Hi,

I've recently bought my first ever brand new engine - an Irvine 53. I've got a World Models 46 P-51 Mustang and am not sure I'm getting the power i would expect.. ..let me explain...

The Mustang is a scale model and as such has the huge spinner to fit flush with the engine cowling - It's a large spinner.

I ran the Irvine in on a 12x6 prop - did it as the book says - rich etc etc..

But found that when I came to fly, the revs were'nt quite reaching that 'peak' you hear which tells you the engine is running at optimum, slightly rich.

I've come down in the sizes and have now reached down as far as a 11x6. What concerns me is that friends are telling me that from this engine I should easily be able to swing a 13x4/5!!

Also I'm getting (as ever..) mixed messages from experienced model shops regards the spinner size - some say you should place a smaller spinner on as this will give more prop area to 'bite' (but surely this would influence the revs not being as high..) - and would certainly not look as realistic. Whilst another shop tells me that this advice is wrong as it's only the ends of the propeller blades which produce the thrust.

Help!!??

okay lets start with the prop size a 13-5 prop is about equal to the 12-6.th the 13-5 will do better verticals but be slower on a level fly by than the 12-6..overall the 12-6 will be faster a better choice than a 13-5 if the plane is on the heavy side.sounds like the engine has not broken in yet or is being run too lean.there are plenty of world models p-51 being flown with the stock size spinner so do not worry about that and yes most of the thrust is from the tips as the roots of the prop due to the diameter are turning very fast so being covered by a spinner is not an issue.borrow a tach and see what rpms the engine is turning with the two props you have.what percentage of nitro are you using..is the engine mounted upright or inverted.you may be running it rich like a said because of a cooling problem .so a picture of your installation could help.

Hi,

Engine is mounted inverted and I'm using 5% nitro (I think that's what it's called - and it's not synthetic but castor..... Flew on an 11.5 x 7 today and it flew the best it ever has...

i was going to suggest an 11-7 prop for a bit more rpm and speed .but if you like the way it flew today leave it alone.

Break down and buy a tach. They have really dropped in price over the last 2 years and it eliminates guessing what an engine is producing. I am not impressed with guys that say they know that the engine must really be pulling because it "is screaming!"

even if you have a tach the true test of a prop is when the plane is in the air.

Re: "even if you have a tach the true test of a prop is when the plane is in the air." < this is true, but you soon learn how fast different length props need to be turning in order to get the plane off the ground. For instance I found out that for a 40 size plane on our grass field while using a 10" or 11" prop it better be spinning around 12,000 rpm for a decent take off speed. If its up around 14,200 like I get with my OS FX engines then the plane will have lots of power for takeoff. If its only around 10,000 then you will be lucky to get the plane off the ground! Also this low rpm means that either you have a prop with too much pitch on it or the needle valves need some serious readjusting. The same 12k to 14k rpms will also work well for the larger 52 sized engines. [8D]

I have two .53's one in a pattern plane and one in a tank the best prop i have for the pattern is a 11x7 or 11.5 x 7 and use 5% Nitro with castor/synthetic mix
The 12/6 bogged it down, it had a lot of power but was slow.. so maybe for scale flights on you p-51 will be good, I'ld use the 11.5 x7 for everyday flying.
Also make sure you have enough airflow inside the cowling to cool the engine, and finally do not run it rich!!

I am flying a 46 size Seagull corsair with the irvine 53 and this is an excellent engin for this plane. I am using an APC 12 X 7 and it performes amazing.

www.densplanes.co.uk

A 13-5 is closer to a 12-7 than it is to a 12-6. The Irvine 53 will spin a 13-5, to be sure, but it will be a fair bit off its optimum. If you need a 13" prop for it, a 13-4 will have ~ the same engine load as your 12-6, but you may not want to limit the level speed that much. I think that a 12-5 is a good all-around choice for that engine.