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Old 12-12-2011, 09:21 PM
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Firewall nut blind nut plate

I'm trying to get a feel for the potential demand for a little device to retain all the blind nuts in the proper position behind the firewall. Actually, the plate and the nuts would be a single piece. the nuts are pressed into the plate and have walls much thicker then the run if the mill blind nut. These will not strip out. There would be a pair of small holes so the plate could be screwed to the back of the firewall to maintain it's position over the through holes in the firewall. Once you screw it in place you can remove and reinstall the engine as often as you wish and never go behind the firewall with a wrench. It will have the added advantage on not pulling into the softer wood in the back of the firewall because the plate gives it many times more bearing area than a normal blind nut provides. I'm guessing it will weigh 1.5 ounces. We would make them for the DA 85-100-120-150. Will also consider the 50 and 60 if the demand is there. I've attached an illustration.

Vern
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Old 12-12-2011, 09:38 PM
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cool idea! the only concern i would have is the square frame would have to be pretty thick. i could see it stressing and breaking as you draw in the screws. i have had this happen with smaller washers. that why i go as big as i can. they may even distort alittle also. i think it's a great idea that should be made and tested. i can see this as a marketable item for sure.
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Old 12-12-2011, 10:03 PM
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I like the thinking behind this. Needs some refinement. I see weight being added to my airframe. Pocket / punch out those vert and horz legs and remove the one across the bottom and your getting there.

Another concern i have is the riv-nut spinning free if your back plate is too then. Been there done that. Maybe you can go with a clip nut so they can be replaced if needed.

This or stick with blind nuts i can replace easy?

i hope you take my remarks as constructive. And these look very much like electrical connnector "C" ring nut plate which have the aformentioned issues.

Look fwd to see rev "A"
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Old 12-13-2011, 06:10 PM
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For this to replace blind nuts and function as they do it needs the connections between the threaded inserts. Otherwise you might as well reach in behind the firewall and use nuts. The vertical and horizontal runners have another function, they provide more area to be compressed by the torquing of the mounting bolts. This is to prevent the tendency of the blind nuts to pull into the firewall as they crush the plywood.

As far as weight goes, I realize that it all adds up but 1.5 oz in relation to the 480 oz weight of the average 35% plane is .3% The frame would be 1/16 aluminum which would have no problem with the torque. The inserts have splines on them that bite into the aluminum frame as well as collapse onto the frame. They are rated for 25 in lbs of torque which is more than enough. They are real aircraft rated fasteners. If you put that much torque on a blind not it will start to bend the ears and crush the firewall.

The comment on triangular bracing impinging on the area is a valid one. I can redesign the plate to position the vertical and horizontal runners further inside the bolt pattern.
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Old 12-13-2011, 06:13 PM
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You can't fix STUPID
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Functional bling is always cool!
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Old 12-14-2011, 03:03 PM
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What would be a simple, yet desired improvement to the blind nut is an increase in the surface area of the clamping side. Maybe a full inch in diameter and slightly longer teeth.
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Old 02-02-2012, 03:01 PM
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available?
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Old 02-02-2012, 04:20 PM
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I like the concept. It resolves a couple of issues we have with mounting large gas motors. Even with fender washers on the back side of the firewall, you still get some compression of the firewall when you secure the motor mounting bolts.
Your concept adds more area and thus helps to minimize this problem. I should mention that compressing the firewall material will eventualy loosen the motormount bolts which of coarse is a problem.
I always use self locking nuts on the motor mounting bolts whether the bolts thread into blind nuts or if fender washers are used with a nut on the back side of the firewall.
I'm not sure how many times your product would be reused but I would favor not having blind nuts built into the frame. I would have "bosses" on the corners that are drilled and taped with an interference thread fit for a 1/4-28.
I actknowedge that the part could only be used one time since the interference fit on the threads would be compamised on the first use. You could however, still use it again if you then used self locking nuts on the back side. If the user doesn't feel that backup self locking nuts are necessary, then reusing it is not an issue at all.
Instead of providing mounting holes to secure the part in place, you might think about marking the center lines of the part on the outside edges so it can be used as a template to mark the holes on the front side of the firewall. The center marks on the outside edges of your part could be easily aligned with the marks usually provided on the front of the firewall by the planes manufacturer. You might even provide an inexpensive "transfer punch" with your part on order to mark the bolt hole locations.
With the bolt holes accurately marked and drilled, I don't think you would have to secure your part on the backside of the firewall. Just hold it in place until you fit the first two bolts.
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Old 02-02-2012, 06:00 PM
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I like the idea. It resolves a couple of problems. A variant of the idea using a CF plate would be lighter, and have still more bearing area.

One problem. For some airframes it would be a beatch to get this into place. Not a problem for kit builders, because you would install when it was still accessible.
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Old 02-02-2012, 06:02 PM
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Good idea.

Btw....are the needle valves available for the DA-60 yet?
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Old 02-07-2012, 01:49 PM
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Great idea! But another concern would be you would have to be a really good driller - that is your holes through the firewall would all have to be perfectly (or nearly so) square or you would put undue stress on the mount mentioned earlier to get all the bolts to line up and thread into the rear mount. Just a thought.
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Old 02-07-2012, 02:20 PM
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Noticed you did not list the DA-170 and 200. Any possibility you will add these into the line?
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Old 02-07-2012, 02:29 PM
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Would this be designed for firewalls with built in right thrust (easy case), or would it be designed for firewalls with zero right thrust? The firewalls on all of my planes have zero right thrust, but the T-nuts are angled at 2.5 degrees so that they are parallel with the mounting holes on the SWB or similar mounts.
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Old 02-13-2012, 05:47 PM
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I was hoping that folks who purchased the nut plate would also use the system I currently sell that includes a heavy duty mount plate for the engine, various standoffs, and an alignment plate that sits on the front of the fire wall and keeps everything aligned and tight. The firewall plate also doubles as a drill jig so the hole placement would not be a problem. I also offer a mount plate that replaces the DA mount plate and it has 2.5 degrees of thrust built into it so the thrust offset is there but the back of the mount plate, the standoffs, and the firewall plate all remain square to each other and in perfect alignment. Here is a link to the the page on my web site that pictures all this.

I always recommend that loctite 242 be used on all threads anywhere close to a two cycle engine. I would include a 50 ml tube of loctite with the nut plate if enough people order them to make the whole project worth while.

http://whiteroseeng.com/products/rst.html

Vern
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Old 02-13-2012, 06:04 PM
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i think this is a very good and marketable idea Vern. Carbon might smash under the torqueing of the bolts so i think youre headed the right direction on material. pocketing the runners would reduce surface area so that would negate the point of having this in my opinion. 1.5 oz in the grand scheme of things on a larger gasser is a non issue, especially when it means not worrying about blind nuts pulling through the firewall.
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