Thrust requirements ?

[omega blood]

What is the minimun thrust to weight ratio for an airplane to fly.
I know there's a lot of factors involved pusher vs tracktor wing area and such. But is there a general rule of thumb for a "regular" plane with motors in front for a min. thrust to weight ratio?

[Sail 'n Soar]

There is no simple answer to your question. The minimum thrust to weight is one divided by the maximum lift to drag. Depending on your specific model (glider, stubby-winged racer, scale WWI with rigging) the minimum thrust to weight could go from greater than 30% to less than 5%. It all depends.

[Dick Huang]

omega blood,
I use wattts per pound delivered at the prop as the fly or won't fly critreia. the number is 20 watts per lb. I have experence with this number-keep it above 20 watts per pound and it will fly.
Dick Huang:)

[omega blood]

Thanks Dick, but how do you figure the watts per pound? What's the procedure and formulas. I am assumeing you need total weight, voltage, and current.

[KOMET 44]

Omga i do static thrust test with a fishing scale.One end planted into the ground .then tie a string around the tail and hook it up to the scale.then take the slack out and push the throttle to full.Then look at the scale to see how many pounds of static thrust you have vs the weight of the plane.48oz plane should have at least 16oz of static thrust.I also have a WATT meter hooked between battery and the esc .This will tell me my static amp draw.But like others say too it depends on what kind of plane you have.Of course if you have a 48oz plane and 24oz of thrust you'll be even more happy:D It's all a numbers game.Have fun KOMET44

[Dick Huang]

omega blood,
I use one of the electric flight simulation programs to determine watts per pound etc. Motocal is free for 30days; I also use E-Calc.
I like both programs.
Dick Huang:)

[Sail 'n Soar]

I second using one of the simulation programs. I just started using MotoCalc and really like it. Minimum watts per pound are very much dependent on the model. Because thrust falls off with flight speed, static thrust by itself only tells part of the story. The simulation programs give a much better idea of what sort of performance to expect than you will get trying to apply one of the "universal truths". Of course, it does give watts per pound in, watts per pound out, static thrust, static pitch speed, etc., etc. MotoCalc at least also gives their opinions on expected performance based on some of the rules of thumb. Based on your initial question, I think you would find them useful.

I guess the thing missing in all of this is, why did you ask the original question? It's interesting reading the different responses seeing how each interpreted what you were wanting to know.

[omega blood]

"I guess the thing missing in all of this is, why did you ask the original question? It's interesting reading the different responses seeing how each interpreted what you were wanting to know."

Actualy no, but since you mentioned it yes. All of you are quite helpful and your expert advice is greatly apriciated.

Well the reason I asked is up to this point all my "design" involved the " that looks about right" method. I've been using the mini-max gear boxes exclusively because you can change from 280 to 270 motors on them and the'll make just about any thing fly with in reason. Any way I was at my local electronics store and saw that they had a copeus amount of N-20 motors for $1. First thing that poped in to mind was a spruce goose. Well these are 5V motors and at that votage they will draw about .6A ( dont't quote me on this) So I wondered how much thrust eight of these could muster? I was thinking of using an 8c pack ( not sure of rating) with every two motors in series that way each motor would operate just below 5V. The bird would be foam and the wing would probably be built up. I was thinking a 36" ws would work. What do guys think?

[KOMET 44]

Omega do a search on the ezone gallery.A guy did the same plane instringer built up fashon.i think he was from n.y. good luck.stefanP