apalsson

My Feedback: (1)

Wow!! What size engines are you talking here with that sort of a fuel flow?
Besides, what do the reeds pass through? Flow of liquid? I don't think so.
What is the purpose of a carburettor in a small two stroke engine? (any petrol engine for that matter) Where does the fuel vapourize?

With the utmost respect to your mate, I think something has gone awash here

jmpups

My Feedback: (1)

You don't put it on a channel that slams the choke shut, you put it on a dial that allows you to slowly close the choke shutting off the air.

a1pcfixer

My Feedback: (7)

Tim,

Hydraulic shock/water hammer applies in full fluid applications, NOT in our gas engines where it's an air/gas-oil mist.

I think you need a new engine tuning friend, or at least one more knowledgeable on these gas engines.

jedijody

My Feedback: (1)

Liquid hammer from quickly shutting off the fuel flow? Your friend needs to learn what the choke does and what actually passes through the reeds. Closing the choke shuts off the air, not fuel. Atomised fuel and air is what is passed through the reeds, there isn't enough fuel flow through a small diaphragm carb to cause any kind of hydrolic lock in a gasser when shutting down with the choke.

I don't work on motorcycles, and yard implements but I do service, factory warranty repair, factory R&D, and prototype testing on model aircraft engines just like what we are talking about. I also used to be factory authorized service tech for Mercury Marine, Johnson, Evinrude, and Force outboards. Been shutting down small to medium sized  2 stroke gas engines with the choke for almost 40 years and it's never damaged a reed yet.

TimBle

I'm completely with you. we have a wet gas passing through the valves, yet he reckons that shutting off this flow suddenly still results in shock this causes damage to the valves.
Either way I prefer to cut off the engine at the ignition, just like all gasoline engines are cut. Until I work out what he's on about I'd prefer to err on the side of conservatism with my first gasser.
Input appreciated

Tired Old Man

My Feedback: (1)

Setting up a gas engine isn't really any more difficult than corectly setting up a glow engine. First order of business is never to build something while subscribing to the law of minimums, which so many of you do. In doing so you assure than the smallest thing can become the weakest link that can take down your plane. That may be battery type or capacity, hardware dimensionality, servo strength, whatever.

Next is to take the time to learn about the products you are using instead of accepting as gospel something you read on the internet. It was on the internet and therefore must be true, right? Yea, right. In learning about what you have, want, or plan to use you learn how to install and use it correctly. Learn about servo to throttle lever geometry. Learn about fasteners, connectors, and securement. learn about wire security. Learn about current consumption with the particular products intended for use. Size everything for a minimum of 25% greater than required. 30-50% is better.

For some reason many of you think glow engines are safe while gas engines are not, or that glow engines are safer than gas engines. I cannot understand that way of thinking. I can kill someone with a 1" blade pocket knife or a 16" blade butcher knife. A blade is a blade. People are reacting to gas engines out of fear. Apparently fear of the unknown, with the unknown being their lack of education and familiarity with the product. Others are responding to titillation from advertisers trying to make a buck...off of you.

The simpler the end result the more reliable it will be. Pretty basic thinking but it works. KISS is still a very functional method of doing things. In engineering if it doesn't break it hasn't been loaded enough or doesn't have enough features yet. It really does work that way but that doesn't mean it's right. Ignition kills fail and do so all the time. Failure to program your tx failsafe will bite you in the ***** long before a correctly set up engine will and that has been proven over and over. I've seen it too many times.

Buying more goodies to overcome a deficiency in knowledge and ability will not make anything safer. Just more expensive with a greater propensity for failure. Where is the problem in flying for 20 minutes to run out a gas tank? Worse, why did someone use such large gas tanks unless they originally intended to fly for that long? Didn't they bother to perform ground runs to see how long the tank would take to empty? Using too samll of an ignition or receiver battery? Another area where the user wasn't very bright or was trying to cut cost corners. You read about them all the time in the 2.4 brown out/lost link threads.

a1pcfixer

My Feedback: (7)

Yep, he's totally off the mark on this issue.

Water hammer is the term used to describe the effect that occurs when the
velocity of the fluid moving through a pipe suddenly changes.

Notice the words "fluid" and "pipe"?

Our choke's deal ONLY with the flow of air, NOT fluid.

From any perspective that guy is missing a few fries in his happy meal.[X(]
Best thing you can do about your friend is to nod your head and politely ignore him.

Good choice!

For the best gas engine tuning info here, rely on Jody (jedijody)

jedijody

My Feedback: (1)

Very nice and perfectly stated, I agree 110%!

Syssa Aircraft

I have to say, it is always nice to see someone set up their first gas plane and, after flying it, say, "wow, that isn't as hard as I thought it was".

There are a few well known parameters to follow when setting up gas engine powered models...it is not rocket science...like TOldMan and JJodi say...as long as the modeler follows sensible parameters, he/she will be fine.

For me, it seems after looking at many aircraft setups 9gas and glow), the layout of the wiring and fuel lines are looking for trouble. Fuel lines rubbing up against hot surfaces or sharp surfaces near any engine are sure to eventually crash your plane and at worst, cause a fire.

