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JET LEGEND VIPER BUILD THREAD

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JET LEGEND VIPER BUILD THREAD

Old 06-03-2013, 03:57 PM
  #701  
noahb
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Default RE: JET LEGEND VIPER BUILD THREAD

I would do a soap bubble test to see where the air is escaping. If it's the main seal between the lower and upper strut, then I would contact Mike at GJC and see if he can get you some new seals. If its the check valve, it may just need to be cleaned and the air put back in.

Few items of interest for those that have built or in the process of building:
1. On the elevator, there are 4 small set screws that set into the metal rod that links the two elevator halves. Mine were loose. Not sure if the glue the elevator halves onto the metal rod, but I put blue locktite on mine and re tightened them down. Also check the two Allen screws that hold the alum. block on the elevator rod just to be sure.

2. On the newer vipers, the tires are air up tires. While nice, I do believe solid tires are a better option. IMHO Mine leak down some (not much) over a weeks time.

I hope to fly mine this weekend. Will post pictures later when I have jet out. I have a JC Rabbit 100 installed. All up weight is right at 22lbs. This is with cockpit, two A123 2500 packs, Hitec 7955's for all surfaces and steering.


For those that glued another control horn for the flaps, was there wood or anything beneath the flap surface to glue into? They still have the flap hinge offset and while I hooked them up, I would like to glue another horn that is better aligned.

Thanks,
Larry
Old 06-04-2013, 11:06 PM
  #702  
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Default RE: JET LEGEND VIPER BUILD THREAD

Is it best to balance the model inverted or up right?
Old 06-05-2013, 12:47 AM
  #703  
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Default RE: JET LEGEND VIPER BUILD THREAD

Balance it upright Steve. As a check I looked at mine Sunday with landing fuel in and noticed it balanced on its mains just like an Elan if that helps.
Old 06-05-2013, 12:51 AM
  #704  
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Default RE: JET LEGEND VIPER BUILD THREAD

Thanks Gary
Old 06-05-2013, 11:15 AM
  #705  
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Default RE: JET LEGEND VIPER BUILD THREAD


ORIGINAL: noahb

I would do a soap bubble test to see where the air is escaping. If it's the main seal between the lower and upper strut, then I would contact Mike at GJC and see if he can get you some new seals. If its the check valve, it may just need to be cleaned and the air put back in.

Few items of interest for those that have built or in the process of building:
1. On the elevator, there are 4 small set screws that set into the metal rod that links the two elevator halves. Mine were loose. Not sure if the glue the elevator halves onto the metal rod, but I put blue locktite on mine and re tightened them down. Also check the two Allen screws that hold the alum. block on the elevator rod just to be sure.

2. On the newer vipers, the tires are air up tires. While nice, I do believe solid tires are a better option. IMHO Mine leak down some (not much) over a weeks time.

I hope to fly mine this weekend. Will post pictures later when I have jet out. I have a JC Rabbit 100 installed. All up weight is right at 22lbs. This is with cockpit, two A123 2500 packs, Hitec 7955's for all surfaces and steering.


For those that glued another control horn for the flaps, was there wood or anything beneath the flap surface to glue into? They still have the flap hinge offset and while I hooked them up, I would like to glue another horn that is better aligned.

Thanks,
Larry
No Wood in mine under flap skin but I droped a couple of pieces in though the slot a squit of cyno, then the horn with some epoxy.
Old 06-05-2013, 11:33 AM
  #706  
essyou35
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Default RE: JET LEGEND VIPER BUILD THREAD

I had ailerons on my fej f-16 that are hollow, so I made my slot, and put tissue paper soeked in epoxy in ther, stuffed it inside, then used a ton of hysol.

Aileron horn comes out = crash 99% of the time.

This is a flap so not as critical but I am just using them as is.
Old 06-05-2013, 05:37 PM
  #707  
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Default RE: JET LEGEND VIPER BUILD THREAD

Hey fellas.
A question for those of you using the Spark T12 turbine.

I just run mine for the first time, and had 3 Flameouts! It says,Speed low.
So Iadjusted the idle speed up tp 35000, happened again. Idle seems very unstable, especially compared to my K 80 and K 140.

Some small flames and popping on start up to, not a hot start, but would like to sort this out. Plane wont fly until I trust the engine 110%. And I really want to fly her soon....
There are no bubles in the fuel system, it's all been checked under load and is working fine. At a loss, cuz all my other engines have always been trouble free. No real learning I suppose.
So now I learn....

Other than that Full power is good and stable, transition is very fast.

