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Author Topic: .049 Black Widow questions  (Read 686 times)

Offline Augsburger

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.049 Black Widow questions
« on: March 04, 2010, 09:41:00 AM »
1.   Would someone please explain how the reed (valve?) works.  Fuel flow controlled by needle valve, fuel travels down center tube and strikes reed, through screen to combustion chamber...  correct?   Does the reed actually atomize the fuel?

2.     Is pharmaceutical grade castor oil OK to use when mixing fuel or must it be something from the hobby store? I would like to use a bit richer oil/fuel mix during break-in.

Thanks for your time...cheers 
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Wilder Eber

Offline philip metzner

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Re: .049 Black Widow questions
« Reply #1 on: March 04, 2010, 10:03:51 AM »
The reed's main function is to act as a one way check valve. It closes after the piston up stroke is complete and traps the fuel\air charge in the crankcase so it can be transfered through the ports in to the combustion chamber and not just blow back out of the carb.
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Offline Tim Wescott

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Re: .049 Black Widow questions
« Reply #2 on: March 08, 2010, 09:45:02 AM »
Quote from: Augsburger on March 04, 2010, 09:41:00 AM
1.   Would someone please explain how the reed (valve?) works.  Fuel flow controlled by needle valve, fuel travels down center tube and strikes reed, through screen to combustion chamber...  correct?   Does the reed actually atomize the fuel?

Like Phillip said -- it's a one way valve.  The two-stroke engines that we use get fuel and air from the venturi and into the cylinder by using the crankcase as a pump to draw in air from the outside as the piston moves up, and to push it into the cylinder close to the bottom of the stroke.  The reed valve lets the air flow when the crankcase pressure is lower than atmospheric, and closes it off when the crankcase pressure rises.

The reed valve probably does little to atomize the fuel -- it's purpose is to control induction into the crankcase.

Quote from: Augsburger on March 04, 2010, 09:41:00 AM
2.     Is pharmaceutical grade castor oil OK to use when mixing fuel or must it be something from the hobby store? I would like to use a bit richer oil/fuel mix during break-in.

Thanks for your time...cheers 

I get fuel from our RC club's raffle; it's invariably 18% all synthetic, and all my engines are old journal-bearing engines.  So I buy 8-ounce bottles of castor from the local pharmacy to add to my fuel.  I haven't destroyed an engine yet -- but I haven't been back in the hobby long, so who knows what damage I'm doing?
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AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline ray copeland

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Re: .049 Black Widow questions
« Reply #3 on: March 08, 2010, 01:07:42 PM »
I mixed castor bought at Wally World with Omega fuel for all my engines from 1/2a to .46 for a couple of years with no problems.
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Ray from Greensboro, North Carolina , six laps inverted so far with my hand held vertically!!! (forgot to mention, none level!) AMA# 902150

Offline Augsburger

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Re: .049 Black Widow questions
« Reply #4 on: March 08, 2010, 03:28:15 PM »
thank you for the excellent explanations...  makes sense to me now...  how would a teflon or other type reed make the engine perform better than the original reed?  more flexible thereby allowing more fuel mixture to the combustion chamber?  are they more reliable than the old metal type reeds?   cheers
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Offline Tim Wescott

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Re: .049 Black Widow questions
« Reply #5 on: March 08, 2010, 06:14:27 PM »
Quote from: Augsburger on March 08, 2010, 03:28:15 PM
thank you for the excellent explanations...  makes sense to me now...  how would a teflon or other type reed make the engine perform better than the original reed?  more flexible thereby allowing more fuel mixture to the combustion chamber?  are they more reliable than the old metal type reeds?   cheers
Davis Diesel bills them as being more reliable.  Cox has used a number of different materials.  The biggest issue is that the reed valve is a high wear item -- it slams against its seat for each engine revolution, and it has to seal pretty darn well for the engine to work correctly.

I don't know of much performance differences between various materials -- it's a poor aerodynamic design that can't really be improved without changing the way valve itself is laid out.  The best that you can hope for from a reed valve is that it gives you a long and trouble-free life.
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AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Pinecone

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Re: .049 Black Widow questions
« Reply #6 on: March 10, 2010, 10:15:12 AM »
Xenalook carries something like three different material reeds.  They sell a pack of one of each to try.

For fuel, I am going to Sig Champion 25% for mine after talking with Sig.  And if you buy quarts, there is no HazMat shipping fees.  50/50 castor/synthetic 20% total oil.
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Terry Carraway
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