RE: CG question?
 

Yes...the horizontal stab being as you described would absolutely make the airplane require some up trim.

COULD you adjust the wing saddle to offset it? Yeah, probably. SHOULD you? Eh...that's up to you. :) Depends on how much work you feel like doing. *heh* Will it have other consequences besides just removing your needed trim? Almost certainly.

==========

And you're right...it probably is "splitting hairs". But who cares, right? For some, the investigation and learning and trial and error of exactly how one change can effect a whole airplane is fascinating. Again, it's all about what you enjoy doing. :)

And as you point out...you've learned some valuable lessons already. You've seen, first hand, how one building method might lead to certain results, and what those sorts of things might do to airplanes. This, too, is all part of the fun. :)

=========

Finally, (mostly because those who know me are probably shocked that I haven't done this already *heh*), IF this sort of thing really intrigues you, then I HIGHLY recommend you pick up a copy of [link=http://www.amazon.com/Stick-Rudder-Explanation-Art-Flying/dp/0070362408/ref=sr_1_1?ie=UTF8&s=books&qid=1244817769&sr=8-1]Stick and Rudder: An Explanation of the Art of Flying[/link] by Wolfgang Langewiesche. :)

While it was written for full-scale pilots, its common language explanations of how and why airplanes do what they do are just as appropriate for RC as they are any other aircraft. It will, i suspect, make for a very enjoyable read, and really give you some new insight into the hobby. :)

RE: CG question?
 

[quote]ORIGINAL: gboulton

Yes...the horizontal stab being as you described would absolutely make the airplane require some up trim.

COULD you adjust the wing saddle to offset it? Yeah, probably. SHOULD you? Eh...that's up to you. :) Depends on how much work you feel like doing. *heh* Will it have other consequences besides just removing your needed trim? Almost certainly.

==========

And you're right...it probably is


Your the second one to recommend that book! A guy at the field suggested it ( also a real pilot )

I probably wont do any major changes to the Tiger other than moving the CG around..
I'll incorperate this knowledge into the next kit build...

Steve

RE: CG question?
 

Heh...it's something of a Bible amongst full scale pilots...and, I admit, argued about as often. :)

RE: CG question?
 

Quick question regarding lateral balancing...

I'm quite honest in saying I have never lateral balanced my planes. But decided I'm going to do that now. Can I balance it by turning the plane upside down (canopy facing downwards)? This should have the same effect? The reason I want to do it this way. The bottom part of the planes body is flat so when I put my strings in the front and at the back around the body and pick it up, it balances. But if I turn the plane inverted (the top of the plane is more round) then the one side drops a bit. Then also is the following method correct then:

Plane turn inverted

1. Sliding one loop (string) around the plane at the back - just canopy side of the vertical stab.
2. Sliding the other loop (string) around the shaft of the engine infront of the propeller (I don't have a spinner as yet on it) and it was the only round part at the front of the plane
3. Holding it by both strings and picking it up inline with the plane

Is this correct?

RE: CG question?
 

Best i can visualize from what you've described, yes...that ought to work just fine.

RE: CG question?
 

LOL sorry for that bad description. I tried to draw it on MS Paing - but damn that was even worst :D

RE: CG question?
 

Wasn't a bad description at all...I just suck at visualizing things. :)

(great trait for a builder, huh?)

RE: CG question?
 

I built my venessa last night.
I was flying my tiger yesterday and added 1.5 oz of weight to the tail in 1/4 oz. increments.
I used the venessa to establish where that put my CG.
I then moved my battery back and was able to only use .5 oz of weight on the tail. I could move my engine back 1/4" on the engine mount if I feel I need more wieght in the tail to get it the way I want.


One change to the venessa will be to hang a small cheap laser pointer in place of the plumb bob I made.
This will shine a beem through my canopy onto the cockpit where I will mark the recomended CG as reference.


I taped a bubble to the wing. I realize now it doesnt have to be level as long as I didnt remove it between adjustments. I found the level to be more acurate than the blumb bob. The whole plane would osscilate back and forth very slightly and the plumb bob always was swinging. I think a laser pointer will work well here. althugh it to will swing..

