Tail incidence

[Piero]

Hi everyone. We are in the process of repairing the rear fuselage structure of series IV speedster (80 hp) that flipped on its back on landing. Kitfox does not provide blueprints or measures of the steel strut, so we will have to eyeball some dimensions, relying on the remains of the damaged structure. We are not particularly worried of the top view (overall length, etc.) but the incidence of the tail plane might be critical. Could anyone tell us what the incidence of the tail plane relative to the wing should be? (or vice versa,...). By the way, the elevator did not seem to provide much authority on final with flaps extended. Is there any mod recommended for the tail rigging (short of enlarging the stabilizer, which I understand somebody has done)? Thanks Piero

[HighWing]

Hi everyone. We are in the process of repairing the rear fuselage structure of series IV speedster (80 hp) that flipped on its back on landing. Kitfox does not provide blueprints or measures of the steel strut, so we will have to eyeball some dimensions, relying on the remains of the damaged structure. We are not particularly worried of the top view (overall length, etc.) but the incidence of the tail plane might be critical. Could anyone tell us what the incidence of the tail plane relative to the wing should be? (or vice versa,...). By the way, the elevator did not seem to provide much authority on final with flaps extended. Is there any mod recommended for the tail rigging (short of enlarging the stabilizer, which I understand somebody has done)? Thanks Piero

Piero,
I loaned my digital level so can'd do part to part measurements until Tuesday afternoon, but using a laser, I have some numbers when plotted could be used for a fairly close starting point. The incidence of the chord of the horizontal stabilizer is 7 inches (17.8 cm) above a line drawn below the #1 wing rib (between two points - the tangent of the lower surface aft of the leading edge and the trailing edge). The 7 inch differential was measured at the back of my hangar which was 188 inches (477 cm)behind the hinge axis of the elevator.

I put 900 hours on my first Model IV and never used flaps. The benefit wasn't significant enough to have to deal with the loss of elevator authority.
The typical report is that with full flaps, the stall speed drops about two mph or about 3.22 kph. And a lot of those 900 hours were spent with friends on back country adventures. And none of them used flaps. Side slips helped lose altitude quickly when needed. When the Model IVs were dominating the email lists, the talk was of closing the gap between the elevator and horizontal stabilizer to gain more authority - and reports were that it did help. The most common way was to use tape. There were several different methods. One one was to cut two lengths of tape long enough to fit the gaps between the hinges and each was fitted to the other strip of the same length with a half overlap and the adhesive sides together resulting in a strip of tape with adhesive on the top for half the width and on the bottom for the other half. these were then fitted to the top of the aft spar on the horizontal stabilizer and the bottom of the forward spar on the elevator (or the opposite - not sure) I will plan on bringing the digital level home Tuesday and and doing some measurements that way as well.

[Piero]

Thanks for answering, Lowell. We will review your numbers. Yes, I've heard that the use of flaps is not quite recommended, as it also reduces aileron effectiveness. we will consider closing the elevator gap, as you suggest.

Piero

[Guy Buchanan]

I get about 5mph stall decrease with flaps and so it's worth it if you really want to land slow. (Rollout varies with the square of touchdown speed.) You do loose a lot of aileron authority, though, so that's a consideration. Gap sealing the elevator makes a noticeable difference in authority. I did Lowell's clear tape thing. Use the heavy duty packing tape and it lasts a long time. (More than two years on this last set.)

[jrevens]

...
I put 900 hours on my first Model IV and never used flaps. The benefit wasn't significant enough to have to deal with the loss of elevator authority.
...

The situation is SO different with the Super Sport. Pretty much all take-offs & landings are enhanced with full (2 notches) flaps. This was demonstrated to me by Paul at Stick & Rudder, and it works beautifully. Sorry, I didn’t mean to get off-topic, Piero.

[Piero]

That's ok. All hints are appreciated (especially when coming from experience).

Piero

[Dusty]

A forward centre of gravity will also reduce elevator effectiveness in the flare.Kitfoxes seem to fly best near their rearward limit.Gap sealing also helps a lot,as do vg,s under the tail plane.

[HighWing]

The situation is SO different with the Super Sport. Pretty much all take-offs & landings are enhanced with full (2 notches) flaps. This was demonstrated to me by Paul at Stick & Rudder, and it works beautifully. Sorry, I didn’t mean to get off-topic, Piero.

