Dave's XL F-71

[ArcticDave]

After pondering all evening and again this morning... I'm going to cut a wedge of .090 and weld it into that gap. I could find no pictures of prior Eagles, except a couple from Steve Kiblinger's site, that show that area in detail.  He filled that gap in too. So if you're out there Steve, thanks for the pics! 

[ArcticDave]

Hard testing of my tailwheel found the weakness. The nicely bent tubing yoke started to deform under severe loads. It didn't fail, but you can see the deformation right in the middle of the bend. 
So I made a new style caster frame with no bent tubing. It's not as elegant as the prior version, but it survived the same test that killed the other one. A fat guy jumping on it like a pogo stick!

[scottiniowa]

Hard testing of my tailwheel found the weakness. The nicely bent tubing yoke started to deform under severe loads. It didn't fail, but you can see the deformation right in the middle of the bend.
So I made a new style caster frame with no bent tubing. It's not as elegant as the prior version, but it survived the same test that killed the other one. A fat guy jumping on it like a pogo stick!

In order for others to learn- what tubing dia. did you use and wall thickness-     As I have built over 200 tail wheels, I find this interesting, and would venture to guess it was more "how it was welded" and cooled, than the tubing.  But then again, if it was some .035 wall material, (and under .750")  it would explain much.  

Also if the yoke arms are built to go around the tire, this makes the cross tube much shorter, thus stronger in bend moments.  Picture a 10" wrench vs a 20" wrench, the power to the nut end, can double just from leverage. Much of the same can be said on the strength of the cross tube, if longer than need be.  A 2" wide tire, could easily get down to a 2-2.5" cross tube (not very long) and far stronger than a 3" cross tube of the same size.


I am not sure how you formed it, but general putting a U bend or slight bend,  "helps" to some degree in the center bending moment.   Many details go into it.  

I build for up to 2500 # gross aircraft and use a strait 1" tube, but .049 or .058 wall depending on future loads.  But how it  is attached to the king post of the tail wheel is entirely different, as I have a sleeve on the king pin, that surrounds the cross tube, and this gets all the welding, vs one side.   Just thoughts

best of success.

[ArcticDave]

It was 5/8 .035 Scott. 

I believe .049 or higher would not have deformed as this one did. I used a much heavier tube under the kingpin this time, 3/4 .049. I also made it as short as possible...just enough to clear the wheel.   2 3/4" I think.

[Sam Buchanan]

It's a repurposed deck chair

http://www.cabelas.com/product/CABELAS-PADDED-LOUNGER-XL/1748326.uts

The bottom section of frame was damaged a couple of years ago by alcohol and poor judgement. Its been sitting in storage since then. With all the grommets on the side you can adjust to whatever length needed. I've got a bit of yoga mat that I was going to slip in there for extra padding.
I think that crossbar that forms the normal seat bottom in the airframe will grow teeth after sitting in it awhile...hopefully the padding will alleviate some of that.

Not sure on what it weighs. I'm estimating ~3- 4 lbs when its laced up with the yoga mat pad inside the bottom. Not incredibly svelte, but lighter than the 6 lb Black Max seat I was looking at....cheaper too.

The seat in the XL needs to be strong enough to withstand a hard arrival, probably talking about at least 3-4 Gs. Most deck chairs are good for ~250 lbs, the pilot bouncing the plane in from three feet will put far more load than that on the seat. When the seat fails the pilot ends up sitting (straddling?) the elevator cables and control torque tube.   ...Ouch....use care when designing an alternate seat.

[ArcticDave]

I had the unfortunate experience of briefly witnessing a chair just like that hold a bouncing load well in excess of 500 lbs and survive. The sling material is quite stout and at least 2 layers thick.  
I will heed your advice Sam and proceed cautiously. Maybe testing its twin to destruction? I'll come up with something appropriate.

[ArcticDave]

Have not had much chance to work on the plane much lately, but I have managed to frame up the legs. Starting on the suspension struts this weekend hopefully.

[ArcticDave]

I got started on the bungee struts yesterday. Got one strut end made before the drill press broke 😕
I needed one end thinner than the tube I made the strut from, so this how I narrowed the end without losing strength. I "milled" the end of the tubing with a hand grinder equipped with a flap wheel. Then cut and shaped two tabs to weld on the now flat faces of the tubing. Next, I drilled a 3/8 hole for a bushing and welded the bushing in place. After a bit of shaping with a flap wheel, the final step was welding a securing strap around the end of the whole assembly. It came out nice :-)
Off to the hardware store for a drill press this morning...

[Dan_]

I got started on the bungee struts yesterday. Got one strut end made before the drill press broke 😕

Nice airplane parts...

[ArcticDave]

Nice airplane parts...

Thanks Dan.

[ArcticDave]

Finished the first bungee strut today. It will be safety cabled to a travel of 3" with a preload of ~1". That leaves lots of travel left to deal with runway irregularities. I cut all the pieces for the second one as I built the first, so it should just be an assembly job. Looking forward to the little bird sitting on her own legs 😊
The shadows make the 3rd pic hard to see, but it shows the strut installed.

[ArcticDave]

The Desert Eagle is finally sitting on its own legs! :-)
This has been the hardest part of the build so far. Everything has to be just so...or caster and camber get all out of whack. A lot of detail that pictures will never show and headscratchers only a fellow builder will understand, but I'm happy with the results.
Now I need to get real wheels and tires for it...those little hand truck tires are just for moving it around easily.

[PropMan]

Looking great  Dave,

I feel your pain on the gear, I rebuilt mine with an extra 2" in height.

[ArcticDave]

Looking great  Dave,

I feel your pain on the gear, I rebuilt mine with an extra 2" in height.

Thank you Frank!
 It was a pain in the royal @$$, but I can run up to a 67" prop and still have 12" of ground clearance. Ya know... just in case I'm ever in a position to pick up a 3vw

Otherwise its lots of room to help keep my prop from flicking rocks and sand.


EDIT******* that was original bigger version*****

I have 12 1/2 " of clearance with a 58" prop. Duh...my memory sucks at times. I shortened the gear because it was hard to get into. Station 2 sits at 30"H  straight and level.

[ArcticDave]

Now that the little bird is sitting on its own legs, being able to sit in it has become the priority. I gave Sam's advice some careful thought and decided to compromise. I kept the folding aspect but used Mr. Milholland's woven aluminum. 
   After sitting on both, there isn't a whole lot of difference and the aluminum is supposedly stronger and IS lighter....and MUCH cooler :-)
The canvas was too damn hot. 
Ruby hung out for awhile, but she got bored and went back inside. 100° is hard on a black dog