Big-Mo

My Feedback: (5)

OK I have NEVER had this happen in 13 years of flying,

got the laser200 all ready to rock on and when i go into a dive it runs out of fuel got it down and checked everything out and it is actually running out of fuel due to the clunk coming out of the fuel and sucking air. i have several air planes of same style sport flying and none of them run out of fuel , any suggestions? i hate dead sticking a flying model instead of a gliding model !


HELP!!!!!!!!!!!!!!!!
lol

Big-Mo

Big-Mo

My Feedback: (5)

i checked my other setups 3 of them doen the exact way and they have no problems/

Im stumped

alan0899

G'day Mate,
The fuel cannot run to the front of the tank in a dive, it is imposible, for that to happen, the fuel must accelerate faster than the plane, & that can't happen unless the plane stops in mid air then the fuel can fall forward. Also the clunk can't fall to the front of the tank in a dive, for the same reason.
That is why it doesn't happen in any of your other planes, so you must have a hole in your fuel line, in the tank, or the clunk is getting stuck at the back of the tank, then as the nose drops, the clunk could come out of the fuel, because it is no longer level, & then it could suck air.
Hold the plane nose straight up, & give it a shake, you should be able to hear the clunk swinging side to side, & top to bottom, if you can't then there is your problem.

BillyGoat

From personal experience, my guess is your pick up line in the tank is just a tiny bit too long.

Even if you can hear the clunk moving around, try shortening the line about 1/8 of an inch.

Jburry

Fuel does run to the front of the tank in a dive. A plane does accelerate in a dive, but only to a point. It must accelerate at more than 1g continuously for the fuel to stay in the back of the tank. This will not happen. The airframe is slowed by drag. The fuel is not. It falls to the front of the tank. This is high school physics.

There was a video making the rounds about this a year or so ago. Showed this very clearly.

In a downline, the engine runs ONLY on the fuel already in the line. If the downline lasts much longer than the fuel in the line, flameout. Very few downlines last this long. At 60mph, you're doing about 100 feet per second. The fuel in the line will last most engines several seconds. How many hundreds of feet are you diving from? Larger engines can thus benefit from having larger and longer lines. Reducing throttle setting during the dive will also extend the available dive time.

J

scratchonly

I have seen the video jberry refers to; it was made in germany with the plane mounted camera focused on an external fuel tank; a flying buddy disputed this saying he often flys 10 second downlines, we timed his long down lines, they lasted 2-3 seconds! Fuel behaved as jberry states.

Big-Mo

My Feedback: (5)

OK so everyones right how do I stop this , as i flew it today and it is almost immediately flamed out ,,, fuel line is only 5 inch long , do I wrap fuel line around the plane to get it to run longer? I'm stumped on this one , I have 3 other planes setup the exact same way and none of them do this, one with a ys 91AC in a super sportster, a super hots with a super tigre 61 in it, and a acromaster with a eyna 120 in it i have none of these problems...

gjesion

I don't have a solution to your problem, but i do have a question relating to it. If the pickup is out of the fuel during the down line and sucking air, why doesn't the engine burp when the air in the line gets to the carb? Or am I missing something?

Regards,
Jerry

Villa

The fuel line in the fuel tank must be flexible enough to allow the clunk to move to the front of tank a little when the front of the tank is pointing down. Many fuel lines are too stiff. It seems to me that if the engine is running on the fuel in the line while in a dive, then the line is filling with air. When the plane levels off, the engine will see a 'chunk" of air in the fuel line and may stop running.

Big-Mo

My Feedback: (5)

Your Absolutely Correct Villa thats exactly what its doing.

Jerry you are also right it is burping to the point of killing the engine,

What fuel line should i use for the tank klunk? I'm using GP 3/32 line, to big? to stiff?


maybe were getting closer.

I hope

TexasAirBoss

My Feedback: (22)

I had this happen on a Cap232. Open the tank and shorten the pick-up. Fixed mine.

Charlie P.

These kind of problems are fun when you're looking back on them . . . but a real pain when they are in process. My thought would also be to shorten the inside line to the klunk. I have also had some real puzzlers from tiny holes in the fuel lines both inside and outside the tank. One of the worst was a split fuel line inside the tank at the stopper tube that had me ready to scream. That was a twisted wire (Sullivan style) that had sliced through the silicone line. The line would suck air when I went vertical and I thought the klunk must have slipped forward. I had the tank out of the model several times before I decided to replace all the fuel lines and found that.

