VIPER TRIM ISSUE:
 

Hi guys,

Got another one to run by you's.

While trimmed to fly straingt and level I end up with the following trims on the plane.

*** 12 Clicks of Left Aileron
*** 5-6 Clicks of Up Elevator

Now the Plane is a Viper and it is set up with 0-degrees across the board. It pulls a bit to the right and down, therefore the above trim. The lateral balance is OK and I'm at 2-3/4" C.G. When flying the course it seems to turn 1 nice and straight and level and goes where you put it. Why? Why would she pull down? Nose heavey , I don't think so in fact I just moved the CG back from 2-1/2". Down trust, it's at zero but even if there was a 1/2 a deg or so, most planes have a little (oe are all bets of because of the type of plane it is). I would not think it would make that much difference or could it? Rolling to the Right? Engine Torque? I am trying to get it to fly absolutely straight and level with all trims as neutral as possible to loose the drag. Any sugeestions. You guys have been awsome before!

Thanks

Ed

RE: VIPER TRIM ISSUE:
 

Well, if you actually plan to race it, I would not trim it to fly level. In 424 you want to trim it to fly at a 45 degree left bank straight where you put it. But you are correct, you want the trims to be neutral when trimmed out to fly in the bank angle to loose as much drag as you can. Make sure you are using an APC 9x6 prop also, so you won't be trimming with a prop that will torque more or less and throw off all your trimming work.

RE: VIPER TRIM ISSUE:
 

Put the plane in a 45 degree angle it should fly about 700 feet hands off. Now put it in same bank and have it come to 2/3 if nose goes up it is tail heavy nose goes down it is nose heavy or fly away from you safety oops

RE: VIPER TRIM ISSUE:
 

Hi guys

I guess what I am wondering is why is the damn plane need about a 1/16th of an inch of left aileron trim to fly straight? I am using all NEPRO guidlines (9x6APC) etc. The little bit of up trim I can understand. I am not a total beginner here but I am a little stumped or maybe brain freeze............

thanks

RE: VIPER TRIM ISSUE:
 

Ed, take good look at the wing to check for twist. Find somewhere flat where you can lay the wing on its top. Block the trailing edge up at the center to where is looks level. Put the ailerons at the neutral position. Next measure the trailing edge from the top of your table to the point of the trailing edge. Do this at 3rds down both wing panels. If the wing is flat and straight these dimension should be the same down the wing. If you get a variance then you’ve got a twisted wing which would cause the need trim.

If the wing is flat take a look at the tail. Make sure the elevators are straight and are adjusted identical. If one elevator is lower than the other this will also cause a rolling effect. Finally make sure the tail is in exactly parallel with the wing. A “V” tail model with the tail crooked will also cause the model to roll.

Hope this helps.

Bob Harris

RE: VIPER TRIM ISSUE:
 

I agree with Bob, check the main wing for a slight twist. The side with the up aileron will more than likely have the trailing edge lower and causing you to need up in the flying surface to compensate. If you have a twist in a wing, what you try to do is to twist the tip to meet the surface. If the left surface is up, the left TE needs to come up.

Hopefully it isn't so bad that you can't twist it to shape and then re-shrink the covering.

RE: VIPER TRIM ISSUE:
 

wing's bent!! yours isn't the first, I had one that needed full right stick to hold it level.

RE: VIPER TRIM ISSUE:
 

I just went through the warped wing thing on a used Predator. Was 2* twisted. Flew about like you described. I clamped it between concrete blocks, twisted it back and ran the heat gun on it. Flys much better now.

