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

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Pops, Nov 11, 2019.

Help Support HomeBuiltAirplanes Forum by donating:

  1. Nov 18, 2019 #81

    Vigilant1

    Vigilant1

    Vigilant1

    Well-Known Member Lifetime Supporter

    Joined:
    Jan 24, 2011
    Messages:
    4,158
    Likes Received:
    1,883
    Location:
    US
    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).
     
  2. Nov 18, 2019 #82

    cheapracer

    cheapracer

    cheapracer

    Well-Known Member

    Joined:
    Sep 8, 2013
    Messages:
    5,478
    Likes Received:
    3,836
    Location:
    Australian
    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.
     
  3. Nov 18, 2019 #83

    Pops

    Pops

    Pops

    Well-Known Member

    Joined:
    Jan 1, 2013
    Messages:
    7,224
    Likes Received:
    6,115
    Location:
    USA.
    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 likes this.
  4. Nov 18, 2019 #84

    Vigilant1

    Vigilant1

    Vigilant1

    Well-Known Member Lifetime Supporter

    Joined:
    Jan 24, 2011
    Messages:
    4,158
    Likes Received:
    1,883
    Location:
    US
    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.
     
  5. Nov 18, 2019 #85

    pictsidhe

    pictsidhe

    pictsidhe

    Well-Known Member

    Joined:
    Jul 15, 2014
    Messages:
    6,974
    Likes Received:
    1,922
    Location:
    North Carolina
    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.

     
  6. Nov 18, 2019 #86

    Topaz

    Topaz

    Topaz

    Super Moderator Staff Member

    Joined:
    Jul 30, 2005
    Messages:
    13,848
    Likes Received:
    5,469
    Location:
    Orange County, California
    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.
     
  7. Nov 18, 2019 #87

    BJC

    BJC

    BJC

    Well-Known Member HBA Supporter

    Joined:
    Oct 7, 2013
    Messages:
    9,731
    Likes Received:
    6,513
    Location:
    97FL, Florida, USA
    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
     
  8. Nov 18, 2019 #88

    Topaz

    Topaz

    Topaz

    Super Moderator Staff Member

    Joined:
    Jul 30, 2005
    Messages:
    13,848
    Likes Received:
    5,469
    Location:
    Orange County, California
    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.
     
  9. Nov 19, 2019 #89

    TiPi

    TiPi

    TiPi

    Well-Known Member

    Joined:
    Aug 25, 2019
    Messages:
    148
    Likes Received:
    149
    Location:
    Mackay (AUS)
    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.
     
    pictsidhe and Pops like this.
  10. Nov 19, 2019 #90

    Pops

    Pops

    Pops

    Well-Known Member

    Joined:
    Jan 1, 2013
    Messages:
    7,224
    Likes Received:
    6,115
    Location:
    USA.
    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
     
  11. Nov 19, 2019 #91

    Aesquire

    Aesquire

    Aesquire

    Well-Known Member

    Joined:
    Jul 29, 2014
    Messages:
    2,341
    Likes Received:
    947
    Location:
    Rochester, NY, USA
    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 :)
     
  12. Nov 19, 2019 #92

    cheapracer

    cheapracer

    cheapracer

    Well-Known Member

    Joined:
    Sep 8, 2013
    Messages:
    5,478
    Likes Received:
    3,836
    Location:
    Australian
    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
     
    Last edited: Nov 19, 2019
  13. Nov 19, 2019 #93

    Vigilant1

    Vigilant1

    Vigilant1

    Well-Known Member Lifetime Supporter

    Joined:
    Jan 24, 2011
    Messages:
    4,158
    Likes Received:
    1,883
    Location:
    US
    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.
     
    Last edited: Nov 19, 2019
  14. Nov 19, 2019 #94

    BBerson

    BBerson

    BBerson

    Well-Known Member HBA Supporter

    Joined:
    Dec 16, 2007
    Messages:
    12,190
    Likes Received:
    2,395
    Location:
    Port Townsend WA
    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.
     
  15. Nov 19, 2019 #95

    plncraze

    plncraze

    plncraze

    Well-Known Member HBA Supporter

    Joined:
    May 12, 2006
    Messages:
    1,621
    Likes Received:
    345
    Kick starting an airplane in flight presents an interesting picture. Especially if it is an open cockpit.
     
  16. Nov 24, 2019 #96

    lr27

    lr27

    lr27

    Well-Known Member

    Joined:
    Nov 3, 2007
    Messages:
    3,226
    Likes Received:
    469
    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.
     
  17. Nov 24, 2019 #97

    Vigilant1

    Vigilant1

    Vigilant1

    Well-Known Member Lifetime Supporter

    Joined:
    Jan 24, 2011
    Messages:
    4,158
    Likes Received:
    1,883
    Location:
    US
    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 likes this.
  18. Nov 24, 2019 #98

    Pops

    Pops

    Pops

    Well-Known Member

    Joined:
    Jan 1, 2013
    Messages:
    7,224
    Likes Received:
    6,115
    Location:
    USA.
    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.
     
    Vigilant1 likes this.
  19. Nov 24, 2019 #99

    103

    103

    103

    Well-Known Member

    Joined:
    May 3, 2015
    Messages:
    136
    Likes Received:
    75
    Location:
    Wauwatosa WI
    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...
     
  20. Nov 25, 2019 #100

    Pops

    Pops

    Pops

    Well-Known Member

    Joined:
    Jan 1, 2013
    Messages:
    7,224
    Likes Received:
    6,115
    Location:
    USA.
    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.
     

Share This Page



arrow_white