Door post rivets and FUS-30's
Posted: Fri Feb 17, 2012 9:37 pm
Rick, this extra set of rivets is staggered either forward or rearward of the original set, that goes up the middle of the post. Center a new rivet hole between each of the existing ones and stagger them from the center line to help negate the "tear here" line and still allow the rivet to go into the tube and not hit the sidewall. I say stagger forward or rearward as the original holes may not be in the center and one direction as opposed to the other may allow a larger stagger. Also if you have the door gap seal coming down onto the door frame to seal, you may have to go forward with the extra set of rivets. The rivets that join FUS-9 and FUS-27 together, above the door opening, are too close together for this double row of rivets so drill them up to 3/16 to add some shear strength were it is really needed. These have to shear before the others can start.
If building new do the MAM float fix strap as this is where the guillotine thing starts to happen. If you hold it together well at the top it can't get going. That is why on the retrofits I do the 3/16 rivets up here as that's how I did my original fix and it's much easier than pulling the windshield, etc to do the strap. I do recommend the strap though if building new, PLUS the double row of rivets up the post.
As for your FUS-30, you are now official another member of the group that know first hand why we have been telling everyone to double this area since before I started to build my first Rebel in 1993! It is unfortunate, but you do need to get it licked before it gets any worse. Use a piece of .032 6061-T6 and do the doubler as shown in the Rebel-Fuselage files. It takes approximately 6 to 8 hours to remove the tailfeathers, drill out the rivets, fit the doubler, chromate, re-rivet and bolt the new one in, etc. Stop drill the cracks in the old one and try to tie the old to the new as much as possible without turning it into swiss cheese. It is easier to use another FUS-30, but can't see the extra work paying to shop one piece from British Columbia to Oz!
One other cause of the cracking in this area is having a tail spring that is loose in the TS1/2/3 clamp pieces. The spring MUST be held tightly or it will allow the spring to twist right back to the attach bolt in the FUS-30/bulkhead fitting and the twisting will cause the cracking below the post.
Good luck,
Wayne
If building new do the MAM float fix strap as this is where the guillotine thing starts to happen. If you hold it together well at the top it can't get going. That is why on the retrofits I do the 3/16 rivets up here as that's how I did my original fix and it's much easier than pulling the windshield, etc to do the strap. I do recommend the strap though if building new, PLUS the double row of rivets up the post.
As for your FUS-30, you are now official another member of the group that know first hand why we have been telling everyone to double this area since before I started to build my first Rebel in 1993! It is unfortunate, but you do need to get it licked before it gets any worse. Use a piece of .032 6061-T6 and do the doubler as shown in the Rebel-Fuselage files. It takes approximately 6 to 8 hours to remove the tailfeathers, drill out the rivets, fit the doubler, chromate, re-rivet and bolt the new one in, etc. Stop drill the cracks in the old one and try to tie the old to the new as much as possible without turning it into swiss cheese. It is easier to use another FUS-30, but can't see the extra work paying to shop one piece from British Columbia to Oz!
One other cause of the cracking in this area is having a tail spring that is loose in the TS1/2/3 clamp pieces. The spring MUST be held tightly or it will allow the spring to twist right back to the attach bolt in the FUS-30/bulkhead fitting and the twisting will cause the cracking below the post.
Good luck,
Wayne
----- Original Message -----
From: Rick Harper (rjwh@ozemail.com.au)
To: murphy-rebel@dcsol.com (murphy-rebel@dcsol.com)
Sent: Thursday, December 20, 2001 1:07 AM
Subject: Re: Firewall position
G'day Wayne !....(and a Very Merry Christmas & New year to you and the "tribe" as well ! :-)
I have just read with great interest , THIS e-mail stating to "double row and stagger" the rivets up the door post
/ hinge as this is "standard practice since '96 "....Got to admit , I hadn't heard of it either ! :-(......I'll have a sticky at the plane whilst I'm out there tomorrow (it lives a bit over an hours drive away from home )
I have a single row of 1/8" rivets down that joint (as per the plans...as I have not been told any different)....should I
1) Replace them all with 3/16" ?
