whizzers

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About whizzers

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  1. whizzers added a post in a topic Let's talk gear geometry   

    Ed;
    Yes, Thanks.
    Actually they are die springs from McMaster Carr. 9584K98. They are six inches long, and will compress to 3 inches. McMaster also lists an eight inch spring. I have the numbers for the Ski-Doo springs. 503190854.  They are readily available for about $50 each. I also kept the dimensions for the spring struts, and can make a replacement set without taking the gear back off the plane. I only need to make the spring carriers. Two bolts on each side changes them.
    Incidentally, the Super Cub only has 3 1/2 inches of travel. Measured it myself.
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  2. whizzers added a post in a topic Let's talk gear geometry   

     
    Member Members14 29 posts 
    Posted just now · Report post
    Update on the gear. One possible fix for existing gear. I had two yokes made similar to the yoke on a universal joint. They were made out of 1 1/4 cold rolled square stock. I threaded them 3/4-16 inside, and turned that end round to give 3/8 inch wall thickness. The fork end I milled out 7/8 inch wide to provide +1/8  wall thickness, and drilled that 1/4 inch.
    I then made new longer axles, but threaded the inboard end to give a tight fit on the thread. The fork was threaded on, then drilled and pinned. I had to make new lower spring strut rods since they are shorter than original. The only issue I had was that the axle end of the spring rod has to be canted a bit to fit to the existing cabane. That and the 3/4 inch tubing AirSpruce provided won't accept a 3/4 inch wheel bearing without polishing it first.
    The top (spring) end of the inner rod should be doubled internally to avoid the hole tearing out. I saw that happen on a Super Cub clone.
    I put the gear back on the plane, but have not tried it yet.
    The other possible fix is to weld tabs to the existing axle tubes. I will try that next.





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  3. whizzers added a post in a topic Bush gear failures   

    Update on the gear. One possible fix for existing gear. I had two yokes made similar to the yoke on a universal joint. They were made out of 1 1/4 cold rolled square stock. I threaded them 3/4-16 inside, and turned that end round to give 3/8 inch wall thickness. The fork end I milled out 7/8 inch wide to provide +1/8  wall thickness, and drilled that 1/4 inch.
    I then made new longer axles, but threaded the inboard end to give a tight fit on the thread. The fork was threaded on, then drilled and pinned. I had to make new lower spring strut rods since they are shorter than original. The only issue I had was that the axle end of the spring rod has to be canted a bit to fit to the existing cabane. That and the 3/4 inch tubing AirSpruce provided won't accept a 3/4 inch wheel bearing without polishing it first.
    The top (spring) end of the inner rod should be doubled internally to avoid the hole tearing out. I saw that happen on a Super Cub clone.
    I put the gear back on the plane, but have not tried it yet.
    The other possible fix is to weld tabs to the existing axle tubes. I will try that next.





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  4. whizzers added a post in a topic Wanted - 582 engine mount   

    https://www.ebay.com/itm/Avid-Model-B-Engine-Mount-Ultralight-Experimental-Rotax-Kitfox-Aircraft/253228472171?hash=item3af597d76b:g:Im4AAOSwbF1Z8qBd&vxp=mtr
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  5. whizzers added a post in a topic Wanted - 582 engine mount   

    there's one on EBAY
     
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  6. whizzers added a post in a topic Let's talk gear geometry   

    I am going to try to build a set of gear to the dimensions and angles used on the Piper Cub. Has anybody built gear where the front leg comes straight down from the fuselage instead of leaning forward 3 7/8 inch. This would put the mains a bit farther back. It would make the gear leg and the cabane easier to build.\
    It would make the tailwheel come up faster but what other effects might it have?
     
    Bob
     
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  7. whizzers added a post in a topic Bush gear failures   

    Yea, I think ideally scaling the gear using the Angles of the cub gear would be the best overall solution, but would involve building new gear all around. I'm thinking about milling a nut out of square stock with a fork on it to thread on the inboard end of the axle shaft. That would be relatively easy and inexpensive, and just might do the trick.
    Good to hear from an expert, thank you. Please stay in touch.
     
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  8. whizzers added a post in a topic Let's talk gear geometry   

    I finally got to do a little playing with the gear. I made a mock-up and ran some tests, and here is what I found, or think I found anyhow. I documented what I did, and since the file is long, instead of posting it here and taking up space, I have attached it as a .doc file. If you are interested, you can read it, if not, ignore it. I figure if you guys find anything wrong, you'll soon let me know.

    Bob Landing Gear Geometry.doc
    Landing Gear Geometry.doc
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  9. whizzers added a post in a topic Bush gear failures   

    I finally got some time to play with the gear issue. What I think I found is surprising, and pretty much confirmed my suspicions. I did document it, but the document is quite long, so I will post it here as a .doc file. I figure if you want to read it, go ahead, if not, ignore it. I also put it here because I figure if there are any flaws in my logic, you guys will find them. Landing Gear Geometry.doc
    Landing Gear Geometry.doc
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  10. whizzers added a topic in Avidfoxflyers General Hangar   

    Bush gear failures
    I have had several landing gear failures since going to the spring "bush gear". I have been researching the subject and have noted quite a few similar failures of that type gear, all in about the same location and of the same nature, Inward bending of the forward strut leg. I have been reluctant to re enforce that leg for fear of promoting a more serious failure elsewhere. The gear is a Chinese copy of the gear used by Piper from the 1930s onward but the Piper gear does not seem to suffer the same failure. Today I made a cardboard model of the gear geometry and I believe I have located the problem. The bottom anchor bolt for the spring leg on the "bush gear" is fastened to a metal plate welded between the front leg and the axle. When the spring strut is fully extended and bottoms out, or the spring becomes coil bound, that point then becomes a rigid fulcrum with the axle as a lever. The upward motion or the axle is then translated into an inward rotary motion on the front gear leg. The failure always seems to occur at the point halfway between the axle and the fuselage, which makes sense. I have never bent a rear strut, nor the spring strut, always the front one.

