The AFB (Amazing FleaBike)

Homebuilt Aircraft & Kit Plane Forum

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jedi

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Aug 8, 2009
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Sahuarita Arizona, Renton Washington, USA
Hi. I'm still agonising over the gear. My preference would be for taildragger gear, but one of my local advisors has strongly cautioned that taildraggers are much less forgiving on the ground than nose draggers. And what are trusted advisors for if not to be heeded? But I'm in two minds. I already have the big fat tundra tyre for the nosewheel, but taildraggers (1) look cool (2) are more in the tradition of other Fleas and (3) are a heck of a lot less complicated to build.

So my question is: for a slow plane like a Flea - how much more difficult would a taildragger be to manage on takeoff/landing? Yes, I know this is a subjective question, but I'd appreciate it if those who fly both types could weigh in with some advice/personal observations etc.
Go with the tail wheel. You will learn to handle it and will like it PROVIDED IT IS DESIGNED AND BUILT PROPERLY.
 

rotax618

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Oct 31, 2005
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Location
Evans Head Australia
Square tube is stronger in bending than equivalent round tube, from my Flea experience, I would use a tricycle UC with a castering nosewheel, the caster would have to be limited to 90 deg to prevent the wheel from striking the prop.21D4B569-DE90-47CF-87F3-87D14C7AC710.jpeg

if the position of the axle suits the CG your triangle with a bar welded to the bottom wouls let you use a bungee.
 

Malcolm C

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May 18, 2020
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81
I hinged the A frame from the fire wall support angles and located the castering nose wheel under the engine after following the advice from helpful forum members. Bungees provide the suspension. Very light and seems to work well on taxi tests. I used 4130 round tubing .035" wall just because I had some left over.
 

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Tiger Tim

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Apr 26, 2013
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Thunder Bay
The main gear on the Pietenpol on display in Lakeland is similar to one of the setups you have in mind:
1659871420573.jpeg

It’s not how I’d do it but at least it exists to draw inspiration from if you go that route.
 

rtfm

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Jan 3, 2008
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3,754
Location
Brisbane, Australia
Here's what I've decided to do:


No welding involved. The gear uses 25x25 steel tubes bolted together, with NAPA shock absorber bushings threaded onto a high-tensile bolt to keep everything aligned. I'm busy 3D printing the jigs to align the steel tubes, and to accurately drill the holes for the 3mm steel overlays (would rivets suffice?). The axle itself is 50x50 square steel tubing, and the stub axle is sandwiched between two pieces of hardwood machined to accept the stub axle, hammered into the ends of the through-axle and then everything bolted together. You will notice that I don't have a welder, can't weld and don't know anyone who does weld. And I'm not about to pay someone to do it for me. Besides, I quite like the idea of being able to dismantle the gear if it gets bent or something.

1659934654689.png
Thank you all for your help and suggestions. Now I can get on with the next challenge...
 
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ragflyer

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Apr 17, 2007
Messages
448
Another quick question: would using a 50mm OD steel tube be stronger/weaker than a 50mm square tube of same wall thickness? A square tube would have a number of advantages: (1) it provides a flat surface for the rubber bushings to sit on, (2) easier to drill so that both sides have identical alignment (3) easier to fabricate the hardwood spacers for internal fitment.

Both are available locally of course. So just wondering if there was any advantage one way or another...
Sorry I have got to say this. If you cannot answer this rather basic question (not to mention its vagueness- stronger in what sense- compression, tension , bending ?) can you really be relied on designing a safe airplane? I would like to be supportive, but it does make me wonder....
 

J.L. Frusha

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Feb 17, 2006
Messages
1,043
Location
Luling, Texas
Sorry I have got to say this. If you cannot answer this rather basic question (not to mention its vagueness- stronger in what sense- compression, tension , bending ?) can you really be relied on designing a safe airplane? I would like to be supportive, but it does make me wonder....
I think it's a valid question for different materials. Square tubing has more surface and cross sectional area than round, though round tubing is generally used.

1660042082091.png
 

cluttonfred

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World traveler
Like so many questions in aircraft design, the real answer is...it depends. What are your load conditions, what are your constraints?

If we are talking about the axle in the drawing, and only about bending loads in the vertical sense, then the square tube will be stronger every time. Think of it like a wing spar...the square tube has the whole top and bottom surfaces as far as they can be from the neutral axis while the round tube has only the very top and bottom of the circle that far away. If you orient the bending loads on the diagonal of the square section, the you'll see that in terms of distance from the neutral axis the square section at its worst coincides with the round section at its best.

If you play around with these calculators you'll find that for a square and round tube of the same outside dimensions (2" x 2" vs. 2" diameter) and the same wall thickness, the square tube is almost twice as strong in bending for only a little more weight. Or you could lower the wall thickness of the square tube to be lighter for the same strength as the round tube. Of course, you have to play around with available standard wall thicknesses because it's never going to be an exactly even swap, but you get the idea.


 
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rtfm

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Jan 3, 2008
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3,754
Location
Brisbane, Australia
This is an EXCELLENT tool. Thank you. It seems (because the Fleabike is so light) that even with 6061-T6 square section, the axle will be able to cope with a 2000lbs point load (i.e. a very poor landing). I won't use aluminium, because it's too expensive, but my 2mm wall thickness 2"x2" pipe is well up to the task. What a cool tool... Thanks again. Add to this my new sprung suspension and the tundra tyres, and I'm very happy...
 
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Battler Britton

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Nov 14, 2015
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561
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Montpellier,LFNG (Candillargues)
In that old French / Swiss video, at 19:15 it shows that the stick moves BOTH the front wing and the rear wing simultaneously for pitch control!
Yes, that was the 1936 version, the 1934 ( only mouving front wing) one was considered dangerous, at that time
after, H Mignet found the way to secure the design with again the front wing only
 

Victor Bravo

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Jul 30, 2014
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KWHP, Los Angeles CA, USA
Here's what I've decided to do:

NAPA shock absorber bushings threaded onto a high-tensile bolt to keep everything aligned.
Hi Duncan, one thing that jumped out at me looking at your idea is that at the moment when the rubber bushings are compressed, the only thing holding the landing gear axle from moving forward or rearward is bending loads on the shank of the alignment bolt. In a normal landing, there is a good chance the rearward loads will bend even the strongest bolt, because there might be a lot of mechanical advantage being applied to the bolt.

I think a trailing link/swing arm hinged at the letter "F" and attached to the axle will constrain the movement better? This would allow removal of 2/3 of that steel tube stucture... the rubber bushings would be further aft, underneath where the rear T shaped joiner plate is, with the axle under that. A simple light "return" cable would prevent the axle from swinging down away from the rubber bushings in flight.

In my sketch below, the left/right trailing arms would have to be connected with cross bracing or a shear panel to prevent the axle from moving in a spanwise direction under side load.

Amazing FleaBumpers.jpg
 
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rotax618

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Oct 31, 2005
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1,609
Location
Evans Head Australia
When you consider the shock absorption of the large tyres and the weight of the aircraft, you only need a U-bolt with an isolation rubber around the axle. Compare the Himax/Minimax UC, it is essentially rigid with a hinge to give the required isolation.
I would simply emulate the Team Minimax UC which is light and simple.
 
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