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Skygate/CARF Viperjet

Old 04-19-2017, 05:44 AM
  #501  
RCFlyerDan
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Originally Posted by pfact View Post
Has anyone modified their rudder to get more throw? My son is not satisfied with the knife edge performance of our viperjet and is wondering if more rudder might solve the problem.

Phil
More speed is the answer. He is trying to fly it like a 3D plane, and it is not. A guy at our field didn't like the jet either, but he was flying it 3D style of flying. You can accomplish a perfect knife edge with speed and use a lot less then full throw.
Old 04-19-2017, 07:02 AM
  #502  
quist
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Maybe you are to nose heavy. Mine has no issue with KE flight. But it isn't slow high Alpha KE.
Old 04-19-2017, 07:48 AM
  #503  
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Friend and i have our cg on he back edge of the wing tube and knife edge is all ok
Old 04-19-2017, 10:02 AM
  #504  
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Originally Posted by quist View Post
Maybe you are to nose heavy. Mine has no issue with KE flight. But it isn't slow high Alpha KE.
Nose heavy makes the jet/plane pull to the canopy in knife edge. He is just too slow for this jet. It is hard for a new jet pilot to get used the fact that a jet needs speed for lift. Coming from a 3D prop plane, there is a false lift that is created by prop's thrust. Jets don't have it.

Last edited by RCFlyerDan; 04-19-2017 at 10:58 AM.
Old 04-19-2017, 01:39 PM
  #505  
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The "kid" has many hundreds of flights with very high performance jets. Our balance point is right at the aft edge of the wing tube.

High speed knife edge is easy, its the really slow stuff a couple inches off the ground that's the challenge.

Phil
Old 04-19-2017, 06:22 PM
  #506  
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Phil,

I am a very accomplished pilot and sold my Viper because of its lack of aerobatic capabilities. The Viper has a stubby fuse and is very short coupled. Therefore it needs a lot of speed to knife edge properly. It's not just a challenge to do really sloooooooooooooooow rolls with this plane at or below half throttle, it is just plain impossible. The plane simply doesn't have enough rudder authority to do so! Just fly an Avanti, or Leonardo and you'll see the difference a longer fuselage makes.

Thomas

Last edited by bluelevel; 04-19-2017 at 06:25 PM.
Old 06-04-2017, 07:06 AM
  #507  
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Question to all.

Having to use a lot of elevator on take off. Tried different flap settings up to 45 degrees with no substantial improvement.
Balance is at front edge of wing tube with 1/5th tank of fuel.
Using electron landing gear and had to remove 3/8" from length of nose leg to have clearance during retraction.
Think I might have to remove 3/8" from the mains?
Anyone using electron gear ?

Thoughts please.

Peter.
Old 06-04-2017, 08:15 AM
  #508  
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Negative angle of incidence on the ground during take off is forcing the jet to hug the ground. Faster the jet goes, the worse it gets. Should have just made a larger nose gear hole. Either buy a new nose strut and make a bigger hole, because if you reduce the mains by 3/8ths then you may have main retraction issues.

Last edited by RCFlyerDan; 06-04-2017 at 11:34 AM.
Old 06-04-2017, 08:23 AM
  #509  
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With the nose gear mounted fully forward, it was still too long and interfered with a main former just aft of the hole.
Plenty of room to shorten the mains and still clear any obstructions.
Old 06-04-2017, 11:35 AM
  #510  
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My Viper uses Behotec C50 electric gear for the Mains and C40 for the nose. Also using the Behotec trailing link struts. Length of all gear was fine but did have to cut a small but of glass on the wing to allow fore the trailing link swing arm to fit. The gear is built like a tank and has worked great for 4 seasons.
Regarding elevator on takeoff, Sounds like it is nose heavy. Not really sure where mine is balanced but initially I balanced using the supplied Jig, center hole. Had to add some weight up front to get the recommended balance (with gear down, empty tank and full UAT). After about 10 flights I took all the weight out. I usually take off with full fuel and smoke tanks and use the stock takeoff flap setting. Rotation is smooth at about 1/2 throttle (45 lb Jet Central Rhino) and requires very little elevator to rotate.
Old 06-05-2017, 04:48 AM
  #511  
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Good Morning Peter!

I don't think either one of us answered your question about the issues you are having with the Viper. I also thought others would have chimed in to help you. I would like to explain my thoughts and ask a couple questions.
First, I don't disagree with Sailing that you might be a little nose heavy, but not to the extent of the issue you are having on lift off. Once you remove the 1/5 of a tank of fuel, which is removing about a pound of ballast in front of the CG, moves the CG more towards the center of the tube. Balance is supposed to be performed with an empty main tank. In my experience, I don't think you are too noise heavy, and maybe where you need it to fly and feel comfortable. The reason that I believe it to be an incidence issue is for the following reasons. You bought a set of matched struts and retracts. The retracts, unless shimmed, don't change with the installation. They still give you a level playing field for the mounting of the struts. You took a matched set of struts and cut the nose strut 3/8's of an inch lowering the nose, which creates negative incidence. The fact that the nose strut doesn't fit makes me wonder if you weren't sold the wrong struts, or sent the wrong struts?
Please answer the following questions to help us figure your issue out. 1. When installing the main struts, did you have to enlarge the wheel wells in the fuselage for the wheels to retract into the wells? 2. With the jet sitting on the struts, power ON your transmitter, receiver and gear, provided you haven't changed your trims since you last flight. What is your elevator position? Is it in center? Or higher then center? If higher, by how much? 3. Do you have an incidence meter? If so, while the jet is on the gear, measure the incidence. I am sure it will show that you have a negative incidence. These questions will give you your answer. Please let us know. Thanks! Dan

