Q-500 Racing Discuss AMA 428, AMA 424, and any other variants of Quickie 500 racing

Yes, another Viper question...

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Old 08-25-2008, 01:00 PM
  #1  
wildnloose
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Default Yes, another Viper question...

Hello everyone,
I have finished putting my Viper together, but now I want to use a bladder tank and place it on the cg. Of course now this means moving the throttle servo and I think, sure, no problem, lots of people have done it.

Now, I am asking myself; where to put it?? Not liking the front area (where the tank was), too much work. No room behind the tank. Uh Oh, now you've done it(I forget I'm not that creative). Lets go to rcu and find out where people have placed them. Well, its not that easy....search comes up empty.

So now the question, for those of you who have put the tank on cg, where are you mounting your throttle servo???

TIA
Wild
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Old 08-25-2008, 01:08 PM
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daven
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Default RE: Yes, another Viper question...

Behind the tank. Should have room there for the receiver, switch and throttle servo.

Battery and servos behind the wing.
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Old 08-25-2008, 02:03 PM
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wildnloose
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Default RE: Yes, another Viper question...

Thanks,
I forgot to add. I am using the 5 1/4 oz. tank, its pretty long. Right now the aileron servo butts up to the tank, so no room for anything else. I cannot move the tank forward without dremeling out the wing hold down and the front former. Not liking that idea. I guess I need to buy a 4 oz tank.

thanks
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Old 08-25-2008, 02:39 PM
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daven
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Default RE: Yes, another Viper question...

What receiver and throttle servo are you using? I remember being able to fit receiver/switch/servo in there under the aileron servo / rods.
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Old 08-25-2008, 02:41 PM
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Default RE: Yes, another Viper question...

I put all three servos in the hatch compartment behind the wing. Three HS-85s fit perfectly.


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Old 08-25-2008, 02:55 PM
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Default RE: Yes, another Viper question...

I place the tank (4OZ) in front of the wing servo and before the #2 former - fits fine. I place the tail servos in the rear with the throttle servo mounted flat (arm has a straight shot to throttle) just behind the tank on throttle side of fuse. I place the battery in rear behind servos and receiver on opposite side of fuse next to throttle servo but also behind tank. This usually gets me in the ballpark balance wise. and all fits very easily. Good luck!
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Old 08-25-2008, 06:51 PM
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Default RE: Yes, another Viper question...


ORIGINAL: daven

What receiver and throttle servo are you using? I remember being able to fit receiver/switch/servo in there under the aileron servo / rods.
For the servos, HS225's for ailerons and elevators, HS85 for throttle.

I have not made my decision on which receiver, either Spektrum AR6200 (mainly for channel conflicts) or the JR700.

I will use a 4cell, 720mah battery.

I made a mount to place the throttle servo and switch behind the tank, but the throttle is hitting the aileron servo. I am now thinking about shaving down the stock aileron servo rails to get more clearance. I hope its enough, I like this location.

Thanks everyone, I really appreciate the input. I know this is a simple procedure for most of you guys, but like I stated before I am not very creative when it comes to this kind of stuff. Especially when I am suffering from lack of sleep for the last 2 weeks (Olympics).

I need to get this done, it needs to be race ready by Sunday....[>:]
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Old 08-25-2008, 06:59 PM
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Default RE: Yes, another Viper question...


ORIGINAL: DMyer

I place the tank (4OZ) in front of the wing servo and before the #2 former - fits fine. I place the tail servos in the rear with the throttle servo mounted flat (arm has a straight shot to throttle) just behind the tank on throttle side of fuse. I place the battery in rear behind servos and receiver on opposite side of fuse next to throttle servo but also behind tank. This usually gets me in the ballpark balance wise. and all fits very easily. Good luck!
Thanks, this sounds good. I will have to check it out...
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Old 08-25-2008, 08:09 PM
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Default RE: Yes, another Viper question...

Step one, put the dremel inside the unbuilt fuse and than put a sanding drum on it. carefully hog out the inside without making the dremel spin. You take a little off all directions. Skinny fingers help. That is a Jett 6 oz. skinny tank. I laid the throttle flat on a little wooden bracket I made. I just use 1 drop of glue, so I can just snap it out for repair
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Old 08-25-2008, 08:47 PM
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Bill Vargas
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Default RE: Yes, another Viper question...


