Fuselage Stretch - best way?

19 posts in this topic

Posted

For you guys that have stretched a C Avid or MK2 Kitfox which is the best way to approach, what tubes etc?

Cheers guys

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Posted

Maybe we can get Randy to chime in here.  He is in the middle of doing the 18" stretch on a MK IV Avid.  He is also putting the mixer under the seat and doing a few other things to it like the Fat avid (avid+).  I have not put eyes on the project yet but will soon.

:BC:

 

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Posted

What about, instead of stretching the fuse, we took the Boeing approach and enlarged the vertical stab and rudder. Assuming the stretch is done for stability and yaw/pitch authoritéé (my salute to Eric Cartman) reasons. This would allow for an increased angle of attack 3 point which is decreased when stretching the fuse. Would also reduced the wetted area. And the fuse is stronger when it’s shorter.  

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Posted

Longer fuselage helps with the typical nose heavy CG as well as stability.  Leni, it will be nice if Randy can keep us updated on how he does the stretch for sure.  JImChuk

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Posted

Ive cn the strech he is doing and sure nice setup ill say.  I also have pic of the fuse he is streching, not sure if he b ok with me posting them or not.  Would have to ask him. 

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Posted (edited)

What about, instead of stretching the fuse, we took the Boeing approach and enlarged the vertical stab and rudder. Assuming the stretch is done for stability and yaw/pitch authoritéé (my salute to Eric Cartman) reasons. This would allow for an increased angle of attack 3 point which is decreased when stretching the fuse. Would also reduced the wetted area. And the fuse is stronger when it’s shorter.  

That's exactly what Dean Wilson did on his personal Piper Clipper (greatly increased size of vstab/rudder and hstab/elevator) That strategy worked very well. I wanted it real bad and test drove it with him. Unfortunately we could not agree on a price otherwise it would be my plane now.

I thought it was awesome. He also streamline it, lengthened the wings and built spoilers similar to a sail plane in the top of the wings. It flew VERY fast on little fuel, flew VERY slow, and the spoilers made it able come out of the sky like an elevator without affecting pitch or approach speed. it was an amazing plane IMHO.

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Edited by ChrisBolkan
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Posted

That is one sexy bird!  Like the lifting tail as well!

:BC:

 

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Posted

Would be nice if Randy could post some pics!! ;)

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Posted

Would be nice if Randy could post some pics!! ;)

give him a little time, he just got back in state.  

:BC:

 

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Posted

Well I have to apologize for not having a very good picture log of the stretched Avid project.  Attached are some pictures taken early on of the stretched area and the added reinforcing in the tail area.  Jack has been helping me with this and it is always nice to be able to bounce ideas off each other.  Before cutting the fuselage we leveled it with reference tubing at the wing root and the horizontal stabilizer areas to be sure we maintained the level and alignment of both sections and mounted the front to a long piece of channel and the back to a tubing frame we could slide down the sides of the channel.  It worked very well to keep everything aligned.  I heated and bent the longerons to align with each other where they were separated and made small splice tubes of the next larger tubing in .058 as you can see in the pictures.  Thankfully, these will all get welded by our own AFF Founder.  I added in all the tubing and truss bracing in the new section and it worked out very well as a new bay but it caused the fuselage to have a bit of a jog in it rather than a smooth shape, so I cut all the side longeron tube mounts loose and replaced them to get a smooth curve and also added an additional bottom longeron tube on each side to smooth the curve along the bottom.  Since then I have the mixer remounted under the pilot seat and the mount for the push/pull cables as well as removing all the tubing at the back of the seat and behind the seat that supported the mixer assembly.  This completely opens up the first two pays behind the seat for cargo and allows me to mount independent (boat) seats about 4" further back.  I trussed across the fuselage at the back of the seat similar to what is at the front of the seat and also added additional truss tubing at the rear door area to widen it at the shoulders by about 2" each side and to add more strength back to the fuselage since the seat back tubing was removed.  I plan to dogleg the brace tubes going to the center motor mounts to give me more foot room and will add the bottom row of motor mounts that my Avid+ has so I don't have to worry about the extra HP of the Yamaha planned for the nose.  I will probably also add the third landing gear mount like I have on my Avid+ and increase the height of the tail and rudder to get some additional area and do a balanced rudder.  I really like the rounded tail but I plan to just square off the tail and rudder since it will be easier and gives the maximum area.  Once all tacked in place, will haul it to Leni to do his welding magic!

I'll post some more recent pictures this weekend or so when I get a chance to take some more.  If I can help anyone else thinking about doing this just let me know.

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Posted

Thanks Randy, nice work!

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Posted

Here are some pictures of the project at its current stage; mixer control under seat, widened at doors, smoothed longeron shape, extended baggage.  Still some reinforcing around cabin to do, additional motor mounts and landing gear mounts to do, etc., plus enlarge tail and rudder.

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Posted


sheeeeeeeit.  gonna be some some rod burned on this one!  I like the way you did the jig too. I might have to copy it for the Coyote when I finally find some time to get to my own projects :lmao:

 

Got a Pitts S1 going on the table this afternoon to jig up, replace sketchy wing attach points then mad the engine mount to take RV3 style gear legs.  Should be a ton of fun, more than a few new words learned and ultimately satisfying when the owner no longer has to worry about the wings coming off the fuse from the shitty work done by the original builder.

:BC:

 

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Posted

Looking good Randy! Are you adding balanced rudder and elevator ala Avid+?

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Posted

Leni, I'm glad I know a good welder; mine are more like the ones done on the Pitts I think. lol.

Doug, I plan to do a balanced rudder but don't think I will bother on the elevator.  My Avid+ just has the stock Avid MKIV elevator.  Does yours have a balanced one?

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Posted

Rudder only. Sorry, not sure what I was thinking there. 

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Posted

Pondering stretching my model C Avid to expand my engine options.

Nice pics and description

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Posted (edited)

I started a topic on the Avid stretch project under Fat Avid, Avid Plus section.  The topic is Avid Stretch (Mini-Plus).  I am planning to use the Yamaha Apex or RX1 motor on this one but have not gotten to the point of starting to accumulate those parts yet.  I posted some pictures that better show where the cut was made in the fuselage although they are posted as the latest post so are out of order.  It also includes converting the controls to be like the Avid Plus, some other mods and enlarging the rudder.

Edited by SuberAvid
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Posted

Randy, You posted " Before cutting the fuselage we leveled it with reference tubing at the wing root and the horizontal stabilizer areas to be sure we maintained the level and alignment of both ".  Can you tell us what the horizontal stab angle is when the fuse is level?

We just picked up a model C that suffered a hard landing(crash).  The entire tail was pushed upward breaking the upper longerons.  Someone cut the other tubes for recovery or transport???  So we have no reference for repair.  We want to extend the fuse while making the repairs.  We were thinking of making the stab adjustable but I prefer to start with the proper angle built in.

Thanks for any info.

Jim Vaughn

Pinola, Indiana

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