Matt

Old 06-05-2013, 10:39 PM
  #708  
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Default RE: JET LEGEND VIPER BUILD THREAD

SpeedLow: The engine has been shut down because the RPM has dropped below a minimum.
Cause could be lack of fuel, air bubbles, problem with the batteries, or defective RPM
sensor.

Checkout all these options and try using a simple seperate fuel supply to see whether it is a problem with the engine or your fuel system. Make sure you use a freshly charged/new battery.

Jeff
Old 06-06-2013, 12:12 AM
  #709  
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Default RE: JET LEGEND VIPER BUILD THREAD

Cheers Jeff,

I suspect the pump may be the problem. Fuel system is good, no probs there.

Matt
Old 06-06-2013, 12:32 AM
  #710  
Mark Vandervelden
 
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Default RE: JET LEGEND VIPER BUILD THREAD

Hi Matt I've ran 3 of the T12 turbine's now and as yet not had a flame out or had one stop at idle. What I have noticed was, and this is true of many turbines is that on the first or even second run is that cycles of the throttle need to be learned by the ECU so it can adjust the pump accordingly depending on each individual tank/fuel supply. As Jeff says its good to have a bench mark to start with so using a freshly charged battery and a free flowing fuel supply directly to the pump is a good way to start. When its started allow it to settle then slowly raise the throttle to accelerate from idle to full power taking 10-15 seconds then leave it for 30 seconds then slowly close the throttle and leave it at idle again for a wile to settle down. This should be enough to allow the ecu to adjust to any fuel flow restrictions and power supply through any particular extension leads or switches etc. As to a few small bluish flames on start up I've noticed this on most Kero start turbines some more than others along with some weird noises! In particular a pals Booster 90 sounds like a steam engine struggling slowly up a hill but it always gets there in the end. If your T12 is still showing a little flame during start-up but after you have ran it a few times and allowed it to learn all the required pump settings it can be adjusted to help smooth things out. I have the ECU settings from mine and I've jotted down for ref and these are the ones relevant to a smooth idle and running and could be checked on yours before you try again. Full RPM 120-123,000, idle 32,000, Stop 20,000, Acc Delay 020, Dec Delay 014, Stability 100. Another thing to do that might help is run the pump in, This was a must in the early days of model turbines but is not bad practise, simply run the pump with a low voltage, I've used a single Nim cell with about a Lt of fuel flowing-recycling through it via a filter for an hour or so that should bed down the brushes and gears if its a bit stiff when new. Hope this helps and look forward to your replies.
Old 06-06-2013, 12:57 AM
  #711  
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Default RE: JET LEGEND VIPER BUILD THREAD



Impressive. a clear canopy instead would be better

Old 06-06-2013, 02:42 AM
  #712  
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Default RE: JET LEGEND VIPER BUILD THREAD

Thanks for the reply, I'll have a look at the settings tomorow.
Ill also give the ecu a chance to learn the Transmitter settings.

This engine I got off a buddy, only has just over a hour on it, but had been sittng still for awile. So we suspect a bit of oil or gunk may be binding up the pump a little. I have "exercised the pump thru about 6 litres, but may do a bit more tomorow.
I ran it again this arvo, and it didnt flame out on me, but still the idle was a bit erratic. Everything else was good. Very fast acceration. Some blue flames on acceration.

Just a bit flamey on start, and certainly makes some interesting sounds.

If all else fails, Ill get a new pump.

Matt
Old 06-06-2013, 06:20 AM
  #713  
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Default RE: JET LEGEND VIPER BUILD THREAD

It may be worth trying lowering the pump voltage one click!
Old 06-06-2013, 04:16 PM
  #714  
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Default RE: JET LEGEND VIPER BUILD THREAD

Hi guys, I'm new to this thread, but have just scored myself a crashed Viper which I have almost finished rebuilding. I have also just completed reading this thread from the start, and it took two stubbies and three coffees!! This jet crashed on takeoff by tip stalling on rotation, due to a nose down takeoff stance and I guess a nose heavy aircraft due to the majority of the fuel being in front of the CG. The aircraft snapped and hit the ground hard. The owner was going to bin it but I made a offer, which he accepted. I will be using my K80F and all digital high quality HiTec servos and my new JR 11x radio. Regarding the person having flame out problems, I had a flameout on my K80F, and it was due to the EGT probe pulling out slightly from the exhaust nozzle. Someone wanted to fit a pilot, so I raided the kid's old toy box and found a GI Joe fits perfectly with his legs cut off below his knees, (sorry!). You also have to cut out the bottom of the pilots seat, so he sits low enough. He actually snaps in without any restraint. I plan on making a joystick and a seat harness, and when I take some pics, I will post them on here. Here is some pics from a real Viper.
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Old 06-06-2013, 04:54 PM
  #715  
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Default RE: JET LEGEND VIPER BUILD THREAD

Hi Aussie,

Check the nose pin on yours. It may have been bent slightly back resulting in a nose down stance. I heard about this crash and was rather surprised as the ones I have supplied and my own one have not experienced this issue. I do let mine run for a while with the P80 before I get airborne and don't need to apply to much elevator.

