Bending Long Sheet Metal like Leading Edges

[EDMO 1078]

Very informative article in April 2016 KITPLANES mag about using vacuum bagging and vacuum cleaner to bend long pieces of sheet metal, like for leading edges or flaperons, and putting in a sharp bend or a radius bend.   Note:  According to my knowledge, only the Kirby vac has a separate air supply for the motor, so be aware of this before burning up your wife's vac.  A Shopvac , or venturi vac supply can also be used.    I plan to try this to bend the radius leading edges for my flaps and ailerons.   EDMO

Edited 24 Feb 2016 by EDMO

[SuberAvid 617]

Thanks Ed, I haven't got that one yet but will look forward to it.

[EDMO 1078]

Thanks Ed, I haven't got that one yet but will look forward to it.

Randy,   One thing the article didn't cover, or I missed it, was sealing the frame/plastic sheet with some of that sticky-putty stuff we used for vac-bagging in Anchorage Avschool.   Oh yes, they didn't mention using a cheap venturi from Harbor Freight for the vacuum, or a vacuum pump, which is $pendy.    EDMO

Edited 25 Feb 2016 by EDMO

[SuberAvid 617]

Thanks Ed.  I hope I can do it with a shop vac. 

[EDMO 1078]

Randy,  If I understand a little about what we were supposed to learn in AMT school:  "The sharper the leading edge is, the sharper or quicker the stall".

I think I would make a radius on the leading edge extension not less than 1/2 or 1/3 of the 2.5" you have now.  Mine is 1.25", I think.

EDMO

Edited 27 Feb 2016 by EDMO

[lostman 198]

Ed, you beat me to it. Since I'm building the Sonerai right now I have done a little research into this area of radius versus stall. It seems a lot of the guys that get a bit over zealous about bending it to a fine point suffer terribly when it comes to stalls. The sharper the point the harsher the stall. I haven't found the research so show why yet but it's consistent among the group on Sonerai builders at least. It seems when it's not a nice round profile the plane wants to drop a wing pretty severely. 

Something to consider anyway. There is a reason that the larger camber wings are also gentler on the stall, bigger radius leading edges with the high lift profiles of the airfoil. 

[EDMO 1078]

Kenneth,  We studied stall strips some in Avschool - they added an angle > point forward, to the inside leading edge portion of some wings (that didn't have enough twist or something) to make that part stall before the outer part, so the ailerons would still be effective.  Of course, like Leni says, "You have more roll control with rudder anyway".

Yes, a too-small radius or sharp leading edge can make the stalls quicker, sharper and without warning, and not like the buffeting that some wings give as a warning before a stall.

 EDMO

Edited 28 Feb 2016 by EDMO

[Geoffrey Thorpe 31]

For those who don't get kitplanes

http://raa.ca/magazine_pdf/tech articles/Leading Edge Vacuum Forming.pdf

And, a video: https://youtu.be/2_QWPoFEhWc

[lostman 198]

Thanks for posting up the video. Good information for sure. 

 

[EDMO 1078]

Kenneth,   The Kitplanes article was basicly the same, but they taped the edges of the sheet together and laid it flat under the plastic and made a sharp bend in it - they said you could tape a pipe, pvc or metal, to the center of the sheet and make the radius bend the same way.  EDMO

[EDMO 1078]

Kenneth,   The Kitplanes article was basicly the same, but they taped the edges of the sheet together and laid it flat under the plastic and made a sharp bend in it - they said you could tape a pipe, pvc or metal, to the center of the sheet and make the radius bend the same way.  EDMO

Note:  The author said this is what he observed at the Hummel factory.   EDMO

[SuberAvid 617]

Ed and Kenneth,  Thanks so much for the further information on the LE profile.  I'm hoping to replicate the Lee Dubay profile as close as I can.  I will lay the cross section up against the KF LE and see how thy compare.  Jack has the KF LE on his and it still stalls very gently.

Randy

[EDMO 1078]

Ed and Kenneth,  Thanks so much for the further information on the LE profile.  I'm hoping to replicate the Lee Dubay profile as close as I can.  I will lay the cross section up against the KF LE and see how thy compare.  Jack has the KF LE on his and it still stalls very gently.

Randy

Randy,  Try also comparing the LE profile with the Kitfox plastic LE profile that you have.  Never mind - I think that is what you are saying?   One more cup of coffee and I might wake up!    EDMO

Edited 1 Mar 2016 by EDMO