euros, but I thought it was about $35k to 40k. Anyways, it was much cheaper than the non-motorized Archaeopteryx. There is also the A-I-R Atos wing which looks interesting, but not sure about its cost or status. Also waiting to see if the Aeros AC-21 becomes available. I saw the predecessor a long time ago at the Coupe Icare (fun) held at St. Hilaire du Touvet (Mecca for paragliders) in France. The construction was very interesting, but a little on the weak side. The new one seems to address that. Waiting.... Speaking of waiting...the Goshawk, Skigull, Robin Ultralight, RV-11, Eurosport Crossover... I asked if there was a possibility to kit the Pipistrel Taurus Electra, but apparently they are worried about builders getting zapped...I don't want to develop my own, but d$#@, I'm gonna die before something useful is produced.

I would prefer 2 place, (side-by-side preferred, especially if it does not change the c.g. much). A single place would have to be much less expensive.

Also, the glider folks pointed out how inexpensively you could get into a glider, yet few people are biting. On the other hand, if you check motor glider prices, they are almost all 6 figures. Seems like there is some room to work.

Topaz likes this.
8. Sep 6, 2019

### Topaz

#### Super ModeratorStaff Member

Joined:
Jul 30, 2005
Messages:
13,876
5,486
Location:
Orange County, California

The mainline ad-blockers also do the trick. I actually don't have ads disabled and, since I'm running AdBlockPlus, I don't see ads here at all. I didn't even know the rest of you were seeing ads until comments started popping up in threads like this.

Either way should work.

That's great news, Hot Wings! Really happy to hear that! I think that, while not "Van's Aircraft" level of demand, there's more demand out there for a moderate-performance plans-built motorglider/self-launcher than most would assume, as you say. I got the same impression listening to the interest expressed at the ESA conference both last year and especially this year. Bodes well, I think.

9. Sep 6, 2019

### ypsilon

#### Well-Known Member

Joined:
Mar 1, 2016
Messages:
269
81
Location:
Austria
Just for the sake of completeness: We haven't touched the Phoenix U15, which exists in an electric variant: http://electric-gliders.com/
Martin Stepanek is part of the development team, and he is active in this forum, too. So maybe he can add a bit of his experience to this thread.

Topaz likes this.
10. Sep 6, 2019

### gtae07

#### Well-Known Member

Joined:
Dec 13, 2012
Messages:
1,823
1,092
Location:
Georgia
Dang, I wish I'd looked at this thread earlier! It's been a long time since I've seen a discussion like this here and I kinda miss it

This is what I'd want in any glider-type aircraft I built. It's what my desire for a "low and slow" would be (and probably all I could afford as a second airplane anyway). Really, what I'm looking for is the airplane equivalent of my dad's little sailboat (a Shell Boats Swifty 12). It's not high performance, it's not a racing boat, you wouldn't take it on the open ocean, and you certainly won't be spending the night on it. But it's small, simple, easy and cheap to build, easy to launch by yourself, and perfectly suited to sailing around on the local lake on a nice afternoon. Its purpose is purely fun and relaxation on a nice day, not competing for badges or records or against some other guy.

I would love something like a Goat, if I had a convenient place to fly it and the means to launch it (no hills here and nobody is going to want to give me a ground tow, then wait around while I have my fun). A powered Goat would be better because it at least solves problem 2.

I've posted on this a lot in the past, as one who wants to fly gliders around for fun but can'/don't want to bother with the traditional aerotow club model:

All of this is to say that I don't think raw performance (or the lack thereof) is really the issue at hand. Those old low-performance designs are rotting away primarily because they're a pain to fly, not because of their performance; improving performance doesn't help that.

11. Sep 6, 2019

### mm4440

#### Well-Known Member

Joined:
Jan 14, 2012
Messages:
182
38
Location:
LA area, CA
Hi, Jay asked for two place and ~100 hp. Can a modified HP 24 handle ~500# more and still perform like a sailplane? Or will it take a new design? With a new root center section can wings from the HP24 molds be extended to 20+ m total span?

12. Sep 7, 2019

### Jay Kempf

Joined:
Apr 13, 2009
Messages:
3,702
962
Location:
Warren, VT USA
Little known fact, most sailplanes are designed to carry that much water ballast. But the point would be that something like HP24 wing could be just plain mounted to an up to 8' wide center section to get more area and to have a stronger carry through at the center. Instead of water bags, you put in fuel bladders...

The design I have been playing with for a long time is a 15 meter span 2 place and it works. With a motor you don't have to have super long wings for those marginal conditions. So you thermal a little faster than most of the super high performance ships, so whawt. I didn't use the HP 24 wing as a starting place but if I did it would come out to 15 meters plus 8' which ain't gonna hangar well in a lot of places but it would in mine Still can remove the wings and drive up on a trailer and tie down. Wings in saddles like is normal with spar stub tie downs. Tail tips come off. Rest of the tail stays on the top of the rudders. So no disconnecting anything. I have put this through a first order CFD, mission, stability, yadda... By the time I got it most of the way there PBS came out with a really nice turbine that would be about the same as a custom motor and folding prop development cost wise. Think Caproni. Complexity much less. But they are thirsty little buggers so drag would have to be really low to throttle back at say FL10 to get proper 4 hours of fast cruise. None of this is pushing any real envelopes. It is all about the total drag budget. The weight fractions are easy to quantify.

