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Thread: Q500 cg


  1. #1

    Q500 cg

    Hey Guys,
    Well last night I thought I would go out & fly my Q500 V-tail racer after moving the battery pack forward now sitting on top of the tank between firewall & front former. I put the Elevator trims back to level with the tail plane, put it up & still had to give it at least 2 / 3 clicks of down elevator trim cause it climbed, The racer flew no better than it did by having the battery pack behind the fuel tank in the fuse. But I find it seems to land faster & bounce a lot more than it did before?
    Your comments would be appreciated.

  2. #2
    speedracerntrixie's Avatar
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    Based on this I would say the incidence is off. Realistically unless you plan to race I would put the battery back and just fly it with the trim. Yes the trim is slowing you down but IMO it would be an immeasurable amount.

  3. #3
    Hey Speedracerntrixie
    Yes that's what I intend doing we have got racing tomorrow so I will see how it goe's.

  4. #4

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    I agree. The incidence must be off. Again being a shoulder wing I would add shim stock to the trailing edge until it required up trim to fly level then back down from there. One other thing to try. When you drop the throttle to idle does the model drop its nose? Do you have a incidence gauge? If so set the wing at zero and lay a level across the mounting lug of the engine and make sure it is level too. If it is pointed up there may lie your problem.

    Bob Harris

  5. #5
    Hey BobHH,
    Yes the firewall is square & wing at zero, just thinking if I had to much shims under the trailing edge wouldn't it do the reverse? E.G. like head towards the ground instead of the trouble i'm having of it climbing. Putting 1/32 ply shim under it still made it climb but of course I did put the elevators back to flush with the tail plane.

  6. #6
    I use two Incidence meters on racers when I set them up I use the Robart Jeweled Movement brand.I will try today to see what happens when I drop the idle from full to nothing & get to you guys.
    Thanks.

  7. #7

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    Quote Originally Posted by spraybar View Post
    I use two Incidence meters on racers when I set them up I use the Robart Jeweled Movement brand.I will try today to see what happens when I drop the idle from full to nothing & get to you guys.
    Thanks.
    How are you using the incidence meter on the tail. I mean such as clamping onto a square plate sitting in the vee?

  8. #8

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    Too many shims would cause you to need more up trim. If 1/32 did not do it try 1/16. I setup a Viper once and it needed 3/32 shims under the leading edge of the tail to fly straight. The key is making sure the wing and tail are in the same line. I use an incidence meter on the wing and bubble level on the tail with square aluminum bar resting between the flat surfaces of the "V" of the tail.

    Bob Harris

  9. #9
    Hi Conrod,
    I use the incidence meter on the wing I then level up the back of the fuse so its level & the wing is at zero degrees I then put a little hand held level running down between the two tail Vs I also recheck it by putting a ply 1/8 Plate between the two v- tails & put my little level on top & it reads that the bubble is still in the middle like the wing so this now tells me the tail & wing are at zero degrees. I also use a big square hard against the fire wall & there is no gaps between the level so this tells me the fire wall is level. I appreciate your return comments to see if this is right, or how you would do it.

  10. #10
    Hey BobHH,
    I tried a 1/32 shim under trailing edge of the wing saddle put the trim back to square with the tail plane & flew it, it did the same thing climbed so you reckon I should try a 1/16 shim & see what that does.I will try tomorrow & put 1/16 shims under the rear of the trailing edge of the wing saddle, put the trims back to square with the tail plane & re: test fly it I let you guys know tomorrow night how it goes.

