LT-40 and 4*60 Kit Bash
 

I finally started this project after making threats to do it for years.

The idea here is to use an LT-40 fuselage, horizontal stabilizer and vertical stabilizer and marry a 4*60 wing to it. I'm moving the vertical stab backwards so that the rudder hinge is lined up with the elevator hinge. Then I plan to split the elevator into 2 separate control surfaces and run the rudder all the way through to the bottom of the fuse. Probably add a small counter balance to the control surfaces. The idea here is to get more rudder surface and extend it all the way through to the bottom of the fuse - sorta like your typical aerobatic setup.

I bought the LT-40 fuse from Sig on closeout for $30. It's the old ARF version that used rubber band wing attachments. The vertical stab and horizontal were $2 each. So, total cost was $34 + about $8 shipping from Sig. The 4*60 wing was built by a friend years ago after his plane was wrecked on landing. He never finished the rebuild and this wing has sitting sitting around for at least 4 or 5 yrs. I inherited the wing for helping him move. [8D]

I'm going to use a TH .75 engine with a Macs header and tuned pipe.

Progress so far:

First thing I had to do was get the horizontal stab mounted. In stock configuration, the horizontal sticks out past the back of the fuse about 3/8" to allow the elevator room for flexing up and down. I wanted the trailing edge of the stab flush with the back of the fuse, so I cut about 3/8" off the LE of the stab and simply moved it forward.

Stab was secured with 15minute epoxy after I made sure it was all squared up with the fuse.

Next thing to do was get out the levels and incidence meters. I set my level on top of the horizontal stab and blocked up the fuse until the little bubble in the level was dead nuts in the center of the lines. As far as I'm concerned, the stab is now set to zero. I'm taking all incidence readings off the horizontal as if it were set to zero incidence.

I had previously taken the 4*60 wing and stood it on a wingtip. Placed a piece of 8.5 x 11 paper under the wing tip and traced the outline of the airfoil. Drew a line from the dead center of the leading edge to the center of the trailing edge - right through the center of the cord. Then I cut this template out of the paper. I taped the template to a 12" level - being careful to make sure the center line that I had previously drawn down the airfoil was perfectly aligned with the bottom edge of the level.

Now, with the fuse blocked up and the horizontal stab as level as I can get it...

I held the level with the airfoil template (taped to the level) up to the side of the fuse and made sure the bubble was in the center. I moved the level up and down until the center line of the airfoil was touching the BACK of the stock LT-40 wing saddle. Now I needed some help from my wife. She placed small pieces of tape on the airfoil template to secure it to the side of the fuse. I then removed the tape that was holding the template to the level. So, now I got my airfoil taped to the side of the fuse and everything is level.

I traced the airfoil template onto the fuse sides with a ball point pen. Removed the template and used a dremel to hog out the side of the fuse to the new wing shape. A little hand sanding with some 150 grit to clean it up.

First pics are some simple microsoft paint images that I created to help explain the process. Will upload more pics in a second.

RE: LT-40 and 4*60 Kit Bash
 

First pic is the wing saddle after I hacked it up with a dremel.

2nd pic shows the leading edge of the horizontal stab where I trimmed about 3/8" off in order to move the stab forward. I moved the stab forward so the hing line was even with the tail of the fuse.

3rd and 4th pics show the wing in the new saddle.

5th pic is the F2 former inside the fuse. Since the 4*60 wing was already built, and it had (2) 5/16" wood dowels sticking out the front, I had to make a hard ply mount. I cut this mount out of 1/8" hard play after taking a few measurements. Drilled the holes to line up with the dowels in the wing. Sanded the plywood mount to fit snugly in front of the F2 former. Checked for fit and then used some 6 minute epoxy to secure it in place.

RE: LT-40 and 4*60 Kit Bash
 

The wing fits in the saddle very nicely. I still need to install a couple hardwood blocks in the fuselage and drill the holes through the wing for the rear mounting bolts.

Since the 4*60 wing fits into the 4*60 fuse from the bottom, there is not a tapered trailing edge on the stock wing. Those of you that have built any of the 4* designs will know what I'm talking about. I will need to add some balsa blocks to the trailing edge of the wing and sand them to a taper in order to fill up the rest of the wing saddle in the fuse.

