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Scottiniowa

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Joined
Nov 29, 2021
Messages
45
Location
Clarksville, Iowa
An ultralight needs to be designed to fail in extreme conditions but the failure needs to be of minor concern and easily repaired.
This is so very true, As some of you may know, I use to build tail wheels and lots of them. Mostly for aircraft up to 2400 gross weight, but the underlying principals are still here. It is fairly simple if you step back and look at the overall picture.
  • You want, all parts to fail, BEFORE the main structure fails, during unexpected difficult landings. That is, you want to fix little things, not the large Frame connection points.
  • The landing gear in this case is a perfect example, to strong of gear tube, will/could transfer up to the main frame and bend/tear out or crack this area. Fixing just the tube or axle is far better than the main frame. same goes for tail wheels or nose wheel assemblies.
  • The trick, as has been eluded to, is to get to the max strength, for a given weight, but still having it fail before the main frame hard points do. Some times this leads to trial and error as some load calculations simply can't forecast everything.
  • Sometimes, and it has been talked about here, it may be best to use a known method of attachment and then work backward (more trial and error) But at least knowing the starting point, is good and proven.
Well, I didn't tell anyone anything new here, just pointing out some obvious things.
 

philr

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Joined
Dec 26, 2020
Messages
208
The idea of this landing gear is to use titanium tubes as the spring element and then steel fittings at the fuse and wheels. The Titanium tubes would be the intended failure point bending or breaking. I just picked a starting point for failure of around 3 "g"s since my gross weight is around 500 lbs so failure at just over 1500lbs. I used 1" x .088" Titanium tubes which since I will need around 4' cost about $156 and weight 1.972 lbs. See the attached pics for calculated strength. For the 12" gear legs I used a point load and a uniform load for the 24" cross tube. Now what I would like to know is how much deflection is occuring but don't have the engineering chops to figure it out.

Screenshot 2022-07-08 161247.jpg be.Screenshot 2022-07-08 160631.jpg Screenshot 2022-07-08 162818.jpg
 

philr

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Joined
Dec 26, 2020
Messages
208
Maybe not. You'll need more triangulation to cantilever those rods. Check out the Rans S18 and Kolb Firefly for inspiration. Also, here's a link to a titanium supplier who has good prices and sells by the inch. Titanium tubes are lighter than fiberglass (for equal strength) and make better springs than 4130 or fiberglass. Tubing - Titanium Joe
What is the problem with fiberglass rods not being springy enough? Is it just more difficult to find the correct size?
 

philr

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Joined
Dec 26, 2020
Messages
208
What do you think an appropriate G force for landing gear failure is for a part 103 ultralight as we want the gear to fail before the fuse tubes break or bend?
 

rotax618

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Joined
Oct 31, 2005
Messages
1,673
Location
Evans Head Australia
The Streak Shadow used 1” fibreglass rods as main gear legs, it used 2 (it is a much heavier 2 seater), as you can see from the diagram they used a thin steel tube across the fuse (wire braced) that the glass rods plugged into.C09569B4-9C3E-4088-8B94-7DA3134B42D1.jpeg
 

wanttobuild

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Joined
Jun 13, 2015
Messages
841
Location
kuttawa, ky
Pretty much agree what you're saying here, more importantly, just having the two spar cap tubes like that, and nothing else, give no torsional strength to the wing, and as the wing is viewed as supported by only a single strut, it will twist all over the place.
Interesting history note, my first ultralight (that was built by somebody else), was a (bad) clone of a Winton Cricket, which used heavy tubes for the caps, and only a few assorted shear webs (😱) and then relied on a cable attached to the trailing edge to stop twist.
Unfortunately it only stopped the wing twisting upwards, but not downwards, so when you applied aileron, they would work like trim tabs and twist the wing giving aileron reversal :oops:😱.
I made new wings with a simple capped web spar, moulded fibreglass ribs (wouldn't do that again), and sheeted leading edge to form a 'D' tube. Retained the single strut and never had any twist.
View attachment 112099
Looking carefully at this photo, one can see I'm holding left aileron, and the ailerons are moved respectively, but you can notice the washout on each wing is different and the cable on the left trailing edge looks a little loose.
For anyone interested, that's a Yamaha RD350 motor bike engine. Lots of noise...

