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Author Topic: Super Tigre .40 Venturi?  (Read 1439 times)

Offline Joe Messinger

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Super Tigre .40 Venturi?
« on: July 06, 2006, 12:18:29 PM »
I have a new (China) S.T. .40  that I have attempted to convert from RC to C/L by replacing the carburetor with a venturi from a S.T. .51 c/l/ engine.   The venturi fit exactly in the .40 and I used a S.T nva. to complete the conversion. The inside dimension of the venturi is 7 mm.. Same as that for the OS LA .40 c/l  engines.

Problem is the S.T. .40 doesn't have much power or develop sufficient rpms.  Same engine with the carb turns a 11-4 prop at nearly 14,000 rpms. wide open.    With the venturi, about 9,500 rpms is all I can get with the 11-4.  The conversion version will barely pull my Brodak P-40 over the top of a loop.

Any ideas or suggestions?

Thanks,

Joe Messinger
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Offline Alan Buck

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Re: Super Tigre .40 Venturi?
« Reply #1 on: July 06, 2006, 02:16:52 PM »
Joe try a 11-5 prop at 9000 rpm it my be fast but you can go with longer lines to slow it down but more info. on fuel and line length will help good luck
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Offline Joe Messinger

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Re: Super Tigre .40 Venturi?
« Reply #2 on: July 06, 2006, 03:59:09 PM »
Thanks Alan,

I'm using Brodak 10% nitro fuel .  The engine is capable of pretty good speed (about 5.7 sec. level on 60' lines) with the venturi but it  lacks the torque needed to pull the plane through maneuvers.

I re- installed the carburetor and locked the throttle open.  As I mentioned earlier the ST turned the 11-4 at nearly 14,000 rpms and the result in the air was about 4.5 second laps which was way too fast for me to even attempt a inside loop.  (Not much experience flying as yet).  I just hung on hoped for a fuel line to pop off due to the excess centrifugal force!

I imagine I could rig up a means of setting the carb for a reasonable speed (rpm) but the carb on the ST  engines looks like it should be about the right size for a  5 hp. Briggs & Stratton.  The engine is very heavy, especially with the ST muffler that is included and my main objective was  to cut down on some of the weight.  I had to duct tape a 6" Crescent wrench on the tail of my plane to balance the thing with that engine on there! (Not really. . .)

Thanks,

Joe
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Joe Messinger

Offline Bill Little

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Re: Super Tigre .40 Venturi?
« Reply #3 on: July 06, 2006, 04:08:54 PM »
Hi Joe,

Can't say much about your set up, but remember, you don't have to run the engine wide open.  In fact, a bit richer than peak will help the engine pull through manuevers.  y1

5.7 on 60 ft. lines is real slow for a stunt plane like the P-40 to fly.

The speed the airplane needs to fly at is pretty much regulated by prop pitch and lap times by line length.  Get the flight speed where the plane is comfortable, then lengthen or shorten the lines to make you comfortable. 

5.7 on a plane with lines that approach 70' from center of handle to centerline of the plane might be ok for a piped full boogie stunt ship, but a profile on 60' lines will be turning closer to 4.9-5.0 usually.

Bill <><

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Big Bear <><

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Offline Alan Buck

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Re: Super Tigre .40 Venturi?
« Reply #4 on: July 06, 2006, 07:21:01 PM »
Joe  how does it turn outsides vs insides nose weight may be a problem .try upright and inverted st 40 is heavy motor vs la 40
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Alan Hahn

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Re: Super Tigre .40 Venturi?
« Reply #5 on: July 06, 2006, 07:31:13 PM »
How big is the RC carb opening? If the ST51 venturi isn't giving you the power of the open carb, I assume the carb with it's needle assembly sounds like a bigger opening than the  ST51 venturi with the ST spraybar assembly. So if that is true, I would try drilling out the venturi a little (but less than the carb opening).
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Offline Bill Little

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Re: Super Tigre .40 Venturi?
« Reply #6 on: July 07, 2006, 08:42:48 PM »
Quote from: Joe Messinger on July 06, 2006, 12:18:29 PM
I have a new (China) S.T. .40  that I have attempted to convert from RC to C/L by replacing the carburetor with a venturi from a S.T. .51 c/l/ engine.   The venturi fit exactly in the .40 and I used a S.T nva. to complete the conversion. The inside dimension of the venturi is 7 mm.. Same as that for the OS LA .40 c/l  engines.

Problem is the S.T. .40 doesn't have much power or develop sufficient rpms.  Same engine with the carb turns a 11-4 prop at nearly 14,000 rpms. wide open.    With the venturi, about 9,500 rpms is all I can get with the 11-4.  The conversion version will barely pull my Brodak P-40 over the top of a loop.

Any ideas or suggestions?

Thanks,

Joe Messinger

Hi Joe,

A thought just struck me, how was the opening in the spray bar oriented when you had the venturi/NVA in there?

Bill <><
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Big Bear <><

Aberdeen, NC

James Hylton Motorsports/NASCAR/ARCA

AMA 95351 (got one of my old numbers back! ;D )

Trying to get by

Offline Joe Messinger

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Re: Super Tigre .40 Venturi?
« Reply #7 on: July 08, 2006, 06:39:37 AM »
Hi Bill,
The opening in the spray bar is pointed straight down.

Joe
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Joe Messinger

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