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Cox Thermal Hopper Two-Needle Carb

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Cox Thermal Hopper Two-Needle Carb

Old 06-09-2005, 07:09 AM
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jetpack
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Default Cox Thermal Hopper Two-Needle Carb

How does a Cox two-needle carb work for the old Thermal Hopper engine? It looks like the standard TD Needle Body but it has two needles??? What is the benifit here?
Old 06-09-2005, 07:46 AM
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Default RE: Cox Thermal Hopper Two-Needle Carb

jetpack,

Using two needles is a primative form of throttle. You used one needle for high speed and two (or the other) for low speed.

Some would have one needle set lean and one set rich and switch between needles. Others used one needle for high speed and added the other (using both) for low speed.

I would imagine the two needle setup is as scarce as the cage mount for the Thermal Hopper. I have a couple of TH's but neither the cage mount nor the twin needle.

You should be able to run it fine with one needle.

George
Old 06-09-2005, 04:19 PM
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Default RE: Cox Thermal Hopper Two-Needle Carb

Thanks George,

You mention its a form of throttle control, was there a throttle ring of some sorts used? I seen one recently but it was just the "modified" TD body as mentioned. How does the two needles control the speed of the motor I guess is the question. I'm still miffed.....lol. All I know is it hit me kinda strange when I seen it, and couldn't quite figure it out.
Old 06-09-2005, 06:57 PM
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Default RE: Cox Thermal Hopper Two-Needle Carb

jetpack,

I think primative is the operative word.

There were only two speeds slow and fast.

The next phase for "throttle" was an exhaust restrictor only. These came mostly in butterfly and barrel type. (Plus home-made.)

Next were the coupled exhaust restrictor with an intake baffle, then finally an intake barrel.

At least, that's the way I remember it.

George
Old 06-09-2005, 07:14 PM
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Default RE: Cox Thermal Hopper Two-Needle Carb


ORIGINAL: gcb

jetpack,

I think primative is the operative word.

There were only two speeds slow and fast.

The next phase for "throttle" was an exhaust restrictor only. These came mostly in butterfly and barrel type. (Plus home-made.)

Next were the coupled exhaust restrictor with an intake baffle, then finally an intake barrel.

At least, that's the way I remember it.

George
George, you didn't mention the two speed points used on ignition engines. Again, just two speeds but Jim Walker could use them on an Orwick to hover a fireball U/C plane and gently lower it into the arms of an eager kid.
Somehow that seems dangerous as h--- now, but it didn't back then. I believe Jim called it the 'Sabre Dance', and I understand that no one else was able to duplicate it even tho it was featured in full page ads in the model mags of the era.
Al Lenz
Old 06-10-2005, 06:19 AM
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Default RE: Cox Thermal Hopper Two-Needle Carb

I remember reading about the two speed points but have never run a spark engine. Someone gave me a Thor once, but it had already been run.

Actually, I do also have a McCoy .60 sparker that is frozen (it was that way when I got it), but I've never started it.

George
Old 06-10-2005, 12:31 PM
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Default RE: Cox Thermal Hopper Two-Needle Carb

Jetpack,
The fuel line (from the tank) split into two feeds, one attached to each needle assembly.
You then pinched off one fuel line or the other to control which NV was getting fed.
The devices I have seen were just an arm that rocked back and forth attached
to a pushrod. The arm was between the 2 fuel lines that ran paralell to each other.
Pushing the arm pinched off one line, pulling it opened the first and pinched the
other closed.
Dave
Old 06-12-2005, 09:37 AM
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Default RE: Cox Thermal Hopper Two-Needle Carb

The other method for two needles is to have the high speed line connected directly from the tank and have the valve on the second (low speed) needle so it will suck fuel (low) or suck air(high). Don't think this works on the TH since both needles are on the same assembly.

George
Old 04-09-2006, 06:04 AM
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Default RE: Cox Thermal Hopper Two-Needle Carb

I can understand how it works now, thanks guys!

The reason why I had asked is I've started to search for a Thermal Hopper motor since the advent of eBay and me finding a 1957 Berkeley ducted fan model of a Douglas Skyray at a garage sale, and decided to make a reproduction of the kit for myself for display. The kit plans called for an OK Cub or a Cox Thermal Hopper motor. I finally saved up and bought a Thermal Hopper which I dis-assembled and polished up, but its still missing the starter spring for it...I really doubt if I'll ever run across one. The plans also call for a Berkeley "Midget" fuel tank and a Stanzel Monoline control unit. If I find these three things it would be a happy day...lol.

Anyways while I was in the process of finding a Thermal Hopper I seen the twin needle valve and thought it was very unique, so I bought it for a Space Hopper motor that was donated to me. At first I thought it was just a "high performance" item and didn't really know that it was for throttle control...I thought it just added more fuel to the motor, or for more precise tuning...never thinking it was a throttle of some sorts. Its amazing that it was actually thought of. I included a picture of it for everyone to see.

I still have to machine a display stand for the Space Hopper. It sports an old transparent blue Kaysun propeller that I have also polished out...its the favorite of the few that I have. I still have the single needle for the Thermal Hopper but I like to display it with the twin needle [sm=sunsmiley.gif], but unfortunatly will have to be taken off when it gets installed into the Skyray for it to be correct to the plans. I sure am enjoying trying to build a period correct airplane! The parts hunt has brought me through quite a journey in model airplane knowlege.
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Old 04-10-2006, 02:00 AM
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Default RE: Cox Thermal Hopper Two-Needle Carb

Jetpack,

I don't remember ever seeing a starter spring on a Thermal Hopper. They were developed, If I understand correctly, by Bob Davis of DDD. Not sure exactly when, probably during the Space Hopper days. The first one I had was on a Cox Olympic .15. The engine was later stolen but I still have the spring.

Be careful of that Kaysun prop. Never saw a blue one. I have a few of the solid red ones...for Cubs only.

I think you can still get monoline stuff through the Victor Stanzel Museum in Texas. I believe Dale Kirn is running it.

George

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