essyou35

My Feedback: (11)

Picked up a k140 to put into this. Anyone flying with that much thrust? Seeing if I can get it to climb and move :-)

No way id open it up except in a climb

roystonflyer

Yes.. a friend has built one with a K140. Handles the power fine although he doesn't rag it too hard. I have had 2 JL Vipers now with the jet legend T12 in them. That turbine pushes out just over 29lb (we measured it) and have flown that really, really hard with no problems

essyou35

My Feedback: (11)

Cool, the K100g is a great turbine but its a bit weak in this jet.

gsmarino2000

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That's interesting, I've been a bit worried about the power to weight ratio with the K100 so I haven't bought an engine yet. I was thinking of making an offer on (probably the same) K140G but I hesitated because everyone on this thread keeps saying how perfect the K100 is for this plane. I don't need to go 200mph but I love having effortless vertical.

I'd be really interested in hearing what you think after you've put a couple of flights on it.

Thanks,
Greg

gsmarino2000

My Feedback: (2)

Question for those of you flying the Spark/jet Legend T-12 in this plane. I'm running diesel in my current planes and prefer to continue that with the Viperjet. It's a lot cheaper and easier to get here and the Kingtechs seem to love it. Is anyone running their T-12 on diesel?

Thanks,
Greg

essyou35

My Feedback: (11)

This jet is not really meant for that much speed, its draggy with its huge intakes and canopy. I've complained about the lack of speed in this thread before, but a 100N turbine is probably the best match. I have about 500 flights on mine with this turbine.
However, I feel that a jet should be able to come over the runway slowly then perform a strong climb out. You cant do that with this jet and a K100 unless you got speed.
I have attempted to build lots of speed on take off and try to pull into the vertical and it stalls out pretty quick full of fuel. An immelman take off is not possible without a hard pull over the top, which is not wise in this jet.

My point is I am not trying to get a lot more speed, but rather more power for strong climbouts. I want it to pull up like a rocket after take off! I think we are on the same page.
I have had old guys ask me after a full throttle pass "is that full throttle?" I can tell is dragging out pretty hard so trying a WOT pass on a K140 will result in some issues eventually. It really makes a loud bellow coming across at full throttle and its not much faster than at 1/2 throttle.

Like I said, I think that much speed in this jet is dangerous but it can benefit highly from the extra thrust at slow speeds. Now it will fly like a jet!
I got a great deal on a K140g so I am putting my K100 into a small yellow f-18 which will have great climbouts as well.

I think we are on the same page. Keep in mind I have 500 flights so I am getting bored with it. I am starting to take more risks with low knife edges and really slow landings. I broke my gear out the end of the season and cracked the top of the wings. So I think this will be a healthier way to respark my interest in it!

Jgwright

I don't know if you guys are flying the same plane we are. As I have mentioned we fly with a very old Simjet 8 Kg thrust turbine and most of the flying is done at 1/2 throttle. The throttle is set up so it is not linear so thrust must be less than 4 Kg. The plane is very slippery and maintains its speed if flown with carved turns rather than yanking on the turns and sharp upwards movements. The best flying Viperjet I have seen was powered by a Jets Munt VT80. I have seen one powered by a Jets Munt 140 but it was not much faster than the VT80 powered one and just needed a lot more fuel so not as nice to fly. With the 8 Kg thrust we have I can hear an airframe sound if we fly level at full throttle that indicates it is at its max speed. If you can hear a bellow then look out for the fuselage to disintegrate and certainly to regularly check for cracks.

Sounds like you are in need of a faster airframe if you have had 500 flights on it and need more speed.

Interesting to note the original has a thrust to weight of 3:5 so certainly not capable of going vertically up after takeoff.

John

roystonflyer

Well John... Im sorry but i could not agree with almost anything you have written..... As for flying the same plane, ive not actually seen you fly yours yet, only seen Dave fly it.
You have seen me fly mine long before you even thought of buying one yourself, then you saw Tims with a P80se.
We have flown with a T12, P80se, Jet Central Falcon, P120, Jet Munt 100 and a k140.
The plane flys better with the larger diameter turbine, whether they be your old simjet or the P120/K140. The smaller turbines seem to be all about the top end power, the take off and vertical are miles better with the larger diameter turbine.
Yes you will fly at around half stick to cruise around, but when going vertical you need the bigger engine
This is why we fly Jets!! and not a 60 size pattern ship.
As for the scale take off. If you scaled up the runway that we fly off, the holes in it would be 3ft deep and covered in boulders.


PS.... AND AS FOR THIS!!!!.......If you can hear a bellow then look out for the fuselage to disintegrate and certainly to regularly check for cracks..... HAVE YOU EVER SEEN ONE DO THIS???????????. IF "NOT" DO NOT MAKE STATEMENTS YOU CANT BACK UP...... I HAVEN'T SEEN THIS IN OVER 200 FLIGHTS.

mikedenilin

My Feedback: (67)

I have been flying my Vipers with T12 for a couple of years and about 200+ flights combined. Mine had been the fastest Viper in our local clubs until last weekend when a buddy of mine upgraded his P100 to a P120. Our vertical climb speed is about the same, but his is slightly faster on top end. He was extremely impressed by the obvious performance gain on take off and vertical climb. Now, there is a different hum that make it sounds like a F1 car passing by. Structurally this plane is strong enough to handle 120N engine and it's not going to break apart if it's well maintained. Everyone that owns this little viper is very happy regardless of the size of turbines they are flying. I recommend 80-100N size turbines for beginners to intermediate skilled pilots. We are now using Viper to train new jet pilots by adding a cortex gyro to smooth out the flights. For hot rods, 120 is a better way to go.

