Anyone running out of nose up trim on final?

[SwiftFox]

Hey guys. I have a new (to me) Model 4 with an electric trim tab.

I find myself running out of nose up trim with higher flap settings on final. Seems to be more than normal back pressure on final to maintain slope with full up trim. Seems to happen with all load configurations.

Anyone else have this issue? Any fixes?

thanks!

[DesertFox4]

Try your approach with less or no flaps. The flaps give you a nose down pitch result with little drag increase so if you don't need that to clear obsticles on the approach end of your runway, try it without the flaps. Should leave you ample trim. I seldom use flaps on my model four. Slips I use frequently.
Flaps usually used for a shorter take offs.

[SwiftFox]

Thanks for the reply DesertFox!

You're absolutely right. I've been experimenting with flapless landings and it is much better. No trim issues. Also much more efficient!

I've been wanting to use the flaps for the additional lift for increased short field (hopefully off airport) performance. From what I've seen so far, at the same touchdown attitude, I can get 20kts slower with near full flaps and relatively high power. Just a lot more stick pressure.

Also, I'll be getting soft bush wheels and want to minimize touchdown wear on paved strips with the lower landing speeds. Might just have to deal with it then..

I was curious if a trim tab extension would help a bit in this scenario? Has that been done?

Thanks again

[HighWing]

Elevator Authority has been an often talked about issue with the Model IV and earlier. Most have used a gap seal between the Horizontal Stabilizer and Elevator. Your post suggests you have adequate elevator authority, but lose trim ability. I suspect it is elevator authority that is the real problem. I seem to recall at one of the Desert Fox Fly-ins in the old days seeing Steve's (Desert Fox 4's) trim tab was about half the length - along the trailing edge - of the factory Speedster tab and he mentioned it was adequate. Am I correct on this one?

[Jch]

I can fully trim one notch of flaps, but I can't trim for full flaps on my SS7. I wanted to ask the same question.

[DesertFox4]

Lowell, my trim tab is about half regular size.
Another point I forgot to mention was I have the larger elevator also.

[jiott]

I reset my electric trim range a little different than the manual states. I set it so I get full nose up trim at the very bottom of the slots at the leading edge of the horizontal stab. This gives me full trim at half flaps, but almost but not quite full trim at full flaps. Full flaps still requires stick back pressure but the force is reduced. I have never come close to running out of nose down trim. I have toyed with the idea of cutting the slots to get even more nose up trim-has anyone done this?

[HighWing]

Lowell, my trim tab is about half regular size.
Another point I forgot to mention was I have the larger elevator also.
I guess that validates my theory that it is elevator authority rather than trim authority. Thanks for validating at least part of this old guys memory. On my IV, I spent a lot of time closing the hinge gap with fiberglass fairings and have had no issues with trim - factory elevator.

[SwiftFox]

I reset my electric trim range a little different than the manual states. I set it so I get full nose up trim at the very bottom of the slots at the leading edge of the horizontal stab. This gives me full trim at half flaps, but almost but not quite full trim at full flaps. Full flaps still requires stick back pressure but the force is reduced. I have never come close to running out of nose down trim. I have toyed with the idea of cutting the slots to get even more nose up trim-has anyone done this?

I think I might try this. I've never used more that 3/4 nose down trim. Even in a high power decent. Whatever helps right?

[cubtractor]

I don't use any more than about 12 or 15 degrees flaps. On mine, there is no change in stall speed between that and full 25 degrees of flaps, and very little increase in drag with full flaps, and it alleviates the need for all the trim. I have installed gap seals on the elevator and VG's on the underside of the horizontal stab. The combination of the seals and VG's made a world of difference. I use a pressure relief type of trim vs. a trim tab and can relieve all the control pressure. At 50-55 mph it sinks like a rock.

[efwd]

I do believe, if I remember correctly, the factory has the Horizontal rigging set up to ensure that on your first flight you dont have too much nose up trim available. I believe they state they aim for a slightly heavy nose to reduce likelyhood of stalling on initial flight. That rigging change mentioned seems totally reasonable.
Eddie

[Dave S]

Probably some differences between the setup on a IV and the later aircraft - Our early S7 which has the "servo" type trim tabs (as opposed to the current HS trim) would not trim off all the back pressure with flaps out.

For the 5-7, Kitfox has an easy to install trim assist kit which applies some additional up pressure to the elevator when flaps are pulled which mitigates the situation.

[trentp]

In my Series 5 I used to be able to trim for full flaps landings. Now with the addition of the STi wing and larger elevator I can not, it now requires a decent bit of back pressure on the stick to keep the nose up. I too have been toying with the idea of trying to get a little more aft trim out of it. The issue is I am out of threads on the end of the screw jack to lower the leading edge, so at this point I would need to do a pretty hefty mod to make it work.

I know everyone has their different styles of flying and ways of landing but I always land with full flaps and try to touch down slow, not only to save my bushwheels but I have also always been of the thought process that the faster you land the more grabby your tires are in a side loading situation and therefore more likely to have any loss of control while on the ground. Less time rolling on the ground means less time taunting the ground loop monster ;) Could just be in my head though...

[jiott]

Trent, you are probably right about running out of thread on the actuator on the SS7 also. Cutting the slot lower probably won't do much good.

[trentp]

Trent, you are probably right about running out of thread on the actuator on the SS7 also. Cutting the slot lower probably won't do much good.

Yeah, cutting the slot won't help without modifying the point that the actuator mounts to the horizontal and moving that to get the leading edge lower. It would be a pretty large endeavor.

[N213RV]

When I fly alone, I install a 25 lb shot bag in the baggage compartment, this does help quite a bit for my plane.