  11. #11

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    The vipers are built so far out of square (and nothing by great planes has been done to rectify this) that it is a trial and error to get one to fly strait at speed, incedence is the first thing, CG is the next
    I got tired of shiming the V tail and shiming & straitening the warped main wing - I went composite - well worth the money

  12. #12
    Hey Scoeroo,
    Yes I believe you are right, composite are so perfect,& when you buy a viper or something of that arf always seems to need trimming badly, same as when you scratch build one the incidence has to be so perfect or else again you will need to trim it. I know a couple of guys with composites & they flew like it they were on rails no trim required on any movement. I can remember a while go when I went & had a look at the pylon racing a guy had a brand new viper, he was trying to start it but had flooded the engine, & cause the engine was so flooded when he went to turn it over again, sort of jammed up the crank from turning over & it broke the back end of the fuse where the v-tail connects to the fuse. Broke it in half before he even got to fly it. Man that would really piss you off ah lol

  13. #13

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    I would keep adding shims until it flew level with no trim. Then pot the wing with the shim in place.

    Bob Harris

  14. #14
    Hey Bob,
    Look went out this morning & flew my racer, I checked to see whether the nose dropped when dropping from full throttle to idle & it did not drop its nose. I did not get a change to put a 1/16 shim under the rear of the wing saddle as it started to rain but hopefully have another go this coming weekend.

  15. #15
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    spraybar, if your wing and firewall are all at zero degrees (as you said you verified with 2 incidence meters, and that the plane didn't pitch under glide), than you need to move the CG forward in 1/8" increments and re-fly it. If you adjust the incidence of one surface out of zero to get rid of elevator trim, you have created the same amount of drag in a different location! Most modern quickies CG is 2 3/4" to 2 7/8" from the leading edge so you stressing about trying to keep your CG at 3" back is silly. Do you know why some planes can carry a more rearward CG? It isn't because it's as efficient as it could be! The airplane is telling you what it needs, you just need to listen to it.
    Scott Smith
    NMPRA 86t - District 7 VP

  16. #16

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    I just told him that in his other CG thread - he might listen ?
    He's playing with to many variables at one time, he needs to work on one aspect at a time

  17. #17
    Hey Scorpion Racing,
    As I am new to pylon racing, I am not really stressing about the cg been at 3 inches its just what I have read & been told by others to do, I do appreciate every body's comments & they are awesome thanks. So I will continue to move the cg forward hopefully until I have no elevator trim. Tell me what would happen if it was to nose heavy what would the racer do in flight etc. 0r would it come into land quite fast.

  18. #18
    Scorpion Racing's Avatar
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    That's cool spraybar, just felt like we were all telling you the same thing and it wasn't what you were wanting to hear so you ignored it! With the configuration of equipment in a Viper with a TT Pro 40, it would be really hard to make it too nose heavy. Even harder with a JETT 40, as it is almost 2 oz. lighter.

    If you got it to the point where you had say 1/8" of up trim to fly level, it would push in the corners and land a little hotter. It would also require mote elevator travel to make the same turn. Conversely, too tail heavy could make the tail search and over rotate in the corners causing an increase in drag and many more corrections (any correction will slow you down) during the flight. You have to find the equilibrium where the trim inputs are minimum and it will fly like it is on rails. There is a ton of set up tweaks that all add up to a proper flying quickie. It starts with correct linkage set up, minimal throws to achieve smooth turns and never putting more throw in it because you think it might come in handy! Your elevator at full pull should just make the 100' torn 2~3 on low rates, and just inside (90' or so) on high rates. Your roll rate should allow one complete roll from turn 1~3 (575'). I also set my down elevator to 1/2 my up elevator to make pushing out easier and smoother. Pushing out? Yes, you should never have to roll 180 degrees,, pull, roll back and proceed. If you over pull a corner, push the elevator down while in knife edge and avoid rolling. You will be amazed at how much that whole mistake will slow down a quickie. If you don't believe me, rig up some eagle tree on-board telemetry and check it out; I did.

    There are a lot of things to do to fly smoother and consistant that will all make you faster on race day. All about plane set-up and your flying style, non about the engine or prop.

    Best wishes,
    Scott Smith
    NMPRA 86t - District 7 VP

  19. #19
    Hey Scorpion,
    Thanks so much for all your help I am learning heaps just been on this site, I also can pass on information to others here in NZ regarding these problems. I'm sure if I or any body else has any problems with there Q500 I will be sure to put it on this site for help. Thanks to all so until I have another problem GO FAST TURN LEFT Happy flying.

