SeamusG

Geez Crank - you hit on the $64K question.

NM2K

My Feedback: (14)

If you have ever been curious about model Diesel engines, the OS .46LA (& .40LA) makes an excellent model Diesel when used with a Davis Diesel Development conversion head.


Ed Cregger

NM2K

My Feedback: (14)

Are you missing a cordless drill in the shop....<G>


Ed Cregger

WacoNut

Balance the plane and give it a try, I am guessing it will still be a good flying plane.
Anthony

SeamusG

I left the backing on the ultracote and epoxied it to the fuse.
I got ahold of some really heavy thin CA.
Little known fact - Titebond II gets heavier when it dries out.
I replaced all of the balsa stock with iron wood.
Those SIG wheels are actually carved bits of coal
I used a stale PB&J stuffed in the tail to support the stab while glue set and forgot to take it out B4 covering.
Lite ply is actually heavier than aircraft grade ply
Die cut balsa ribs are denser the laser cut ribs - thus they weigh 5x more than laser cut ribs.
Hitec servos are supposed to weigh 1.6 oz - I musta got the ones that weigh 1.6 lb.
The servo screws are made of heavy metal - lost the titanium ones while unpacking the box

I ran out of dumb things that I coulda done to build it heavy ...

Oh, I forgot - I used black hole glue (by the same guys that brought us Gorilla glue) - it creates a black hole that sucks all the pieces together - only downside is that it results in infinite gravity - resulting in a really tail heavy plane ...

Cheers,

SeamusG

Thought I'd give ya exceptions to the build ...

Wing assembly: all joints were glued with Titebond II (TB). I "fingered" a skin of TB on surfaces 10 min. before applying glue and then pinned them to the plans. After glue set over night a bead of TBwas applied to each joint. Only oops was cutting the top main &rear spars flush with the tip rib - spliced them back on with 1/32 ply splints. All wood as provided by SIG

Wing join:30-min epoxy used to glue up the dihedral braces and the root ribs.

Ailerons: torque rods were expoxied (30-min) per instructions. No deviations from plans. A 1/8" lite ply support was fabbed to support the single servo mount to provide servo screws with a better bite & to account for the angle of the dihedral. Glass tape was "thin-CA'd" to the wing. The wing was finished with Hobbico lite filler & sanded

Firewall was prep'ed per instruction. Engine was positioned on the firewall per instructions with prop washer 4 3/8" from firewall (if I remember correctly). SIG3" mount was used as was all mount hardware including the nose gear stuff.

Fuse: assembled per instructions except 30-min epoxy was used to glue the firewall to the fuse. Thin CA used to tack components followed by medium CA fillets on all joints. Exceptions included: 1/8" x 1/8" balsa stock (4 1"pieces)to support the lite ply stab support between the fuse sides at the tail - about 1/32" below the fuse sides. Added 1/8" x 1" x 2" lite ply pieces to 2 formers providing for additional control rod support. 4 pieces of 3/8" x 1" balsa tri-stock used to reinforce main landing gear hardwood blocks. 3/16" x 3/16"x 4"balsa stock was added on the bottom of the servo tray to reinforce the servo mounting screws. 1/4" x 1/4"x 6" balsa stock added under the tank tray to provide mount for "removable" tank tray. Lite ply hatch tongue was eliminated. SIG-provided elev &rudd control rods were replaced with Sullivan units 'cause the SIGpieces had excessive resistence.

Tail feathers: thin CA used exclusively. All wood was extremely hard balsa.

Assembly (before covering): Wing saddle needed shimmed 1/16" on the starboard side. Wing saddle was "filled"with finishing resin &micro-balloon mixture. The stab was epoxied to the fuse. I use a thin spatula to skin coat both surfaces removing all excess glue, test fit the pieces, pull apart to ensure complete coverage, add epoxy as needed and then final fit. Same with fin after stab glue set up.

All control surfaces were installed using CA hinges (again, before covering)

1/2" pieces of Ultracote were cut to length for each hinged joint and applied creating sealed hinge joints.

