Dave Wilshere

Most of ours the batteries are back of the canopy,..with light JR servos even around the fuel tank.

Skunkwrks

Using those JR 8911 coreless so a beefy servo, using a Jeti Lion 3200 for engine start, two A123 batteries 6.6volts for the CB210.
One Life1800 pack for the GS200 landing gear and a 2100mah 11.1 pack for Navi lights, a total of five batteries.
Dave, how does your Viper fly with CG at the back of the wing tube?

Skunkwrks

Once I inputted the new position of the rear of the tube, 30mm behind of being at the front

The xicoy then said I only needed 454g of weight as far forward just behind the front bulk head for the gear..

I can move my battery setup back if it's to nose heavy .

I'm using JR 8911 servos so 76gram 2.71oz, with three in the tail makes it harder to get balanced without ballast being added.

Next time I'm doing to use 5000-6000 Liion batteries as ballast first, first build of a jet.


Thanks for your input.

FlyJ

Only 450g?! Only?!

I would try to balance it the old fashion way. I have my turbine battery up in those nose, and the receiver packs are midway on the canopy and I’d say it’s about perfect. King tech 160, JR 8611s in the tail.

Dave Wilshere

It’s an aeroplane with a huge stabiliser, so the balance range is also large. The Rebel series are also similar. Using the no wings, balance on the wing fixing screw holes you end up with a perfect flying aeroplane. I have a (well documented) dislike for the electronic scale method.
What ever you have to do to balance as I state in this thread (ideally with no additional weight) do that and enjoy a great aeroplane.
Ensure there is some fuel in the tank or you are going to be adding unnecessary weight and flying nose heavy again.

Blancr

I can confirm that Dave's advice is exactly right. I balanced my Viper as per Dave's instructions and it flew perfectly. More specifically I have an 'electronic balancing machine' but have now reverted to the 'piece of wire / string' method. Much simpler and ultimately, for me, much more precise.
Enjoy the Viper - great flying plane.
Bob

Agrav8ed

I assume that balancing this way is with the rudder and stabilizers on? (I know, I know but I had to ask). Is the nose gear down or up when you balance this way?
Thanks,
Tone

ECalderon

Hi
Following Dave's recomendation I have the turbine Life 9.9 V 3800 mah batteries on top of the back of the fuel tank, and two pulse 3600 mah batteries below the windshield. Al JR 8711 servos. It is still a little bit nose heavy (nose tends to drop a bit in knife edge. Initialy I had in the nose the turbine battery, two Duralite 5000 mah Life batteries and about 400 grs or more of lead way up in the nose.

Follow Dave's advice, you won't regret it.

Regards
Eduardo

Dave Wilshere

Yes, as posted. Tails and canopy glass on. Just no wings.

Skunkwrks

About 1" of fuel/ 1000-800ml in the tank is on for balance. I believe those large tail surface help with a large CG window.

The Xicoy is very accurate for weight but flying it well tell you exactly where the CG should be.

Skunkwrks

Thanks, Bob I will enjoy this Viper hopefully a long life of many enjoyable flights.

Skunkwrks

A fellow F3A pilot mentioned the same thing about balancing with the noes gear up as it will shift the CG backwards during flight.
That's very fine-tuning of the CG position.

Skunkwrks

Sound like your has a similar weight setup as mine.

At 45 incline does the nose drop after a couple of seconds, also do the same manoeuvre invert and take your hands off the sticks to see if it raises or falls down.

Knife-edge has a lot to do with the side surface of the fuselage helping to hold the fuse steady while on it side found this on my Imac planes.

Skunkwrks

What a thread without photos, here some of my Viper with the batteries position for final balance, still have to glue in the front canopy.
Front 3200 Jeti Liion and 2100 Li for Navigation lights

The Jetmunt display is at the front edge of the photo with CB210 box and GS 200 module

Main tank with vent to bottom of fuse and JetsMunt 166.

Wing connection in the plastic loom to protect wires from the intake air.

Skunkwrks

Here a few more photos of the install of my Cayman Viper.


Front left One of three receivers with the vent tube on the side of easy access. Fuel valve and filter downstream before engine consumption.


Front left nose both LiIon packs 3200 mah and 2100 mah. The display for the Jetsmunt engine is on an adjustable base. The receiver switch is located up here.


Nose front right both A123 batteries and Life 2150mah for the GS200 module. A lot neater on this side.


Just behind on the right nose, the bulk of the control wires plus the third receiver, second one for the CB210 unit. You have the pump and ECU control for the Merlin 166 engine.

Dave Wilshere

You should really use the SMC clear for both the tank supplies, plus keep the overflow tube as short as possible…
Tygon will collapse slightly under maximum draw.

Skunkwrks

Only using a short piece of Tygon from UAT to the pump. The clear tubing didn't want to bend around to reach the pump and applying

that amount of heat to it can make the clear tubing brittle. So Dam if I do and Dam if I don't.

The Other Tygon is for filling the tank, I have found a long overflow tube helps to prevent siphoning of the fuel during the flight.

I experienced with my friends Avainti last year noticing fuel on the outside of the fuse, a couple of feet more of tubing and the problem was resolved.

Dave Wilshere

I loop the clear tube when it’s close. No heat needed.
Tygon on filler is right.
All you need is the pipe looping up above the height of the tank and it won’t siphon. A long overflow promotes high pump figures…it’s not good.
Your balance battery position allows for canopy/glass etc?

Skunkwrks

The batteries with the front canopy in I can get my thick fingers in there and pull out the batteries.
High pump number from a long overflow tube, explain why?

Dave Wilshere

No, I’m asking whether the balance check included all the items. Your set up looks nose heavy.

Because the air that has to go in to replace fuel is dragged along the long tube line.

Skunkwrks

Dave, I'm using the Xicoy balancer with the CG point being at the rear of the tube and not the front.

I'm no concerned with the longish overflow, it's actual 14" short than what I had planned. Those Jetsmunt have a brushless pump so I'm not concerned with the vent line.

Dave Wilshere

The question was are you checking the balance with everything installed.

Still too long…

Skunkwrks

Oh yes, everything in and on including the canopy front windscreen with five batteries in and like other suggested the rudder is on the fuse.

Skunkwrks

My concern is releasing unburnt fuel into the air which happens will doing rolls, so a long overflow helps prevent and slow the fuel from being thrown out of the overflow vent.

My friend when he added a whole circle of the tube above his tank, it stopped the fuel from been thrown out of the vent, plus added additional flight time with no fuel down the fuselage from aerobatics.

Dave Wilshere

Out of tank, up high above tank in a loop, then straight down and out. Each way up the fuel head stops siphoning when the fuel draw is not high enough to stop it venting.