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Red Cube Mount

rockitdoc

Well Known Member
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I didn't like the plans method of mounting the fuel flow transducer to the intake runners, so came up with this mod after three prototypes:

Angle mounted with foam between sump and angle on two ¼-20 tapped holes on the port side sump. Then, red cube mounted to bracket with foam between bracket and cube.

Red Cube Mount Front.jpg

Gotchas:
Cube has to be mounted with bolts (AN3-20) with washers and nuts. I suppose the bracket could be tapped so a machine screw could be attached from the top, but then safety wire would be needed. Countersunk machine screws from the bottom with nuts on top would be elegant, but the runners prevent the screws from being inserted from below (ask me how I know).

Cube has to be mounted far enough from the sump so the cube does not touch the drilled bolts going into the sump (otherwise, all the effort to isolate the cube is lost because of vibration from bolt heads to cube).

Red Cube MOunt Rear Closeup.jpg

The pads are fabricated from a product called Poron (https://www.stockwell.com/data-sheets/poron-4790-92-extra-soft-slow-reb.pdf). It is the most vibration absorbing stuff I could find. Used for isolating really sensitive electronics from vibes. Highly temperature resistant.

I used this stuff because of the discussion I found here regarding vibration possible affecting the transducer readings. This solution should provide more damping than the Adel clamps on the runners (which presumably works well, and that is why the plans specify this method)

I plan to mount my Vertical Power PPS to firewall with this stuff as well.
 
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Poron can take a compression set. I found that out when, a long time ago, I had a sample sent to me. It arrived with a depression clearly showing that something had left its mark. Now that might not happen on an airplane, but the USPS, even then, certainly was able to do it.

More to the point is that with the hoses, the Red Cube is already isolated to some extent, and the hose stiffness itself will conflict with the isolation of the Poron. Certainly your bracket will, too. Without vibration testing, you can't be sure how effective your attempt at vibration protection is, and even with that testing, you can't be sure how helpful it is. If you set up a vibration test, don't neglect to put fuel in the system. To design vibration isolation, you need to know what you are isolating it from and design accordingly.

Frankly, I regard Poron as a product that has no use in an airplane, and feel that the Red Cube's instructions, or the RV-14 instructions, which differ, are adequate to obtain a good serviceable installation.

Dave
 
Hey Doc, From what I can tell, your installation will be fine, as that material seems to compress to a very solid state, and your bolts and nuts look secure. I'm all for experimenting and it's how we progress. I thought of doing some isolation mods for my red cube as well. In the end, I bolted it to the engine, and after about 135 hours, it's still working.

My thinking was, if the vibration kills the red cube, I lose fuel flow indication from it. If I do something untested and not vetted by the 1000s of other engines with this red cube, then the failure might kill me and my passenger due to a fire under the cowl.

I think the kit that's sold and was discussed in Fabio's recent red cube thread (https://vansairforce.net/community/showthread.php?t=204224) seems to be the best way to mount it. I didn't use that since I had already installed mine, but if it does fail, I'll re-do the hoses and use the kit. BTW, it's "hard mounted" to the engine with no vibration isolation.
 
What you've built looks great but the bolts will transmit the vibration into the red cube. The rubber may offer some damping but the cube will still see some engine vibration. What's wrong with using the fuel hoses as a damper, the cube is light and doesn't need much support.
 
What you've built looks great but the bolts will transmit the vibration into the red cube. The rubber may offer some damping but the cube will still see some engine vibration. What's wrong with using the fuel hoses as a damper, the cube is light and doesn't need much support.

Yes, the pad between the bracket and sump prolly damps out only some vibration. The pad the red cube sits on damps out more and the holes in the cube and bracket are 1/4” while the bolts are AN3’s so there is a gap between these connectors and the cube reducing some contact. Its not perfect, but prolly reduces at least some vibes. As far as fire is concerned, I dont know how resistaant Poron is, and may change the pads to the material on adel clamps, which Ipresume is fire proof.
 
Poron may not be best

It turns out Poron has a max continuous temperature limit of 90C (194F). Not high enough. I will find out what is ysed on Adel ckamps, and use this, instead.
If anyone knows what this stuff is, let me know.
Thanks.
S
 
Remember that damping requires relative motion to function. No relative motion, no damping....

Dave

Well taken. The bolts and nuts need silicone washers. Otherwise, the bolts and nuts transmit the engine vibration directly to the cube.

Testing reqd.

Of course, it could be the cube needs some vibration to function correctly. Hmmm, better contact manufacturer.
 
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'Final' ?

Here's what I finally came up with for mounting the Red Cube. Decided the foam between the bracket and sump served no purpose. Thanks for the feedback. Bolts transmit vibes to bracket. But, if the Cube is isolated from the vibrating bracket some benefit might ensue. SO, the Cube sits on some white silicone I pirated from the Adel clamps that are intended to mount the Cube on the intake runners. And, to help reduce the vibration from the mounting bolts to the Cube, I sandwiched some white silicone 'washers' between the Cube and the nuts and washers. Fire should not be a problem for the white silicone and the cube now has improved alignment to the hoses.

Red Cube Final MOunt.jpg
 
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