One of the guys in my club has reverted to a single tank in the front and smoke tanks in the rear. Mine is running the standard configuration and both get off in the same amount of space with take off flaps.

If you need any info or want some pics drop me a line and I'm more than happy to help.

Cheers

Jeremy
Old 06-06-2013, 05:15 PM
  #716  
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Default RE: JET LEGEND VIPER BUILD THREAD

Hi Jeremy, all hardware was removed and what I bought was a empty airframe plus the thrust tube. This jet does not need the full intake duct, so I have cut into the middle of the duct and fitted a 2.4 litre juice bottle, straddling the main spar, and am using a PST air trap, which holds about 300 ML. The nose was damaged, so I removed the 350gms of concrete nose weight. When ready for my fitout, I will balance at 35mm behind middle of spar, with empty mains, and T/O config. My CG will not change much during the flight, and I expect that I will get about 7-8mins of flying, as this engine was in my Falcon 120, and that is a much draggier airframe. Looking forward to getting this bird in the air, but it may take awhile due to work commitments over the next couple of months.
Old 06-07-2013, 09:12 AM
  #717  
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Default RE: JET LEGEND VIPER BUILD THREAD

For you guys flying off grass, what size main and front wheels work the best...............This Viper is my first jet...... Will be installing Robarts with trailing link Robostruts and I need to order the wheels and brakes.

Thanks
Old 06-07-2013, 09:22 AM
  #718  
essyou35
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Default RE: JET LEGEND VIPER BUILD THREAD

Why would you be installing robarts? The stock gear are trailing links..
Old 06-07-2013, 12:44 PM
  #719  
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Default RE: JET LEGEND VIPER BUILD THREAD

HI all I have just done the maiden on my Viper today,it was the easiest maiden I have ever done two clicks of right aileron was all that was needed,with a Merlin 140 power was not an issue,veticals endless with cruise at half throttle,a real peach of a model and one to keep,thanks to all on this forum for all the info regards Keith
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Old 06-07-2013, 12:47 PM
  #720  
jeff sewell
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Default RE: JET LEGEND VIPER BUILD THREAD

You should stick with the stock jetlegend gear, as essyou35 says, it's robust, operates very well and actually fits the viper.

Jeff
Old 06-07-2013, 12:49 PM
  #721  
jeff sewell
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Default RE: JET LEGEND VIPER BUILD THREAD

Well done Keith... It is a great jet, enjoy it lots!

Jeff
Old 06-07-2013, 01:30 PM
  #722  
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Default RE: JET LEGEND VIPER BUILD THREAD

Glad it went well Keith, I thought you'd like it.
Gary.
Old 06-07-2013, 03:47 PM
  #723  
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Default RE: JET LEGEND VIPER BUILD THREAD

Congrats Keith!! Glad you like it
Old 06-08-2013, 10:32 AM
  #724  
noahb
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Default RE: JET LEGEND VIPER BUILD THREAD

Maiden mine today. All went well. Few questions for you guys that have flown yours for sometime now.

1. Do you notice it kind of wiggle in flight? We had some wind today, even a quartering cross wind and I noticed it seemed to wiggle in flight. It would have been the air here as it was heating up rather quick and the wind was kind of bumpy.

2. On landing, when I start to pull elevator for flair, it seems to get a bit squirely on landing sometimes. This did this with just flaps, and then flaps and crow. Again, could have been the cross wind.

I am running about 30mm on cg with UAT full, tanks empty. I have the two smoke tanks (for fuel), and one tank 1500ml up front. Outside of that, she flew really good.

Thanks,
Larry
Old 06-08-2013, 05:09 PM
  #725  
noahb
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Default RE: JET LEGEND VIPER BUILD THREAD

Well, flew it again this afternoon (100 deg heat...ugh!). The wind was not near as bumpy and it flew really nice. It will still "wiggle" some every now and then, but most of that was caused from the rough conditions this morning. I wonder if a gyro on rudder would help any?

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