OR
2) ADD another row,(of 1/8" rivets) staggered to the first ?
Also, I just noticed today, some small cracks at the bottom of the tailcone (down below the bottom Rudder
pivot)...... ( I have 85 hours to date and 169 landings), ...I know that there has been some talk of this area having a "doubler skin" fitted....but I was hoping to "get away with not having to do it" as I fitted a real SPRING on the tailwheel...which has lots of "give" and allows the tail of the plane to move around "a bit"...NOT like the solid / unmovable hunk of aluminium that was supplied with the kit.
Should I fabricate a doubler from .032" 6061 T6.....or thicker....and / or from something stronger , say 2024 T3
(and what do I do with the small cracks already in the tailcone... (about 3/8" long), apart from stop drilling them ?)
Any help will be gratefully received
Thanks
Rick & Wendy in OZ
541R
----- Original Message -----
From: Wayne G. O'Shea (oifa@irishfield.on.ca)
To: murphy-rebel@dcsol.com (murphy-rebel@dcsol.com)
Sent: Thursday, 27 December 2001 15:15
Subject: Re: Firewall position
Well Peter! There is the double pitched row of rivets up the forward door post (with the top 3 or 4's pitch left as is but upsized to 3/16") that I have recommended since the winter of 1996 FOR ANY ENGINE INSTALLATION (well before MAM put out the "float fix" bulletin after a couple aircraft, including the factory Elite, were damaged at Osh and something had to be done officially then). I can show you the pictures of why I started doing this in 1996, next time you are over, but I'm not going to post them! Lets just say that the original rivet pitch (with an O-235 engine) didn't hold up to one ski, 2 G landings on ice!!!! Like I keep telling you guys/gals I am rarely offering "theory" and/or calculated loads. I am passing on specific things that I've found necessary, to keep the thing together, from proven "destructive testing". In support of MAM, for their lack of offerings on some of the stuff that has been found necessary to reinforce the Rebel over the years, MAM doesn't hold onto their airplanes long enough to see most of this and I have yet to see Robin screw up a landing either!!!!
I really don't buy the "shorten the moment arm to reduce the loads on the cabin structure" bull. If the O-235 was supposed to be fine at the original engine position, the O-320 isn't going to make a big difference. The weight difference in engines is only about 30 pounds. If we were talking moving the engine in a foot maybe, but not 3 inches.
In a (-)2.5 G (ouch!) landing that is only 75 pounds extra load (less than one extra RV1410 rivets shear strength). I am not going to try to figure out the load values difference on the rivets at the top of the door post by moving the engine in 3" to 36.5", from the original 39.5", but will only say it's not going to make a big difference structurally (changes c of g significantly, but not load on door post rivets that are in "shear"). If you have added the float fix doubler at the top of the post, or have done the double staggered row of rivets up the door post (so the "guillotine" effect can't get started at the top of the door post and shear all the rivets out right down to the wing strut attach fitting!) you will be fine. I can state this with confidence only because I have tried the same "testing" on my Rebel, with the extra rivets up the door post and an O-320 engine, and have determined that this type of "landing" is now a NDT (non-destructive test) instead!!!
'night,
Wayne G. O'Shea
www.irishfield.on.ca
----- Original Message -----From: Peter Cowan/Lexy Cameron (cowcam@pipcom.com)
To: murphy-rebel@dcsol.com (murphy-rebel@dcsol.com)
Sent: Wednesday, December 26, 2001 9:49 PM
Subject: Firewall position
In scanning the manual (from early 90s) I see a comment that has not been mentioned that I can recall about the reason for moving the firewall back for the heavier engine. The reason stated is to shorten the moment arm to reduce loads on the cabin structure.
Wayne, I don't recall you mentioning any reinforcements that specifically address this aspect. Have I missed something?
Thanks
Peter.