Big tires for the 7ECA

Eagledoc

Eagledoc

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Dec 16, 2020
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Location
Oregon
I have a '65 7ECA with standard 6.0x6 tires on Aeronca champ gear. Looking through the FAA STC web page I found 2 sites for larger tire STC's for the 7ECA, The group in Alaska was bought out and the new owners will not honor the STC that the prior owners had developed. The guy in Las Vegas who is listed as the other STC holder has not responded to my mailings and I dont know if he is still alive. The factory has been offering 7.0x6 tires on some of their new aircraft, Does any one have any experience with 8.0x6 or 8.5x6 tires on their 7ECA's or Aeronca 7AC's with the old no-bounce gear? I have spent the past 5 years rebuilding the aircraft after the right wing spar broke while doing a simple loop = got down ok, but the only thing holding the wing tip on was the fabric, the leading edge aluminum and the aileron. Both wing spars broke and the outboard 3 ribs shattered. It now has new fabric, new factory wings, wing VG's, Spades, new lift struts, new interior, new panel with Electronics International digital panel/engine analyzer, fuel flow, Uavionix ADSB, GPS, prop and overhauled engine. Has been fun fixing it up for a great little single seat back country plane. Just could use some larger tires for the gravel bars.
 
I don't have no-bounce gear because my early 7ECA was updated in the late 80s. But I do run Desser 8.50x6 tires and they have been great. They weigh the same as 7.00x6 which is an added bonus.
I had similar luck with the folks in Alaska. That STC is for only one type of tire. The other one you're looking at is the STC for the 8.50x6, 4 ply, Type III tires is free to use (read it). I've also read that 8.50x6 are now on the TCDS but I have not confirmed that myself.

I've got hundreds of landings (300 is a conservative estimate), mostly on pavement and occasionally I'm providing dual instruction which is quite abusive.
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Back in the olden days folks just mounted whatever tires they wanted.

You might check with Grove - they have wheels approved with tires ranging from 6:00 to 26". I am close to installing them on a Cub under STC. Yes, 337; no, no need for field approval. Don't know if they are approved for Champs yet.
 
Yikes, that is a hair raising story about the spar. Any indication why it failed?
 
I was coming down the back side of the loop doing 120mph and 2 "G"s on the meter. I heard a loud crack in the right wing and felt some stiffness in the controls. I unloaded the airplane and gradually leveled off and slowed down, It control checked sort of ok so I stayed in the plane, spiraled down and landed. On the ground, I grabbed the wing tip and the tip flopped up and down about 6 inches with a crunch/crunch sound. I took the wings back to the factory in Wisconsin and had them look at the wood spars. The right main spar failed at the lift strut with a green stick fracture at the pin carry through bushings and the rear spar split lengthwise probably on a pitch grain. the ribs from the lift strut out all fractured into multiple pieces, The left wing also had cracks in the main spar root that you could not see until you removed the main spar attach bracket at the fuselage. The fellows that I bought the airplane from had been using it to practice for the Western Regional Aerobatic completion and the factory surmised that they had over "G"ed the airplane at some point. It had not had a ground loop in the past that anyone would own up to. The pre buy inspection did not uncover any cracks in the spars. I don't do aggressive aerobatics in the plane -go get a Sukoi or an Extra if you want to do that. 1 G barrel rolls or an easy egg loop or a one turn spin or a falling leaf are what I call fun. Am looking forward to taking it back to Oshkosh again (yes you can go cross country in a Citabria) when the virus epidemic has settled down.
 
Wow, that is hair raising. You handled it well. Good thing you were pulling light. Damage could have been worse with someone like me at the controls pulling 4G.

That's one thing in favor of wood spars. I have heard several stories of partial failures like yours. When metal goes, it usually fails completely.

OTOH, this is why we have the spar AD, and this is why the factory went metal.

Great argument for wearing a chute. I was just exchanging emails with Greg Koontz about buying a new softie. Your story helped convince me.
 
Talk to Rainbow Ron about the difference between Scout and Decathlon wood spars.
 
