What do you think about JETLEGEND L39?
#1927
Join Date: Feb 2017
Location: Grimsby UK
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I will measure up this weekend and post, but it's around 50mm down flap but will confirm.
my mate has the mark 1 version and it was interesting to note that the mark 1 has its nose leg mounted lower in the fuze so nose is higher up on his than mine.
my mate has the mark 1 version and it was interesting to note that the mark 1 has its nose leg mounted lower in the fuze so nose is higher up on his than mine.
#1929
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Maidened my BVM/JL L-39 this week, and my gosh it was a handful. First of all, the nose down is really tough to overcome on a grass strip with this particular nose gear. After a long takeoff roll, it jumped off the ground and almost stalled and snapped when it did finally get airborne. Secondly, it flew heavy and almost uncontrollable at times, like a high wing load warbird. I flew BVM’s demo L-39 plane and it was beautiful to fly! Not sure what’s going on with this particular airframe as it was set up exactly like theirs. After the flights, I made some changes to throws and expo, along with adding a spacer in the strut to stiffen the spring. Flew it again and it still can’t get off the grass very well. Did the jump into the air again, but luckily I was ready. 3rd flight, I made the mistake of adding smoke fluid and that increased the takeoff roll quite a bit and it flew even worse. Seems like the smoke tank is about 96oz or something. It’s huge and I only filled it 1/3-1/2 way. I am running a JC Cheetah, with an AS3000 gyro and the recommenced throws and expo. CG is almost exactly at the factory placement. I have purchased a CortexPro to replace that AS3000 as I’m not keen on it’s functionality in a Jet. Some people like it and others have felt it’s not really locked in as well a CortexPro. So, I’m willing to do whatever to get this model to fly well. Any tips or suggestions are welcomed. It’s a pretty airframe and the build quality is nice. Just not a great flier yet. Thanks in advance!
#1930
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Had the same issues on grass as you, would not rotate and lift off smooth , I added spacer in the nose leg to stiffen it up, eventually kept putting more take off flap in and this helped it lift off better, I was going to try to fit weaker springs in the main legs to it sits down at the back more I'm sure this would help it no end.
unfortunately after 5 flights I add a high speed stall it recovered but clipped a tree and is totalled. I've ordered a replacement and intend to lengthen the nose leg this time and cut the fuze to allow wheel to retract.
hope you get the better of it as they are such a nice plane to fly, other than the high speed stall mine flew fine it was just the take off I think JL should have designed the angle of the plane to sit flat.
Brian
unfortunately after 5 flights I add a high speed stall it recovered but clipped a tree and is totalled. I've ordered a replacement and intend to lengthen the nose leg this time and cut the fuze to allow wheel to retract.
hope you get the better of it as they are such a nice plane to fly, other than the high speed stall mine flew fine it was just the take off I think JL should have designed the angle of the plane to sit flat.
Brian
#1931
The rear springs are already soft, on tarmac there is no problem, on grass the nose leg is pulled back creating a negative incidence on the wing.
Cure is to use stiffer nose leg spring.
Cure is to use stiffer nose leg spring.
#1932
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My friend has the early version and the main springs are a lot softer than my latest version was, even with a stiffer spring in the nose leg the plane still sits nose down and compresses the front leg on take off on grass and Tarmac , there is about 20mm difference in the height on the nose between the two models, his takes off smooth and just rotates easy were mine did not but as I said before more take off flap did help.
#1934
We're talking about the 1/5 JL one.
Brian, mine is the earlier version, isn't it possible to pack the nose leg to lower it?
I'm flying the larger FB one nowadays.
Brian, mine is the earlier version, isn't it possible to pack the nose leg to lower it?
I'm flying the larger FB one nowadays.
#1935
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I’ll look into possibly installing softer main gear springs and adding an even stiffer nose gear spring. That with the increased takeoff flaps will hopefully make the T/O less eventful. Looking at the BVM video on the L-39, that plane looks to be almost perfectly level on the takeoff roll and eases into the sky. Granted that’s on a paved surface too. Thanks for some ideas guys!
#1937
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Spent the whole afternoon working in the shop with my Xicoy CG calculator. I started over with all the CG setup and distance calculations. I double checked the factory marks and they match the manual spot on. I used those marks and the balance came out perfectly matched to those using the manual’s criteria. These are the weights I logged for different phases of flight based on fuel loads:
CG weight w/UAT full & 1/2 full header tank = 38.3 lbs
Takeoff full fuel (w/o smoke fluid) = 44.1 lbs
Takeoff full fuel with only 50oz smoke fluid = 46.4 lbs
Landing with 1/4 fuel load & no smoke fluid = 40.5 lbs
No wonder this thing dogs so bad on grass. 46+ lbs takeoff with 50oz of smoke fluid.
