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LT-40 Century Model

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Old 05-27-2004, 07:14 PM
  #1  
bojangle
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Default LT-40 Century Model

Quick facts: I'm 65 but not retired. From records, photos, and a good memory, I estimate about 99 planes have left my hangar over the past 50 years, about every design and configuration you can think of. My records show 28 kits in the total.

So what does an old timer build for his 100th plane? Decided on a kit this time, tired of scratch building, although the kit will undoubtedly have to be upgraded (bashed?) to my liking. Has to be big, bright and colorful for these tired old eyes. Slow when I want it to be, but lots of fun when I'm in the mood, a workhorse, able to handle our sometimes 25+ mph winds.
.
I grew up with Sig, first of their kits was a Senior Kadet. So I decided to go Sig for this one. After months of research, I narrowed it down to 2. I didn't order the LT-40, got another (to remain nameless). The kit was a mess, must have been made at 4:59 Friday night. Bottom line, I hated it. I called Sig, sweetest customer service lady I have ever talked to. She made me sweat a little, as I didn't get the kit direct from them. Then she said Sig doesn't want unhappy customers, and that if I would send the kit to them, she would replace it with any plane in their line within the same price range at no cost whatsoever to me. The LT-40, which was my original second choice, is on the way. I think fate meant for me to have this one. Thanks Sig, you were the first, and still the very best!

It will remain a trike gear for my cow pasture fields. I have a .46FX just waiting. Exterior and/or redundant plywood will be replaced with balsa. Dihedral will be a compromise of stability and agility. It will bear the name "Sky King", an alias, my AMA Number 47446. If flaps are a good mod, I would consider them.

Other than that, I am open for suggestions, mods, improvements, pitfalls, personal successes and failures, colors and schemes including best orientation colors/contrasts.

As a rancher, I am going into my busy season. Progress will be slow, with much study and planning. I plan to post a few pictures, but mostly of my own little "trade secrets" of construction learned over the years.

Thanks for your input

Bob "When life throws you lemons, make lemonade"
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Old 05-27-2004, 11:06 PM
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Default RE: LT-40 Century Model

Have fun , I have a mag.52 for stroke on mine and fly it more than any thing I have. You can bash It or build it stock , plenty of room for anything you want to put in it. Some guy's here put 61's or 91fs on them and fly cross country with them. This plane can be taken off in 20 feet but need some ground to land flaps might help! Wind is no problem it likes it . it builds fast and true and will take a jolt or two . I give instruction on this plane and it never gets a rest and yes I am one of those old guys 14 planes in hanger and 7 rigged to fly and I love my 1/5 Sig J3 flys like a dream and that would be one for you to play with.
I have rambled long enough have a good one .
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Old 05-27-2004, 11:27 PM
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bojangle
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Default RE: LT-40 Century Model

I have a Sig 1/4 Cub, full wing, with a Gemini 160 four stroke. Yes, it's an awesome plane.
With 3 other Cubs in the hangar, I thought would try something simpler, an "everyday" kind of plane.

I have a well broken in FS-48, might try putting that in the LT. Also have an FS-70 if the wind gets too fierce. Decisions, decisions........

Bob
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Old 05-28-2004, 08:55 AM
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JimTrainor
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Default RE: LT-40 Century Model

I have a customized LT-40.... nearly ready to go.

- Rounded the horizontal and vertical stab to roughly match the contour of the wing tips. Much prettier than square.

- Added a small filet the bottom/leading edge of the vertical stab as is typical in a vertical stab.

- Flying wires on the horiz/vert stab. Many people seem to add something to stabalize the vertical stab. Wires were my choice. It also looks neat.

- Lights for late evening flying: Red/Green at wing tips and white strobes at wing tips. A red strobe at the vertical stab top - ran the wire inside a dubro antenna tube that runs inside a balsa channel that was attached to the leading edge of the vertical stab. Two red strobes on the fuse bottom. Two narrow beam lights under the forward fuse (landing lights). These are all ultrabright leads from here: http://www.curtek.com/

- Coverall and dope covering.

- Wing bolts

- Some blind nuts attached under the fuse in a few strategic locations as "hard points" to mount who-knows-what someday.

- Similar "hard points" in the wing bottoms to attach struts (if the mounted accessories are heavy) or to mount whatever (more lights?, streamers?, smoke-riter?)

Powered by an aging OS Surpass 48. I intentionally do not want the model to be overpowered.

The LT-40 is so quick to build, that even with the mods it does not take too too long. The koverall and dope is bit tedius - it's a learning excercise for me.

