RE: Skymaster L39 build
 

Now that the rear cockpit has arrived I can start to do the final installation. The cockpit arrived damaged, I was given the option to send it back and get a new one the only thing that stopped me was the fact I was convinced it would happen again. The plastic used is far too thin and brittle they really should be glass. I repaired the damage with 1/64 ply glued with Hysol at least now it's good and strong particularly important on the aft cockpit as this will be removed frequently to access the switches etc... I had to cut away parts of the cockpit so it could fit over the tanks, I then reinforced the hole with ply. These cockpits were obviously an after thought in the design process which is a shame as the rest of the model has been good bar the lack of servo mounts. Once you've put a bit of time on the cockpits they do eventually look good and add a lot to the model. I wouldn't enter it in a competition, but for standoff they're perfectly acceptable. the SM pilots were replaced with something better as detailed earlier. Anyway here's some pictures of my butchery............. and a few detailing how the cockpits secure. I've also added two carbon tubes to the fuz sides as it needed to be strengthened at this point. The fixings/cockpit just need to be cleaned up, painted then it should be up to standard.

The forward cockpit is held in with supports at the front and two screws at the back making it very solid. The rear cockpit just sits in its hole and is held down by the canopy. Ive also added an extra fixing for the canopy at the front.

Alex

RE: Skymaster L39 build
 

Having said that the air system was reliable with the standard airpower 5U valve, It's now far from it. The valve I used to test the system wasn't the one I ended up installing.
My valve developed a very worrying defect. After about a minute with the systems turned on the rx would lose it's bind and the control surfaces would make random full deflection movements this would clearly have caused the model to crash, I've since tried other 5U valves with no problems
but having lost confidence in this particular product I decided to get the pro version which has had no reports with regard to what I experienced. I was advised by Todd at dreamworks to fit a couple of water traps to the valve as moisture can caused problems. I mounted the valve where it's visible as the pressure gauges are displayed on it's LCD screen. It did require me to make a new top mounting plate as the unit is bigger and required things to be moved around to accommodate it. I ran out of carbon effect ABS so had to use two bits on the top tray, I'll remake the tray at some point as the join is too obvious. It will look better with one piece for continuity. I fitted some Tamjet restrictors which slowed the cycle down nicely.

RE: Skymaster L39 build
 

he radio set up was simple enough using a 12 channel system. I decided to give every servo a channel avoiding the use of y leads so it was just a case of plugging all the leads in and fine tuning everything on the radio. The only thing of note is it's necessary to add negative differential to the ailerons because of the top hinged surfaces. I started with 10% but will fine tune after the first flight. I always add a fixed on-board flight log which gets checked after each flight and of course during the initial range checks etc...
All the horns where painted using acrylics having been masked accordingly.
The turbine was installed for the last time with the addition of a FOD guard, I wouldn't normally bother on a jet like the 39 but it will be flown almost exclusively off grass so I thought it a good idea.

Alex

RE: Skymaster L39 build
 

Alex, thanks for the help and the pics. this info you are posting will really be a big help when I am working on mine......

Thanks again.

Mark

RE: Skymaster L39 build
 

Alex,


Thank you for your time to explain how you mounted the servo in the Fin. There really must be only one way to mount that servo. Today I finally came up with the same approach you did. I need to drill a hole further forward to get at the other screws.

It would have been nice if SM had given some sort of direction on this install instead of having us spend a lot of time to get it right.

Your decals are looking really nice.

Stan

RE: Skymaster L39 build
 

I don't know, but maybe in BVM's detailed 18 page colored manual, there might be detailed info on how to install this servo.. just a guess.

RE: Skymaster L39 build
 

With the main installation complete I can turn my attentions to the scale details.

I've never been an advocate for lighting models as you can never tell in the daylight that they're on. Recently I was persuaded by a supplier to try some new mega intense 8mm landing lights called Ultralights and thought the L39 would be the perfect testbed. Upon opening the package I was pleasantly surprised to see they were not LED's. I duly soldered an appropriate resistor for my 6v supply and turned it on. I walked to the other side of the workshop for a look and soon wished I hadn't as for the next 12hours I had a large white dot following me wherever I looked. These certainly are some of the most intense lights Ive seen. In-fact they're in laser categorization for brilliancy. However they are still tiny lights in a model used in a full-size environment so I'll reserve judgment until the test flights.

To operate them Ive got a small dual rc switch with a separate supply input y leaded into one of the flap channels (When are JR going to make a 14 channel radio!?!) and a few 2 pin ashlock connectors for the wing.

The 39 has the landing lights mounted in the nose of the tiptanks. I made some lens covers installed a reflector then designed the whole unit to be removable and etch primed it, just need to add rivets then paint the tank accordingly. I'll install the light unit with interior sealant just in case it has to be replaced at some point.

Part of the lens cover will be painted as the real ones had a relatively small light cover as you can see in the last picture. Its been made removable on the scale panel line.

The picture with the light on was taken in daylight hours, I also had two 200watt daylight bulbs on and used a flash.

The pictures below should explain the sequence for you.

Alex

RE: Skymaster L39 build
 

Hi Alex,

How far out the back does your pipe extend?
Are you even with the bottom of the fuse or are you even with the top.

Both of my stainless steel straps just fell off. A bad weld job. I am using a P-120 and would like to have the turbine as far forward as possible for balance. Then the pipe appears to be to short. I am going to keep the distance between my exhaust pipe and the bell mouth 3/4 of an inch.

Thanks,
Stan

RE: Skymaster L39 build
 

Hi Alex,
Nice touch on the lenses. I did mine a little different. I used a glass light bulb and cut it to size. Not something I would recommend but it worked great for my application. Nice and solid.

