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Avid+ Convertible

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Posted

What if...

I want to make my Avid+ TD into a convertible.

I will probably modify the attach bushings on my Avid+ firewall to accept a Kitfox 912 engine mount and series 5/6 smooth cowl for Rotax. I've considered using their nose gear engine mount version and a Kitfox nose gear to turn the Avid+ into a convertible like the Kitfox 6, 7 and SS.

The big hangup is main gear. Unfortunately, I don't believe I can use my Airdale W.I.B main gear without modification like you could on earlier Avids, ie. just flip and swap sides, move back a bracket and add bungee hooks to the rear seat truss. My fuse is different down there, maybe I can get some pics of Chris B's Avid+ tri-gear to see exactly how Airdale did it.

If I need new main gear to pull this idea off, seems the most flexible option would be spring gear with clamp blocks that could be moved between the front and rear fuse brackets as necessary. I plan a 1320lb MTOW for my Avid+ so it would require a stronger Grove spring gear than what is sold for an Avid Mk-IV or KF-4. I would think the spring gear for the 1400lb. gross KF-5 would be best suited, but the gear for 1550lb. gross KF-6/7/SS might be too stiff.

Maybe a Grove main spring for the 1400lb. MTOW Kitfox 5 and clamping blocks that would work with that spring gear and my Avid fuse.

Your thoughts?

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Posted

-pulled from other threads-

Doug, The only "bug" I see in your convertible plans is the height of the main gear. If you use the main gear for the nose-gear setup, then your prop is going to be about 6 inches lower than standard when you go to TD.

I went the other way, and am using the TD gear and made my nose gear higher to match for more prop clearence.

Will have to put a step on the gear leg so my short legs can get my fat butt up to the seat, which, in my plane, has been raised up another 6 inches higher than the original, or carry a ladder to stand on, which I need anyway to get to my gas tanks!

Kitfox failed to mention that their plane was actually a nose-dragger and converted to a low-slung tail-dragger.

They sort of advertised it the opposite way, which wasnt true.

And, I have no clue as to how they moved the main gear.

ED in MO

Doug,

When I was working on the gear configuration on my Avid Plus, I talked to Steve Winder about using the long wide gear on a tri-gear Avid and he recommended against it. While the gear will line up in the rear position, the placement of the axel on the wide gear is further towards the rear of the plane and would make it harder to rotate on take-off, and could cause the nose gear to slap down when landing.

If you look at the pictures I've posted in "Jack's Avid PLus" album on the Yahoo site you can see the difference on the location of the tire in relation to the gear structure.

To configure my Avid Plus as a tri-gear Steve recommended using the Mark IV tri-gear. Even using the standard tri-gear, he was a bit concerned about the strength of the stock nose gear if used off-runway. They've been known to buckle with a Rotax up front and with my Subaru, he suggested that the stock nose-gear would be marginal. In the picture I posted you can also see the bungie cord attach ears with the bungie on them. I wasn't as concerned about the strength of my nose gear because the gear was fabricated for me in the Ukraine with heavy wall stainless steel for the upper, with chrome-molly for the "U" shaped portion. The size of the "U" allowed me to use a 15x6.00x6 tire on the nose-gear. The tire is shown mounted on the plane with the faired nose-gear. Even with the stronger gear and larger tire, Steve recommended caution because the heavier weight of the Subaru would cause an increase in speed at landing, and he didn't know what the outcome would be.

I hope some of this information is useful, it's been some time since I had the discussion with Steve.

All the best,

Jack

Jack, Is there any way you could post photos of your nose gear here? I dont get on Yahoo. How much time did you put on that gear, and what kind of terrain?

I am making a similiar setup with the Subaru. Still debating whether my original design with the 600 x 6 tire, or the spring-loaded with the 500 x 5 would be best. My original only had belleville washers for spring, and a fork like the Tri-pacer, except set at a 30 degree rake.

Doug, The "engineering general rule" for nose draggers is to draw a line vertical from the main axle in the most tail-down position, and your most aft CG should be not less than 3 degrees forward of that line - If that helps.

