CLBetten

My Feedback: (16)

I have started flying 1/2 A control line after a few years. I have a lot of experience but I have a problem I can't seem to beat. I have an .051 that sings a fairly rich 22,000 on a 6X3 prop. It's connected to a Perfect tank level to the spraybar. I have the pickup in the tank oriented to the bottom right corner. On the ground it will run the tank empty in almost any attitude. I have a super fine needle set on it. No matter how I tune it as soon as I launch it it quits instantly. Two feet from my hand. I can have it blubbering rich, doing a perfect 2-4-2 break, or nearly peaked. As soon as I launch it it quits like someone flipped a switch. Any ideas?

Pond Skipper

Can you post a pic of the set up?

aspeed

Sometimes it works best if the pickup in the tank is about 1/4" from the back so it doesn't richen on acceleration. Might be worth a try. Could also be a large venturi. They are kind of fiddly without pressure, if that is the setup you are using. It could be from the tank being outboard or inboard too much, but I doubt that is the problem if it only goes two feet.

small_rcer

When i switched to very small tubing such as the Sullivan 1/2A tubing, and put a full circle of tubing between the tank and venturi that launches went better. I suspect that the surface tension in the small tubing causes the fuel to resist moving back on launch. The small circle of fuel tubing rather than a straight run seemed to help as well. Again I suspect the inertia of the fuel in the tubing is causing it to flow backwards on launch. The fine tubing ( and the surface tension being higher in the small tubing ) and the loop or circle resists this rearward motion of the fuel. YMMV.

I also always mount my venturi equipped COX engines at 90degrees so the venturi is lower and it is easier to get the venturi opening closer to the horizontal center line of the tank.

combatpigg

My Feedback: (3)

In general, the tank should sit on padding and be held by rubber bands to help isolate from vibration.
22,000 with a 6 x 3 sounds almost impossible.
Make sure the prop and prop bolt are running nice and smooth with no vibration.
You can hold a running model in your hand and cancel out fuel foaming, but shortly after release the foaming begins. I'm not saying this is your problem, but it's something to keep in the back of your head.
I agree that Sullivan brand small tubing is the best stuff.
A handy tool for fueling and trouble shooting fuel plumbing issues is a Monoject 2 oz syringe with a short hunk of 3/32" brass tubing pressed into the tip. You can use the syringe to pressure check the plumbing and to suck out any possible clogs.
I would also entertain the idea of buying a couple 6 x 2 props from APC, or maybe a 5 x 3 rubber prop from Cox International instead of using 6 x 3s. The lower load props are easier on the engine, making tuning less critical. The 6 x 2 might give you the laps times that are slow enough to enjoy but still plenty of inertia to maintain line tension. It depends on the model's weight and wing loading. Experimenting with different props can be dangerous if adequate line tension is lost, so always be cautious.

CLBetten

My Feedback: (16)

I suspect fuel tubing size may be an issue by effecting or enhancing a fuel pressure change. There has been no evidence of air in the line. This engine is running about 18,000 on a 6X3. I had that wrong. Here are a couple pictures.

Pond Skipper

Ahhh the proverbial picture is worth a thousand words. Tank / feed line is way to high the breather line.

Unscrew the venturi put the Needle valve between the cylinder and venturi
Gently bend the tank tube down I used a bit of piano wire inside the brass tube to keep it from bending and closing
You can pass the fuel line thru the firewall to keep it more level with the needle valve.
Use one continuous 1/2A fuel line from tank to engine .

Pond Skipper

You can glue in a short piece of brass as shown through the firewall allowing the use of two short sections of fuel line.
You are stressing the plastic carb body by having the needle valve forward it is not meant to be facing that direction and rubbing on the bottom.

CLBetten

My Feedback: (16)

Thanks for all of the input gentlemen! I hit this little bugger with both barrels. It was too late to save my carb body. It was cracked. Maybe not cracked enough to leak but darn sure not helping anything. Having the needle further from the prop should have been a no brainer. I resized and rerouted the fuel system. The only carb bodies I have have the pressure tap open. As it is now I have a brand new .049 #4 cylinder and piston, screened venturi, fine needle and a Texaco head with one shim. I switched to a 5.7X3 prop. I haven't flown it yet. What do you think? Is it ready to fly? Thanks again, Cliff

combatpigg

My Feedback: (3)

Hook up a pair of lines to your leadouts and observe how the model hangs [like you are dangling a plumb bob].
The nose should be pointed down [past level] just a little bit. If not, then the leadouts should be moved back a little.
Too much "leadout rake" isn't good either, because the model will have the tendency to wobble [hinge] while doing loops with the model pulling too much of an angle away from it's flight path.
A penny is usually used on the outboard wing to help offset the weight of the flying lines. The last thing you want is a model that flies with the inboard wing banked towards you.
The line spacing at the handle should roughly match the spacing at the bellcrank for adequate response, but not too sensitive.
Don't forget to check the planes' CG. Wear a noose type lanyard that connects the handle to your wrist especially if you are flying around people].

