Opinions please on Design of 3D Aerobat

[WoFlyer]

I need help designing a new 3d capable aerobat for myself. My last design was O.K. but a little to much Funflyer, not enough patern aircraft. I am interested in hearing ideas and opinions on things like airfoil possibilities, tail moments, stabalizer ratios and setup. Does anyone out there have some good laymen formulas for this type of design? The last design was good at rolling and tumbling, but did not track very well. It had bad pitch coupling to the canopy, and not suficent forward fusealage area for sustained knife edge. It is not that I can not design a plane that flys. I want to design a plane that is more persice. Lots of you guys design great planes, how about a few tips on this subject.


Wo, aka TpStrk in AH

[Sparky Paul]

Since you know the features of your last that you don't care for, find what causes the problems, and don't do it that way on the new plane.
It's an iterative process

[Ollie]

Much less than five percent of modelers have ever designed a plane. Today, the majority of modelers don't even scratch build. Much less than one percent of modelers design great planes. I believe that good design is just about the rarest of modeling activities. Knife edge flight requires enough fuselage side area, low weight, lots of thrust and lots of yaw control authority. The rest is pilot skill and transmitter programing.

[DaveGherardini]

This might be old news but my input would be. ALL tail surfaces symetrical airfoils. And as you have pointed the fuse sides for edgeing are critical. My first 3D plane was small. 29"ws. I used flat surfaces for the tail feathers and that is fine for hovering for a light plane(16oz electric). But it had the same bad tracking properties you have described. I made the sides flat half way up the bulkheads or formers as others call them. The rest had longerons in the useual half oval shape profile. As Paul pointed out, I learned from those mistakes and the next one incorperated different feathers Taller fuse and more stuff that i thought would work better. The other thing i did was to find some local 3D flyers and study their birds very closely. Im one of the few electric flyers in my area. and all the 3D planes i studyed were glow powered. min 56" ws. The biggest was 76".
I hope this is good input. Im no designer, i just build my own planes to fly. I build a kit once in a while but find it more enjoyable to build my own. I have no aeronotical design education other than experiance.

Dave G

heres a pic of the little electric i started of with

[DaveGherardini]

I used balanced rudder and elevator wich was handy when hovering. But when trying to fly a patteren they were way to much. As Ollie pointed out, Having 3 rates for these surfaces would have made it a hole lot better. I use a cheap radio with 1 rate. But i learned to fky it with the trim tabs. I didnt use balanced control surfaces the next time. I put the hindge at 25% mac.

2 more cents worth

Dave G

[WoFlyer]

Good looking plane Dave. Feels good to be part of the "Five percent" does it not. I promised myself three years ago that I would not buy another ARF, or lazer cut dummy proof kit. I had become just a flyer, not a modeler. Now it's 50-50, I build from plans or draw my own. I have saved so much money. When I take my latest design to the field, I feel really proud, this is my work. To bad the other "95 "percent can't feel that. I won't touch the 1 percent part.

Yes, flat plate tail feather are out. Foam, full section, hollow cut, sheeted with pre sanded 1/16 balsa. Very light. E 198 airfoil, 914 sq. inches. ailerons 30% of cord. Tail moment will be 232%MAC, horiz. stabalizer and elevator 27% of wing area, or 246.78 sq.inches. The CG will be at 32% to start I belive this will give me a stability margin of 15%. This CG point may change with design of the fuselage. I am not sure of the lifting area of the nose of the plane.

Please feel free to comment, just be constructive. Wo

[DaveGherardini]

Ha Wo, Thanks for the compliments. I was wondering if you could help me, If you have the spare time. I understand if you cant. I have watched quite a few ships knife edging and most of them are mid wing design. The best full scale ship ive seen was Jim Leroys Bipe. "The Guys Nutz"... I know this is off the subject and i dont want to bother you with questions but you have a better understanding of the engineering of a plane than I do. I just build what feels good for the application, I know that sounds crazy to most but you understand. Im up on the roll control difference with the chord center line to the incidence line but, It would seem to me that a bipe would be the best for unobstructed airflow over the fuse when its on its side. (like J. Leroys edging under stall speed) So if I were to build a bipe with the ability to hover should, i keep one of the wings out of the prop wash? I assume that what keeps my plane hovering in one spot is the evenly distributed airflow over the wing to keep the plane from moving parrallel with the ground.(if every thing else goes rite) Thus the reason for the sym wing. I think. When you built your plane did build it mid wing?

Thanks for your help if your interested. I know im not helping you with your questions but I was hoping you could help me with a couple questions.

Dave G

[WoFlyer]

Well Dave some of what you are asking I understand, but I don't have any Quotes from books to give you. Here are some of the things I have figured out that work with models. Knife egde flight is all about the speed you whant to fly it at. To do it slow you need alot of trust, I do this with gear drive and a Big prop. I keep my pitch down to a maxium of 7". unless there is a clearence problem. Heavy planes don't knife edge well, keep it light the side area is now your wing area. Next would be Rudder design. The rudder needs to extend as far down below the trust line as possible. This keeps the rudder from twisting the plan through the air, the rudder area above the trust line acts like a aileron. So the closer you are to having equal amont of area above and below the trust line the less "twisting" you get. This helps to keep aileron usage in the manuver to a minimum. I have not come up with a fool proff formula for location of the wing and Hor. stab. relative to the trust line. Last is side area.