Last edited by RCFlyerDan; 06-05-2017 at 04:55 AM.
Old 06-05-2017, 05:14 AM
  #512  
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Just post a picture of the model sat on its wheels. Almost certainly angle of attack or main wheels a long way behind balance
Old 06-05-2017, 06:12 AM
  #513  
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He has posted a picture in post 488. Truly shows nothing other than a pretty jet in the living room.
Old 06-05-2017, 06:25 AM
  #514  
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I meant from the side so we can see the 'sit'
Old 06-06-2017, 03:13 AM
  #515  
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I had the opportunity to measure a stock set of landing gear and wheels on Sunday.
Calculations reveal a more favourable stance than first anticipated with my set up having .5mm lower on the mains relative to the nose than the stock set up.
Balance is at front of wing tube with 1/5 tank of fuel.

1- No modification required to fit mains.
2- Slight down elevator trim in flight mode.
3-Yes I do have an incidence meter, I will set it up tonight and take side view pictures.

Report to follow,
Thank you gentlemen,
Peter.
Old 06-06-2017, 04:49 AM
  #516  
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Good Morning Peter!

Thank you for your answers. It is good that there is only a .5mm difference between stock gear. Still ashamed that you had to cut the nose strut. If you had to cut the fuse for the mains to fit, then your mains would have been too long. When you say: Slight down elevator in flight mode". Am I understanding gear up, flaps up? If so, then the down elevator is telling us that you aren't nose heavy, but rather tail heavy. IF you have a slight down elevator with flaps down, then this is normal. To me, it is still pointing at incidence. Also, when you do the incidence, fill the tank. This will add more weight on the nose strut to give you the worse possible measurement for the incidence at take off.
Old 06-06-2017, 05:54 AM
  #517  
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Flight mode 1- Normal flight , Slight down elevator (Gear up, Flaps up) level flight 3/4 throttle setting.
Flight mode 2- Take off, Neutral elevator (Gear down , Flaps down tried 15 up to 40 degrees).
Flight mode 3-Landing, Down elevator 8 degrees (Gear down, Flaps 85 degrees).

Check incidence with full tank - Roger.
Old 06-06-2017, 06:32 AM
  #518  
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From your Flight Modes, definitely incidence. You are actually a little tail heavy. Take off flaps above 25 degrees is actually adding more drag than lift. Also, the greater the flaps, the smaller the Angle of Attack until stall. This makes your flair in the landing more flat and more possible to land on the nose gear. Personally, I only use 30 degrees of landing flaps. Full scale usually don't go over 30 degrees, with some going to 40 degrees landing flap. Again, this is for the flair, drag to lift, and go around capabilities. Two other buddies that have Vipers at my field use a little more flap, but are starting to reduce the degrees. Also, as one of my buddies found out a couple weeks ago, the more flap you are using puts more strain on the servo with a higher chance of failure. He had a servo fail on downwind, and fortunately, he was high enough and got the flaps up after a hard roll. On short final, you would probably be done.
PS-Your P47 likes a lot of flap to get the two point landing. Again, so that you can land flat.

Last edited by RCFlyerDan; 06-06-2017 at 06:39 AM.
Old 06-06-2017, 07:05 AM
  #519  
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Here is a video showing a little of what the jet will do. It also shows landing with 30 degree flaps. The camera was an older GoPro 3 with no stabilization.

Old 06-06-2017, 12:18 PM
  #520  
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Ground incidence is 1.5 degrees up.
Old 06-06-2017, 12:27 PM
  #521  
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Originally Posted by peter w h View Post
Ground incidence is 1.5 degrees up.
I'm lost then....other than not enough throws. Sure it isn't 1.5 down? They are easy to read backwards. I guess take a side picture for David.

Last edited by RCFlyerDan; 06-06-2017 at 12:31 PM.
Old 06-06-2017, 12:45 PM
  #522  
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Yes - it's up.
Old 06-06-2017, 12:46 PM
  #523  
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Main wheel position relative to balance? How far behind

Old 06-06-2017, 12:48 PM
  #524  
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Originally Posted by peter w h View Post
Yes - it's up.
What a brain teaser!!! All indications is that with 1.5 degrees nose up, not nose heavy, due to down trim in level flight, it should take off on it's own. Is this your first jet? The other thing that I can think of is too much expo. But, I am truly lost. Everything that we went through indicates nose down incidence. Level flight with down trim indicates tail heavy. What are you comparing this too as far as other jets that you have flown?
Old 06-06-2017, 01:36 PM
  #525  
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I presently fly Boomerangs, Skymaster Hawk and this Viper.
Elevator expo is @ 35

Agreed - It should lift off or a least get light by itself.

Dave - the main wheel position is I believe in the only place it will fit and still retract up into the fuselage cut out.
Perhaps I am missing something in this regard?

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