I wouldn't say my work is of the quality that bojangle is shooting for.
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Old 05-28-2004, 07:26 PM
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bojangle
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Default RE: LT-40 Century Model

Jim
Really great ideas, especially the "hard points" for any future "what ifs". I will possibly either lower the horizontal stab slightly, or raise the turtle deck line, to allow for a "fill" over the stab. Sig typically doesn't have a dorsal fin, I always add one. I think it looks nicer, and perhaps decreases drag on the forward fin surface, although very slight. I also feel a modest fin adds to the vertical stab area, should improve stability.

I used to use coverall and dope, I can no longer tolerate the fumes. So now I'm a "Mono Addict". I think a fabric covered plane looks great, but don't have the experience for it.

I am afraid it is true that I am one of those dreaded "perfectionists". But I don't demand perfection in others, only for myself. All my life I have been striving for that one "perfect airplane". By that I mean perfect for me. So far I have never achieved my goal. Little mistakes creep in unnoticed. No one else would notice, but I know they are there.

I don't think I am alone in this respect. Most modelers have many planes in their hangar. I think that is because they too are still searching for that one "exactly right" plane. When they find it, all the others gather dust.

I will log every idea posted here, no matter how slight the detail.

Bob
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Old 05-29-2004, 08:10 AM
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Default RE: LT-40 Century Model

Bob,

Below is mine; four years old, 200+ flights, and still going strong. It has trained a half-dozen people, and will be used by yet anoither fledgling today.

I rescued a tired old 48 Surpass from my brother's junk pile, replaced the bearings, and it made a new plane out of the LT-40. Not as much grunt as the .46 two-banger I had in there, but the model seems a bit more 'majestic' now. Consider a four-stroke for yours.

Check out the spreader bar soldered to the gear legs. A half-hour's work saves much grief down the road.
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Old 05-29-2004, 08:15 AM
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Default RE: LT-40 Century Model

One other thing, Bob; if you plan to use #64 rubber bands on the wing, add some hardwood reinforcement to the LE and TE where the bands will go. The LT-40 wing has a rather broad chord that is really too wide for #64s. Sig used to sell #67s that were perfect, but dropped them some time back. The only place I can now find them is from an industrial supply place in two-inch wide trim...[]

So I have to carefully cut some out every now and then. Still better than crunched balsa LE and TE....

.
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Old 05-29-2004, 10:57 AM
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Default RE: LT-40 Century Model

Steve: Thanks for posting the pic, would like to see more if you have them.

I picked up one box of #67 at a hobby shop. I can't imagine Sig dropping them since they are needed for the LT. Anyway, I will possibly bolt the wing on. RTL Fasteners has 10-32 and 1/4-20 brass threaded inserts that would work great for this. The stock main gear is 5/32, I plan to either replace with 3/16 or a dural gear. I have an old Breiting wire bender that should do the job.

I do have a barely broken in FS48, I wasn't sure if it would have enough power. But after reading some posts here, I will strongly consider the four stroke. (I just hate breaking them in). The engine kept throwing props, since it had only one prop nut. I was able to get a locking nut set from Tower, same as used on the newer FS52. Hopefully that will solve my problem.

This first LT may turn out to be a proto type experimental, a "dry run" so to speak, then get another kit for the final build. The LT is undoubtedly a proven design, just want to add my personal touches.

Bob
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Old 05-29-2004, 11:34 AM
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Default RE: LT-40 Century Model

Steve...as a follow up to my PM, and to others that may read this. I called my LHS in Grand Junction (150 miles from here), they said they stocked the Sig #67 bands, and as far as they knew the size was still available. They sell a lot of LT-40s, and the #67 is the required band.

Apparently Sig was shut down for a month or two as they were re-warehousing. During that period there was a shortage of some items. Sig is back full strength now, better than ever.

Bob
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Old 05-29-2004, 07:40 PM
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Default RE: LT-40 Century Model

Great; I'll check it out.

As to your four-banger throwing props, that's a sure sign of too lean.

A strong 48 Surpass will turn a 12x6 prop at 8500-9000 all day without breaking a sweat. A tired one, like mine, does better with an 11x7. Either will pull the plane with authority, unless you make a real pig out of it with too many modifications, etc. Even with all the plywood in this ARF, it is still well under six pounds.

What other views of the model would you like to see? Its a plain-vanilla ARF version; the only modifications I made was to replace the elevator pushrod, add triangle stock to reinforce the vertical fin, and put that speader bar on the mains. With that bar, 5/32 is plenty stout. 3/16 will just add weight and extra drag.

As with any high-wing trike gear trainer, it doesn't taxi worth a hoot in wind. Making a tail-dragger out of it cures that. Mine is still a trike because it is used as a primary trainer for total newbies; less drama on take-offs...