Bob Turner said:
Talk to Rainbow Ron about the difference between Scout and Decathlon wood spars.
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I'm fortunate enough to have reason to pass through Moses Lake where Rainbow Ron's shop is. If you're ever in the area I strongly suggest a visit. He has several spar sections in his front office. He'll show you the type of compression fractures which are enough to ground a Citabria, and the failures can look very much like a small defect in the varnish. Then he'll show you a nasty section with a "green stick" failure. The owner of that plane flew it for quite some time after buying the plane and had no clue.
Eagledoc said:
It had not had a ground loop in the past that anyone would own up to.
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Having been a flight instructor at a busy flying club I can assure you that the majority of renters will not disclose aircraft damage. I once preflighted a C182RG and noticed about 1/4" missing off both prop tips and the flap tracks were bent to hell. That would have required two very different knuckle dragging efforts in one flight. All it takes is the next person doing a preflight to not notice and the trail goes cold.
 
I've heard that 8.50x6s are now on the type certificate and asked Dale Gauger about it on the Citabria scout decathlon facebook page a few months ago. He responded that they are on the factory drawings, which he indicates makes them fair game to install without an STC or 337.

I have 8.00x6 4 ply tires on my 7KCAB and they work well for off field work on reasonably smooth surfaces. They weigh in at 10.0 pounds each.

I'll eventually put Aero Classic 8.50-6 tundra style tires on it. They also weigh in at about 10 pounds each, but stand about 22" tall.
 
Here is a possibility:

I am installing Grove wheels on a Cub. The wheels themselves are PMA for 8:50s and 26" ers, among others. My guess is these wheels and brakes are the same parts as now used on all ACA, except for bearing ID. Worth looking into, I think. Quality parts - I converted a mechanical brake Champ using these parts. Everything fit beautifully.
 
BB57 said:
I've heard that 8.50x6s are now on the type certificate and asked Dale Gauger about it on the Citabria scout decathlon facebook page a few months ago. He responded that they are on the factory drawings, which he indicates makes them fair game to install without an STC or 337.

I have 8.00x6 4 ply tires on my 7KCAB and they work well for off field work on reasonably smooth surfaces. They weigh in at 10.0 pounds each.

I'll eventually put Aero Classic 8.50-6 tundra style tires on it. They also weigh in at about 10 pounds each, but stand about 22" tall.
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Thread revival. I do some mild back country flying in my 7KCAB, but on the 6.00’s with no wheel pants. Did you have to run a spacer or anything to accommodate the 8.00’s or 8.50’s?
 
ehaecker said:
Thread revival. I do some mild back country flying in my 7KCAB, but on the 6.00’s with no wheel pants. Did you have to run a spacer or anything to accommodate the 8.00’s or 8.50’s?
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Howdy,

Spacers are available from Bushwheels, and I am told that you have to get a 337 (Minor Modification) signed off in the log book to use them.

This is for 8:00x6 or 8:50x6 tires. Some will rub on the brakes and other brands have the room not to rub.

Being an open forum, a lot of guys will NOT share info on their bird's mods in fear of someone snooping around at a later date.

I personally "Always" do what the FAA mandates! That's why folks ask for a person to PM them. I am running Aero Classic 8:50x6 (22 inch tall) and they are good on rough fields @ 9psi. I have not spun them yet but do not do hard braking on pavement. They slip across the ground on grass.

I did put a dab of yellow paint next to the valve on the tire and I check it before and after each flight to see if it moved, They say it is easy to shear off a valve stem when pressure is low.

Ken "Cowboy" Winiarski
Cowboys Air Ranch (84ME)
 
darrell whitley said:
I air the mains to 25psi. operating on mostly paved surfaces.. Just saying... I also have the 337 sign off.. For what it's worth;)
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Howdy,

Are your Air Trac's 4 ply or 6 ply?

I was running my McCreary 8:50x6 6ply at 19psi, 80% of the time from pavement. This is in the winter.

Everyone has their own preference I guess.

Ken "Cowboy" Winiarski
Cowboys Air Ranch (84ME)
 
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