ORIGINAL: wildnloose

Thanks,
I forgot to add. I am using the 5 1/4 oz. tank, its pretty long. Right now the aileron servo butts up to the tank, so no room for anything else. I cannot move the tank forward without dremeling out the wing hold down and the front former. Not liking that idea. I guess I need to buy a 4 oz tank.

thanks
Don t worry to much about doing some sanding on the bulkhead and the wing hold down to make the tank fit,,, its a common practice with most wood Racers.


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Old 08-26-2008, 12:32 PM
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PylonDave
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Default RE: Yes, another Viper question...

If you are useing a TT pro you only need about 3 OZ of fuel for a 10 lap heat.
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Old 08-26-2008, 03:00 PM
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Default RE: Yes, another Viper question...

SS, thanks....a pic is worth a thousand words......definitely makes easier to visualize.

Bill, thanks I feel a little better about it...

Dave, I'm not sure how much fuel I will need yet, I will run my mag .52. We just started racing this year, they went a little easy on the engine size to get more participation. They are currently allowing .40's and .46's, but you have to use a 9x6 apc prop and they will provide fuel. My .52 is an extreme exception. They are allowing it because they do not think I can fly (most have never seen me fly, my field is 35 miles away). But I am sure that if I win any heats it will soon become an issue..

Boy are they going to be sorry....
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Old 08-26-2008, 07:02 PM
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Bill Vargas
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Default RE: Yes, another Viper question...

your welcomed

I don t even use bulkheads in the Quickees that I build, they were just a PITA so I quit using them,,, but do make sure them wing blocks are beefed up with some triangle balsa and epoxy.


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Old 08-26-2008, 07:23 PM
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daven
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Default RE: Yes, another Viper question...

Not if they are slotted and tabbed Bill
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Old 08-26-2008, 09:41 PM
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Bill Vargas
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Default RE: Yes, another Viper question...

True!

Them lazor cut tabs and slots are nice and are the cats meow for most builders without question. But as a scratch builder I kinda tend to try different things to see what works and/or isn t really quite necessary such as those 2 bulkheads in my scratch build projects.

So in other words, I just got tired of cutting out bulkheads and reduced my scratch build time [sm=shades_smile.gif]


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Old 08-28-2008, 12:43 AM
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Default RE: Yes, another Viper question...

i really think Bulkheads are the structure of any fuselage other than glass types. when i cut these i will only leave approx 1/4 inch of wood material to all 4 edges and use 2 x 1/16 inch ply laminated to form cross grains, this method is very strong and very very light. the same goes for fuselage sides where i use the good old method of balsa doublers set at 45 degrees and lightly laminated to the mains.
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Old 09-10-2008, 11:27 AM
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Default RE: Yes, another Viper question...

Update, first let me say thanks again to everyone...

After scratching my head a little bit I installed everything pretty much like the pics Super Splatter posted. I did mount my receiver behind the elevator servos.

The cg was about 2 7/8. My Mag. 52 was turning the apc 9x6 at 16.7k, backed off to 16.4k. Still need to back off some more (unloads like crazy in a dive). Even though I did not push it hard I know it was doing around the 100mph mark.

The viper shot straight down the runway and lifted off without incident. It's easy to fly. It tracks well, floats forever, and boy do I like turning on a dime. I thought I had set up dual rates and I was flying on low, but forgot I changed radios, so I flew on hi rates. I never felt it was out of control during the flight. I decided not to shim any surfaces until I see what I had to deal with. Well, lets just say that it was pretty cool doing outside loops without any stick input .

I did not get to race (family obligations), but you bet I will be ready for the next one. But it does not matter, I like this plane, it will probably become my sport plane.

Oh, and I noticed that everyone says to shim the tail. But I want to ask, I thought the wing provides the lift, so I thought you would shim the wing. Pushing the tail down to put the wing at the right angle to provide lift does not seem right to me.

What do you guys think???
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Old 09-10-2008, 11:45 AM
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Default RE: Yes, another Viper question...

Your shimming the tail to take out the necessary trim you added to get it to fly straight and level.
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Old 09-10-2008, 01:17 PM
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Default RE: Yes, another Viper question...

Look at it like this,,,

lay a flat peice of wood on the table(wing) then lay another peice of wood behind it(Horizontal stab). Lets say we know the wing is at zero degrees and if the tail(horizontal stab) is off,,, the plane will pitch accordingly.


