Avid Stretch (Mini Plus)

[SuberAvid 617]

SuberAvid    412

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Posted 19 November · Report post

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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Randy Tyler

Palmer, Alaska

Avid+ / N316DT

Subaru EA-81, IVO Medium IFA 72"

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Firesteve    1

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Posted 20 November · Report post

Thanks Randy, nice work!

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SuberAvid    412

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Posted 21 November · Report post

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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Randy Tyler

Palmer, Alaska

Avid+ / N316DT

Subaru EA-81, IVO Medium IFA 72"

 

 

 

 

 

 

[SuberAvid 617]

New Tail:  I wanted a little bigger tail and balanced rudder to be more like the size of the Avid+ so after a little sketching and head scratching this is what Jack and I came up with.

[akflyer 1427]

That is a pretty significant increase!  Looking good mr.

 

 

[TJay 1041]

Your gonna have a great Airplane there.

[allonsye 85]

Outstanding!  Really really nice!

[nlappos 413]

Fantastic work! please keep us informed.

[SuberAvid 617]

Adding a few more early pictures of the chop and stretch in case someone is interested in where it was cut. and also some o removing the tubing behind the seat to move the seat back and open up the baggage area.  Sorry for these being out of order, they should be first in the series.

Edited 1 Jan 2020 by SuberAvid

[Airplanenate 3]

Randy,

 

What fuselage did you start with? And what did you follow for the modifications?

I have a model C that I want to make taller, wider, longer.

Any input/advice you or anyone may have would be most helpful!

 

BR

Nate

[SuberAvid 617]

Hi Nate,

I started with a MKIV fuselage.  I was fortunate to get a new unfinished kit that had no real work completed on it and had been stored in a storage unit so all the components were in new condition.  I have the advantage of having an Avid+ that I built and fly regularly so it is a perfect pattern for most of the mods.  After using my Avid+ for everything for the past 10 years I am pretty hooked on what it will do and how much it will haul.  You get used to having the fun flying of the Avid with larger seating comfort and room to haul all my hunting gear for multiple week long hunting trips.  This mini-plus will not be quite as big but will be close.  The C model should be great candidate for these same mods. 

Let me know if I can help with information.

Have fun,

Randy

[Rex Reeb 1]

Hi Randy, I am very interested in doing this exact thing to my new C model fuse. I have access to a good fabricator/welder and I'm engineery type myself, so I think I'm up to the task. Jim Chuk has been very helpful so far getting me up to speed on what I have and how to do the widening at the door mod. I am interested in your efforts to increase internal room and stretch. I want to do a larger 4 stroke motor as well. Maybe Yamaha power as Teal Jenkins lives not too far from me. I have been studying your pics, Where would be the best place to start the mods? As in which is best to do first? Also I love the tail mod, but I had a question there. Do you take the angle out of it and trim for thrustline another way like at the engine mount? I know a thousand newb questions..... But I do want to build a plane I want to keep rather than finish and sell to get a more capable aircraft. I'm also in the middle of CAD'n up a new Cub style gear wider and four to 5 inches taller. I'll be happy to share that as it comes along if anyone wants to do DIY gear.

[Rex Reeb 1]

Also, what are the issues involved with making the cockpit several inches taller? I figure New Wing Struts would need fabrication etc, but is the overall geometry close enough or would Flaperon geometry be compromised? Thanks, Sorry for all the newbie questions, I'm just jetting ready for the first round of mods. I want to start with building a set of Cub style gear and the widening Mod to get started with, then move on to building a jig to keep it all lined up for the stretch.

[SuberAvid 617]

Hi Rex,

I don't know if it matters where to start but I started with the stretch so I could build the support jig with everything in original place to start and to keep the position of the front and rear parts of the fuselage at the same position relative to each other before I cut it and spread it apart 18".  You can see I based it all from a C channel run down the center of the fuselage with cross tubes bolted into the gear attach points and tacked to the channel, leveled with the door frame tubes and the tube where the HS goes through and jigs built to support the tail bolted through the tow bar tubes and clamped to the channel so when I cut the fuselage all would stay in position and I could just slide the tail section back 18" and fill tubing in between.

On the later model Avids, at least the true MKIV's, they no longer had the offset angle in the tail.  I am not sure exactly when they made that change though so you should check yours.  I think you could cancel it with your motor mount angle though if needed.

