Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

OS.15 CV-A or OS.25LA ???

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Old 08-04-2005, 08:56 AM
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nexxa
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Default OS.15 CV-A or OS.25LA ???

I actually have an OS.15 CV-A with a Mac tune pipe tune for a 7X7 APC sport prop on my Wonder. Fast but not enough. I prefer it when I put an 8X5 APC prop, less fast but more trust... the acceleration is very impressive... My Wonder is a little bit heavy, ready to fly weight with gas: 3 pound (48oz). This is why I want to run it with an 8 inch prop.

I don't have a lot of money to spend on a new engine.... I was looking to replace in my Wonder the .15CV-A by an OS.25LA without tune pipe and try to run it on a 8X8 APC prop...

I just want to know if the difference between these two engines is considerable... and I don’t want to loose my time by replacing the .15 by .25LA?

My goal, go faster without spending all my money in a new engines. My Wonder is just a toy for me... and a little bit heavy for a 7inch prop
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Old 08-04-2005, 09:54 AM
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Default RE: OS.15 CV-A or OS.25LA ???

The 25 LA is rated with 20% more power than the 15 CV-A, and will turn the bigger diameter prop. But an 8-8 is too much prop for a 25. Try an 8-6 or 8-7 cut down slightly.
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Old 08-04-2005, 10:44 AM
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Default RE: OS.15 CV-A or OS.25LA ???

If you have the room, CG margin, and desire to move up to a .25 size engine - get one with some power to it.

TT, Magnum and ASP .25 - .36 engines are wonderful. All inexpensive. All are far better than an LA or FP engine. Any of them will turn up an 8x8 fairly well with just the stock muffler.

The Novell .25 is probably the lightest weight. Very popular with the combat crowd. Not all that expensive. Very good performance.
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Old 08-04-2005, 11:14 AM
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Default RE: OS.15 CV-A or OS.25LA ???

tt36 is a great in the 25 size class, with a pipe it'll turn an apc 9-6 17.8k, stock muffler on the same 9-6 is 15.3k
no tests on the 8-8 yet tho
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Old 08-04-2005, 02:45 PM
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Default RE: OS.15 CV-A or OS.25LA ???

Thanks for all recommendations.... maybe I’m going to keep the OS.15 in it and change nothing. This weekend, we have a Fun-Fly, this is why I want to change the engine, I want more speed... but I don't want to spend 3 or 4 hours to rebalance and fit everything together just for a little amelioration. The OS25LA cost nothing and I can have it now, other engine need to be ordering.

I will only change my 10% nitro fuel for 25% and retune the pipe. Maybe I will saw a difference. Yes, I no 10! [&:], but with 10% nitro I can fly full throttle for 4 minutes on 4oz tank, and 25% less than 2 minutes!

Next project:
Shrike 10 with a .25 in it, and try to make it light weight!
I’m starting to like these small and fast planes.

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Old 08-04-2005, 07:15 PM
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Default RE: OS.15 CV-A or OS.25LA ???

The 7x7 is too much prop for the CVA .15. You will see good results with the MAS 7x5 and 7x6. These props kind of look like the old TOP FLITE series, if you ever see those old thin blade, light weight beauties,[TF], snatch them up! APC used to sell a 6.5x6.5 that worked real well, but I don't see it listed.

A little scratch built plane with a balsa sheet wing of 3/8" thickness, with about 240 sq" of area will be what you really need if you ever want to see that CVA .15, "be all that it can be".
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Old 08-05-2005, 09:19 AM
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Default RE: OS.15 CV-A or OS.25LA ???

This week-end I will try two different setup.. 25% nitro, 8X5APC and 7X6APC... and retune the pipe.
Maybe there is something wrong with my settings for this engine. Yesterday I was looking and old video and I can see me adjusting an OS.15 LA on a 7X6 APC prop. On the video I can read the TAC at 17450rpm on .15LA!!! The only mod I made on this engine is modification on the stock muffler. I just enlarge the exhaust hole to the maximum and double the size of the baffle hole. Great sound.

The best I can do with my .15CVA is 17000 with a tune pipe!

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Old 08-05-2005, 09:38 AM
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Default RE: OS.15 CV-A or OS.25LA ???

ORIGINAL: nexxa
The best I can do with my .15CVA is 17000 with a tune pipe!
Have you done anything with the pipe length yet? Perhaps it's too long.
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Old 08-05-2005, 10:02 AM
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Default RE: OS.15 CV-A or OS.25LA ???

Yes... The Hearder was 10inch long at begenning. I cut it by removing half inch of header at the time and tac the engine with a 7X6 APC prop. Finally I finish with a 4inch hearder.
But like I said, this weekend I will test my old OS.15 LA with 7X6 prop and 25% to know exactly the RPM. My CV-A is suppose to do better then LA engine. I will retune the header and the engine... and check everything....
Go to the top of this tread, there is picture of the Wonder with the pipe. Look the setup.


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Old 08-05-2005, 11:37 PM
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Default RE: OS.15 CV-A or OS.25LA ???

I looked up what I get with a 7x5 MAS, MACs pipe, and my own header, which is right around 4 inches, 15% fuel, and that CVA .15 puts out 23,000 rpm. I did a construction thread about it over in the 1/2A forum titled, "LIL DUST STREAK" a couple of months ago. The engine is on a 2/3 size DIAMOND DUST that weighs 29 ozs RTF, and it's about 2/3rds as impressive as my .32 powered DUST.

Did you shorten the header to the point where you started to see no increase in RPM? If you don't take it that far, then you aren't tuned yet.
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