on behalf of Andrew W ****** Forwarded Message Follows *******
--- Begin Message ---Hello Anthony (I can not submit to Aus-soaring but this might be interesting for the group to know.) A company overseas called "Jet RPM" already has retrofit jet engines from 30 to 70 kg thrust for gliders for sale. The web site is; http://www.jet-rpm.com/en/indexEn.htmAccording to my calculations I will get 2 knots climb rate with a 22 kg jet. In Europe they give ASH25Ms a short car tow to get them off the ground quickly on short strips and then they climb away on the engine. I would be more than happy to take a winch or short autotow and jet away with 30kg of thrust behind me. I'm ready to become "Roger Ram Jet" anyday. Regards Andrew Wright Date sent: Mon, 26 Mar 2007 11:35:42 +0950 From: Anthony Smith <[EMAIL PROTECTED]> Subject: RE: [Aus-soaring] Jets To: David Lawley <[EMAIL PROTECTED]>, aus-soaring@lists.internode.on.net Copies to: Send reply to: [EMAIL PROTECTED], "Discussion of issues relating to Soaring in Australia." <aus-soaring@lists.internode.on.net> > >From a standing start the prop will probably get around > 50-55kg thrust depending on engine and prop. > > As you get moving the props ability to produce thrust will > start to reduce but the jet will keep on producing a > relatively constant thrust. > > You will get to a speed where the jet will start producing > more thrust and start to overtake the prop. > > Where the jests get an additional advantage is they are > significantly lighter than the piston / prop combination > > > Far out guys! > > > > It sounds to me as though the only way to get an answer is > > for me to get a LARGE spring balance scale, fixed firmly > > to the ground and a rope attached to a glider with say > > 60HP self launch, on a bitumen runway, go to full throttle > > and see how hard it pulls, then do the same with a 25 kg > > jet, as that will give a comparison of the actual standing > > start power(But the prop type will need a spring balance > > that measures to infinity, doesn't sound right to me > > somehow) > > > > Well either that or go get a math's degree! > > > > Thank goodness I didn't ask for the complex answer! > > > > Dave > > > > -----Original Message----- > > From: [EMAIL PROTECTED] > > [mailto:[EMAIL PROTECTED] Sent: Monday, 26 > > March 2007 9:36 AM To: David Lawley > > Subject: RE: [Aus-soaring] Jets > > > > For a prop aircraft: > > > > Thrust available = prop efficiency x power / speed. > > > > which so far doesn't make a lot of sense when speed = 0 > > because it makes the thrust available infinite. > > > > Prop efficiency largely depends on the prop adavance > > ratio: > > > > Adv ratio = speed / (rpm x prop diameter) > > > > The prop has a polar curve in effect with peak efficiency > > occuring at a particular advance ratio - hence you have > > climb props and cruise props. The props are set to have > > max propulsive efficiency at a particular advance ratio. > > > > > > However at very low speeds we can say that the > > realtionship between efficiency and advance ratio is > > linear: > > > > Prop efficiency = k x advance ratio = k x speed / (rpm x > > prop diameter) > > > > where k is the ratio between efficiency and advance ratio. > > For a climb prop k may be around 1.43 or a little lower > > depending on actual prop design. > > > > So thrust available is now: > > > > Thrust available = k x speed / (rpm x prop diameter) x > > power / speed. > > > > The speed now cancels out > > > > Thrust available = k x power / (rpm x prop diameter) > > > > This is for low speed only. As you speed up k decreases. > > > > > > > > > Hi all, > > > > > > Let me rephrase the question, what is the conversion for > > > thrust to horsepower assuming 0 airspeed, idea being > > > what acceleration a jet powered glider will have from a > > > standing start, ie takeoff? > > > > > > Regards > > > > > > Dave > > > > > > -----Original Message----- > > > From: [EMAIL PROTECTED] > > > [mailto:[EMAIL PROTECTED] On > > > Behalf Of Anthony Smith > > > Sent: Monday, 26 March 2007 7:50 AM > > > To: 'Mike Cleaver'; 'Discussion of issues relating to > > > Soaring in Australia.' Subject: RE: [Aus-soaring] Jets > > > > > > Actual Thrust = prop efficiency x power / speed. > > > > > > Working out the prop efficiency is the interesting bit. > > > > > > -----Original Message----- > > > From: Mike Cleaver [mailto:[EMAIL PROTECTED] > > > Sent: Sunday, 25 March 2007 10:32 PM > > > To: [EMAIL PROTECTED]; Discussion of issues > > > relating to Soaring in Australia. > > > Subject: RE: [Aus-soaring] Jets > > > > > > At 21:36 25/03/2007, you wrote: > > > >Yes, but it isn't straightforward, which is why people > > > keep refering to >either thrust for jets and horses for > > > props. > > > > >It is probably easier to convert horsepower to thrust - > > > but you will >need a chart of your propeller efficiency. > > > > > > > > > > > > > > > >-----Original Message----- > > > > Anyone know the relationship between thrust and > > > horsepower? > > > > > > > > > The old Physics teacher in me (yes, me too!) says > > > thrust = force > > > work = force x distance > > > speed = distance / time > > > power = work / time = force x distance / time > > > therefore power = thrust x speed > > > > > > with appropriate factors to convert from various units, > > > but if you use the old imperial units then 1hp = 550 > > > ft-lbf/sec but then the aerodynamicists went and stuffed > > > it all up by requiring the density of air to be > > > expressed in slugs per cubic foot to make the imperial > > > system work. (actually the error is using a pound as a > > > force unit when it is really a mass unit - a slug is > > > 32.2 lb mass!) > > > Wombat > > > > > > > > > > > > >_______________________________________________ > > > >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-soarin > > > g > > > _______________________________________________ > > > 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 > _______________________________________________ > 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 ANDREW WRIGHT
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