  20. #20

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    We are all assuming the plane is a Viper??
    No mention of the planes name in spraybar's first post under the heading, Q500 V-Tail.

    Hi Guys,
    I am new to building these V-Tail pylon racers, can any body help me with the following answers to these questions.
    I have built a Q500 racer, I have glassed & painted it & it looks really awesome I test flew it the other day fly's really good, but it was climbing so
    I had to feed in about three trim clicks of down Elevator, now what I want to know is if somebody can tell me, if I sand the back trailing edge of the wing saddle
    Would that square up the elevators to the tail plane, & then the elevators would be neutral to the tail plane. I don't want to cut the tail plane out of the fuse just
    To move either the trialing edge or the leading of the v-tail up or down cause its all been painted so nice ah! so could i just sand the back of the wing saddle & would that correct the neutral position of the v-tail by doing this or would I have to sand the front of the wing saddle to correct this problem can some give me some advice please.

  21. #21

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    How does it fly when gliding? Trim for a glide first (right at engine shutdown from speed), then adjust the thrust line. As far as the CG goes, you want a good turn (50-60 foot radius) with full up elevator. If you get that with 1/8 to 3/16" (neutral to full up) at the trailing edge, then you have a good balance point. You want to be able to smoothly make the turn at 2-3, with the ability to turn tighter to avoid traffic if necessary.
    - Supplementary insipid innocuous inane vacuous proclamation

  22. #22
    Hello Highplains,
    What I have done is checked the racer at low speeds does not drop it's nose, since putting the battery pack forward has reduced the trim on the elevator I reckon if I go a wee bit more with putting the battery pack right behind the fire wall will bring the elevator flush with the Tail Plane with out distorting the flying characteristics of the racer. I will try again & get back to this site.

  23. #23

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    I don't worry about the trim at low speed, it's getting it trimmed at high speed that makes an effective racing plane. So trim it at speed to fly level, then kill the engine. If it stays on it's path just as the engine dies, then you have the wing and tail incidence correct. If it climbs or dives, then you have the thrust working against airframe errors.

    A few years ago, I was experimenting with the engine set with 2 degrees of down thrust, which meant that when I killed the engine the plane would climb very rapidly until the speed burned off. This was just an experiment to find out a few things about props on pylon models, but it made trimming the model rather difficult.
    - Supplementary insipid innocuous inane vacuous proclamation

  24. #24
    Highplains,
    Yep I will do what you have said in your first paragraph above, & see what the racer does I will get back on this site with my result.
    Thanks.

  25. #25

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    Hi!
    Been racing for many years and the first thing you should do is to trim it out right . But first you have to set it up right on the building board.
    With a V-tail this could be a Little tricky as there is no flat ,horizontal, stabilizer to put the Robart meter.
    But if it's a Viper most of the time you have to lower the leading edge around 2-3mm to have a perfect flying airplane.
    Cof G is ok as it says in the instructions, just check it out by holding both of your index fingers under each side of the wing at the right positions. The Viper should tillt slightly ,but only slightly, forward at this point.

    Elevator throw should be around 3-4mm meassured at the trailing edge of the elevator. That's not much ,but it's all that's needed ,both for racing and for landings. No dual rates are needed. When so small movements is used it's vital that you use a very short servo arm. I drill an extra hole in my servo arms apprx 5mm from the center of the servo arm and use 100-150% travel adjustment! Never ever! I repeat! Never ever use the electronic travel adjustments in the radio when final trimming the airplane! At least do not go below 75% on electronic trim.

    It's also vital that you balance the plane latteraly. Holding the spinner nut and at the same time holding under the tail of the plane should keep the planes wings level.
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    Last edited by jaka; 03-14-2014 at 09:37 AM.
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