Avid Stretch (Mini Plus)

[Doug123 26]

Looks great, and once the welding is done it should just as strong.  I have an unrelated question you may be able to me with on my Model C.  The plane has a Subaru EA81 NSI engine with the CCW Prop.  When I took it out for the taxi trial after the tail (elevator/stabilizer) repairs,  the plane will easily turn left and will reluctantly turn right while sitting in the cockpit. Light to no brakes used.   I have checked the rudder pedal rigging compared to rudder.  With both pedals even the rudder is slightly left a degree or so.  The vertical stab is welded offset to the left as to compensate for a CW propeller. I get full throw on the rudder to the stops left or right, and she has a  Matco 6” inner tubed tailwheel.  

I thought the tail wheel chains to the springs were to tight, but adding one link to both chains made it worse.  She’ll always turn left not right with full right rudder.  No flying until this gets corrected.  Any thoughts and suggestions are welcomed as I am humbled to find the solution.

Avid Model C 

at KMYF San Diego

Doug123

 

[SuberAvid 617]

Hi Doug.

The plane with a CW turning prop as viewed from the cockpit will always turn left a lot better than it will to the right due to the torque of the prop under power.  Your attention to the TW is a first place to start.  Make sure your chains and springs are snug as it is sitting on the TW, but not super tight.  Sometimes they are different rate springs on each side; use the stiffer spring on the right side. Make sure your TW axle is vertical when your is siting on the TW with the weight on the tail spring.  Make sure your TW is disconnecting correctly at full rudder deflection to allow it to caster.  Then, you will really need to put GOOD brakes on your plane with independent master cylinders on your rudder peddles.  The single puck Matco brakes are pretty marginal.  I went to the triple puck Matco brakes in mine to get the power needed for the larger tires and the master cylinders with the remote reservoir so you can mount the piston closer to the hinge on your rudder pedal to get more mechanical leverage.  Good independent brakes give you a lot more landing directional control as well as maneuvering control.  For example, the pictures show what we had to maneuver through to get from the gravel bar in the river to a protected tiedown spot where we were hunting this year.

[SuberAvid 617]

The Avid Mini+ fuselage is back home all welded and now for me to get back to work doing little stuff like welding in tabs and getting it ready to primer.  Meanwhile while Leni and I were talking about Avids, and wings and things, Leni came up with this great idea that it would be pretty neat to see what a stretched Avid with 150 hp would do with a set of Catalina wings on it?  Well folks, we are going to find out!  After a little more thinking he came up with this perfect exchange of parts where John gets my old Avid HH wings since the ones on his (Leni's old Avid) suffered some deterioration and wind damage that tore off one flaperon (time for a full rebuild), and I get the Catalina wings for the Mini-Plus.

We checked the fuselage depth and it appears that the Avid MKIV and the Catalina have the same depth so the lift struts and wings should go on without much, if any, modification.

Should be fun; do you think they are long enough?  (16 feet) .

 

[TJay 1041]

Those wings will flap like a bird

 

[STOLpacer20 6]

I’m assuming you will keep the “dual” jury strut configuration of the Catalina?

[ChrisBolkan 130]

I have wondered if I should put my Catalina wings on my Fat Avid. I probably would have done it if the Cat wings had fuel tanks in them, but they don't, and I still want to see the Cat fly and am not up for installing tanks in them (at this time). I am super excited for you doing it though! It will lower your stall speed considerably!

[SuberAvid 617]

Unless someone knows some more about the jury struts than I can deduce from the ones I have, there is only one jury strut in the middle of the lift strut.  The other "jury" strut is the strut for the sponson floats and mounts at the end of the lift strut and is braced back to the lift strut.  They may be a good safety feature if you ever have to ditch in the water but I don't plan to use them.  On these wings, AK Flyer Bob installed a nice set of 6 gal aluminum tanks in the first half bay of the wings but I am in the process of taking those out and installing 14 gal Avid fiberglass tanks from the new Avid Aircraft since I want the longer range (and plan to get another set of football tanks for it as well).

If anyone wants the 6 gal aluminum tanks built to fit the Avid HH rib profile, they are for sale.

Leni and I are with you Chris, it is going to be neat to see how it performs!

[STOLpacer20 6]

I have no wisdom  whatsoever on these birds! I read somewhere that Avid added a second set of jury struts to stiffen the longer wing spars and struts of the Catalina... I have looked often at the Catalina 150 sq ft wing area and wondered how they would perform on a Mk4... I simply asked an ignorant question out of my interest and excitement in your plan to actually use the Catalina wing on your bird! 

