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Author Topic: New Limited Pennyplane (mostly)  (Read 22882 times)
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olddog
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« Reply #25 on: January 07, 2012, 09:30:36 PM »

Hi Bill (rewinged):  if you really want to save weight, try using fewer wing and stab ribs.  Get yourself some light film and use 3M spray to lock your covering.  Check with Ol Bill, looks like that's the method he uses.  I start out with Ltd pennyplane and gradually worked my way to reg pennyplane.  That was back in the early 90's and I had a plan published in SAM 86  newsletter,  The best time I had was 10:04 in a Cat I ceiling.  The indoor scene has pretty well been taken over by a group that flies indoor R/C and they have no regard for people trying to fly rubber powered light weight models.  Haven't flown indoor in years.  Ron (another grumpy old guy)
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Olbill
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« Reply #26 on: January 09, 2012, 12:31:21 AM »

Fred and Mike
For joints between carbon rods I usually use CA. Acetate glues would probably work okay but the contact area is so small that I feel better with a glue that makes a little bit of a fillet. End to end joints like at a dihedral break work okay with CA but if you don't feel confident with the joint you can add a little carbon tow across the joint.

I'll have to check my plan tomorrow but I believe my LPP wing has the tubes 3/8" from the centerline.

Btw - the LPP did a no-touch 17:54 at Tustin on Dec. 30.
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mkirda
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« Reply #27 on: January 09, 2012, 09:06:01 PM »

Fred and Mike
For joints between carbon rods I usually use CA. Acetate glues would probably work okay but the contact area is so small that I feel better with a glue that makes a little bit of a fillet. End to end joints like at a dihedral break work okay with CA but if you don't feel confident with the joint you can add a little carbon tow across the joint.

I'll have to check my plan tomorrow but I believe my LPP wing has the tubes 3/8" from the centerline.

Btw - the LPP did a no-touch 17:54 at Tustin on Dec. 30.

Hi, Bill.
A couple other questions if you don't mind.

The tip plates are off I think on both the stab and wing.
Wing chord is 5", but tip plates are 5.25". Stab is also over-sized by 0.25".
I assume that you meant that the stab tip plate top is 1" less and wing tip plate top is 1.25" less. (i.e. 1" + 3" for stab and 1.25" + 3.75" for wing.)

How much offset and droop for the tailboom? Any stab tilt?

And if I'm reading this correctly, you used stacked 0.020" carbon for the wing, but single for the stab?

Can you also describe how you apply thin CA so sparingly? I'm thinking two thin wires (maybe 0.015 or so) put maybe 0.010" apart (Think two tined fork) dipped into CA might be the right way?

Thanks in advance.
Mike Kirda
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Olbill
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« Reply #28 on: January 10, 2012, 01:25:58 PM »

Mike
I've just added a new plan to the plans gallery that will answer most of your questions. Here are some quick answers:

Tailboom droop is 3/4".

Stab tilt is approximately 1/4".

Boom offset for left turn is approximately 1/4" (I almost always use left rudder on my models in addition to stab tilt).

Wing is washed in about 1/8" on RIGHT side (to keep the right wing up in high torque launches).

Wing offset is 1/4" from center line of wing. I'd rather my models fly with a left bank than a right bank so I don't ever use a lot of offset.

Not shown on new plan: wing posts are mounted on opposite sides of motor stick to give left thrust (front post on right side of stick)

The tip plate dimensions are correct. The wing and stab are glued to the tip plates with 3/4" spacers underneath and the extra material is cut off as shown on the new plan.

Yes - two .020 rods stacked for wing spars and single .020 rods for stab spars. The doubled spars are tacked together at 4 or 5 points with thin CA and then glued full length with thinned Duco. The ends of the ribs are cut to match the spar heights. There have been other ways suggested for doing the wing spars but my new wings will be built per the plan. I also tapered the wing spars slightly toward the tips with a sanding block to remove a little bit of weight.

There are a number of different schemes for applying CA. I just use a single piece of wire around .015 to .020 thick. I dip it in a puddle of CA with the wire horizontal and then when I hold the wire in a vertical position a tiny bit of CA will run down to the tip. The way you are suggesting is fine but probably will give a larger drop.

The motor stick dimensions shown on the new plan require a really exceptional piece of wood. You will probably be better off with a little taller cross section. Before any shaping was done this motor stick took 800 grams of load in a column test.
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Tapio Linkosalo
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« Reply #29 on: January 10, 2012, 01:36:55 PM »

Wing is washed in about 1/8" on RIGHT side (to keep the right wing up in high torque launches).

