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Old Apr 29, 2012, 05:17 PM
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United States, TX, League City
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Build Log
Funny wing a 3 channel scratch build

OK. This is my second build thread. I am currently approaching the finish of another plane on a different site, so I thought I would do this one here.
I have had this 95% finished wing since about 1995-96. I scratch built it. My own design. It was originally built for a club weight carrying contest, .25 engines. The plane was never quite finished do to moves, retiring from the Navy, and halt to flying for a while, etc.
There was a logic to this very odd design.
First a little history and explanation of this ODD wing.
We thought the wings forward sweep would possibly be slightly more efficient.
Polyhedral eliminated a servo, and ailerons (three channel plane). A very small weight savings. It was also thought the polyhedral would help with turns over standard dihedral. At the extreme wing loading the planes had a tendency to start a slide side ways. Hence the big tips (paddles?). They are 2" wider than the rest of the wing. We thought they would improve turn stability at the extreme wing loadings.
I was originally going to name it “CARGOYLE”, for cargo and gargoyle. A pun on the looks and function.
So much for the theory and reasoning behind this wing. If we were correct or not, is still an unknown. The wing has never flown, EVER. Life interrupted.
The measurements
The span is 54" STRAIGHT ACROSS TIP TO TIP
The root chord is 8"
The tip chord is 10"
The tips are actually 9" each in span by 10" chord for a total 180sq"
The center section panels are 20" x 8" (x2) for 320sq".
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Last edited by greyflight390; Apr 29, 2012 at 05:24 PM. Reason: change thread type
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Old Apr 29, 2012, 05:18 PM
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United States, TX, League City
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So this is a three channel plane. Rudder, Elevator, Throttle.
It will be a tail dragger.
A very simple box forward fuselage, and an arrow shaft for a tail boom
The cargo box that would have originally been required will not be included.
Obviously the wing is done. Or 95% done (some very minor finish covering at the tips).
I have cut tail feather from 1/8” sheet balsa. Horizontal tail = 125sq”
Did not measure the vertical area. It just simply looked about right.
I am using a arrow shaft for the tail boom. I thought it was a carbon fiber shaft till I started cutting it, and found out it is aluminum. Darn well I think it will still be OK.
I have epoxied the stab to the arrow shaft. Just waiting for the epoxy to dry, Then I will epoxy the vertical to the stab.
I have a firewall cut out of ¼” hard ply (aircraft 5 laminates).
I now need to cut out fuse sides, tops and bottom. I will use some 1/32 ply for fuse side doublers. That will be strong enough for the .25 engine.
The fuse box will only extend from the wing center section trailing edge forward. It may need to be a bit long in the nose to get the correct balance on this forward swept wing.
I calculated the cg Should be at the leading edge of the wing AT THE CENTER SECTION to achieve a true 33% cg. Due to forward sweep. If this wing was a straight wing that would put the cg at or just forward of the spar at 33% of chord.
I will measure and calculate it one more time, before I finish the fuse box.
I am going to glue the front of the arrow shaft to the bottom of the fuse (on the inside).
Here is a very rough drawing.
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Old Apr 29, 2012, 08:33 PM
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United States, TX, League City
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The tail boom and tail feathers are done and epoxied together.
The firewall is cut out. Need to drill the mount holes.
looks like it is time to start making some fuse sides and then add the ply doublers.
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Old Apr 30, 2012, 02:04 PM
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I just did a double check of were I think the cg should be.
This is how I went at it. If this was normal non swept wing, then the cg should be at roughly 30%-33% back from the leading edge, or at or just forward of the spar.
Since the sweep is even I picked the mid point span wise and on the spar of each panel, and measured straight across to the wing center section. The intersection of that line and the center of the wing span is were I think the cg should be.
There is a mathematically better way of saying what I did. But for the life of me I have no idea how to say it in those terms. Would love to hear some one chime in and correct or concur with my reasoning.
The fuse side doublers are epoxied to the fuse side. And the fire wall and fuse sides are joined.
I mounted the engine to the fire wall and laid the wing on top of the fuse. I also laid the tail feathers and boom on the fuse in the location it will be glued at. I then found that balance point and shifted the wing, and checked again. The actual balance point is at the wings center leading edge. It doesn't seem right but I think it is. We are so used to straight wings and balancing at the spar.
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Old May 01, 2012, 07:46 PM
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Need to finish off the fuse.
Here are a couple of pics. I am just hold the parts together at this point.
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Old Dec 25, 2012, 07:42 PM
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It has been a while since I last posted on this thing. Other projects were worked on. And one plane finished and ready for test flight. My building situation became to crowded and cluttered With zero room to put any thing. So getting organized as best as I can in such a small area and cleaned up was the first order of business.

Then I resumed work on this plane. Made a fairing for the back out of $ tree foam board,paper off, to give some stream lining, and improve the looks a bit.
Then installed servos and nyrod linkages.
Put the engine on.

Now the kicker With gear installed I rechecked the balance. OH CRAP OFF BY 10 MILES. The wing has a forward sweep of 7" and with gear in the only place it could physically fit, it really threw the cg off.

