I have a new SkyRaider Mach I with a used Evolution trainer A .46 and a 12x7 prop @ 12000 full throttle. The engine works OK at idle and 1/2 throttle.
At full throttle I have bubbles in the vent line, supply line, and carb line with consequent surging. I have replaced the line from the remote mixture to the carb and the supply line from the fuel tank to the remote mixture control. I have leak tested the tank with the vent line and the supply line attached. No leaks. I dismantled the muffler, but it was fairly clean with no blockage of the vent line. ( 31 flights since new ). When putting the plane together I changed the
restrictive aluminum tubes in the fuel tank to less restrictive brass ones. What can be causing fuel and bubbles to be in the vent line?

griesel, You may be having a problem known as "Fuel Foaming"

When the vibration conditions are right, fuel can turn (temporarily) to foam.

If you have another tank, try hooking it up to the engine, but leave it outside the plane and see if the engine works as it should (You can even use your fuel jug for this test)

If it works, try padding your plane's tank with foam rubber to help keep the vibrations down.

did you check the fuel line that are attached to the clunk at the fuel tubing inside the tank?those tubes have very sharp edges and can cause a tear in the fuel line when you slide it onto the tube.checking the tank for leaks externally wont show a fuel line leak inside the tank.

One of these will also help fix foaming in the fuel tank. I use them on all of my planes. They work great.

http://www2.towerhobbies.com/cgi-bin...?&I=LXXF25&P=7

DS

Three good replies. Tank outside the airframe - that sounds good. I carefully deburred both tubes which were replaced. The inside line
was new; but this was happening with a completely full tank. An OS bubbless clunk. I never heard of such a thing. A little pricey but worth it if it works. Thanks Guys

I searched tower hobbies and discovered a Dubro Tank Filter which is a filter clunk and looks similar to the OS for a whole lot less money
$2 versus $14.50. I also found on pspmfg.com a clunk with a filter for $4.20. I have a clunk that came with my manual pump from h9
that has a screen filter. There are also some felt pad clunk filters that state they will eliminate bubbles. Changin the clunk is a whole lot
easier than trying to dremel out clearance for tank padding.

12-7 turning 12,000 with a 46 [X(]

Those are some great numbers
What plug, fuel, and prop brand are you using

h9 han3011 plug; byron fuels 15% nitro; 18% synthetic castor mix; Master Airscrew GF3 11x7. I don't think it is so hot. I am pretty sure
an OS FX .45 or a Super Tiger .45 will beat it a little bit. And even better a MACs muffler with either of those two engines and a 11X6 prop
and a Sky Raider Mach I gives excellent vertical performance. Two experts at my club, Tucson Radio Control Club, have them and its
unbelievable what they do with what is essentially a trainer.

One of the most overlooked items to rid a fuel system of foaming is a small "Hopper" tank. A 2oz. tank between the main tank and the engine will do wonders to give better runs.
I have used them both internally on larger models, and the hopper externally on smaller models. Sometimes a 2 oz. tank and a 6oz. tank can be used to replace/supplement an 8 oz. or whatever size you need reference the model. Two fuel-line system or 3 line works. However, You have to fuel the hopper first, with the hopper vent being the receiver of the master Tank's fuel. Pressure goes into the Master tank. Be sure you plumb so the clunk can move in the hopper as well as the master. If the clunk cannot follow the fuel, you will come up short when the tank gets low.

try putting foam around the fuel tank the vibs are causing th fuel to foam

Hi

I have a dubro type clunk in one of my planes, can't remember which i assumed it was just a filter. i do have a few smaller planes that there is little or no room for packing around the tank for which these would be useful.

I have heard somwhere of an addative to add to fuel to stop it foaming anyone know where it might be available?

Simon

The OS bubbleless clunks were just an example of what you can use. I personally use the Dubro type of bubbless clunks and they are much less expensive. I can't find the link right now, but I usually ask the LHS to order them for me. I believe they are something like $4.00 each or some such thing.

DS.

I have heard that a shot of WD-40 in your fuel jug will work - but then, here in Minnesota people use WD-40 and Duct Tape to cure most of the world's problems.

This may be a little off-topic, but here they even spray their fishing bait with WD-40. They say they catch more fish that way. And you know what? It works!

One thing nobody has mentioned yet- make sure your prop is balanced. Even if it is brand new, it needs to be balanced. This will cut down vibration (a lot) and make your engine last longer.
Jason

Have you replaced the fuel line inside the tank to the clunk? I have several WM planes and have found that the supplied fuel line has a tendency to split on the tube. The first one I found was also on a Sky Raider. Had bubbles, and engine ran for only a couple of minutes. I now replace the supplied fuel line.

thats some good revs from yout 46

Replace tank with a Hayes, get rid of the brass tubes and stopper etc, your engine problems will go away!