You can see a square hole on the right side of the wing. Since the wing was originally intended fro a 4*60, this hole was cut for aileron extensions. I'll patch it.

I have dremeled a new hole in the bottom of the wing for my extensions.

My friend hates sanding, so he fills with drywall mud and then sands that. Apparently it sands real easy. :eek: I HATE the stuff and think more time should be spent with a sanding block and some elbow grease. It doesn't take all that much effort to sand a balsa wing down 99% smooth and then use little tiny bits of filler here and there. I know I'm going to have a hard time getting monokote to stick to this part of the wing. I'll probably try some balsa rite over the drywall mud in hopes that it will make the covering stick easier. :eek: I could sand it all off, but there comes a point where you're into the wood and you're just going to weaken the structure trying to get all the drywall mud out of the low spots. :eek: Did I mention I hate drywall mud? [:@]

Anyway.........

I am still planning to drill through the trailing edge of this wing for my hold down bolts. The 4*60 wing has hard balsa blocks built inside to accept the bolts. I don't see any reason to add balsa blocks to the back of the wing, sand them to shape, and then drill my hold down bolts through there. Seams like it would be weaker since the 2 center ribs don't go all the way back. Who cares if the bolts are 3" from the tapered trailing edge of the wing? [:-]

RE: LT-40 and 4*60 Kit Bash
 

A few more pics of my progress.

1st pic shows the wing in the new saddle. It's about 3/4" lower than the stock wing. The reason for this is because the wing needs to be set at zero degrees incidence. With the trailing edge of the wing in the saddle and the airfoil level, the curve on the bottom of the wing dips down deeper into the fuse.

I'm going to add a couple balsa formers and some sheeting to fill in the area on top of the wing and taper it back into the trailing edge of the wing.

2nd pic is a view from the top. I secured a couple pieces of 1/8" hard ply to the trailing edge to prevent my wing bolts from smashing the balsa.

3rd pic - my messy work bench. :)

RE: LT-40 and 4*60 Kit Bash
 

Power plant and aileron servos.

The TH .75 engine is fairly new. It had about 1/2 gallon of fuel run through it when the black metal throttle arm fell off the carb. You know how Tower is about getting parts for some of these items..... :eek: After 6 months of waiting for a carb, I decided to buy an SK .90 carb instead. It's pretty well known that the SK .90 carb will fit the Tower engine case. The SK .90 carb is about 1/16" too long on the throat, so you have to sand a little off the bottom where it fits into the crankcase. I removed the barrel and stuck the carb body on a bench sander. Took about 2 seconds to remove 1/16" of aluminum from the bottom of the throat. I installed the carb with an o-ring and a little RTV black silicone sealant.


JR 7005 low profile coreless servos should do the job nicely. I can't remember the torque - I think it's around 60-70oz in. I've had these servos for years. One of them is factory reversed. I cut my servo doors from 1/16" hard ply wood. Laid out the holes and cut the openings with a dremel.

RE: LT-40 and 4*60 Kit Bash
 

Nice job, can't wait to see the completed model.

RE: LT-40 and 4*60 Kit Bash
 

Trailing edge pieces are 4" wide on each side. That leaves about 2.5" of solid trailing edge hanging out past the fuse. Something for me to lift under while carrying the model to the flight line

RE: LT-40 and 4*60 Kit Bash
 

Wing block and bolts.

I used a piece of 1x2 pine for the block. I cut it to full inside width of the fuselage and then notched the top corners to help "key" it into the fuse doubler. Secured with 6min epoxy and a clamp.

RE: LT-40 and 4*60 Kit Bash
 

Tossed the vertical stab down on the bench and scribbled a rough outline for the rudder. Used some sticks to make a rudder out of 5/16 x 3/8 balsa.

The counter balance is 1.5" tall. From the LE of the counter balance to the TE is 6 inches.

Bottom of the rudder is 6 inches from LE to TE.

Basically, the taper is equal to the distance on the top of the vertical stabilizer. About 2.5 inches.

