Why Cabin Floor Panel Fasteners not flush/removable?

[RudiGreyling]

Hi Guys,

Busy with the center fuselage section and noticed 2 things on the plans:
1) The bolts that attach the floor panels is not flush..
2) The aft floor and baggage floor is attached with pop rivets, while the front floor is removable with platenuts installed..

Being a first time builder I want to know the following:
1) Why is the fasteners not flush, does it not interfere somehow with carpeting or something etc. It just seams more logical to keep everything smooth on the floor?
2) Why is it not all floors removable, seems it is a perfect place to store some electronic components like strobe boxes etc?

Can somebody please shed some light and maybe some photos?

Thanks
Rudi

 

[roee]

Re: 2) removable floors

I made my baggage floors removable, and I think a lot of people do. It's added work, but my motivation was 1) I don't like having closed compartments that I can't inspect, and 2) it's a great place for strobe power supplies, etc. In my case, I just replaced the pop rivets with nut plates and screws. Yes, that's a lot of nut plates.

If yours is a QB like mine, you'll find a problem installing nut plates where the forward ends of the baggage floor ribs meet the bulkhead. Here's my solution:
http://www.kalinskyconsulting.com/rvproj/floorsncovers.htm

As for the seat floors, I kept them per plans. The forward ones are removable, which gives limited access to the bays under the aft floors as well. I wouldn't install equipment under the aft seat floors, but the access is good enough for inspection.

 

[dan]

Something we're not exposed to very much on the RVs, at least not exposed to it by Van's (since I don't believe they use any of these), is a Tinnerman nut:

http://www.aircraftspruce.com/catalog/hapages/tinnerman.php

The "U" type (NAS 395) is what comes to mind for this type of scenario. I know lots of builders install nutplates in the baggage ribs and talk about how much extra work it is. In a way, 29 cents a pop starts to look pretty attractive...zero work beyond just drilling the fastener hole and sliding the nut into place.

Just an idea...don't know if there's enough flange on these ribs to use 'em, but I'm sure there's probably some type of clip nut that'll work!

 

[rv8ch]

tinnerman nuts

Something we're not exposed to very much on the RVs, at least not exposed to it by Van's (since I don't believe they use any of these), is a Tinnerman nut: ...

Very true. I discovered these after trying very hard to install nutplates along the sides where it's really hard to get access with a drill or squeezer. The tinnermans work great so far, but I'm not flying yet. I also tried rivnuts, and they are horrible, IMHO. Expensive installation tool, you have to drill a huge hole, and if they rotate after they are installed, you are hosed. Tinnermans don't have any of these problems.

PS: Anyone want to buy a rivnut tool and a bunch of rivnuts? Forget what I said above, they are GREAT!

 

[scard]

I would sure like to hear a structures person comment about a flimsy attach (tinnerman nut) of the baggage floor. It sure seems to me that there is some real structural value to having the baggage floor and seat pans very securely fastened.

 

[dan]

I would sure like to hear a structures person comment about a flimsy attach (tinnerman nut) of the baggage floor. It sure seems to me that there is some real structural value to having the baggage floor and seat pans very securely fastened.

Ever seen how the Mooney's belly skins attach? Well, at least the ones on the M20F and M20J I used to have (unless memory isn't serving me right).

 

[thallock]

Dan,

I'm pretty sure that the baggage floor is a structural component, and anything that you replace the pop rivets with should be at least as strong as the rivets being replaced. I think nutplates meet this requirement, but I doubt that the Tinnerman clips would. I guess, we could always ask Van.

Rudy,

I was going to add the nutplates in the baggage area a few weeks ago, but decided against it. There are 66 nutplates needed to do the job. I had a bunch of K-1000-08's, but then I would have ugly screw heads sticking up. I had a few K-1100-06's (I think), which take a flush screw. When I looked at my Van's catalog, these were $.48 a piece (.vs. $.18 for the K-1000-08's). For $33 I decided Van's plans were good enough. I know, I'm cheap.

BTW, the weight gain for the 66 nutplates and screws would have been 4.5 oz.

Tracy.

 

[dan]

I'm pretty sure that the baggage floor is a structural component, and anything that you replace the pop rivets with should be at least as strong as the rivets being replaced. I think nutplates meet this requirement, but I doubt that the Tinnerman clips would. I guess, we could always ask Van.

Yeah, I hope I didn't come across as recommending the Tinnerman nuts as acceptable. I have zero idea if they would be ok structurally.

But I have a question about screws & nutplates and their structural integrity. What exactly makes them acceptable structurally? My understanding is that it's mostly the "friction" between parts that the tight fastener produces which contributes to structural integrity. Yes, the fastener is in tension to some degree, but I think it's shear strength that matters more (I'm not an engineer, grain of salt here!).

