Has anyone be thinking of designing a more modern, light weight powered sailplane ?

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Vigilant1

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I would like to have some information on compression release with the exhaust valves. Believe a shaft could be run above the rocker arm with lobes to push the exhaust rocker down about .015" for compression release. The shaft would have to be run through the rear of the valve cover ( oil seal needed ) and extended to the cockpit with a handle for the pilot to rotate for the release. Both shafts from the cylinder heads would have to be coupled together for one release handle.
Ideas ?
Sorry, Pops, the only compression release I'm familiar with is the systems used on B&S engines, which is automatic and not what you want. Your intent is to be able to shut down the engine normally, glide around awhile with the prop stopped (due to compression), then restart by releasing compression so you can get starting RPM (so, no need for a starter and electrical system). Right? Your idea of an actuating rod through each valve cover, with cams to hold the exhaust valve (rocker) open slightly (could be twist or push-pull) sounds fine. It does complicate valve cover removal (I seem to open mine up often). I'd probably consider the pro/con of this idea vs adding a starter (without an alternator, just a larger lightweight battery good for a few starts).
 

cheapracer

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I wouldn't do it to the valves, why not just drill a hole somewhere and fit a compression release, the advantage of an air cooled head, you won't drill through a water jacket!

... or through the upper side of a barrel maybe, been done before.
 

Pops

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Sorry, Pops, the only compression release I'm familiar with is the systems used on B&S engines, which is automatic and not what you want. Your intent is to be able to shut down the engine normally, glide around awhile with the prop stopped (due to compression), then restart by releasing compression so you can get starting RPM (so, no need for a starter and electrical system). Right? Your idea of an actuating rod through each valve cover, with cams to hold the exhaust valve (rocker) open slightly (could be twist or push-pull) sounds fine. It does complicate valve cover removal (I seem to open mine up often). I'd probably consider the pro/con of this idea vs adding a starter (without an alternator, just a larger lightweight battery good for a few starts).
Yes, right on, compression release for windmill starting.
For valve cover to be removed easy, the cam with bearning would have to be on each end of the valve cover so when the cover is removed the cam and bearing are removed as part of the cover. The cover should be firmly attached with bolts and not the spring keeper ( as the after market cast alum). Universal joint in the shaft at the end of the cover so the cover can be swung out of the way for valve adjustment.

Another thought, but I like the compression release better. Starter gear on the flywheel end (prop on pulley end) and a shaft with a Bendix and a shaft being turned by an battery drill for starting. There is an STC for this for the Cont A-65. On the 65 the shaft run over the top of the engine to a starter gear behind the prop.
 

Vigilant1

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Another thought, but I like the compression release better. Starter gear on the flywheel end (prop on pulley end) and a shaft with a Bendix and a shaft being turned by an battery drill for starting. There is an STC for this for the Cont A-65. On the 65 the shaft run over the top of the engine to a starter gear behind the prop.
I recall one of the Rheinbeck Aerodrome guys was using a similar setup to start his plane (VW with PSRU?). It would talso be handy for the folks flying industrial engines. Selling kits would be a good (but small) business for somebody, and it would be a good addition to the Great Plains catalog.
 

pictsidhe

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I suggested folding tips as they don't carry much load but would make a big difference to performance. 3' folding or removeable tips shouldn't be too hard or heavy to engineer and would take the span up to 44'. The hard bit would be if they break the ailerons.

That is why the span is 38'. I want span PLUS low wing loading. Folding wings would be nice, but adds weight. I want it as light as possible and still go in my hanger without hitting the sides of the opening. Gives me 3' of clearance on each wing. I'll be using the same airfoil as used on the SSSC and its 16 %.
 

Topaz

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Does anyone know the current status of the GosHawk?

It seems to be at a standstill.
I heard anecdotally from someone (I don't recall who it was) at the ESA conference that the GosHawk was still an ongoing project. However, like you, I haven't seen any evidence of that personally.
 

BJC

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I heard anecdotally from someone (I don't recall who it was) at the ESA conference that the GosHawk was still an ongoing project. However, like you, I haven't seen any evidence of that personally.
I really want to see if its performance comes close to Greg’s projections.

