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61Flyguy

Member
Inspection of this -4 reveals damage to firewall as shown in this photo. My concern is that there is underlying structural damage other than what is visible. Prelim. inspection reveals no other visible damage to longerons, gussets, engine mount, etc. Does this look to be similar to the firewall issues others have seen on their -4's? I can't visualize how a hard landing could have caused this without severely damaging surrounding structure.

http://home.mchsi.com/~ecdamm/100_0342.jpg

Thoughts?
 
Need more info

Is this your plane and did this crumpling occur because of a hard landing? I don't see any other indications of problems.

I probably won't be able to help but more info may help someone else provide good advice.
 
I rebuilt a wrecked RV4 with the same damage except much worse. There are .125" angles behind the firewall running vertically from the top motor mount bolts to a weldment in the lower corner where the lower motor mount bolts are. I will venture a guess you have damage there. I would also think, if you removed the gear leg fairings, you will find the mount and/or gear legs are most likely bent. This is all replaceable with raw angle and some sheet aluminum. Motor mount and gear legs from Van's was $1000 and I can't remember what we paid for a new firewall but Van's will support their product. There is no such thing as prepunched or even preformed parts for the 4. However, the firewall is two pieces, preformed but not drilled. The rest is just angle and sheet along with a healthy dose of labor. I started the project about December working about 35 hours weeks and all damage was repaired by Mid-February with the airplane on its gear with no engine or prop. I am retired so I had the time. Modifications were done after that including a glass panel, backseat controls, new C/S prop and repaired cowl with patched paint. It was ready to fly in June but most of the time spent was in modifications. If this is a nice airplane, fix it! Parts will not cost more than $2500...UNLESS the engine or prop took a hit then that will have to be dealt with. One word of caution here. The sheet metal aft of the gear legs which wraps around the bottom of the fuselage and forms the sides of the "tunnel" where the exhaust stacks exit the cowl is NOT the floor or the bottom skin of the fuselage. That is a fairing to round out the forward fuselage. The load bearing skin is under that fairing which is most likely bent which I repaired with a gusset that now resides under that fairing. Looks good and flys good but is damaged merchandise to some. Good luck and if need be I have many pictures of what all this looks like when apart. I do think you will have to take most of the front end apart to repair this right.

Dick DeCramer
N500DD RV6
N149KC RV4
RV8 Wings
Northfield, MN
 
My concern is that something must have broken in order for what to appears to be the engine mount contacting the firewall in the area which is now creased. How could this have happened without surrounding structural damage occurring???
 
Good question..

I've never understood the mechanism that causes the firewall corner to get creased. It's not uncommon. It's also not uncommon for the plane to be otherwise fine. However, the damage you show is pretty significant. I haven't personally seen one like that.

If this is a pre-buy situation, I would probably pass. If not, and it's otherwise fine, I'd plan a winter project to re-do that firewall. BUT, I would be reluctant to invest that much work and just replace the existing structure.
I would like some assurance that I was building a better firewall and would not have to do it again. I'm not sure how to get that assurance......

Good luck

John
 
Buckled or Bent?

I can't tell from the photo, too grainy when I zoom in, but can you tell if the firewall was bent from coming in contact with the welded gusset or has it buckled from torsional loads? Have you removed the bolt and inspected it?
 
I had the same two questions myself. There was no evidence the gussett impacted the firewall, it appears to have been related to stress imposed on the fw. The bolt has not been pulled yet, I was thinking it may have sheared. It should be checked.
 
I've seen this before...

If you are not the builder...make sure someone didn't just hammer in this area to gain access to the firewall, engine mount area to make it easier to get to the bolts, to change to tall gear or change to thicker gussets on the mounting area. In other words, the 'damage' was thought out and is NOT structural.

Now if it appeared on its own.........
 
Need More Evidence

61Flyguy said:
I had the same two questions myself. There was no evidence the gussett impacted the firewall, it appears to have been related to stress imposed on the fw. The bolt has not been pulled yet, I was thinking it may have sheared. It should be checked.
Click to expand...

I'd consider pulling the outboard-most, top and bottom 404 bulhead bolts and have them NDI'd, and dye-penetrant on the firewall frame inside. If you don't find any other broken parts or bent metal I'd have to say you're OK, but inspect more often.
 
firewall

It is common to see this on the -4 for some reason. After about 2 hours of flying I noticed this on our -4 (only it is on the other side and perhaps not quite as pronounced). I have to tell you that I had made 1 hard landing but nothing that should have bent anything. Of course I was just overwhelmed with worry that the structure was damaged but upon very close inspection there was absolutely no other damage.

Van's informed me that the firewall was not a structural part of the fuselage and not to worry.......


I contemplated rebuilding or repairing the firewall as some builders have done. What I did was leave it alone and keep a very close eye to make sure that it was not getting any worse. That was 6 years and 200hrs (hey don't laugh I live in Canada where winters are long , 50 hrs a year is lots of flying :)) and I am happy to say that other than cosmetic appearance there is not a thing wrong with the airframe........

I believe that there were built in stresses from the building process and the weakest part of the -4 is this part of the firewall which is where the stresses unloaded and it showed up.
 
Marc - I was interested in your post. (It must have been very frustrating at the time but I guess time heals.)

My question is do you have the current firewall gussetts installed? I think they last changed in '94.

No one has ever been able to say if the damaged firewall -4s are ever post '94 parts.

Thanks
 
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