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Just joined the Fat Avid Club

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Posted

One other very important thing. I want to reiterate that I am 100% convinced there is no risk of wing "failure". An 18 inch plywood stiffener is in the correct place in the wing and now the wings are no longer than STD MKIV wings. The wing does not flex anywhere near a concern of failure. It does appear to flex more than my other Avids.

What does concern me is the stick forces required to move the flapperons in flight that are not there on the ground. That may also have something to do with the push pull cables which I have no previous experience with. The stick/mixer/push pull cable setup has a GREAT deal more play than the more direct linked regular Avids. This could also have something to do with the stick forces. There may be drag in the cables when force is applied that is not in them when not under load.

There are a LOT of variables to sort through. It could well end up being a combination of things and not one root cause.

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Posted (edited)

Chris, 

The cable forces can vary depending on the manufacturer.  Mine are a little easier to move that Jack's plane and the first set I had were the best! (But got broken as I sat out a windstorm with the wing covers on not letting the flaperons return to neutral.)  Anyway the comparison should be between the force needed on the ground vs. force needed in flight.  There is more slop than the push/pull tubes but I was able to minimize it by carefully adjusting as much slop out of the mixer and stick assemblies with washers and snug castle nuts.

I wonder if you could build in a little preload flex in your flaperon hangar mounting so with in flight wing flex they would be straight?

Edited by SuberAvid

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Posted (edited)

I have thought about cutting the wings off to the 144 inch standard length, but honestly I LOVE the additional performance that 18 inches of extra wing on each side brings to the table. It really is awesome even with the wingtips cut off! (And it now has the same wingspan as a std MKIV so it now fits in my hangar easily. It barely fit with the wingtips on. So.... I will only cut the wings as a last resort If there is nothing else that works. if I should end up doing that it looks like I may I have an extra set of wingtips available to use.

I have thought about re-mounting the flapperons on the hangars so they are "pre-stressed" in the negative direction on the ground and become neutral in flight. But there is the issue of how to do that safely because of the existing holes in the flap hangars. But honestly, I need to fly in a MKiV (Which I do have access to) and see what wing flex there is. There may be some and I am not remembering correctly. It's been 5 LONG years since I was flying regularly in the magnum and many more since I owned my MKIV. There may be flex I don't remember.

Right now I am focusing on cable drag as a contributor and trying to figure out if there is any way to reduce play. I can quite literally move one flapperon 3/4 inch up and down at the trailing edge before the other flapperon starts to move! There is less play when moving the stick, because of course the stick is in the "middle" of all of the play in the linkage and cables.

I seldom use flaps landing or taking off as this plane lands super slow b/c of the extra lifting bay on the wing. I have thought about getting rid of the mixer as it is now and running flapperons more directly to reduce some play. My estimate is that at least half of the play is from the mixer/stick linkages and the other half is push pull cable. 

I do not want to cut the wings off unless there are no other workable solutions.

The plane keeps getting better and better as I work through these issues. Right now it is well past the more fun to fly than work on phase of rigging, so things are going in the right direction. At first it was scary, now it is fun to fly, but I have clear memories of my Magnum and original MKIV and this plane is not as good as either of them yet.

Edited by Chris Bolkan
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Posted

My friend Ron took these yesterday from his mkiv when we were flying around the farm fields after work.

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Posted

That just looks fun!

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Posted

Any updated flight reports or fixes for us?

:BC:

 

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Posted

I have just been flying and working out minor issues that happen with any new build. I have put about 25 hours on so far, and plan to fly through this month. Then I will take take it out of commission to do some more bigger projects in the winter. It will kill me up to take it out of service since I have not had my own plane to fly for so long, but there is still all of the cosmetic work to complete like painting the cowl, replacing the metal door bottoms with clear plastic, re-positioning the battery further aft to get rid of the lead I put in the tail, replacing or enhancing the wing spar stiffeners to reduce wing flex, capping the wing ends properly, rebuild the gearbox in the engine as it was beaten up pretty badly by a prop with too much inertia for the first 300 hours of its life, and touch up painting the wings and fuse. Hopefully that work won't take long. In the mean time I'm just flying and enjoying.

Even tho I prefer to fly a tail wheel configuration, this plane is tri gear and I couldn't be happier with the rans nosewheel conversion. I run low pressure in the 21 inch mains and in the 600X6 nosewheel. The plane just cushes over bumps and uneven terrain. The big surprise is how little rolling over rough terrain kick back to the rudder pedals. It is amazingly smooth. That was one of my concerns with this untested nosewheel configuration.

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Posted

Been working on the Avid this winter after flying it in the fall. Cleaned up a lot of mechanical and electrical loose ends and now working on cosmetics. Here are some pics. One is of plane in hangar as I was flying it this last fall. The other pics are of fabric work and painting cowl. i still have to figure out how to best bring blue trim cosmetically through the cowl. I also replace the metal on the bottom of the doors with lexan and added some cowl windows. Those two things will really improve the already great visibility.

Next project is to try an replace wing spar stiffeners in the wings, cap the wing tips and cosmetically "finish" the wings.

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Posted

I realized I never posted pics of the wings with tips cut off. The wingspan was 33 feet or so till I cut the tips off. With the tips cut off wingspan is just a bit wider than 30 feet (like a standard Avid) feet because of the wider fuselage.

Problem with the 33 foot wingspan is that the strut was not moved out accordingly so the portion of the wing beyond the strut was heavily cantilevered leading to the wingtip bending up too much under load. I do not believe it is/was a structural issue, but it did seriously impact the flapperons.

