Seat Rib Questions

[nplayle]

Hi,

I'm slowly plodding along on finishing one of those '90%' complete RV-6A builds. Tonight I was looking at doing some work measuring up brackets to add a 5 point seatbelt harness, but I started looking at the seat ribs themselves and started to question everything.

At first I noticed that they were kinked like someone had manhandled them trying to wedge something into place. This really didn't give me the warmest of fuzzies. But then on closer inspection it looks like the ribs have been cut away and mended.

I checked the plans and from what I can tell the ribs are supposed to be cut to fit the control column in there, but not in this manner. View F F' on drawing 33 shows the cut is supposed to be cut which starts from where the rear flat section is and goes towards the hole... this is not that. It does seem kind of patched like the ribs on an RV7 but there is no missing flange. On this one the flange is missing and the web is cut completely away. From the other RV6 builds I've seen none of them are done this way, so it's got me questioning if this is correct.

So 2 questions:
1. Are the kinks in the rib concerning / warrant replacement or reinforcement?
2. Has anyone seen this kind of cutting before (i.e. is it a common mod?)
3. Can anyone share some pictures of their seat rib section here? The one's I've been able to find are a bit small and blurry.

In parallel I'm sending an email off to Vans, will report back with what they say.

Thanks!

 

[Stevea]

The kinks are a bit concerning to me. Given the ribs are fully installed at this point, and the "challenge" to remove from the fuselage and replace them, I would try the following: Straighten them as much as possible. Fabricate a doubler piece, and attach a the doubler to the damaged rib area.

As for removing the material in the second "main rib cut away" photo, middle arrow.......yes, I had to do the same thing in order to make everything fit once the wing spar splice plates were installed. The reality is that the remaining thin strip of material that was removed wasn't providing much (if any) strength anyway. It was only getting in the way of installing the splice plate bolt and nut.

Here is a dropbox link with all the pictures I could find showing that seat rib area from my build. Some may help, others maybe not so much. Take a look and see what questions get answered and what new questions you have. We'll take it from there.

Dropbox

www.dropbox.com

Good luck.

 

[rvbuilder2002]

The removable portion at the top front is normal and is a different method from what is shown in your plans for making an opening in a few of the ribs to get the control column in and out if needed. It is what is typical on an RV – 7 or RV-9.
The cut away portion at the most forward upper area of the ribs is not part of a standard build, and I’m not sure why someone would have done that.
Perhaps it was someone short in height that needed to sit way forward in the seat and they were trying to adjust the stick travel range so it didn’t come as far aft as is typical. If that is present on all the ribs that would restrict forward travel of the control column, that would be my best guess for the reason. Or while building, they had zero understanding of what the actual travel range of the control column is when the control system is fully assembled.
That likely compromised the strength of the ribs.
It also does look like there is some compression buckling evidence further aft on the ribs that raises some concern. Particularly without any understanding of why it would’ve happened. Perhaps because of the excessive cut away portions at the front of the ribs along with someone quite heavy standing on the seat pan?

 

[JonJay]

The kinks are a bit concerning to me. Given the ribs are fully installed at this point, and the "challenge" to remove from the fuselage and replace them, I would try the following: Straighten them as much as possible. Fabricate a doubler piece, and attach a the doubler to the damaged rib area.

As for removing the material in the second "main rib cut away" photo, middle arrow.......yes, I had to do the same thing in order to make everything fit once the wing spar splice plates were installed. The reality is that the remaining thin strip of material that was removed wasn't providing much (if any) strength anyway. It was only getting in the way of installing the splice plate bolt and nut.

Here is a dropbox link with all the pictures I could find showing that seat rib area from my build. Some may help, others maybe not so much. Take a look and see what questions get answered and what new questions you have. We'll take it from there.

Dropbox

www.dropbox.com

Good luck.

Nice work

 

[JonJay]

If you elect to repair these in place, download AC 43 13.b.
There are some really good examples of acceptable repairs, rivet spacing for doublers, etc….
It might also be an opportunity to incorporate your belt brackets as part of that repair effort.
I used Vans crotch belt kit for the 7 on mine and it was a good starting point but took a great deal of modification.

 

[nplayle]

The kinks are a bit concerning to me. Given the ribs are fully installed at this point, and the "challenge" to remove from the fuselage and replace them, I would try the following: Straighten them as much as possible. Fabricate a doubler piece, and attach a the doubler to the damaged rib area.