I also logged the CG change with adding fuel and smoke fluid. My location I chose for weight placement is the nose cone. Full fuel load and no smoke oil, causes the CG to shift forward enough, that the calculator says to remove 0.5 lbs from the nose cone. Add in the smoke fluid and it says to remove 0.6 lbs from the nose cone. At landing fuel load and no smoke fluid it was showing to remove 0.2 lbs from the nose. Not terrible by any means for all those scenarios.
I think I’m just shocked at the weights and trying to figure out how much overweight my bird is than everyone else. Or if I’m worried about it for no reason, and to just adjust takeoff flaps, and flying technique for the first few minutes of a flight.
CG weight w/UAT full & 1/2 full header tank = 38.3 lbs
Takeoff full fuel (w/o smoke fluid) = 44.1 lbs
Takeoff full fuel with only 50oz smoke fluid = 46.4 lbs
Landing with 1/4 fuel load & no smoke fluid = 40.5 lbs
No wonder this thing dogs so bad on grass. 46+ lbs takeoff with 50oz of smoke fluid.
I also logged the CG change with adding fuel and smoke fluid. My location I chose for weight placement is the nose cone. Full fuel load and no smoke oil, causes the CG to shift forward enough, that the calculator says to remove 0.5 lbs from the nose cone. Add in the smoke fluid and it says to remove 0.6 lbs from the nose cone. At landing fuel load and no smoke fluid it was showing to remove 0.2 lbs from the nose. Not terrible by any means for all those scenarios.
I think I’m just shocked at the weights and trying to figure out how much overweight my bird is than everyone else. Or if I’m worried about it for no reason, and to just adjust takeoff flaps, and flying technique for the first few minutes of a flight.
#1941
Join Date: Oct 2007
Location: bois des filionQuebec, CANADA
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#1942
Join Date: Oct 2007
Location: bois des filionQuebec, CANADA
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Sounds about right 44 lbs full fuel.
I had 6.2 liters of fuel on board.
Flew like a dream.
Sold it though.
Will get another one some day.
I had 6.2 liters of fuel on board.
Flew like a dream.
Sold it though.
Will get another one some day.
Last edited by artchristic1; 03-18-2020 at 04:44 PM.
#1943
Join Date: Oct 2007
Location: bois des filionQuebec, CANADA
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Spent the whole afternoon working in the shop with my Xicoy CG calculator. I started over with all the CG setup and distance calculations. I double checked the factory marks and they match the manual spot on. I used those marks and the balance came out perfectly matched to those using the manual’s criteria. These are the weights I logged for different phases of flight based on fuel loads:
CG weight w/UAT full & 1/2 full header tank = 38.3 lbs
Takeoff full fuel (w/o smoke fluid) = 44.1 lbs
Takeoff full fuel with only 50oz smoke fluid = 46.4 lbs
Landing with 1/4 fuel load & no smoke fluid = 40.5 lbs
No wonder this thing dogs so bad on grass. 46+ lbs takeoff with 50oz of smoke fluid.
I also logged the CG change with adding fuel and smoke fluid. My location I chose for weight placement is the nose cone. Full fuel load and no smoke oil, causes the CG to shift forward enough, that the calculator says to remove 0.5 lbs from the nose cone. Add in the smoke fluid and it says to remove 0.6 lbs from the nose cone. At landing fuel load and no smoke fluid it was showing to remove 0.2 lbs from the nose. Not terrible by any means for all those scenarios.
I think I’m just shocked at the weights and trying to figure out how much overweight my bird is than everyone else. Or if I’m worried about it for no reason, and to just adjust takeoff flaps, and flying technique for the first few minutes of a flight.
CG weight w/UAT full & 1/2 full header tank = 38.3 lbs
Takeoff full fuel (w/o smoke fluid) = 44.1 lbs
Takeoff full fuel with only 50oz smoke fluid = 46.4 lbs
Landing with 1/4 fuel load & no smoke fluid = 40.5 lbs
No wonder this thing dogs so bad on grass. 46+ lbs takeoff with 50oz of smoke fluid.
I also logged the CG change with adding fuel and smoke fluid. My location I chose for weight placement is the nose cone. Full fuel load and no smoke oil, causes the CG to shift forward enough, that the calculator says to remove 0.5 lbs from the nose cone. Add in the smoke fluid and it says to remove 0.6 lbs from the nose cone. At landing fuel load and no smoke fluid it was showing to remove 0.2 lbs from the nose. Not terrible by any means for all those scenarios.
I think I’m just shocked at the weights and trying to figure out how much overweight my bird is than everyone else. Or if I’m worried about it for no reason, and to just adjust takeoff flaps, and flying technique for the first few minutes of a flight.
I had 6.2 liters of fuel on board.
Flew like a dream.
Sold it thought.
Will get another one some day.
#1949
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Update: Had the incredible opportunity to have Rob from BVM fly my L-39 and give his input and his mastery of setup knowledge. He changed some stuff in the cortex pro and adjusted the landing gear springs. The jet takes off so much better from the grass with the new spring changes, and the cortex adjustments made the airplane fly SOOOO much better. I can’t wait to get more flights on this bird now!
