ameyam

I fitted my Reactor 46 with a 75ax and had one day of flying couple of weeks back without too much balancing. It flew OK but just a bit nose heavy, so I put in some tail weight and packed it away.

Need to fly tomorrow and so took it out for rebalancing.

Lateral balancing:

Tied a piece of rope to the tailwheel and spinner backplate (not enough space on the crank to tie, ensured that the prop turned freely after tying) and held it up with the rope held in a rectangular shape so as not to get stuck on any part. Lateral balance is perfect (Had already balanced it for the 55 this way earlier and added weight to one wing)

CG:

I tried to check the balance holding it at the cg inverted with the thumbs on the cg line (12.1 cm from LE at the fuse) and it was just impossible to check without a helper. Problem with the CG machine is that the two vertical rode twist and add some non-linearity to the system. (Thats the best way to describe it) i.e. one of the rods is slightly behind the other and out of alignment and that causes a mismatch. I cant use the CG machines scale as the uprights intefere with the LG so I am just using the pads on the ball-socket joint.

Secondly, its frustrating to find out whether it is nose heavy or tail heavy- If you hold the nose slightly down it drops and if you hold the tail slightly down it drops. Have had this issue before as well, after balancing on the CG machine, Had to recheck with hand (two people lifting at the tips ) and its either nose or tail heavy but very slightly. (Yes, I have the ceiling fan off even though it madly hot that way)

Thirdly, this is balancing with an empty tank. Once I put in fuel (about 240cc) it will be nose heavy again.

So, after that extensive description of my problem, what do I do? Have been flying this airplane for a year with a 55ax, have just fitted the 75ax and I definately want to do more 3D now

Ameyam

gboulton

My Feedback: (15)

1) Move the fuel tank to a more CG neutral location.
2) Build a Vanessa CG Machine and learn to use it to both determine the current CG, AND determine the appropriate location/amount of ballast weight, if necessary.

ameyam

I read through the Venessa CG machine and I think it is a bit too much instrumentation. I read somewhere that the recommended CG is just ball park and we need to check the same in flying. Is that correct and how do I do that?

Ameyam

MinnFlyer

My Feedback: (4)

The Reactor Bipe comes with a balancer. If you still have it, use it. It works really well.

If you don't have it, balance it right-side-up under the top wing with the tank empty

ameyam

This is the Reactor 46 not the Bipe

Ameyam

billd76

My Feedback: (3)

I have also used masking tape to mark the CG location on the wings. This way you can reach under the wing without a helper and once the tips of your fingers are on the edge of the tape, they are where they need to be, then just lift to check CG. If you were only slightly nose heavy, why did you add tail weight? Could you have moved the Rx battery more to the rear to compensate and checked the CG, before adding weight? But do agree the only way to perfect the CG is to fly it and make adjustments as required.

MinnFlyer

My Feedback: (4)

Ooops, my mistake.

In that case, you are correct in doing it upside-down, but the center of mass is so close to the wing that you will usually find the problem that you are having, which is, that it will fall to either side. However if, when held level it will indeed fall to either side, it is balanced.

If it always falls to the tail, it is tail heavy, ditto to the nose. But if, when held level, it will slowly start to fall one way or the other, you are on the money.

Granted, once it STARTS to fall one way or the other, it will pick up speed the more it tilts, but as long as it starts slowly and/or falls to either side, you're good to go.

opjose

That is correct.

There is a rather long document that details trimming proceedures for FAI airplanes.

Google for it... you'll learn a lot from it.

Most sports planes fly with a somewhat nose heavy C.G. position.

Some 3D'ers shoot for completely neutral positions.

For the latter the "rate of change" of the dive ( or nose dropping ) from level should be equal both inverted and upright, and very mild in both cases.

It should seem that the plane will fly almost hands off in both positions WITHOUT any trimming.

Note that with the plane trimmed this way, it may balloon up upon landings catching the novice unaware... you have to fly the plane to the ground... quite different than what some are used to.


For a more nose heavy plane, check the FAI trimming guide.

ameyam

the first thing I did when I fitted the 75 few weeks back was to try to rough balance and try to rebalance. I now have the battery all the way back in the hatch compartment. I hold it there with some foam padding. Then, when I realised it was still nose heavy, I added tail weight- I opened up the very last part of monokote and added weights just infront of the rudder hinge. If I am not mistaken I added in 5 nos GP segmented weights- 1/4oz each so about 35g or so. But when flying it on that day, it still felt a bit nose heavy so I added in a washer- about 10g or so after the flying day. That is the reason I wanted to check the balance.

I cant move the tank any further back, its already snug with the rear bulkhead of the tank section.

When placed on the CG machine it slowly falls either nose or tail down. I was very carefully able to manage to level it once. Guess that means I am very close to the CG

Now, regarding the flying balance- on that day before adding the washer, I did fly it inverted and it required just a touch of up elevator. So little I didnt notice it any different from flying the 50cc version from the sim. It doesnt baloon much at landing- I tend to idle all the way down to about 1 ft off the deck and then add a or two click of throttle to flare and soften the landing. I know what kind of balooning you are referring- my Topstar (Flip3D / Frenzy / UCD60 / Twist60 whatever you want to call it) does that, so much so that I have to very ofthen cut throttle to land it in the wind

I tried some hovering and it maintains vertical very well. But the flat spin wasnt too flat KE was OK, I didnt have time and confidence to do much else that day as everyone else was also flying. Tomorrow the crowd will be less, so I will try some more things

Ameyam

TedMo

From what I have read within this post I have to wonder if I'm doing it all wrong?I obtain a simple balance then try it in flight. After which I determine if I feel it needs any adjustment to achieve the flight performance I desire. Been doing it this way for 60 years hate to think wrong all this time.

opjose

No you're doing it right.

The FAI testing proceedure does just that, but it also clearly defines the in-flight tests that should be performed.

It's a pretty good guide for fine tuning planes.

SeamusG

One of the cool things learned from using the Vanessa contraption is that if you add 1/4 oz to the tail it will (typically)move the CGback 1/8". If you add 1 oz. to the firewall the CGwill be moved forward 1/8". This proved to be pretty accurage for a Kadet Senior, a Hog Bipe, a ShowTime 50, a 4Star60 and a LT-40.

If the plane flies a bit nose heavy asis - use double-sided 1/4 oz lead weights and attach them to the tail until your "in flight" balancing tests demonstrate that you got it like you want it then make use of moving components to allow you to eliminate the external weights. Alcohol does a decent job of cleaning the surface before mounting.

Have fun ...