Also, the weight on the nose wheel in level position should not be less than 8% of total weight, and not more than 12%, as a general rule.

Thanks,

Ed in MO

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Posted

:siterocks:src="http://www.avidfoxflyers.com/public/style_emoticons/default/siterocks.gif"> Thanks guys for the input.

I think some photos from Chris showing his stock tri-gear setup will go a long way.

Hi Chris!

Hi!

Are you talking stock Tri Gear photos for the Avid Plus? I can take a couple photos if you want, but it is nothing more than a Vans RV6 style castoring nosewheel stuffed into the nosewheel weldment and bolted through.

Chris B

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Posted

Hi Doug, don't think this really applies to your situation, but I believe the Avid main gear legs are different for tailwheel verses tricycle gear. With the tailwheel gear, the axel is ahead of the front gear attachment point, and in the tricycle gear, the axel is about in the center between the two attachment points. I think the tailwheel gear is also taller. Take care, Jim Chuk

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Posted

Hi Chris,

At the moment we are just trying to sort out what main gear options might work best if one wanted to turn an Avid+ TD into a convertible (quick change between TD / Tri-gear like the Kitfox 6/7). I have some pics of your tri-gear at a distance but can't really tell if the gear legs on it then were stock oem Avid Mk-IV, Airdale W.I.B. gear flipped or something all together different and 'one-off' aircraft specific. Would very much like to see some pics of the main gear, axle position and bungee truss etc. when you get a chance. Also helpful would be measures such as leg length, wheel track width, fuse height etc.

No rush at all, I have two other projects to finish before I get back to the Avid+. Thanks.

Doug

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Posted

Hi Doug, don't think this really applies to your situation, but I believe the Avid main gear legs are different for tailwheel verses tricycle gear. With the tailwheel gear, the axel is ahead of the front gear attachment point, and in the tricycle gear, the axel is about in the center between the two attachment points. I think the tailwheel gear is also taller. Take care, Jim Chuk

Jim I think you are correct. However, IIRC, a lot of Avid TD folks just flipped and swapped sides with their original TD main gear legs when converting to a tri-gear. At least that's what my not-getting-any-younger memory seems to think.

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Posted (edited)

Jim I think you are correct. However, IIRC, a lot of Avid TD folks just flipped and swapped sides with their original TD main gear legs when converting to a tri-gear. At least that's what my not-getting-any-younger memory seems to think.

Problem with that is, the Grove gear is symetrical - so it has to be moved.

ED in MO

edit: Well, Duh - my old mind is slow today - Of course you knew that - You are wanting the position of the axles for each configuration - Sorry. But, if you swap sides, the the extension for the bungees is in the rear and not front where bungees go????

ED

Edited by Ed In Missouri

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Posted

Hi Chris,

At the moment we are just trying to sort out what main gear options might work best if one wanted to turn an Avid+ TD into a convertible (quick change between TD / Tri-gear like the Kitfox 6/7). I have some pics of your tri-gear at a distance but can't really tell if the gear legs on it then were stock oem Avid Mk-IV, Airdale W.I.B. gear flipped or something all together different and 'one-off' aircraft specific. Would very much like to see some pics of the main gear, axle position and bungee truss etc. when you get a chance. Also helpful would be measures such as leg length, wheel track width, fuse height etc.

No rush at all, I have two other projects to finish before I get back to the Avid+. Thanks.

Doug

Hi Doug,

i can tell you without a doubt that the gear legs for tri and tail are different for the Avid Plus. Since the gear mounting spots are the same on the fuse as for other Avids, it will require tail gear to be taller and swept forward compared to the tri gear which is shorter and centered between the mounting points on the fuse. It is the same gear for Tri or Tail as the original MK IV unless you build something custom.