#1950
My Feedback: (48)
This thread has been quiet for awhile, so I thought I'd share how I addressed my two major faults with this plane.
1) Canopy Hold Down
This mechanism is hokey at best. Four tabs have to be perfectly aligned and are engaged by four cones mounted on a CF rod. You release the mechanism by pulling on a cable that is attached to the rod. To hold the canopies down a weak spring engages the tabs. If one tab is misaligned it can cause the canopies to be loosely engaged.
On a friend's L-39 the cable pulled off the rod and there was no way too open it. It took over an hour and slight damage to the canopy to get it open. Consequently it couldn't fly that day.
On my L-39 apparently the tabs weren't full engaged and the rear canopy came off in flight. It took three months to get a replacement and by then flying season was over.
To address this situation I removed the cable, got a CF tube with a 2 mm. ID and epoxied it over the 2 mm. rod that contains the cones. The rod is now extended to the front access panel. I pull on the rod to release the mechanism, and more importantly now I can gently push it rearward to insure that all tabs are securely engaged.
2) Leaps Off Runway due to Negative Wing Incidence
It doesn't speak very well of Jet Legend to get wrong something so basic. In looking at numerous YouTube videos you can notice that some JL/BVM L-39's sit with a nose down attitude and tend to leap off the runway on take off. Others, along with competitive models (CARF, Fei Boa, Skymaster, etc.), sit more level and take off smoothly. My guess is that when JL came out with the Gen2 version the nose gear is mounted deeper into the fuse than on Gen1, and JL didn't want to spend the money for a new slightly longer nose strut.
I put in a stiffer nose spring and slightly more TO flap which helped slightly. I toyed with the idea of weaker main springs, however I was concerned that it would bottom out too easily if I bounced a landing. Finally I decided that a longer nose strut was required to remedy the situation. I wasn't able to find a suitable longer strut so I decided to extend the one I have.
I started with a 5/8" OD, 1/4" ID 3/4" long aluminum spacer. I removed the steering arm from the top of the strut, drilled and tapped the spacer to mount the steering arm there, then drilled and tapped set screws to attach it to the steering pin. Then I got a longer steering pin to attach it to the top of the strut.
The nose retract had to be mounted 1/2" rearward to accommodate the gear door. Then the opening behind the door had to be extended 1/2" and a new cover made.
Now the plane sits with zero wing incidence with no fuel onboard. I expect that it will have a slightly positive incidence with a full load of fuel. Now I'll have to wait until spring to see how well it takes off.
1) Canopy Hold Down
This mechanism is hokey at best. Four tabs have to be perfectly aligned and are engaged by four cones mounted on a CF rod. You release the mechanism by pulling on a cable that is attached to the rod. To hold the canopies down a weak spring engages the tabs. If one tab is misaligned it can cause the canopies to be loosely engaged.
On a friend's L-39 the cable pulled off the rod and there was no way too open it. It took over an hour and slight damage to the canopy to get it open. Consequently it couldn't fly that day.
On my L-39 apparently the tabs weren't full engaged and the rear canopy came off in flight. It took three months to get a replacement and by then flying season was over.
To address this situation I removed the cable, got a CF tube with a 2 mm. ID and epoxied it over the 2 mm. rod that contains the cones. The rod is now extended to the front access panel. I pull on the rod to release the mechanism, and more importantly now I can gently push it rearward to insure that all tabs are securely engaged.
2) Leaps Off Runway due to Negative Wing Incidence
It doesn't speak very well of Jet Legend to get wrong something so basic. In looking at numerous YouTube videos you can notice that some JL/BVM L-39's sit with a nose down attitude and tend to leap off the runway on take off. Others, along with competitive models (CARF, Fei Boa, Skymaster, etc.), sit more level and take off smoothly. My guess is that when JL came out with the Gen2 version the nose gear is mounted deeper into the fuse than on Gen1, and JL didn't want to spend the money for a new slightly longer nose strut.
I put in a stiffer nose spring and slightly more TO flap which helped slightly. I toyed with the idea of weaker main springs, however I was concerned that it would bottom out too easily if I bounced a landing. Finally I decided that a longer nose strut was required to remedy the situation. I wasn't able to find a suitable longer strut so I decided to extend the one I have.
I started with a 5/8" OD, 1/4" ID 3/4" long aluminum spacer. I removed the steering arm from the top of the strut, drilled and tapped the spacer to mount the steering arm there, then drilled and tapped set screws to attach it to the steering pin. Then I got a longer steering pin to attach it to the top of the strut.
The nose retract had to be mounted 1/2" rearward to accommodate the gear door. Then the opening behind the door had to be extended 1/2" and a new cover made.
Now the plane sits with zero wing incidence with no fuel onboard. I expect that it will have a slightly positive incidence with a full load of fuel. Now I'll have to wait until spring to see how well it takes off.