Unilight.at

Hi!

I thought I'd share some pics on a modification I did on my FB L-39. I love the quality of this kit (far better than some european so called high quality manufacturers). Anyways, I thought the whole flap mechanism somewhat suboptimal with the on-top elastic hinging. The flap surface was quite small and with a gap between the released flap and the wing I expect improved effectiveness of the flaps (correct me if I am wrong). Of course I will not extend the flap 90 degrees but I can have a much larger throw now.

There are not even a handfull flying videos of this bird and somewhat all of them seem to land very fast and a little unstable. Maybe this improves the handling. I will see and report in a couple of weeks. I am 3 hours of work away from maiden flight.

Specs:

Behotec 180 Gold
Lado Gear
Grummania Tailpipe
Intairco Hopper
JRDS8711 all around

Cheers

T

Thanks for the reply. It helps me to make my decision. I like as much scale as possible. I am looking at the skymaster 1/4 hawk as well.

Its the airbrakes that want modifying not the flaps!!

Well I disagree

But you could share your flight report. It may be useful for me and others.

Thanks

T

Ok, since you ask I'll talk you through some issues I've had.
Generally, as you say, it's a very nicely made model, a decent size and flies very nicely as you would expect.
I had one of the first to be produced, the fuselage is well made and faultless, unfortunately the same cannot be said about the wings and the springing side of things.
Even without a fuel load the springs bottom out very easily with just a little downward pressure on the airframe, in other words the legs bottom out which of course means that on landing, even a good one, a substantial shock goes through the wing as the springs compress so easily.
To make this situation even worse the wing root and second ribs have very large lightening holes in the front and rear. The front is not a problem but the rear hole leaves only 6mm or so material at the top and bottom of the hole which makes it very weak. The landing shock puts pressure between the main spar and rear anti rotation pin which is in the area of the oversized hole!
I have damaged the wings twice and informed the factory of this weakness and of course nothing got done about it.
At JetPower last year I looked at the FB stand and they had a very nice yellow and black one on show, now bearing in mind that this was a bare shell with no installation weight in it I pressed down lightly on the model and again it just sank the legs to full deflection. Nose gear springing is ok btw.
To cut a long story short I had to purchase a new set of wings eventually after only 19 flights and have just finished modifying them today. I am going to see if I still have any pictures and if so will post them on this reply.
The geometry of the cylinders on the air brakes means that it's only possible to get about 30 degrees opening whereas my JL one had almost 80 degrees! They were servo operated.
I don't like slagging anyone off in public which is why I have not mentioned this before but since you asked I feel guilty hence this reply.
Gary.

Hello Gary

I have purchased one of these off Ian George and it really is an excellent model it has been built to an excellent standard and painted over here in the UK. He has fitted it with a P180. I have just finished setting it up and will hopefully get Geoff White to maiden it for me shortly. Ill post a video of my maiden.

Mark

Jut took these for you.

Hi Mark, Ian's was the first in the UK, mine was the second although it did fly first!
Overpowered with a 180 imo though.

Thank you for the information.

Mark

Hi Gary,

thanks for your feedback.Sorry to hear what happened with your wings. But it looks like a weak point indeed. I didn't see that as an issue so thanks very much again. I noticed the low travel of the speed brakes as well, but didnt see that as a big problem because on my JL L39 i never really had to use the speed brakes. I have yet to test the load of the oleo springs with fuel but without its still "ok" - They only sink in a little. Maybe this has been improved, but i will see once i have the model fuelled up. My kit was from an early 2015 production. Fitting the cockpit btw, is a real PITA....

Thanks again

T

Hi,
the mine is almost ready, what throws are you using?

Hi Tuggs

Have you flown the L39 with the new flap layout ?

thanks

Mark

Ready to fly, 19.53kg dry + 6L querosene, kingtech K210G turbine, JR28X guidance.
CG 160mm

Hi Mark,

Yes i did indeed fly the L39 with the modified flaps and I must say that I am very happy with how the plane slowed down. I will have the next flights on video I hope. Its hard to tell the real difference with the original setup, but from what i've seen from the few videos on the internet its an improvement.

Way too much power with the 180 and the 6 Liter tank is just crazy.

Cheers

T

Hi all,

I maidened on last saturday, It was good, 3 flights to put the CG on the right place. The best one was 170mm.
K210G is to much power, half power in all flight except on verticals, after 8 min. left almost 1/4 of tank.

if need stiff spring, please send e-mail to [email protected], thanks.

I'm pleased to report an update on the springing of this model re fbjets last post.
The factory have obviously taken notice, I emailed them and within a week a complete set of new springs has arrived and I have just installed them.
The nylon bushes have also been modified and I had to turn down the o/d a little to get them to fit.
I have to say that they do indeed feel a lot better on the bench but I won't know until I get out and fuel up etc. I'll report on this when I know the difference, I have also promised to let the factory know the results.
I have refused to fly with the new wings up to now for fear of damaging them but I'm much more confident after fitting the new springs.

I'd like to thank FB Jets for attending to this problem, nice to know that they are taking notice of my comments.

Gary.

Managed a test flight today with a new set of wings and new factory springs.

I have to report that these new springs are a 100% improvement, thank you Catherine at FB Jets, good job done!

As usual she flew awesome! (The Albatros, not Catherine)

Gary.

Hi Gary

The L39 is looking good. I have received an email regarding changing the springs on mine which ill arrange this week.

Mark

Did you contact FB initially Mark or did they get in touch with you?

Awesome news Gary! I'm glad it worked out for you. You'll be a happy camper now.
Steve

Gary

I emailed them and received an instant reply very good service.

Mark

Thanks Mark, that's excellent news, yes Steve, very happy now thanks, nothing worse than having a Hanger Queen you daren't fly in case you break it!

Two more nice flights again today, I must say the new springs are great, problem solved!

A guy turned up with a camera so may be able to post some flight pics soon.