SILVER sLUG Takeoffwith new winter doors

[Tom H]

Vince, I made Hoerner wing tips for our LEU Treehugger a number of years ago.  Made out of the pink home insulation foam board, covered with fiberglass/epoxy.  By the way, the foam is polystyrene, and epoxy has to be used, or the foam will disintegrate.  Anyway, from the picture the finish was not great, but we tried them out.  We were looking for increased climb during takeoff.  We only got a couple flights before ole Treehugger acquired its name, but it seems that they did make an improvement over the flat plates on the tips.

Hope you can get them made and do some more testing.

[scottiniowa]

Matthew,
I wanted to save weight by removing the original tips and replacing with Leonard's design tips.saved quite a bit allowing me to build doors for use in winter ops .
Scott.

Scott, are you planning on using the rule of - 

• at deepest thickness of wing- go out 12"
• what ever angle that gives you (lets say it was 41 degrees)
• use that same angle out from all places of the wing rib profile (thus the top will always be flat across the span-and the bottom angle will always be the same)
• This gives you the predefined curve, and basically a easily to create shape that has a calculated value.  

The 12 inch rule was used for cub like aircraft, I don't know if it would be best (could be) for our Eagle sized birds, if this would be the number, remembering the lessor the distance the higher the used angle would be.  I guess a person has to start somewhere.   Certainly can and perhaps should use the lost foam-bulkhead technique to save weight, as the retained foam-super strength would not be required.

   I have done this shape in CAD many times, just never for the XL  

Was wondering what formula you were planning on?

cheers

[s johnson]

Well.....

Scott, I honestly had no plan. Just built to fit sort of thing Mostly not what you wanted to hear but..... seems to work just fine so far. Yep... nope as you guessed it. I'm not n engineer But am having loads of fun making things work. :-) By they way, where do you come up with all these formulas, your making me feel kind of stupid.. Haha
Scott J.

[ParQld]

As Leonard says its only and airplane... just build it !

[Vince Carucci]

Tom H,

Thanks for posting the picture and comments on the wing tips. A pictures worth...!  

I wonder:

• Did you hollow out the material in the tip or did you somehow form thin sheets of foam to that shape?
• What's the best way to shape the foam [knife/saw/file/abrasive/razor/blow-torch/TNT]?
• Do you think the same material used to cover the wing could also cover the tip [ex. Dacron rather than fiberglass]?

One more thing. Did you make peace with the tree or did you turn it into firewood? 

Vince

[Tom H]

Vince, I made the tips sorta like this:

- I saw this technique somewhere on-line
- stacked, glued 2" thick pink foam to make a block somewhat larger than the final tip.  Used 5 min epoxy, but made sure that it was only dabbed onto areas that would not have to be cut
- fastened a plywood template of a wing rib to each end of the block with long deck screws
- cut the wing profile using a hot wire.  I used SS safety wire in a crude light weight frame.  The power supply was an old 10 amp transformer type car battery charger, powered by a Harbor Freight tool speed controller to get just the right temperature on the wire.
- left one template on the end, removed the other.  Then attached a narrow strip of 0.025 aluminum sheet to the surface of the foam near what would be the tip end
- hot wired along the bottom of the plywood template and the alum strip.  this gave a curved shape to the cut.  The leading edge and trailing edge corners need hand shaping, if I remember correctly.
- I noticed that some Hoerner tips look like they have been run through a large vertical band saw set at around 45 degrees.  Don't know which way is correct or better.  Probably would be easier if run through a large bandsaw, though.
- I used epoxy/fiberglass boat cloth, one layer.  The fiberglass cloth is woven in a style that allows it to conform to compound curves.  I don't think dacron cloth will do that.  Also, some type of dacron is used as a peel ply material with epoxy because it does not stick.  Better check the compatibility first.  And, if you use the Polyfiber products, they will destroy polystyrene foam because of the MEK.  (note, if you want to use the cheaper polystyrene or vinylester resins, as used on boats, you can use urethane foam.  But, don't hot wire urethane foam - fumes are toxic.)
- finally, I initially did not plan to hollow out the foam, but did it to reduce weight.  I think I used a variety of techniques, knife, hacksaw blade, hand held die grinder, but no TNT.  Tried to leave the foam thick enough to support the glass.

Sure wish that I took photos of the build - my recollection would be better.  Hope this helps, though.

A limb was amputated from the tree - some would say "a just punishment".

[scottiniowa]

Well.....

Scott, I honestly had no plan. Just built to fit sort of thing Mostly not what you wanted to hear but..... seems to work just fine so far. Yep... nope as you guessed it. I'm not n engineer But am having loads of fun making things work. :-) By they way, where do you come up with all these formulas, your making me feel kind of stupid.. Haha
Scott J.

Ha, certainly the case for "what ever works" and what is built is 10 times better than what is proposed to be built.

Formula came from a Tip builder in the state of Washington. but he was building for 100 mph aircraft, so I have no idea, if they are to much, or even effective. But certainly liked the established rule that he used, thus he could make the same basic shape, no matter what rib profile was used. Again, this might be completely a pie in the sky approach.

I really liked how you did yours, I don't think any stupid event prevailed for you. It got done. Top notch.

Scott in Iowa