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May 29, 2006, 05:30 PM
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DiveBombDave's Avatar
Thread OP
Galenm,

Is the wing cover a single sheet folded at the front?

*Yup. I bevel cut the topsheet and bottomsheet's leading edges to 45deg.

I have a 32" wing built from FFF. It has only a lengtwise spar, no ribs and is very strong, how necessary are ribs?

*On a smaller wing like that, ribs probably aren't needed. On a 72"x11" wing, they make boxes with the FFF spar strips, and provide torsional strength. Like, without them my wingtips would wander/flutter from positive to negative incidence angles. I've even started adding another FFF strip 3" back from the spar strip, for more "box" strength.

My biggest motor is an AXI 2212/34. If I were to buy new would you still advise the geared motor vs the direct drive AXI?

*There's two crowds on this one: direct drive vs. geared. I generally prefer geared (only metal planetary, doesn't wear out really) because they can spin larger props for a given current draw, which always gives more climb rate and more duration at loiter. The drawback is they are heavier, more expensive, and make more noise. The smallest axi I have is the 2808-24 on a 9-10" prop, and can easily carry a 50oz+ rig up at about 200 watts. The 2814 axi.... no one ever uses it, I can't figure out why - it seems that you can almost wring out a 2808 to get the 2814 performance (by the specs). The big axi step is the 2826/10 or /12, and they are good to over 100oz AUW but need about 400 watts.

I saw Goodwinds kites has dihedral blocks that accept 8 or 9 mm shafts. Would this be a simple sub for your built up dihedral block. Not sure I understand how you did this. What makes up the insert that provides the angle?

*I would be careful with kite dihedral blocks just because we have so much more weight and nose-dive loadings... The way I make the arrow-shaft block now is: tape arrows at measured angle onto a board, tap epoxy a 6-10" section of arrow across the top of the angle (I drum sand/dremel the arrow ends so they mate up with the spars more flush). then measure the shallow triangle you've created and cut out of light ply, make two more triangles just slightly larger. When you sandwich the smaller one in between the largers, it creates a nice groove to meet the round arrows. Then epoxy it all in, wrap with heavy fishing line (I use spectra fishing line). Let dry, then try flexing it and listen for epoxy cracking and re-evaluate. On large wingspans I add bamboo chopsticks out from the arrow brace on each side, lashing and epoxying. Haven't had one fail yet.

Is the long wing spar a doubled piece of FFF.

*Yes, more or less. You can use 3 pcs of FFF in a sandwich around the spar (one short piece between two longer ones to 'saddle' the arrow). It doesn't add spar strength over what the arrow is already providing, but does help with the rib/spar box effect (torsional strength).

Are arrow shafts stronger than the pultruded tube available at Goodwinds or Hang-em high.

*Not sure on that one... the wall thickness on the arrows I'm using is .03" I believe. If you're going to order carbon you might consider carbon 'slats' - used for sparring you place it upright and it just about can't be flexed (very stiff in that one direction). The round tube arrows are a little wasteful in this respect, heavier and more flex, but I like a little flex before break ya know.

Hope this helps!

Dave
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Jun 02, 2006, 10:25 AM
Registered User
You have me interested.
I will test your patience with a number of questions.

I have never seen a CF arrow shaft. Do they come in different sizes? A local supplier said theirs are about .25" dia.

What is the arrow OD? l
length?

I am looking at your drawing of AP4 12.5%

Does the wing spar not extend to the end of the wing?

Tail Boom spars...

Could you give me tail boom segment measurements

Spar to back of wing
Spar to front of tail feathers?
Spar to back of tail feathers? (oveall length)

How far apart are the wing spars?

I printed the spar drawing
It measures 7.5" What should be the length? What are the grid sizes on the paper?

I saw you used a single lg wheel. Is that working well?
I take it you hand launch.. Overhand?

Attached are a couple of my pictures taken with a Slow stick.

thanks a lot

Galen
Last edited by GALENM; Jun 02, 2006 at 10:31 AM.
Jun 04, 2006, 12:53 AM
Pull out early!
DiveBombDave's Avatar
Thread OP
Galenm,

No sweat - another user pm'ed me for the tail moment measurement.