Off to the field to try it out!!

Steve

RE: CG question?
 

That's an AWESOME idea. I'm absolutely doing that.

RE: CG question?
 

I got carried away and spent 1/2 hour grinding down the blump bob from some pipe only to think of the laser pointer afterwards..
I think it still needs somethin? the angle of the plane is still a variable... nose up / nose down..??

RE: CG question?
 

I was actually just out in my shop thinking on this. I've got a laser level that projects a horizontal line...I'm thinking I can work out a way to use that, then have a line right through the CG all the way across the wings. I'll let ya know how it works out.

That's what the dowel is for. Rotate it whichever way necessary to bring the nose or tail up, and bring the airplane level. The laser pointer/plumb bob is only pointing at the CG if the airplane is sitting level. (Back to our discussion earlier of how to know)

On the aircraft pictured, looks like you could set a very small/light "string level" (Any hardware store should have one) right on the foredeck in front of the canopy. Being so light and so close to the CG, it probably wouldn't impact the balance enough to matter. If you DID want to get crazy precise with it, you could certainly weigh the string level, and then offset it using the W*A=M formula talked about above.

RE: CG question?
 

gboulton, now you have me thinking about using my laser level to check my incedence?
In my picture I have a sring level taped to the wing.

RE: CG question?
 

Absolutely you can use the laser level for that. It's an excellent way to check that. Most of them can be turned "on end" for a vertical line...or they already project one...and be used to strike a centerline down the fuse as well.

RE: CG question?
 

The laser level is perfect with the venessa machine. With the plane hanging on Venessa, I mounted my laser level on my tripod. this allows me to raise the level to align with the wing or the stabelizer.

I level the plane with the laser going right through the cord of the wing then I raise the level ( by cranking up the tripod ) and align it with the stab to check incedence. It was pretty close, not as bad as I suspected...

RE: CG question?
 

Very nice!

I'd never really even THOUGHT about the uses a laser level could be put to with this thing...you've really opened up some new ideas here.

RE: CG question?
 

"Stick and Rudder" YES!!

CGr.

RE: CG question?
 

I just got my "Dynam I can fly" airborn today and it wants to roll right as soon as it leaves the ground. I have read that when you roll balance a top-mounted wing (this is what i have)it should stay up-right and a bottom-mounted wing will flip belly up. I have read 2 different ways to roll balance: 1)Wrap string around fuselage near propellar and another at the beginnig of the rudder and lift off ground. 2) Same as 1 except put string around prop/engine shaft.#1 stays upright, #2 rolls right and bellies up. Do I need to add weight to my left wing to keep it upright?

Thanks
Troy

RE: CG question?
 

If you're going to be using laser theodolites, then all you'd need to do would be to scan upwards to the suspension point to get the longitudinal position, then downwards to the fuselage with the aircraft aligned at 90 degress to the plane of scanning to indicate the CG line.
My workshop has been misappropriated by my other half for beehive storage, so I don't have room to get the necessary distance off.

One thing about the design of the Vanessa.
The CG of the aircraft and the Vanessa combinedis directly below the suspension point of the whole thing. The plumb bob is directly below the suspension point of the plumb line. It would be possible to get enough friction on those loops under the wing to get the dowel supporting bar out of line with the main suspension cable. So the suspension point of the plumb bob would not be directly below the suspension point of the whole jig.I concede that you'd have to work at it, but this Seagull Edge 540 I have has a tiny range of CG suggestedin comparison to the overall size of the beast.
If the dowel support bar is short in comparison to the main cable and the loops from the dowels are long, with a good long length overall, then this possible source of error will be irrelevant.
Guess what I'm building over the weekend!

RE: CG question?
 

Schrockie- Use two pieces of string, one on the prop shaft and the other on the rudder hinge. Adjust the balance until the plane sits straight, then line up your ailerons perfectly straight. Unless you have some wing warp, that will give you straight and level flight both upright and inverted once you fine tune it with in flight trims.