Tuesday, April 14, 2009
An RV4 damaged firewall
This is pretty typical (I think) of the damage that occurs on the (older?) RV4 firewall. I hasten to say it is not G-IKON, my RV4.If you look closely at the picture, you may need to double click it to get a larger image, you will see shadows coming out and upward, at about 30 deg. from the lower corners of the F-413 bulkhead assembly. The F-413 is the inner fore and aft bulkhead which transmits much of the landing loads through to the wing spar.
These shadows/creases are indicative of stress running (I think) along the axis of the crease. This eventually results in cracking of the firewall at the right angle bend where the stress concentrates, due to landing loads, with a result that the firewall is no longer air/fire tight.
I have to say I have never actually seen the problem with my own eyes, only pictures like this. The grey primed bits of angle I presume are to cover cracks and probably, together with some RTV, there to make the firewall gas tight once again. The problem with fixes like this is the problem is not solved just moved and will soon reoccur if heavy landings take place.
If you are buying a used -4 I would inspect the firewall carefully for signs of similar damage.
I dont know if RV4 that have the newer steel firewall corner weldements (see point 3. if you go there.) are suceptible to this or not. Time will tell. I am not aware of any other firewall fixes to amelorate the stresses on the stainless sheet.