Will it work? Probably

Did I use some scientific method of figuring out how many square inches to make the rudder or how much taper on the TE? No

I used an old redneck engineering principal known as, "That looks about right." ;)

RE: LT-40 and 4*60 Kit Bash
 

NIce work RC pilot! Can't wait to get a pull on her next season!

I like the Rudder- looks nice and sporty!

RE: LT-40 and 4*60 Kit Bash
 

Thanks buddy. [8D]

Give me a call if you're around this weekend. The Turkey Fun Fly is Saturday. I might run out there with Pete and harass the boys. Maybe see if we can eat all their donuts. :D

RE: LT-40 and 4*60 Kit Bash
 

Finished framing the elevators tonight. Still need to sand them and bevel the LE for hinges. I just taped them on for the pics. :D

RE: LT-40 and 4*60 Kit Bash
 

Need a little help with the ailerons. Standard aileron stock won't work because I want to make very large ailerons. I'm shooting for a cord about 3" or maybe a little more. I could build them out of sticks, but thats a lot of sticks and I don't have that much on hand right now.

I was planning to cut a bunch of long, skinny triangles (ribs) from 1/8" sheet and lay them in between (2) pieces of 1/16" sheeting. A piece of sheeting for the bottom of the aileron - glue all the triangles on top - sorta like ribs. Then sheet over the top with another piece of 1/16" sheeting. Then use a standard piece of triangle stock to cap it all for the LE.

I've attached a pic of what I originally intended. The blue lines are the triangle ribs. There's a side view and a top view here. The brown block in between 2 of the ribs is the control horn hard point.

Anybody got any other ideas on how to make large ailerons? [sm=confused.gif]

RE: LT-40 and 4*60 Kit Bash
 

Figured it out.

I want a solid TE for the aileron and a solid LE of triangle stock. But I want a pretty solid, yet open structure in the middle.

I had some aileron stock here, but the taper was wrong and the cord was too short. So, I set up my little table top saw and ripped 3/4" of the trailing edge off the aileron stock. Kept that part. Tossed the leading edge back in the scrap box.

Next, I turned that TE piece sideways and bumped it against the saw blade every 4 inches to create a little cut out about 1/8" deep. My trusty Harbor Freight 4" table saw happens to have a blade width of just a snerch over 1/16". Next, I made a rib template out of 1/16" hard ply. It's 3/16 tall at the back where it will tab into the TE aileron piece that I ripped and notched. It's 3/8" tall at the LE, same as the thickness of the TE on my wing.

I cut out 7 more ribs from 1/16" hard ply. That gives me one on each end of both ailerons. Thats 4. And I want 2 side by side right in the middle of each aileron. I'll install the hard point for the control horn between the 2 center ply ribs. Thats 4 more - 2 per wing. And the rest of the little notches are for balsa ribs that I cut out of 1/16" balsa sheet.

I have notched the back side of the triangle stock yet. I will probably do that to help key the ribs into the LE of the ailerons.

I'll post real pics tomorrow after I get them built.

RE: LT-40 and 4*60 Kit Bash
 

Got one aileron framed up. I still need to cut the outboard end off and cap it, but I'll do that after I make sure it's the correct length. It could be off 1/16" or so right now.

The aileron is extremely light, but it's also very flexible I can easily twist it with my hands.

The main ribs are just 1/16" balsa. There are 2 ply ribs in the middle that line up with the servo bay in the wing. I'll have to add a hardwood block for the control horn.

For now, it's really flexy. Not sure how to fix it. I could cut diagonal ribs and run them in between each rib - same way as the 4*60 wing is built. It has diagonal pieces running from corner to corner between all the ribs. But I'm not sure if it will add enough strength to eliminate the twisting. Can't sheet them because they are already the same thickness as the TE of the wing.

I could notch each rib and run a little 1/8" balsa spar the length of the aileron. Would probably have to do that on both sides - top and bottom. Not sure how much that would stop the twisting either.