Only solution was to cut the nose off. I then taped the engine and battery to a stick and started shifting forward till I hit my balance point. Then made nose extension. Now the cg is spot on at the LE of the wing center section. Wich if measured at the mid span point of the wing puts the cg at the main spar.
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Old Jan 06, 2013, 03:23 PM
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I ended up giving up on the tail boom. I originally thought the arrow shafts I bought were carbon, but when I cut into one I found it was aluminum. Decided to go with it anyway. Well that was a mistake. It bent before I even finished building the darn plane.
It was very flexible. I was none to sure it was flight worthy and after some checking I found that was bent.
I went to the sporting goods store to get a REAL CARBON shaft, and they only had them in boxes of 6 or more and far more than I was willing to spend.

SO OFF WITH IT'S TAIL.

I cut off the arrow shaft and the remove the tail feathers from it. I then made a new aft section out of balsa and glued the tail feathers back on. Still have to glue the blue outer down.

Put the radio back in, and the motor back on. With landing gear on and wing on time to recheck the cg. Ended up really close to the desired point. Pleasant surprise that!

Some sanding (maybe a bunch) then cover the body. Repair the really old Monocote on the wing that is coming loose.

What a pain in the hind quarter this thing has been.

My wife thinks it looks a lot better this way. I tend to agree. And it sure is a lot stronger. with no appreciable weight gain.

Ken
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Old Jan 06, 2013, 03:31 PM
The Prez....... again
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United States, IA, Rockwell
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Do you ever let the missus out of the chair? LOL

Looks good with the "real" fuse on. It will be an interesting experiment!

Ken (the other one)
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Old Jan 06, 2013, 03:56 PM
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Quote:
Originally Posted by kenh3497 View Post
Do you ever let the missus out of the chair? LOL

Looks good with the "real" fuse on. It will be an interesting experiment!

Ken (the other one)
Are you kidding? She sits there and tells me what to do and I go Yes Ma'am
Just kidding.

Thanks Ken
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Old Jan 06, 2013, 04:30 PM
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Hey Ken I let her out of the chair!!

Actually she had a stroke a few years ago and so sometimes for her holding a plane and reposing it takes the 2 of us to do safely.
Less risk of me getting whacked by her cane if she is in the chair.

The first picture really shows the forward sweep. The spar sweeps forward a full 6 inches from center to tip. Other than the center and dihedral it is straight. No place else to measure sweep.

Ken
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Last edited by greyflight390; Jan 06, 2013 at 04:42 PM. Reason: Just adding an additional comment
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Old Jan 07, 2013, 12:06 PM
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Looks good...just keep plugging away..1 day she will be finished ( or Outt'a Code)
Pat
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Old Jan 07, 2013, 12:24 PM
The Prez....... again
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United States, IA, Rockwell
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Quote:
Originally Posted by greyflight390 View Post
Are you kidding? She sits there and tells me what to do and I go Yes Ma'am
Thanks Ken
Don't worry, you're not alone

Quote:
Originally Posted by greyflight390 View Post
Hey Ken I let her out of the chair!!
Less risk of me getting whacked by her cane if she is in the chair.
Ken
Ya have ta watch out for them canes, they hurt

Ken
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Old Jan 07, 2013, 01:29 PM
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The 'Wack, BC, Canada
Joined Oct 2002
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Greyflight, good call on switching to a box tail. From my own nearly disastrous experience the last thing you want is a tail boom with some flex in it. It leads to the tail and wing arguing badly and crashing in the confusion. I darn near lost one model that way. I got it down OK in the end and immediately used the existing carbon tube as a form for rolling some carbon tow and expoxy around to flesh it out to a thicker shape and increase the wall thickness. The result was that it became as stiff as a good golf club shaft. And that level of stiffness is my new "yardstick" for tail boom stiffness. If it ain't that stiff it don't go into the air. I don't need any more surprised like that.

Hurry up and get this thing finished. Spring is coming! ! ! !
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Old Jan 07, 2013, 04:30 PM
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United States, TX, League City
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[QUOTE
Ya have ta watch out for them canes, they hurt

Ken[/QUOTE]

No Kidding she has one that exactly matches the top of my head. OUCH!!

Just kidding but she does remind me how much reach she has with it.


Ken
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Old Jan 07, 2013, 04:41 PM
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Quote:
Originally Posted by BMatthews View Post
Greyflight, good call on switching to a box tail. From my own nearly disastrous experience the last thing you want is a tail boom with some flex in it. It leads to the tail and wing arguing badly and crashing in the confusion. I darn near lost one model that way. I got it down OK in the end and immediately used the existing carbon tube as a form for rolling some carbon tow and expoxy around to flesh it out to a thicker shape and increase the wall thickness. The result was that it became as stiff as a good golf club shaft. And that level of stiffness is my new "yardstick" for tail boom stiffness. If it ain't that stiff it don't go into the air. I don't need any more surprised like that.

Hurry up and get this thing finished. Spring is coming! ! ! !
BMatthews
When i was a teen I made some planes using arrow shafts and they worked ok. But thinking back on the they were .049 .09 sized.
What was I thinking? That is a .25 up front, yeah I will run something like a 4 or 5 inch pitch. That will keep the speed down.

Thanks for the tip. I may try to use an arrow shaft on something else someday even if just a wing spar. Now I know the limits and how to strengthen the shaft.

I mostly have 'coting the fuse left.
I want this thing done so I can get back to the original plane I was working on. That one is so close.
Then I have several designs floating around in my head.

Ken
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