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Author Topic: close - first shot at P-30  (Read 827 times)
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carpetbagger
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« on: September 23, 2013, 01:01:06 PM »

airframe parts in pic weigh 37 grams so after I mount tail feathers, finish pylon wing mount, add nose block, GG propeller assembly, and rear peg this plane will be over 40 grams, but not bad for a first try. Plane is a modified Teacher's Pet, tip dihedral rather than poly, and a rolled balsa tube fuse, which is heavy since it is 1/16" balsa grabbed from stock pile and wasn't a light piece. I will most likely do a 1/32" contest balsa tube roll and save a few grams.

Question?  Wing/pylon is adjusted fore & aft to establish a CG - how is it attached to remain adjustable? 
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close - first shot at P-30
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danberry
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« Reply #1 on: September 23, 2013, 01:37:35 PM »

Tape.
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Rewinged
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« Reply #2 on: September 23, 2013, 06:41:08 PM »

Model looks great!  Assuming the model is designed to use 6 strands of 1/8, it should fly fine even if it was heavier, even at 50 grams.  Obviously lighter is better, but you should be fine.  Overweight with lighter motors is a bigger problem, since the model won't climb at all if it gets too heavy when using 4 strands of 1/8 or 6 strands of 3/32.  Six strands of 1/8 is a lot more power, and at least it will climb.

To expound upon what Dan said, you just need to temporarily attach the wing.  Attach, check CG, move and re-attach, check CG, etc. until the CG is at the proper location on the wing.  If the wing has to be too far back (or forward, although this is much less of an issue) you need to determine why and try and remove tail weight if possible.

Without checking various plans, my assumption would be that the CG should be between 60% and 80% of the chord back from the leading edge.

Assuming the wing is in a reasonable position with the CG at the right point on the wing, you can permanently attach the wing mount for that location.

--Bill
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Dave Andreski
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« Reply #3 on: September 23, 2013, 07:25:24 PM »

Plane is a modified Teacher's Pet.



Modified Teachers Pet? I don't think so...
The only thing I see that even remotely resembles a "Teacher's Pet" is the outline, NOT construction, of the fin!
Dave
« Last Edit: September 23, 2013, 07:50:04 PM by Dave Andreski » Logged

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carpetbagger
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« Reply #4 on: September 23, 2013, 08:58:36 PM »

Plane is a modified Teacher's Pet.



Modified Teachers Pet? I don't think so...
The only thing I see that even remotely resembles a "Teacher's Pet" is the outline, NOT construction, of the fin!
Dave

Yes, modified, all of which added weight. The fin has additional diagonals, otherwise built to plan. Stab is very close to spec save for the TE which was slightly sanded down 1/8" x 1/2" TE since I don't have access to 3mm x 9mm TE wood. Wing has the same TE deal, tip dihedral and flat center section, double ribs at dihedral breaks, and 1/8" square spar instead of metric size which was close to 1/16" x 1/8". Few added bits at both stab and wing LE at the center part.  Oh yeah, and no under camber. The fuse of course is not even close, rolled tube instead of framed up.  Outline of wing and stab are on plan as well as the fin.

I hardly ever build anything dead on spec - must experiment.  Of course I figure my "experiments" added a few grams. Next up, roll a 1/32" tube using select contest (light!) balsa. Oh, I rolled another P-20 tube with carefully selected (lightest I had) 1/32" and is was way lighter than tube #1, like close to 25% lighter. 20", 5.8 grams,tissue inside and out, two coats dope.

I'm learning . . .
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carpetbagger
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« Reply #5 on: September 23, 2013, 10:43:03 PM »

Tape - thanks, Dan. Yes, test glides coming soon. I have a P-20 in the works as well, scaled down and of course - modified - Teacher's Pet, but "soon" may be a few weeks as upcoming shortly is a week at the beach and our participation in the Nags Head Surf Fishing Tournament.
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Tapio Linkosalo
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« Reply #6 on: September 24, 2013, 12:30:13 AM »

Be careful with the tape, and once you get the CG in place, glue the pylon in properly! In my latest model (n the "Show us your P-30" -thread) I had the pylon (plywood, and kevlar motor tube) tacked in with drops of CA. Worked for a couple of outings, then on one energetic launch the pylon separated! So I had to glue it in with epoxy. Should have done it in the first place, as soon as I found the decalage to be OK...
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carpetbagger
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« Reply #7 on: September 24, 2013, 08:31:16 AM »