.
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Old 05-29-2004, 10:00 PM
  #11  
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Default RE: LT-40 Century Model

The 48 only threw the prop a couple times while starting. I tried it today with the new lock nut, no problem.

I am particularly interested in the tail section. None of my planes have the stab on top of the fuse, and I like the looks of a dorsal fin. I'm sure once I see the plans it will all work out.

At present, the only tail dragger I have is a GP Cub 40. With 3-1/2 wheels, it handles my rough field well. I have seen a few pictures of LT-40 conversions. I thought to leave the LT as a trike, but would welcome any comments, pictures and details, as well as challenge all LT dragger enthusiasts to convince me why I should convert it. Lay it on me gang, I'm open to all suggestions.

Bob
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Old 05-30-2004, 10:08 AM
  #12  
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Default RE: LT-40 Century Model

Your choice, really. A tail-dragger is just more stable on the ground when trying to taxi in wind. That high, wide, and fat wing acts like a sail.

Dorsal fin not needed. However, triangle stock along the fin IS a good idea. Not sure how the kit is, but this area is very weak on the ARF. If you look close, you can see a piece of triangle stock behind the rudder pushrod in the following pix. Hope these are of help...
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Old 05-30-2004, 01:34 PM
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JimTrainor
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Default RE: LT-40 Century Model

The vertical stabilizer in the kit is the same as the ARF.

I converted mine to tail dragger - for no particular reason other that I like the look of it.

oh yeah... I added a fairing between the wng and fuse. Kind of like this:
http://airfieldmodels.com/informatio...ruction/13.htm
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Old 05-30-2004, 09:40 PM
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Default RE: LT-40 Century Model

I found a picture of a dragger LT, and I have to admit it does look a lot better. (Hope "Mike" doesn't mind me borrowing the pic)....

I don't know the make of the main gear or tail assembly in the pic, was going to write the guy to ask, but forgot to bookmark the site, now I can't find it. The dural gear Sig uses on their MidStar has a 14" stance, would probably work, but the one in the pic looks better. Dubro has a composite main.

There are several good tailwheel assemblies available for a .40 size plane, kinda leaning toward the GP version if I make the conversion. I've never done a "pull-pull" setup, thought would just run a pushrod wire from rudder servo to the tiller arm.

My field is pretty rough, although I keep the grass short. Do you think the dragger would handle better? Not just for taxi, but also for take off and landing?

Please explain why the dragger taxis better in the wind, I would think setting at the higher angle would make it more difficult? Maybe I'm just so use to the trike I hadn't noticed. Enlighten me.

Another suggestion I found was to make the windshield and hatch more rounded, in which case the fairing you mentioned would blend nicely over the leading edge. Sorta Kadet Mark II style only more streamlined.

Bob
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Old 05-30-2004, 10:07 PM
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Default RE: LT-40 Century Model

The three-point stance of the tricycle gear is less stable than a tail-dragger configuration; primarily because the three points of contact on the former are much closer together than the latter.

As a practical example, let's say you're taxiing with (or against) the wind, and need to turn around. As soon as you reach just beyond crosswind, the model is going to try to tip over; because the short distance between the nosewheel and the main wheel opposite the wind is not great enough to overcome the wind's attempt to push the model over.

The distance between the three points is much greater on the tail-dragger, and it therefore resists the wind's efforts better. Of course, this is also the reason why a tail-dragger is a bit tricky on take-off; the longer fulcrum of the steering element (the tailwheel) means that it is MUCH more effective than a shorter-coupled nose wheel; and every error or correction is multiplied.

Hope I 'splained it well enough. But if I didn't, trust me; the phenomenon exists.

.
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Old 05-30-2004, 10:27 PM
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Default RE: LT-40 Century Model

You just struck a nerve lol. When I was a small boy I had a tricycle, and every time I turned too sharp it tipped over. (ouch)...Also some time ago they outlawed "tricycle" ATVs for the same reason. I have tipped over trike planes quite often while taxiing. I understand the longer leverage principle of the taildragger now that you have explained it. It is also my understanding that a taildragger exhibits "wind cocking", wants to always turn into the wind while on the ground, more so than a trike. Is it necessary to have the tailwheel steerable, or is just a swivel sufficient?

As I said, my taildragger experience is pretty limited, but I'm getting the fever. If you get time, can you post some pics of your LT, especially closeups of the tiller connection?

Dang, I wish that kit would get here, I'm getting anxious now. I cleaned my shop today while watching the race, I'm READY.
Thanks
Bob
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Old 05-30-2004, 11:17 PM
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Default RE: LT-40 Century Model

I used CB/Tatone leaf spring tail gear. It is similar to the pictures in post 14.

