CG help !

OK after looking at the finish product and looking over the plans to make sure nothing was missed putting the plane together I saw the little CG icon. So I picked up the plane from the fuse about where the CG icon was on the plans and "klunk" the front of the plane hit the table. Do you check the CG before the engine, tank, and wheels are mounted? I hope the answer is DUH!

Thanks
Paul

>I saw the little CG icon. So I picked up the plane
>from the fuse about where the CG icon was on the plans and
>"klunk" the front of the plane hit the table. Do you check
>the CG before the engine, tank, and wheels are mounted? I
>hope the answer is DUH!
>
>Thanks
>Paul

No, you check the CG with everything ready to fly, less fuel. Now, how accurately did you place your fingers? When you are close to the actual CG it doesn't take much movement of the fingers to go ahead or behind. So, try again and see where it balances. Then mark the spot (visually, or place a piece of masking tape on the plane so you can put a pencil mark on the masking tape) and measure where it is. If you are close--and especially if it is *slightly* nose heavy, go out and fly it. You can trim it and move the CG back as you go--if it is needed. If you are considerably off, then add some tail weight (A little solder wrapped around the tail wheel strut will work temporarily.) Most planes that are off end up being tail heavy. It is highly unusual if you got significantly off in the nose heavy direction.

What is the total weight, by the way?

I will have to get the details when I get home tonight. This is a Flight Streak Trainer BTW.

Thanks
Paul

>I will have to get the details when I get home tonight. This
>is a Flight Streak Trainer BTW.
>
>Thanks
>Paul

A Flite Streak Trainer won't suffer too much being a little nose heavy. Matter of fact, you might even like it. Just get it close for the first flights.

Len,

Before adding tail weight. I'd try to see if I could lighten the nose. Lighter muffler, spinner, plastic tank instead of tin, lighter gear, whatever. Once that's done, then add tail weight.

>Len,
>
>Before adding tail weight. I'd try to see if I could lighten
>the nose. Lighter muffler, spinner, plastic tank instead of
>tin, lighter gear, whatever. Once that's done, then add tail
>weight.
>
>

Randy Powell

I agree, and from the looks of things He can get a new tank and move it back and then move the engine back and this may solve the whole problem.

I knew someone who cut out the CG logo from the plan and pasted it onto the plan - that may help!

Thanks Tony, I will give that a try. What type of glue do I use?
JK'ing.

THe CG is right on the LE of the wing. It is about a good inch off of whats on the plan. The total weight of the plane is 24oz. I got some lead weight from my pinewood derby kit and put 2oz of weight on the tail of the plane. That about put the CG within the range.
Here is what I am thinking:
The McCoy is old and heavy, I could not mount the engine all the way back in the engine mount because I would not have room for the tank.
The tank just fits between the landing gear and I had to put a screw hook in place to keep the fuel line off the engine head. So with the heavy engine and not mounted all the way back in the slot it pushed the CG too far forward.

Thanks
Paul

One thing I've done with those types of landing gear is mount some small pieces of plywood on either side of the wire - this lets you move the tank back so it's actually sitting over the landing gear (it keeps the tank more-or-less level), so you have more room to move the engine back a bit. The Flite Streak is notoriously short-nosed - not much room for engine and tank, and I'm thinking of the full-sized one - I imagine the smaller Trainer would be even more difficult. You might think about putting a smaller engine on it, like a .15 of some sort...

Hokay, two things. Get a profile tank. The pickup tube will come out the top or bottom of the tank and will allow the engine to be mounted closer. Then put some balsa in front and behind of the landing gear wire to level the area out so you can move the tank back. Now, finally, move the engine back. It is much better to move the engine back and get it in balance than to add two more ounces of useless weight.

WoW you guys are great!
Now what is a profile tank. Brodak suggested this tank from the list of other items needed for this plane. Can you guys suggest a tank?

