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Author Topic: Tank for Combat Cat  (Read 1482 times)

Offline kevin king

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Tank for Combat Cat
« on: June 03, 2022, 06:12:46 PM »
Hi everyone, I was recently given a partially built Combat Cat from an original kit. I'm asking for sugestions on what type of tank to use,  or should use a Bladder? I think the engine is a Fox 35 cs and i think the nva is for running a bladder.
Kevin.

Online C.T. Schaefer

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Re: Tank for Combat Cat
« Reply #1 on: June 04, 2022, 05:03:02 AM »
Since it is mostly assembled I think the best/easiest solution would be a  'Veco' style pressure tank that the CC was designed for. For sport flying 3 oz will be plenty. I have built a couple of Cats recentlyish and put the motor mounts in line with the wing.  Using a Vienna Sausage can is an easy way to use a pacifier style tank.  Have fun!!

Offline kenneth cook

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Re: Tank for Combat Cat
« Reply #2 on: June 04, 2022, 05:05:10 AM »
                     Tom beat me to it. Hi Tom!!!         Kevin, your engine is a Fox .35X. A bit hard to see in the picture but these engines came with a square aluminum insert with a hole in the center that fit into the large venturi. A bit hard to tell from your picture but I should be able to see it in the case and I can't. If you don't have this in the engine, your not going to be able to run the engine using a tank unless you run crankcase pressure. I don't really care for using case pressure as you have to drill the nipple on the back of the backplate. If your not familiar with starting, the engine will flood the case in short order.

        As for your needle, it's nothing really special, it's designed for suction but may possibly work on bladder. It appears new so I can assume it's a Supertiger clone like the version RSM offered. I've used actual Supertiger needles on bladder, I can only say that my experience was so so. I had some work, I had some leak and be problematic. You can only try it , the importance is the fit of the needle to the internal threads. On my versions that were problematic, I removed the locking collet and used small Tygon chainsaw tubing which was very hard to push over the threads to seal and this also provided enough friction to hold the needle.

         As for a tank, most of these early models used a Veco T-21  or similar. I believe the T-21 is a 3 oz. It all depends on how much room you have within the bay as the tank widths were the same, it was the length that changed for more oz's. They used nothing special as these were wedge tanks about 2" wide. The problem is the pipe configurations. Veco made a pressure tank which was designed for using engines setup for backplate pressure, I essentially made the same type by converting Brodak style tanks using the same configuration as the Veco. I generally remove my bottom overflow pipe and have it exit the front  of the tank or out the top . You don't want pipes hanging out of the bottom as they can get bent or broken off.

          The one thing you don't want to do is find a old tank that's new and install it without taking it apart first. None of the manufacturers properly cleaned tanks and by now the internals of the tank are more than likely corroded. I highly recommend even taking a new on apart as removing the end cap is a simple process just to inspect.

          I know you've mentioned your experience with bladders is limited but in reality, it truly works the best for performance in this application due to the maneuverability of the plane. Hard, quick maneuvering on a wing will tend to pin the fuel in the corners of the tank causing hiccups, and possibly flame outs whereas a bladder doesn't suffer. Another concern though is experience in doing so with a larger engine. If the engine needle is set lean, on start up, when the pinch off is released, the engine will surge forward and then starve for fuel. This causes the wing to lunge forward. The engine will then starve for fuel and go back and then it will surge forward doing this quite violently until the needle is opened up. One without experience could certainly get hurt  trying to adjust the needle with the plane  going back and forth and not accustomed to what is happening here. This is why getting a good drip setting on your needle is important prior to starting.

Offline Motorman

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Re: Tank for Combat Cat
« Reply #3 on: June 04, 2022, 02:17:58 PM »
I'd get a better bellcrank in it if you want to go fast. At least a Fox 3".


Offline kevin king

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Re: Tank for Combat Cat
« Reply #4 on: June 04, 2022, 11:39:50 PM »
Thank you for your fuel tank set up suggestions. And yes, that bellcrank surprised me. It is a 3" bellcrank,  but what ever alloy its made from seems a bit too light for my liking.

Online Ken Culbertson

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Re: Tank for Combat Cat
« Reply #5 on: June 05, 2022, 07:47:04 AM »
Thank you for your fuel tank set up suggestions. And yes, that bellcrank surprised me. It is a 3" bellcrank,  but what ever alloy its made from seems a bit too light for my liking.
That was the standard BC in the 60's. That one looks like a kit version.  Most were cheap steel, a few aluminum.  They wore out pretty fast unless you bushed them but they rarely failed.  However when they did it was spectacular.  The arms on the steel would bend over and aluminum ones would break off. 

Ken
AMA 15382
If it is not broke you are not trying hard enough.
USAF 1968-1974 TAC

Offline Motorman

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Re: Tank for Combat Cat
« Reply #6 on: June 05, 2022, 09:24:30 PM »
That's an aluminum 3" Perfect bellcrank you have there. Good for something with .15 power. They are thinner than the Fox 3" aluminum job which is slightly better. If you plan on getting up over 100 mph you should think about something stronger than either of those.

Motorman 8)

Offline kevin king

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Re: Tank for Combat Cat
« Reply #7 on: June 07, 2022, 01:41:46 AM »
Definitely. The arms bending over is exactly what went through my mind. Exciting indeed. No one used seat belts back in the day either.


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