    Looking at photographs and real life examples of Piper, Hatz, and Pietenpol gear shows that the anchor point on those gear is at the inboard end of the axle. My model shows a significant difference in the movement of the middle of the forward gear leg when the anchor point is moved to the end of the axle. As a matter of fact, the farther inboard the pivot is, the lesser the rotary movement at the front gear leg center.

    I have yet to figure a force analysis on the gear, but I think i am onto something. I'll post more as I find more.
    On a positive note, my welding is getting better.

    Bob McCaa
    • 26 replies
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  11. whizzers added a topic in For Sale and wanted, you got it, I want it   

    Clean out the shop
    Trying to clean up the shop for more projects; Somebody needs these;
     
    Set of controls sticks and rudder pedals off "B" Avid set up for cable brakes,
    Set of control sticks and rudder pedals (hydraulic brakes) for a KF 1
    Set of lift struts for a KF I, also horiz stab, elevator, and rudder for KF i also set of tail "V" struts.
    Set of front mount radiators for Avid with brackets. Missing some grommets.
    Top section of KF I fuselage/ front and rear spar carry throughs.
    Gotta move this stuff guys or it's going to the yard.
    Bob McCaa seven one seven/ three six three/ seven five five two
    whizzers /at/ verizon /dot net
    Located in Central Pennsylvania
     
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    • 188 views
  12. whizzers added a post in a topic Nearly a giveaway   

    Is this a Speedwing or a STOL wing? Interested in the airframe if it is a STOL or Heavy Hauler
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  13. whizzers added a post in a topic Fuel flow issue.   

    Thanks for the input. Have already done the fuel pump tests. The pumps are in series, with a by-pass check valve in parallel with the electric pump, which is a Facett. Fuel pressure with the Facett alone is about .3 Bar, and with the mechanical alone is about .4 Bar. (PSI= 14.7 x Bar) We did a free flow test after the work was done and with five gallons in each tank, it flowed about a half gallon per minute from either tank  through the header tank without the pumps running. The engine is a Rotax 912 80 HP and burns about five gallons per hour in climb, so we are more than adequate using either or both.
    My Avids are 582 gray heads, and I agree with C5engineer.
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  14. whizzers added a topic in Close Call's and dumb stunts   

    Fuel flow issue.
    My brother recently bought a KF Classic IV. While doing taxi tests, it ran for about an hour and a half, then quit. The EIS said Low Fuel Pressure. He loaded it on the trailer and took it home, where it promptly started and ran on the trailer with the wings folded back. He was unable to find any problems. About two weeks later, he was flying with an Instructor, and after about an hour and a hale, it quit in the air. Again "Low fuel Pressure". They tried a successful re- start. They made it down safely, and he loaded it and trailered it to my place for diagnosis. We talked to Lockwood, and Kitfox, and the best suggestion we could come up with was possible vapor lock. Unlikely in the air since it was cool that day. We began checking the fuel system end for end. Eventually we found the problem. The fuel line where it exited the wing and entered the fuselage had been fastened to the carry through inside the fuselage. This caused the lines to kink in the wing root when the wings were folded forward. When the tanks were full there was enough head pressure to keep the header tank full. When the head pressure went down, the kink prevented adequate fuel flow. What threw us a curve was there is a low level sensor in the header tank that never came on. Turns out it was defective. The "test" button on the instrument panel only tests the indicator light, not the unit.
    We replaced the hoses with AEROQUIP steel braided hose, and put a new sensor in the header tank . Added two items to the preflight and run up to: 1. run the electric fuel pump without starting the engine and check the pressure to confirm it works, and 2. Run the engine with the wing tanks shut off to confirm the low level sensor in the header tank is working.
     
    Bob McCaa
     
     
    • 29 replies
    • 749 views
  15. whizzers added a post in a topic speed wings/stol wings.   

    The speedwing does not want to get off the ground. I believe it would run the length of our 5000 foot paved runway with the tail in the air and never lift off. With the flaps at 10 degrees and the tailwheel hard on the ground it will "pop" off the ground and then climbs like a rocket. On approach at less than about 60 per it will come down at about 750 fpm. It stalls suddenly and without warning except that it begins a flat  turn to the right. In its defense, it doesn't bounce. When it's on the ground it stays there.
    I am skeptical that it would lift two people.
    I talked to Snaps down in North Carolina and he basically said "that's the way they are".
    Before you ask, it has been measured, weighed rigged, re- rigged, and compared dimensionally with other Avids at least fifty times. I have not tried VG's yet.
    I had a STOL wing that was a pleasure to fly. It wanted to float.
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