Chris

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Posted

-pulled from other threads-

Ed,

My Avid+ is still under construction, so no time on the nosegear. The nosegear is patterned after the stock avid gear, but built using thick stainless and 4130. When we were figuring out the dimensions, I just increased the length and width of the fork to allow for the larger tire and wheel. The thickness of the leg is the same outside diameter as the Avid gear, but as thick as the stock gear with the recommended doubler installed, I also made it a bit longer to allow me to level the fuselage before cutting it to final length. I'll try to get some pictures of the nosegear and post them.

Jackak

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Posted

Ed,

My Avid+ is still under construction, so no time on the nosegear. The nosegear is patterned after the stock avid gear, but built using thick stainless and 4130. When we were figuring out the dimensions, I just increased the length and width of the fork to allow for the larger tire and wheel. The thickness of the leg is the same outside diameter as the Avid gear, but as thick as the stock gear with the recommended doubler installed, I also made it a bit longer to allow me to level the fuselage before cutting it to final length. I'll try to get some pictures of the nosegear and post them.

Jackak

Thanks for that - Does it bolt up like the Kitfox, or different? I'm just nosey, since I couldnt find any info or photos of the attachments before I designed my own. Mine dont have much give to it, so guess I need to be gentle when letting the nose come down. I made my leg from a scrap streamlined 4130 bicycle frame - but it should work if I got it far enough forward.

ED in MO

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Posted (edited)

Thanks for that - Does it bolt up like the Kitfox, or different? I'm just nosey, since I couldnt find any info or photos of the attachments before I designed my own. Mine dont have much give to it, so guess I need to be gentle when letting the nose come down. I made my leg from a scrap streamlined 4130 bicycle frame - but it should work if I got it far enough forward.

ED in MO

Ed,

The gear attaches to the stock Avid nosegear weldment, you should be able to see it in one of the pictures. I'll also try to attach some photos of the nosegear, the steering linkage and the conventional gear set-up I'm going to start with. On the pictures of the gear leg I attempted to do some streamlining with foam and fiberglass.

Jackak

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Edited by jackak

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Posted

Ed,

Sorry about the scrambled pics, I think you can see what I was attempting.

Jackak

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Posted (edited)

Ed,

Sorry about the scrambled pics, I think you can see what I was attempting.

Jackak

Those are some good photos - ingenius steering method - I thought you were talking about the Kitfox/RV type of trailing fork. I looked closely at a RANS when they first came out - he had a good method of disconnecting stearing until it had weight on the nosewheel, a little different than the way Cessna does - so you dont have a crooked nosewheel when you come in fighting a crosswind.

Mine is planned to be castoring - Never flown that kind before - hope I am not sorry.

Thanks again,

Oh - Do you have a measurement from the center of mains to center of nosewheel - or a good guess?

I believe my strut is farther forward than yours, but with semi-trailing fork, it could be about the same for the wheel. I hope to post some photos someday when I get that part done - right now my torn rotary cuff has put me a year behind and putting the leading edge extensions on has taken too much time.

ED in MO

Edited by Ed In Missouri

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Posted

Those are some good photos - ingenius steering method - I thought you were talking about the Kitfox/RV type of trailing fork. I looked closely at a RANS when they first came out - he had a good method of disconnecting stearing until it had weight on the nosewheel, a little different than the way Cessna does - so you dont have a crooked nosewheel when you come in fighting a crosswind.

Mine is planned to be castoring - Never flown that kind before - hope I am not sorry.

Thanks again,

Oh - Do you have a measurement from the center of mains to center of nosewheel - or a good guess?

I believe my strut is farther forward than yours, but with semi-trailing fork, it could be about the same for the wheel. I hope to post some photos someday when I get that part done - right now my torn rotary cuff has put me a year behind and putting the leading edge extensions on has taken too much time.

ED in MO

Ed,

A WAG on the distance from the center of the nose tire, extended out to the side of the fuselage, back to the approx. center of the mains is about 50". Very short, huh? But, if you land full stall, the nosegear doesn't touch 'til the wings quit flying anyway, or so I was taught. Crosswind? Another story. I've never flown an aircraft with a trailing fork nose gear, hope it works out for you. With a big rudder it shouldn't be too bad. Good luck.

