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I was wondering,if I moved the battery and reciever. Maybe even the servos from the bottom of my Sig Lt40 to as close to the wing as possible would this increase the aerobatic ability of the plane.I am building a intermediate plane currently, this would be until the new plane is finished.I am,flying the plane now doing knifedge and other tricks, but the plane has a strong tendency to self right.I know that's the idea in a trainer. I would just like to minimize it appreciably if possible.

Crashem

1. Increase the control throws

2. Move the balance point to make it more tail heavy (carefull make it too tail heavy and that will be its las flight)

3. Cut the wing and remove the dihedral

flash over

I have increased the throws and moved the cg back the rear spec.Iguess I cold move it further.As for removing the dihedral,that's a big job for a possible no gain as I epoxied the wing together.

exeter_acres

My Feedback: (2)

Naw.... took a friend and me a couple hours and there is a BIG difference.....

Cut it in halve (the wing...mine was epoxied too)(table saw works well... I used a large miter saw!)

then lay the two halves on a FLAT table and use a straight edge to line them up...
we epoxied in a small piece of hardwood to the old brace,,,

then laid the wing upside down and used a bit of epoxy and tacked the edges together... once that had set...
we flipped the wing over...
cut out a few pieces of balsa to fill the gap. ..just enough so epoxy doesn't flow down into the servo area... then started filling the gap up with epoxy.... lots of epoxy!

epoxied a piece to the front... so I can still use the stock bolt down set up...

flies inverted well... more responsive on rolls, etc. etc.

really was easy (scared me at first, but I am glad I did it...OK, my buddy did most. Thank you!)


next we are going to epoxy some basswood sheeting to the ailerons and recover it so the control surfaces are larger


but the dihedral removal was fun!!

CRFlyer

I agree that removing the dihedral will be a big step in the direction your looking to go. Another mod, but more difficult would be to remove one wing bay from each half of the wing. With the shorter 'span, your roll speed would be quicker. Another thing you could do is to increase the area of the rudder a bit.

JohnBuckner

My Feedback: (1)

I would agree to most of the above but probably the single most significant mod you could do to give it that aerobatic feel is to attempt to approach that elusive nirvana 'neutral roll' stability. Eliminate positive stability (self righting) without dropping into divergent behavior. In other words its that often talked about 'stays where you put it' feel.

The way to do this is as above is to eliminate the dihedral but this only partially completes the job. With a high wing cabin or parasol type to achieve neutral roll it is neccessary to use anhedral (drooping wings). A mid wing airplane most nearly reachs that perfect point and a low wing usually will require some dihedral or other means such as wing bottom taper or the dihedral effect of wing taper to acheve that neutral roll effect. A low straight chord wing that is totally flat will be divergent (never stay where you put it and always rolling off).

As the guys have mentioned above it ain,t that hard to do, just go a little further and droop'em an inch or so at the tips. Looks silly and everyone will think you are crazy untill they see it fly. I,ve mod'ed a few various trainers for folks and one for myself and they all love it. Mine is lettered on the top of the wing "Dumbo"

John

flash over

Thanks Guys, anyone else.

britbrat

The LT-40 has relatively weak wings, so WHEN you remove the dihedral (not if), you should sheet the wings to the spar. It is also very beneficial to drop the wing into the cabin to bring the chord line closer to the thrust line. Use a dremel to cut ~ 3/4" - 1" out of the cabin top -- it is not very difficult & it has big benefits in flight performance. If you do this mod, you can reduce the downthrust by 1/2 -- & remove all right thrust as well, while you are fiddling with the firewall/mount. If you clip the wings, don't take much off -- the full span helps in inverted flight.

I assume that you are going to do it as a tail dragger, of course, & add lots of power as well (a good BB .46 will do the job nicely).

Trainers can be made into amazingly agile machines that still look like trainers -- real sleepers that can give an eye-popping show.

Rcpilot

My Feedback: (78)

Want to do it really simple and not screw up your wings??????

Buy a set of ARF LT-40 wings from Tower Hobbies and just cut a new dihedrahl brace from hard plywood for it. Leave around 3/4" --1.25" of dihedrahl in the wing. That will give you a huge performance boost. It will look droopy if you make a flat wing. You don't want a flat or drooped wing. It might work well on high performance planes and jets-- but a drooped wing or flat wing on your LT-40 is NOT going to fly well-- or make you happy. Leave a little dihedrahl in it. Just a little.

When you reduce the dihedrahl in the new wings from Tower-- your going to have a gap in the top of the wing. This is because the root ribs are glued in at the right angle for lots of dihedrahl. When you reduce the dihedrahl-- the seam at the top is going to open up.

You want to fix this gap.

option #1--just fill it with epoxy and allow the wing to dry while sitting flat on the table. Wipe it with an alcohol soaked rag constantly-- once it begins to kick off and cure. This will assure a nice smooth finish.

option #2--make your new dihedrahl brace from hard plywood or basswood. DRY fit the wing together and determine how big the gap will be. Make a little balsa fillet or lite-ply fillet and sand to the right angle. It's going to look like a long skinny traingle when your done.
Then glue your fillet in when your joingin the wing halves together. Wipe with alcohol soaked rag as it cures and slap a piece of trim tape over the joint if it bugs you.