Thanks
Paul

>WoW you guys are great!
>Now what is a profile tank. Brodak suggested this tank from
>the list of other items needed for this plane. Can you guys
>suggest a tank?
>
>Thanks
>Paul

It is interesting because Brodak makes the others as well. What you want is a short nose Oval profile. They are made in uniflow and standard vent. They come in 2 to 6 ounce sizes in half ounce increments. Two ounces are 1 3/4 inches long, 3 ounces are 2 1/4 inches long, 4 ounces are 3 inches long. And the tank can fit right up behind the engine with no kinking of the fuel line.

LA_Flyer

Paul (aka Rootbeard)

Nice to see your photos of the new plane and pilot! I like the way the paint came out. As an aspiring-to-be-infamous "Newbie Profile Puke" myself, I'm following your questions and all the expert advice. I know what you mean about that tricky little CG mark. I'm not really convinced you can trust those designers and drafters when they employ that little symbol. If they stick it in the side view, they generally don't get the vertical location right (nearly all modelers ignore that direction). And if you can't trust 'em in one direction, why do we trust 'em in the other? (I really liked the suggestion to hang the plane by the leadouts and see if it hangs straight.) Sometimes the designers are inspired and hide that little sucker in the plan view. And when they do, they usually center it on the fuselage (symmetry is ALWAYS RIGHT! Right?) when we all know that the outboard tip generally carries around all your spare change epoxied inside somewhere....

My first plane had a similar problem to what you are describing. Nose heavy. Big time. It balanced right at the leading edge. The Brodak Lightning Streak has a real short nose and I mounted an O.S. .35 in it along with the standard muffler. The engine was as far back as the spinner and prop would allow. And I could just squeeze in a fat 3 oz tank. (You appear to have lots more room between the tank and the wing leading edge. HooYah, you still have options!) The L-Streak has a reasonable size elevator and isn't too short coupled. And I had decent control throw. So I had enough control authority to overcome the forward CG both in powered flight and during (dead stick) landing. I think in full size planes, the case the FAA looks for is sufficient control to flare the plane for landing at minimum airspeed when at the forward CG limit. I got lucky and Jerry Silver, one of the local experts, offered to fly it on the first flight. I think everyone was afraid I'd smash up a brand new airplane and never come back. (I haven't taken a poll to see if they think Jerry made the wrong choice!) The only thing he changed was to loosen the engine bolts and tip the motor down within the slop of the holes. And then they turned me loose!

I really liked the slower control response on my first flights and the way the plane kinda settled into nice level laps. I gradually shifted the CG aft by using lighter wheels, upgraded the tail skid to a tail wheel, added a stooge attachment, etc. I tried it without the muffler, but it ran better with pressure. I added a little lead to the tailwheel strut, and was about to buy a tongue muffler, when it sort of became a moot point. My flyin' buddy was really impressed with the small size of the balsa chips and the large size of the debris field. But I did get all my spare change back....

What about a fuel filter? That's a little bit of nose weight that's worth it! I also used a plastic spinner in the hope that serious damage to the engine could be avoid if I, uh...you know...uh, if that happened.

It looks like you went with slotted holes in the tank strap for tank adjustment. Nice. I tried two tanks: the Brodak 3 oz. wide wedge and a 3 oz uniflow. I had to make the uniflow. Kinda fun if you like working with metal. And polished brass looks great! And almost nobody else has one. The uniflow was marginally better. I could get a lot of flying done with either one of 'em. Betcha your oval would go around pretty good too....

So I would at least try all the improvements the experts are recommending, but if I had a nice lookin' plane and the weather was good, and the grass was nice....

Dave
Newbie Profile Puke
from somewhere near Manhattan Beach

PS - Now that that one's done, whatcha planning next? Ya gotta tell us about it!

Thanks Dave,
I always look to the experts and try and follow their advice. Some of these guys were flying C/L before I was born. I wish I knew everything they have forgotten.
I had hoped to take the boys to our airfield tomorrow (Sat.) and let the pilot put up his new plane. I may be able to get the engine and tank moved tonight, but will not be able to get the right tank until I find it on the web someplace. So we will have our .049's to fly.

Our next project is a Shoestring for my younger pilot. I snagged it off of ebay for a very low price. Someone donated a .15 to him. He is just about ready to step off his "Platter" and will move to a Cadet that we scratched built from plans I got off the forums. I figure by the time we get the Shoestring ready the Cadet will have been repaired a few times. =)

The Flight Streak moves back to the build table tonight. =(

Thanks
Paul

Before you begin to cut like mad, why don't you see how much extra weight you really need. Put your fingers under the CG, and have your son add weight to the stab area. The weight can be some washers or nuts, but see how much you need. Maybe you don't really need that much since the lever arm to the tail is longer than the lever arm to the engine area. I bet you need less than an ounce (WAG )

I started to lay little bars of lead on the stab last night. When it got within range of the CG I had 2oz sitting on the tail.

Thanks
Paul

That is a fair amount (sorry for not noticing that you had already answered my question!) I see that would bring the weight up to 26 oz
Also is your engine really that heavy? I always thought the McCoy's were relatively light? Also what is the engine range for that kit?

I guess I might put an oz of tailweight on and give the plane a try, just to see how she flies.

Here is the plan now.... We fly with what we got.( Unless you guys change my mind.)

I was able to add wood around the landing gear and move the tank back to the LE of the wing. Much more room now. I was going to move the engine back, but I am afraid that I will just make matters worse. I already had to fill in the holes once with JB weild and re-drill the holes. And I would only be able to move the engine back about 1/4 in. So I added 2 oz to the tail. Total weight is 26oz on the FS trainer. Do you think this 2oz will make or break our first flight? The CG is about 3/4 in off the LE now.
Thanks
Paul

Paul, one question nobody has asked or I missed it.. What are you expecting the airplane to do. If just fly level, don't worry about the cg, probably better off nose heavy anyway. If you expect to go out and do the beginners pattern then you might think about adding some lead to the tail, start with an ounce and go from there.

Personally on Flight Streak airplanes I don't pay any attention to the CG on the plan. If it won't turn like I expect, add weight to the tail, if it's a little too sensitive add weight to the nose. My Flight Streak balances a good inch forward of the CG shown on the plans and it will fly the full pattern just fine.

Hey Bob,
Right now all we want it to do is take off and do some climbs and dives and maybe a lazy wing over. We will not even ask it for a loop. Just a controled flight.

Thanks
Paul

What you have there is the blackhead Testors McCoy 19. It is carrying a fair amount of excess metal. I would guess it is about an oz heavier than the earlier redhead 19. 3/4 inch back from the leading edge is about right for the CG on that airplane. The airplane is a primary trainer for learning to keep out of the ground while flying level and doing mild wingovers. I would seriously consider cutting the motor hole back furthur. Althought the airplane will go around in circles fine at 26 oz, if it hits hard with 2 oz of lead on the tail the tail will break off. If you can keep from hitting it hard, no problem.

Incidentally, I have a Guillow's #2 trainer powered by a redhead McCoy 19 with a 2 oz Higley heavy hub in front of the prop to make it balance. Too bad we don't live next door to each other. We could have swapped some parts and solved both our CG problems without added weight.

>Here is the plan now.... We fly with what we got.( Unless
>you guys change my mind.)
>
>I was able to add wood around the landing gear and move the
>tank back to the LE of the wing. Much more room now. I was
>going to move the engine back, but I am afraid that I will
>just make matters worse. I already had to fill in the holes
>once with JB weild and re-drill the holes. And I would only
>be able to move the engine back about 1/4 in. So I added 2
>oz to the tail. Total weight is 26oz on the FS trainer. Do
>you think this 2oz will make or break our first flight? The
>CG is about 3/4 in off the LE now.

In answer to your question, for just a "round and rounder", you are probably fine with that weight. A little extra wing loading won't hurt you for learning to fly level and even a little climb and dive stuff. However, you do have some space behind the engine and between the front of the nose and the prop. so you could slide the engine back and drill another set of holes. Having a second set of holes (somewhat evenly spaced between the first set) won't manke any difference. You don't need to worry about filling them or whatever. But that would help a bit with the balance and either get it closer to "right" or allow you to get a little of the lead out.

Lots of good advice. Maybe after we get a few laps under our wings we will try some of these ideas to "get the lead out".
I wish I knew half of what you guys have forgotten about C/L stuff.
Thanks
Paul