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bbryan
02-09-2009, 08:00 PM
Anybody ever chop the wings off of a model III for speedwings?

JimS
03-10-2009, 12:47 PM
Not a III but I shortened the wings of my modelIV by one rib bay per side to make it the same as the speedster. Built them stock and just took a hack saw and and cut them off. Made the cutoffs so they could be plugged in as extensions if needed but have never even finished covering them. Worked great. I did it to up the wing loading for a little better ride and to make it fit in my shop better as I trailered it to the airport. Mine had a 582 for power and flew fine. (90 mph cruise at 6000rpm) I upgraded to a 912 last year. Now get 100mph at 5000rpm burning one gallon less per hour.
JimS

DesertFox4
03-10-2009, 04:17 PM
Seems like a waste of effort on the model 3 wing. I had a 912 equipped Model 3 and I could easily go over red line with an Ivo prop installed. I think it would just reduce your climb rate with no top end improvement. The 3 wing is not meant for speeds much above 85 mph. Unless you have a trim system installed, anything above 85 - 90 mph will induce extreme forward stick pressures to fly in level flight. In very smooth air I could cruise my 3 easily at 100 to 102mph but if I let go of the stick it would do a loop and you shouldn't and I didn't use the flapperons for trimming out stick pressures at those speeds.
Want to go faster, you can put a model 4 wing and control system on your 3.

DesertFox4
03-10-2009, 04:20 PM
Jim, with a 912 engine and short wings you should be seeing 110mph easily at 5000 rpms with the right prop and strut fairings installed. What "speed" mods do you have on your 4 and what prop?

P.S. what tach are you using ?

JimS
03-11-2009, 07:42 AM
Desertfox4,
I've got the fairings on the lift struts, wheel pants, and closed up the gap above the horizontal stab but no gap seals on the elevator or rudder and don't have the radiator fairing either. I have been using a warp drive wide tip prop that I just sent back to warp to have the tips tapered. Two reasons for this, 1, my prop has the steel leading edge inlay and some people more knowledgable than me suggested I may be exceding the inertia limits for the prop on the rotax which could lead to problems with the gearbox or other parts. 2,after reading the artical on the EAA Experimenter web site about prop design, it sounds like tapering the tip should increase efficency. I,m going to see.
I'm sure I could have dialed in some more pitch and have gotten 105-110 mph at 5000rpm but I had the prop set to give me 5500 right at the start of my takeoff roll for better short field performance.
I'm using a westach tachometer.
JimS

DesertFox4
03-11-2009, 02:45 PM
Jim, if you've got a ground adjustable Warp you may not be able to achieve the speeds I mentioned and still keep you rpms optimal for take off.
An in-flight controllable pitch prop would easily get you there but of course is not allowed if you are in Sport Pilot mode.
Lots of folks run the Warp props so I'm pretty confident you are doing no damage to your gearbox.
Reason for the tach question is so many people have had tachs that read higher than the actual engine is turning for rpms therefore are not achieving the power they believe they are. I've seen them off by 800 rpms and that really affects take off and cruise performance. Best way to check is to get an electronic prop tach and read the actual rpms of the prop at cruise and then multiply in the gearbox ratio to see what is really going on . Sounds like yours is pretty close from your performance numbers. You also have done well on cleaning up your 4 already. The biggest decrease we can make in drag is the lift strut fairings.

Good luck with the prop trimming. Hope it helps.

DesertFox4
03-11-2009, 06:16 PM
Well call it fiddling if you want but the only way to get max performance is with an in-flight adj. prop. I get incredible climb and then pitch in about 1 second of switch and increase my cruise by 25 mph. If a ground adj. prop is set for climb then cruise will suffer. Too big a compromise for me. Like driving your car all day in 1st or maybe 2nd gear. Great acceleration from the light but takes all day to get to the next intersection. Set a ground adj. prop for cruise and suffer longer take off runs. You always have to set it somewhere in the middle and compromise both take off and cruise. Only reason to leave all that performance behind is the stupid Sport Pilot rule that says we're all incapable of operating a 3-way switch for 1 second twice per flight..

JimS
03-12-2009, 06:04 AM
DF4,
I agree with you on the variable pitch prop thing. My flying buddy has an Avid MK4 with the inflight adj. Ivo and he can dial his rpm back to about 4300 while I'm still turning 5000 and fly at the same speed while burning less gas. On the other side of things, with my fixed pitch prop I can cruise at the top of the green arc (if I'm so inclined) and still have very good take off performance, so is the variable pitch worth the money? If my goal was to fly as fast as I could, I would have built a Vans. The gas savings would be nice though...and it is fun to try to get maximum performance from our planes. I have taped the gaps in the empanage and made some temporary fairings for the gas caps and a few other things just to see what the improvement would be and saw about a 3mph increase in cruise when I had a 582 in the nose. Now like I mentioned earlier with the 912 I can cruise at the top of the green if I want. And usually thats as fast as I want to cruise.
After all that, Have you or anyone you know ever tried to fair the area behind the rear spar into the turtledeck? I've looked at it but haven't come up with a method for doing it that wouldn't interfer with the install and removal of the turtledeck.
JimS

JimS
03-30-2009, 05:26 PM
Just thought I'd let you guys know how tapering the Warp prop worked out. I've got to give it one more tweak yet but performance wise it seems just a tad better. Maybe 2-3 mph better at cruise and the same or just a tad better in takeoff and climb. The big difference is in the smoothness of the engine. I had had a kind of a slow pulsating rumble at 4600-5200 rpm and that is 90% gone. So even if the performance had been exactly the same, having the prop tips tapered would have been worth the money for the smoothness gained. Just thought I'd share that.
JimS

bbryan
03-31-2009, 05:13 PM
Thanks for the fantastic response, this site is great. Good information on props and numbers also. Looks like this wing will be a Mod 3 for now. I once had an Avid Flyer with the 43 hp engine. Seems like the wings were 29ft with about the same performance numbers but it was 100lbs. lighter.

Thanks Again