Capt Kremen Posted June 27, 2020 Share Posted June 27, 2020 One for the aerodynamicists among us ... I have a low aspect ratio sport model, flies well but I fancy trying a lower wing loading. Current Main Wing Span is 50 inches with a Chord of 11 inches. It has a 20 inch Span Conventional Tailplane, with an average chord of 6 inches. What if ... I add say another 3 rib bays to each tip, making the new main wing span approx 70 inches? (The wing is a constant chord, tailplane a small taper). Reading full-size accounts suggest keeping tailplanes as small as possible due drag however they (e.g. airliners), have very smart electronics to keep things sweet trim wise. Without such aid, what, (if any other), changes might be made or just go ahead, increase the span and keep the tailplane as is? Adjust the C of G? Quote Link to comment Share on other sites More sharing options...
Phil Cooke Posted June 27, 2020 Share Posted June 27, 2020 If the wing design is constant chord and has zero sweep (you dont specify whether its a straight wing) then adding 20" to the span won't change the CoG. I'm no aero specialist but with the size and layout as you've described I'd expect no need to alter the tailplane design in any way. With the lighter loading you may find a slight reduction in speed througout the flight profile, as such you may find a slight increase in control surface throws are required to keep the same sport like feel. But by the magnitude you are changing things here I dont think you'll see a lot of change in performance. It should climb a little quicker and land a little slower. It should all feel a little 'tamer'. Quote Link to comment Share on other sites More sharing options...
Capt Kremen Posted June 27, 2020 Author Share Posted June 27, 2020 Thanks Phil. Yes, it is a constant chord, no sweep. The potential effect(s) you suggest are just what I seek, i.e. a little slower landing, a little 'tamer' overall. Quote Link to comment Share on other sites More sharing options...
Phil Cooke Posted June 27, 2020 Share Posted June 27, 2020 Go for it! I really dont see a need to alter the tailplane design, maybe just a little more throw on the elevator as it slows up. What model is it out of interest - any pictures? Quote Link to comment Share on other sites More sharing options...
Peter Miller Posted June 27, 2020 Share Posted June 27, 2020 Just caculate the tailplane percentage of the wing. The 20% area is usually pretty safe. If it is down to around 15% I do like the CG at about 25% chord. Most of my aerobatic designs use these figures very successfully Edited By Peter Miller on 27/06/2020 21:03:00 Quote Link to comment Share on other sites More sharing options...
Peter Miller Posted June 27, 2020 Share Posted June 27, 2020 double post Edited By Peter Miller on 27/06/2020 21:03:18 Quote Link to comment Share on other sites More sharing options...
Frank Skilbeck Posted June 27, 2020 Share Posted June 27, 2020 You could run it through a c of g calculator which takes account of the tailplane area and moment arm. Quote Link to comment Share on other sites More sharing options...
Gary Binnie Posted June 28, 2020 Share Posted June 28, 2020 I had the same idea for one of my gliders, what I hadn't bargained on was the weight of the extra structure, the wing loading remained identical. The increased aspect ratio improved the glide angle and the minimum sink rate. I have another glider that uses the same fuselage and tails for 3.5, 3.8 and 4 metre wings. Later versions of it use the same tail surfaces with optional longer fuselage. The lower photo has a 10 cm longer centre wing panel. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.