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Feb 21, 2019, 03:07 PM
A Day @ a Time - Matt. 6:25-34
ruff1's Avatar
Will do sir. Back off work again until Monday, still trying to shake off this crud.
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Mar 09, 2019, 12:44 PM
A Day @ a Time - Matt. 6:25-34
ruff1's Avatar

Sorting Out Wing Mounting


Since the wing comes from Tony's Pirahna design, it has four holes where I used the standard nylon commode bolts and nuts for mounting. Stupid me, I did not salvage the Ply plate with the nuts from the carcass when I trashed it. A few minutes of cleaning up would have it ready for mounting in this airplane. Oh well...

I wanted to get the mounting sorted before completing the remainder of the fuselage. The nice thing about this design is the wing mounting and nose area piece will let me sort that out now. I can avoid banging the fuselage around by doing this first. There is a risk of getting the wing crooked, but I can do some trammeling to a reference line when gluing it up.

I did some component placement, and unless I cut a hole in the bottom part of the piece the servos will be too tall to fit. I still might do that, but also considering laying them on their side to allow for clearance; this will avoid compromising the piece too. I think I can place the servos fore and aft of a solid foam piece that runs from behind the aft bolt holes to in front of the fore holes. This should provide very good structural support for the wing. I have some Owen's Corning Foamular, which when placed allows for placement of the ply piece on top with nuts underneath. It might require a bit of thin foam to put it at the correct height. A channel will be pre-cut in the foam piece for the rudder push rod. Elevator servo will go behind the wing. Gotta review geometry on the rudder/nose gear servo so I get things oriented correctly. This time I want the servos in this area, not outside.

The receiver can be placed in the forward part of the piece.

Two pics included, showing the area where the foam piece goes and the wing mounting area. I think this will be just as strong as it was in the Piranha.
Mar 09, 2019, 02:10 PM
Registered User
Ruff1, just a comment about the servos...
If you lay them on their sides it may be difficult to get at the servo arm screws for any adjustment or replacement. That is why I chose to cut holes in the servo bay floor and mount them upright as in the photo below.
Fred
Mar 09, 2019, 03:00 PM
A Day @ a Time - Matt. 6:25-34
ruff1's Avatar
Yes sir, that is all I need to hear to mount them upright. Thanks for the tip!
Mar 09, 2019, 07:16 PM
A Day @ a Time - Matt. 6:25-34
ruff1's Avatar
I decided to layer some FFF pieces to fill in under the wing instead of the thicker Foamular. I glued a few of the pieces together to gauge how many I would need to stack. Since the rudder/nose gear servo is in front of the wing, I had to figure out where I needed to run the control wire that runs to the rudder. A couple of pieces together with a channel cut for a stir straw was just right. I went ahead and glued the stir straw as the control wire run through it to the servo arm was not binding.

I still need to get a steerable nose gear, so I'll wait a bit on sorting out the wire leading to that.

I installed the rudder / nose gear and elevator servos before gluing in the fill under the wing. This gave me a lot of room to install. Crossover to the left side of the rudder will probably be required.

Created the ply piece to epoxy the nuts, it will be glued to the top of the foam fill with space taken out for the nuts and bolts. This was the approach I took on the Piranha and it was very strong.
Mar 09, 2019, 09:17 PM
treefinder
springer's Avatar
Thread OP
Coming along! I'm with tic tac. I only lay servos on their sides in on wings where they are about same thickness as the kfm2 wing. Even there it is hard to unscrew the horns.
Mar 10, 2019, 08:13 PM
A Day @ a Time - Matt. 6:25-34
ruff1's Avatar
I did some math on the strip ailerons, they are very large. Probably because the Piranha is an aerobatic trainer. They are currently 19.3% of wing area, and I'm thinking that is way too much. If I take 13 mm off the trailing edge, that puts them at 15%. The threads I have found say a good percentage for strip ailerons is 10-15%. Even with this reduction, there should be plenty of authority.

I welcome your comments.
Mar 11, 2019, 09:42 AM
treefinder
springer's Avatar
Thread OP
I think I would leave them alone for a half inch of chord. You have sized/located the wing based on it's full chord. While traditional gasses used skinny ailerons to apparently good effect, foamies tend toward wider ones, and they seem to be fine for the weight/power conditions we now have.
Mar 11, 2019, 04:41 PM
A Day @ a Time - Matt. 6:25-34
ruff1's Avatar
10-4, that sounds like a good approach. I know I was over-controlling the Piranha at times, but a lot of time the handling seemed good. Just mediocre flying.
Mar 11, 2019, 04:51 PM
treefinder
springer's Avatar
Thread OP
Easy enough to put lower rates (reduced throws) on a switch when I am concerned about how "hot" a plane is gonna be.
Mar 11, 2019, 04:54 PM
A Day @ a Time - Matt. 6:25-34
ruff1's Avatar
I'll get some FB advice, we'll get it dialed in close enough so there are no surprises on maiden.
Mar 11, 2019, 06:15 PM
A Day @ a Time - Matt. 6:25-34
ruff1's Avatar
Well, I got lucky; several FFF pieces has the ply perfectly aligned with the top of the side pieces.

I cut holes in the piece immediately below the ply and glued it up.

Next will be setting up to trammel and align the wing. I don't know that this mandatory, but making sure the wing is on straight by using a reference point will avoid a flawed TLAR.


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