John Sinclair wrote on 2/8/2021 12:02 PM:
Your reduced pilot weight (165+ 15 parachute) only reduces the fuselage load by 20 # below my LS-3a example, and that still leaves you something like 50# over the max allowable fuselage load. I’d nail down all these little problems before committing to the project..........you will find plenty of unforeseen issues that you haven’t even thought about.
I agree that a pylon motor mount is far superior to a FES, because there is no big CG issues to deal with. The FES nose motor weight must be counterbalanced with an aft battery which is located as far behind Your CG, as the nose motor is in front of the CG!
A big problem in selecting a ship to modify is the area you wish to install a pylon is the area where the wing controls are located on most ships.........ailerons, flaps and dive breaks......... need to come up with a plan on how to redesign the control linkage? BTW, installing a ballistic parachute shares this same problem........the chute and rocket need to go in the area where the wing controls are located.........?
I would think batteries located inside a wings D tube should be attached to the vertical shear web and strong enough to withstand a 5G load, none of which is taken by the wing skin? I’d place the batteries as far out in the wing as they will fit and you will need to design a way to get cooling air to all the battery cells. Make sure to properly repair any holes you cut in the D tube as that section takes some of the bending load and all of the twisting load seen by the wing!
What have I missed? Oh, how about a fire extinguisher......Inside the wing would be nice?
Have fun,
JJ

It's not quite so bad, JJ. A 20kw motor might weigh only 7 kg; a 4.7kWh battery would weigh
about 22kg, so the battery can usually be mounted behind the wing. That also puts it clear of
the wing control mechanisms. The total added weight will easily be below 45kg/100lb. If that
still exceeds the non-lifting weight limit, the Vne, etc, can be reduced to keep the structure
safe.

There are many advantages to the fuselage mounted batteries. A major one is easy removal for
charging elsewhere. A BRS is desirable, but the only there aren't many that offer it. The GP15
and the Silent Electro are the only two I know of. A fire extinguishing system is also
desirable, but I only know of one glider that plans to offer one (GP15).

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorg...ad-the-guide-1