Tall Person mod

[RyanB]

Hi Eveyone

I have done a lot of searching regarding moving the seat back on my RV4. I have just started building the fuselage so am trying to plan ahead.

From what I can find on the net most people just say move the roll bar back 1 to 1 1/2 inches, and this is where I get confused with the following:

1. Does one simply move the roll bar backwards, or must the F405 and F406 bulkheads also be moved as don?t they give strength to the roll cage mounts?

2. Regarding the bottom of the seat, does one simply move back the seat back hinge?

3.Will the roll cage now interfere with the canopy frame, and if so how do we get around this?

4. Will the aft stick need to be modified to get full movement?

Sorry for all the questions but this mod is definitely something I need to start planning for.

Thank you for any help

[Michael Henning]

I moved the roll bar back the maximum allowable distance (IIRC, 2”). The bulkheads stay I their original location. The bottom seat hinge moves back the same distance. No interference with the rear stick. If you try to go farther than plans allow, roll bar will interfere with canopy. I’m 6’2”, 34” inseam, and plane is comfortable on a 6 hour flight.

[RyanB]

Thanks Mike

That is great news and keeps it simple, I must just go relook at the plans as I couldn?t find where it said anything about moving the roll bar back.

I am about the same height as you and also have the long leg problem, so this is great news.

All the best

[fixnflyguy]

First off, I don't know hall "Tall" you are, but I'm 6'1", tall to some, not very tall next to others. When I built mine, I had sat in a standard, per plans build RV-4, and had an idea what I would be comfortable in. I did not relocate, but slightly adjusted (AFT) the F405/406, but positioned the roll bar aft as far as possible without interfering with the canopy center bulkhead, which is the real overall factor for the seat back angle. The RV-4 is a fairly upright seating position, so moving the hinge at the seat back bottom can make that worse if you move it very far. Plan on thin but firm seat cushions, and get your rudder pedal travel to hit stops with pedals nearly touching the firewall (watch brake throws too). Since I am nearly always with a back seater (wife who likes to fly!), I needed the rear stick functional, and have it adjusted so full forward is 1/8" from my seat back. She is 5'11" and I installed the rear seat footwells (a must), and we are comfortable on 2 plus hour trips non-stop. You will love the -4!

[RyanB]

Thank you for the detailed response Bill, I really appreciate all the info. Any idea how far you moved back F405/406?

[fixnflyguy]

Its been 15 years since I built mine, but I kept the floor level positions as per plans and shifted the top slightly aft. There is a lot of stuff going on at the upper longeron /rollbar attach point to make sure fits well, such as the roll bar bolts, ect. . Can't say exactly how far I moved them, but its probably no more than 1-1.5".

[Michael Henning]

And like Bill said, you WILL love the -4. It is a fabulous airplane.

[rv7charlie]

Does Van's endorse moving the roll bar without moving the bulkheads? Sounds like something that isn't a problem until it is.

FWIW, I followed the lead of a friend, and simply moved the top of the seat back from the front of the cross bar to the back, using a couple of hand made 'adel clamp' type straps around the crossbar and screwed to the top of the seat back. I notched the tops of the vertical angles to nest around the crossbar. It made a huge difference in the comfort of the seating position. I'm not that tall, though (~5'9"). I really don't know if this mod would have you hitting your head against the roll bar.

You might want to find a -4 to sit in, and see if just reclining the seat a couple more inches would accomplish what you need.

Charlie

[Michael Henning]

I did the mid as exactly per the plans, and no bulkheads needed to be moved. That area is extremely strong.

[RyanB]

Great responses, thanks gents. I am 6?2 and have sat in a standard 4 and one that has been modified. The mod makes a huge difference.

Sadly I don?t have access to the modified one for reference