CG location for Goldberg Shoestring

Where is a good starting point? The leadouts are fixed in the stock position and it has a 35 stunt.

It is a judgment call. Bring it back a little at a time until you get it to where you like it.

What's the make-up of your "Shoe"; mods; engine; tank; etc? Others may like to know too, so help can be calculated.

Also: For a on-line MAC and CG calc. program (no downloads) try here. www.palosrc.com In the instructor sections is the MAC and CG calc. programs that you can use. I've added this inf. into a excel spread sheet I did a couple of weeks back on "Wing Loading" and will put it out for any who would like it later this week sometime. HTH.

>I have a 25+ year old, never flown shoestring that I
>took out when I returned to C/L I know it is nose heavy,
>and that was OK for getting the feel, but I want to move
>it back and make it turn a little better. Loops are
>scary now.
>
Dave, how about telling us exactly where the plane balances right now? Right from the kit, because it starts with a relatively short nose, it seems to me that it would be unusual to end up so nose heavy without using some extra-heavy combination of muffler, engine, spinner, and wheels. What is your plane's total weight before you make any changes? Can you substitute another muffler, lighter wheels, and leave the spinner off? How about using a wood prop instead of a heavy composition type?

I like the idea of taking weight OFF much better than to add weight. And it wouldn't hurt to hear what these "scary loops" look like, either. You are remembering not to just pull full up and hang on, aren't you?

>Where is a good starting point?

I've just done a quickie "fingertip test" on a Shoestring here that flies nicely with a Fox 35. It balanced on my fingers when I held it at the wing tips right where the sharp radius part of the tip begins to straighten out. That's about an inch in front of the spar, maybe a bit more.

> The leadouts are fixed in the stock position and
>it has a 35 stunt.
>
The front leadout on the one in the other room is about 3/8" in front of the spar.

Kiwi

I am not just giving it full up (I don't think), but it is still a figure 9. The bottomes come out below my entry point. I could just be freakin and slamming full up. I does a nice corner on a wingover.

I just added a fairlead to the pushrod, and I'll try taping the surfaces. I'll try it that way and see then move it back a little.

I just wondered what the plans said as a starting point for a CG.

Thanks

If your loops ARE shaped like a figure 9, that represents a stall condition on the back side. To learn the round loops, start very high, 15 feet or so up, and apply only a partial up control, such that the plane turns very wide, well above your head (past 90 degrees is just fine for learning).

After entering the loop, the plane's speed will usually slow down (which is why a 4-2-4 "stunt run" setting is nice, since the engine automatically compensates for some of the slow-down). You may need to increase the amount of up control as the plane points straight up, and then lessen the up input after reaching the top of the loop. You need to "fly" and maintain control throughout the entire maneuver, and at first your loops may be egg-shaped, but allow yourself plenty of air to learn in.

As the plane points downward and gains speed, the engine should automatically drop back to a four-cycle, and the plane will want to turn tighter (a scripted lower case "E" figure), so you open up the turn to end up finishing at the same 15 foot altitude as you started.

There are other messagers who may be able to describe this same process in fewer, better-chosen words, but I hope this is clear enough to help some.

Kiwi

Contrary to what most say about the learning curve for inverted flight training, the time it takes to learn inverted flight, using the above technique is rather short: About ooohhh say 2.2 to 3 seconds ..tops!

Technical Notes: For the above to work successfully the following flying site conditions need to be present:
1) The grass should be like that found on the average school yard playground soccer field area. Hard packed, short trodden down Kentucky blue grass, ..with the sporadic tufts of uncut crab grass. (the Crab grass is critical to the mix.)

2) You must ensure that you snag at least one tuft of Crab Grass with the "up" line of the control system, but not be aware of this fact prior to engine start, ..then proceed with the rest of the training syllabus as mapped out above. Also note: A "two tuft snag" has never been tried successfully that I know of, ..stick with just the one tuft.

And that's what worked for me!! Hope it helps some.

I suggest you lighten the nose, if that's possible in your case, per The K's suggestions, then, if it's still sluggish, drill a hole through the rear of the fuse & install a 4-40 blind nut on the outside. Brush a little "whatever you have that's fuel proof' in the hole & bolt a quarter ounce of lead to the inside of the fuse. I use a socket head bolt & a flat washer. I also use the standard Brodak lead weights for a tip weight box with the hole already drilled, in both quarter & half ounce sizes. Now, go fly the thing & see how it feels to YOU. How it feels to YOU is the important thing, numbers just dont matter at this point in your learning. If it feels better with the quarter ounce-add another one! Fly it again. Does it feel better, or does it feel slightly twitchy to you? If it feels better, add more. If it feels twitchy, remove the second weight & fly it until you're comfortable with it, then start adding again. This method of adding lead is fairly tidy & fairly well hidden under the stab. Once you get it how you want it, put a dab of Loctite or skinny glue on the bolt threads & it will stay put. A light airplane will generally (not always, ask Scott Riese), fly better than a heavier one, but a balanced airplane will fly better than an unbalanced one, I don't care how much lead you have to add. Adding lead a quarter ounce at a time is not going to make the airplane suddenly unflyable. Go for it!
Nils