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ratio : weight/thrust ?????
Hello
I was planing to fly a 220 lbs scaled model with 2 engines of 45 lbs thrust each, but I'm afraid it will not be powerfull enough . What do you think ? Don't you think 2 100 lbs would be more appropriate with this application ? What is the ratio weight/thrust which is normally used ? Thanks for any informations Marc |
RE: ratio : weight/thrust ?????
If you are designing a simple rocket, then thrust to weight may be all that you need to care about, but for an aircraft you have an additional factor called "lift" that seems to be missing from your equation.
Gordon |
RE: ratio : weight/thrust ?????
yes I know,
someone told me that a ratio of 1.2 is good for little airplanes. but I think that there is a limit of weight compare to thrust which wouldn't have to be crossed. what do you think ? Marc |
RE: ratio : weight/thrust ?????
There are many airplanes out there today operating at a T/W ratio of .25 or even less - like a maxed out B-747 for instance. Many of the Korean War vintage fighters and even some Century Series fighters operated at .4 to .5 (non-afterburner). We're all just used to highly powered model aircraft today. I once did a 50 pound twin ducted fan aircraft that operated at a measured thrust of 13 pounds installed. The drag of your configuration will probably be a more limiting factor in terms of climb, acceleration and speed.
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RE: ratio : weight/thrust ?????
Electrics (EDF) fly fine on a T/W of .3. These are real models not the parkflier types. .3 will just takeoff safely from a paved surface, .5 provides good performance and easy pavement takoffs, .6-.7 with the right aerodynamics will RO short grass and give strong vertical and 120+ level flight speed. These are all for say 4 - 8 pound airplanes. A 200 + pound monster will have scale effects on its side, I suspect .5 will be a very enjoyable model to fly.
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RE: ratio : weight/thrust ?????
I think what Gordon was saying is very true. What are you building ?...There would probably be a big difference in the PW ratio needed to fly a U-2 compared to an F-104 starfighter.
Jay |
RE: ratio : weight/thrust ?????
I'm building a little UAV of about 10 foot of length and 13 foot of wingspan.
My estimation of the total weight is about 300 lbs. Marc |
RE: ratio : weight/thrust ?????
just reading your thrust/weight ratios.. I have a Mirage delta wing jet with a OS91/ramtec im installing this week.. the plane weights 9-11lbs dry, and the ramtec puts out approx 12lbs of thrust.. should this setup be able to go vertical on take offs?:D, dont know until I try.. btw this is my first jet, tried to fly it once before with a k&b.45/turbax setup... was underpowered.. so I havent attempted again, unitl NOW!! [:-]
thanks for the info... -Ron |
RE: ratio : weight/thrust ?????
ORIGINAL: Aerodesigner I'm building a little UAV of about 10 foot of length and 13 foot of wingspan. My estimation of the total weight is about 300 lbs. Marc In any event, 30-40% is good for scale models, but since you did not divulge speed, acceleration, flying characteristics, etc., it will be difficult to answer. |
RE: ratio : weight/thrust ?????
ORIGINAL: razorice79 the ramtec puts out approx 12lbs of thrust.. should this setup be able to go vertical on take offs |
RE: ratio : weight/thrust ?????
so its just like a plane needs to work up speed first.. gotcha ya.. 12lb of thurst, i just saw that statement under ramtec's homepage or one of their dealers.. whats better for more thrust dynamax or ramtec in your experiences? I thought that dynamax and ramtec with an os91 both put out like 12lbs of thrust.. guess you cant believe everything you read/[&:]
-Ron |
RE: ratio : weight/thrust ?????
Opinions vary greatly on Dynamax vs Ramtec. Nobody seems to have presented any truely quantified side by side data. I prefered Ramtec but I had both and used both.
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RE: ratio : weight/thrust ?????
If you are making a UAV, then you will also have programs that can calcualte performance with a given configuration. If you don't have this, create it otherwise you are pissing in the wind. Obviously this is a school project, because anyone who is doing this for real, wouldn't be asking this Basic question on how to do a simple design. In short, create that program if you don't have it, or simply open an aero text book and start reading! Because you aren't going anywhere without that knowledge, ESPECIALLY IF YOU ARE MAKING AN AUTONOMOUS UNMANNED AERIAL VEHICLE! you will have to program the onboard processors with the proper inputs and equations for the UAV to actually fly...
Open a book you might learn something Success is when it comes back in a paper bag |
RE: ratio : weight/thrust ?????
ORIGINAL: BFoote If you are making a UAV, then you will also have programs that can calcualte performance with a given configuration. If you don't have this, create it otherwise you are pissing in the wind. Obviously this is a school project, because anyone who is doing this for real, wouldn't be asking this Basic question on how to do a simple design. In short, create that program if you don't have it, or simply open an aero text book and start reading! Because you aren't going anywhere without that knowledge, ESPECIALLY IF YOU ARE MAKING AN AUTONOMOUS UNMANNED AERIAL VEHICLE! you will have to program the onboard processors with the proper inputs and equations for the UAV to actually fly... Open a book you might learn something Success is when it comes back in a paper bag |
RE: ratio : weight/thrust ?????
bfoote ,i think uav is short for [unmanned aerospace vehicle], but i,m not a know it all like some here.
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