Final assembly included SIG-provided Dubro 8 oz tank, 1/2" foam added, servo tray pushed 7/8"in front of specified location, battery (wrapped in 1/2" foam)was lodged against the back of the firewall, MPIswitch mounted just behind the F-2 former, Spektrum AR6100 mounted (removable mount) on F-2 w/ remote mounted on port side. Sullivan 2-56 clevis' were used for all elev &rudd connections. SIG-provided controls used for nose gear and throttle linkage. Same for soldered 2-56 rods on the aile servo. Main gear &nose gear installed per instructions.

Gaps where the stab LEmeets the fuse were filled w/ finishing resin / micro-balloons putty. Same for the gaps around the outer tube of the rudder control rod where it exits the fuse.

Covering: All surfaces covered with Ultracote white. Ultracote yellow, blue and red trim added on top of white. Windows were the only SIG-provided decals used.

Final assembly: the rubber band dowels were installed.

Note: SIGdope was used (as specified in the instructions) to paint the engine bay, wing saddle, hatch support and the tips of the rubber band dowels.

With that laid out - I have no clue how this thing ended up requiring 14.5 oz of lead sitting on the motor mounts to get it to balance at 3 5/8" back from the LE.

Go figure. I hope that you can see my frustration. If you see any building / gluing technique used that would result in this imbalance and is not needed for strength of structure PLEASElet me know. This is not the LASTplane that I plan on building.

buzzard bait

You sound like an experienced builder, which certainly does make it very puzzling. Especially since the ARF is so light. A buddy flies his LT-40 ARF with a Fox .40, which weighs 12 oz with muffler. One of the lightest .40s available and no noseweight. It'll go straight up from takeoff into inverted, no problem. Another ARF version in the club flew reasonably well with an OS .40 LA without nose weight. So is Sig selling kits with different construction from the ARF? Jim

Live Wire

I'm back
I still say it is a great build. The wood sent in the kit could have been of a different grade than the normally use or fresh wood which would weight more. other than that there is not much you can do other than outting lighenig holes in the control surfaces of the vertical and horizontal, Some times they are made of a more dense wood to make them ridged. Then I sill think that the balance point or CG is in the far possition back at the center of the side windows. Any way that is where the plans show it.
Larry K

Live Wire

The wood they put in ARF's is a lot different than what they use here in the states for kits A lot of it isn't even Balsa. And they use hot glue is spots.
Larry K

oldvet70

My Feedback: (10)

Wow this forum has been an eye opening experience for me. I built 3 LT-40's for people, all of which were powered with Thunder Tiger GP 42"s and they flew great. It's been a few years but they needed little weight to balance. I did 1 ARF and that plane had an OS 40 FP. Again plenty of power and little added weight. Our club bought one a club member built and put it on GP fiberglass floats so we could teach kids how to fly from a lake, one of our flying sites. It has an OS 46 FXi from a Nexstar that decided to attack a 200 foot tall tree one day. The float plane is overpowered for a trainer and kids can fly around at half throttle. All of these were early kit's and the Arf was pretty early. Maybe the grade of wood has changed as you noted to make the plane heavier. It's too bad if that's the case at it is a wonderful trainer.

SeamusG

The LTnow weighs in at a portly 7 lb 2.6 oz.

Mods include:
Evolution 52 NXreplacing deceased OS46 LA(RIP) - added 6.0 oz
SIG3 1/2"mount replacing SIG3"mount - added .7 oz.
Higley heavy hub replacing dubro 2" spinner - added 2.5 oz.
1400 mAh 6.0 v NiMHreplacing 1500 mAh 4.8 v NiMH - added .7 oz
Moved motor forward 1 1/8"

Total added weight: 9.9 oz.

CG - center of main spar (3 1/2" back from LE- most docile CGspec'd by SIG)

Savings in overall weight 4.6 oz.

What a pain ...

Available adjustments to move CGback:

Replace battery with 4.8v unit and move it back.
Move the engine towards the firewall

I'm gonna name the plane Jimmy in memory of Jimmy Durante and his schnoz 'cause the engine is so far out front that it looks stupid (not that JDwas stupid).

Oh well,

Btw - gonna have to reinforce that poor skinny pair of main landing gear wires. Glad Ihave some wire&solder - get to practice rigging float gear.

Live Wire

Jim
Don't reply but from SIG when the kit first came out. They put a note in the kit to make sure you remove all lightening hole top bottom an both side before covering.
I had one of the first kits in my store and some of them you would think they were there to stay . The knock outs that is
Have a good evening.
Larry K

WestCoastFlyer

My Feedback: (1)

SeamusG, did those wheels/tires come with the kit? They look heavy like the heavy type. Maybe change those out with foam/plastic wheels.