View attachment 112100
TLAR asked if I have drawings?
Unfortunately no.
The wing section was derived by drawing a 48" centre line, then adding an 8" vertical line 12" back from the leading edge, which was marked as a point 1" above the centre line at the leading edge, and then just drawing a pleasing curve to join all said points up!
Turned out to be something like one of the later Gottingen wing sections, and actually flew pretty nice.
Structurally the wing is a 0.016" spar web with 1/2"x1/2"x0.063" extruded bulbed stringer angle, solid riveted as caps.
Doublers of 0.025" at the wing attach and strut attach points are fitted, then 5/16'x1.0" straps for the actual pickups.
I think the rear spar was a 0.020" folded 'C' channel, also with matching doubler and straps as above.
All sheeting is 0.016", as is the entire aileron structure.
I just remembered I detailed this build in my Stollite description here; #14
I never weighed this wing, but I think was actually lighter than the original alloy tube spars and trailing edge, polystyrene and plywood ribs with fibreglass sheeted leading edge wings, and definitely stronger.
I Love your airplane!
 
Last edited:

wanttobuild

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Joined
Jun 13, 2015
Messages
841
Location
kuttawa, ky
I also love the concept and think it could find a ready audience, but my initial reaction was that the fuselage and boom are a bit too complex. I think that coming to a point at the bottom of the point-down triangular boom and then going back out again for the rest of the triangle makes the structure very busy.

I would use the triangular boom from engine to tail but base down, point up (except in the last bay at the tail the two base tubes come together at the tail post). You could move the horizontal stabilizer to the bottom of the boom if desired and even have a triangular fuel tank. Now the top of the triangular truss forms the attach points for the wings just like triangular cabane struts and all the "frames" that form the sides and back of the fuselage can be simple rectangles or trapezoids with X-bracing or corner bracing. The seat back, for example, would be a single rectangle or trapezoid all the way up to the bottom tubes of the truss.

Another approach would be to eliminate the triangular truss boom from the forward fuselage, and instead bring everything to a point like triangular cabane struts, then built out the existing triangle behind the pilot's head to form the boom for the tail. This reduces the parts count considerably but does't really work with your engine location. It would work with a paramotor engine as a tractor on the nose of the pod or a pusher behind the pod. Taken to its logical conclusion you end up with something all triangle like Ed Fisher's Flitplane.

View attachment 112039
It is so easy to suggest a bunch of changes. THAT ADD WEIGHT, when the initial design would have been lighter and work just fine.
 

wanttobuild

Well-Known Member
Joined
Jun 13, 2015
Messages
841
Location
kuttawa, ky
Pretty much agree what you're saying here, more importantly, just having the two spar cap tubes like that, and nothing else, give no torsional strength to the wing, and as the wing is viewed as supported by only a single strut, it will twist all over the place.
Interesting history note, my first ultralight (that was built by somebody else), was a (bad) clone of a Winton Cricket, which used heavy tubes for the caps, and only a few assorted shear webs (😱) and then relied on a cable attached to the trailing edge to stop twist.
Unfortunately it only stopped the wing twisting upwards, but not downwards, so when you applied aileron, they would work like trim tabs and twist the wing giving aileron reversal :oops:😱.
I made new wings with a simple capped web spar, moulded fibreglass ribs (wouldn't do that again), and sheeted leading edge to form a 'D' tube. Retained the single strut and never had any twist.
View attachment 112099
Looking carefully at this photo, one can see I'm holding left aileron, and the ailerons are moved respectively, but you can notice the washout on each wing is different and the cable on the left trailing edge looks a little loose.
For anyone interested, that's a Yamaha RD350 motor bike engine. Lots of noise...
Every time I see this post I fall in love all over again!


View attachment 112100
TLAR asked if I have drawings?
Unfortunately no.
The wing section was derived by drawing a 48" centre line, then adding an 8" vertical line 12" back from the leading edge, which was marked as a point 1" above the centre line at the leading edge, and then just drawing a pleasing curve to join all said points up!
Turned out to be something like one of the later Gottingen wing sections, and actually flew pretty nice.
Structurally the wing is a 0.016" spar web with 1/2"x1/2"x0.063" extruded bulbed stringer angle, solid riveted as caps.
Doublers of 0.025" at the wing attach and strut attach points are fitted, then 5/16'x1.0" straps for the actual pickups.
I think the rear spar was a 0.020" folded 'C' channel, also with matching doubler and straps as above.
All sheeting is 0.016", as is the entire aileron structure.
I just remembered I detailed this build in my Stollite description here; #14
I never weighed this wing, but I think was actually lighter than the original alloy tube spars and trailing edge, polystyrene and plywood ribs with fibreglass sheeted leading edge wings, and definitely stronger.
 

philr

Well-Known Member
Joined
Dec 26, 2020
Messages
208
Philr

Do the drawing dimensions on the single place reflect the dimensions of the Tyro?

I am trying to reverse engineer the Tyro.
No Hero is its own design and I like the lines of the Tyro but had no way to measure one and weight and balance would likely be very different since it has heavier engines.
 
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