Here is the link of our last Viper out.

https://www.facebook.com/pages/Globa...51?ref=profile


Mike

Jgwright

Mike

I agree with what you say. This is a great plane and can be safely flown with a variety of engine sizes. I just was concerned about the description of "a loud bellow". Yes I have heard the hum you talk about.

Sean

Pleased to hear you disagree with me. I was just saying that there are different views out there. You are dead right about the holes in the runway!

John

essyou35

My Feedback: (11)

John, who is we? Are there two of you in your head LOL. Just kidding.

The bellow noise is caused by too much air entering the airframe with too little ways for it to escape. So it is acting like a parachute due to the intake size. Once I did a WOT with some dive and as I came across my back hatch blew off, indicating there is some pressure back there.

We do have the same jet, if you reread my post I am looking for climbout, I thought I made that clear. This jet is not that fast over al..

Mike: One possible solution is to make some intake inserts, clear ones, that will taper down the intakes up front. I did this before on an f4 and it had a huge impact. I may have to try it sometime.

Roy: I agree with everything you said. It sounds like a bigger turbine will wake it up a bit. Like I said, the canopy and intakes are working against us. I'd love to hear form Mike why the tail is not swept as well. Vipers have swept tails. Is there a reason for it? This is also causes some drag.

Jgwright

I come from the era when the use of the 'Royal we' was quite common. Maggie Thatcher was one who used it a lot. I slip into it occasionally.

It would be very interesting do do some measurements of pressure, both positive and negative to see exactly what is happening. I do know we all underestimate the suction of the turbines. If you are blowing a hatch off then as you say you must have positive pressure when at speed. I am developing a large engine at the moment and I was really surprised at the suction even at modest thrust.

John

smaze17

My Feedback: (60)

Mike, what surfaces do you use the gyro for? Rudder and ailerons?

M3Baker

On my viper the cortex is set up on rudder, elevator and ailerons.

M3Baker

I also just upgraded from the Rabbit to the Rabbit SP. I'm seeing a big difference.

Desertlakesflying

My Feedback: (28)

Do the Vipers fly as good as they I hear they do.

mikedenilin

My Feedback: (67)

This Viper is designed with a concept of "Simple, Durable, Reliable, Affordable and Sporty". Its an effort that we had spent a lot of time and resources with JL to come up with this idea of revamping the old Viper a few years back. The swept back on Mark II is more costly and complicated to installed for reliable set up (2 pieces), so it's not implemented. The large intake is also chosen for wide variety of turbine sizes, and possible EDF in the future, without making it super fast. It's a jet that looks cool, easy to fly, compact enough for transport, wide speed range instead of designing it for speed. It works out well and has been very popular because of these implemented concepts.

Cortex gyro set up - aileron, rudder, and elevators, just like Paul's.

Overall it's a great jet that you would easier put a lot of flights to it. The hum is becoming "Registered" sound of this Viper.
Mike

gsmarino2000

My Feedback: (2)

This is the original Viperjet ... or Mark I if you want to call it that. Notice the flares at the wing root and the straight horizontal tail. The JL version is not accurate scale but it's a reasonable facsimile.

Greg

gsmarino2000

My Feedback: (2)

There really isn't much information available on the T12 turbine. Any answer to my question on running the T12 with diesel?

Thanks,
Greg

mikedenilin

My Feedback: (67)

Greg, you can run T-12 with diesel. That's what the jet pilots in China use. T12 stands for 12KG of thrust. Full Kero starts, internal ECU, fuel valves. I have been flying my T-12 for the past 2 years without major issues. Factory has not officially released this engine in the States yet until all tests are completed and satisfactory.

Mike

essyou35

My Feedback: (11)

Mike what you say makes sense! I'm looking forward to the K140G in mine for better climbouts!

M3Baker

Man, this jet is a winner. I love mine and if somebody offered me every penny I have in it, I wouldn't let her go. It has so many great qualities. Flys great, looks great, easy to transport and assemble. Very strong too.

Desertlakesflying

My Feedback: (28)

I'm considering a first jet this year. I am well experienced and fly some very fast 125mph+ prop planes. I'd like something sport that flies well, and by all accounts the JL Viper is looking very tempting.

gsmarino2000

My Feedback: (2)

I'm sure that some will disagree, but here is how I see it having made the transition to jets and turbines myself over the last year or two. High speed prop planes like a Jackal get you experience with general complexity, retracts and flaps. You probably wouldn't have much difficulty taking off or flying, but landing a turbine jet consistently is a different type of challenge. You have to deal with high wing loading (by comparison) multiple seconds of throttle lag, high residual thrust and lack of propwash over the control surfaces. I find that the throttle lag means I need to be a lot more accurate and consistent when descending and making base and final turns. You could certainly get your waiver on the JL Viperjets (heck, I've seen people do it with a Flash), but personally I would consider this plane too nice to ding up by bouncing it in, knocking the gear out, etc. I'd suggest getting a fiberglass EDF like the Habu 32 or 32X and mastering the landings. The H32 is a lot of fun to fly (it's still one of my favorites) and it flies pretty much like a turbine jet (minus the throttle lag and residual thrust).

Just my 2 cents ...
Greg

gsmarino2000

My Feedback: (2)

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