Author Topic: Cooling Fan for model I.C. Engines  (Read 6632 times)

Offline Johnmcc69

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Re: Cooling Fan for model I.C. Engines
« Reply #15 on: July 07, 2014, 10:39:31 PM »
Why not just mill some 1/16" slots to locate the blades?

 John

Offline Brian Rupnow

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Re: Cooling Fan for model I.C. Engines
« Reply #16 on: July 07, 2014, 11:51:34 PM »
Johnny--I thought about that, but I like the look better the way I designed it. I have a lot of scrap setting around to make a jig. One way or another, I will show my results.---Brian

Online Jasonb

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Re: Cooling Fan for model I.C. Engines
« Reply #17 on: July 08, 2014, 07:50:12 AM »
I think you will loose a lot of heat into the jig and have to put extra into the work which will melt existing joints and possibly even the brass blades which will heat up before the hub.

Lay it on a flat firebrick with small blocks of metal at the tip of each blade to keep them in place

Dose it really matter if you suck or blow? Seen plenty of electric fans mounted either side of car radiators.

Offline Maryak

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Re: Cooling Fan for model I.C. Engines
« Reply #18 on: July 08, 2014, 08:01:21 AM »
Dose it really matter if you suck or blow? Seen plenty of electric fans mounted either side of car radiators.

Yes, I wondered about that too.

Best Regards
Bob
Если вы у Тетушки были яйца, она была бы Дядюшкой

Offline Ian S C

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Re: Cooling Fan for model I.C. Engines
« Reply #19 on: July 08, 2014, 02:27:05 PM »
Phil, sorry no video.  That motor, built in 1994 has done over 2000hrs of running,  I tried to run it to death, at 2000 hrs I had to replace the crankshaft, and the con rods.  When I reassembled the motor I had to open out the carbon impregnated bush in the piston that guides the displacer rod, it must have got oil on it, and swelled.  It goes as well, or better today than it did 20 years ago.

Offline Graham Meek

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Re: Cooling Fan for model I.C. Engines
« Reply #20 on: July 08, 2014, 04:40:39 PM »
This is just a casual observation and in reality it probably does not matter. The question of whether to blow or suck air over the engine is a vexed one. The Gas laws tell us that if a gas is compressed it heats up, therefore a fan forcing air over an engine is going to warm that air up initially. Now whether there is a benefit in that as soon as this air expands it cools down and during this cooling down cycle it will absorb more heat from the engine I cannot say. On the other hand air being drawn over the the engine is already at ambient and not subject to any compression, no matter how small.

If there is someone more versed in thermodynamics that can answer this conundrum I for one would appreciate the information.

My best regards
Gray,

Offline Brian Rupnow

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Re: Cooling Fan for model I.C. Engines
« Reply #21 on: July 08, 2014, 07:30:09 PM »
The jig worked very well. It looks a bit crude in these shots, but it did keep everything aligned while I silver soldered the blades to the hub. Heat from soldering the blades on did not cause the solder on previously soldered blades to let go and have the other blades fall off. (I have experienced that kind of thing when working with soft solder.)


Offline Brian Rupnow

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Re: Cooling Fan for model I.C. Engines
« Reply #22 on: July 08, 2014, 07:34:03 PM »
Needless to say, there was a lot of clean-up, filing, and sanding required to get the fan into any kind of presentable shape. It looks pretty ragged in around the actual solder joints, but the blades are really solidly attached and the hub area will be hidden by other components when this is assembled. Only the blades will be visible.

Offline Brian Rupnow

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Re: Cooling Fan for model I.C. Engines
« Reply #23 on: July 08, 2014, 07:37:17 PM »
This is what the fan will look like when mounted in the protective ring that goes around it, with the hub which supports the shaft bushing setting in front of it.

Offline Brian Rupnow

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Re: Cooling Fan for model I.C. Engines
« Reply #24 on: July 09, 2014, 04:07:47 PM »
I'm done to the point where I need to make up the shroud that surrounds the fan. I have the outer rim from mild steel, and the hub from mild steel. I have some 1/16 #316 stainless steel for the 3 "spokes" between the inner hub and outer ring, but I don't know whether or not I can braze it.---But I will in about 10 minutes. Fortunately the piece I have is quite large. I will snip off a couple of pieces and conduct a test.

Offline Brian Rupnow

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Re: Cooling Fan for model I.C. Engines
« Reply #25 on: July 09, 2014, 04:36:01 PM »
And the answer is--The 316 S.S. can be brazed or silver soldered equally well. In the picture, the part on the left has been brazed using oxy acetylene and flux coated brazing rod. The item on the right has been silver soldered with the paste flux being applied to the joint first. The silver solder seems to flow out better, requiring less clean-up after the fact. The brazed joint had a lot of small "welding berries" around the main weld, which required clean-up with a grinding disc.---Which is fine when working on automotive car bodies, but not really desirable for model work. So, my question is answered. I will use the 1/16" stainless steel for my spokes and silver solder the joint. That is a good thing, otherwise I would have had to go down street and buy some 1/16" mild steel material.

Offline Brian Rupnow

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Re: Cooling Fan for model I.C. Engines
« Reply #26 on: July 09, 2014, 04:55:26 PM »
This is going to be one of those situations where the jig to hold the pieces in alignment for silver soldering will be as complex as the soldered assembly. The central hub must be held concentric to and parallel to the outer rim, and the 3 "spokes" will be set at 120 degrees apart. Fortunately, the "jig" is mostly lathe work with some accurately placed holes. The position with 4 blue posts is the actual soldering station. The other two positions are intended to let me turn the part in the jig and maintain the 120 degrees between spokes.--In fact, looking at it as I post this, I probably only need one of the double post stations at 120 degrees to the main "soldering" station.

Offline Allen Smithee

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Re: Cooling Fan for model I.C. Engines
« Reply #27 on: July 09, 2014, 05:39:44 PM »
A silly question - why not put a centrifugal fan on the flywheel hub and duct the fan efflux onto the cylinder fins with some sheet-metal shouds?

On the questiopn of suck vs blow - blow is better because you're more likely to direct the stream of air where it is wanted, whereas a suck-through system would need cowlings around the cylinder fins to ensure that the air isn't just being dragged in from all directions.

0.03 supplied,

AS
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Offline Brian Rupnow

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Re: Cooling Fan for model I.C. Engines
« Reply #28 on: July 09, 2014, 06:37:36 PM »
Allen--I agree 100% about your take on the suck versus blow issue. As for why I didn't add a fan to the flywheel hub and add a duct--the ductwork would hide too much of the engine.---Brian

Offline Brian Rupnow

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Re: Cooling Fan for model I.C. Engines
« Reply #29 on: July 09, 2014, 10:06:59 PM »
That all went surprisingly well. The jig was a lot of work, but it held everything located very well. I didn't even bother removing the soldered parts from the jig, just set all 3 spokes in place (all of the locating pins were in the jig) and put enough of a tack at each end of each "spoke" to hold everything solid. Then I removed the shroud from the jig and tacked everything on the back side, then went around and soldered everything solid. It was more work cleaning it up afterwards than it was doing the soldering. I didn't get too crazy with the clean-up, because the shroud is going to get painted flat black when all of the brackets are soldered onto it.  This pictures shows the jig, the shroud, and the fan, from the front side.(The side facing away from the cylinder.) and one shot from what will be the side facing the cylinder..