At Oshkosh, Van said that his personal motorglider project is idle. That is another project that I was hoping would be completed.


BJC
 

Topaz

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I really want to see if its performance comes close to Greg’s projections.

At Oshkosh, Van said that his personal motorglider project is idle. That is another project that I was hoping would be completed.


BJC
AFAIK, Van's motorglider project has been idle for years. Many years. I don't think he'll ever complete it, simply because it's a back-burner thing and he's got a regular business to run. Which is a shame - it would've been nice to see someone with his reputation working in the motorglider design space.
 

TiPi

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Yes, right on, compression release for windmill starting.
For valve cover to be removed easy, the cam with bearning would have to be on each end of the valve cover so when the cover is removed the cam and bearing are removed as part of the cover. The cover should be firmly attached with bolts and not the spring keeper ( as the after market cast alum). Universal joint in the shaft at the end of the cover so the cover can be swung out of the way for valve adjustment.

Another thought, but I like the compression release better. Starter gear on the flywheel end (prop on pulley end) and a shaft with a Bendix and a shaft being turned by an battery drill for starting. There is an STC for this for the Cont A-65. On the 65 the shaft run over the top of the engine to a starter gear behind the prop.
have you thought about a manual pull-start, taken from a larger industrial engine? I have seen them on VWs in Europe, pull rope with a T-handle located in the instrument panel. Needs to be configured at the right ratio as the pull distance can be quite short. For inflight restart, only a light pull should get you over the compression.
 

Pops

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have you thought about a manual pull-start, taken from a larger industrial engine? I have seen them on VWs in Europe, pull rope with a T-handle located in the instrument panel. Needs to be configured at the right ratio as the pull distance can be quite short. For inflight restart, only a light pull should get you over the compression.
I have thought about it but that is about all. I have looked at the old Mc Dowell pull starters used on some of the Cont A-65's in the old Aeronca Chiefs. My neighbor used to have one. Looks simple.
I'm sure that could work on the flywheel end of the VW with a little work.

http://www.joea.com/mcdowell_safety_starter_information.htm
 

Aesquire

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https://www.denniskirk.com/search/Compression+release+valves.q

Much simpler to add the compression release to the heads. The big twin Victory motorcycles used them to ease starting.

You can use your valve train,but you introduce a new failure mode. And potential oil leak spots.

You also add a new failure mode with separate compression release, but diagnosis, repair, and in flight mitigation is easier. ( jiggle the handle!) I'd guess your failure odds are lower with a separate system, but I don't have hard data :)
 

cheapracer

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One simple way also is to simply drill a 1/4" hole about 1" down the bore.

At cranking speed it bleeds off enough compression to notice a difference, but at engine speeds it has close enough to zero effect.

Suzuki used it on a couple of big bore single motorcycles, as did a few others to ease kickstarting.

And I just remembered, Australian Victa Lawnmowers (pull start) have a vacuum operated decompressor. It's always open until the engine runs and vacuum closes it.

DEC608-SC.jpg
 
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Vigilant1

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On remote/manual starting: I'd think it might be hard to get much speed in pulling a standard recoil starter rope while seated in a small cockpit. When I was a kid we had a Craftsman mower with a wind-up spring starter. Crank it a few times, fold in the crank handle and that released the pawl that let the spring crank the mower. In a plane, 10-12 strokes on a foot operated pedal between the rudder pedals might be all the that is needed to tension such a spring. Easy on the back, no bashed elbows.
The cordless drill would be easier and about the same weight. But, the pedal/spring start would be more fun to explain/show off at fly-ins.
 
