Giants From Down Under

[SBR_RV]

	Quote:
	While the newest airplane engines do have fuel-injection systems that automatically adjust the fuel/air mixture entering the cylinders, older engines only have carbureters.

if you look under the hood a beachcraft bonanza (fuel injected), its amazing at how simple and old school they are. now look at a carbureted engine on cessna 172, yet you still pay thousands for an overhall.

[towball]

Unfortunately the RAAF Base is closed to model aircraft from the 12th February to 4th April.

We will not be able to run a competition at the RAAF Base.

Towball

[3W.]

Off to China! nice LIGHT planes

[notorious_benny]

The amount that your mixture is richened by a hot day is not much. You might have to make an adjustment of between1/16 to 1/8 of a turn at the most!! Thats why I dont touch mine.

If you are already on the lean side for a cool day the thinner hot air might not make the mixture sufficiently rich enough to give adequate cooling leading to overheating especially on long uplines resulting in a motor stopping.

These motors we run can be significantly out of tune and still run, so if you have a motor that is lets say 1/8 of a turn too lean on a cool day (easy to do) it will run well, make good power and probably wont overheat, when the hot day comes around, your mixture does in-fact richen up (this is a fact), however the comparitively small amount that the mixture has richened means that it is still lean of ideal tune, this is what causes the problems, you are still slightly lean however its now bloody hot so your motor suffers from the heat.

[morerevsm3]

being that it is the MASS of air through the venturi that draws fuel through the jets, a walbro carburetter will lean the mixture on a hot day due to lower air density and mass, it then will run hot and cause detonation and possible engine failure due to either seizing or burning a hole through the piston

[notorious_benny]

The following comes from a website for guys who use the Walbro Carb on motors for motorised parachutes.

Considering that the metering system (not discussed in this article) is properly set, I must stress that before every flight, even at the same field the carburetor must be tuned because the density altitude or in other words the atmospheric pressure changes often. If the pressure increases, the air becomes denser and because there is more oxygen in the air, it will create a lean mixture if the previous carburetor tuning was performed before the atmospheric pressure increased. Conversely, if the pressure dropped, your mixture will become rich. Also, if you climb to higher altitudes your mixture will become richer and richer, and as you climb above approximately 3,000 ft your fuel mixture will be too rich. For this type of flight I strongly recommend a remote mixture adjustment system that is available on the market.

http://poweredparaglider.us/tuning_a_carb.html

[excelpoint]

Some good stuff comming out of this thread.

[notorious_benny]

This guys page is really helpful, I used it when I needed to adjust the bend in the metering arm on my walbro pumper for better midrange response. Remeber these guys are putting their lives on the line, we only put our models and pride on the line.

http://www.aerocorsair.com/id27.htm

[L plater]

So tell me, How do I host an IMAC event at my club. What do you IMAC boy's need and what do you expect from the host club.....

[notorious_benny]

Where is your club L-plater??? I started trying to get one organised up here, my club president and vice presidents were quite enthusiastic, however I must say that some of our commitee members made it very difficult for me so I have just decided to attend as many as I can get my backside too.

Talk to Matt aka excelpoint

also talk to Rick Gell, the president of the ASAA. The website is www.scaleaeros.com.au his email should be there.

I spoke to Rick when I was finding information and he was very very helpful, if you have members in your club who want to participate then you shouldnt have too many troubles getting an event going. The problem up here is that no one in my club is very interested. We have one pattern flyer and myself who flies IMAC thats it, outa of 100 odd members!!!!

[fredo]

Just 2 cents question. Where is the sun most of the time through the day? If it interfers with the box, that could be a problem. That's the reason why we can't organise IMAC in our club as from about midday you are looking into the sun!

[The Hobbyman]

L Plater I will talk to ya on Thursday about it.