Remote engine kills of any kind are quite handy to have. If something were to go really wrong (on any size gas powered plane), how much fun would it be to try to shut the engine off by the switch mounted on the front of the plane?

TimBle

I had a bit of a sleep on his views vs the conventional wisdom and I think I know where he has gone wrong.
Air or liquid are considered fluids.
However air flowat subsonic speeds is considered to be incompressible and inelasticso pressure changes through a venturi is a result of a change in velocity of the fluid b lah blah blah.
So if the choke is shut rapidly there is a rapid shiftfrom dynamic pressure to static pressure (which was low when the choke valve was open) and that can send a pressure pulse into the fuel chamberof the carb.
So anyway I wonder if he is not refering to the Diaphram in the carb or the float valve being damaged since shutting the choke quickly does have a "shock" effect. As someone mentioned, close it slowly and theproblem goes away....?

jedijody

My Feedback: (1)

Waste all the time you want trying to figure out his logic, the fact is he is 100% wrong. The only shock to anything is to the reasoning of knowledgeable people in the small engine field that someone would actually believe it.

With all due respect to your friend your second sentence described it exactly for what it is, a bunch of blah, blah, blah, from someone trying to impress his buddies with how little he knows about the subject.

a1pcfixer

My Feedback: (7)

Tim,

Air can be compressed, liquids can NOT, but can be pressurized in an enclosed system.
From that most basic premise you'll find everything else he claims has no basis in fact.

Stick around here and you'll find out good info from those that truly know.

TimBle

exactly, he made a serious error in believing it to be incompressible flow when is it is fact compressible pulsating flow through a carb.
Indeed a case of speaking with convinction but making incorrect assumptions.

kerwin50

Guy's it's not that I've learned anything new but brought to light, for instance gas tank size.
Thanks to TOM he reminded me of this. I've got a GW MX2 that came with a tank that would fly this plane for a long time.
I'm going to adjust my vent tube for 15 minutes of full throttle.

jedijody

My Feedback: (1)

The best place to start is make sure your throttle return spring is connected, make sure your engine dies with the throttle all the way closed. Then use quality 4-40 bolt through ball link hardware on your throttle linkage, be sure to put a flat washer on the bolt first. Make your linkage as short and direct as possible. Don't use a cheap old beat up pre-crashed servo for the throttle, use a new, quality brand servo sized for a flight control surface.

Consider the smaller tank as a contingency in case Murphy does strike. Then, after all that one must annual the plane every year. I always find something that has worn to the point that it could make it unreliable for the whole season.

TimBle

ok so spring stays and throttle stop screw goes

Tired Old Man

My Feedback: (1)

Good call on the "annual" Jody. There's a lot of evidence of people thinking that once installed something should last forever. That just ain't so.

Truckracer

My Feedback: (19)

Man, you guys are raining on my parade. Ya mean I can't reuse those old beat up servos for throttle? And .... I actually have to maintain my stuff each year? I actually have to do work on this stuff?

TimBle

speaking of longevity. What's the deal with tygon vs neoprene fuel hoses?

jedijody

My Feedback: (1)

Ethanol deteriorates neoprene in a fairly short length of time. After a couple weeks or so there will start to be small black pieces of the hose in your filter or the filter screen in the carb, it will continue to disintegrate until it fails completely or plugs up your filter, which ever comes first. Tygon F-4040-A is the best to use, Oregon aslo makes a very good and flexible fuel line that works great for small fuel tanks, you can get it at your local saw shop that sells Oregon equipment.

jedijody

My Feedback: (1)

DP

apalsson

My Feedback: (1)

Guys,

If you have access to a lawn mower shop that sells Briggs & Stratton parts, get 1/8" Tygon from them.
These shops sell Tygon tubing by the box. From memory, each box has some 50 feet and is sold around here for around $10 - $12
The Briggs & Stratton branded fuel tubing is quite good, it's very flexible and seems to hold up well.
I use this in most of my installations and have had good experience with it

MetallicaJunkie

man i screwed up...i have removed the spring on 3 of my gassers.....am i doomed? i thought it was the right thing to do...not aymore

jmpups

My Feedback: (1)

You didn't screw up, all these experts have there own ideas. The first thing I do with a gas engine is remove the return spring for smooth operation of the throtle servo.

Tired Old Man

My Feedback: (1)

Some of those experts are indeed experts, and get paid, some rather well, to work on and perform gas two stroke R&D. Others have been working on, repairing, and modifying gas two strokes for longer than many in this forum have been breathing. Others have owned engine design or manufacturing firms, and/or have been the primary distribution and service network for particular engine brands. We're talking thousands of engines in experience. You've done how many?

Of course it's a matter of individual choice whether or not one pays attention to them. Those that don't have a great tendency to repeat history and ask silly questions later.

Jody,

By DP I hope you didn't mean double penetration

Ari,

B&G generally sells the good stuff but without the correct part number and material type on the tube you really don't know what you're getting. The Type F IS the good stuff. Anything else does not hold up as long or as well.

For you others, neoprene is a no-no but Viton is an excellent material. It's also black which may confuse some people.