The motor stick does not twist, so that at launch the wash would be "normal"?
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Olbill
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« Reply #30 on: January 10, 2012, 01:58:25 PM »

Mike
See Reply 16 here for the tip plate technique I use.
http://www.hippocketaeronautics.com/hpa_forum/index.php?topic=2191.0

Tapio
I've never seen a motor stick that doesn't twist! I think your statement is correct - initial torque increases washin on the left side and decreases it on the right side, so having a little washin on the right helps prevent the right wing from going negative and tucking in on launch. For me this can cause either a death spiral or racing around in circles and wasting the launch torque. F1D's don't seem to suffer from this malady as much as the models I fly.

Actually extreme high torque launch behavior is normally only important in the highest of sites. For this LPP in a site like Tustin or Lakehurst I want the nose pointed up in an aggressive climb as soon as the model leaves my hand. The same goes for A6 (see the Tustin video for proof).
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Tapio Linkosalo
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« Reply #31 on: January 10, 2012, 02:47:50 PM »

About the stick twist: to my understanding it is a common practise for models with a stick (instead of a tube), like EZB, have some "inverted warps" when at rest, to reach a proper amount of wing wash (washin on left) for the flight. Moreover, I have found that the twist of the motorstick helps the initial trim; my F1D's do that, and the increased washin at high torque prevents a roll to the left, followed by sideslip and flying straight to the wall, as the increased wash on left wing also adds drag and turns the model to the left. On the opposite, my old F1M has a too stiff tube, which makes it difficult to launch in a small hall (and it even limited my max launch torque in Belgrade), as lack of twist does just that left sideslip which keeps the model flying straight. It often does not last two long, but still makes launching difficult, if the model flies even one or two circle diameters straight, you really need to figure out the right starting spot to be in the right position when the model eventually starts to turn! Incidentally, I witnessed quite a few people running with the steering rod behind their models at the EuroChamps last summer, so the initial trim problem seems to be common even with F1D models?
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Olbill
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« Reply #32 on: January 10, 2012, 04:52:50 PM »

Tapio
Agreed on all points - except I don't have any kind of launch problem with my F1M.

A condensed quote from Lew Gitlow's book:
"Your best friend may not tell you that you have to adjust...until you get enough washin on the right side and washout on the left side to compensate for the twist and avoid the tucking in of the right wing panel"
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Maxout
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« Reply #33 on: January 10, 2012, 11:02:38 PM »

It often does not last two long, but still makes launching difficult, if the model flies even one or two circle diameters straight, you really need to figure out the right starting spot to be in the right position when the model eventually starts to turn! Incidentally, I witnessed quite a few people running with the steering rod behind their models at the EuroChamps last summer, so the initial trim problem seems to be common even with F1D models?

Tapio, I'm finding that the high-torque washin adds a lot of drag, so I avoid it as much as possible. I'm getting proper turning at full torque by tilting the motorstick so that it flexes in some left thrust when tensioned. My bracing wires are taught only for the first 30 seconds on a quarter motor. I also have started using long noses (~3") with extension shafts to get the prop out as far as possible. This allows me to crank in as much left thrust as I need (my flying site is only 30' wide, so there is no margin for error). Because of the tight turning radius and poor flying conditions, I'm happy when I get quarter motor flights over 6 minutes. Pretty pathetic, really, but I reckon that in a wider building, a lot more is possible. Then again, in less turbulence, a lot more is also possible!
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Tapio Linkosalo
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« Reply #34 on: January 11, 2012, 02:32:57 AM »

Bill: My "current" F1M's were built in 2004 in Montreal, from the hobby shop balsa I bought there. The motor tube is way too thick, does not twist at all under torque. Hence my trim problems at the start. In comparison, my F1D tubes are from nice thin balsa sawn by mr. Benns, and they give me the twist I need. Nice turn right from the start.

Max: I agree that the twist of the wing in the start probably adds some drag, so it is not a good thing to have too much of that. But then, on the other hand, the initial high torque only last for a minute or so, and if during that time you need to chase the model and steer it every 15 seconds to avoid drifting to the wall, you also risk spoiling the flight altogether. In my opinion. Besides, if you tubes twist a bit, then you probably have a model which climbs with the wing twist "by the book", and cruises down with a flat, untwisted wing. Should make the latter part of the flight envelope more efficient?

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Olbill
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« Reply #35 on: January 11, 2012, 01:09:12 PM »

Besides, if you tubes twist a bit, then you probably have a model which climbs with the wing twist "by the book", and cruises down with a flat, untwisted wing. Should make the latter part of the flight envelope more efficient?