I replaced the clunk with a dubro tank filter ( clunk). $2.10 + tax. Only a few bubbles now and it runs decently.
The problem is you have to go with a 3 line system - vent - fill - supply. I am going to try to fill with the vent
and with the supply tube open. And then drain with the supply with the vent line open. Dubro says not to run
fuel thru the filter in reverse. Next question is how to get the clunk to go to the front of the tank. I have two
h9 tanks and one world models tank and all three, the clunk is allways near the rear of the tank. I assume if you
have the nose down and at full throttle ( which seldom happens ) its dead stick time.

First of all, you can't fill through the vent - that will only result in fuel coming out of the feed line. If you can't fill through that clunk, you'll either have to add a third line, or get rid of the clunk.

Second, the clunk should never go to the front of the tank. In fact, I add a stiff piece of tubing to the clunk line to prevent this from happening in the event of an abrupt stop.

Did we come up with a solution, change the tank, add foam(which will be difficult, add clunk. My evo .46 power trainer(new) ran for 5 min then at 1/4 throttle started fading. Raised it to half throttle and the motor died quickly. Sound like the bubbles I'm seeing are the culprit?
Guess I'll start with removing the tank and inspect the interior line. Does the cork just pull out when unscrewed. Sorry, total newb here.

Replace all tubing and there should be no bubbles anymore. Those no-bubble clunks are nice and may prevent some of the bubbling, however it's what we dutch call 'fighting the symptoms rather than the problem'. The fuel shouldn't foam, period. Lots of people are flying with this engine, or similar ones, without having these problems.
[edit]better put: an OS 46 AX on a roughly 80oz (5lbs, 2.2kg) plane with a wingspan of about 65" (1660mm) shouldn't cause so much vibrations that the fuel foames[/edit]

Did you balance your prop?

A header tank (hopper?) like used in some helicopters may possible solve the problem as well, but makes your setup more complex and it shouldn't be needed.

My guess is that there is a small puncture in a tube somewhere, leaking air into the fuel. That or maybe your prop is not balanced (or somehow got unbalanced) and this causes extreme vibrations (which will also ruin the bearings).

As far as hooking the whole thing up; you might want to consider a uniflow setup, though again that shouldn't be neccesary. The advantage is that you'll get the same amount of fuel all through the tank, as oppose to your engine running leaner as the tank empties.

http://www.fraserker.com/heli/uniflo...flow_works.htm

I'm not using foam around my fuel tanks and so far have had no problems with it. My closest setup was an OS .46 FXi, which ran fine with a normal clunk in a normal (dubro) fuel tank. All ARF's i have owned so far (5) had a tank installation in such a way that you simply couldn't put foam around it.

I do like to use filter clunks, at least, if we're talking about the same thing


Filter clunks are supposed to filter. If you want it to do that, you shouldn't fill your tank through one, since that will put debris/sand/whatever from your fuelcan into the inside of your filter, meaning that it would be the first thing to go to your engine. Another reason might be that the filter loosens or might even be washed off when refueling.

However, I used two filterclunks, one in my fuelcan and one in the tank. and use a fuel-filler valve between tank and engine to fill the tank. Periodically I check both the tank as the filter, and so far i have seen no problems. This has lasted for about 300 flights now, without any problems.

I changed the prop. The previous prop I balanced by grinding off the tip. The prop was statically balanced but not dynamically balanced which caused the
foaming. We flew friday with the filter clunk and had a few bubbles on first run up but none on subsequent run ups. On landing I hit the outer plastic barrier
and knocked off the tail skid ( Sky Raider Mach I - hi wing ). I was told that this was a weak spot with the Sky Raider and you should just leave it off. I bought
some Dubro wind skids and will put one on the rear to protect the covering.

In the future, scrape and sand material off the front of the heavy side of the prop.

Here's a good prop resource page.


http://www.sentex.net/~mec1995/hobby/props.htm

----- Original Message -----
From: Paul
To: Jansen Lim
Sent: Wednesday, April 11, 2007 8:11 PM
Subject: Paul




Hi there ,yea the weather don,t look to good.


No ... if the forecast accurate, next week will be good. See how it goes.

yep had a play with plane as I said put a larger tank in 50% bigger ,but don,t think that was the problem because when I changed the fuek in line into carbywhich had a bigger internal diameter the plane ran great .top end got 12900 revs at idle 800 rpm

Good rpms. At least you got it running.

,I still think its a bit rich the mixture I mean put 2 tank fulls through it ran O.K only problem is there are a lot of bubbles coming through fuel line into carby not sure how to fix ,_any ideas ??


Cause: Vibration of the tank.


Solution : Pack in some more sponge to secure the tank.

Or add a squirt or two of ArmourAll to your glow fuel to cut down on foaming and lean runs. Won't hurt the engine. Armourall is anti-foaming agent and car plastic protectant.



also charged batteries and they went flat after 2 hours so down to DICK SMITHS in the morning for some decent ones
That under carriage you are getting should be strong enough you should 3 D it in and get someone to catch it for you


Good idea .... you want to volunteer ?


then no landing problems well thats it for now so take care see next time you are out there Paul



Time you take a look at your Mustang after sorting out this one .... !!

Jansen This is a copy I,ve pasted from a club member re air in fuel line lets know if it helps anyone sounds O.K to me




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