RE: Skymaster L39 build
 

Alex what size cylinder did you use on your main doors on the L-39?

Stan

RE: Skymaster L39 build
 

Hi Stan

2 inch travel, 7/16 bore.

Cheers

RE: Skymaster L39 build
 

If you look at the below link there's a video of my L39's gear, notice how smooth the main doors actuate with the UP rams and pivot further outboard compared to the front gear door using a SM ram with the pivot on the hinge. All three doors have the same pressure going to the ram and have been restricted in the same way. Just need to fiddle a bit more with the timings but you get the idea..

[youtube]http://www.youtube.com/watch?v=F06QymN1_Iw[/youtube]


Alex

RE: Skymaster L39 build
 

Stan i would brake the hinges too but i used the UP valves on the L39 that they can move the doors in slower speed.

Alex ill be in west sussex in May if you run out of pilots;)

by the way a restrictor closest to the cylinders on the UP line will stop the leg to snap and hit while lowering

[youtube]http://www.youtube.com/watch?v=uARMUHOSryE[/youtube]

RE: Skymaster L39 build
 

I'm from West Sussex originally, where abouts are you staying? Hopefully it will have flown by May. :D Its maiden is penciled in for the Classic Jets meet on the 16th April.

If your ever up in Cambridge give me a shout your welcome to have a go.........

Cheers, Alex

RE: Skymaster L39 build
 

why not!
ill let you know mate! not to fly but i would come for a drink!
i ll be in worthing for a few days!
by the way.....you let me know if you ever want to visit Greece;)


regards
George[8D]

RE: Skymaster L39 build
 

Alex and George,

Thanks for the videos. Alex I see what you mean about smoothness on the main doors.

George I have restrictors on the doors and they are not slamming shut. They close like Alex's doors close, not that hard..that's what is making this so frustrating for me.

Some one at the flying field today suggested putting a wheel colar on the shaft to stop the cylinder from going to far down and stressing the hinge connection point.

Alex Where did you get the attach fitting for the cylinder on the gear door? I had not seen those before.

Again guys thank you for the extra effort to explain how to fix this problem,

Stan

RE: Skymaster L39 build
 

Hi stan

The wheel colar is a good idea, I didn't realise the ram wasn't fully closing when the door was shut. This will probably slove your problem, shrink sleeve works well too.

I made the attachments myself, when I'm back home I'll take some pictures of what I used.

Cheers, Alex

RE: Skymaster L39 build
 

Hi Guys

Yes, well..........I probably did lack a bit of common sense really. Two good flights but not without incident...

I took it down to my main flying site at 'Ramsey Model Aero Club' with the intention of doing some proper fuel checks at sustained full thrust, range checks, and some high speed runs etc... Conditions were not ideal as the grass was a little long having just started to grow again and very wet with the recent rain. When I first pushed the model onto the grass out of our paved pits area it sunk in the ground with a nice load squelch, at least the wind was in my favor, SSW at about 8mph giving me the longest run available on our field of about 200 soggy yards.

Undeterred I did a high speed run and was pleased with the acceleration and tracking also the gear seemed to be handling a very soggy and bumpy field well. I did replace the nose gear spring last-night to help with its stance and stop it burying it's nose when thrust was applied, again this seemed to work out nicely.

At the start of the second high-speed run everything felt right so I decide to commit to getting airborne which it did surprisingly quickly given the conditions. I immediately eased back the power to around 50%. I found for cruising around and sedate aeros I was constantly at quarter to half thrust the only time I went above this was on the take off. Not one click of trim was required for steady level flight, even when exploring the low speed envelope with flaps out trim wasn't necessary. You can fly this thing very slowly........... The landing was uneventful did a few circuits slowing it down and setting the flaps, with around 1/4 thrust and full flap it was set up on a nice 3 degree(ish) glide. During the flare I started to feel like I was running out of elevator but it touched down nicely on the mains. I couldn't keep the nose wheel off the deck once the mains had touched. Probably need a bit more elevator throw but mostly I think due to the sogginess of our field it decelerated rapidly without the use of brakes.

All in all very happy :) :)

I did have a few issues with the gear. During both my flights the nose wheel would not retract. It worked well on the ground but refused to move once airborne. I think it's over restricted so I'll remove these and try again. On the second landing the nose oleo snapped backwards. The pin that holds the oleo into the retract had sheared. There was no damage other than the pin. Both landings were on the mains. I think the tendency for it to snatch the nose down once the mains had touched didn't help This was more a consequence of the conditions more than anything else IMO. Also on the second take off I hit a massive bump that got it airborne far too early I had to level the wings and hope for the best really. It landed on all three wheels at once before getting airborne again 15 meters later, This probably didn't do the pin any good.

Despite the gear issue it flew on rails with no trim needed in all phases of flight. It's a very easy model to fly, it certainly made me look better than I am.

I'll try and get some photos next time. There was one forum member there giving me some much needed encouragement............. Thanks John!

