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

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Old 02-07-2003, 11:56 AM
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im gonna build a Magnum with a MVVS GRRT rear induction rear exhaust, which i entend to enclose as much as possible
The tank bay will have a floor fitted under the small turtle deck so the pipe starts in there, then enters the larger Fiberglass canopy area which is separated from the rest of the plane, then exits just behind the high point.
I'm not sure how much of the engine i will be able to cowl in, i don't want to spoil the looks with a lump where the engine is but I'm guessing only the top 1/2" will be showing.
This should keep the head coolish, but what about the crank and middle .
There will be a hole on the bottom of the plane in front of the firewall to get at the carb with a finger for priming and stopping if necessary ( any special shape it should be to let air into the carb not scavenge it out? )
If I make the nose ring with a large inner hole the air should be able to flow in here if it wants maybe, the prop hub might even serve to force air in, i don't know... but with a couple of small forced air holes would this be enough to push the air around the engine, through the small turtle deck area and into the canopy?
I know warm air is fussy and wont just let the cold air in.
Where would exit holes be best placed here and what shape again to aid suction.
With the GRRT being a bit longer than normal the whole front end of the Magnum will be re-designed and i might as well incorporate as much cooling help as i can.
Thanks, Phil
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Old 02-07-2003, 02:44 PM
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Just my opinion... Don't even worry about the lower part (crankcase). The fuel entering the crankcase is what does 95% of the cooling in that region. You could call Dubb Jett and he could give you the best advise on this. His number is (713) 680-8113. I don't think I'm too far off on this aspect though. I have cowled in engines, and there is never a cooling problem on the bottom end.

The hole in the bottom for the carb will be your biggest problem I see. Landing in grass puts a lot of debris in every corner imaginable. You will likely see a lot going through the engine unless you are able to do a complete clean out after every flight.

Best shape for exits are the NACA inlets and outlets. Rule of thumb... Double the outlet size compared to the inlet size.

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Old 02-07-2003, 02:55 PM
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unfortunally this part of the Magnum where the carb hole is IS the place it lands on, and the sheep like to leave us stuff too :S maybe the hole would be better placed on the side? my rule of thumb was going to be 3 times out for whats in, its how to get it in and where, that concerns me, in the Plyon forum i have been told about tight fitting tubes and ducts, but thats for fully coweled engines, as i dont think mine will be, i'm not bothed with the bottom, let the carb inlet and nose ring do that if they want to, enough? and air that wants to go, can via the canopy.
i'm not sure what NACA in and outlets are... unless its just a cowl put over the hole, forwards facing to let air in, reawards to let it out....??????
Thanks for the reply
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Old 02-07-2003, 07:48 PM
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This is the optimum outlet shape for a cowled engine for the least amount of drag. This takes time to make, but if you want top results...

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Old 02-07-2003, 07:58 PM
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so.. i make two of those somewhere on the rear of the canopy by making the cut in the fibreglass, push it down using the narrow end as a hinge and add a couple of ply sides, any air that enters the engine bay via the carb access hole, nose ring and around the head flows to the cooler canopy and gets sucked out these holes right? the rectangle exit hole is my area to be considered and compaired to the entry areas.. think i've got this.
last question, what shape should the carb hole be to stop air being sucked out as it passes, i dont want to ram air in there by adding a scoop, should i put a small lip on the LE of the hole to create a dead air area that the engine can breath from?
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Old 02-08-2003, 04:08 AM
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That's a good question... I don't have any idea. Someone else jump in here!

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Old 02-11-2003, 10:59 AM
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I suspect that if you put a lip on the front side of the hole you're going to suck air out of it... maybe if you keep the lip really small...

I'd do it this way: make the height of the lip level with back end of the hole viewed in repect to the centerline of the model... and then see what it does.
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Old 02-11-2003, 12:36 PM
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you know what, when i make up the new cowling I'm just gonna get my brass tube and cut a hole lol the carb WILL suck air, whether it gets this from around the nose ring, from the main body, from the hole, i doubt it will care sourced a Magnum for 35 quid now, add a 15 quid GRRT, cheapest Magnum ever?
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Old 02-11-2003, 12:45 PM
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Well it sure is a lot cheaper then ordering one with the West engine...
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Old 02-11-2003, 12:52 PM
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well seeing as i have to chop the nose off, remove the canopy, probably the little turtle deck at the front as well, it would be a shame to do that to a new one
becides, this is a first gen one, and from whats going a round they are better than the new ones... my mate had one with lifting film the other day, a problem that was wide spread on this bored about two-three months ago.. his fuz sides also have the grain running the wrong way!
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