WOW that is more like it.

[flyguy]

Ok, so for a while I have known that a Tcart with a 85 has a little problem with flat out full throttle speed. I've come to understand that there is just too much lift that you have dump by getting the tail way up and then you're dragging the fuselage through the air sideways (vertically.) So today I learn something new that makes perfect sense, but I had never carried the logic on out to that point. I was checking minimum power to hold altitude at the lowest drag speed. After that I climbed to 8,000 just to check speed again at the 75% power at full throttle altitude. Found 67 statute mph indicated to be my best steady climb rate. At 7,500 it was holding a steady 500 ft/min.: Maybe 75*F on the ground. Nice. You really have to keep the wings level and the ball centered though or it will drop right off. That is with a "cruise" 71 inch prop.
So at about 8,300 I set the power to 2000 rpm (not sure why, except I've been putzing around at that setting lately what with avgas at $4 per.) and do a couple of runs in both directions checking the GPS ground speed.
Amazing: at 2000 it averages out to 97 statute. AT 2000 rpm! And then the bell went off. (I can hear some guys thinking, well duh. ) I had really been complaining in my beer about the 85 not being much faster than the 65's I've had. Now I understand why. I get 850 ft/min consistently up to about 2000 ft, but the power doesn't make it go much faster down low. Now I find you don't have to be going flat out to get the same effect with the fuselage drag, even a fast cruise wipes out the efficiency. So, the plane doesn't like to fly much over the indicated equivalent of 97 true at 8,000. Dummy me I didn't write the indicated down but it may have been between 85 and 90. But the indicated airspeed is the trick. At some altitude, above 8000 ft, the wing will be flying at the best angle of attack to make the fuselage trail straight back at the lowest drag angle, at full throttle rather than 2000 rpm say, and it is really going to honk. And it will be the same indicated as the best down lower. Amazing.
Just gotta do a few more tests flights, and then I can start working on the mixture control to get it functional. Great fun. I are a test pilot.
Darryl

[Acroeric]

Re: WOW that is more like it.

Darryl- Us clip wing guys have been doing a simple mod to get the angle of incidence more in line for the larger engines. Both Swick and Cole raised the leading edge of the horizontal stabilizer around an inch. I flew a clipwing that did not have this mod (0-200 powered) and it only went 110 at full throttle plus I ran out of down trim. Mine that had this mod and would do 130 on the same engine and prop combination plus I had plenty of trim.

On the clipwing I am building now I plan to raise the trailing edge of the wing a bit (1/2") and leave the horizontal stab position alone. It should do the same thing and look alot better than the new tube on top of the longeron in the tail. I will simply change my wood formers to smooth the transition between the wing and fuselage. If you noticed- the stock configuration leaves the trailing edge of th ewing a little lower than the upper longeron. This mod should even things up a bit.

The angle of incidence is the same from when the old 50 hp Lycomings were on the nose and they designed the incidence with that in mind.

I recently flew a 180 hp Super Cub and looked back at the tail in cruise. The elevator halves were way out of line with the horizontal stabilizer indicating the same problem. I think this is fairly common-

[flyguy]

Re: WOW that is more like it.

I think the horizontal stabilizer drag is probably a smaller percentage of the problem and fixing it mostly lets you fly the fuselage cockeyed more efficiently. Still have the drag from the fuselage. Just too much wing there at any kind of speed. The wing angle seems to be close to optimized for climb, I don't think I would mess with that. Anyway the easiest fix seems to be to fly really high and to fix the mixture control. IF I can get down to 4 gallons per I can approach 6 hours endurance. Maybe at considerably over 100 statute. Hey, here to Salt Lake City non-stop. Don't know yet, still have some more testing and work on mixture control to do.
I can imagine a Tcart with a small turbocharged engine. Maybe a German Diesel? Normalized to 15,000 ft. Wouldn't help down low, but up high, oh my.
DC

[VictorBravo]

Re: WOW that is more like it.

There are a couple of airplanes that have approved STC mods to adjust the wing angle of incidence. I know they do it on Bonanzas and I think LoPresti was fooling around with that concept on more than one certified airplane.

In my humble opinion, on a Taylorcraft, this experiment could be done using a simple welded assembly. A steel frame, approx. square in planform, made from the same size tubes as the top longerons, with some tabs welded to it. This frame mounts to the existing wing attach fittings front and rear, and has new tabs to bolt the wings on. The clever part is that you design it so the new attach points are slightly above and slightly inboard of thew previous attach points... so the lengths of the wing struts remain the same. Of COURSE this would require a structural engineer to go through and come up with the right thicknesses and dimensions... but it would not be a huge problem for a qualifieed engineer.

This would enable you to lower the incidence angle to be commensurate with an 85 or 100 HP engine, a nd not tear up an original antique airframe.