As for removing the material in the second "main rib cut away" photo, middle arrow.......yes, I had to do the same thing in order to make everything fit once the wing spar splice plates were installed. The reality is that the remaining thin strip of material that was removed wasn't providing much (if any) strength anyway. It was only getting in the way of installing the splice plate bolt and nut.

Thanks for the photos - they're really helpful! Looks like you ended up with a similar cutout to what my ribs have in that the top and bottom of the front flange of the seat rib aren't connected to each other?

I was largely of the same opinion as you that the missing strip wasn't contributing an awful lot to strength as the F604-B bulkhead should be providing most of the strength at the front of the seat rib flange.

How did you come up with your 5 point seatbelt attachment?

The kinks are my largest concern at the moment as well. I like the thought of repairing them in situ if possible. A doubler but bent as an L bracket should stiffen the bent rib fairly substantially I'd think.

 

[nplayle]

The removable portion at the top front is normal and is a different method from what is shown in your plans for making an opening in a few of the ribs to get the control column in and out if needed. It is what is typical on an RV – 7 or RV-9.
The cut away portion at the most forward upper area of the ribs is not part of a standard build, and I’m not sure why someone would have done that.
Perhaps it was someone short in height that needed to sit way forward in the seat and they were trying to adjust the stick travel range so it didn’t come as far aft as is typical. If that is present on all the ribs that would restrict forward travel of the control column, that would be my best guess for the reason. Or while building, they had zero understanding of what the actual travel range of the control column is when the control system is fully assembled.
That likely compromised the strength of the ribs.
It also does look like there is some compression buckling evidence further aft on the ribs that raises some concern. Particularly without any understanding of why it would’ve happened. Perhaps because of the excessive cut away portions at the front of the ribs along with someone quite heavy standing on the seat pan?

It does look pretty typical of the cutaway on a the -7. I'm not sure why it would be done that way instead of the way the plans suggest, and I'm not sure why 3 ribs were cut instead of just 2.

I'm starting to think that the cut away at the front of the seat rib flange was to fit the splice plate like Stevea suggested.

I managed to find 3 old photos from much earlier in the build phase. My latest theory is similar to yours - with the front of the seat rib cut away it is very weak, and someone crawling around in the fuselage, perhaps installing avionics or doing wiring sat on / stepped on / grabbed the ribs that caused the buckling. The three photos I found are from what I believe is an initial wing fit test and then some wiring. The 3118 photo is from April 2018 showing the seat ribs roughly in tact, though not perfect, and 3127 in October 2018 shows some fairly good damage. Passenger floor is from 2020 where it looks like it's been cleaned up a little. I don't have any without the seat pans in, so can't really tell what happened there. But based on the fact that the splice joining the cut away portion of the rib isn't present in any of these photos, my thoughts are that the missing piece comprimised strength enough and over the course of months / years of moving around in the cockpit caused the ribs to get kinked.

If I'm able to reinforce it in place I like the idea of putting some kind of doubler on the buckled ribs. My initial feeling is some kind of L angle might be enough, or some kind of 90 degree flange riveted to the side to try and give it some extra strength. Any thoughts / concerns? Fortunately the ribs should get a fair amount of support against buckling from the 5 point seat belt harness, but I don't think there's any harm in reinforcing it a bit more, particularly on the two ribs that have the aileron trim which have minor amounts of buckling.

 

[nplayle]

If you elect to repair these in place, download AC 43 13.b.
There are some really good examples of acceptable repairs, rivet spacing for doublers, etc….
It might also be an opportunity to incorporate your belt brackets as part of that repair effort.
I used Vans crotch belt kit for the 7 on mine and it was a good starting point but took a great deal of modification.

Thanks for the pictures, particularly of the 5 point attachment. I've found people have tried a bunch of different ideas for adding the 5 point harness in the -6, ranging from a bolt through the bottom skin to modifying the -7 bracket and a full custom setup. I've got a break and some scrap aluminum so my thoughts right now were to bend my own based on the -7 design, largely because so many people who started with the -7 bracket seem to say the mods to make it work are so time consuming.

Is there a reason you went with screws in your design over rivets?

 

[JonJay]

Is there a reason you went with screws in your design over rivets?