Pond Skipper

Hi Cliff,
The fuel line set up looks much better.
You can make a brass collar for the black cracked carb body, slip it over the venturi's carb body wont allow the crack to expand.
I see you have a pressure line connected is the nipple on the carb body. Did you or has someone drilled through the aluminum crank case?
From the factory only the nipple is there with the option to drill thru all the way would require you take apart the engine prior to drilling.
The red carb body is the .051 RC version with the thick wall tab to support the RC muffler in your case the extra plastic will help avoid splits.
They always tend to split on the back side. I noticed the engine prop plate very unique wonder what the purpose of it is.

CLBetten

My Feedback: (16)

I didn't realize that nipple in the carb body wasn't effective if the case isn't drilled. The case is not drilled. Guess I may want to get rid of that line. Hehehe. Is the prop back plate unique because it's hex shaped? I have a few of them. As to the balance the manual said 1/2-1" from the leading edge. I set it at 3/4". That's on a wing with a minimum 5" chord and a bit of taper in the rear. That's puts the CG about 20% at 1". The bellcrank center is factory positioned. The lead out guide it set with the rear line (down control) paralell to the leading edge as per the instructions. Does that sound about right?

Jennifer Curtis

Use a stooge rather than hand launching.
When you hand launch, the fuel immediately
sloshes and may get air in the line instead of fuel.

Don't use the crankcase pressure (at least until
you get everything else worked out). It it
very high pressure and makes tuning quite
sensitive. I tried it on one engine, then plugged
it and was happy ever after.

22,000 on a 6x3 without the high compression
head sound kind of high unless it is too lean.
Too lean the engine will quit as soon as it starts
to pull hard.


Jenny

combatpigg

My Feedback: (3)

I didn't realize this was a commercial, well proven design...so every thing that's been engineered ought to make it fly like a champ.
My advice is "Rule Of Thumb" to get scratch built C/L planes safely in the air. Beyond that, it's still up to the pilot to fine tune the balance points and the control geometry for his personal taste.

Propworn

My Feedback: (3)

I kept calling him a stooge now he refuses to launch it for me any more

combatpigg

My Feedback: (3)

With ROG launches, it doesn't take munch of a "snag" from a blade of grass to cause the plane to cut across the circle. The other problem is running the engine so close to dirty ground. Hand launches don't need to be so....vigorous that the engine gets fuel starved. The problem a low time pilot has with hand launches, is typically jerking the handle to "full up" and stalling the model. It really does help if the pilot adjusts the control linkage so that "full up" with his handle only produces 15 degrees of elevator movement from neutral. I doubt a plane that is balanced at 15 to 20% of MAC could make use of much more than 15 degrees of throw before the elevator becomes a "drag brake".

Jennifer Curtis

An old piece of carpet or a cheap runner from Ollie's
http://www.olliesbargainoutlet.com/ or some similar store
will take care of the snags. I've also used a 4 by 8 sheet of
1/4 inch plywood with one end raised about 6 inches as a ramp.
(Too much incline and an 049 plane won't reach flying speed.)

On a particularly difficult I've also whipped it a bit.

It also takes a bit of trying to find the perfect point
between downwind and crosswind where roll off
board takeoffs work best.

Jenny

aspeed

That plane looks like a Lil Bat. I got one too, it needs a TD I think, or a Norvel.

combatpigg

My Feedback: (3)

There's a coroplast version of this plane called the "Grin Reaper". I believe the Balsa Beavers have it at their web site.
I'll bet the balsa version flies better, though.
This Summer I'll set up an area for my neighbor and his Son to give this stuff a try.

CLBetten

My Feedback: (16)

It's a Lil (com) Bat from Black Hawk. The other (they come two to a box) flies nice with a Black Widow but could use more line tension. Launching and handling is a little awkward due to the shape/ planform. I fly over grass. I hope to fly the heck out of them tomorrow. The RC flying is banned for a couple days within a 30 mile radius of my house because the President is visiting the Air Force base about a mile from here.

aspeed

The only one I heard of is the Man Win at the Balsa Beavers. The Lil Bat was ok, maybe a bit lighter than a Man Win. It could do a loop anyway, with a Baby Bee. I made a plane similar to the Mn Win with a TD, and it was fairly fast and did loops too. Not real tight or anything approaching square. I still have it and fly it maybe every other year. It predates the Man win by a bit, so the coro is pretty good stuff. A control horn broke once because it was brittle with age, and well, I crashed it. I have moved the motor back a bit since that pic. and put on a Norvel. Still flies about the same either way for 25 years.

combatpigg

My Feedback: (3)

I'll probably never remember the name of the club that got a feature article in one of the main model magazines years ago about how to build a reed valve equipped C/L Combat plane with a 1/8" sheet balsa wing. Things happen so quickly in 1/2 A combat, that unless you have one of those minds that can "slow the game down mentally".....you won't know what happened while you pick up the pieces.

Mr Cox

The Texaco heads are lower on compression in order to work with very large props. I guess they will have about the same compression ratio as the regular Babe Bee heads. I think you would be much better of with the stock TD head and a few shims.
18000rpm on the 6x3 sounds about right though, and it should run better on the 5.7x3 prop.

MJD

My Feedback: (1)

Yes, it is possible that plugging the tank vent could have something to do with your troubles..

smallrc

APC 5.7 x 3 is my favorite all-purpose prop for a TD...