Always interesting discussions. My take, though, my model IV with me on board weighs in the neighborhood of 350 lbs. less than the typical 7 LSA with two on board. Take off roll and landing roll might be somewhat reduced with two notches of flaps, but, I seriously think the 7 would still be struggling to meet the take off, climb and landing performance of the typical IV. This, of course with similar power plants and props. A challenge to all. On one departure from Johnson Creek in Idaho, a buddy and his teen age son took of in a Model IV, flying behind a 80 hp. Rotax 912 and flew straight out and over the "gun-sight" notch of the ridge north of the strip. I barely missed it and attribute my failure on not doing max angle for a while until I realized what Mark was trying to do. Certifieds are rarely half way up the side of the ridge before turning to follow the descending river to Yellow Pine. I would like to hear if anyone else has done the "Straight out Departure" there. (Not the flight mentioned, but the following clip shows the notch)


https://www.youtube.com/watch?v=EKU0tjGMzLo (https://www.youtube.com/watch?v=EKU0tjGMzLo)

[jiott]

By the way FYI, the SLSA's that Stick & Rudder uses have different flap notches than the SS7 kit plane. The SLSA 1/2 flap notch is not quite as much flap angle as the kit, and the full flap SLSA angle is definitely not as much as the kit. I don't know the numbers, but I'm sure the factory can tell you. I trained at S&R and then came home and flew my own kit plane, and I know there is definitely a difference. At S&R we always used full flaps for landing; in my own plane I rarely use more than 1/2 flaps. I believe I was told the difference was to make the SLSA a little less aggressive and safer for newbies than the kit plane. I post this information because when people give their opinions on flap use during landing, you NEED to know whether they are talking SLSA or Kit. All of this only applies to the model 7; I have no idea the situation for earlier models.

[jrevens]

That’s real good to know, Jim.

[airlina]

By the way FYI, the SLSA's that Stick & Rudder uses have different flap notches than the SS7 kit plane. The SLSA 1/2 flap notch is not quite as much flap angle as the kit, and the full flap SLSA angle is definitely not as much as the kit. I don't know the numbers, but I'm sure the factory can tell you. I trained at S&R and then came home and flew my own kit plane, and I know there is definitely a difference. At S&R we always used full flaps for landing; in my own plane I rarely use more than 1/2 flaps. I believe I was told the difference was to make the SLSA a little less aggressive and safer for newbies than the kit plane. I post this information because when people give their opinions on flap use during landing, you NEED to know whether they are talking SLSA or Kit. All of this only applies to the model 7; I have no idea the situation for earlier models.

That explains it , because on my Series 5 full flaps make handling very awkward. Roll authority and control harmony goes away with full flaps. I always use 1/2 flap (11 degrees) for takeoff and landing , but the next notch to full flap (22 deg) changes everything. If there is any wind or turbulence, positive control comes into question. Bruce N199CL

[Dave S]

By the way FYI, the SLSA's that Stick & Rudder uses have different flap notches than the SS7 kit plane. The SLSA 1/2 flap notch is not quite as much flap angle as the kit, and the full flap SLSA angle is definitely not as much as the kit. I don't know the numbers, but I'm sure the factory can tell you. I trained at S&R and then came home and flew my own kit plane, and I know there is definitely a difference. At S&R we always used full flaps for landing; in my own plane I rarely use more than 1/2 flaps. I believe I was told the difference was to make the SLSA a little less aggressive and safer for newbies than the kit plane. I post this information because when people give their opinions on flap use during landing, you NEED to know whether they are talking SLSA or Kit. All of this only applies to the model 7; I have no idea the situation for earlier models.


I concur with Jim 100% on this. Our kit S7 behaves similarly to Jim's description regarding full flaps. Half flaps is 11 degrees and full is 22 degrees. Although the plane takes off and lands in any flap configuration I almost always use 1/2 flaps for landing. I found the stall speed reduction between half and full is not much at all - maybe 1 mph or so, so not much of an advantage while the yaw generation, particularly in rapidly varying wind conditions with 22 degrees can keep a person busy.

Yes - for the S7 you have to consider if you are flying a kit or an LSA when discussing flaps.

[efwd]

Just wondering. Why would you not tweek the settings of the flapperon angle so that you can utilize the multiple flap settings. Or does the last flap setting come into play if the aircraft is heavy with Passenger and bags? Seems to me that if it were rigged so that you don't ever use a notch or two then you could adjust it to be less aggressive.

[jiott]

Eddie, there is no way to tweak the flaps. You have to set them at neutral with the lever in the most forward notch (per the rigging instructions). What you can do and I wish I had done it, is put another notch in the flap lever detent about 1/2 way between the 1/2 and full flap notches. This keeps the 1/2 flap notch where it is (a very useful setting for T/O and most landings), but adds a 3/4 flap notch which is very close to the SLSA full flap notch. I think this would be the perfect setup, giving a slow but not too tricky setting for shorter fields, and then still have the full aggressive flap setting for those rare real short fields. This can be done with a simple addition of a notch on the detent before you rivet it in place and cover the console with fabric. I understand it can be done with the detent plates in place, but it is kind of difficult. I believe Scott (Airfox) has done it. I may try to do it.

[efwd]

Got it. That makes sense. Thanks

[HighWing]

Could anyone tell us what the incidence of the tail plane relative to the wing should be? (or vice versa,...). Piero

Using my digital level it looks like the horizontal stabilizer angle of attack is about 2.5 to 3.0 degrees lower than the angle of a line created by a straight edge on the bottom of the wing at the first wing rib. This would give the typical nose up pitch with power, but result on the nose down pitch when power is reduced.

[Piero]

Thank you Lowell, this is the information I needed. All other suggestions from the community are also very much appreciated. Now we will try to get plane back in flying conditions. Wish me luck.

Piero