Getting a gun or squeezer in there would have been a challenge. It was just easier.
I also have a shear and brake but decided to buy the kit more to see how things went together. I could absolutely fabricate this, but…..
You will also notice that I used some angle for the flanges. The ribs were not perfectly parallel. The 7 parts did not fit well. I just cut off the flanges. I had the angle laying around and it made it easy to adjust everything and drill in place. Far easier than trying to get these bends right.
I think you would find every 6 to be a bit different. Like I mentioned earlier, this might be a good opportunity to incorporate the repair of the ribs into your bracket design. It may not even be necessary as the bracket adds support to the assembly regardless.

 

[Stevea]

How did you come up with your 5 point seatbelt attachment?

My 5th point seat belt mount was fitted and installed after the original -6A seat rib fuselage structure was done. (My original -6A plans did not have provisions for a 5th point on the belts.) I started out trying to fit the 5th point attachment from a -7/7A, but couldn't make it work without a lot of changes to the 5th mount point width, and the screw pattern through the seat pan into the 5th point flanges. Long story short, I ended up coming up with my own design made from 0.062" flat stock and 0.062" angle stock riveted together with 1/8" solid rivets. The 5th point bracket is attached to the seat ribs using pulled LP4-3 steel rivets.

I would have preferred using the 5th point design from the -7/7A.......just couldn't make it fit with the existing structure.

 

[RV-9erA]

Hi,

I'm slowly plodding along on finishing one of those '90%' complete RV-6A builds. Tonight I was looking at doing some work measuring up brackets to add a 5 point seatbelt harness, but I started looking at the seat ribs themselves and started to question everything.

At first I noticed that they were kinked like someone had manhandled them trying to wedge something into place. This really didn't give me the warmest of fuzzies. But then on closer inspection it looks like the ribs have been cut away and mended.

I checked the plans and from what I can tell the ribs are supposed to be cut to fit the control column in there, but not in this manner. View F F' on drawing 33 shows the cut is supposed to be cut which starts from where the rear flat section is and goes towards the hole... this is not that. It does seem kind of patched like the ribs on an RV7 but there is no missing flange. On this one the flange is missing and the web is cut completely away. From the other RV6 builds I've seen none of them are done this way, so it's got me questioning if this is correct.

So 2 questions:
1. Are the kinks in the rib concerning / warrant replacement or reinforcement?
2. Has anyone seen this kind of cutting before (i.e. is it a common mod?)
3. Can anyone share some pictures of their seat rib section here? The one's I've been able to find are a bit small and blurry.

In parallel I'm sending an email off to Vans, will report back with what they say.

Thanks!

Just for reference -- two photo attached from my RV-9A build between 2000 and 2004. When I'm working under the forward seat pans, I like to keep the floor-rib removable bridge sections in-place for added floor rib strength. I also sit back away from the forward ribs with a cushion or pillows, which prevents over stressing the forward floor ribs. These ribs don't have much strength without the removable bridge sections in place and the floor pans screwed down.

 

[Bobman13]

Not to try to poach onto your post but although I currently am not in the same position, I am however trying to sort out what cutouts I need to do for the control stick so there is no interference on the Pilot/Co-pilot side’s anyone have a suggestion I have all the plans but it not clear on the material for the angle needed or exact dimensions.

 

[bardample]

Not to try to poach onto your post but although I currently am not in the same position, I am however trying to sort out what cutouts I need to do for the control stick so there is no interference on the Pilot/Co-pilot side’s anyone have a suggestion I have all the plans but it not clear on the material for the angle needed or exact dimensions.View attachment 92552

Its worthwhile waiting til after you have connected empennage and aileron controls before you cut any more access for control stick movement. I found the movement of control stick was much less than I thought once all connected.

 

[PaulvS]

Not to try to poach onto your post but although I currently am not in the same position, I am however trying to sort out what cutouts I need to do for the control stick so there is no interference on the Pilot/Co-pilot side’s anyone have a suggestion I have all the plans but it not clear on the material for the angle needed or exact dimensions.View attachment 92552

As Jeff said above the cutouts for the stick should be made after connecting all of the push rods while rigging the controls.

Here are some pics of the seat ribs on a 6A that has been rigged and cutouts trimmed.

 

[johnbright]

Beware insulation on the cold side of the firewall.

Bad Firewall Insulation Choice

Recently had an opportunity to remove the "firewall insulation" from an RV-7A. Although I can't determine a particular brand, the material type is common enough, a fiber mat backed with a fiberglass net and aluminum foil. It was a popular option 20 years ago, and I still see it under panels at...

vansairforce.net