|Aug 20, 2010, 08:54 PM|
Guillows A1H Skyraider conversion <video added>
Video of maiden flight is here. http://www.rcgroups.com/forums/showt...1#post16149418
After the T-28 then having just finished an F6F Hellcat from Truckerboy's plan it's on to the next one.
This time we'll convert a Guillows Skyraider.
I have a few Vapor bricks hanging around so this model will be rudder/elevator like the Trojan.
Thought I would share the build this time.
The first step is to reduce the wing incedence. While fine for rubber free flight, it's too much for our purpose and will result in nasty throttle/pitch coupling.
Start by drawing a datum line on the fuse. Try to follow the centerline as close as possible.
Now is a good time to check the angle of the horizontal stab too. On this model it's flat to the datum line, cool.
|Aug 20, 2010, 09:01 PM|
Next up is to prep the parts sheets by sanding the heck out of the backside. Unlike the Trojan kit, the two sheets of wood that contain the side pieces were pretty well matched in density.
I sand off some of the wood thickness to reduce weight a bit keeping in mind every gram counts.
The side pieces were popped out of the sheets and the spar notch is 'moved'.
The new notch was cut and the original notch piece glued into the sides.
We can adjust the notches once we fit the wing into position.
|Aug 21, 2010, 08:57 AM|
There are always differences in the wood grain and density from one side to the other. This will make one side easier to bend. Assembeling the fuse in the usual way will almost always result in a bananna shaped fuse because one sheet side will bend and the other will try to remain straight.
So I build sheet side fuselages a little differently.
I find doing it this way makes it easier to get it perfectly straight.
Start by aligning the sides perfecly one atop the other then tape the tailpost together.
Next glue the first former on and allow the glue to dry.
Position the next former in line and glue it place, checking the alignment and that the fuse is straight and formers square to each other.
Add the next former. At this point if the fuse sides are starting the taper toward the tail I loosen the tape at the tailpost and glue the former in place.
Bring the tailpost back together and check for straightness. If you see the fuse is starting a bananna, adjust the tailpost by slinding one side forward/aft. This will bring everything back in alignment. Tape the tailpost back together.
Keep working back to the last former and once they are all in place and everything is straight, glue the tailpost together.
Next up, the lower fuse hatch.
|Aug 21, 2010, 12:12 PM|
Lovely, straight fuselage you have there. What is the "usual [fuselage construction] method" that you speak of? This is the same technique that I use for my builds also. It works great!
How did you decide on a new wing incidence? In what case would you adjust your horizontal stab also, changing the decalage altogether?
|Aug 21, 2010, 07:48 PM|
The "usual" method of gluing the tailpost together and adding one former to start then add the remaining formers bowing the sides as you go.
The amount of wing incidence is just something I've learned through trial and error. One or two degrees is plenty.
To much incidence will cause the model to pitch up as speed increases. You end up feeding in down elevator to keep it level. Adding downthrust and moving the cg forward are not the correct adjustments to compensate.
I set the horizontal stab to zero in relation to the fuselage datum line.
|Aug 21, 2010, 08:46 PM|
So excessive positive incidence in both the wing and horizontal stab will cause bad speed/throttle coupling?
Don't the full scales usually have a few degress of negative incidence in the horizontal stab to offset the lift of the wing?
Sorry for all the aerodynamics. I have never really looked at the decalage on any of my models, although I know that I should. I'd really like to learn more about incidence in the wing and stab and how they effect each other; that is why I ask all of these "boring" questions.
-PC49 (always up for an aerodynamics lecture)
|Aug 22, 2010, 05:10 PM|
Thanks PC49. At least somebody's watching....
On to the hatch.
I build the hatch in place, that way I know it fits!
I start buy making sub formers for the front and rear of the hatch.
A notch is cut in the center former for the hatch side rails to slide into.
A strip of balsa is cut that will form the side rails and it is slid through the notch in the middle former.
The front and rear sub formers are put in place and the rails glued to them.
Next the hatch stringers are glued into the former notches.
The middle former is split with a #11 and the whole hatch is cut free.
All that's left to complete it now are the front locating pins and the magnet retainer.
That's all for now on the fuse. It's done enough to fit all the other parts to it and will be finished last.
<sorry about the washed out pics, didn't need the flash>
On to the wings.
|Aug 23, 2010, 07:04 PM|
<tap tap> Is this thing on? Hello?
Started out built per plan using the kit parts.
Didn't think the rib/trailing edge connection was very secure so added gussets from ribs to TE.
I don't like sheet tips, not very strong and hard to cover without wrinkles. Made new ones out of 1/4" sheet and will shape into solid tips.
The plan calls out 1 7/8 dihedral, at each tip! That'll look goofy and is not necessary for a controlled flight model. Reduced the dihedral to 1" per tip.
Made a new dihedral brace cut to the new angle and full rib height. This will also be the 'landing gear spar" to carry the load to the fuselage. Another landing gear spar piece extends out to the next rib bay to support the gear mount ribs.
Another spar was added to help prevent the covering from bowing inward between the ribs at the leading edge.
That's about it for the wings. On to the tail feathers.
|Aug 23, 2010, 08:42 PM|
SoCal "The High Desert"
Joined Nov 2003
Interesting subject and incidence discussion.
I have found that a flat bottom wing is very sensitive to throttle settings on it's own, meaning that high throttle results in pitching up. I've also learned that raising the trailing edge of the main wing can/will cause a tail down flight path which isnt prototypical of the Skyraiders level to tail slightly high flight characteristics. Were you planning on incorporating a Phillips type entry on the lower leading edge? That really helps to tame down a straight flat bottom airfoil.
I'm not trying to poo poo your reasoning, and I'll be watching your build since I have a 900 series Chipmunk waiting for some attention.
|Aug 23, 2010, 10:09 PM|
Yes, I'll shape the leading edge to more of a Clark Y section.
That's one reason I like to use the rock hard kit balsa strip for the leading edge. There is enough strength there to remove quite a bit for shaping.
I use that airfoil on most of my models for the reason you mentioned.
|Aug 24, 2010, 01:52 PM|
Been away. Also lost my building privileges with a few home repair and improvement projects . By the time I finish the P-39 and P-40 you should have the entire 900 and 500 series complete .
Watching with much interest master, Maiden tomorrow?
Mark, the student hiding behind the desk hoping not to be called on .
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