It will cost you a few bucks to buy ARF wings from Tower-- but MUCH MUCH MUCH easier to do than cut your existing wing in half and re-glue it.

While your at it--- you got 2 new wing halves there----------cut the covering on the bottom of each wing and install a servo tray in each wing. Make it a 2 servo wing. Then you can have flaperons. Or you can do what I did and make your LT-40 wing with flaps and ailerons. Just cut the stock strip ailerons about 1/3 of the length and then use the insides for flaps and the outsides for ailerons. Then its a 3 servo wing. Use the stock ailerons servo location for your flaps servo and cut an aileron servo into each wing. Make the aileron servos right in the center of the ailerons-- so your gonna cut your hole and install the servo tray towards the 7th or 8th rib bay.

Make it a tail dragger.

You can install a small servo--like an HS-81 or an HS-225 and hook it directly to your tailwheel with a nylon linkage rod for really nice positive control. Use a Y-harness and run it into the same port as your rudder servo. Or plug it into it's own port and mix/slave the rudder servo and tailwheel servo together with your radio. Then you can set endpoints, centerpoints, and travel for each servo individually. It's a sweat setup.

When you set it up for a taildragger-- also add a rear mount for floats. Most floats have a front and rear mounting system. You can buy floats and use the main LG mount as the front mount for the floats. Then you just add a little plywood and some blind nuts to the fuselage for your rear float mount and you got a dual-usage plane. You can then remove the main gear and bolt your floats right up in 5 minutes. They work great on the snow.

Get a bigger engine. Nothing like a .60 size engine to hop up your LT-40.

Maybe slap a bigger battery in her. 1000-1200mah should be plenty.

I just recently got an LT-40 and did all the mods I described; along with a TH .75 engine. I've been flying for 6 or 7 years now. It's an absolute HOOT to have a nice knock around trainer with TOO MUCH power,big flaps, barndoor ailerons(I scratched my own bigger flaps and ailerons with a 2.25" cord), and a taildragger with optional float mount.

Hope this helps.

britbrat

I agree with Rcpilet, except the bit about leaving a bit of dihedral in the wings. High wing aircraft exhibit positive roll coupling upon rudder application (the plane will roll in the direction of the applied rudder), & dihedral increases this coupling. This effect greatly interferes with aerobatic capability (it shows up the instant you try a knife edge, or stall turn for example), & it increases sensitivity to cross winds. To reduce, or eliminate this couple from a high wing aircraft, it is necessary to remove all dihedral from the wings (or even add a degree or two of anhedral -- droop).

Removal of the dihedral makes the plane go where it is pointed, roll more axially, fly a tiny bit faster, & behave better in inverted flight. It has no serious negative effects, except for a bit of adverse yaw in some (but not all) aircraft, & that is easily prevented with the proper use of rudder &/or a bit of aileron differential.

Rcpilot

My Feedback: (78)

I still say to leave just a little bit of dihedrahl, but no point in getting in a pissing match over it.

Either way-- if you make it flat or leave 3/4" in the wing---- it's going to be a HUGE improvement over the stock wing.

I don't know about the cost difference, but you could buy a wing kit from the LHS and build it yourself.

If you frame and cover your own wing-- then you will be able to do all the above described mods really easily. Making mods to a wing while it's still being framed is a lot easier than cutting covering and trying to patch it later.

If you decide to buy the wing kit and frame it yourself-- consider leaving the rounded wingtips off. Just cut a piece of 1/8" lite ply the shape of the rib at the tip of the wing and glue it on each wingtip with CA. That will help to keep it from shredding if you knock a wingtip on landing.

You can install the servo trays in the wing halves when your framing it. It will be a lot simpler to cover the wing if you leave the rounded tips off.

Glue the root ribs into the wing at the right angle for the dihedrahl that you want. No point in glueing them in at the angle for the stock angle. That'll just leave the gap I discussed in my earlier post. Glue the root ribs in so that when you have it all ready to assemble-- you won't have a gap at the top-- where the 2 wing halves meet.

The wing is sheeted in the center section. Consider glassing the wing. I use 4oz cloth from the auto parts store. Its heavy duty stuff- and 1/2 the price of fiberglass cloth at the hobby store.

Cut the cloth to the width of the sheeting or maybe 1" less. I would think a 4" or 5" wide piece would be fine. Cut the top piece long enough so that it will wrap over the front of the wing and go around to the bottom side about 3/4". Leave the TE side 3/4" long too.

Flip the wing over so that your looking at the bottom of it. Start with thin CA. Lay the glass in place on the bottom of the wing at the LE. Line it up and use the thin CA to tack it in place. Only use a little bit-- just enough to hold it in place. A small, tight bead across the whole edge will be more than enough to hold it. Your going to use thinned epoxy to glue the rest of the glass on later. Now that the LE on the bottom is tacked on-- flip the wing over so that your looking at the top of it. Pull the glass across the top of the wing and strecth it over the TE of the wing. Tack it in place with thin CA. Flip it over again and finish running the glass 3/4" onto the bottom of the wing. Tack with thin CA.

