RV-4 Cockpit Stretcher

Bought a 4 kit. I would like to increase the distance from the pedals to the front seat back by 1-2 inches. Any problem with moving the roll bar back a little? Any other suggestions ?

The canopy cross bulkhead/bar goes right behind the roll bar.

Not having built a 4, I'm guessing a little bit here but it looks to me that would be troublesome. The roll/crossbar is positioned directly above the inverted-V shape of the fuselage stiffeners, which would carry the weight of the inverted aircraft after a flip. If you move the rollbar aft of that point without carefully re-engineering the support structure, you are exposing yourself to a fuselage collapse in the event of a tipover, which would result in your head/neck trying (with predictably poor results) to hold up the aircraft instead of the rollbar doing it.

If you move it aft without redoing the structure, you're an experiment waiting on a tipover before you know the result. If you move it aft and redo the structure, you're a test pilot waiting on a tipover before you know the result.

Either way, caution is advised.

I moved my seat back aft 4 inches. Moved the side-wall braces and their support structure under the floor as well. No big deal. Also moved the front stick aft 4 inches with a new-from-scratch torque tube weldment. So far it all adds up to a very comfortable front seat. Because it is a Rocket the PAX seat was extended 4 inches so all I did was take that back for the PIC. Moving so much in a standard -4 may present problems for the PAX.

Moving Seat Back

PF....I moved the lower front seat attachment back one half inch and the rollbar (the upper seat back support) back one inch. This required moving the canopy cross-support back an inch or more for clearance. Of course I was already remaking the canopy frame for the HR Turtledeck. This hasn't made much negative difference for the backseater, but the little extra space for me was a good move.

Good Luck,

Bill

Thank you all for your input

I believe Van has advocated moving the seat/roll bar back up to two inches for tall pilots (tall pilot option) Mine was built with everything moved back 2 inches, my inverted-V shape fuselage stiffeners where not moved back but it looks like they would still do the job in a roll over, I have passengers often and get no complaints, one was even 6?4?, he was a tight fit but he would be tight in the back of any -4. My -4 was first flown in may 1983 and built in 18 months so this mod could not have been all to hard to complete.

The other direction...

I inspected a 4 owned by a 6'6" individual who extended the footwells slightly and modified the rudder pedal attachments to allow longer legged folks more room. This also required some creative mods under the hood but was well done.

Smokey
HR2

I've always wanted to do this.......

I inspected a 4 owned by a 6'6" individual who extended the footwells slightly and modified the rudder pedal attachments to allow longer legged folks more room. This also required some creative mods under the hood but was well done.

Do you know what the mods were ? It always seemed to me that this was the way to go ( to gain more legroom ). I just haven't been up for the effort. At least not yet

John

If you do it, don't forget to adjust the C.G. moment arm for the pilot.


Lee...