I didn't change the height of the cabin tubing but will be raising the skylight like I did in my Avid+ by 1.5" in front and 3" in back.  I might even go a bit more but that works pretty good for me and I am 6'-1".  By removing the tubing cluster behind the seat, you can move the seats back 4" and recline them some. This is a huge help. This also means moving the mixer under the pilot seat and adding/reinforcing the seat cross trusses back and front, trussing the sides at the shoulders and adding reinforcing tubing across the cabin where the shoulder belts connect.  It is well worth it though; having used my Avid plus for 10 years now, it really is a great plane for back country and hunting, so my objective is to make this come close to it with a minimum amount of rework of the MKIV fuselage.  I built heavy duty bungee gear for my Avid+ that is 5.5" taller than the Airdale wide gear (that was taller than the stock Avid gear already).  I really like it but want to go to cabane gear on it with ACME shocks to get the long travel, so will be building a new set for the Avid+ and use the current Avid+ gear on the Mini+.  Fortunately I still have the jig I built for the gear.

Best wishes on your project!

Randy

[Rex Reeb 1]

Thank you, and I'll post pics as I go along....and probably as more questions! Mine does still have the rudder angle set into it, I was thinking about removing it and building a larger tail somewhat like the one you did. How far have you gotten on yours? Also, moving the mixer under the seat looks like a whole nother issue, but I think I will go for it too. I want to make as useful of an airplane as I can and now is the time! I am about 6ft one half inch tall. You wouldn't happen to have drawings or a bill of materials for the gear would you? I'm drawing mine up in CAD now but I would like to at least see what others have done or use a proven design. Thanks again!

[Rex Reeb 1]

Oh, BTW I have a CNC mill in my garage, I can make most anything, if you need stuff let me know, we'll figure it out

[SuberAvid 617]

Hi Rex,

Having a CNC Mill will be perfect!  I am using the old hand cut, grind, heat and bend to fit method.  I do have the rough sketches and tubing sizes I am using for my gear and the bill of materials.  I will get it sent to you soon.

[Rex Reeb 1]

Thank you!!

[Rex Reeb 1]

Also, I'll be happy to share the CAD file for it when I'm done. I'll make a Solid Model Assembly. Will make it much easier to make, and or modify. 

[SuberAvid 617]

Sounds good, thanks Rex.

Attached are pictures of the gear leg sketches and the bill of materials, along with the mixer under the seat.

Randy

[Mikeysuds 2]

does anyone know the (aerodynamic) limit for widening the cockpit? I'm thinking 40 inches max, but I can't remember where I read it.

[TJay 1041]

What does aerodynamic limit mean on a slow airplane?

[1avidflyer 1983]

Funny thing, an Aeronca Chief and Champ use the same wing, although the Champ has tandem seating, and the Chief is side by side.  The Chief is also a bit shorter but of course wider then the Champ.  Here is the funny thing, with same engine and all, the Chief is a faster airplane.  I went 3" wider on my Avid MK IV, and 4" wider on the Kitfox 4 I just finished.  I think Merhle Williams has gone 5" with his widening kit.  I never flew the Kitfox before I rebuilt it, so can't compare on it, but the Avid is no slower, maybe a bit faster even.  JImChuk

[Mikeysuds 2]

TJay, Aerodynamic limit in this case refers to the fuse shape adversely effecting the flight characteristics.

[Mikeysuds 2]

Thanks Jim. you gave me something to scratch my head over!

[Supermotive 49]

Hello. Any updated pictures to the stretch? I am looking into doing a very similar mod to my MKIV. What are your thoughts on whether or not you may be Losing structural integrity in performing  the stretch mod? That is what I am fighting with in my mind. 

[SuberAvid 617]

Well Leni just let me know he finished up the welding so I hope to catch him on his next turn around back home and pick it up!  Then it will be back on me to make more progress on it.

I am not worried about losing structural integrity because in addition to the continuation of the existing truss tubes I added additional longeron tubes, mainly to smooth out the shape of the fuselage but it will also add to the truss strength of the fuselage.  I also added other structural reinforcement to be more like the structure of my Avid+.  In the end, it will be somewhere between the Avid MKIV and the Avid+ in strength.

Randy