LT-40 Modifications
 

I am learning to fly a Dynaflight motorized glider. I have an ALPHA trainer that will be my primary training plane this spring. I recently aquired a partially built LT-40 that I now want to modify as my eventual third plane in the training process. My end objective is warbirds so I want to use this LT-40 as a learning/experimental platform.

Here is what I am doing to this plane: adding flaps and and dedicated aileron servos, bomb bay doors, reducing dihedral, pull-pull rudder, bolt-on wings, conversion to tail-dragger and Estes Sidewinder Missles on wing pylons (just kidding on the last one).

The purpose is to learn procedures and techniques. I am hoping that by posting some pictures of my progress I receive critiques and suggestions. I am building by the seat of my pants in a sense so I expect that I am doing a lot of things the hard way and some things the wrong way. I have absolutely no problem with ripping freshly completed construction back out for structural and/or cosmetic reasons and have already done so many times so don't hesitate to impart some hard earned wisdom or how to do it right the first time stuff. I really like the "why did you do it that way" type questions because I generally have reasons that either do or don't stand up to review and emerging with a much greater understanding. I already recognize one of my biggest problems and that is overkill building, too much wood, too much glue etc. Again the goal is not to end up with a flawless LT40, but to learn as much as possible about the building process for that future warbird!

Here is the first picture. I made the flaps about 1/3 the length of the original strip aileron. I knew this would decrease the aileron area so I increased the aileron and flap width from 1.5" to 2.5 inches. I did not relocate the original wings TE so the wing maintains the original chord length plus an extra inch of aileron and flap chord. I would imagine that this at least affects the CG location a little to the rear? Let me know if I am building something unruly to fly. I am using Robart hinge points, three per aileron and two per flap. The flap hinges have there pivot point at the very bottom surface of the wing TE. The hinge barbs go up into the TE and the flap at about 30* angles. The aileron hinges are centered between the top and bottom wing surfaces. The hinges are epoxied into the control surfaces but not yet into the wing unti covering is complete. I have four servo hatch supports built into the wing for independent servos and after the fact holes cut into the ribs for the servo leads. I haven't figured a way to put paper tubes for wire routing into the wing so I guess I'll lay in some string in there for fishing the leads through later. I'll post again and show what I did after I cut the already built wing in half to remove most, but not all, the dihedral. I haven't not yet figured out how to operate the bomb bay doors. I hope my reasoning is correct in centering the bomb bay directly under the Center of Gravity. Still a little fuzzy on exactly the pull-pull rudder/tailwheel final configuration but have been doing much reading. A lot of great sites out there and Cafeenman's site has been particularily helpful!

Haven't decided on the engine but either a .046 BB or some four-stroke. Remember this plane is a learning platform, comments?
Thanks,

FarmBuyer

RE: LT-40 Modifications
 

What? No retracts?

For inserting paper tubes in a already-glued-up-wing: take a thin walled pipe big enough for the servo connectors to fit inside, sharpen the INSIDE with a round file or sandpaper, put a few nicks in to act as saw teeth, twist it slowly by hand while pushing gently into the wing ribs.

I wouldn't bother with it - too big a risk of cracking the ribs. With the flat-bottomed aerofoil you're not going to be performing whip-crack manouevers that might batter the inner wing with the leads, anyway. IMHO you're putting a lot of work in and learning building techniques, but your test horse is still a plow horse and not a thoroughbred. Unless you remove the dihedral and taper the wings you won't get the slow-speed stall response a warbird has. You still have the pendulum stability of the high wing. You haven't done anything to make the LT-40 squirely, but you'll need to work in some down elevator when you drop all that flap area and the wing ballons. You might not be able to get it to come down at all!

In the old days (oh, here we go . . . :eek:) we bashed Ugly Stiks to experiment with such things. At least you'll have a stable platforn to experiment with control changes (and getting used to manipulating them without looking away from the plane) - you just won't see much effect. Kit bashing is almost as much fun as flying. A tail dragger, eh? Did you move the wheels up so that the axles are about 1/2" ahead of the wing's leading edge? Doesn't look like it from the picture. You'll have to. Enjoy and keep the pictures coming.

Our club president is making a twin-engined float plane from a LT-40 in a construction class we are holding with a local Explorer post. The other four planes are stock LT-40's. (3 'adults' from our club and 16 kids. I'm learning a LOT about correcting mistakes.:D).

