1990s vintage LT40 build thread
Am going to build my first kit, an old LT40. Been sitting in the box in a barn since the '90s.
The piano wire is a bit rusty, but that's the only flaw I see so far.
I have gotten as far as spreading out the plans.
Planning on 5S on a 700 KV GEForce motor, with a 12 to 15 inch prop.
Maybe 14 is the largest that will fit, we'll see.
A 13x10 would probably give it unlimited vertical, so I don't need to go crazy on prop size.
Oh, I will be looking for the best way to convert it to a bolt-on wing.
2 pins and 2 bolts or 4 bolts, either way is fine with me.
Another Q- I'm sure it's easy, but for this plane is there a real advantage in putting a servo on each wing?
I won't be using the ailerons for flaps or such.
I'd have to go out and buy 2 servos (I'd like 'em to match if I did it that way), and funding is tight.
I have a LT -25 so it should be very close to your LT-40 other than size.
I made a rigid and structural cap over the leading edge of the wing instead of wing dowels. It seemed on my plane dowels through the front point of the leading edge would have been above the former. Maybe a tongue of plywood glued to the bottom of the leading edge, projecting through the opening in the former would work also.
I made the windshield part of the tank hatch, to make my life easier when changing batteries.
I only use 1, 1/4-20 nylon bolt to hold rear of wing down. Nylon bolts are stronger than many people think. I saw a wrecked plane where the wing tore the fuselage apart after the wing tip hit a post. The 4 bolts did not break.
I used pieces from the diecut sheets to refill the notches in the fuselage sides, that were for the nitro motor. My motor is mounted with nylon spacers from Home Depot, it is very solid.
The motor is a power 32 clone I bought a few years ago, on Ebay. I wish I had known how good a motor it is, I would have bought 3-4 more.
800kv on 4s 4400mah APC 12x6 prop. I get 850 watts. plane ready to fly with camera weighs 6 lbs. It will go unlimited vertical.
I started with 1 aileron servo in the center.After the first flights we found the plane glides so well that i moved the servo 1/2 width over and installed a second servo for flap function. It seems to help slow it down.
I also beefed the bottom of the fuselage just behind the trailing edge, for mounting floats.
Either the balsa pieces cut for the upper and lower spar doublers are too long, or the first rib past the doublers is cut wrong.
My doublers end right past the rib, the rib is cut to fit the spar with no doubler.
I just cut the rib notch deeper (didn't think to cut the top spar notch before gluing it in, though...). I think it is the first W5.
One wing mostly built, need to add rib W1, cut the dihedral, and cut off the excess spar on the tip end ... mulling lessening the dihedral, and bolt-on method.
Going to get the other wing to the same state then worry about the dihedral, I'll worry the bolt-on method after I have a fuse to hold it up against.
Check your stab mount area
My LT-25 developed cracks on both sides of the fuselage, from the bottom front corner of the horizontal stab recess, running forward and down into the lightening hole just in front of stab. This happened during a flight.
I have stripped the covering just ahead of the stab all the way around the fuse.
I am now in the process of wrapping some unidirectional carbon fiber around the entire fuse, overlapping it across the bottom.
lightweight fiberglass cloth would work fine also.
When I stressed the cracks, I realized the entire rudder/elevator could have possibly ripped off in a high speed loop or pull out.
Check your plane in this area, if it is designed the same as my LT-25 it may need some reinforcement. My fuse does not have any reinforcement pieces in the inside corners, so it is only the sheet sides at that point.
My rudder and elevator are held on by 3 bolts, to allow me to disassemble the plane for a much smaller traveling box, as I am going to start pulling my Airstream trailer all over the USA this summer.
I don't believe glueing them on, would have stopped the cracks from forming. Maybe delayed it but not totally prevented it.
Thanks for the heads-up on that. I'll give that area extra attention.
I am a constant wiggler of wings, motor, tailfeathers, etc after seeing some undetected cracks while doing some other repairs.
If I can wiggle it uncracked a few times, it's amazing how little it needs to be cracked for it to feel different.
I usually grab a wing and wiggle the Hstabs up and down (looking for a fuse crack), then grab the Vstab and one Hstab, try to move them towards each other and apart, then the same with the other hstab. I grab the prop or spinner and shake it like a terrier would!
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