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

Screamin Demon X2

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Old 11-06-2012, 01:46 PM
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rcaircraftnut
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Default Screamin Demon X2

I have 2 SD's scratch built by a friend. I have one flying on a Jett Q500 .40 with an 8.75x9 ww apc pylon. Goes pretty good for about 4 mins on a 6 oz tank. I am pretty happy with it but had to go faster. So the second one is getting a Jett F.I.R.E. .50 with a tuned at the factory Jett pipe. The engine was supposed to be ported for ducted fan and is supposed to turn an 8.75x9 ww apc pylon at 20,000 static. I have yet to run it and it is NEW! I am hoping for at least 180mph out of this setup. What do you guys think? I am guessing the first one turning 19,000 static is in the 150-160 mph range. Next up is the Diamond Dust kit I scored NIB with the Jett .50 so I will be looking at ways to streamline the thing without overheating the engine ect.
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Old 11-07-2012, 07:53 AM
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Default RE: Screamin Demon X2

Just don't try to put too much prop on the Jett and you won't overheat it.
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Old 11-07-2012, 07:54 AM
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Default RE: Screamin Demon X2

Just don't try to put too much prop on the Jett and you won't overheat it.
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Old 11-07-2012, 08:19 AM
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Default RE: Screamin Demon X2

a 1,000 rpm will not get you another 20-30mph. i would scrap the Jett 50 and get a Q-40 motor. that will get you the speed you need. They like to run around 28,000
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Old 11-07-2012, 08:42 AM
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Default RE: Screamin Demon X2

Even fully cowled in? It won't get to hot?
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Old 11-07-2012, 10:33 AM
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Default RE: Screamin Demon X2

Look at Combatpigg's 200 mph SD his flew fully cowled with a nelson FAI engine with no overheating problem. Done properly a cowl will add some speed and cooling should be no issue as long as you keep a good ratio of inlet to outlet dimensions. Take a look at the German Speed cup planes for some inspiration of what to do, another good source for information on cowl setups is Andy Lennon's book "Basics of model aircraft design" chapter 17 ducted cowl design. Another thread to look at is Mike Connor's "(something fast?) Delta Build thread" Mike designed the SD and there is a lot of good information to be gleaned from reading the entire thread.
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Old 11-07-2012, 04:20 PM
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Default RE: Screamin Demon X2


ORIGINAL: rcaircraftnut

I have 2 SD's scratch built by a friend. I have one flying on a Jett Q500 .40 with an 8.75x9 ww apc pylon. Goes pretty good for about 4 mins on a 6 oz tank. I am pretty happy with it but had to go faster. So the second one is getting a Jett F.I.R.E. .50 with a tuned at the factory Jett pipe. The engine was supposed to be ported for ducted fan and is supposed to turn an 8.75x9 ww apc pylon at 20,000 static. I have yet to run it and it is NEW! I am hoping for at least 180mph out of this setup. What do you guys think? I am guessing the first one turning 19,000 static is in the 150-160 mph range. Next up is the Diamond Dust kit I scored NIB with the Jett .50 so I will be looking at ways to streamline the thing without overheating the engine ect.
You should be able to get up in the 170's and may exceed 180 with that .50. Jett .50 powered examples have been radared at up to 182, and that wasn't an FIRE.

General cowling rules - force the air through the fins with close fitting ducting, outlet to inlet area ratio 1.4, blending in the air inlet in the style of a smooth duct rather than a sharp lipped hole improves airflow a lot.
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Old 11-12-2012, 05:36 PM
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Default RE: Screamin Demon X2

My Nelson lands pretty cool after a full high speed flight. I have run it with the cowl on and also with it off and don't see any obvious difference with temperature.
It runs a prop that it can turn with ease, a cut down 7x7 model that has had some thickness removed from the blades...this helps prevent runaway heat issues. The other things that help keep it cool is having the right compression/nitro combo [in this case no nitro] and I'm running straight castor, 25% total.
It sounds extreme, but I believe the extra oil has helped keep this engine from very much wear.
It's not my 1st Nelson .40 engine, but it's my most long lasting one.
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Old 12-18-2012, 05:50 AM
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Default RE: Screamin Demon X2

Screamin Demon am I doing.
Question.The aircraft's center of gravity where it is?
Thank you for your response.

Regards: Balázs Bundik
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