RE: LT-40 Modifications
 

I did think about retracts until I remembered I'm dealing with a high wing[X(]> I cut the holes in the accessible ribs with a ball cutter on a dremel and the innaccessible ribs under inboard wing sheeting with a sharpened piece of tube. What I can't figure out how to do is insert the paper tube itself. I didn't even think about it's purpose also being for leads slapping the covering in the higher performance birds.

I did remove all but about a half inch of dihedral and what is left is based on some comments here about a flat wing looking droopy while on the ground. The decision to remove the dihedral was made late in the wing construction so i just sawed it completely in half. I made some short 3/16" thick 4-ply dihedral braces and epoxied them on both sides of the main spar about 2" up each wing and then glassed the whole joint with two layers of glass 2.5 inches wide and finishing epoxy. The rear spar remained cut and I am hoping the glass joint carries his load. there is a wider glass joint where the wing bolt holes penetrate the TE. You make a good point about the constand chord wing not giving me a warbird stall response. In this case I just get the construction experience and hopefully riduculously slow flight capabilities. Time to (re)learn something, what is the aerodynamical purpose of the tapered wing?

I have made preparations to move the landing gear forward enough to clear the bomb bay doors. The gear is the bent aluminum type with tapered legs that either taper forwards or rearwards depending upon which way you orient them when mounted. One way puts the axles exactly in line with the LE and the other puts them 1" forward of the LE. The looks are affected slightly if the "lean" goes backwards but I only care about the best performance. Any thoughts? The holes are symetrical and for (4) 10-24 nylon screws so it can be reversed in the field. I have thought about bigger tires as in a bush plane. One of the pictures shows the wooden blocks for the gear mounting.

I also epoxied, screwed and glassed (probably that overkill thing going on here) an aluminum plate to receive the wing dowels. Hitting the middle of the wings LE with a 1/4 " dowel left little plywood for the receiving holes in the fuse so I added metal. I am nervouse about 1/4" wood dowels so I might go with aluminum dowels. They are 1/4" because I am nervous about big holes in my LE. I will probably add additional glass to this area of the wing as well once the dowels are in place. The drill in the picture is to show intent, the wing is not anchored well enough yet for drilling.

What engines are going on the LT40 twin? That sounds fun.

Thanks for the input.

RE: LT-40 Modifications
 

Here is the glassed wing joint with the extra glassing for the rear wing bolts. Here is also a shot of the epoxied in blocks in the fuse for the wing bolts. Keep in mind the plane was already built up through the wood phase by it's original deceased owner so I did a certain amount of backing up and "after thoughts" for all these mods. The woodworking was excellent however and everything is straight. I'm sure he'll jump in the cockpit when this thing takes to the air!

Your right about the plane never being a performer, just a workhorse. Reminds me of the Budweiser commercial during the superbowl where the donkey wants to be a Bud Clydesdale:D.

RE: LT-40 Modifications
 

A pair of 1/4" beech or ramin dowels anchored in the plywood bulkhead will take everything that plane can give in the air (provided you don't add too much weight;)), and when the balsa meets the pavement it's often better to have wing hold-downs that 'crumple' to reduce damage. Your hold-down blocks look like you could do chin-ups on them. If you dig a wing tip in a hard landing, either the wing bolts will need to shear quickly or the wing will snap along it's length (or pull a section of fuselage out).

Old Russian saying: "Perfection is the enemy of good enough."

The LT-40 twin has a pair of .25s in nacelles.

I'm guessing you'll want the wheel axles at the leading edge instead of 1" ahead.

RE: LT-40 Modifications
 

Hey Farmbuyer Welcome aboard

Glad to see your having fun. You really don't need the aluminum two layers of 1/8" cut to fit and epoxied will work quite well. same with the wing dowels. Also including a site which explains the pull - pull Http://www.member.cox.net/bdfelice/

I've done this on the rudder and tail wheel on an lt-40 myself and it works well. I kind of did my tailwheel as an afterthought and ran it off the rudder but both can be run off of the same servo, I also suggest that when you hook your cable to the tail wheel that you put a spring on both sides at the tailwheel to absorb shocks from rough ground.

As far as the ailerons go you had plenty to start with I barn doored mine at half length I still had more than needed. The flaps are gonna be fun I don't think you'll ever get it to land.

On your wing at the trailing edge where your going to put your hole for your wing bolts you will want a layer of 1/8 Ply to add a little strength over any portion of the hollow rib area and to protect the soft balsa trailing edge. also on the inside and outside where your are going to fasten your landing gear I recommend a 1/8 " piece of ply big enough to over lap your gear by at least 1/4" fore and aft. and full width of the fuse on the inside and outside of the fuse for extra support the fuse in this area is only 1/8" to start with and dosen't take a lot to rip it out on a rough landing.

