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Sawed off cupola

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vtsteam:
Thank you kindly Dsquire!  :beer:

vtsteam:
The guts.

The original blades were made of aluminum, as I said. They melted almost instantly in the heat of the pulsejet. As did the ball retainers (plastic) in the cages of the cheaper ball bearings (skate) I had used.

I replaced with steel blades (made from stovepipe) and better bearings, and all was well. The blades are fastened in place with steel pop rivets. I used a hub from a discarded utility fan for the hub here and welded it in place.

vtsteam:
It's funny, to size the turbine (fan) I built some of the equipment normally used to power a cupola furnace. I built a manometer (blast gage) and used it on the pulsejet to characterize exit pressure and velocity. That was what told me they were surprisingly low -- indicating to me that the volume was good and it might respond to a broad flat blade fairly well.  Just like a spinnaker or square sail is a good running sail for high volume low velocity air by comparison with a Marconi rig. on a sailboat -- I was pretty familiar with those.  Because velocity was low, blade area needed to be big, and RPM low. If I remember correctly I shot for about 3500 RPM in the design of the turbine, and hit it pretty close in reality,

Anyway, the funny thing is I have never used the manometer to characterize the fan. So I have no idea how it will perform when I add a motor. Normally you'd build a fan for the requirements of the cupola and then  blast gauge to characterize the fan output. So it's all going to be new to me, though I've had this stuff for many years.

Here's the manometer (blast gauge) that I built.  (Needs some water -- a lot has evaporated.)  believe I used David Gingery's fan book to build both, Though Steve Chastain repeats a lot of that information in his cupola furnace book.

Mayhem:
VT - thanks for the info.  That is really useful stuff.

vtsteam:
You're welcome Mayhem.  :beer:

The end of the probe for the blast gauge is what is called a pitot tube. Pilots are familiar with those. They measure relative airspeed. They can also measure dynamic pressure.

This one was made from some copper tubing. The end is a turned brass plug and has a hole drilled in it. A very thin copper tube is soldered to the plug internally and runs inside the outer copper tube to the far end of the probe where it exits in a tee fitting. I believe I used the tubing from a heating furnaces pilot light probe. These are available as replacement parts.

You can also see a ring of small holes drilled further back in the outer tube. This outer tube also exits from a different leg of the tee fitting.

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