[[email protected]]

Hi Group,

I am planning to use the Showplanes FastBack kit for my RV8. Recently someone pointed out the possible safety issues when going this route. To be honest, I did not think of that when buying the kit.

Two questions related to this:

1)
The additional roll bar has to be welded on the WD-808 Front Seat Back Support. This looks somewhat similar to the RV4 roll bar setup. How dow you other RV8 FastBack builders feel about the safety aspects of going this route? The original roll bar (WD-814) seems to be mounted on a relative strong point of the airframe (near the gear towers), the WD-808 'only' has the arm rest structure and the skins to support the roll bar. (think flip-over, glide along runway upside down..)

2)
I would like to compare the RV4 roll bar setup to the RV8 \ Showplanes setup. Does anybody have a "mid fuse side skin structure" or a "roll bar setup" drawing from an RV4 available as a scanned document?

Thank you in advance for views on this (and for the drawing).
Kind regards,
Duncan

 

[Andy_RR]

For me too, the roll-over hoop of the RV-8 is enough of a negative to consider a tip-over conversion of some type, so I've had a bit of a browse for pics etc. I'm still building wings at this stage, so it's still theoretical for me...

Steve Sampson's fantastic blog at http://gikonfuse.blogspot.com/ shows some detail of the fuselage construction around the roll-over brace on the RV-4.

It's somewhat different from the RV-8

Don't forget that the gear tower structure doesn't exist on the RV-8A model, so in this case, the RV-8 structure around the original hoop isn't as strong as it appears on the taildragger-8

FWIW,

A

 

[DanH]

I am planning to use the Showplanes FastBack kit for my RV8. Recently someone pointed out the possible safety issues when going this route....
1)
The additional roll bar has to be welded on the WD-808 Front Seat Back Support. This looks somewhat similar to the RV4 roll bar setup. How dow you other RV8 FastBack builders feel about the safety aspects of going this route? .....

Here's a link to a Steve Sampson RV4 photo so all can compare with Andy's RV8 photo.

http://photos1.blogger.com/blogger/2531/2999/1600/HPIM0090.jpg

All in all, my non-professional guess regard the sidewall, longerons, and bulkheads is "not much difference".

The weak link with the stock Showplanes hoop involves sliding along upside down. In this regard the weld-on hoop doesn't have a prayer; it can be expected to bend/fail in the fore and aft direction. Another fastback builder (and qualified engineer) did some FEA models exploring stress in various rollbar configurations. Not my work so I shall not report specifics, except to say some kind of brace is a very good idea.

This is what I did. Be aware this bracing is not optimum, just better than nothing.

 

[[email protected]]

Hi Dan and Andy, thank you both for your replies. I will look into some sort of bracing as well.

 

[Calvin25]

Duncan, I had this same exact question a couple months ago.

I looked close at how the roll bar would take an impact in the event of a nose over, primarily forced landing on rough terrain. I didn?t see how there could possibly be a
large amount of forward momentum after the plane has made a complete nose over. My uneducated guess is that most of the forward inertia would be absorbed into the nose of the plane then act as a ?flop over?.

It would be interesting to see the average distance the plane travels from the point it is nose to dirt then final resting spot on its back. I wouldn?t imagine it to be more then a few feet in most survivable cases.

Then, I took note that the Extra 300 does not even have a roll bar and a few fastbacks don?t either as it used to be an option from show planes.

I messaged Dan Horton off sight to see what he did. I think he has the right idea with the added braces. It looks like enough to soak up that small amount of forward energy if it is present.