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Author Topic: New Limited Pennyplane (mostly)  (Read 22905 times)
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Olbill
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« on: March 31, 2010, 04:26:10 PM »

At the Pikes Peak Ceiling Climb I destroyed my number one LPP wing by sticking my steering pole through it - which happens to me fairly often. My backup wing was a completely different design but seemed to actually perform better. The sub wing is based on the Steven Richman Open Cat 4 record holder except with a carbon rod LE and carbon rod tip plates.

Also, my Open Pennyplane - which is a tandem using 2 LPP wings - has been wingless for a couple of years. This led me to building 3 new wings and a couple of new stabs. Since I try to not ever do the same thing twice I decided to try a different structural approach. The spars for the wings are 2 .020" carbon rods stacked vertically. I tacked them together in a few spots with CA and then filled the joint with Duco, wiping most of it off before it cured. This put my spar weight at about .28 grams each. I taper sanded the thickness of the spars and finally wound up with six spars that weighed .248 grams each. This is a little lighter than the .030 tubes I use on my F1M wing.

Tip plates were made from .020 rods split to a little over half their original thickness. Ribs are .059" thick x .054" high 4.6# balsa.

The new stabs have .020" rod LE and TE. Ribs are .050" thick x .040" high from 3.9# balsa. I'm not sure the .020 rods are stiff enough for the spars. Time(s) will tell.

Uncovered weights so far:
wing frame .59g
stab frame .22g

More to come.............
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New Limited Pennyplane (mostly)
New Limited Pennyplane (mostly)
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Tapio Linkosalo
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« Reply #1 on: April 01, 2010, 02:14:33 AM »

The spars for the wings are 2 .020" carbon rods stacked vertically. I tacked them together in a few spots with CA and then filled the joint with Duco, wiping most of it off before it cured.

How good does Duco hold onto carbon, would CA throughout be better, or is it too heavy?

Is there a reason to make the spars from two pieces, instead of starting from a larger one and then cutting down one piece to desired dimension?
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Olbill
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« Reply #2 on: April 01, 2010, 10:45:12 AM »

Here are some pics of the first wing and stab on my old fuse. The weights came out like this:

spars 2x.020 carbon rods tapered slightly at ends .247g avg. each
ribs 4.3% 14”R .059" x .054"h. 4.6 pcf - avg. wt. .091 g for 5
bare frame wt. .587g
covered .631g
tip plates split .020 rods 3” high
frame wt. w/tip plates .772g
w/tubes .792g

stab spars .020 rods
stab ribs 18”R .050 x .040h 3.9 pcf . - 044g for 5
frame wt. .215g
covered .237g
tip plates .010 rods 2” high
frame wt. w/tip plates .299g
w/tubes .307g

Tapio
Well you've just made me feel pretty stupid! I hadn't considered starting with an .040 rod and stripping it to a smaller size. I actually don't think I have any of those right now but it sounds like a good idea for a future build.

I think full span CA would add too much weight. I haven't tried it so I can't say for sure. Duco seems to get a pretty good grip on carbon rods. I used Duco for the rib to spar joints throughout. For the tip plate attachment and the tissue tubes I use thick CA.
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Tmat
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« Reply #3 on: April 01, 2010, 12:27:27 PM »

Very nice Bill!

I know that there are carbon half rounds available, but I think that they are still a bit too big for this application.

So I assume that the vertical tip plates are used to make the low aspect ratio wing more efficient (make it seem to be higher aspect ratio) act like dihedral and take the place of a vertical stabilizer?


Tony
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Olbill
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« Reply #4 on: April 01, 2010, 01:10:16 PM »

Tony

It's very easy to split rods into smaller pieces. I just use a single edge razor blade. The fibers are very straight and you can usually get a very uniform cross section. This provides a method for getting in between sizes. In the case of my wing tip plates I feel like .010 rods are too fragile. An .020 rod is 4 times as heavy so using a half rod gives me double the material in an .010 rod.

Yes on all counts to your tip plate questions. I've been flying this type model in a few different classes for most of my indoor career. It started with early Science Olympiad models because the flat wings are so much easier to cover when paper is specified. The tall tip plates on this model and my F1M are direct descendants of Steven Richman's Cat 4 LPP record holder. I don't think this design is a good fit for higher aspect ratio wings like F1L or for classes without minimum weight rules like EZB or F1D.

For Mylar covered models I don't think there is a building advantage to flat wings because building and attaching the tip plates is a more complicated task than putting dihedral breaks in a conventional wing. Whether there is an aerodynamic advantage is an open question. My F1M has certainly proven itself and Steven's Cat 4 LPP record may stand for a long time.
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« Reply #5 on: April 03, 2010, 01:43:45 AM »

Can I tag onto one of your threads again, Bill? I'm staying totally on-topic!

Here is my first real indoor model. First time covering with condenser paper, not that I've done much covering of any type. The model is a Lew Gitlow "Time Machine."

This is almost 50% overweight, but I don't feel too bad about it, since it generally came out OK, and my first effort. Plus, it shows definite signs of flight in the living room. It will get its first real flights in a low Cat II gym next weekend. Hopefully I can keep it together and out of the speakers etc. near the ceiling (assuming it ever gets that high!) I'll have 4 propellers to try. The two completed ones have slightly different pitches. One is pretty much per plan; the other has a slightly lower pitch to make sure the plane will climb since it's overweight. I obviously saved the good balsa for the last and biggest prop. All of the blades weigh about the same so that the CG won't move as I try different props.

--Bill
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Olbill
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« Reply #6 on: April 03, 2010, 03:24:34 PM »

It looks nice Bill and should fly well. FYI my wings use 5 ribs to your 11. Also switching to Mylar would save a lot of weight.
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Olbill
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« Reply #7 on: April 10, 2010, 07:28:14 PM »

The model pictured in Reply #2 had its first 2 flights today. With less launch torque than I usually use it slammed the ceiling and broke a tip plate on the first flight. The second flight with still less torque was near perfect for 8:34 - my second best ever in Cat 1.
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« Reply #8 on: April 11, 2010, 03:36:31 PM »

Congratulations, Bill! That's great.

My model tried to have its first flights yesterday. All I can say is that it is still intact, and I'm not sure whether that is a good thing.
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Olbill
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« Reply #9 on: June 02, 2010, 11:33:13 AM »

Update on the new LPP:

At Kent State on April 24 there were problems from wing twisting on launch. I got beat at the end by Leo Pilachowski. Upon inspection afterwards I discovered that the motorstick had gone mushy in the front. A new motorstick that was much stronger seemed to cure the problem. A week before USIC the model did 3:48 on a quarter motor at a max height of 23'. This indicated a possibility of 15 minutes at USIC.

At USIC on Saturday before the LPP event a worn half motor flight topped 7 minutes and again showed promise for good results.

The next day my first official flight at an overly safe launch torque was 12:25. The next flight drifted into the scoreboard wires while cruising at the the top of the dome. It slipped off the wire at the top of the scoreboard and continued flying for a 13:12 after losing 50' of altitude. A little less launch torque on the next flight got a 14:39 which was my best ever LPP time. Bumping the torque for flight #4 yielded a no-touch 15:22 which at that point was the best official flight in LPP at USIC in over 10 years. At this point I put the model away and switched to F1M.

As the contest was nearing the 3:00PM cutoff for launches I learned that Tom Iacobellis had logged a flight of nearly 16 minutes. While my F1M was in the air for its second flight I got out the LPP and wound it a little tighter for a last attempt. Evidently the air had changed slightly in the couple of hours between flights 4 and 5 and I didn't get all the way to the girders where I wanted to be. The model still did 15:20 but left me in second place.

In all 5 of my official flights my only contact with the building was when I hit the scoreboard wires. This is the best LPP I've ever had. It gave me zero problems. It's very easy to reproduce. Now maybe for that Lakehurst trip.......
« Last Edit: June 02, 2010, 11:46:18 AM by Olbill » Logged
Tmat
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« Reply #10 on: June 02, 2010, 03:09:41 PM »

Well done Bill!

So that's the plane shown in the photos in this thread? With the carbon leading edges and the tiplets?

Does LPP require a solid balsa motor stick?

Tony
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Olbill
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« Reply #11 on: June 02, 2010, 04:07:45 PM »

Tony
Yes it's the same model except I changed the motorstick. All wing and stab spars are carbon rods. Yes, in LPP the motorstick has to be one solid piece of wood, and the same goes for the tailboom. There are no other material restrictions.
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« Reply #12 on: June 02, 2010, 06:36:33 PM »

I've heard some grumbling from some parts about the use of carbon rods for a limited pennyplane. Not in the spirit of the rules and all that rot. Somehow, I like the idea! Should be simpler to get consistent material (specific stiffness) without resorting to buying indoor balsa in bulk. And should be tougher too!

Tony
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Olbill
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« Reply #13 on: June 03, 2010, 12:14:42 AM »

Yep - I'm pretty sure I know who's doing the grumbling. Interesting though that a Canadian complains about the AMA rules.
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« Reply #14 on: June 03, 2010, 01:12:23 AM »

 Grin Cheesy Shocked Wink
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« Reply #15 on: November 05, 2010, 11:23:37 AM »

I thought that I had done a write-up on my latest LPP prop but apparently got too involved in preparing for Lakehurst on Labor Day (which didn't go well). Anyway here are some pictures of my new prop for real high ceilings. It's almost the same as my other props except the blade is set farther back on the spar for less flare. This prop proved that a flaring prop can still climb too much at Lakehurst!