Cheers, Alex

RE: Skymaster L39 build
 

Congratulations Alex,

Good job, Now you can relax. It is done. Sounds like you are very impressed with the way it handles.
Mine is ready to go. I had planed for Monday, but we are expecting windy conditions Monday and Tuesday. Your description of your flight has me eager to go.

That's great Alex,

Stan

RE: Skymaster L39 build
 

thats great news:eek:Congratulations my friend![sm=thumbup.gif][sm=thumbup.gif]

RE: Skymaster L39 build
 

ok, you guys have test flown yours and mine is a few weeks away. all I have to do is mount the canopy and balance. and ready to go. we were up at the flying field shaking the bugs out, but the wind never let up, so we will do it another day.

question..............

flaps. I can get mine 90 degree with the runway, straight down...... is that to much flap?

and did you have to use any mix with elevator when the flaps were fully down?

I did take the P-120 out and put in the P-80 and finish up the lighting system.

Mark

RE: Skymaster L39 build
 

Although my L-39 Has not flown, It is ready. I purged the 120sx today and ran it for the first time. Unreal power for this airframe. It will be fun.

Here it is sitting with some of the other fleet chomping at the bit.

Stan

RE: Skymaster L39 build
 

Thanks guys :)

I was very impressed with the way it handled one of the nicest jets I've flown. Looking forward to my next outing.

I do like my models on the nose heavy side of things. I setthe cg to 115 which was forward of the recommended spot. Thisworked well.

With regard to flaps.............mine have abot 40mm of movement from the wing route when set to full. This was a good starting point as the landing was slow. I'd start here and progressfrom there. I'm going to add more flap once I get used to it. I wouldn't start with 90 degrees.

Good luck with your maidens.

Happy holidays

Alex

RE: Skymaster L39 build
 

Forgot to mention, no mixing was reuqired on the flaps if deployed at an appropriate speed.

Alex

RE: Skymaster L39 build
 

I put mine on the scale tonight. 26lbs 9 oz.......... or 12.246 kilograms............ dry, zero fuel, even with dry UAT.

just have to set throws and balance.


Mark

RE: Skymaster L39 build
 

Mark...maybe you full the UAT only before balancing?

RE: Skymaster L39 build
 

just a quick question, I cut the canopy too night and I am happy with the way it fits. did you guys Hysol yours in? or did you use a different method?


Mark

RE: Skymaster L39 build
 

Hey Mark

yes
sand carefuly for better bond use hysol and forget it[8D]

RE: Skymaster L39 build
 

Hi guys

Used 18 liters of fuel today :D All the snags now sorted. Really happy with it. Full thrust low passes with the 120SX are quick and the vertical is pretty much unlimited, well until I'm uncomfortable with seeing it anyway..... Knife edges well. Inside negative pushes don't seem to affect the airframe, a nice solid jet that's very easy to fly and operate. Cheers Skymaster! and Al's hobbies who's service has been excellent.......

I'll get some pictures next Friday when I take it to one of the Jet meets here in the UK. Good luck with everyone's maiden

Alex

RE: Skymaster L39 build
 

I have a Tech/repair question for SM L-39 owners and modelers in general: When I began the process of fitting the servos into the Stabs, I noticed the hinge material was making a "tearing sound" when I flexed it back and forth. When I held it up to the light for inspection I could see where the factory installed hinge was "torn" in some places as if it had been flexed way too much. Needlessly to say, it has to be replaced/repaired before first flight. I can go at this in one of three ways:

1) Rough sand the existing hinge and attempt to apply fiberglass cloth and resin over the hinge.
2) Rough sand the existing hinge and attempt to apply a long strip of CA hinge and Med CA over the hinge.
3) Completely remove the existing hinge and reapply a long strip of CA hinge in its place.


There is a 4th Option which is to order a new stab from SM but that will take???????????
Any comments or suggestions would be great. It is very difficult to post any pics of the damage on here because the tear can only be seen when held up to the light and can be heard when flexed....there are only so many flexes left before it becomes two parts instead of one.

Other than that setback, I am on leave this week and I plan on working to get this jet ready for the first ever North Carolina Jet rally being held in Wilson, NC the weekend of 28-30 May 2010 (Memorial Day weekend).

Thanks in advance for the replies.

RE: Skymaster L39 build
 

Hello

You should be able to get the hinge fabric from Skymaster. Send them an email or ask your distributor for some.

Cheers, Alex

RE: Skymaster L39 build
 

Thanks Alex....

RE: Skymaster L39 build
 

Hi Guys

Finally some photos to share... Had a great day out at a UK's jet event today. Loads of help from the Al's Hobbies team, thanks.

Had a problem with the nose gear not retracting I didnt bother trying to fix it at the event as I have a feeling it's more of a workshop job, didnt spoil my fun got through a good amount of fuel and promptly ran out so nicked a bit of Ali's when he wasnt looking.....

Cheers, Alex

RE: Skymaster L39 build
 

A few more pics taken by Lozza....

I'm definitely going to make some drop tanks and rocket pods for this, think it will really add to it's airborne appearance, just need to find some time...