The carbon fiber arrows are pretty standard - About .25 OD, 32.5" long. I used the whole thing for the tail booms, and the stabilizers start at 26.5" back and run the remaining 6" to the end of the arrow. The ruddervators are an additional 3" deep from there. The stabilizers are 6" deep at the boom, and taper to 4" deep where they meet. I tried very hard for a 110degree angle between them. Since the arrows 'droop' a little even under their own weight, and adding the tail assembly on them causes a couple of degrees of droop - so on AP3 I "chocked" the tailbooms before they leave the rear of the wing so that I end up with about 3 degrees of positive incidence angle on the wing, compared to the stabs on the tail. And the tailbooms are 18" apart on AP3.....

On the spar stopping short of the wingtip - yes, I feel it's wasteful to extend it that far, but won't hurt. But you put two 32.5" arrows together for the spar for 65" span on the spar, and that only leaves 3.5" short of each wingtip on my 72" bird. On the 60" wing you can get away with a 48" spar, really.

The grid paper I use has 1/4" grid spacing, by the way, so you should be able to go from there on the measurements.

And after many landing gear designs, the one that works everywhere (for me) is the 'monowheel.' Since I hand launch, I only need to be able to land on a variety of surfaces from blacktop to gravel to short/tall grass. And the monowheel does this without snagging and nosing over like conventional gear in grass. The depth of the fuse (6") is what protects my hand from the prop on launching. I hold it by the wheel, right about at CoG, and give it a firm toss level.

Hope this helps!

Dave
Jul 31, 2006, 09:21 PM
Pull out early!
DiveBombDave's Avatar
Thread OP

New power system!


Well, AP3 is now on it's third iteration of power system.

1st - Kontronic fun 400-28 geared 5.2:1 on APC 13x8E, 5500rpm, 18amps on 3s1p2100.

2nd - Multiplex bl480-4g geared 4.4:1 on APC 13x6.5E, 6200rpm, 24amps.

3rd (now) - Axi 2826/12 on APC 13x8E, 6500rpm, 27amps.

I had broken the gearbox prop shaft on a hard 'landing,' and decided to go with the axi based on what people are doing with it on the 6' Telemaster. My TP prolite's are happy with the 27 amp draw, but I cut the throttle soon after launch back to 18-22amps and I get about 1400'/min around there. My loiter time has increased, unexpectedly (motocalc predictions). Before I would land after 20mins, now I can stay up 25+ mins and still have juice for a couple of go-arounds without low voltage cutoff. I can maintain altitude with 4-4.5 amps, under 50 watts. The AUW has now grown with equipment to 60oz.

Got a bwav patch antenna for my receiver.... wow. Locked in like cablevision.

Just wanted to update - this has been the greatest bird.

Dave
Jun 01, 2008, 07:55 AM
Registered User
LittleG's Avatar

Awesome AP Twin Boom Build Thread


I just discovered this thread... I'm a big fan of twin boom planes and always searching for new ideas and designs here rcgroups.com...

I like to build the AP4...

LG
Quote:
Originally Posted by DiveBombDave
Well, AP3 is now on it's third iteration of power system.

1st - Kontronic fun 400-28 geared 5.2:1 on APC 13x8E, 5500rpm, 18amps on 3s1p2100.

2nd - Multiplex bl480-4g geared 4.4:1 on APC 13x6.5E, 6200rpm, 24amps.

3rd (now) - Axi 2826/12 on APC 13x8E, 6500rpm, 27amps.

I had broken the gearbox prop shaft on a hard 'landing,' and decided to go with the axi based on what people are doing with it on the 6' Telemaster. My TP prolite's are happy with the 27 amp draw, but I cut the throttle soon after launch back to 18-22amps and I get about 1400'/min around there. My loiter time has increased, unexpectedly (motocalc predictions). Before I would land after 20mins, now I can stay up 25+ mins and still have juice for a couple of go-arounds without low voltage cutoff. I can maintain altitude with 4-4.5 amps, under 50 watts. The AUW has now grown with equipment to 60oz.

Got a bwav patch antenna for my receiver.... wow. Locked in like cablevision.

Just wanted to update - this has been the greatest bird.

Dave


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