The bombbay doors should be fairly close to the cg depending on how big you plan on making them and what you plan to drop. You should be able to hook these up to operate from one servo again depending on choice of control horns and such.

Egor

Keep us posted on your progress I love these lt-40s. Trying to decide right now on bashing an lt-40 or 4* to a twin for the experience and to break in the engines for my p-38 project.

RE: LT-40 Modifications
 

Charlie P, I got this building heavy thing all figured out. I didn't even think about the wing bolt blocks being part of the energy dissipation system. Do you think it would be worth backtracking to replace these block with balsa or possibly use smaller nylon wing bolts than 1/4x20? If I leave it as is, it looks like I run some risk here in the event of an event. The landing gear looks kind of cool as it sweeps back slightly to place the gear even with the leading edge. I'll start with this configuration.

Egor, Thanks for the site address. Looks like good stuff. I think I want to run both the rudder and tailwheel off the same servo and the springs sound like the thing to do. I can start to see this configuration in my head now. Do you reccommend this one servo at least be double ball bearing? I debated about the plywood on the wings TE area and opted for the extra glass in that area because it didn't make a big hump. I hope it's strong enough. You do have me reevaluating the landing gear area. (Seems like I got the wing block and the gear block construction strength methods mixed up[X(].) I believe I'll add a layer of plywood for the gear.

The bomb bay doors still have me puzzled. I tried the Robart door hinges but these doors are at 90 degrees to the fuselage sides so they don't seem to be very suitable. I can make my own hinges or use small piano hinge. As to the servo to actuate these doors would that be a retract servo or a standard servo?

Also , are the flap servos just standard servos controlled by the radio?

Thanks Guys,

Farmbuyer

RE: LT-40 Modifications
 

Farmbuyer,

I have a stock LT40 with a Magnum .46 on it. I can tell you straight up that you won't be needing the flaps. I have to dial in down elevator on mine just to make it fly level! The thing floats like a balloon. The CG is very forgiving on this plane. I converted my wing to bolt on some time ago. To lower the dowels to grab more of the header I cut a couple of slots in the bottom edge of the wing, epoxied the dowels in and then epoxied a small piece of ply over top. I learned to fly on this plane and it has taken a HUGE amount of abuse but the wing dowels have never failed and maybe it's just luck, or I learned to crash properly, but I have never done any serious damage to the wings. This is a great plane. Hope you have fun with it.

Bruce

RE: LT-40 Modifications
 

Bruce,

Doesn't take me long to switch teams[sm=idea.gif]! Here's the before and after proof. Your method seems like it would nicely integrate the loads into the wing by way of LE, spar and the sheeting. My way was to put a big hole in the LE and left the dowel unsupported till it got to the spar which had me worried. My way also generated that hunk of aluminum and screws that when cut out weighs almost as much as a standard servo[sm=bananahead.gif]. I epoxied in a piece of 1/8 lite ply to replace the ply I cut out and then I doubled it with some 1/16 plywood.

My objective with the flaps is really slow flight at times other than landing and construction experience (which I am now getting, thanks). I really like seeing a plane fly on the wing.

Greg

RE: LT-40 Modifications
 

Farmbuyer just a crude drawing but I'd cut the floor between formers 1 & 2 and split it length wise use a Dubro nylon pinned hinge a standard control arm like what you would use on an aileron and a couple of bellcranks. You'll have to make up something to hold the bellcranks to the insides of the fuse and your own connecting rods/push rods to operate.I'd stay far enough away from the formers so that I could lay in some 3/8 or 1/2 inch triangle fore and aft of the opening and maybe a small piece of flat stock or allow the tri-angle to over lap the opening by say 1/4 inch so the doors have something to close against. I'd use a standard servo depending on the weight your putting on the doors. what do you plan on using for a radio. You'll also have to make something to hold the servo. this is interesting let me think on this a bit and see if I can maybe draw something up for you.

egor

RE: LT-40 Modifications
 

Egor,

The Dubro hinges might just be the ticket. Then I could use my Great Planes Slot Machine and get a good job done. Here is a shot of the bay door that I already cut out. I cut out only half of the area between the formers with the idea of the radio being on the part I didn't cut out. I read once where someone took that oval ply panel that you remove from the fuselage bottom and turn it into a hatch cover and attach the radio to it. Makes it an easy to access radio installation and I was headed in this direction. It appears that the available area between the formers is 13". WoW! Wonder what the payload on this guy could be?? I like the idea of a BIG bay so it kind of looks like I could mount the servo tray and the radio up on a high shelf so to speak. The fuse here is 6" tall so if I dedicated the bottom three inches to bay area.....that yields 108 in3 of bomb space to work with!! I look forward to dropping those maple tree helicopter seeds.

