Rudder leading edge - To Roll or Not To Roll?

[Rallylancer122]

Hi All,

Through a series of unfortunate events the rudder on my RV8 was damaged. I got a new one from a builder who built a tail kit and stopped there. The workmanship is great, but he did something I haven't seen before.

The leading edge of the rudder is not rolled and riveted per Vans. Instead it's gently folded in, with a significant gap, and not riveted together. He said some builders were doing this now, with the idea that it reduces the gap between the back channel of the fin and the rudder, in theory reducing drag. In other words, it effectively turns the leading edge of the rudder into a gap seal.

This makes sense to me, but I wanted to make sure I wasn't missing something? I tried searching it but didn't come up with anything. (If I missed a previous discussion, my apologies!)

Thanks!
DEM

[bruceh]

Never heard of anyone doing that. I would assume the riveting of the two sides together would add some significant strength to the rudder. I don't think the aerodynamics of leaving it open would be much reduction in drag.

[Snowflake]

I too would wonder about compromising the structure by not closing the two surfaces together. I understand leaving it more open to close the gap more, but if nothing else, i'd want to rivet a spacer in between the free ends to maintain the "D-tube" that the spar and forward section creates.

[Rallylancer122]

That was my thought, to roll up a piece of aluminum and use it to "bridge the gap". I not so much worried about overall stiffness of the rudder as I am air forcing that metal out and jamming the rudder at 200+mph.

He made it sound common practice, though, so if it's not broken I won't fix it!

DEM

[Ironflight]

I'd be very cautious about doing anything other than the factory design with control surfaces. I'll be honest - I've been doing the RV thing now for a long time, and have flown a huge number of different machines - not once have I ever heard of what you are describing.

Just because a couple of guys have tried it and not had a problem doesn't mean they have explored every corner of the envelope with it, and there could be be a trap out there. There are 10,000 of these flying the way Van's designed them, and you know nothing of the pedigree of what this small faction has done.

Ask Van's - I bet I can predict what they'll say.....

[Larco]

If what I think was done? This was done by the Harmon Rocket Guys back when they were being built. You might see one or more done this way if looking at HRs at fly ins as I did one early on as well. It was decided afterwards that to avoid these kind of questions I would on future rudders just do it Vans way. Can't say it's wrong just different. Worked for me. :-) To verify, a picture would be nice to see.

[scsmith]

I think the leading edge 'D' tube does contribute a fair bit to torsional stiffness.

The torsion of multi-cell monocoque structures is resisted by the enclosed area of the cells. The cross section area of the closed D is a fair percentage of the total rudder cross section at any station, perhaps 20% or so.

You wouldn't want to just willy-nilly reduce the stiffness of anything by 20%.

[Rallylancer122]

Originally Posted by Larco

If what I think was done? This was done by the Harmon Rocket Guys back when they were being built. You might see one or more done this way if looking at HRs at fly ins as I did one early on as well. It was decided afterwards that to avoid these kind of questions I would on future rudders just do it Vans way. Can't say it's wrong just different. Worked for me. :-) To verify, a picture would be nice to see.

Larry,

So this is a Rocket thing? Just trying to make sure that if I keep that way (which is not yet decided) it won't kill me.

Thanks,
DEM

[Larco]

A picture would be worth a lot. I would need to see for sure before saying.

[vlittle]

The Rocket way:



The way I did it (on my Rocket):