The first pics show my plane next to my friend's 912 MKIV. You can see that my plane has an extra 18 inch "bay" before the wingtip, making the total wingspan 3 feet wider than stock Avid. The second pics show the wing tips cut off and taped with vinyl tape to "cap" them. The wingspan is now the same (+4 inches because of wider fuselage) as the standard Avid and the wings flex MUCH less. I still want to improve this with new spar stiffeners though. I will also experiment with wing tip fences since it is set up perfectly to do that now.

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Posted (edited)

A little more progress on the cosmetics of the Flat Avid. Got the stripes on Cowl and blue on bottom to sort of match up to what the original builder did on the fuselage. I think it is turning out pretty nice. Now on to the wings. Trying to see if it is feasible to replace spar stiffeners with longer ones and figuring out how to cap the wingtips as well as cosmetic fixes. The cowl does actually match the fabric much better than the lighting in the photo would lead me to believe.

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Edited by Chris Bolkan
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Posted

Looks great....if this beauty were mine I would continue the blue colour from bottom of fuse along bottom of cowl to make the cowl look slimmer and unify the fuselage...

 

My 2 cents...very subjective

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Posted

Funny you should mention that. I spent hours agonizing over how to carry the blue on the bottom of the fuse thru the cowl. I used a roll of blue masking tape to try and figure out how to do it and the cowl window just kept screwing everything up as well as how to carry the blue around the front or terminate the stripe, so this is what I settled on for now. I have plenty of blue paint and it is easy to change or add later because fortunately the plane was painted in Poly Tone which is what I also used on the cowl. It is super easy to work with as far as adding/changing stripes and so forth.

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Posted

Hey Chris.....something in those lines maybe.....

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Posted

Hey I like that nice work.

I Bet that drain is full of nuts and washers. :)

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Posted

Wow! How did you do that? Very cool! You obviously have an artistic side I that I do not! Now I have lots to think about.......

Yes occasionally I remove the grates from the pit and go mining for lost artifacts :-) The pit has proven very useful many times though. It's 12 feet long and 6 feet deep. I somehow got it past the inspectors when I built my house. Pretty sure it is not fully compliant with all safety regulations!

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Posted

I know that cowl represents a lot of work but definitely time well spent. Looks great, even better with the lower color carried forward imho.

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Posted

Tons of work and a few pictures. Got the wing work completed. Made up and installed bungees. Installed wings this weekend. Started the engine and taxied it around for a while last night. No leaks! Yeah!

Gonna do a thorough inspection and take it for a test flight hopefully this afternoon. 

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Posted

By Golly, I think you're gonna make it! Will be a thrill to fly her into the UL Field at OSH. I camp right along the strip, if you call/text me 10-15min out I will video your arrival and departure with my phone. Same offer to everyone. Got some pretty good pics/video of AV8r3400 over the years. 

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Posted (edited)

So I've been flying the Fat Avid around shaking it out since I got it together still hoping and planning to fly it to Oshkosh. The only troubling thing I am seeing is excessive oil temp when it is really hot out. Rotax wants to see over 212 every flight to burn any water out of the oil but 230 or lower during continuous operation. On a 95 degree day I saw continuous over 240 once the temp had stabilized and 250 at times. Rotax specifies 285 as a max temp but that seems pretty high to me. I want to stay in the recommended temp range. So I have ordered a larger oil cooler. It looks like it will install exactly where my current small rotax cooler is installed and in exactly the same manner but will give me 30-50% greater surface area. I will also be able to eliminate the only tight 90 degree bend on the oil suction side which I think will also improve things and will also better physically decouple the oil cooler from the engine. The tight 90 will become a sweeping 90 bend instead. It was hard finding a sweeping 90 degree barbed SS elbow. I finally found them looking at beer brewing and beverage dispensing suppliers. And they are cheap! only few dollars. i will post photos once I get the new cooler installed. in the mean time I am not flying when it is much over 90 degrees out.

Edited by Chris Bolkan
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Posted

Keep in mind that synthetic oil will not begin to coke until over 400º F.  Even the semi-synthetic Sport +4 will easily handle 300º or more with out degrading.  The 230º number is extremely conservative IMO.

These engines like to run hot and fast.  That's what they are designed to do.

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Posted

Ronna my girlfriend shot these little videos of my first takeoff and landing last week after the winter's work on the Fat Avid. Pretty boring but something to put up here to show progress. I am REALLY lucky to have 1000 feet of grass surrounded by flat farmland to do these test flights that's for sure!

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Posted (edited)

Thanks for that input Larry. Good to know. I won’t be so concerned about the elevated temps. I am currently running aero shell because that’s what my friends with 912s are running. I haven’t done any of my own research on oil for the 912. My reasoning for increasing oil cooler size is to try as much as possible to stay in rotax recommendation.

Edited by Chris Bolkan

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Posted

Different gauge, but I lowered the radiator on my Kitfox one, only to discover the gauge was reading 15 or 20 degrees high.  Might be worth confirming if the gauge is accurate.  JImChuk

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Posted

Thanks Jim, i will see if I can figure out how to test the oil temp sensor. The engine is monitored by one of those Grand Rapids EIS modules, and everything is working correctly with solid readings and this thing measures EVERYTHING! It seems about right to me but it never hurts to check.

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Posted

I ended up changing out the small Rotax oil cooler with a larger Setrab oil cooler and it reduced oil temps to those specified by Rotax. I did this right before flying the Fat Avid to Oshlosh. We flew in some pretty brutally hot temps out there and oil temp remained within spec.

It was a hectic few days before leaving for Oshkosh that I did not know if I was going to be able to go or not, but in the end I decided to just head that direction and see how it went and the Fat Avid got me there and back!

I'm not going to call the Fat Avid finished quite yet, but since it made the flight from Washington to Oshkosh and back without incident, I can call the build a success.

I think I will slow down on the Fat Avid and just fly and maintain it for a while and start working on the Magnum project.

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