Thanks Mike, That accords with my experimental results so far.
I am talking retrofit here. Launch is still just out of reach because of weight considerations. It has been done with very light weight gliders. Sustainer is practical, but range is limited. 20 minutes sustainer power seems achievable with either LiFePO4 or LIPolymer for about 10-12kg battery weight (perhaps a bit less) . Motor is lighter than petrol so it is an option currently. That could be get home from quite a lot of situations, especially if you have applied some judgement during the flight. On Sun, Jun 22, 2014 at 11:23 AM, Mike Borgelt < mborg...@borgeltinstruments.com> wrote: > Unfortunately there is a "maximum weight of non lifting parts". > > You may need to put the batteries in the wings. See The Binder EB29DE at > http://www.binder-flugmotorenbau.de/eb2900.html?&L=1 > > Not a show stopper but extra complication. > > To raise a 500Kg glider through 2000 meters(launch plus retrieve) requires > 10 megajoules of energy plus what energy was required to keep it in level > flight for the time taken to get there. Say 1/3 of that. More powerful > motors are better but prop efficiency suffers as you put more through the > same diameter prop. Interesting tradeoff and design iteration. > > 1 kilowatt hour = 3.6 megajoules. > > Prop efficiency and motor efficiency losses will be at least 50% so you > need around 7.5 kilowatt hours of energy in the battery. You won't want to > discharge it deeply if you can help it so a little extra helps. Say 8 > kilowatt hours. > > Currently the LiFePO4 batteries (currently safest Li technology) can get > around 100 watt hours per kilogram so 80 Kg of batteries. Maybe 100 Kg > installed with portable charger, motor, prop and controller. > > It will end up similar to flying a motorless glider with water ballast. > > Not impossible. That retrieve should get you to an airfield of some sort > at least but probably not home if you like the longer cross country flights. > > Li - ion batteries may do a little better but need more protection > circuitry/physical barriers etc all of which add to weight. > > Mike > > > > > > > At 08:09 AM 22/06/2014, you wrote: > > http://www.zeromotorcycles.com/au/ > > > 54 horsepower for 20 Grand, FES and electric refits for old sustainers and > self launchers are getting closer by the day. By the look of it you can add > power packs easily. There is a video in there some where about supermoto > racing, for those of you not into motorcycles the standard engine is very > similar to a self launcher albeit in 4 stroke mode. > > I know it's simplistic but > > Keep mast, prop and prop flange. > Remove engine and fuel tanks. > Epoxy in battery holders and bobs your uncle. > > Justin > > > > Justin Sinclair > 17 Queen st. > Scarborough Qld 4020 > > Hm 07 3885 8949 > Mob 0421 061 811 > > Email jjsincl...@optusnet.com.au > > > Sent from my iPad > _______________________________________________ > Aus-soaring mailing list > Aus-soaring@lists.internode.on.net > To check or change subscription details, visit: > http://lists.internode.on.net/mailman/listinfo/aus-soaring > > *Borgelt Instruments* - > *design & manufacture of quality soaring instrumentation since 1978 * > www.borgeltinstruments.com > tel: 07 4635 5784 overseas: int+61-7-4635 5784 > mob: 042835 5784 : int+61-42835 5784 > P O Box 4607, Toowoomba East, QLD 4350, Australia > > _______________________________________________ > Aus-soaring mailing list > Aus-soaring@lists.internode.on.net > To check or change subscription details, visit: > http://lists.internode.on.net/mailman/listinfo/aus-soaring >
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