My assumption (ASS-umption) is that there's no significant difference in tension strength with nutplates or Tinnerman nuts. And as far as shear is concerned, if it's the friction that's doing the job, then it wouldn't matter if there's a nut, nutplate, or clip nut on the back side. The screw still passes through the same size hole in both pieces, and the screw is tight.

I would also posit that a screw + clip nut will be stronger in both tension & shear than a pop rivet.

Somebody with aircraft structural engineering expertise, please chime in!

 

[Mike S]

tinnermans

One thing that comes to mind about Tinnermans is that they have a nasty habit of scratching the sheet they are put onto. I have even seen some with "teeth" bent into them to hold their position better.

What happens when you scratch a piece of aluminum with a ferrious material, and then leave them in contact??

Mike

 

[rv8ch]

Tinnerman or clipnut?

...My assumption (ASS-umption) is that there's no significant difference in tension strength with nutplates or Tinnerman nuts. And as far as shear is concerned, if it's the friction that's doing the job, then it wouldn't matter if there's a nut, nutplate, or clip nut on the back side. The screw still passes through the same size hole in both pieces, and the screw is tight.

I would also posit that a screw + clip nut will be stronger in both tension & shear than a pop rivet....

My bad - I confused the tinnerman and the clipnut. I used clipnuts on my floors.

The clipnut is nothing more than a holder for a nut. I think the tinnerman would probably be strong enough, but I used clipnuts. Besides, clipnuts are only 7 cents more than a tinnerman.

 

[az_gila]

Clipnuts

Clipnuts would be a better choice if your are mixing them with nutplates..

They take the same screws .... the Tinnermans take sheet metal type pointy screws....

gil in Tucson

 

[LettersFromFlyoverCountry]

Very true. I discovered these after trying very hard to install nutplates along the sides where it's really hard to get access with a drill or squeezer.
!

That's a good point and worth passing on that if you THINK you might want removable floors, put the nutplates in before you rivet on that side skin.

 

[LettersFromFlyoverCountry]

Re: structural integrity of nutplates in the baggage area. I checked with Van's before using nutplates on both the floor under the seats and the baggage area and was told this would be no problem.

If the difference between my airplane staying together is the difference between a nutplate and a pop rivet on the floors, I'm thinking I've got bigger problems somewhere.

 

[RV7ator]

Meet 'em half way, platenuts on one side of the bag floor, pops on the other. Flush or pan head screws, your choice. One side's all you need for an ELT and strobe supply, which, BTW make sure you've enough room in the cavities for the thingies AND what ever restraint scheme you intend. If you do use rivets, consider dimpling for CS4s instead of the plans LP4s.

Caution with the clip nut: take care to never let the screw's threads engage the metal edge and not the nut. You may wind up bending the clip by pushing on the nut instead of threading into it. I make a practice of drilling out the screw clearance hole .032 (or so) larger than the screw's major diameter. Assures engaging the nut and not dragging on the hole edge.

John Siebold

 

[RudiGreyling]

Meet 'em half way, platenuts on one side of the bag floor, pops on the other. <SNIP> If you do use rivets, consider dimpling for CS4s instead of the plans LP4s. <SNIP>

John Siebold

John,

I like the way you think, last night while mulling over this I thought of maybe doing it 1/2 way only. fitting the goodies on the RH side, Passenger side.

I send an email of to vans about countersink platenuts and dimpled rivets and got a response:
"Cheaper, simpler as per plans. IF you want them flush, you can make them so...it's up to you.IF you think the benefits are worth the considerable extra work, a bit of extra weight and cost then go ahead. Again....it's up to you."

Now I just need to make my decision which ones to do...

 

[kevinh]

I send an email of to vans about countersink platenuts and dimpled rivets and got a response:
"Cheaper, simpler as per plans. IF you want them flush, you can make them so...it's up to you.IF you think the benefits are worth the considerable extra work, a bit of extra weight and cost then go ahead. Again....it's up to you."

Especially if you consider that you'll probably be putting a layer of carpet over this floor (at least I did - stops rattles and prevents dents from luggage). I don't see how you'll ever know that those LP rivets or screw heads are sticking up.

As for having nutplates at all: I don't see the point (except for a little hatch for ELT or strobe). While still building I had to remove the floor panels after they were already riveted in (to add steps - long story). It took all of 15 minutes to drill out all the pop rivets - it might have even been faster than unscrewing screws.

 

[szicree]

I say aluminum pops. Don't pull them until the very end. As was already mentioned, drilling them out (several times even) is still a LOT less work than installing all those nutplates.