[1avidflyer 1983]

It's kind of funny, but I remember a set of Catalina wings that were for sale a couple of years ago.  I think they had two sets of jury strut fittings.  I looked at some Catalina pictures last night, and never saw any with two sets of jury struts.  May have been someone's better idea on just one set of wings.  JImChuk

[STOLpacer20 6]

Yes, there’s always some new guy with erroneous information polluting the thread!

(that would be me...)

[1avidflyer 1983]

Well, maybe I repeated the two jury strut thing thinking it was on all of them.  And if you had read that, then it was the fault of the one who posted the incorrect info.  (me)    JImChuk

[STOLpacer20 6]

I have a question (maybe an ignorant one)... if the Catalina wings measure 16 ft on each side and the wing chord is 51 inches, how do we get 150 sq ft of wing area? (This is what I am referencing for measurements and specifications...) 

 

 

[STOLpacer20 6]

Are the Catalina wings closer to 17ft per side?

[1avidflyer 1983]

Good question.  I don't have an answer.... (still can taste the feet just a little bit)  JImChuk

Edited 30 Jan 2021 by 1avidflyer

[SuberAvid 617]

It looks like they include the flaperon width in the wing area (51" Chord) and apply that through the fuselage width as well.  I just measured the catalina wings and they are 16' 4.5" from root to tip but some area is lost in the curve and taper of the wing tip.

[STOLpacer20 6]

Interesting, I wonder if Avid counted the shape of the “hull” as a “lift producing surface”...(maybe the logic behind counting the width of the fuselage in the “wing area” advertisement”)

So how much more “wing area” will the Catalina wings have over your extended wings on the Avid+ ?

[109jb 181]

The "wing" across the fuselage is always counted in wing area calculations. Take my Sonerai as another example, but virtually all airplanes are the same. Sonerai has 54" chord rectangular wing,  18'-8" wing span. Wing area = 84 sq ft = 4.5'(chord) * 18.66. It doesn't subtract the 2 foot width of the fuselage which contributes 9 sq ft more to the calculation. The reason is because the fuselage of all almost all airplanes produce a little lift.

[STOLpacer20 6]

109jb-

Thanks for the response/info! I did not know that. This explains a lot. I am trying to figure out the  “wing area” increase/difference between the Mk4 (STOL), the Magnum and the Catalina... So I guess now I need to figure out how wide the Magnum and Catalina fuselage is at the wing attach point?

[SuberAvid 617]

That is a very good question comparing the wing area between the Avid+ and the Mini+...

Here is what I came up with:

Avid+: Fuselage carry through pin to pin width is 41", Wing length is 14' 9", chord with flaperon is 51", Slats add 6.5" in front of wing leading edge x 12' 2.5" in length.

So the Avid+ extended wings without the slats are 20145 sq in. and the slats add 1904.5 sq in for a total of 153.12 SF.

The Mini+ fuselage is stock MKIV width of 36" carry through pin to pin and using that width and the 16' Catalina wings gives 21420 sq in which equals 148.75 SF.

So by straight comparison in wing area they are pretty close with the edge going to the Avid+ But the slats also change the way the air stays attached to the wing at slow speeds so I am not sure if they can be compared just by wing area.

Now if I add slats to the Catalina wings ...

[SuberAvid 617]

A few more progress pictures on the Mini+

All the primer grey areas of the fuselage are where changes were made to stretch it and make it like the Avid+.  With the color contrast it is easier to see how much was done to it (and how much welding Leni had to do).  Also, latest progress fitting the new 14 gal Avid tanks into the Catalina wings.  I decided to leave the butt end ribs n place to ensure the accuracy of the spars and pin hole alinement since the new Avid tanks are semi drop in from the top, so don't position the spars exactly like the original Avid tanks do.

[1avidflyer 1983]

Wow, lots of new bits and pieces in the fuselage.  Keep at it, I'm sure it's going to be great when it's done.  JImChuk

[STOLpacer20 6]

Thanks for taking the time to answer questions and post so many updates on your projects! I am very grateful for the patient willingness to help/assist and share info on this site by yourself and many others here...

[Supermotive 49]

That's going to be an awesome bird! I can't wait to hear reports on how it flies

[flywise 169]

It's kind of funny, but I remember a set of Catalina wings that were for sale a couple of years ago.  I think they had two sets of jury strut fittings.  I looked at some Catalina pictures last night, and never saw any with two sets of jury struts.  May have been someone's better idea on just one set of wings.  JImChuk

Hey Jim, indeed the Catalina wings have two sets of jury struts each side......I am the one who bought the catalina wings as I thought it be a good idea to have a spare If I where to ding my wings into a dock...

[TJay 1041]

Very nice guys keep it up