SeamusG

Hey Larry - I'm guessing that most of the parts were die cut at that time. The main fuse components are all laser cut lite ply and the "holes" fall out freely. If a student (or me) breaks this thing I'll consider taking the old Dremel sanding drum and start freeing up the "holes".

I'm still stuck on the idea that I should have been way more sensitive to the weight of the wood used in the fin and stab. The elev and rudd stock was fairly light (and milled). I should have gone to my friendly LHS and replaced all of the SIG stock. I'm guessing that that effort would have saved several ounces which would equate to saving maybe 6 or more ounces at the firewall. Maybe the Sullivan control rods are heavy.

It's all about developing good practices and following through on all builds.

But I gotta say - I really enjoyed smashing that OS 46 LA to pieces!!!!! Stress management professionals call it "venting".

TFF

The problem is you built it too nice.
What an unexperienced modeler would be going through who does not know of options would be tough. Sounds like the tail feather wood and some of your smoothing got you; any extra glue not between wood is just riding along too. You could build 20 of them stock and not one will be perfect. Because it is built, the best you can do is heaver engine, longer motor mounts, heavier nose wheel, lighter rear wheels or dead weight. As bad as it seems, it is a trainer so it can handle the weight and if it is windy in your neck of the woods the weight and bigger engine will be better; also, being a trainer it can fly at the aft CG without a lot of fanfare and being a club plane it will be flown by good pilots helping others. It will be just fine.
I like building because I get to solve problems; some are easy some hard and some necessary; it is not a give-me. Whatever the problem once it gets into the air they all disappear.

SeamusG

WCF - them's SIG items. I've got a bunch of foamies from old Kadet Senior inventory. It'll help a bit on overall weight. Thx.

Ya gotta luv the fake chrome look. Too bad they don't have spinners ...

Live Wire

Well we will both keep wondering what that LT 40 ate . Is there a rodent in there with a family
Might meet up with you some day , Have a good one.
Larry K

SeamusG

Just a note: Sullivan gold-n-rod weighs 1/3 less than an equivalent length of SIG-provided tubing. Also, Sullivan uses a short threaded 2-56 rod (1 1/2" maybe) while SIG specifies a couple of inches of 2-56 rod, threaded on one end, be inserted into the inner tube. Wash on clevis.

Was it Marriott that said "the devil's in the details" ...

SeamusG

TFF - to me the thing about building is to come up with a set of best practices. A friend, LHS owner and gr8 builder keeps pushin' to have a build look good with transparent covering. Guess that there's a couple of different goals - and ya use the appropriate set of practices to attain that goal. If it's to be a show winner (trailer queen) that's one thing. If it's a pattern plane (like my work in progress Bridi Killer Chaos 60) then it's flight characteristics and performance. If it's a sport flier or an aerobatic bastid (my best New England accent). If it's a club trainer - KISS 'cause it's gonna get broke

TFF

If you built if full of warps and open gaps it would have weighed 4.5 lbs ready to fly. And that is the reality of model building. I hope you will show the Chaos; they fly great one of my favorites.

SeamusG

I have a build thread going - now that the LT is nearing an end it's back to the Killer Chaos thread ...

Rcpilot

My Feedback: (78)

Good job Jim!

7lbs 2.6oz (114.6oz) RTF. My math says the wing loading is 18.336 oz per sq ft.

It's STILL gonna fly like a kite. I guarantee the first time you slam the throttle wide open she's gonna climb like a homesick angel.

Can I have the smashed 46LA?

jib

Hmmm, this is going to be interesting. I have a used LT-40 given to me (as he downsized) by a very competant flyer who indicated all it needs to return to being a good flyer is a battery and a receiver to fly. It has an LA 40 on the nose. My son and I were discussing getting it back in the air in the next few weeks.

jack

Rcpilot

My Feedback: (78)

The ARFs are lighter than the kit. The ARF has balsa fuselage sides and the kit has plywood sides.

NM2K

My Feedback: (14)

I don't know what the difference is in wing area between the Goldberg Cub and the LT-40 kit, but my Cub flew just fine at 7.5 lbs.


Ed Cregger