I can see where the bellcranks would be handy for both a direction change and a ratio change. What I can't quite see yet is going from one servo to two doors and two arms per door, keep thinkin' - I guess I could have two servos, one to open the doors and one for a bomb release. Sequential operation...that would be nice. Can a radio make a standard (non retract)servo open and close as if it's operated by a rocker switch or only in a proportional type of way?

The radio is an open question. I am willing to spend the money to get a decent one and it's already got to be at least 6 channels. The only possible constraint is to go with JR because my other radio is the low end JR Quattro and can work as a buddy box and my father, who is learning this hobby with me is on JR.

Thanks for the diagram.

Greg

RE: LT-40 Modifications
 

Here is a possible location for the bay doors servo. Might put an HS-81 small servo somewhere in there beside it to operate a release mechanism or something. Still like the idea about enlarging the bay from former to former. Might be able to drop the servo down closer to the bay and extend it's shaft with a 13 inch long 1/4 dia. wood shaft or so from former to former and put a plywood arm on each end of with four wires to operate the doors. I would like for the doors to be able to support some weight however. If the servo actuation was 180 degrees then I believe I could orient the linkages such that the servo wouldn't be straining from the cargo weight except initially during the drop when arms come off of top dead center to open the doors.

RE: LT-40 Modifications
 

The gentleman had already covered the fuselage so I cut away the covering to access the control rods. I am going to use a sullivan pushrod for the elevator because of comments on the supplied rods giving subtle trim variations with temperature. The rudder will be my pull-pull initiation. Also the pushrod and cables needs to make their entrance into the cabin area much higher due to the servo tray being lifted up in the cockpit due to the cargo bay.

RE: LT-40 Modifications
 

Farmbuyer:

Still working on the bombay thing and yes depending on the load resting on the doors you may want or need to use two servos for the doors. Useing a six channel radio you could use either the flap or landing gear to operate your bombbay doors. I use Futaba & Hitec radio so I have no knowledge of JR equipment but the difference's should not be severe. I know that one or two of the futaba servo's can be modified to operate 180 degrees. If I remember correctly Servo city has futaba s-148 servos that operate 180 degrees. Do a google search on lt-40s there are several sites that have a large number of these planes with various modification's and I know that one of them did a test to see how much the cargo wt. wise the plane could fly with for their own amusment. Your servos Do Not have to remain in the area under the wing, The throttle servo can be moved up near the firewall where the engine mounts, and the rudder, and elevator can be move to the open space in the rear it may just require a little more effort to balance.


Egor

RE: LT-40 Modifications
 

Egor,

I might just keep the bay size length to 6" in order to generally keep the bay under the CG and this gives me plenty of room for the radio gear and servos. After your response, I did a lot of searching on google and found a lot of things. I was doing my searching here on rcuniverse and didn't think about elsewhere for some reason. Still looking for some pictures of an operating bay doors setup.

It's a shame Servo City now charges for shipping. I might call them up and quiz them on various servos etc. I did find a site that took a Kadet and lifted 12 lbs. or so of cargo! One guy made a bush plane out of his with extra tank, Trexler ballon tires and a three bladed prop. That was nice.

Thanks for all your help, and others too. I couldn't imagine going through this r/c experience without the internet.

Greg

RE: LT-40 Modifications
 

Farmbuyer:

Glad I could be of some help. wanted to work on a bombay setup but the mickey mouse drawer guides in my work bench fell apart and dumped stuff all over the floor. I've got most of it picked up and stacked on the floor and I tripping over everthing. tonight I'm going to try and empty out the bottom area and stand on my head long enough to replace the drawer glides and start putting stuff away so I have room to work. I'll be back after I wade through this diaster area.

egor

RE: LT-40 Modifications
 

Farmbuyer:

Well I finally got some free time last friday, and I needed to get my mind of some crap that was floating through, and getting me a little hot under the collar. So I spent about an hour building up a small box type arrangment, and put bombbay doors on it. It's not anywhere near perfect, but it can give an Idea on where to start. If I can get some decent pics with my digital I'll post them here for you to look at. I think you've already got a good Idea on where your going so this might just be for the fun of it. Just wanted to let you know I hadn't forgotten about it. How are you coming with the rest of your project.

egor

RE: LT-40 Modifications
 

Hi egor,

The first picture shows the bomb bay module built up ready to slide into place. In front on the table is the cover to put in place when the module is not installed. My plan right now is to delay any more effort on the bomb bay module until I am further along on the rest of the plane. I have installed the servos and bought an engine, a Saito .56 four stroke. this will overpower it enough that I might have to use the ailerons as brakes to get the plane down, something about CROW flight...?...I'll see, it's my excuse to learn four strokes.