When something like this happens now I start with all fresh fuel lines and THEN worry about the next steps.

pt19 flyer

My Feedback: (1)

hi

one solution to this which has worked in the past is to loop the fuel line to the carb around the fron of the engine. this gives a little reserve to the engine if fuel in the tank is low enough to let the clunk out of the fuel briefly in a dive

good luck and happy flying

pt19 flyer

dbacque

My Feedback: (3)

I had a very draggy quarter scale bipe that had this problem. I tried everything including pumps and it still died in dives. Finally I put a 1 oz. header tank in front of the main tank. The vent on the main tank is still connected to the muffler, the fuel line from the main tank goes to the vent line on the header tank and the fuel line from the header tank goes to the carb.

When you fill from the carb line the fuel fills the header tank then overflows into the main tank. Now when you run (in level flight) the header tank will stay full until the main tank is empty, then the header tank will empty. When you dive, any bubbles picked up in the main tank will go to the header tank but the bubble stays in the header tank and the engine still has a steady supply of fuel. Make the klunk line short in the header tank, to about the center of the tank. You'll never pass another bubble to the engine.

It fixed my problem.

Dave

Villa

Hi Big-Mo
When I had the same problem I found that the majority of the fuel line sold at my local hobby shop and at Tower Hobbies was just to darn stiff. The smaller the fuel tank, the worse the problem. I kept purchasing different fuel lines until I found something that worked. As I recall, the Great Planes fuel line was more limber than most. I also shorten the inside tank line so I have at least 1/4 inch clearance at the back of the tank. Maybe even 3/8 inch. I think the line may stretch as it ages.

Sarges_heroes2003

My Feedback: (6)

use the 1/4 " rubber foam they sell at the hobby store to wrap ur tanks. the engine vibrations can stir up the fuel into bubbles there by drying up the tank prematurely. I showed this to the guys at me old field and they didn't believe it. they still have intermittent dead stick problems (which they wont own up to).

Big-Mo

My Feedback: (5)

So what size lines do you all use inside the tanks?

Cashpoboy

My Feedback: (7)

10 bucks says it turns out to be leaky lines.

I've been flying for a long time. Whenever I see this stuff it's bad lines. I bet there is a hole in one of your lines.

Pull the tank and put new lines on it. Size and flexibility of the lines I highly doubt. If all your other planes work with the set up you have then what is different? HOLES!

Villa

Hi Cashpoboy
I fully agree with you. A small air leak can also cause this. Like you I have been flying for many years. I change ALL of the fuel lines at the first sign of an air leak. I also replace the fuel tank occasionally if a problem persists. I replaced all of my fuel tanks once I discovered the Hayes fuel tank. That tank is superior to any fuel tank I have seen in my 36 years in this wonderful hobby.

Cashpoboy

My Feedback: (7)

I agree. Hayes tanks are very nice.

OK Big-Mo get a Hayes tank and your troubles are over.

Big-Mo

My Feedback: (5)

Well istn that a kick in tda butt, i have a hayse tank replaced the lines twice with sulivan fuel line,. the tank is brand new less than 1 qt of fuel through it. so I dunno .


thanks anyway


Don

bkdavy

My Feedback: (1)

The loop in the line to the carb is what I use to prevent this problem. I usually have about a 2 inch diameter loop between the tank and the firewall. that translates to roughly 6 inches of fuel line in the loop alone. Tack on the 3-4 inches in the fuel tank (clunk line approximately 1/4" off the back wall of the tank when vertical), plus the 3-4 inches between the firewall and the carb, and its easy to have 10-12 inches of fuel line to run off. With only 5 inches, I can easily see how a plane in a dive at more than idle will quickly starve.

As far as the bubble in the line causing the engine to burp, the air bubble will very quickly exit the fuel system at the carb. If the engine is properly tuned, this very short lean burst should not cause the engine to deadstick.

Also throttling down on downlines will minimize the air bubble in the line. And don't punch the throttle coming out of the down line. Ease it up. Your exit will be smoother, and the engine should keep running.

Brad

Cashpoboy

My Feedback: (7)

It's not your tank.

I didn't see anywhere in the posts, is this a glow or gas setup?

Also, what size engine is this?

Are you using muffler pressure setup?

I know this may not be related but I need a clear image to put it all together.

Big-Mo

My Feedback: (5)

OK lets see it is a glow setup,

a supretigre 90(Italian) motor using muffler pressure with a check valve it is on a lanier lazer 200 1/4 scale

mvallyman

My Feedback: (32)

Everyone seems to be fixated on a fuel problem, this could also be engine related. I have had deadsticks when slamming throttle down to idle from mid to high RPM,s, turns out the idle mixture was too lean.