For sure! (at least I think so)

What makes this such a maddening problem to figure out is all the other things that affect the flight efficiency in a negative manner like wing offset, left thrust, stab tilt, stab wash, etc, etc. Sometimes you just have to do things that might not seem correct in order to get the darn thing to fly.
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jakepF1D
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« Reply #36 on: January 11, 2012, 01:39:51 PM »

Torque is an evil mistress.  Necessary to climb, but a pain to control.
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mkirda
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« Reply #37 on: January 17, 2012, 09:04:16 AM »

Hi, Bill.

Can I assume that you use normal side cutting pliers for cutting the carbon? Or do you use a cutting wheel on a rotary tool?

Regards.
Mike Kirda
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Olbill
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« Reply #38 on: January 17, 2012, 11:52:14 AM »

Mike
For .020 or smaller I just use a single edge razor blade. For larger sizes a cutoff wheel is probably best to keep from splintering the end of the rod.
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mkirda
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« Reply #39 on: January 18, 2012, 09:04:54 AM »

Thought I would share my experience.
I experimented last night and found that side cutting pliers work best for me.
Single-edge blades sever quite violently - if a structural joint is nearby, it fails.
With the pliers I can cut the 0.020 rods a little proud, then wet slightly and sand with 400 grit paper.
It cleans up quite nicely.

I have the main components for this plane framed up and should have it up in the air within two weeks.
Thanks, Bill, for sharing your experience and design.
Getting back into the hobby, this thread has been quite helpful.

Regards.
Mike Kirda
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Olbill
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« Reply #40 on: January 18, 2012, 10:32:38 AM »

Mike
I'm glad to hear that you're trying the model. Keep me informed on how it goes.
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Tmat
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« Reply #41 on: January 18, 2012, 11:35:34 AM »

I've used nail cliipers with good results in the past. You can get very close to the exact area you want to cut and they are small and easy to handle.

Tony
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F1B guy...
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Olbill
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« Reply #42 on: January 18, 2012, 07:15:51 PM »

Yeah - I used to do that also but forgot about it. They're especially good for clipping off little stray ends of rods.
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mkirda
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« Reply #43 on: January 18, 2012, 11:44:29 PM »

Mike
I'm glad to hear that you're trying the model. Keep me informed on how it goes.

It seems to me that this design is faster to build in many ways than standard wood pennyplanes.
Covering using Super 77 spray and film was simpler than I imagined - just do not cut it with scissors!
Use a soldering pen.

Only real question is how to clean the soldering pen afterwards...

I hope to have it flying at the next Bong Eagles session (early February).
Hopefully the last question - What do you use for wing posts? Standard 1/16" round balsa or do you go carbon here as well?

Regards.
Mike Kirda
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Olbill
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« Reply #44 on: January 19, 2012, 01:52:32 AM »

On my two current motor sticks I'm using bass for the wingposts. Hard balsa is the usual material. I think I bought 1/16" bass dowels for the posts.
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Maxout
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« Reply #45 on: January 23, 2012, 10:32:30 AM »

Bill, have you investigated carbon posts? I've been thinking about this a lot lately... To get the necessary stiffness on my LPP, I'm using hard 3/32 round, but I know that has to be producing a lot of drag. I'd think that you could get the posts down to .040 or so wide with the right materials, but that could be a pipe dream with my high-mounted wings.
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Olbill
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« Reply #46 on: January 23, 2012, 01:26:10 PM »

Yes but I didn't like the tiny tissue tubes. I also found that getting a fit that was adjustable without being too loose was difficult.

Carbon rods are also pretty heavy. If I did the math right 6" of 1/16" round 18# balsa weighs about 85mg. 6" of .040" carbon rod weighs about 175mg.
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mkirda
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« Reply #47 on: January 23, 2012, 11:21:10 PM »

Well, I'm done with it. ~3.6 grams without really trying to choose the wood. I know my motor stick is way overkill as are the 0.050 carbon rods used for the wing posts.
This is an easy plane to build. Will see how it flys on Thursday hopefully.

Regards.
Mike Kirda
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mkirda
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« Reply #48 on: January 26, 2012, 11:43:51 PM »

Will see how it flys on Thursday hopefully.

It flew beautifully right off the board. Best flight so far under 23 foot ceiling, 4:42.
My last flight drifted into the wall and hung on the score board at over 3 minutes -
it would have been over 5 minutes based on the flight profile.

Regards.
Mike Kirda

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Olbill
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« Reply #49 on: January 27, 2012, 06:44:30 PM »

Good job mike!
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