Kitfox Aircraft Stick and Rudder Stein Air Grove Aircraft TCW Technologies Dynon Avionics AeroLED MGL Avionics Leading Edge Airfoils Desser EarthX Batteries Garmin G3X Touch
Page 1 of 2 12 LastLast
Results 1 to 10 of 17

Thread: Tail incidence

  1. #1

    Join Date
    Oct 2016
    Location
    Milano
    Posts
    4

    Default Tail incidence

    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

  2. #2
    Senior Member HighWing's Avatar
    Join Date
    May 2009
    Location
    Goodyear, AZ
    Posts
    1,743

    Default Re: Tail incidence

    Quote Originally Posted by Piero View Post
    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.
    Lowell Fitt
    Goodyear, AZ


    My You Tube Channel

  3. #3

    Join Date
    Oct 2016
    Location
    Milano
    Posts
    4

    Default Re: Tail incidence

    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

  4. #4
    Guy Buchanan's Avatar
    Join Date
    Mar 2009
    Location
    Ramona, CA
    Posts
    119

    Default Re: Tail incidence

    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.)
    Guy Buchanan
    San Diego, CA
    Deceased K-IV 1200 / 912uls / 70" Warp 3cs

    gebuchanan@cox.net

  5. #5
    Senior Member jrevens's Avatar
    Join Date
    Aug 2009
    Location
    Arvada, CO
    Posts
    2,146

    Default Re: Tail incidence

    Quote Originally Posted by HighWing View Post
    ...
    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.
    John Evens
    Arvada, CO
    Kitfox SS7 N27JE
    EAA Lifetime
    Chap. 43 honorary Lifetime

  6. #6

    Join Date
    Oct 2016
    Location
    Milano
    Posts
    4

    Default Re: Tail incidence

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

    Piero

  7. #7
    Senior Member Dusty's Avatar
    Join Date
    Dec 2012
    Location
    Christchurch, New Zealand
    Posts
    378

    Default Re: Tail incidence

    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.

  8. #8
    Senior Member HighWing's Avatar
    Join Date
    May 2009
    Location
    Goodyear, AZ
    Posts
    1,743

    Default Re: Tail incidence

    Quote Originally Posted by jrevens View Post
    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
    Lowell Fitt
    Goodyear, AZ


    My You Tube Channel

  9. #9
    Senior Member jiott's Avatar
    Join Date
    Jun 2010
    Location
    Portland, OR
    Posts
    2,959

    Default Re: Tail incidence

    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.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  10. #10
    Senior Member jrevens's Avatar
    Join Date
    Aug 2009
    Location
    Arvada, CO
    Posts
    2,146

    Default Re: Tail incidence

    That’s real good to know, Jim.
    John Evens
    Arvada, CO
    Kitfox SS7 N27JE
    EAA Lifetime
    Chap. 43 honorary Lifetime

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •