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Author Topic: Limited Penny Plane "Big Daddy" -Build-  (Read 2821 times)
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Sundance12
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« on: October 20, 2009, 07:33:49 AM »

I have begun to draw out the design for a LPP based on an enlarged version of Alan Cohen's Minislick plan that is found in the plan gallery. What I liked about this design style was the curved motor stick that serves two purposes, one that it allows for room of a bunched up motor on the motor stick and second, that the tail is slightly lower than normal to allow for a lower wing on wing posts. Now all of this is an experiment, as the conversion to LPP from ministick makes this airplane shorter in length compared to a ministick. But I am happy with the overall layout and will begin to draw the wing and stab out next.

Here's to experimenting.

Sundance12
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Limited Penny Plane "Big Daddy" -Build-
Limited Penny Plane "Big Daddy" -Build-
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« Reply #1 on: October 20, 2009, 08:38:35 AM »

Lookin' good - I'm quite taken with the curved shape too (for purely aesthetic reasons) Wink
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Alan Cohen
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« Reply #2 on: October 20, 2009, 09:22:49 AM »

Looks good to me too. Another thing that curved motorstick might do for a limited penny plane that it won't do for a ministick is flex under full motor winds. Depending on how you distribute the meat of the motorstick, this will have the effect of either adding downthrust at launch, gradually decreasing as the motor torque burns off, or pulling the tail down for less incidence. Both scenarios will retard climb at high torque. Not a bad feature if you can get the flex right. Might be worth a little extra experimentation with static hooks on both ends and a full motor in between.
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Sundance12
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« Reply #3 on: October 20, 2009, 11:19:14 AM »

Thanks guys, glad to know that I am on the right track. Now, I have drawn in some downthrust in the prop hangar already, it's perhaps 2 degrees, is this ok?

The other thing that I was wondering about was the thickness of the motor stick and its requirement to be stiff. I see by Alan's comments that a degree of proper flex is perhaps desirable, so now I have to develop some tests to see how thick a motor stick is needed and how more or little downthrust I can incorporate in the pigtail bearing up front. I am going to find this design very interesting and challenging, now that's got me fired up.

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« Reply #4 on: October 20, 2009, 12:12:32 PM »

On the topic of downthrust, I've found it to be my enemy indoors. It's useful under higher ceilings, but in low ceiling, I do everything possible to minimize flexing. My current LPP has a deep flaring prop, so I can get away with a loop of 1/8 even in cat I ceilings (yes, it does bang around in the rafters a bit), but I can't launch with full torque because the excess flexing drives it into the floor. Wouldn't be a problem with excess climb, as the prop flare makes it go pretty flat for the first minute or so of the flight, then it climbs away nicely.

I've run into this exact same problem with ministicks, by the way. My current thought is that the best bet is to remove structure in overbuilt areas so that a thicker motorstick can be used without going overweight.
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« Reply #5 on: October 20, 2009, 12:39:07 PM »

Unless you're flying in very high sites you're not going to get a huge amount of bending in a LPP motorstick. For Cat 1 you'll typically be launching with torques around .25 in-oz which won't put a lot of stress on the MS unless you're flying on really short motors.

Most indoor flyers don't use any downthrust. The thrustline is normally in line with the hooks and the wing is set parallel to the thrustline. This will produce a nose high attitude that some think is beneficial in making the prop run slower. My personal preference is to set the thrustline in line with the hooks and use positive incidence in the wing. I think I wrote a bunch about this in the one of the threads I started.

Here's some data from my records for various ceiling heights. (the one with all the question marks is one of my typical last flight of the day scenarios where I have to throw all my stuff in the boxes and get out of the building to keep from getting yelled at by the organizers)
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Re: Limited Penny Plane "Big Daddy" -Build-
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Sundance12
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« Reply #6 on: October 20, 2009, 01:18:23 PM »

Ok I see where I am going to make changes, as I have only Cat 1 locations to fly in, so I will remove the downthrust angle, and I see that with the lower torques that I will be operating at I will have less motor stick bend than anticipated. All this input is priceless, and keeps me from going down development paths that are dead ends. So back to the drawing to make some minor changes.
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Alan Cohen
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« Reply #7 on: October 20, 2009, 01:44:29 PM »

Vote #3 for no downthrust. And since this is your first attempt, and an experimental design, I too think the motorstick should be as stiff as possible as not to influence flight profile too much. The only question is whether that is possible given an already curved motorstick. That would have to be some pretty stiff wood!
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Sundance12
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« Reply #8 on: October 20, 2009, 01:48:32 PM »

Ok, no down thrust it is, and I feel that I will have to choose the motor stick wisely, but I feel that what I will use will be fine. I am enjoying the collaborative input to these problems.
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« Reply #9 on: October 20, 2009, 03:03:02 PM »

Here's some data from my records for various ceiling heights.

Thanks for the data Bill, this data adds to my overall perspective and helps me to understand the relationships involved. I wish I was focused enough to track all that information but I will learn.
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« Reply #10 on: October 20, 2009, 03:08:01 PM »

Unless you're flying in very high sites you're not going to get a huge amount of bending in a LPP motorstick.

You should have a look at mine with a fully wound motor... Like I said, it's the limiting factor on how much power I can use. Back when I was using .090-.1 rubber, it wasn't an issue, but it sure is now that I've got a prop that can handle more torque.

This is probably all irrelevant to Bruce, though, as props with that much flare aren't going to happen without a carbon hub.
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Sundance12
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« Reply #11 on: October 20, 2009, 10:27:02 PM »

Further work on the plan, which includes the wing and stab planform. Not that much that is significant with these items other than the low aspect ratios that struck me as interesting. I had a bit of trouble deciding how much wing to have overboard to the left, or inside the turns. In the Minislick plan, there is no offset of the tail boom so I have planed to make the tail boom straight as well. Feel free to add any other inputs to my progress that you can think of.

I corrected the downthrust to zero and made the thrustline parallel to the hooks, while the wing has 2 degrees positive incidence and the tail I will attach at -1 degree.
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Re: Limited Penny Plane "Big Daddy" -Build-
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« Reply #12 on: October 21, 2009, 01:09:03 AM »

You might need a little tailboom offset to get enough left turn. I usually build in a little along with 1/2" or so of stab tilt. Also it's normal to use about 3 degrees of left thrust in the bearing. I hate friction so I've started doing that by putting the wing posts on opposite sides of the motorstick and turning the whole motorstick to the left. The wing and stab dimensions should be 18" x 5" and 12" x 4" per the rules. Smaller is okay of course but probably wouldn't be a good idea. Also watch out for the other two magic dimensions - 10" max from front of bearing to the rear hook and 20" overall length max including the prop.

Wing offset is a personal preference thing. Probably about 1" longer on the left panel than the right would work okay. In other words, from the midpoint of the wing your attachment point would be 1/2" to the right of the midpoint and you'd wind up with 8 1/2" on the the right side and 9 1/2" on the left side.
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Sundance12
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« Reply #13 on: October 21, 2009, 01:23:03 PM »

I will update the design with a bit of motor stick offset and some slight tail boom offset and some minor stab tilt. I am getting close to start building, and selecting wood. At this stage I am going to do the best I can with the wood I have and see what develops during the build.

I have followed all the recommended dimensions and allowances for props and such so it's all good there. I will re-measure the wing offset.
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« Reply #14 on: October 30, 2009, 10:01:43 AM »

After suffering all day with a headache, by 9pm things started to get better enough to get to the building board and do a bit more creating. I took time to lay out my plan on some blue foam building surface and cover it with a layer of plastic film that I had. On top of that is a wing form template that I made from pieces of 1/20th plastic that came from a big poster that I got from some office somewhere. This plastic is like styrene and all it takes is some scoring along a measured line and then this line is cracked to separate pieces as needed. It's great because you don't need to cut it straight through even the curved portions. I have used this in the past on other projects and really like it. In the last image is the sub rudder and almost complete stab outline. By this time it was nearly midnight and I refused to turn into a pumpkin... so I stopped there.

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Attached files Thumbnail(s):
Re: Limited Penny Plane "Big Daddy" -Build-
Re: Limited Penny Plane "Big Daddy" -Build-
Re: Limited Penny Plane "Big Daddy" -Build-
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« Reply #15 on: October 30, 2009, 01:09:31 PM »

I'm glad to see you're finally getting to the building part of this project!
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Sundance12
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« Reply #16 on: October 30, 2009, 03:31:23 PM »

Thanks Bill I will try to keep things moving along, I feel like I am building tooling as much as building an airplane with this project. However, the templates will be good for a number of airplanes in the future. Glad to have you follow along.

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« Reply #17 on: October 30, 2009, 09:10:48 PM »

I actually think you're gonna need new templates with not so many ribs but for LPP you'll probably be okay. It will be a very unique looking ship if you stay with the curved fuse.
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« Reply #18 on: October 31, 2009, 02:32:16 PM »

I have made some progress on the Big Daddy LPP wing today and it is going ok, I am getting a feel for how small some of these wood dimensions are and I am going to take some time to learn to slice really thin wood. so far working with .060 leading and trailing edges is interesting, let alone getting them to 0.045 for the stab. The first image is with the outlines installed and the tips curved from soaked wood. This technique went ok, I mucked with the strips and the water for a while then got to wrapping them around the form and pinning them down. In the second image, the ribs are installed. These are typical sliced ribs from 1/32 and I know I could have made them from slightly thinner wood but with my first attempt I just completed the task. The wood for the rudder is a little too large and I did end up changing the front leading edge with thinner wood as the original piece did not hold its shape at all. Over all I am not too worried about weight, I did weight and classify my wood to 5 lbs cubed and hope that is ok.

So later I will lift the wing and see how it all comes out.
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Re: Limited Penny Plane "Big Daddy" -Build-
Re: Limited Penny Plane "Big Daddy" -Build-
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« Reply #19 on: October 31, 2009, 04:10:01 PM »

The more I work on this plane, the more this curved fuselage intrigues me, should be interesting to say the least.
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« Reply #20 on: October 31, 2009, 04:19:26 PM »

Nice work so far Sundance. You might get me interested in building one myself.
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Sundance12
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« Reply #21 on: October 31, 2009, 04:28:34 PM »

Thanks Alan, I will certainly make the plans available, I will get them to Ratz and he scans them to PDF but I will prove this build first and then get you guys to try one. You will be able to make one finer than mine...
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« Reply #22 on: October 31, 2009, 06:21:23 PM »

Lifted the wing from the plan and it weights in at .085 grams that is with no film and no wing posts, I don't know if this is good or bad but the numbers are there. Next is the stab and it's completion.
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Re: Limited Penny Plane "Big Daddy" -Build-
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« Reply #23 on: October 31, 2009, 06:53:57 PM »

I think you mean 0.85 gram which will be okay.
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« Reply #24 on: October 31, 2009, 07:43:16 PM »

Hi Bill
Yes, I did mean 0.850 grams, and I am glad that it measures out ok.
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