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

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#### proppastie

##### Well-Known Member
Log Member
Question. ...many European glass ships were experimental in USA? .......is modifying one of those an option.?

#### proppastie

##### Well-Known Member
Log Member
I see a pop-up turbine in the HP-24 future.

#### Jay Kempf

##### Curmudgeon in Training (CIT)
Lambada/ Sundancer is close to what you are looking for. 30:1 at 15 m.
40:1 at 17 m in a homebuilt? https://www.distarairusa.com/sundancer.html
https://www.motorgliders.org/ Worth joining. I was able to fly a Stemme and a Lambada at one of their fly ins.
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.

#### Jay Kempf

##### Curmudgeon in Training (CIT)
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.

#### Hot Wings

##### Grumpy Cynic
HBA Supporter
Log Member
I agree entirely with the statement "I believe we need to build/produce what we want for our own self gratification." That's what I believe as well.
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".

#### BJC

##### Well-Known Member
HBA Supporter
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.
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

#### PiperCruisin

##### Well-Known Member
Ooh, it's the SWIFT (Swept Wing with Inboard Flaps for Trim) or its successor the Millennium. Originally designed by a team headed by Ilan Kroo and featuring my friend Steve Smith. My suspicion is that this general configuration and planform is the most likely to achieve the cost and utility targets being tossed around in this thread. Several of these have been motorized.

The prototype was made with moldless foam core using Kevlar over some sort of styrene foam.
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

##### Super Moderator
Staff member
Log Member
... 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.

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.

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".
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.

#### ypsilon

##### Well-Known Member
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.

#### gtae07

##### Well-Known Member
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

an easy to build, easy to fly self-launching plane with one simple mission: allow me to head to the local airport only 10 minutes away and launch quickly after work for an hour or so of just drifting around enjoying the fall colors, turning those nasty summer bumps into micro-thermals, or watching the sun set... In my mind a low min sink is more important than max L/D, and an electric motor and slow-turning feathering prop much quieter than a 10000 RPM 2-stroke. 'Glide ratio' is mostly about needing less energy to climb, an ability to maintain altitude, and being able to return safely to the airport sans motor.
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.

Need to chime in here.
Yes, it seems that state of European soaring is different. I live about 8km from the next airfield. After that the next one is 15 km, the next one 20 and the next one 30. This to show how dense the soaring infrastructure in Europe is laid out. Depending on the airfield you get winch ropes and aircraft towing during the week (if the conditions are good), but for sure at the weekends.

So from what I read, it's really a lot easier to fly sailplanes here in Europe than in the USA. But why is that the case?

First of all I think it has to do with density of population. Clearly (central) Europe is more densely populated than most parts of the U.S., and I guess that in the more densely populated areas of the U.S. you'll find more soaring spots as well.

Secondly I think there IS a difference in culture. Let's avoid stereotypes, though. (No, not all Americans are lonesome cowboys)
I think however that culture is something that is self-perpetuating.
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:
Flying as a club activity in general is not (relative to the general flying population) very popular here. There are probably a bunch of cultural reasons for it that we could discuss over a few beers, but I don't think gliding does as well over here because it's flying that you almost have to do with other people. It's a longer time commitment, you have to (at least to an extent) work around others' schedules, and you have to share. Right, wrong, or indifferent, Americans want their own plane, to fly when and where they want. Gliders don't give you that, unless they can launch themselves.
even renting a Cessna/Piper/Diamond/etc. is a much different ballgame than renting a club sailplane. Your rent-a-spam-can is generally available every day, not just on weekends. You can go fly when just you and your instructor (or later, just you) want to go--you don't have to rely on a couple other people who aren't going flying (and may be impatiently waiting their turn) in order for you to go.

Americans are loners; if we can't have our own thing we often tend to prefer renting it commercially and keep things "at arms' length", rather than sharing ownership and dealing with all that messy stuff of whose job it is to wash the airplane, how to split up the maintenance bill, what to do about John who hasn't paid his dues for two months and keeps leaving bugs on the wings, what to spend the upgrade budget on, etc. These things get complicated and need lawyers involved because inevitably someone's going to screw it up for the rest. And that's just for a shared ownership model; get a club involved and you start dealing with power-trippers, getting people to show up, building resentment because it's the same guy who's always organizing the events and cleaning up by himself afterward, etc.

Again, I can't speak for soaring clubs in particular; all I really know about them was from my investigations into learning a few years ago, when I realized I had the time and money to fly, but not the time to spend running wings, waiting around, hangar flying, going to club meetings, etc. I suspect the same is true for a lot of people who would otherwise be interested in and enjoy soaring--they can't or don't want to deal with the club thing.

That's why I don't think that a cheap-to-build trainer is going to do anything to improve participation--the airframe cost, and even the number of such airframes, is not the limiting factor. The non-flying time commitment and the heavy reliance on multiple other people to be present in order for one person to fly, is (IMVHO) the bigger obstacle.
Admittedly, I'm looking at this from the perspective of "what's keeping me from doing a glider rating".

My only realistic option for glider training is the local (~45min away) club. They are exclusively aero tow, so not only is the minimum fee per flight \$30 (rental plus tow) but that requires a couple of other people (instructor, tow pilot, ground crew). That adds up quick when practicing landings.

Plus, this being a club, one can't just fly and then cut and run--one is expected to do one's turn as ground crew. That's all well and good, but it presents a problem (well, two problems) for me. First, I can't afford to be spending an entire day out at the airport right now. Maybe when my wife has finished recovering from her surgery and my son is a couple years older, I'll be able to, but right now I'm grateful for an hour or two a week to work on my project. The other is that, being a club, the only days they're "open for business" is on weekends. And I work weekends.

A self-launch option reduces the number of people required to two--the student and the instructor. You don't need other people there for ground crew, you don't need a tow pilot or winch operator, and you can go any time is convenient for just the two of you without having to wait around and let everyone else take their turn. It would also really speed up landing practice and make it cheaper, since you won't be paying per flight and having to wait for a new tow hookup. One could subsequently do your tow/winch endorsement later on in another aircraft (or do it in the trainer if it's designed to allow it...)

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.

#### mm4440

##### Well-Known Member
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?

#### Jay Kempf

##### Curmudgeon in Training (CIT)
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.

#### BoKu

##### Pundit
HBA Supporter
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?
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.

#### Jay Kempf

##### Curmudgeon in Training (CIT)
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.

#### BJC

##### Well-Known Member
HBA Supporter
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.
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

#### Jay Kempf

##### Curmudgeon in Training (CIT)
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?

#### Jay Kempf

##### Curmudgeon in Training (CIT)
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.

#### BJC

##### Well-Known Member
HBA Supporter
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.
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

#### mm4440

##### Well-Known Member
A Stemme like homebuilt is a huge challenge. A self launching single place with ~30+:1 performance is much more doable.
A HP 24 with an FES is a no brainer. Bob, do not be distracted. Get one flying.

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