RE: VIPER TRIM ISSUE:
 

I will have to jump in on this one just a little and say, Scott you are not giving good advise here .... I'm sorry for being direct but when trimming any pylon racer, you should ALWAYS trim the plane to fly straight, complete hands off so it will fly off in the sunset straight. And to race 424, when you come out of #1 or #3 you want to get the Viper as flat as possible because it doesn't have enought speed to carry a 45 degree angle throughout the course. But to get back to the nose heavy in the turns, if the nose goes down, the upper part of the wing is light... my suggestion after you staighten your wing is to put a some tip weight on the bottom side of the high side of the wing. Lateral trimming should not be done on the bench, only in the air. I would put the CG as close to 3" as possible, your first thought at 2 3/4 is better than the 2 1/2 ...

the number of clicks really means nothing, you should measure the difference at neutral and let us know how far out of trim it is... the Viper is known to have trim in the Elevator ... there has been many thoughts on the subject .. most shim the LE up to fix the issue ..

In one of the next couple articles of MA columns, I will go over "how to trim a racer"


Scott Causey
20V

RE: VIPER TRIM ISSUE:
 

Well Scott C, that is the way I was taught to trim out a plan in 424 by some very well know pilots here in central Florida. As far as the speed, I have never had an issue with carrying a 45 degree angle on the long course, and the drag you create by rolling the extra 180 degrees per lap (45 degrees x 4) will more than offset any small trim required. I have tested this with on board telemetry (eagle tree system), and with only rolling 1/2 as much, you loose less speed in the turns (spending 1/2 the time rolling(induced drag)), and begin accelerating out of the turns faster. We fly with the 16.5K rule here, so keeping the speed up without being able to let the engine unload is a bigger deal here than other places where you can leave the line at 17.5K or better. If you have some data to the contrary, I would enjoy hearing about it Scott. Anything that will make me faster on the course, I would welcome the information and experiences you have. I am all about setting fast times! :D

I agree the plane should fly flat and level from horizon to horizon in 428, because you got the power and speed to hold knife edge from pole to pole. For the CG location, I tend to watch it in the turns and make sure the fuselage tracks straight (parallel to the ground) in the turns. Moon shots? Better get the throw meter out and check each elevator deflection first, then adjust lateral balance like Scott C. says. ;) If you still have to carry elevator trim, shim the elevator (assuming you didn't glue it in!) to get it to neutral. If you are carrying UP trim, I think you may want to slightly sand down the LE of the elevator to raise the TE.

RE: VIPER TRIM ISSUE:
 

Hi Guys,

Looks like you steered me in the right direction. I proped up the wing on the workbench last night. I placed the bottom side up and blocked the trailing edge of the wing. I took measurements an specififc intervals on the trailing edge and then measured the height to the table.

*** I have 3/4" at the Root to start with.

*** The Port wing (left while upside down) at the Tip was 7/8".

*** The Starboard wing (right while upside down) at the Tip was 5/8".

So viewing from the back of the wing, on the fuse the left wing goes up an 1/8th of an inch and the right wing goes down a n 1/8th of an inch. I guess thats an issue, huh? This would make it roll to the left and would explain why I need about 12 clicks of right to get it to fly straight. Agreed???

OK, So the Million Dollar question: How to fix. I was thinking about useing the Heat Gun on the bottom only and see if I could get the twist out. Any angle I should follow while trying this? I am thinking either diagonal from the center of the leading edge to the wings tips or just along the lower 3-4 inches of the wing from the trailing edge up. Any suggestions or is it mostly hit or miss with this one? Any other suggestions would definitely be appreciated.

Again Thanks for all of the help , Now and in the Past..........



PS.
Not that I am any sort of beginner, but I like to bounce idease around with other guys like the group here. Its Great to get info and new ideas or solutions to new and old issues from other guys such as yourseleves. After lookng at the views , there also seems to be a lot of guys who may not participate in a discussion such as this, but they are reading it. As of last count there were 128 guys who read this post, I bet some of them have picked up info as well.

Thanks Again


Ed


"As my Caller and Son would Say" - " 1-2-3- Ready "TURN RIGHT"

LOL....