Engine and cooling drag packaging during soaring is a tough problem.

Low wing config for shorter gear and easier ingress/egress without blowing the drag budget out and killing the 40+:1 is a tough problem that I think I have solved in both modes.

High speed cruise without flutter or beating the occupants to death is a tough problem (solved through modern computing power or a clever idea Jarno came up with a while back).

My original goal was to have close to Mooney/Bonanza cruise speeds. Clean air assumed, higher up assumed but up towards 200mph would be something that doesn't exist and would make this a one airplane quiver for the soaring curious. That is actually what put me in this direction. One airplane for the same mission you would fly a Mooney on but you take your high performance sailplane with you and you ditch the tow plane and club. I haven't had good track records with clubs.

Anyway, blathering on. It's designed and there is a big thread about the single place version of this before I headed towards the dual place version. It think there was a little traffic on the two place. It took me a long time to come up with a two place pod/wing that solved all the CG and drag issues. But I got it eventually.

Topaz likes this.
13. Sep 7, 2019

### BoKu

#### Well-Known MemberHBA Supporter

Joined:
Aug 16, 2013
Messages:
2,359
3,005
Location:
Western US
The HP-24 project has proven out some technologies that would be of use, but few of the actual shapes and profiles are well optimized for the role being described.

Wings beyond a span 20m or so are a serious, serious undertaking. Cost increases exponentially with span. Carbon fiber has flattened the curve out so that 18m can be done relatively economically. But beyond that the curve starts getting pretty steep. And I'm not particularly interested in going there; it makes operation more serious and less fun in a way that I'd just as soon do without. I'm not even all that enthusiastic about 18m, but the focus groups behind my original business plan made it clear that for many it would be a decisive factor, which has proven true. As it is now, the pure-glider version is way too light for its area in even 15m span unless you add FES or self-launch. It climbs like nothing else I've flown, but doesn't really scoot until you really pile in some water or lithium (but not the two mixed).

If I'm reading this right (big if), what's called for here is less span, more area, and a modest wing loading. The sort of thing you'd traditionally get with a lot of fabric covered area. The picture I'm starting to get is like a Cygnet with long wings on which the outboard sections fold or detach to fit into a hangar. I like the Cygnet's configuration because it allows good visibility of the type you need in thermals. I've soared Aeroncas and Taylorcrafts, but the high-wing configuration has poor turning visibility even with a transparent skylight.

TerryM76 likes this.
14. Sep 7, 2019

### Jay Kempf

Joined:
Apr 13, 2009
Messages:
3,702
962
Location:
Warren, VT USA
20m is too much if you have an engine. 18m is too much. But AR rules the roost not span. Wing loading can be higher which helps with cruise. With an engine you need not scratch out the most marginal lift. Just start the engine and fly somewhere where it isn't marginal. 15 meter span, similar to a successful OML wings, planform, boom(s), etc... reduces the aero unknowns. Then the designer can concentrate on the source of thrust, cockpits, landing gear and drag reduction of the overall package. Very doable.

15. Sep 7, 2019

### BJC

#### Well-Known MemberHBA Supporter

Joined:
Oct 7, 2013
Messages:
9,757
6,538
Location:
97FL, Florida, USA
If the motor glider is intended to attract pilots other than those that currently hang out at sailplane ports, then it will need to fit on a typical county airport taxiway, runway, and fueling ramp without hitting lights, signs, or parked airplanes, and make it straight through a 40 foot hangar door. Having to get out and fold or remove wing tips or place it on a dolly may be acceptable to glider pilots, but severely limits the utility of the aircraft for many of us who otherwise might buy one.

BJC

litespeed likes this.
16. Sep 7, 2019

### Jay Kempf

Joined:
Apr 13, 2009
Messages:
3,702
962
Location:
Warren, VT USA
Bob,

Would you sell a 15 meter wing kit? If so (not holding feet to fire) what is it worth. Not talking about ordering one, just trying to get an order of magnitude for what it would contribute to the total package. What does a set of wings weigh?

17. Sep 7, 2019

### Jay Kempf

Joined:
Apr 13, 2009
Messages:
3,702
962
Location:
Warren, VT USA
Not intended to attract those that aren't sailplane curious I have a friend that has a Pipistrel Taurus. Nice machine. Close to the goal. But a self launching thing with clear cruise restrictions in the manual and it teeters on its mains same as the Stemme. He also has an RV8 and a Yak and is a high time Bonanza pilot. Only really flies with 2 SOB ever. He is torn trailering the Taurus long distances to have the sailplane with him or to fight with the club locally or to just fly the Rv8 which gets him here faster. And he has to store all those options, register them, yadda.

The power guy who wants either the Bonanza or the Mooney is not the target audience. You have to understand the soaring OCD problem. It's the same as owning a sailboat but in 3D.

18. Sep 7, 2019

### mm4440

#### Well-Known Member

Joined:
Jan 14, 2012
Messages:
182
38
Location:
LA area, CA
19. Sep 7, 2019

### BJC

#### Well-Known MemberHBA Supporter

Joined:
Oct 7, 2013
Messages:
9,757
6,538
Location:
97FL, Florida, USA
OK, if you say so.

But consider that I have seriously considered purchasing a Phoenix motor glider, but have not, primarily for the ground handling reasons I mentioned above.

BJC

20. Sep 7, 2019

Joined:
Jan 14, 2012
Messages:
182