Now cut a piece of glass for the bottom of the wing. It should just overlap the glass that you wrapped around from the top. It doesn't need to go all the way around and overlap onto the top of the wing. Just cut it the exact length of the bottom of the wing. It will overlap the other glass by 3/4" at the LE and TE.

Tack it on with thin CA.

Finishing resin is good stuff for this. It's thin and it will take 24 hours to cure. This is good- cause you don't want it curing up on you as your trying to smooth the glass out. That'll leave a nasty lump or bubble somewhere-- and it ain't easy to sand out.

You could also use 2hr epoxy. Just anything thats generally thin and takes a long time to cure.

Mix it up and squeegee it on with one of them foam paintbrushes from the hardware store.

Do the bottom first. Start at the center and work the epoxy out to the edges. Make sure all the little strings at the edges are stuck down good. Get them nice and wet with epoxy and smooth them out from the center and work out to the edges.

You don't want a big glob of epoxy on the glass. Just enough to wet it down and make it stick to the balsa. You gotta sand it later-- and epoxy lumps don't sand easily- so wipe the whole wing down with a foam sponge soaked with alcohol. You just want a thin sheen of epoxy left-- just enough to stick the glass down.

Wipe the TE and LE of the bottom really good. Then let the wing cure overnight in a warm room.

Now do the top of the wing the same way. Let it cure overnight.

After all the epoxy is cured in a day or 2-- then you can sand it. Start with smething really course like 60 or 80 grit and knock the high spots off first. Move on down to 100 grit and finish with something as fine as youd like. Don't sand all the epoxy off.

Glassing the joint in this manner will add a lot of strength- and a bit of weight-- but considering how you plan to fly this plane-- I'd glass it and take the weight penalty.

If you make it a 3 servo wing-- then use the stock supplied torque rod in the wing for your flaps. Just make a little Y linkage to hook the flaps together-- that way you can drive both flaps from a single servo.

Consider some better hinges than the CA hinges. You can use the small Robarts or Great Planes makes a hinge just like the Robarts--but a bit smaller. Just make sure to add a small balsa block in the TE of the wing to allow for plenty of glueing surface for each hinge. Do the same, and add a little balsa block where each hinge will glue into the ailerons and flaps.

If you want to scratch build bigger ailerons and flaps for it-- then here is a fairly simple way to build them:

Decide on the cord. I used 2.25" only because I fly at 10,000 feet above sea level. For a lower altitude application-- you could easily get away with under 2" on the ailerons and flaps.

Let's say you plan to have a cord of 1.75". Get a couple pieces of 3/8" triangle stock to make your LE of the flaps and ailerons. Lay a sheet of 1/16" or 3/32" balsa on the bench and cut it to length and also cut it to your cord of 1.75". Make 8 of these. You need a top and bottom of both ailerons and also a top and bottom of each flap.

Cut a bunch of little ribs from 3/32" balsa. They will be as thick as the LE of the surfaces and as long as your cord. So, they'd be 1.75" long and about 1/4" thick. You'll want about 5 ribs for each flap and maybe 7-9 ribs for each aileron-- so cut 1 and use it for a template to make the rest. Tape them together on 1 side and sand them all to the same profile. Then move your tape and sand the other 2 sides as well. Then you got a bunch of traingle shaped ribs that are all the same size and shape.

Lay a sheet of your aileron sheet balsa on the bench. Glue the traingle stock to the front side of it and using a protractor-- assure that the tri-stock is perpendicular to the sheet. Now glue your 2 end ribs in.

I take 2 of the ribs and glue them about 3/4" apart-- right in the center of the aileron span. Then you can glue a piece of heavy balsa or spruce in between those 2 ribs for a hardpoint to hook your control horn up to. Now glue in the rest of the ribs. Then glue a small piece of balsa in--on the hinge line where your hinges will glue in. That will give the hinges something to grab onto. Glue your top sheeting on. Sand it a bit and then continue in this fashion untill you got the other aileron built and then build the flaps the same way.

Remember to add a piece of balsa in the flaps for the torque rod to glue into. It will have to be located right at the root rib---where the torque rod exits the TE of the wing. This should be a balsa block sanded to the same shape and profile as your ribs. Glue it in right next to the root rib. This will give a nice piece to epoxy your torque rods into.

These flaps/ailerons will be light and stiff. Easy to cover.

I left an 1/8" gap between my ailerons and flaps. I used the small Great Planes pivot hinges. I can't remember for sure--but I think I used 3 hinges per flap and 6 on each of the ailerons.

Hope this helps.

flash over

Now there's an idea I hadn't thought of buy a new wing.I'm going to have to check into that.Surprised I didn't think of it.AsI said I'm building an intermediate plane now and I'm looking for a quick significant improvement till it's finished.Plus with a new wing I could still use the old wing when I want to use the plane for training purposes.

flash over

Guess what tower doesn't have a listing online for a replacement wing arf or kit. Do i have to call them for it.