Sheeting seams like the best way to stop the twisting. I'm wondering is I could notch out each rib 1/16" deep and maybe 1" wide. Run a wide strip of sheeting down the length. It wouldn't be fully sheeted, but I think it would help stop some of the flexing.

No matter what I do, gonna be a PITA. Might just start over and toss this one in the round file.

Any ideas?

RE: LT-40 and 4*60 Kit Bash
 

Em, how about a spar or two (top-n-bottom). Maybe 1/8 x 1/8 or 5/32 x 5/32. It'd keep the rectangle from turning into a parallelogram. And pretty easy to cut with a back saw.

RE: LT-40 and 4*60 Kit Bash
 

Finally decided to just sheet the darn things. I sheeted the bottom first and noticed a significant improvement in the stiffness. Was going to leave the top open and just cover it, but a flying buddy came over today and said the top sheeting would probably make them stiff as a 2x4. He was right.

Here's a couple pics. You can see one is fully sheeted and the other is still open on top. The fully sheeted aileron is very stiff. Almost no twist with my hands. The one that's only sheeted on the bottom is still quite flexible. I'll be curing that problem here in about 20 minutes. :D

RE: LT-40 and 4*60 Kit Bash
 

And you believed him? Geez RC, you're a pretty darn gullible sot. http://www.rcuniverse.com/forum/js/f...ey/msn/lol.gif

Did ya leave any donuts for anybody else this morning?

Keep up "da posts" ...

RE: LT-40 and 4*60 Kit Bash
 

I skipped the fun fly. They had all the donuts they wanted. :)

Codiddley was just here, he thinks the plane is large enough for a 20-30cc engine. After assembling the parts for some bench flying, I think he's probably right. [X(] I flew my last LT-40 with stock wing and slightly improved control surfaces for about 6yrs with a Tower .75 engine. It was very sporty, but it would not hover. It would do very slow tail slides at full throttle. The current version that I'm working on, with the increased wing area and larger control surfaces, is surely going to be heavier than a stock LT-40. The TH .75 engine - even with a pipe- ain't gonna make it hover at this altitude.

I'll have to start looking at small gassers. The firewall is narrow, so I need an engine with a pretty small foot print. I'll add another piece of 1/8" hard ply to the firewall and pin it.

RE: LT-40 and 4*60 Kit Bash
 

Or - maybe build a standoff from the OEM firewall. I'm looking at a Extra 300 manual and it uses a standoff to move the firewall an inch or so ahead of what I would call a normal firewall. Just a thought. Be kinda like a Jimmy Durante bulb on the end of the nose ...

On my 4Star60 - I just chopped everything off flush with the OEMfirewall. Makes engine swaps trivial 'cept for the throttle cable of course ...

RE: LT-40 and 4*60 Kit Bash
 

The DLE20 would fit, but I'm not sure it's enough motor to hover this bird at this altitude.

The DLE30 would certainly hover it, but the footprint is just a snerch too wide.

I'm not worried about the weight. I've calculated my wing area at 1060 sq. in. and a projected flying weight of under 9lbs. Wing loading should be around 19 - 20oz per foot. [sm=lol.gif]

RE: LT-40 and 4*60 Kit Bash
 

So how did you deal with the thickness differences between the TE of the wing and the LE of the aileron?

RE: LT-40 and 4*60 Kit Bash
 

Good job, learned some new tricks here.

Best flying sport/low wing trainer that I've had. Building another one now but converting it to electric. The hardest part is coming up with a covering scheme that I like the looks of. I wish that someone would make up my mind for me.

RE: LT-40 and 4*60 Kit Bash
 

I sanded the front half of the ailerons down 1/16" and slapped the sheeting on. [sm=lol.gif]

RE: LT-40 and 4*60 Kit Bash
 

Hey RC,

I have a couple of instruction manuals from 1st US R/C Flight School - David A. Scott.

In the Sports Aerobatics manual he talks about Improving Airplane Performance - Thicker Control Surfaces. Not to bore ya with the details & nettin' it out - he recommends adding 1/16" each side of control surfaces (aile, rudd & elev) - most important being the ailerons - "resulting in smoother and more layered air flows".

Just sayin' ...

Keep on truckin' dude!