The first picture is the heart of the prop - my "secret" carbon rod hub. The hub consists of 4 .020 carbon rods 5" long. These are glued to the sides of a 1" long piece of 1/16" square balsa with thin CyA. After curing the corners of the balsa are sanded off to remove some wood and excess glue. The prop hook is inserted thru the balsa, bent over at the front and glued with thin CyA.

The blades will be inserted into the space between the rods that is parallel to the prop hook. To get the required pitch the hub can be twisted slightly before a light finish coat of CyA is applied to the wood.
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Re: New Limited Pennyplane (mostly)
« Last Edit: November 05, 2010, 11:39:19 AM by Olbill » Logged
Olbill
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« Reply #16 on: November 05, 2010, 11:31:41 AM »

The blades are from .030" 4.5 pcf C-grain balsa from Indoor Model Supply. Two sheets had to be joined lengthwise to get the required width. The blades are 5.25" long and 2.125" wide. The first picture shows the blade blanks, then the blanks with paper patterns glued on with a very light spray of 3M77 on the paper only, then the blades cut out and sanded to the outline shape, then the finished blades before very light tapering and airfoiling on the edges. After finish sanding the blades weighed 290mg each.
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Olbill
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« Reply #17 on: November 05, 2010, 11:46:51 AM »

Here are the parts required for forming the blades. Top left is the blade itself which will be soaked in water for about a half hour. Top right is my trusty and well used prop block built about 10 years ago. Bottom right is the camber form that goes next to the block. Bottom left is the cover plate to protect the blade and keep it in contact with the camber form and prop block. The camber plate and cover plate were actually made for a different shape blade but worked okay for this one. Normally the camber plate will be about the same size and shape as the blade and the cover plate will be the same shape but slightly larger all the way around.

The second picture shows the whole assembly ready to go in the oven. My wife's new convection oven has a lowest temperature of 170 degrees so that's what I use for baking parts. I leave the assembly in the oven for about a half hour.

For thin blades for F1L or EZB I usually stack both blades together for baking. I did the LPP blades one at a time.
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Olbill
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« Reply #18 on: November 05, 2010, 12:05:47 PM »

Here's the finished prop. I didn't make pictures of the attachment process but here is approximately how it was done.

I put the hub in my pitch gauge, inserted the blade between the carbon rods and propped the blade up on the adjustable part of the gauge with the blade at the proper angle. I tacked one rod to each side of the blade with CyA. Then I pulled the tip of the second rod on each side against the tip of the first rod and tacked it in place. After I was happy with the pitch I used thinned Duco to glue the rods full length to the blades.

The hub can be twisted in the field to change or equalize the pitch if necessary. Also the amount of flare can be tuned by removing part of the wood in the hub for more flare or adding some thick CyA to the rods to decrease the flare. Note that these blades are not very flexible. Pretty much all of the flare takes place in the hub. This is important because field conditions of humidity or temperature have very little effect on the carbon rod hub.

There is another huge advantage for the carbon rod hub - it is almost impossible to break. The blades can be broken but a broken blade can be field repaired easily without having much if any effect on prop performance. My first prop of this type had a blade break a few years ago where there was only a small chunk of wood left glued to the spar. It is still in use and works as well as it did when new (see USIC results).
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« Reply #19 on: November 05, 2010, 12:13:28 PM »

What's the finished weight Bill?


Tony
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Olbill
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« Reply #20 on: November 05, 2010, 04:33:32 PM »

.84g
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« Reply #21 on: November 05, 2010, 07:07:09 PM »

Hi Bill - These LPPs look cool. I've never built one... thinking I might order some carbon rod and have a go at one of these down the track having seen your pics. Great info.

Tim
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Olbill
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« Reply #22 on: May 30, 2011, 05:27:55 PM »

The LPP flew perfectly at USIC this year. I finished in second place (again) with Tom Iacobellis finishing first (again).
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« Reply #23 on: January 07, 2012, 07:21:19 PM »

Hi, Bill.

I'm wondering how much offset there is in the wing? Looks to be roughly 1/2".
Also, when you glue the carbon on the tip plates, I assume you use Duco as well?
Never used carbon here, so not sure how to glue it together there.

Thanks in advance.

Regards.
Mike Kirda
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« Reply #24 on: January 07, 2012, 08:21:15 PM »

Can we readily cover a flying surface with C-fiber rod or tube LE and TE flat, then crack or cut the LE and TE and add dihedral? What adhesive is recommended for the dihedral joint?

I've built a few flat surfaces and some with vertical tip plates by following Olbill's instructions. Thus far, none have dihedral joints.

Fred Rash
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