is there a ratio rule-of-thumb for thrust vs. weight in an edf?
I did plan on burying 2 edf-75's into a 3dfoamy f-18 but the airframe is just too small and modification to the tail to fit 'em made for one UGLY cad drawing... finally picked a design (x-02) and need to know how much plane I can build (weight wise) with roughly 24oz. of thrust (will hopefully have more thrust with b/l motors, just calculating conservatively now with regards to scale...)

There are a lot of things that go into getting those things off the ground. Clearly, thrust to weight is one, but one has to look at what the wing loading is, and how drag fits into it. Not to be obvious, but to make a not too subtle point, what is the thrust to weight ratio for a glider? But beyond that, one could have a decent TTW ratio at .70; i.e. 24oz thrust to 34 oz acft.

I am still in the CAD stage yet, aware of most of the things involved (wing loading/drag/airfoil/FSA for intake and exhaust ducting/MAC/CG/etc...) but still figuring out how to calculate and measure the variables.
I just figured a rough idea of a weight cap now would be easier to design around before parts are hotwire cut from the FFF.

Don't know if you have advanced past the CAD stage of things. But I'll toss this out for what it's worth.

My Kyosho T33 develops about 14 oz of static thrust. The t/w for this plane is .35, the wing loading is ~18.5 oz/sq.ft. and the air frame is "draggy". The fan is a stock Ky unit, power input is 99 w/lb. The airfoil is a Clark Y, about 12% at the root, thins toward the tip. Hand launch is a non issue, just a shove and it is gone, top speed of perhaps 45 mph, generally a nice flying plane to fly in a small area.

My GWS A10 weighs in at 23.5 oz, the thrust might be 10 oz total for t/w of .42. With a power input of 120 w/lb, very easy hand launch, can be flown very fast but slows nicely for landing. The airfoil is an undercambered something or other, maybe a Clark. The wing loading is about 16 oz/sq.ft.

The previous comments about wing loading and drag are valid. The choice of air foil will come into play as well.

An EDF with a t/w that approaches unity would be a blast to fly, allowing true verticals. Further I would think a t/w = .3 is an absolute minimum, any thing less will have to be a floater. If you want to ROG, I would guess a t/w of .5~.7 would be a good target. But without retracts the air frame drag will be very high, keeping the top speed down.

I have a quick question/worry,
I have built mine and am about to test fly buy I fear it will not fly give what you have just said,
I have not had a df plane before, but the plane at full thorttle blows HEAPS of wind out the back,
BUT the aircraft does not feel like it is pulling at all??? I dont understand when the plane is
airborne and there is air flow through the intakes will this change things??
Why would it blow so much but not have the thrust??
Stumped.... []

I understand binary,it's two canary's flying in formation-right?[sm=lol.gif]As far as T/W is concerned,all you need is about .2! What you need is LAUNCH SPEED with a pusher! Remember,a piper cub with a 65hp. engine takes-off and flies just fine on a power to wt. ratio of just 1:10 or so.The F-18 needs about 20+ mph for launch in order for the control surfaces to BITE the air.Would "trinary" mean-3 canary's flying in formation?[sm=bananahead.gif]

"...The F-18 needs about 20+ mph for launch in order for the control surfaces to BITE the air..."

I would not dispute that at all. But 20 mph is just about 30 feet/sec. which sounds like a mighty toss for a hand launched plane. Last summer one the the guys had an F18 with a MF480, MEGA 16/15/3 on 11 cells. He could launch it by running then throwing.

Two other options are available. You could always mount fixed landing gear. Or you could use a bungee launch.

Bungees, when done properly, will get your plane to 45 mph and 30 feet of altitude in less than a second. But a bungee launch gone bad is not a pretty sight.

I am hoping that my simple system for variable exhaust nozzles will allow max static thrust for takeoff and then higher efflux for speed in the air. I found a cool way to mechanically link the tail to the canards and thus will have the extra channel for retracts after all.