Cabin Heater Box - Not attached to F'wall?

[Noah]

Did anybody notice that the plans don't call out any attachment between the heater box and the firewall vertical stiffeners? Unless I missed it, there are only 2 screws fastening the top of the box and the firewall recess, but nothing securing the sides of the heater box where they nest just inside the firewall angle (F-601N-R).

With all the vibration expected at and around the firewall, I would think that there would be an opportunity for fretting. Any reason why this isn't fastened? Removability? Why not use nutplates and screws?

 

[andrew phillips]

If I remember correctly

The unit is attached with 2 screws and nut plates. These are located on the left and right sides 1/2 way up. The box is also sealed to the firewall with proseal or rtv to prevent leakage which also heps secure it. One of the screws doubles as a place to attache an adel clamp to secure the control cable on the inside.

 

[Noah]

Thanks Andrew-

That's the way I thought it should be attached as well, but I can't find the drawing with the callout - Drawing 34/34A doesn't show anything...

If I may ask, where in the plans did you find this information?

Thanks!

 

[andrew phillips]

I think the drawing comes with the firewall forward kit. My plans are at the airport so I can't check now but I am pretty sure it shows the attachement.

 

[David Mozingo]

HEATER valve/box

I was installing mine yesterday.
I noticed the same thing, and in fact if you put much silicone atv, it causes the box to not mate with the firewall.

I had to pull it off and clean up the silicone. Messy. dries fast.

I am drilling several holes in the box and firewall to add more attatch points. Maybe a doubler on the inside if the firewall also. The plans say not to use much sealant/silicone and i thought i was careful. it appears the sealant and pressure of the ( two only screws) pull at the flimsy firewall and cause gaps.

i am choosing to use small screws vs. nut plates, i am worried about bending the flush side of the box, and the closed position not sealing well if the riveting action bends the box.; so going with screws.

looks like you have to crawl under the panel in the furure to get the two existing screws out anyway...

 

[Noah]

Now I'm really lost

Maybe I'm missing a drawing or something. I can't find any reference to using silicone RTV to attach the heater box to the firewall.

However, I bought the aftermarket all-stainless heater control valve, and it didn't come with hardware or Van's install drawing, so maybe that's the mystery drawing that calls this out.

Anyone have a drawing number for this callout?

Anyone, anyone?

Beuhler?

 

[Bob Martin]

heater box

Remember to point the outlet side of the box down or towards the exit air area.
You really don't want the hot air off the exhaust pointing up towards the mag or accessory area. The box expels lots of hot air when the heater is not selected, as in all summer!

 

[kentb]

Need to use screws and rtv...

Looks like one screw each side and rtv to seal on the edges. Don't know which plan page the information was on.
Note that I attached a small piece of AL on the top to deflect the hot air downward if it is not going into the cabin.



Kent

 

[Noah]

Nomenclature Problem

OK, I think I know what's going on here. We have a nomenclature problem. You guys are talking about the cabin heat valve. I agree, it is attached with screws, nutplates, and RTV.

I am talking about the center cabin cover inside the cockpit, P/N F-782C, which is to say the volume which the heater valve dumps into, and which has louvers on the front and sides to direct heat around the cockpit. I referred to this as a "heater box" without looking at the plans and using the proper nomenclature. So, are screws and nutplates used to secure the center cabin cover to the vertical firewall stiffeners, or are they just fastened at the top to the firewall recess?

 

[Brantel]

With the screws that attach that to the floor stiffeners and the two that go to the back of the recess, there is no additional need for any screws.

It is hard enough to get that thing in and out without adding more fasteners to it.

 

[Captain Avgas]

Remember to point the outlet side of the box down or towards the exit air area.
You really don't want the hot air off the exhaust pointing up towards the mag or accessory area. The box expels lots of hot air when the heater is not selected, as in all summer!

Vans drawings show the exit air vented to the side. Actually I suspect there MIGHT be a conflict with the prop governor (if one has a prop governor) if the heater box was orientated with the exit air down (and the scat tube up).

The idea of adding a deflector to deflect the hot air downwards seems to have some merit.