Rive-nuts and smoke oil tank

I am intending to install a 5gal smoke oil tank in the back luggage compartment of my RV-8 (need to move the CG back while having some fun with it...).

Looked at Marvin's system and when reading through the installation instructions it says that one can use 4 rive-nuts to attach the tank to the floor ( I would assuming going through the floor AND the flange of the ribs below it).

Now that made me think about how well rive-nuts actually work as I do fly my RV within it's full envelope once a week... . I am not an expert by any means but would never have thought to use rive-nuts for structural purposes.

The tank full with oil, pump etc. should be in the 40-45lb range. I would suppose on positive loads it shouldn't matter as the rive-nuts don't have to hold anything in that case. That leaves side loads (e.g. snap roll) or negative loads.

As my max negative load is -3G which should put the ultimate load to -4.5G. Let's add 10% for good measure making it -5G.

So that would mean the 4 rive-nuts would have to hold about 250lb on pull. Not sure what a realistic side load would be. As I have little concern that they would hold this once I am a little bit worried that adding/removing that load frequently as one does flying would eventually lead to failure.

Are my concerns justified?

Also what size rive-nuts would one use as they obviously have to be small enough to have sufficient edge distance on the flange of the rib in the floor but large enough to hold the load.

Oliver

I added a bottom plate to the smoke tank

I'm about finished installing the smoke tank in the rear baggage compartment(not flying). I opted to build a bottom plate and rivet it to the tank. Then the plate/tank assembly is fastened baggage floor. This was for few reasons.

1. I built the baggage floor to be removable, but at the time had not planned on the smoke tank there. The net result is that I have pan head screws in place of the LP4's that the tank would sit on(similar issue with the LP4-3's though the head is smaller). The plate is thick enough that the heads of the machine screws do not contact the tank.

2. I preferred to use the nut plates already in place for the removable floors rather than add new ones/rivnuts. The metal plate is larger than the tanks footprint with enough material for me to use 4 pan head screws to hold down the tank. Each MS35205-245(AN515-8R8) has a breaking strength of 770lbs.

One downside is the added weight of the plate ~1.5lbs, however it is attached to the tank and will be removed along with the tank/pump when not in use.


I went looking for numbers on the rivnut but came up empty. They and other hardware come with the kit. Marvin has been great work with, give him a call he'll answer all your questions.

I wouldn't trust a 4 gallon tank of oil to 4 rivnuts, even if they are installed in floor ribs. I would use -10 bolts attached to floor ribs, or .032+ angles attached to the floor (underneath), that are then attached to the floor ribs. The rivnuts that I've used are aluminum and you can easily strip them if you aren't careful - even the ones you get from aircraft spruce or Vans. Tensile strength on these fasteners must be relatively small. OK for many applications, but not when you're using them to hold down a heavy (flamible) object when pulling negative G's.