RE: Skymaster L39 build
 

Hi Guys

Like your tip tanks, was it difficult to cut the bulb? It's not something I've ever done.

My pipe sits flush with the bottom of the fuz, I opened out the back a bit more to give the pipe some room. I also gave the inside three coats of BVM ceramic paint up until the aft most former.

How longs your pipe? I had to trim some of the inlet ducting off to get the turbine positioned correctly with the pipe sitting flush with the bottom of the fuz. This convieniently meant the turbine was as far forward as is possible. Shame about the quality of your pipe, will your supplier get another for you? If not you could mount it as Ali did over on the 'New Project L39' thread think its around page 5.

Alex

RE: Skymaster L39 build
 

Hi Alex,

Just what I needed to know, Thank you. I will do the same and mount the pipe flush with the bottom of the Fuz at the rear. That works out to move the turbine as far forward as it will go.

My main concern is exposing the rear portion under the rudder area. I have an elan, and the rear of the turbine is slightly inside the rear fuz and this has worked out fine. I did use BVM heat paint in that area. I will do the same on the L-39.

Jeff from SM USA sent me a new pipe with the tabs on it. It is almost 4 inches longer then the one that came with my kit. It is about 2 1/2 inches too long so I cannot use it.

I looked at Ali's method and that seems a good alternative.

KingAir 41 told me that is the way he has set his pipe up with out any problems.

Again I say, If SM had given us these little details in there construction info, the build would go a lot smoother.

Thanks again,
Stan

RE: Skymaster L39 build
 

Managed a little more this evening. The probes on the leading edge were made with various sizes of aluminum tube, etch primed and sprayed appropriately. I tapped some aluminum and glued it into the leading edge to mount the probes in. They just screw in and out now. I did a few more decals on the underside too but unfortunately that was all I managed to get done on my own toys for the day.

Alex

RE: Skymaster L39 build
 

My probes are made from a plastic hangar, inner pushrod tube, heat shrink, and the tip off of an epoxy glue tube. I made it with the dumb dumb rule in effect. I knew I would hit it while handling, fueling, starting, etc..... It's made to bounce back and it does. No bent alumunum tubing to replace. I would have gone through 10lbs of aluminum tubing by now if I didn't make it out of plastic.

RE: Skymaster L39 build
 

I am in the final countdown to get my L-39, Sunday morning I will pick it up.........

RE: Skymaster L39 build
 

Alex,

I have glued my rudder hinges into both fin and rudder. I took great care in doing so.

I can get the one inch of throw they call for each way if I put a lot of preasure to get there. It appears that I get 1/2 inch each way without any strain or preasure pushing on the rudder.

Were you able to get the full inch of throw without straining the servo?

I cannot figure out what I might have done wrong.

I wonder if it is possible to get the full inch the way it is set up.

Stan

RE: Skymaster L39 build
 

Stan just set the throw equal each way and set your servo with whatever throw show you is comftable with.

RE: Skymaster L39 build
 

Hi Stan

I agree with what George advises. I did sand a couple of angles on to the bottom of the rudder and take some off the top so I could achieve a healthy throw, I'll take a photo for you and measure what I get.

cheers, Alex

RE: Skymaster L39 build
 

Thanks Alex,

That will give me an indication of how far off I am.

George,

Are you saying to stay with whatever throw I get and don't worry about achieving 1 inch that SM recommends?

I wonder how effective the rudder will be on the SM L-39?

Stan

RE: Skymaster L39 build
 

To show you how addicting this hobby is......................

I picked up my SM L-39 today, I went down to Simjet headquaters to pick it up from kerry, a little over an hour each way. BUT today, it Took 9 hours there and back, on the inerstate rt 80, 5-10 miles an hour all the way there and some of the distance back, seems when I left this morning, weather forecasters didnt get it right....we had a real nasty ICE storm. my daughter joined me for the ride, several cars in ditches, 2 roll overs, cars into guide rails, and even one state trooper cars crushed, and here I am driving my 15 ft cube van. but it's ok, the SM L-39 made it home and into the shop with out a scratch. ok time to head into the shop and open the box.

Mark

RE: Skymaster L39 build
 

Stan rudder can get very effective in jets becouse of the wide speed range we have..
..so if you need to knife it all day long then you should cut everythink is on the way and get as much throw as posible...or have another plane to enjoy knifes?
..but if we talk about landings in cross wind it depens on the force of the wind!a way to enjoy your l39 for many years is to learn better not to take off at all
if landings are so demanting..

..now if you want rudder help on flite and some on landing then you should leave it as is and go on!..it will be okey so scale flite and crouzing around!
...and you can always change your mind after a few flites that you need more rudder and start then working on the extra throw...but dont open more work now...

sorry for the poor englsih
my 2c

RE: Skymaster L39 build
 

George,

I have no problem understanding you.

Your English is far better then my Greek :-))

Good suggestion.

I can always sand down the edges of the fin later.

Thanks,
Stan

RE: Skymaster L39 build
 

ok, mine is out of the box, and cant wait to start the build.................

RE: Skymaster L39 build
 

[8D][sm=thumbup.gif]

RE: Skymaster L39 build
 

Alex.........

are you using the carbon fiber bypass that comes with the kit?


Mark

RE: Skymaster L39 build
 

hi Alex , are the bottom decal you apply on your l -39 are the stock decals from sky master or you made your own.i am looking all over the net to find some pic's and placement of the underside decals.
let me know , and if you can e - mail me close up pic's of your application i will appreciate very much .
i make mine in black ,
thank,
Isaac
[email protected]