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Old 09-10-2008, 02:26 PM
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Default RE: Yes, another Viper question...

wildnloose, you think like I do.

All the tail is doing (whether it's carrying trim or not) is adjusting the angle of attack on the wing to get to the correct flight attitude. Personally I'd adjust the wing to keep the tail at zero. You'll find that most racers set their airplanes up with the wing at zero and usually have some negative (up elevator) in the tail. The negative is there to push the tail down, and get the wing up where it wants to fly. I just put the tail at zero and adjust the wing to where it wants to be.

The way I look at it is that if the tail doesn't have to work at pushing the tail down (along with the fuse, plus changing the engine thrust line), it's creating less drag. But that's just me.

Most racers are bore-sighted on "everything should be 0-0-0", and if that doesn't work, they adjust the tail. I don't believe in that thinking, it all depends on the airfoil of the wing, and numerous other factors. However I do believe that the engine and tail should be zero, and I'm not against a slight bit of right-thrust.
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Old 09-10-2008, 02:33 PM
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Default RE: Yes, another Viper question...

Well, lets take it one step further. I measured the wing, tail, and engine (fuse it reference). All were set to 0 (actually they were already there, just had to trim the tail a little to get a better fit). With all at 0, the plane pitches nose down hard (I used all the up trim on my radio and it was still not enough). Of course I could be off with what I measured, but lets just say that I am not for the moment.

Now, I thought the main function of the wing was lift and roll, while the rudder and elevators controlled pitch and yaw. In my mind this tells me to create lift with the wing, not the tail. And let me add this, there are about 6 guys that are racing locally, all of them shimmed their tails. To me it looks like their tails are dragging a little while flying straight and level. Would shimming the tail to create lift cause this??

And let me say that I am not trying to argue or disagree with anyone here, I am learning and having fun doing it.
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Old 09-10-2008, 03:02 PM
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Default RE: Yes, another Viper question...


ORIGINAL: wildnloose

And let me add this, there are about 6 guys that are racing locally, all of them shimmed their tails. To me it looks like their tails are dragging a little while flying straight and level. Would shimming the tail to create lift cause this??
I believe it would. The reason being is that the tail is "pushing" down to get the wing to the correct angle of attack. I think you should shim the leading edge of the wing up to eliminate the elevator trim and see how it goes. I bet it looks more level in flight. I'd also bet that you'd be faster by shimming the wing instead of the tail.....whether or not its enough to be measured I don't know.
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Old 09-10-2008, 04:11 PM
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Default RE: Yes, another Viper question...


ORIGINAL: garys


ORIGINAL: wildnloose

And let me add this, there are about 6 guys that are racing locally, all of them shimmed their tails. To me it looks like their tails are dragging a little while flying straight and level. Would shimming the tail to create lift cause this??
I believe it would. The reason being is that the tail is "pushing" down to get the wing to the correct angle of attack. I think you should shim the leading edge of the wing up to eliminate the elevator trim and see how it goes. I bet it looks more level in flight. I'd also bet that you'd be faster by shimming the wing instead of the tail.....whether or not its enough to be measured I don't know.
Well... I have always set the tail with negative incidence for this wing... never being afraid to try different and potentially better, based on advice of faster pilots than me, on my latest Viper I set the engine and tail to 0 and shimed the wing to a positive incidence (about 3/16" at the leading edge). I think this should be close... if not... I will shim it some more and re-pot it. Makes a lot of sense to me and I bet it will track better on the side down the straights. I will report back my unbiased and maybe unreliable observations after I test it.


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Old 09-10-2008, 04:21 PM
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Default RE: Yes, another Viper question...

3/16" sure sounds like a lot to me....
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Old 09-10-2008, 04:53 PM
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Default RE: Yes, another Viper question...

Agreed, 3/16" sounds like a lot. I know our Proud Bird Q40 has just under 1/16" pisitive in the wing, which if I remember right, was just under half a degree. I think most the QuikV's were designed with about half a degree or 1/16" as well (haven't built one in so long I don't remember, but the wings were never at zero). I think you can probably get by with a smaller amount in the wing that you can with the tail, so if the tail's at 1 degree, you can probably get by with 1/2 or so in the wing. I never use incidence meters, just flat workbenches, triangles and rulers, so I never really paid a lot of attention to how many degrees.
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