Houston Hawk...Phoenix...Build - Page 25 - RC Groups
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Nov 18, 2012, 11:25 PM
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Originally Posted by ray foley
hi there from Toledo

Hi Guys;

I've been busy with a new job for the last few weeks and have missed a lot, but now I have caught up and I must say the prototype build is delightful. Of course there are always things learned and adjustments made in any design. The prototype woodie fuselage is magnificent.

You might want to try a 2s A123 1100mah pack instead of a 4 cell nimhpack they would probably fit better in the nose. I used hs81 servos in my Houston eHawk for rudder and elevator, hs55 servos for the spoilers do the job just fine.

And JOLLY, that mold of the Condor/HH fuselage, WOW! What an undertaking!! Any idea when we will see an HH flying with a fuselage made from the mold? Might they be available any time soon? Hmmm?

I seriously applaud the effort you guys have put into this endeavour, bravo!!

ciao -rjf

It's been far to long for the HH community not the have a source for the fiberglass fuselage. So I took up the cause. While I was at it I also made a few other molds... for 3 different sailplanes.

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Nov 19, 2012, 11:35 PM
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CG and servos

Tonight I installed the servos and decided on the location for the receiver and battery. My first attempt was the conventional battery in forward bay, servos in the next bay back and receiver in the third bay back.

With the sides at the nose lower than my revised plan, the 4-cell block of AA batteries required major carving of the canopy/hatch in the foremost, thinnest section. Even with this, once the wiring was in place the hatch would not close easily. I could use a smaller battery, like a 900 mah 4-cell AAA pack. Ray suggested a 2-cell A123 pack, but, at 2.55" in length, they would be too long to fit in the forward bay, which is 2.2" in length.

But this was not the only issue. It's looking like I will need nose weight (no surprise) and, with the battery in the first bay and the servos in the second, there is no room in the nose for anything like the weight I am anticipating (2-4 oz.).

So, I uninstalled everything, moved the servos back to the third bay, the battery in the second bay (fits perfectly) and the receiver in the fourth bay behind F3. This leaves the entire first bay (drilled-out nose block back to F1) for balancing weight and the canopy/hatch closes perfectly without trouble at all.

Now I am thinking about CG and nose weight. I knew that with the long tail moment, I would need weight in the nose. But here is a question I wonder if anyone can help me answer.

I'm guessing that the final wing with 2 small spoiler servos in it will weigh about 26 oz if I build well. Here's the question: since about 45% of the wing chord is forward of the CG (a bit less than that, actually, since the LE is swept back toward the tips) and since the wing structure is heavier forward of the CG than rear of the CG due to the thicker section, spar location, and D-tube, how much weight from the wing will contribute to improving the need for nose weight in the finished plane? Oh, and the stream is running NW at 4 mph, just to complete the story problem.

With the fuselage loaded with all the radio gear but the tail not yet covered, if I put 4.5 oz. of carbide steel bits in the nose, the fuselage, without wing but with the adapter and joiner rod, balances at the planned CG. How much more or less weight will I need once the wing is on?

I hope there is someone out there who is interested in those questions because for me all I can do is build the wing and then find out by experience. Someone must know the theory and calculation, though, right?

I just found this CG calculator here in RCGroups:

I crunched rough estimates of the numbers and it says I'll need 9 oz. of nose weight! Could that be right? Do you other Hawk pilots need that kind of nose weight to get the the planned CG? Yikes. Of course, I might (probably) have some numbers wrong in my calculation... Even with that, the wing loading is in the high 6 oz. to low 7 oz. per sq. foot zone. That seems about right based on what I have read in these HH discussions.
Last edited by wingloada; Nov 30, 2012 at 11:36 PM. Reason: Corrections in data and charts
Nov 21, 2012, 07:47 PM
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I have a friend with access to a metal shop and I was able to bend the joiner rod today. 7 with a large vise and a 3' long breaker bar tube. A little pulling and it's done. It's hard to imagine that the wing will take the force needed to bend it even more, but then that's the power of 11 feet of leverage with a sturdy spar!

It turns out that the brass tubing I got had an inside diameter of 0.498 rather than 0.5. The aluminum joiner was exactly 0.5 OD so I needed to remove some material from the rod for the tubing to fit well. One side is done here the other not.
Last edited by wingloada; Nov 24, 2012 at 11:42 AM. Reason: Added photo
Nov 22, 2012, 01:35 PM
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happy Thanksgiving to the HH fambly.

Nov 24, 2012, 11:54 AM
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The wing build

After gathering Jack's instructions and many photos including those at the Houston Hawk's build page, I began working on the wing. I have decided to build one wing through the kevlar wrapping stage and then the other to that same stage before bonding the spar to the lower sheeting and notching the TE for both.