I have an assortment of tape - like seam stick tape I used on sailboat sails which is double side and very strong, but I agree - once I figure out the right position the pylon will be glued down snug. Probably with aromatic Sigment glue, epoxy if kind of heavy and I'm already over the minimum.
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Tmat
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« Reply #8 on: September 24, 2013, 09:03:18 AM »

Back in the early 90's my F1B's had small adjustable pylons held on with .... tape. And not just for a short time. The tape was always there.
The pylon used a thin base (early versions used several layers of carbon motor tube) or flange that extended aprox 1/2" in front of and behind the pylon. This way the pylon could be held in place with dbl sided tape and then secured with a strong tape (I used Polyester vacuum bagging tape, but really any decent flexible tape will work) around the base at the front and back of the pylon.

Tony

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carpetbagger
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« Reply #9 on: September 24, 2013, 09:36:35 AM »

I thought about that, Tony, just have a tab poking out fore and aft and strap it down. For quick and dirty testing I could loop a rubber band around it figure eight fashion and go . . . I have also considered a alignment strip - say 1/16" square spruce - running down the fuz centerling like a rail for the pylon to slide while adjusting and keep it centered. 
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applehoney
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« Reply #10 on: September 24, 2013, 10:05:37 AM »

>1/8" x 1/2" TE since I don't have access to 3mm x 9mm TE wood.

1/2" x 1/8" is somewhat overkill for a P30 stabiliser TE ..         "TE wood"  .. may I assume you mean preshaped TE stock?   Your 1/2 x 1/8 could have been trimmed to  1/8 x 3/8 and carved to wedge section but, even so, still somewhat oversize.    1/4" x 1/16" works fine for all my P30 stabs
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Dave Andreski
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« Reply #11 on: September 24, 2013, 07:34:18 PM »

Bill,
Looks like a fun experiment!
I'm jealous.
Dave
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carpetbagger
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« Reply #12 on: September 24, 2013, 09:38:19 PM »

>1/8" x 1/2" TE since I don't have access to 3mm x 9mm TE wood.

1/2" x 1/8" is somewhat overkill for a P30 stabiliser TE ..         "TE wood"  .. may I assume you mean preshaped TE stock?   Your 1/2 x 1/8 could have been trimmed to  1/8 x 3/8 and carved to wedge section but, even so, still somewhat oversize.    1/4" x 1/16" works fine for all my P30 stabs

So true, applehoney. Lazy choice, grab shaped TE stock and go with it. I will build another wing and pay attention this time. I did another rolled balsa P-30 tube today since #1 was so sturdy (read heavy) I could hand it off to the local T-ball squad to use as a bat. I have discovered that preshaped sections are heavy, so cutting strips and whatever from sheet stock seems to be the way to go.
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carpetbagger
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« Reply #13 on: September 24, 2013, 09:48:14 PM »

I'm getting better at this . . . did a P-20 wing today, frame no covering came in at a tweak over 4 grams. Did a new P-30 rolled balsa tube and it came out a third lighter than my first one. The challenge of hitting the weight target is fun!

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carpetbagger
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« Reply #14 on: September 24, 2013, 09:52:46 PM »

Bill,
Looks like a fun experiment!
I'm jealous.
Dave

Okay, I did scale the Teacher's Pet plans to 67% to go for a P-20 but this one is nothing like the TP. The TP plan was an inspiration, but not a "plan."
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Tmat
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« Reply #15 on: September 25, 2013, 03:27:52 PM »

For quick and dirty testing I could loop a rubber band around it figure eight fashion and go . . . I have also considered a alignment strip - say 1/16" square spruce - running down the fuz centerling like a rail for the pylon to slide while adjusting and keep it centered. 
Both are good ideas.
I once had an old F1B pylon that used a piece of soda can cut into a strip that ran around the fuselage (like a strap) and up inside the pylon walls and was joined at the top of the pylon (inside). I added a small piece of plywood with a nut epoxied to the bottom which was glued to the underside of the top of the strap. A bolt which was accessible from the top of the pylon allowed me to tension the strap to secure the pylon to the motor tube. To change the CG you loosened the bolt, slid the pylon fore or aft and then tightened the bolt. Some high friction tape on the bottom of the pylon was needed to stop slippage.

Tape was simpler..... Grin

Tmat
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