VSXA380X800 From United Kingdom, joined May 2004, 421 posts, RR: 1 Posted (9 years 4 months 3 weeks 6 days 9 hours ago) and read 8522 times:
I have a A380-800,A340-500/600, A320 Family and a 777-300,all are 1/50-75. I'm thinking of doing the craziest thing to cut out a hole in the in the engine case and make a similar engine using 2 race car motors per engine case. With a larger fan in the front and a smaller behind. Then I might have it controlled by RC.
Has any one tried this with their model aircraft and what tips or advice I should look at ?
VSXA380X800 From United Kingdom, joined May 2004, 421 posts, RR: 1 Reply 6, posted (9 years 4 months 3 weeks 4 days 18 hours ago) and read 8443 times:
I found some Ducted Fan motors that produces 0.90 killos of thrust(2 Pounds), each. Thats 0.90x4= 3.6 killos of thrust(8 pounds). That is also 2 more pounds than the wieght of the aircraft. Is that good enough or do I need more thrust ?
BTW what is the formual the aircraft manufactors use to figure out how much thrust they need to power the aircraft ?
Doug_or From United States of America, joined Mar 2000, 3303 posts, RR: 3 Reply 8, posted (9 years 4 months 3 weeks 4 days 10 hours ago) and read 8424 times:
don't forget weight of equipment. batteries to power electric r/c aircraft can easily equal the structural weight. In addition you may need reinforcement, especaly around the batteries and wing root.
Regarding the wing, I was more intereested in what type of airfoil it appeared to have. A precise model of an airbus would have a very thin semi syemtrical airfoil, which would be a problem. You'd probably want a thicker clark y type airfoil (flat bottom). Also, what is the total wing area? as a general rule of thumb, the wing loading should be around 15 oz/ sq ft for a trainer and 22 for a hot rod I believe. thyou might want to be significantly lower than that, though, since you don't know how much lift your airfoil will produce.
Bottom line is most R/C airliner models made by non pros will be purpose built to save weight, have enlarged wings with decreased sweep to improve handling, and larger than scale engine pods to facilitate bigger blades (to accelerate more volume of air). No offense or anything, but I'm not betting in your favor. If you do have the spare $ and time to go thorugh with it, I'd strongly recommend you go for the A319 or 340-500 as they'll have larger wings compared to the fues. And if you do go ahead with it, do EVERYTHING you can to reduce weight.
VSXA380X800 From United Kingdom, joined May 2004, 421 posts, RR: 1 Reply 9, posted (9 years 4 months 3 weeks 4 days 8 hours ago) and read 8417 times:
Also, what is the total wing area?
it has an Area of 276 inches
I'd strongly recommend you go for the A319 or 340-500
Wouldn't the cargo hold be smaller in volume (1:50 even though that's big) than the 340-600 and wouldn't the 340 be able to hold most of the equipment, despite the wing area and lift produced? Besides the A380Thats the biggest model I have( that I don't mind damaging for a good cause)
I was more interested in what type of airfoil
The aircraft is made of Resin and Fiber Glass. I'm not sure if the wing is fiber Glass or Resin, vice versa with the fuselage
No offense or anything, but I'm not betting in your favor
Zrb2 From United States of America, joined May 2000, 895 posts, RR: 0 Reply 10, posted (9 years 4 months 3 weeks 4 days 8 hours ago) and read 8412 times:
I agree with one of the other posters. If your model looks like the pic you provided.....don't bother ruining it. You are surely going to crash the thing. Even if you add servos and balance it the odds are stacked against you// I speak from experience.
Doug_or From United States of America, joined Mar 2000, 3303 posts, RR: 3 Reply 11, posted (9 years 4 months 3 weeks 4 days 5 hours ago) and read 8402 times:
when I say airfoil, I mean just that. Not material the wing is made out of. the shape of the cross section of the wing.
with just under 2 sq feet of wing area, assuming you have a good airfoil, you need to keep the weight under 38 oz (3 lbs) to maintain an already hefty 20 oz/sq ft wing loading. With equipment that means you'll need to get the structure under 1.5 lbs. 1/4 of its current weight. and you shouldn't worry about the interior area of the fues. all the equipment should fit, since you'll need small (light) stuff.
Once agian, don't mean to rain on your parade, but I sincerely doubt this will be possible. If it does fly, it won't be enjoyable. it will be all you can do just to keep it in the air, and landing will be exceptionaly difficult, especialy with those wing mounted engines. and don't even say retracts. just don't even go there.
VSXA380X800 From United Kingdom, joined May 2004, 421 posts, RR: 1 Reply 13, posted (9 years 4 months 3 weeks 3 days 9 hours ago) and read 8365 times:
Thanks for the link,It will surely help me.
Now I know I'm not the only crazy one. When you said that this wasn't going to work Doug_or, was it because if the model and size I chose? The person who did what I am now had a good flight( except it took him 20 yards to take off) and landing was also a breeze. I know I might not have the same results because his was a 2 engine model and mine is a 4. I might have better results( in a way) because my motors will produce more thrust than his did and with the additional weight, it still might perform just as good. My model is signifactly smaller than his.
His Wingspan-67.5 In / Mine 47 In
His Length-67.0 In / 58 In
His Motor (x2) 480 BB 7.2v/ Mine (x4) 500-600 BB 11.5 v
Thanks for you help and suggestions.
BTW-The shape of the cross section of the wing is just like the real thing, same angle of attack. The only thing That I won't have control over is the Spoilers and Flaps.
Doug_or From United States of America, joined Mar 2000, 3303 posts, RR: 3 Reply 14, posted (9 years 4 months 3 weeks 3 days 6 hours ago) and read 8359 times:
The point was he scratch built an airplane to fly. It was light, it had much more dihedral, reinforement in key areas, and a good airfoil. His wing loading was marginal on an aircraft much larger. Having a similar wing loading on a smaller aircraft will make it much more difficult to control. I would also advice you agianst landing gear, though I'm not sure how to propperly brace the engine naceles for impact.
RE: the wing- AOA is the angle of the wing to the relative wind (direction of flight), which varies with speed. What I beleive you are referring to is the angle of incidence (the angle of the wing to the body). When I talk about the shape of the airfoil,I'm referring to the SHAPE of the x-section of the wing. airbus aircraft usualy have a fairly thin airfoil, which has been optimized for effienct cruising around .8 mach. These things do not scale. The most effective airfoil for you application will likey be much thicker (to get more lift from the available area).
While his airplane flew, and he said he wasn't very expereinced, you have to understand a few things. Hes writing an article for poeple who know much more thna he does, so he is most likely being somewhat humble. I'm almost sure hes has done previous scatchbuilt projects. I know you said you have flown an R/C aircraft, but from this conversation, I do not believe you would have been able to handle his model (a big interpolation, I know), and you have essentialy zero experience with aircraft design.
But the bottom line is that what you are proposing is a brick with wing-like protrusions. And in my experience, those don't usually fly. There is no way you'll be able to get you model to a weight where those wings will provide adequete lift at a sane speed.
Now with that said, you learn from experience, and a few failed projects will eventauly lead to success (if you have the time, money and interest). I just don't think a project that is so inevitably doomed is really the best way to start. While its uglier, you will have much better luck starting out with a big foam glider you might find at a toy or drug store (I've seen these convereted to prop and fan r/c aircraft). It will also be much better at remaining in one piece while you are learning to fly it.