Balance weight - Model B

[svyolo]

To Mark;
I just did a balance of one elevator to pour the lead. For Oratex it came out to 47 oz. Did Bob make the elevator balances bigger on the model B?

I included the trim horn, taped in position, and the trim control pushrod, taped a bit aft of the installed position. I calculated just 1.6 sq yard of cloth per elevator.

I hope this is right. I dislike 3 lbs of lead a lot less than 5 lbs. A necessary evil.

The B model plans also spec 23 deg up and 17 deg down for the ailerons. Did you notice any decrease in adverse yaw when you retrofitted model B wings?

[Mark Goldberg]

The weight sounds about right. We are now pouring about that much lead into that leading edge triangle of the elevators ourselves at the factory. Bob told us how much to put in. If a builder wants to put 10 layers of paint on the fabric (exaggeration), they now have a place to put more lead. Mostly a slurry of epoxy and lead shot.

I did not really notice a difference in adverse yaw. There obviously is some but it decreases if you rig BOTH ailerons UP a little bit on the ground. 1/4" to 1/2". And according to Commander Battson in New Zealand, this also makes the ailerons forces lighter. Mark

[svyolo]

Another factor for the weights is the profiled ribs. They are a lot fatter up by the leading edge. That moves the center of mass of the weights an inch or two forward of the flat ribs, think.

I think I remember the ballpark differential aileron as about 2 degrees up for every 1 down for a flat bottom airfoil.

[svyolo]

Here are 3 pics. First one is balancing.

I calculated how much the fabric plus tape and adhesive weighed, filled a water bottle to that weight, calculated the center of mass of that fabric, and tied it to elevator at the appropriate place. 1.5 inches forward of the middle of the elevator, forward to aft. Took a gallon jug of water to 5 lbs, way too much. Dropped it down to about 3, but had to guess where the center of mass was of the lead. The model B has an airfoil, and is much thicker than the model A so the center is farther forward. I don't know if the balance is the same. A SWAG said 3 lbs.
I just allowed to elevator to rotate on a wood frame. I figured rolling was less friction than tying the elevator in the air with string.

There is one small and one large hole in the elevator balance rib. I cut .020 aluminum a bit larger and epoxied in place to fill the hole. Then just rough cut some already used 5 times doorskin, 1/8 inch and clamped in place.

I also weighed the elevators before hand and recorded. I melted the lead in an old small pan on a shop hotplate. Poured the lead. One I overpoured probably 6-8 ounces, the other one a couple. I will rebalance in the morning.

Actually one of the easier jobs. I did it outside, with a little wind with me staying upwind. I have poured lead before but last time I was a teenager. A couple hours, tops.

I have tried to upload 3 pics several times, it keep saying invalid URL.

[svyolo]

Hopefully this works.

[Nev]

I did not really notice a difference in adverse yaw. There obviously is some but it decreases if you rig BOTH ailerons UP a little bit on the ground. 1/4" to 1/2". And according to Commander Battson in New Zealand, this also makes the ailerons forces lighter. Mark

Ive flown recently with a couple of home builders and they’ve suggested that off-setting the aileron bell cranks would give differential ailerons (which took me some time to get my head around).

It led me to wonder if this would also reduce the aileron control force somewhat, and enable the ailerons to be rigged back to the neutral position with normal forces. Interested to know if some on here have more experience with this. If it did work, it may also have a small side effect of a slight increase in lift/drag and possibly a slightly slower min speed. May also effect any wing drop tendency.

[Mark Goldberg]

Bob has already designed in differential deflection of the ailerons. I am guessing that changing the neutral position of the bellcranks would limit travel. Just a guess on my part. Mark

[Collin Campbell]

The differential deflection of the ailerons is acheived in the design of the aileron hinge. Don't mess with the bellcranks. The neutral position is what is shown on the plans...parallel to each other. If you were to off-set them you will experience cable tension difference. Not good...any adjustments to the ailerons should be made with the pushrods themselves. Some like them up slightly on the ground. Lighter aileron forces but gives up somewhat of the "slipping" ability I think...Collin

[svyolo]

You can get differential ailerons a couple of different ways, but they both are essentially the same. One is you would use bell cranks other than 90 degrees, like 60 deg or 120 degrees, or use an offset in the control horn. Bob used the control horn.

I am not sure if there is a limiting factor in having the aileron move up more (aileron interference with top skin), or maybe the linkage will bind. Maybe something I will play with down the road sometime. I will probably be happy with how it flies as is.

[Nev]

Thanks Mark and Collin. I didn’t describe this very well, but Svyolo has added a better description above of what I was getting at - having the bellcrank made at other than 90 degrees (it would have to be manufactured in this manner as opposed to a field adjustment). But obviously differential aileron has been designed in by Bob already.

[svyolo]

The weights came out to 48 oz. I weighed the elevators before and after. Some of my "guesses" I thought were pretty accurate, but where the center of mass of the lead was a total SWAG. I had 5 lb fishing weights, I looked at them and the horn, and were 3 lbs of it would be. Lucky.

I overpoured, and melted a little out at a time with a torch. With me upwind.