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On Jan 18, 11:20*am, CLewis95 wrote:
This EDF approach may never compete commercially or performance wise with Jet Turbine or current conventional gas or electric prop systems ... I'm just curious if adapting small EDF's could achieve the very limited goals in my proposed scenario. - 60lbs Thrust - 10 minute duration (no reserve) - Climb from 1,000' MSL to 1,500' AGL - Using Paved Runway - No taxi .. prepositioned on runway - No tailwind component While certainly not a feasible commercial solution .. it would be a really neat experiment ![]() It seems to me to be far too little thrust to be useful, except as a sustainer. Back in 2000 I ran some calculations for various thrust levels for glider takeoff using engines of a type where the thrust doesn't vary with speed (i.e. rockets and, to a large extent, jets): http://groups.google.com/group/rec.a...484c08689379af At the time I was not aware of any jet or rocket-power gliders, but there are now quite a number. I concluded that anything from 100 kg to 250 kg (220 - 550 lbf) of thrust looked very usable. I see the "BonusJet" in fact has 240 lbf of thrust on a two seat glider. Bob Carlton has 225 lbf on his Super Salto. His earlier Silent had twin 45 lbf engines for 90 lbf total. It obviously worked, but the videos I've seen make the takeoff look pretty anaemic. I can only imagine what it would be like with only 60 lbf! I think these machines verify that my calculations in 2000 were in the ballpark. My constant thrust calculations are not as relevant to a prop or ducted fan where the static thrust is quite a bit higher than the thrust at 50 or 60 knots, and they're really starting to drop off after 100 knots. One conclusion that will still be relevant is that you use less total energy for the launch if you have a reasonable level of thrust. WIth low thrust you spend so much more time dragging the aircraft through the air that you use a lot more energy in total -- my figures showed 17% more fuel needed with 50 kgf (110 lbf) of thrust compared to 100 kgf (220 lbf). WIth only 60 lbf available it would be a lot higher again, because you'd be using a substantial proportion of the available thrust just to fly straight and level. 120 lbf for 5 minutes or 180 lbf for 3m20 would be much more useful than 60 lbf for 10 minutes. |
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