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

HomeBuiltAirplanes.com

Help Support HomeBuiltAirplanes.com:

lr27

Well-Known Member
Joined
Nov 3, 2007
Messages
3,822
Or maybe you've figured out how not to make large amounts of drag. I think a folding prop and tight cowl flaps could make a big difference, at least after 5 minutes. There's a 1-26 out there with two completely retracting jet motors in it, though I think the motors haven't dropped in price yet. Or several electric motors on the wing with folding props, I.e. hobby stuff.

I don't know how hard it was to make, but I suspect Reg Todhunter's Blue Wren met or exceeded the performance I'm talking about. Strojnik's S-2 considerably exceeds the performance we're talking about. Maybe a simplified S-2 with a somewhat shorter, partly fabric covered wing with a turbulent airfoil would still foot the bill. From the other end, the Sky Pup is supposed to get 12:1 with an exposed engine, no windshield, and garbage all over it. I suspect a longer wing (carbon spar?) and a serious aerodynamic clean up might get it above 20:1. Since it's significantly under part 103 minimum weight, and there are lighter motors we can use, some of that weight margin could be used on aerodynamic modifications.

If we decide it can't be done, then for us it can't be done.
 

lr27

Well-Known Member
Joined
Nov 3, 2007
Messages
3,822
BTW, high end self launching gliders greatly exceed the performance of a 1-26. It's a modest target. Even some hang gliders can do it.

"Desired performance" will, or should, always be more than you can get. How much priority one places on performance is another matter.
 

Victor Bravo

Well-Known Member
Joined
Jul 30, 2014
Messages
7,037
Location
KWHP, Los Angeles CA, USA
I'd like to throw another lump of coal on this barbecue if y'all will allow it.

Several years ago Greg Cole brought one of the Sparrowhawk gliders to the ESA event in Tehachapi, CA. Looking at it with a clean set of eyes and no previous baggage, he had come up with what looked like a good solution with a smaller number of compromises:

Apparently he saw that the problem was not adding self-launch power to a sailplane, the problem was adding an engine to a sailplane.

If I recall, Cole had two small 2-stroke engines mounted on short pylons on the fuselage. They were oriented at the 10 and 2 O'Clock positions, not the 12 O'Clock position.

The smaller propellers were able to clear the fuselage, but they did not have to be as high above the CG, so the pitch-power problem was minimized. But the propellers were still above the wing, so the ground/brush clearance issue (of having propeller in the nose) was also mitigated.

These days, using good electric motors (IN-runners with planetary gearboxes) would yield two very small streamlined pods, which would be a fairly manageable amount of parasite drag. If the stock Sparrowhawk is 35 or 37 to 1, then the motor-equipped version with streamlined pods would still be over 30 as a guess.

I'm guessing you could install or remove the motor pylons and the electric connectors in a few miniutes to put it back to a UL Sailplane.
 

proppastie

Well-Known Member
Log Member
Joined
Feb 19, 2012
Messages
4,416
Location
NJ
I thought at least one Sparrow Hawk owner added retractable model turbine
 

lr27

Well-Known Member
Joined
Nov 3, 2007
Messages
3,822
From what I've seen on video, those installations need a fair amount of runway. I think one of them even had to be pushed at first. They seem to work ok, though.

I'm imagining some hobby sized motors with folding props installed like the motors in Pathfinder.
 

Victor Bravo

Well-Known Member
Joined
Jul 30, 2014
Messages
7,037
Location
KWHP, Los Angeles CA, USA
It's easy enough to estimate, based on the thrust from the motors and the weight of the airplane. The Sparrowhawk weighs 155 pounds without the motor system, I'm sure the motors and batteries would be another 60 pounds.
 

lr27

Well-Known Member
Joined
Nov 3, 2007
Messages
3,822
Unless it's overbuilt, or the pilot is light, that might be too much extra weight. For a Sparrowhawk, anyway.
 
Top