On the bomb bay doors, I really want to have a single servo operate the doors from each end as in your diagram. This will require a crank that runs end to end. The servo turns the crank which operates the doors. I'll get on AutoCad and lay out the arm ratios to make this work.

The wing hold down blocks are getting in my way. The servo in the center rear is for the pull-pull rudder. One of the side servos will operate the elevator and this pushrod would benefit by not haveing these blocks in the way. I am considering cutting these out and doing it a more conventional way now that I know how.

The servo tray is moved aft a fair amount and I am wondering about my CG. The heavier engine will help compensate for this I hope.
Greg

RE: LT-40 Modifications
 

Good to see you on this project. A friend and I have done a few of these LT's, or at least one or two several times. Going into its 5th season in some form or another, am flying a "T-Craft" LT-40 taildragger, Ugly Stick mains with weed whip wire bungees , flaps and ailerons (3 servo wing), Koveralll and dope, Supertigre .90 two stroke (have had on this machine os .46, os 70-II surpass, OLD Enya .90 4-stroke (sounded like Jack Benny's Maxwell). One suggestion if it's not too late which has worked well: take total aileron area before. drop 8" to flaps, and make the remainder aileron, but widen to make the identical area as before. That has given us nice flaps, but still plenty aileron, considering we have eliminated all but 3/4" dihedral from wing (left some otherwise wing appears to droop). Mine weighs 7lbs 5 ozs. for what it's worth, this wing is scratch built, cap stripped, and sheeted all the way out for D-tube construction. (shear webs all the way of course, with this power.) We call these "bean patch flyers", long past trainers, but you'd be surprised what an everyday airplane these are. have been used to break in engines, drop 'chutes, golf balls etc. also used to tow gliders, work with disadvantaged kids, test aerodynamic theories, win slow flight and fly backward races, and anything else we can think of. we are doing a 100" Kadet now from blown up plans, plug in wings, but identical profile. Tail dragger with 5" blow up tires, O.S. 1.60 power. We're calling it Kolossal Kadet, building it for floats or wheels (we use floats here for snow flying, no water flights). you ought to see those ribs stretched out to 17" - what a hoot.

good luck on yours.....i'll check back here from timt to time- -you can't go wrong with a kadet, so versatile....

RE: LT-40 Modifications
 

Meathook,

Sounds like I did it about right on the ailerons. I made the ailerons (and flaps) 2.5" wide instead of the original 1.5". This gives me a total increase in aileron of 5.5 sqr inches. The wing has had almost all of the dihedral removed. You now have me looking at the wing again for strength. The D-tube construction is only for the middle fifth of the wing but it does have two sets of spars and I really glassed the joint.

Is your 100" kadet a big LT-40?

Greg

RE: LT-40 Modifications
 

Farmbuyer:

Looks good, I think you've got this thing pretty well worked out. It looks alot better than my little demo box. I'll keep my eyes on this and watch your progress if there's anything I can help with let me know, and I'll give it a shot.

egor

RE: LT-40 Modifications
 

Egor, Thanks for the help. We'll see how this turns out.

Meat hook, anyone, with a .56 Saito four stroke on the front would I need to change the specified engine downthrust any? Anything else I should be considering?

RE: LT-40 Modifications
 

Farmbuyer:

The downthrust will be fine. I've had upto a .61 two stroke on mine no need to change.

egor

RE: LT-40 Modifications
 

Everyone in our club clips a one bay off of each side of the wing. Also, we prop up the back of the wing with 1/8 ply to take away some of the incedence. Makes the plane not climb so much when on the throttle. I used two servos in the center of the wing with the stock torque rods, then set up flaperons on my radio. Works great for carrying heavy bomb loads, or when I have the floats on it.

RE: LT-40 Modifications
 

Looks like I'll leave the thrust angle alone then.

I am all for matching the incidences so now I am thinking it through. The wing is designed to have 1.5 degrees of incidence and the stabilizer has zero. If I repositioned the stab to 1.5, would this mean that the fuseage would tend to travel through the air in kind of a pitch oriented skid? I see an easy way to cleanly and permanently reposition the stab but wouldn't want to if there is a penalty in performance that I would notice in which case I'll change the wing. What do you all think?

Greg