[WoFlyer]

Side area has proven to be deciving. I now try to keep the side area up front closer to the 25% piont of the fuselage from the nose. I keep it down in the tail. Any advantages to having side area behind the wing trailling edge is lost in the extra weight you now need to put in the nose to counter the extra structure. You can have a taller fuselage by giving up width. As far as Bi planes go I just don't really have any expieriace with them. And as I said I am not going to type in some quote from a book. Alisdair Sutherland has a great book, he is a really nice Brit. who writes for RC Model World. I have given my copy away to someone? I have written down the formulas I found usefull. But I will make you buy the book. Sorry but he really is a nice guy. One tip I just learned, balence the plane hanging down from the propnut. If it all hangs right under the prop nut it will do it in the air. If it hangs down with the tail pushed out to the side it will act that way in the air. I'm sorry I don't have ant scientific/layman things to say. It all just layman to me. But we can discuse our experiances.

[Al-Parkflyer]

Quote:
Side area has proven to be deciving. I now try to keep the side area up front closer to the 25% piont of the fuselage from the nose. I keep it down in the tail. Any advantages to having side area behind the wing trailling edge is lost in the extra weight you now need to put in the nose to counter the extra structure.
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I am glad you pointed that out. I would just add that more fuse area up front also moves center of lift during KE more toward front, thus increasing the moment generated by rudder.
I took me a while to straigten this out. My earlier planes had funny looking fuselages and huge rudders but still coldn't execute KE.

Al

[Ben74]

it's great that you guys can design and build your own planes, but don't get all high on your horses just because you don't fly ARFs. this is a hobby, not a contest. i have designed and flown my own planes, and am currently working on a 48" 3D plane. i am also in the process of designing and building my own helicopter. however, i will never delude myself into believing that i am better than people who fly ARFs.

[WoFlyer]

Well Ben I am not sure where you are coming from. There is no one so far in here being delusinal. We have in no way said anything negative about the people flying ARF's. Please don't get this tread all messed up with negative vibes. We are disscusing building our own, not the negatives of ARF's. thanks for your future resraint , Wo

[DaveGherardini]

Ben, I dont get high while riding my horse. He would know and put me into a loop. Also curious as to your 3d ship in the works. How are making the fuse? What i mean is round front to back or flat....ect...

[dwood99]

WoFlyer,

How much foam do you hollow out? Do you do this with wings also? Thanks.

Dave

[WoFlyer]

I leave about 3/16 of an inch of foam around the perimeter of the airfoil. But leaving the elevator and rudder solid in most cases. Using a long hack saw blade I make a groove in the foam inside on both surfaces, at 25 % cord tip and root. A Balsa spar is cut to slide into this groove so that the spar is touching the balsa skin. Usually a balsa cap at the root and tip to cover it all up and join all the pieces. This is the basic idea I use, but I have changed things hear and there dependeing on the design and it's use. Carbon fibre strips can be added to the skin before it is attached to the core in places to make this very ridged. Of course all adding weight. I skin the core first then using paterns I remove the inside area, entering and exiting the core from the trailing edge. The wing is different and is not skinned first. I will be useing a wing tube setup on this design. Because of this I will be getting the cores cut by CNC.

[WoFlyer]

I have attached a diagram that was sent to the prospective CNC cutter for a quote. It is not very clear hear, but shows the basic idea of the hollowing out of the main wing. To offset the extra prices involved with this, ie, the extra programing for the extra cuts. I am designing a wing that will be used on future designs also. I need to basicly cut three sets of wings to make it even out.

[DaveGherardini]

Wo, Heres what iv e been workin on in the cad. I would be interested in some of those ribs if you would be interested in selling about 24 of them. Plus any other advice on design would be cool to.

[WoFlyer]

Well Dave you are getting along nicely on your project. I am dragging a bit. It has been an unusually calm summer here in Sant Fe, so I am spending more time at the flying field ( local soccar field). Cool Cad stuff I just can't sit at the computer that long, so I draw by hand. That "rib" is actualy the patern for the root of the foam core wing.

[reznikvova]

I want to nuild that out of Fan fold, but wheres the wing? lol

[DaveGherardini]

The wing planform is the same on my first drawing. Heres the pic.
Ive also been changing the fuse above with the help and advice from Wo. Narrower and longer. Also the rudder has been changed after i discoverd a flaw in the hindge points.

This is the drawing of JAX

[WoFlyer]

Excellent Dave. Have not check out the web site yet but I will. Wo

[DaveGherardini]

Heres a pic rite before maiden. Good looking little rascal... It is a hand full for me. too dang small......

[WoFlyer]

Dave hows the project coming? I can't find anyone that can beat the 145$ per set I was quoted on the wing cores. Looks like I will have to go all wood on the wing at least. Just finished my Half size drawings, looks cool. Now just need to redraw to the full size and start cutting pieces. What type of aircraft is your model in the picture sitting on. Looks like a home built, with STOL type ailerons? Wo

[DaveGherardini]

Hello Wo. Well sir, i havent put much effort into it lately. The weather has been great and ive been spending me free time flying. (dejavoo) Im geatin alot better with the Jax though. Cant knife but im getting close. Im still down on power for hover but saving for a BL. Not sure if it will be worth it but i can use it in other planes too. I started a hotliner and keep geting side tracked when im at home trying to get it ready for a flyin in a couple weeks. I wish there were 8 days in a week!!..

Yes its an experimental my brother just completed. Its a Kolb Firefly. Ive also been busy helpin him get this plane ready to taxi test and ect for its maiden. He built it from a kit. Real cool plane. Its 100 knots vne and should cruise at 70 knots with a 45hp swingin a 61" 3 blade IVO. This pic was taken on sunday while i was flyin at his house and he was finishing the engine testing. Im pissed at him because its a single seater and ide like to go for a ride in it. but he promised to let me fly it after he feels im ready.

Dave G

He painted it with a real cool american flag drapeing style paint job. I must say im real proud of my brother. His name is Don and hes an awsome guy. He helps me with my rc planes alot with very extensive AE knowledge. Im very lucky to have him as a brother.