Jackak

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Posted (edited)

Ed,

A WAG on the distance from the center of the nose tire, extended out to the side of the fuselage, back to the approx. center of the mains is about 50". Very short, huh? But, if you land full stall, the nosegear doesn't touch 'til the wings quit flying anyway, or so I was taught. Crosswind? Another story. I've never flown an aircraft with a trailing fork nose gear, hope it works out for you. With a big rudder it shouldn't be too bad. Good luck.

Jackak

I guess if all the RV and Kitfox nose drivers can do it, then it cant be much harder than tailwheeling.

They taught us to quickly center the pedals on the Cessna to engage the nose steering after we landed with a crooked rudder.

The Ercoupe nose steering didnt disengage, and it was nose heavy and you had no pedals to stear it - there was a heck of a jerk on the steering wheel when you landed in a crab - took lots of relearning.

All I was concerned about is the amount of weight on the nosewheel - I remember doing all those calculations about a man walking across a bridge, and how much weight he put on each end as he moved across.

50 inches really looks short when you have a 68 inch wide main gear and add a tire on each side of it.

guess time will tell.

Thanks,

ED

Edited by Ed In Missouri

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Posted (edited)

Doug, Jack, anyone,

Does anybody have any knowledge of why the Grove gear for the Avid TD is 66 inches wide and the tri is only 62, when Kitfox uses 68 inches for both?

Just wondering why the decision was made for the differences in the Avid - I have no clue.

My design books say that a 1:4 landing gear width : wingspan is the most stabile - that would mean an 8 foot tire track for a 32 foot wing. Of course we've all seen planes with about a 1:10 ratio, and about 3 feet between tires, but that was poor designing, IMO.

ED in MO

Edited by Ed In Missouri

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Posted

Doug, Jack, anyone,

Does anybody have any knowledge of why the Grove gear for the Avid TD is 66 inches wide and the tri is only 62, when Kitfox uses 68 inches for both?

Just wondering why the decision was made for the differences in the Avid - I have no clue.

My design books say that a 1:4 landing gear width : wingspan is the most stabile - that would mean an 8 foot tire track for a 32 foot wing. Of course we've all seen planes with about a 1:10 ratio, and about 3 feet between tires, but that was poor designing, IMO.

ED in MO

Ed,

I just looked in the construction manual for the MarkIV, and if the gear was sized for the Speed wing span , the 1:4 ratio is pretty close. For the short wing the spar is only 108" long. 'm guessing that the 144" spar on the long wing would be close to the 1:4 ratio also.

Some more guessing, if the height of the Grove gear is the same for the tri and the conventional geared Kitfox, standardization may have been the goal.

Just guessing,

Jackak

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Posted

Ed,

I just looked in the construction manual for the MarkIV, and if the gear was sized for the Speed wing span , the 1:4 ratio is pretty close. For the short wing the spar is only 108" long. 'm guessing that the 144" spar on the long wing would be close to the 1:4 ratio also.

Some more guessing, if the height of the Grove gear is the same for the tri and the conventional geared Kitfox, standardization may have been the goal.

Just guessing,

Jackak

Tri gear for the speed wing, conventional for the hauler wing.

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Posted

Tri gear for the speed wing, conventional for the hauler wing.

Sounds like good reasoning to me - However, the Kitfox gears are different heights for TD and Tri-gear.

ED in MO

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Posted

Sounds like good reasoning to me - However, the Kitfox gears are different heights for TD and Tri-gear.

ED in MO

Dog gone! That leaves us with reading the book, Kitfox manual, or calling them! So much for finely reasoned out guesses.

Jackak

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Posted (edited)

Dog gone! That leaves us with reading the book, Kitfox manual, or calling them! So much for finely reasoned out guesses.

Jackak

Going back to your theory - The wings on the later Kitfox Tri and TD are the same, so the 1:4 ratio would keep them the same width, and only the height would change for the Tri-gear. My guess, I guess.

Ed in MO

Edited by Ed In Missouri

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