The tiller arm is about an inch behend the rear of the fuse. I checked the elevator clearance before settling on that position. An extra push rod drives it. It's straight forward. Mine happens tobe dissembled for covering at the moment. When it is together I'll post pictures if I can get my camera talking to my computer.

I can see Steve's point about the cross wind turn while taxiing. I did expect that bonus. Great. Will test soon, myself.
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Old 06-02-2004, 11:38 PM
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Default RE: LT-40 Century Model

I called Tatone today for information. Their part number 5510 is suitable for planes up to 10 pounds, with allowable wheel size up to 1-3/4". The double horn that goes on the rudder is for 3/16", however a horn for 1/4" thick rudder is available separately for $1.10 from Tower.

Alas, my LT-40 is on backorder. It seems that Sig has run low on balsa. So I'm rounding up the things to make the dragger conversion. The next thing I need is a dural mount for the mains, and information as to optimum placement.

Whoever said "you can't teach an old dog new tricks" was wrong. After using trike gear for many years, I am now convinced that a tail dragger has many benefits to offset any handling difficulty. A friend just built an LT-25 that came with a pull-pull setup. On the maiden, he was practicing taxiing and said "hey, I think this thing wants to fly". He pointed it down the runway, gave it full throttle with a little up elevator at first. When the tail came up, he was expecting it to veer left, it never did. It went straight down the runway and took off. This was his first taildragger. He was impressed, I'm convinced.

If anyone else has experience with the LT-40 dragger conversion, please comment.

Bob
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Old 06-03-2004, 12:22 AM
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Default RE: LT-40 Century Model

By the time the tail lifts there are significant aerodynmic loads on the fins. I guess that is enough to keep it running straight.

I used the Great Planes "Large 60" size dural gear for mine. That may sound large, but is just about perfect IMO. The 14 inch wheel spread matches the stock gear. Line the wheels up under the leading edge. The gear tucks in neatly just to the rear of the former at the front of the radio compartment under the wing (F2?). Just add an extra 1/8 sheet of ply from scrap and some blind nuts, voila... like it was meant to be. I used some 1/2 inch tri stock to beef up the inside of the fuse around the mounting plate.

Here is the tail dragger picture that influenced my decision to convert it:
http://webpages.charter.net/rcfu/Kit...SigLT40TD.html
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Old 06-05-2004, 05:10 PM
  #20  
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Default RE: LT-40 Century Model

Good review and nice plane. The main dural looks narrower than the GP large.

In the picture it appears the dural gear is forward of F2, maybe it's just the angle. I usually mount the plywood plate directly behind F2, so the front of the dural plate lines up pretty much with the wing leading edge. Looking down from the top with the plane level, about 1/3 to 1/2 of the wheel is exposed. I have heard it is not too critical, though some have said don't put the gear out in front of F2 or gets squirrely.

I'm not sure how I will do the tailwheel tiller. A friend showed me his pull-pull setup on his LT25, looks easy enough. Have to play it by ear as I go along. I could put a small servo near the tail and Y it to the rudder servo. Anyway, at this point I have decided to go the taildragger route.

Thanks
Bob
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Old 06-05-2004, 06:55 PM
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Default RE: LT-40 Century Model

You won't regret converting the LT-40 to a tail dragger. I really like mine much more since the conversion. With the nose gear the plane almost seems underpowered because of how long it takes to take off with the extra drag of the nose gear. The other thing that seems to happen is the spring on the nose gear tends to compress and drop the nose closer to the ground during takeoff. This also causes the incedence of the main wing to almost point downward so the wing takes more time to start flying.

I have gotten good enough with my LT-40 to taxi it on the ground with the tail wheel still in the air. It gets a chuckle from the other flyers at the field to watch the plane rolling along on its mains and making a turn towards the pits.

I'm on my second LT-40 which is the ARF version. The first one I built from a kit was lost in a mid-air. I used the Great Planes .60 size dural gear on the first and on the second I used the DuBro composite gear which works great. It tracks really well since it has some give over bumps. Either one works fine. The DuBro is a bit wider which makes it a little more stable. I used the same CB/Tatone tailwheel on both planes which I set up using DuBro pull-pull wires.

If I were going to customize an LT-40 the one thing I would do is add a cowl similar to the Kadet Senior and add wing bolts if it has rubber bands (the ARF now comes with wing bolts.) I added tail support on my kit version but found it wasn't necessary on the ARF.

