trab1925

I have the minimum recommended size 2-stroke for my .40-.46 size Midwest Corsair. I'm at 5500ft. elevation, is this going to be a big problem?

I understand this is considered under powdered, but am I really risking it with this size? I've tried searching for this topic but the only temporary solution I've read is to up one inch in diameter for a propeller. I'm going to ask some people at my field about it but I'm curious about anyone else's thoughts on this.

I do plan on getting a larger engine, but is this suitable to at least get off the ground??

Thanks

trab1925

Well I did some more searching old threads(more specifically in my area) and it looks like the majority of people think this is a doable feat.

big max 1935

My Feedback: (9)

I think it depends on just what .40 you are using. They all don't put out the same power. I run my LA ,FP,& GP engines on a 11X4 prop. The ball bearing ones like a 11 X 5 or 6 better. You may also need to up the nitro some . All up weight is also a factor. Best to give it a try ,you can up grade to suit your tastes. Good luck & have fun. Max H.

jetmech05

This is just my opinion so take it for what it's worth....I find the minimum recommended engine to be too small....Yes it flys the airplane without it dragging it's hind end all over the field but it just doesn't give you that big grin.....I find that the maximum engine recommended or perhaps a size larger does it for me.
Remember throttle is not an on/off switch....

Augie11

I fly routinely in your area. The .40 will get her up but performance will be limited, You'll want to upgrade to a good .46 (or even a .55) ultimately. At out altitude I always power my planes at the high end. That may save you if you get into a difficult situation.

jetmech05

Better to have the power and not need it...than to need the power and not have it

PropsnWings

My Feedback: (9)

I agree.. I always tend to over power my birds. I figure I can always throttle back some.

jester_s1

Try it first on a fairly calm day if you get many of those. If the engine will get it off the ground, it'll fly it. I understand that engines run better at elevation with more nitro than down here near sea level, so you might experiment with some 20% to get a little more oomph out of it.

trab1925

My understanding of using more nitro is that the lack of oxygen is what is actually limiting the power. So more nitro won't help, because there is not even enough oxygen to get the maximum performance out of 10% nitro.

I started the engine today for the first time and there is a decent amount of pull on the engine. I would guess maybe 7.0-7.5 lb thrust estimating. It should get it in the air but I won't have all the power I feel I would need to do any low altitude aerobatics.

Augie11

It would also be wise to make the first flite before the heat of the day makes the altitude density go against you. This time of year the cooler the air temperature the better the engine will run.

Best of luck.

jester_s1

Nitro adds oxygen to the mix, so more nitro will somewhat compensate for the altitude. There is a point where more doesn't help because more nitro also causes your ignition to advance, which makes you have to richen the mix to retard it which reduces power. Much of that situation is based on compression, which at altitude is reduced anyway (less head pressure). So flyers at altitude can go higher in nitro content and actually see power improvements than flyers at sea level because of the difference in air density. You'll never get the engine to make the same power that it would at sea level obviously, and even if it did the prop isn't as effective in the thinner air, but you can improve things by using more nitro.

JohnBuckner

My Feedback: (1)

High density altitude is a triple whammy and it is not a fixed figure, it is an extreme varible affected by actual barometric pressure, temperature and actual elevation. Humidity is also factored in to arrive at density altitude.

Density altitude is a triple whammy simply because high density altitude negatively affects not only engine power output but also negatively affects the the airplanes aerodynamic performance as well as negatively affects the propellors efficiency.

Its Also an extreme varible as Augie mentioned simpy by the time of day which tends to make folks at vary high elevation either early morning or evening flyers during the cooler hours.

Actual elevation and real time density altitude can be often a hugh spread. For example if your actual elevation is around 5500 feet above sea level then during periods of high temperature perhaps 90 degrees (among other factors) or more then your density altitude could easily reach up to 1500 feet or more than the actual elevation. To put it bluntly that means your airplane will fly and respond like it is at 7000 feet.

It is typical and advisable to use higher nitro fuel. My friends at field east of my location which is at around an elevation of 7000 normally use in two strokes 25% nitro as a minimum but its important to remember that only helps to retain engine power but does nothing for the loss in the airplane and propellors performance.

John