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BBerson

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Doesn't take much to start the Limbach (VW) windmilling in flight. On the Grob with the feathering prop I can usually get it windmilling at 60 knots just by moving the prop pitch lever back and forth from feather. About three times to get it just past compression and away it goes. The prop is 64" diameter, which helps.
A kick starter would be easy to use.
 

plncraze

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Kick starting an airplane in flight presents an interesting picture. Especially if it is an open cockpit.
 

lr27

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Thinking about motorgliders, from specs I've seen it seems that a fixed prop adds quite a bit of drag. Some way to fold or feather would probably help the performance quite a bit, though of course it might add significantly to the effort or expense. And a re-start might require a starter motor. However, if a prop had a frontal area of 250 square inches, we assume a 600 lb aircraft, and an airspeed of 40 mph, then we're looking at an extra 41 fpm or so. (I thought it would be more. Are my guesses reasonable? I really don't know just how much blade area props have.) At 60 mph, that would be an extra 92 fpm.
Another place to lower drag might be with cowl flaps that could seal up the engine compartment. However, I don't know how long it takes for the engine to cool down enough to use them.
For wood/carbon ideas it might pay to look at the Carbon Dragon. I think the plans are still on line someplace. These days pultruded carbon instead of tow might be a good change. Obviously, for a motorglider with a VW engine, things would have to be scaled up and modified. I'm guessing that the tailboom style the Carbon Dragon uses might be a way to save a reasonable amount of weight with carbon for the labor involved. As I recall, it's pretty simple. It would also have less drag than a conventional rear fuselage.
For those who want a minimal airplane with 17:1, maybe a cleaned up Skypup would do.
 

Vigilant1

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Thinking about motorgliders, from specs I've seen it seems that a fixed prop adds quite a bit of drag. Some way to fold or feather would probably help the performance quite a bit, though of course it might add significantly to the effort or expense.
The VW engines do best with regular solid wood props. If I owned a motorglider with a VW engine, I think I'd be content to just let it run at a very moderate throttle setting, the prop just keeping pace with the airflow, while I soared around. It will sip fuel, the engine will be ready when I need it, cabin heat will be there if I want it, and it avoids the complications of any kind of special prop. Of course, I guess the magic of silent flight wouldn't be available, but I like motor noises just fine.
 

Pops

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The VW engines do best with regular solid wood props. If I owned a motorglider with a VW engine, I think I'd be content to just let it run at a very moderate throttle setting, the prop just keeping pace with the airflow, while I soared around. It will sip fuel, the engine will be ready when I need it, cabin heat will be there if I want it, and it avoids the complications of any kind of special prop. Of course, I guess the magic of silent flight wouldn't be available, but I like motor noises just fine.
That is what I done when working lift with the SSSC. The engine had a very reliably idle at 900 rpm with the 60" dia prop. Yep, just pull the carb heat to on and not worry. At idle rpm the wind noise is louder than the exhaust.
 

103

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On the geodesic design the strips are below the surface of the wing and do not touch the fabric. I always rib stitch everything. An all CF D-tube with the CF spar would be nice but its a little over my head in designing for the strength needed, I would need help.
On building the Geo wing, I start with the spars and ribs all lined up true and epoxied. Have to be sure of any twist you want in the wing because the geo strips locks the wing solid. Think of a geo wing as a fully sheeted wing with lighting holes. I do the flat bottom first and run one row of strips from the root to the tip. Maybe takes a couple hours, then the next day run the geo strips in the opposite direction (lots of cloths pins ) then the next day turn the wing over and do the top. So 4 days working about 1.5 to 2 hrs each day, the geo strips are finished. Really the extra work of varnishing the strips takes longer. That is the extra work.
The SSSC Geodetic wing is much easier to rib stitch compared to the Cygnet Wing. https://www.homebuiltairplanes.com/forums/attachments/img_20191016_170507005-jpg.90352/

My builder Zig chose to rib stich the top surface only before covering the bottom as a compromise the designer suggested there is so much more surface area glue alone was enough. I have peace of mind knowing my builder diverged from the plans in this area. If Recover it in the future I will do the same. But first I must build something to fly while the Cygnet gets new skin...Hmmm SSSC...
 

Pops

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I rib stitched top and bottom as the normal practice , but due to the geodetic strips getting in the way of the wing stitch layout, I had to use 3 different layouts in the length of a wing panel. I don't know why you would consider the SSSC Geodetic wing being easier. The 1/8" x 3/4" geodetic strips are on 6" centers.
 
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