I made one minor mistake (can we call it an 'interpretation' in hindsight? ) and that was that I potted the brass joiner tubing while building the ply shear boxes before I understood Jack's instructions to wait until both panels are built to install it in both at the same time. My understanding is his approach is for getting them perfectly aligned. I think that I can still do this by waiting until the second wing is built before installing its joiner tube. That way I can install a straight 1/2" rod between them both and I can adjust to whatever alignment is necessary with the first wing panel. At least that's my (rationalized) plan--I do see the flaws in my thinking . For what it's worth, I was very careful to get the installed tubing centered and straight. We'll see when both are finished if I was careful enough.
Last edited by wingloada; Nov 26, 2012 at 10:43 PM.
Nov 26, 2012, 01:07 PM
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Over the holiday I learned how to use layers in my CAD software. For fun, I drew up a multi-layer dwg plan of a pod for the Yardbird wing (or HH with adapter) that has a replaceable nose section for either glider or electric (I know, horror of horrors!). I have added that drawing to the Yardbird Pod dwg folder in my Blog download list. Here are the pdfs for anyone who is interested.

Last edited by wingloada; Dec 08, 2012 at 11:47 AM. Reason: Updated drawings
Nov 26, 2012, 11:38 PM
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I think I may have hijacked this thread to loneliness.

I'll give it a break for a while. Sorry if I was hogging the space.

Nov 27, 2012, 04:52 PM
Hot Dawg Glider Pilot
schrederman's Avatar
Nope... no breaks... stay on task! We're all watching and waiting for your maiden and I doubt anyone is worried about your "hogging" the thread. I am nearing completion of my garage sorting and cleaning, so my work area is next... I did sketches of my man cave with suspended shelf and lighting, etc... so I'll begin my preliminary wing building and fuselage design work in December... ... finally!
Nov 27, 2012, 05:41 PM
registered weapon
No way man... You don't get to just quit now! Keep building AND posting. It's a long winter here in Montana. Don't leave us.

Shreder, get that cave dug out, EL HEFE needs a nest to hatch in!
Nov 27, 2012, 06:51 PM
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That's El Jefe... Amigo! ... And I need to get busy on that one...
Nov 27, 2012, 06:58 PM
registered weapon
sorry Jack, Failed spanish Lookin forward to seeing it,
Nov 27, 2012, 07:08 PM
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OK, onward!

Nov 28, 2012, 12:25 PM
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Wing inner sections

The wing inner panels are built up to the point of installing the spoiler servos, spoilers, and top sheeting.

Next I will begin on the outer panels and tips.

Last edited by wingloada; Nov 28, 2012 at 07:49 PM.
Nov 28, 2012, 02:48 PM
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Learning is good

Things I learned while building the inner panels (otherwise known as mistakes I made), or, what I would now do differently if I were to build it again :

1. In addition to cleaning the CF spar caps with alcohol before assembly, also sand them to remove the sheen for better bonding.

2. The joiner boxes are built empty and the joiner tubes inserted later.

3. Don't use CA to edge-glue the bottom sheeting and the TE spruce strengthener strip because it's difficult to sand later.

4. In addition to rounding the edges of the Joiner box ply shear webs, the last bit of the CF spar caps toward the tip from the ply section also need to be sanded round before wrapping in Kevlar tow.

5. When cutting the inner ribs to glue to the spar front and rear, not only does the 1/8" ply on each side need to be accounted for but also a bit more for the Kevlar wrap thickness. Matching the location of the 1/4" sub spar notches will help.

6. Carefully check that ALL of the laser cut shear webs are the same length and height after laminating and sanding them. If not, the rib spacing can get a bit off as you go (yes, I admit it). For some odd reason, my rib spacing drifts a bit from the plan because, considering the reports of plan dimensions changing with expanding and contracting paper, I decided to build the rib-shear-rib-shear process trusting the shear webs laser-cut lengths rather than correcting them (as Jack warns) to match the plan as I went. This shouldn't effect wing structure, but when the panels are held up back to back the ribs don't line up perfectly by about 1/8" in places toward the tip end of the panels. But hey, perfection is a joyless trap anyway, right?

7. Mix 25 grams of cabosil-thickened epoxy to use when building the rib-sheer-rib-sheer part for both left and right wings.

8. Drilling out the Joiner box cleanly to insert the over-sized 9/16" brass joiner tube needed for the 1/2" rod is not a simple step when the box has lumps of cured Cabosil-Epoxy inside it. The relieving of the inner walls of the ply sheer pieces is better done before the spar is built rather than after.

9. Getting each rib, especially the split ones, to be exactly 90 to the spar is tricky, especially where there is Kevlar tow wrapping.

10. Measure the distance from the spar back edge to the TE front edge carefully on both panels to match them rather than rely on the plan, which can change dimensions from humidity, etc. Again, this is correctable, but it's not perfect.

11. Mark each shear web for front back top bottom and then, here's the important part, set them that way when building the rib-shear-rib-shear part of the wing (I reversed one accidentally in the inner panel).
Last edited by wingloada; Nov 30, 2012 at 04:40 PM.

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