|Jul 20, 2011, 12:10 AM|
Well, decided to repair the last P-40 after thinking about what could be done about it. This always seems to happen a few days after what looks like a total.
Tonight I hot glued the wings back up along the breaks. This was then covered, top and bottom with "Extreme" fiberglass packing tape.
While that gave a good attachment to the wings, it did nothing to increase stiffness. I found a strip of white pine I'd once ripped out, about 1/8" x 1/2" x 22" long, left over from making little planks for a dollhouse barn for my daughter.
I cut a slot in the fuselage just below the wing, at the leading edge -- 1/8" x 1/2" to fit the strip of wood, and threaded it through. I then glued it to the wing panels and fuselage flat. Because of a slight sweep back of the leading edge of the P-40, I shaved off the new spar to match. This gave it a long taper, which is good for evenly spreading out flying loads.
I don't know how this thickened leading edge will affect flight characteristics. Guess we'll find out. Kind of a micro KFM if it works out. Kind of a bad idea if it doesn't.
Here are some pix of the start of repairs. Bent up, but re-glued nose will also receive some wood reinforcement -- probably balsa sheet doublers. Then will touch up the paint -- flat camo is good at, well, camouflage. I'll just stipple it on with a brush
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|Jul 20, 2011, 08:15 AM|
I was flying it this morning, and it was flying level really well! However, after about 20 feet, it would keep nose diving. I don't think it has anything to do with signal issues, rather something else.
Before I could adjust the trimming, one nose dive broke the motor mount area AGAIN! Sheesh, this is so weak! Actually the parts where it broke previously remained intact as I reinforced them a lot. Now it cracked from another point on the nose, and the whole nose fell off again...
Oh well, I'm busy today, hopefully I can fix it tomorrow. Let me know how your repaired plane flies!
|Jul 23, 2011, 08:06 PM|
Haven't had a chance to fly or work on it again this week, but hoping to finish up nose repairs/stiffeners tonight and fly tomorrow.
astronaut, tough to know what you mean about flying well level, but diving after 20 feet. Can't picture it. Do you mean it flew level for 20 feet and then just dove in by itself?
Did it stall in or dive in? Was there wind? Was there a structural failure first?
If there was no control input change, no wind, and the plane didn't stall first, there must have been a radio glitch, or a control breakage, or control surface break, or shift in the thrust line to make it suddenly change direction like that.
|Jul 24, 2011, 10:59 PM|
To follow up here, I had my first really successful day flying the P-40. I added balsa doublers to the forward sections of the fuselage, and they really did the job of protecting the nose area in a hard landing and stiffening the previously creased area up front.
On first launch I found a real need for up trim -- as much as I had available on the transmitter, and even thn had to hold some up elevator to fly. However I was able to get in about 5 minutes of flying without problems. When I brought her in I decided to try to dead stick the landing to see how the glide was. Well it was very steep, but I figured I'd flare at the end.
No go, I had insufficient elevator authority to pull it out of a hard nose in.
The plane broke, but this time in a very different location than in the past. The nose area was completely undamaged, as were the wings. There was simply a clean snap itn the fuselage toward the tail. That was easily glued together at the field with 5 minute epoxy.
I then worked on the elevator authority problem. A quick check showed that the CG was too far forward, so I shifted the battery in the Velcro. I also increased the rates on the transmitter. I also checked the aileron alignment and noticed there was a little droop. So I re-bent the Vees in the control linkages to shorten them and move both ailerons up a small amount.
On second launch things seemed just a little better, but still I had to hold the stick back when flying. The landing was no better, and the fuselage snapped again in a nearby location to the last break. Out with the epoxy, and ten minutes later the plane was whole again,
This time I looked at the up-trim in the elevator. Not a lot, and I was at the the limit on my transmitter so I re-bent that control linkage to give more. It was at that point that a flying buddy noticed that I had moved the battery forward last time, instead of backward, making the forward CG problem worse. Duh!
So I moved it back 2 inches and checked the balance against the CG mark, and things seemed right on.
On launch this time things were greatly improved. I could trim for straight and level, I had plenty of elevator authority, and the prior flights had corrected roll trim. The plane flew finally in a controllable manner. The beefing up of the wings and nose had proven out through two hard nose-ins.
I did some fast rolls and some sloppy loops -- not sure why those were so loose since the plane has a good amount of power. It really seemed to slow on the up side, and was quite sensitive to being blown off by wind. But anyway, generally very satisfactory flying.
I did notice that the plane seemed a little nose -high at all times ,and so felt like it was wallowing a little. I felt like it could have gotten a lot more speed if the attitude was lower.
But I finally realized that the leading edge spars I'd put in had probably lowered the effective wing incidence -- since the midpoint of the thicker LE was now below the midpoint of the TE.
So the plane needed to fly at a higher attitude to get sufficient lift. Probably also these planes do this to some degree, even without a spar like mine. Since the wing is dead flat and set at 0 incidence, anyway. Mine might be a little exaggerated in trimming upward. A fair amount of up trim is needed to fly this plane and it will always look a little high in normal flight attitude.
Well it's a good flying plane now and looks good, too, in the air. I touched up the camouflage in the repaired areas, and they are practically invisible, now.
I want to re-iterate that Scotta's original design called for a carbon fiber spar set into a slot in the wing, and the two planes I built did not have this -- a fiberglass strapping tape stiffening was tried, based on the practice with combat planes outlined by Irone in the "No Fear" combat thread. I'm sure many of the problems I had were a result of this change. Actually, it may have worked if strapping tape had been applied across the upper surface as well as the lower one. My wings broke downwards from negative G's.
I do feel that the foam nose construction of this general type of combat plane is very fragile and susceptible to damage on anything but a perfect landing. There is no landing gear to protect it. But using 1/32" balsa doublers here makes a very sturdy and crash resistant nose structure. If I build one again, it will certainly have that from the start.
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