AeroDave

Guys,
I like to design and scratch build 3D profiles. I thought it might be fun to discuss what works best in our designs or in airplanes we purchase. I know there are many gifted designers/builders/flyers on here who can really teach us a lot, so I thought I would just get it started.

I've made a ton of profiles along the lines of what I call "my" basic design. Nothing new, just what works for me. I've been consistent, trying to change one perameter at a time so I can learn the pros and cons of each change. For example, I have found better harrier performance with low aspect ratio wings. These are just general comments, nothing too specific. I just wanted to mention a change in this direction has improved the harrier performance of my profiles. Assuming, of course, everything else remains constant, such as type of wing (hershey bar, double taper etc.) and everything else. I also like a long tail moment. It seems to smooth everything out and make precision more obtainable. The last general thing I've found (besides airfoil) is design of the tail. I like to make mine similar to a Cap 232. Stab high and forward, rudder behind the elevators.

Once again, I know these are very general comments and, of course, when designing one I get really specific and use the calculator a lot. But I just thought this kind of discussion might shed some light on what makes a good flying 3D profile.

So what works for you?

Thanks,

Dave

65 Chevy

My Feedback: (1)

This is a great thread. I agree with the longer tail moment. I have found for my flying that I like a ratio of 1 inch ahead of the CG for every 3 inches behind the CG. I set the CG at 33% of the wing cord behind the leading edge of the wing. I prefer a constant wing thickness but tapered trailing edge and square leading edge.

One thing that I have found to be a great help in my balancing is to build the fuse thick enough to house the battery pack and receiver. This also greatly simplifies another feature that I really like which is removable wings. I put an access hatch in one side of the fuse and thereby can move the battery for and aft to adjust the CG very easily. I use padding to hold everything in place. Then when I go to the field, if I want to move the cg, it is as easy as removing the hatch and sliding things around.

I have even built a stand off scale profile Decathlon with 2 piece removable wing. The wing is nearly 6 feet long and runs an Evo 1.00. Plane weight 5lbs 7 oz all up and wet. 71!QUOT! wing span and 14!QUOT! chord. 12 ounces per sq ft wing loading. You would be surprised how well this high wing design flat spins and how well it harriers. I have been able to fly a stable harrier for 4 laps around the field and drag the tail for about 200 feet down the runway. .

Keep the information and ideas coming guys, I live to design and build profiles.

mrbigg

My Feedback: (21)

Let us see some pics of the Decalthlon. I would like one of those! Love the Decathlon and would love a profile plane of one.

65 Chevy

My Feedback: (1)

I would love to post some pics. I dont have a digital camera

GoldenEagle

My Feedback: (1)

AeroDave and Chevy,

Good post! I love to design and scratch build also - especially since it gives me a chance to put forth ideas that "fly in the face" of the usual stuff we see out there. You are right on track with the low aspect ratio wing ("Big Square Wings") being the most stable in high alpha. Even QQ Somenzini is stating in his recent ads that placing the "center of lift closer to the fuselage" is the solution to stable high alpha. Nothing new but the popularity of those long tapered wings are hard to fight. My big square wings are a breeze to elevator and harrier around. And, nothing I can do will make one tip stall at any speed.

Chevy's views on fuselage length and construction are almost identical to my own (shameless plug) Talon F1-P. I'd love to see your Decathlon too - great to hear that the high wing aerobats are not forgotten. Did you see the 1/3rd scale clipped wing Taylorcrafts that were at the Joe Nall Flyin last year? They blew us away with their IMAC quality preformance in a classic high wing design.

Chris
www.goldeneagleaircraft.com

65 Chevy

My Feedback: (1)

How Cool Chris,
Just checked out your talon. That is a slick looking plane. Much bigger than I have been flying. The biggest I have had the guts to fly is my BalsaNova 1.20 which in my opinion is almost a profile. I bashed the rudder and elevator by adding 2 1/2 inches behind the hinge line. That really woke that plane up. I fly it with a 1.50 saito. Only had 4 flights on it so far and am not comfortable with it yet. I did the decathlon just because several people at our field were saying that a high wing will not 3D and barely will fly aerobatic moves. When they watch me drag the tail with 2 feet of air under my main gear, they sorta get real quiet. Then when they see that great BIG gentle landing plane hover and flat spin, the get out the ketchup and mustard to eat their words.
I will try to borrow a digital so I can post a pic or two for you guys.

Chris Keep up the good work, If you had a 60 size Talon, I might be convinced to try it, so keep me in mind

Thanks again

AeroDave

yeah, guys! This is what I hoped would happen. I know we have forums for design and aerodynamics, but I thought this would be more of a practical application discussion (which its turning out to be). Even for those that don't build. Did the last three planes you really liked have common characteristics? Is there a reason why they fit your flying style other than "QQ flies one"? I thought it might be helpful to get us thinking about the attributes that enhance desired results in our profiles.

Play on!

Dave

mrbigg

My Feedback: (21)

[quoteI will try to borrow a digital so I can post a pic or two for you guys.

][/quote]
Great! I want to see that Decathlon. They're one of my favorite planes.

I really like airbatic high wingers. I would love to have a profile one for sure.