RE: VIPER TRIM ISSUE:
 

Hi Scott,

The Elev. has 1/16th of Up trim and I am familiar with the V-Tail issues on the Viper. My tail is Glued at this point the only thing I can do is to cut and re-do. I am not going to bother with that. If I need a few clicks of UP at this point theres not much more at this point. Next plane we will get perfect. As for the Aileron trim - the 12 clicks equates out to 1/16th of trim on the aileron. I hope that puts a number on the amount of clicks for you.

Ed

RE: VIPER TRIM ISSUE:
 

These issue's are why we created the vortex in 424 version, the wings are perfectly straight, the directions will show you how to put the tail in perfectly straight and you won't have these issue's, the issue's your having with that kit have been the same since it came out, they have never taken the time to fix the tail incidence or the wing twist. There are several ways to fixing a twisted wing from heating it with a heat gun to cutting a slot in the wing to help twist it back, only problem is that it will probably eventually go back to it's original state. You will find yourself fighting the trims and bench twisting the wing over and over. If you have 3 incidence meters that is the best way to see how far out of whack it is, put a meter in the middle and on both wing tips at the same time and see how out it is, and then twist accordingly until all 3 meters read the same, no matter how the wing is sitting.

RE: VIPER TRIM ISSUE:
 

Ed, you may want to see if, like Scott C. said, that clears up by moving the CG back to the rear just a bit. With the fuel tank in the nose of the Viper, the fuel load moves the CG forward causing you will have to trim the elevator up some. I bet when you are near the end of the fuel load, it wants to climb just a bit as the CG moves to the rear some. 2 3/4" ~ 2 7/8" from the LE of the wing with the fuel tank empty would most likely take some of the up elevator trim out.

RE: VIPER TRIM ISSUE:
 

You should try to mount your fuel tanks in these quickies more in the wing saddle area on the CG, that way the CG doesn't change as the flight progresses, and you should also not use such big tanks if your only racing the airplane, I mean I think I only have a 4 ounce tank in my 424 airplane.

RE: VIPER TRIM ISSUE:
 

Hi Guys,

Scorpion and Marcus

I am running only Bladder tanks right on the CG. Also the CG is at 2-3/4" back. Weight of plane overall 3lbs. 14oz.

Ed

RE: VIPER TRIM ISSUE:
 

Ed,

Understand also that the further back your CG is that faster you become. When you move the CG back, your elevator throw become a lot less, meaning less drag .... faster

Just don't go back too far and create the bad snap ...

Good luck with everything and hope you do well.



Scott Causey

RE: VIPER TRIM ISSUE:
 

Hey Scott,

Is that true. The farther back the CG. the faster the plane flies? Actually I was not aware of that. Any other speed seceret tidbits like that out there?


Ed

RE: VIPER TRIM ISSUE:
 

Hi!
All pylon racers (as well as all airplanes) should be trimmed so that they fly straight a full throttle!
That's very important!
Second . You should always trim a plane as tail heavy as possible as this means the plane will fly faster and less elevator will be needed to alter its cause.But be careful ,Too much rearward C of G and the plane will be impossible to fly.

The wiper is best trimmed as the manual says, C of G 75mm (3" ) from the leading edge.
You can easily check the plane for any tendencies to be nose heavy by flying straight at full throttle and doing a sharp 90 degree pylon-racing turn, just using aileron and elevator. The plane should just "swooop" trough the turn without an tendencies to nose dive or ballooning. No correcting aileron,side-rudder or elevator should be needed.

RE: VIPER TRIM ISSUE:
 

Your fix is simple.... I had a Viper with a terrible twisted wing last summer. To remove the required aileron trim I cut one side of the offending trailing edge loose and bent it/reglued into position to be straight - took three tries but the third time was perfect and I was carrying no aileron trim. Two incidence meters help diagnose where the twist is and what needs to be done.

For the elevator trim... if your tail is glued at zero... leave it alone!!! Shim the leading edge of the wing up until the elevator trim is neutral... makes a world of difference.


