Forget about bellcranks, Install some small servos out in the wings. Much better.
Bellcrank? You said bellcrank, right?
I didn't think anybody used them anymore.
I certainly wouldn't use them on a '90' size warplane. Use a servo. It will save you money in the long run when you don't have to replace the plane due to loosing a aileron, because of fludder.
snip a lot of stuff
because of fludder.
Bellcranks will double the slop and halve the fun (as in watching your ailerons flutter away at altitude). Servo's just don't weigh that much so put it out in the bay ahead of the aileron arm and you'll only have about 4" of straight control rod to mess with.
MJC
Nope, none of those bell cranks will do. _WAY_ too sloppy.
Nelson have purportedly changed the design, going from double truss to single truss, and I've not used any of the new offerings, but the originals are somethin' else !
The Nelson bell cranks are supported by ball bearings and use ball joint connectors. Zero, and I mean _zero_, slop.
I'll be adding photos of a bell crank aileron installation in a 1/3 scale L-4 when TD Bill gets past and I can get out to the building shed. There is one photo of a Nelson bell crank setup in the photo album "Split Elevator Linkage", third photo, at
Not the best photo in the world, but you can see the double-truss bell crank. First class setup, _if you have the room_. Cheers, Fred McClellan the dash plumber at mindspring dot com AMA L180201 IMAA LM 090 NASA 6512 LHA 3
Hi Gordo,
Glad you liked it. It was probably the best show we've done in quite a while. Short and sincere. I didn't know that my combat ship would flat spin like that.
Fludder is what the rudder does. Doesn't do it very often and is very difficult to detect.
How'd you like the "The Dragon and His Tail?" The 'Morning Deseret News' said that it's the last B-24 flying.
Hmmm...
Sounds to me like you put too much slop in the control system when you used bell cranks or left too much gap in the hinge line.
Many put control rods into bell cranks, servo arms, and control horns with oversized holes created by slightly large diameter control rods for ease of installation. The problem is that the holes were wallowed out and the control rods used are smaller than the ones that created the holes. This BUILDS in slop from the beginning and it only gets worse. The other common problem I have seen is not straight rods coming out of or going into a control surface or bell crank. This is also another serious source of flutter that you may have seen.
I have used bell cranks on planes that exceeded 120 mph and not had a problem. In fact, after the elevator servo died, I built a new bird and reused the exact same linkage. That version died because of an engine failure at an inopportune location. The replacement has the linkage in it now and shows no evidence of flutter even in WOT dives.
-- Jim Branaum AMA 1428
Six_O'clock_High Target snipped-for-privacy@Guns.com
There may have been a bit, IIRC there was a tiny "click-click" when I wiggled the ailerons, but the connectors and holes were properly sized. However there are twice as many connection points and it stands to reason that slop will be more of a problem than with a short direct connection. The hinge gaps were reasonable. This was a Sig Kommander (I think - it was a shoulder wing right?) kit, that I flipped upside down into a low winger and flew with a .60, so it moved pretty fast and I beat it up every chance I got too. These were lightweight barn-door type ailerons, so that likely contributed to a propensity for flutter. I didn't dork it that time btw, managed to get it down on the remaining aileron. Before I realized I was near sighted and my depth perception was less than perfect though, I flew it through a dead tree at >100mph after pulling out of a vertical WOT dive. That was entertaining - the engine and fuselage stayed in the tree but a shower of foam and covering sprayed out the other side. A stick rammed itself down through the carburetor throat and into the crankshaft port and ther cooling fins were plugged with wood and bark. Oops.
I guess my main point was that right after this episode (circa 1985) I started using twin servos and right awaysensed an improvement in control feel, and never went back. I immediately retrofitted a couple of aircraft with outboard servos and things were better. Thus I can't see why I would choose bellcranks versus twin servos, as it seems hard to make a case that bellcranks have any functional benefit in comparison.
Mike D.
PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.