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Xtra wing incidence

 
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Vic Peters



Joined: 30 Oct 2009
Posts: 54
Location: Millinocket, Maine

PostPosted: Fri Mar 19, 2010 5:29 am    Post subject: Xtra wing incidence Reply with quote

All,
Has anyone with an Xtra done the mods that TNK did to the wing (lowering leading edge),
for lower stall?
If so, do you have any before and after numbers/
Vic 912 Xtra
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PostPosted: Fri Mar 19, 2010 6:18 am    Post subject: Xtra wing incidence Reply with quote

Vic/All

I heard that Kolb recommends that the leading edge be lowered on MKIII C & X when you install the longer gear legs. I wasn't exactly sure why. Figured it was to retain Homer's design philosophy of not being able to take off till you had good flying speed.

I talked to Barnaby Wilifan the year they introduced the Xtra (he did the Xtra design). He seemed to think the nose was flying a bit low. Lowering the leading edge would raise the nose in flight. It might be a bit faster?

Rick Neilsen
Redrive VW Powered MKIIIC
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PostPosted: Fri Mar 19, 2010 7:07 am    Post subject: Xtra wing incidence Reply with quote

Vic,
 
  I have done extensive research on this subject, since I have not only added the taller steel gear legs, I've also converted my airplane from the MkIII C to be a MkIII X.
 
  Two years ago, I talked to Brian ((at)TNK), and said that when the very first Xtra was test flown, the wedge-shaped nosecone created a significant "nose down" tendency.  To alleviate this unfavorable flight characteristic, the lowered the leading edge of the mounting point if the horizontal stabilizer.  This new hor. stabilizer incidence seemed to work well, providing the Xtra retained the shorter, aluminum landing gear.
 
  However, if you change the Xtra's landing gear to the longer, steel gear legs, the main wing's incidence becomes way too steep to allow for proper take-off and landing techniques, so the next modification requires the front of the wing to be lowered.  This process allows for the main wing to cut through the air (in the T/O & landing mode) at a more desirable incidence angle.
 
  If a person has an Xtra, and they have installed the steel gear legs, the digital angles of incidence are to be the following;     (I just did all this about three weeks ago!!)
 
A)  First, level the motor mount, both left/right & forward/back directions.  Check main wing crosstube to verify cage is level side to side.
B)  Boom tube SHOULD be -6.1 degrees (mine was within .05 degrees)
C)  Now, set the front mount for the hor. stabilizer to make the hor. stabilizer be -4.8 degrees
D)  Move on to the main wings.....the factory says the incidence is to be 3.4 degrees, and there is to be 1.6 degrees dihedral.  
 
  It is important to point out you absolutely MUST use a digital level.  A bubble level will NOT be as accurate in matching one wing to the opposite wing.
 
  Since I already had my wings and tailfeathers mounted a long time ago (as a MkIIIC), I already have my wing struts made.  In my case, rather than cut down the length of the struts, to give the stated 1.6 deg dihedral, I left them alone!  This essentially had the effect of giving me 2.6 deg dihedral, rather then 1.6 deg.  (from what I have been told, this is not a bad thing, having a little bit more dihedral, that is)
  In resetting my main wing's incidence angles, the rear mount has no adjustment, the unchanged strut has no adjustment, so if you lower the leading edge, the wingtip rises as the incidence is reduced.  Just a fact.....
 
  After it was all said and done, it was NO easy feat, either, my angles turned out to be EXACT!!!  It was a LOT of work!!  I should have taken care of this step long before I finished the Poly Fiber!!  Oops.
 
  As far as the old incidences go, I'm sure I have them in a spreadsheet.  I can send them to you if you want.
 
Hope this is a little help to you.
 
Mike Welch
MkIII CX
 
 
 
 
From: vicsv(at)myfairpoint.net
To: kolb-list(at)matronics.com
Subject: Kolb-List: Xtra wing incidence
Date: Fri, 19 Mar 2010 09:21:33 -0400

All,
Has anyone with an Xtra done the mods that TNK did to the wing (lowering leading edge),
for lower stall?
If so, do you have any before and after numbers/
Vic 912 Xtra

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Vic Peters



Joined: 30 Oct 2009
Posts: 54
Location: Millinocket, Maine

PostPosted: Mon Mar 22, 2010 6:54 am    Post subject: Xtra wing incidence Reply with quote

Subject: Re: Xtra wing incidence


Mike, all
Your right Mike I was looking for any change in stall and top end speed or any other pros or cons. Just wondered if it was worth the work. Your experience will come in handy if I were to attempt the mod.
I have the short legs and hor. stab. about flush with top of tail tube. 2 up full trim requires some stick back
pressure. Not too much. I haven't flown solo so don't know how that will work. Had I listened to Travis(as I should have) Stab LE would be 3/4" above tail tube centerline as per plans.
Anyone else that flew solo was just having too much fun to remember anything.

You brought up another question I can't figure out. If your tail comes up on take off how does gear length matter?

Also, seems like someone was telling me dihedral is less beneficial in a cross wind.
Don't have a clue, just asking.

Befuddled
Vic

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PostPosted: Mon Mar 22, 2010 8:24 am    Post subject: Xtra wing incidence Reply with quote

Hi Vic,
 
  As the MkIII's wings and stabilizers were originally configured, with the shorter aluminum legs, and the higher front mounting location of the hor. stabilizer, the main wing's incidence evidently created a problem with the landings. 
  If I recall correctly, in order to get a decent landing touch down, if the tail end was allowed to lower (due to longer steel gear legs), the plane could possibly become airborne....at a point you do NOT want that to happen.
 
  I'm only relaying information as I think I understood it.  I do not speak from firsthand experience, so maybe someone with a MkIII that has changed from the aluminum legs to the steel legs can explain it better.
 
 
Mike Welch
 
From: vicsv(at)myfairpoint.net
To: kolb-list(at)matronics.com
Subject: Re: Xtra wing incidence
Date: Mon, 22 Mar 2010 09:02:51 -0400

Subject: Re: Xtra wing incidence


Mike, all
Your right Mike I was looking for any change in stall and top end speed or any other pros or cons. Just wondered if it was worth the work. Your experience will come in handy if I were to attempt the mod.
I have the short legs and hor. stab. about flush with top of tail tube. 2 up full trim requires some stick back
pressure. Not too much. I haven't flown solo so don't know how that will work. Had I listened to Travis(as I should have) Stab LE would be 3/4" above tail tube centerline as per plans.
Anyone else that flew solo was just having too much fun to remember anything.
 
You brought up another question I can't figure out. If your tail comes up on take off how does gear length matter?
 
Also, seems like someone was telling me dihedral is less beneficial in a cross wind.
Don't have a clue, just asking.
 
Befuddled
Vic

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