2-7/8 CG is a good staring place for that airfoil... I would make this adjustment first before any others as it will affect your elevator trim slightly.


Like the other guy said... lateral balance in the shop is just a quess. I put it close to neutral in the shop just because I know I will only need a few quarters at most on the wingtips or tail to achive an acceptable racing trim.Good luck!


dan


P.S - My Viper with the terrible twisted wing took fast time on the third heat of it's first race after being fixed! Not too shabby for what looked like a lemon! Flew great after fixing and trimming.

RE: VIPER TRIM ISSUE:
 

I would check to see if Great Planes would warranty it first. If you want to see how to properly set up a racer, check out Jett's site (crap trap series) http://www.jettengineering.com/

RE: VIPER TRIM ISSUE:
 

Hi Duane,

Thanks for the input, but I have 2 Vipers we race now, both of which are 2 years old, so warryt is not an solution nor do I think it is needed. I have been to all of the web sites Jett, Daroll Caddy etc. As for the Crap Trap Series - Some Great stuff, I have printed it out almost all of the chapters and have them Highlighted and Underlined in RED. I highly recomend some of Dub's chapters, especially the one on "Trimmimg for the Race". Just trying to work out the plane to get it to be the ultimate racer for what it is worth. I think Vipers fly pretty good and it seems like a good precentage of guys are racing them. Its the challenge to get it to fly as smooth and fast as possible I guess, by "Testing and making Adjustments thru Trial and Error".

I do Race in the NEPRO Series of Racing - 424-Standard Class, a GREAT bunch of guys. I am far from most of them and travel to race a few hours each time we race. Thanks Again for all of everyones input and help, it really does help and I think a lot of it goes Un -Thanked.


Thanks a Bunch again to all who respond, and PLEASE keep up the responses.

I know I am not the only guy who appreciates it. Check the view count!!!


Ed

RE: VIPER TRIM ISSUE:
 

i am so happy with my Vipers after knowing the exact set up tips, [ thanks to this forum ] had a race last week and Viper one powered by the o.s. 46 ax blew away the expensive Shotgun powered by a super tiger 46. imagine if Viper two was racing with the TT Pro 46. this was won not just by cornering but also straight line speed.

RE: VIPER TRIM ISSUE:
 

Hi Guys,


We'll we had our first race of the year last weekend. Our first heat we had there was an interesting twist to it ( at least for me it was interesting). It was the 4th or 5th lap of the first heat and I was in second place about 100 feet behind the leader. Now my son was calling for me and the adrenaline was pumping in both of us, he was watching my plane and the leader trying to get me into 1st place. We were coming out of turn 3 and hot on the tail when as we approached pylon 1 he saw the leader turn, so naturally when he saw the leader turn, he yelled turn. Yikes, now being about 100 feet behind and turning when he yelled turnI now just cut pylon #1. I now had my first cut. So now being a lap down I had my work cut out for me. I was able to catch up a bit and finished in 3rd. So now I had to make up for that. The next heat I took first and in the 3rd heat I took first. We broke for lunch and of course 20 minutes after we got started again the rain came down and the race was called for the day. The end results put me in 2nd place overall for the day. I must have been really trying hard because in the 2nd heat I beat me own fastest time overall from last year. I ran a 1:26.4 and got fast time of the day in 424 standard class. Not to bad for the first time out this year. The plane was really doing very well. I was able to get out to the field the last 2 weeks and get about 5-6 flights on it to really get it dialed in. It is good but there is still room for improvement. We will continue to work on it. I was able to get the plane tweaked better due to the help I have recieved thruout this Q-500 forum.

So I say Thanks again who all were involved and gave help.

Maybe one day we will meet and I will get the priveledge to race with some of you guys, and with the help you guys have given me, maybe I just might win!!! Wouldn't that be kick. Huh.....

LOL....

Thanks Again

Ed

RE: VIPER TRIM ISSUE:
 

From Marcus posts, Wing warp check set-up and tank on the balance point.

Ed s