Here are a few pics. The white plane is my current ARF and the yellow is a picture of someone else's I saved while researching how to do mine. Simply line up the mains with the leading edge of your wing and it will work great.
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Old 06-05-2004, 10:28 PM
  #22  
bojangle
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Default RE: LT-40 Century Model

I forgot that the fuse was open at the rear. That makes a great way to run the cables. On the LT-25, they have a wood bellcrank for the cables, and a short pushrod from the servo to the bellcrank.

Since I won't be getting the cable and crimps with the kit, I'll have to buy them somewhere.
I would like to add tiny turnbuckles to tension the cables.

I have had the same problems with my trike gear, my field is just a pasture mowed short, pretty rough in spots. Last night I converted my Easy Sport 40 to a dragger, using some leftover parts I had on hand. (pic below). Little off topic, but practicing for my LT when (if) it ever gets here. My Cub 40 has 3.50 main wheels, handles the field great. I think the LT will complete my "hangar". I may not build anymore, I'm old, and tired lol...

Thanks for the pictures, they really help.

Bob
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Old 06-06-2004, 10:00 PM
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Default RE: LT-40 Century Model

Nice job on your conversion. The LT-40 is even easier since the tail of the fuse is open. The only hurdle is the last former in the tail of the fuse. On my ARF I had to use an extra long drill bit to make two holes for the pull-pull wires to run through since the former completely closes off the back end of the fuselage. Don't worry too much about getting the wires completely tight since shock loads will be transferred to your rudder servo if they are too tight. I suppose you could put a couple springs on one end so the tail wheel will have a little give as it hits bumps. The wires will loosten a little as the tail wheel flexes upward as well.
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Old 06-06-2004, 11:17 PM
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Default RE: LT-40 Century Model

No word on my LT-40 yet, balsa is on a slow boat from Equador.

Two things bother me on the LT. First is the lack of support for the fin, and the exposed stab/fin junction. Fix is to raise turtledeck line a bit, add filler blocks over the stab and alongside the fin.

Second is the pushrod exiting the fuse top. It works, but I would prefer less conspicuous, and located for tiller hookup. I have done the conversion shown below on other planes, only difference was to have the horn ( a small nose wheel arm ) centered on the fuse side, with the arm only protruding through a small slot.

To transfer the control point, I use a standard 3/32" aileron torque rod and nylon bearing. The bearing is glued or clamped to a plywood/balsa laminated former, aft side of former in line with the aft edge of fin. The torque rod extends to the fuse bottom. The horn can be a double steering arm (Tatone, about $1.00) or a 1/8" Goldberg nose gear arm. Replace the 1/8" collar with 3/32".

Once the control point is at or near the bottom, the pushrod can exit normally through the lower side. Tailwheel bearing shown is a Dubro, can be either a 1/16" or 3/32". Linkage to the tiller can be springs or a short z-bend wire.

After flying today, there is no doubt about converting the LT to a dragger. In my last post, I mentioned converting my Easy Sport. On my rough grass field, takeoffs were difficult with a trike, runs of 100 - 150 feet just to get enough airspeed to rotate. With the dragger setup, the takeoff runs were as short as 50 feet, with the plane leaping into a 45 degree climbout. Maneuver were much smoother without the nose wheel drag. Cross wind taxiing no problem.
(Thank, Steve, for the tip)

Lots of other good ideas showing up here, greatly appreciated.

Bob
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Old 06-11-2004, 10:57 AM
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Default RE: LT-40 Century Model

The "balsa boat" arrived, Sig is now back in production on the LT, should have the kit in a few days.

There seems to be a lack of information about mods for the LT, other than converting to tail dragger and adding triangle stock to the fin. Yet I see a lot of "bashing" ideas for planes such as the 4 Star. All my previous kits had balsa fuse sides, I'm beginning to think that mods to a ply fuselage might be more difficult. Perhaps therein lies the challenge.

As one member wrote, and I loosely quote "bash the LT all you want, it's still a basic trainer".
Perhaps I am out of synch in this forum, since most of my planes are scratch built, but I think it will be fun to see what I can do with the kit, not to improve it but rather "personalize" it. So far all the LTs I've seen all look alike. To me, part of the fun is having something different.

At this point I think flaps are out, with all the lift built into the plane, why add more? I don't want to add to the weight, in fact I intend to trim off about 8 ounces if possible. As for dual aileron servos, I think that option is a matter of builder choice, not a necessity, at least for the LT.

So far the best dural gear I've found is the LT-25 main, it has the height I need for 4 stroke props, except it only has a 3-1/4" mounting area. Can someone (Jim or Steve) give me the overall fuse width at F2 so I can get the gear ordered?

Bob
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