To fair or not to fair..

I have recently purchased a previously flying RV-4, which is currently in boxes and racks in three different hangars. As I daydream/plan its' ground up restoration, I am developing quite a list of questions. Most of them I have been able to classify through forum and archive reviews, into "do it how you like it" and "best practice" questions/answers.

One area in which I've found no answers is the question of wing root treatment. I've seen RV-4s with wing root fairings and those with wing root 'gaskets' ala Extra 300L.

As I will fly Sportsman aerobatics with this aircraft, I am particularly interested in any input from those pilots who have flown both types of wing root treatments through aerobatic maneuvers. Is there a difference?

In noise level? Stall characteristics? Top speed?

Looking forward to all of your input!

My old -3 had the simple rubber gasket style. My new -4 (not yet flying) has the wide glass root fairings. For simplicity, the gasket just can't be beet. But it does sacrifice some (maybe 2-3kts) of top speed.

Given the generous wing loading, Hershy bar plan-form and predictable airfoil; I'd honestly be _SHOCKED_ if anything at all even unperceivable changed between the two. The wing is also aligned so it's wake does not interfer with the elevator at any normal AoA/airspeed, that's why there's litte or no pre-stall buffet.

Now the acro-folk RV'rs I know install VG's to take out some of the moosh in the handling around stall and widen the acro window. I believe it snaps better too. My -3 snapped just fine, but I never did it above 80mph. The tail is is weak. Do this one carefully.

The straight-8's have had a serios problem with tail-plane stalling before the main. The apparent fix is to cleanup the gear leg root. But obviously, they're gear legs are in a totally different place than the -4 and no -4 has complained of tail-plane stalls.

All that said, all the sporty RV's are really poor-man's acro ship IF they're kept light. I hope you dont have your hopes up that this will be a compedative vehicle. It's fine for Sunday afternoon loops and rolls, but much more and you've got the wrong idea going in.

-Bruce
RV-4 Fastback
N254MM (reserved)

Thanks for your insight Bruce

No, no high level aspirations at this point in competitive aerobatics, just a desire to have an aircraft that can perform Sportsman level maneuvers. I really don't expect to snap roll it for many years, if at all. Having not built the basic structure, I will expand the flight envelope verrry slowly.

My PPL was obtained in a Citabria, including the check ride. Although it has 160 HP, it's draggy and heavy on the controls. I've flown aero in Decathalons; same issues. At the other end of the spectrum, I have access to the aforementioned 300L, but it's far too quick for me at my current skill level. Just can't keep up with 360 deg roll rate and I dish the rolls out.

Anyway, I stumbled on an unbeatable deal on the -4, which may prep me for building a -7.

That's the story to date and I greatly appreciate your considered response.

BruceMe said:

The wing is also aligned so it's wake does not interfer with the elevator at any normal AoA/airspeed, that's why there's litte or no pre-stall buffet.

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Mine shakes like a banshee just before she stalls...don't know if it's a characteristic of certain -4's, but I get a pretty good shake before it breaks....I've got the gasket wing root fairings.

My old -3 Doesn't.. Just plop nose over. I thought the -4 would too, it's so similar. I retract that statement then on the -4.

What do you think it is?

Interesting. Do either of you believe the buffet is related to the wing root treatment, or the airframe dimensions and horizontal stab placement?

Dragon Tail said:

Interesting. Do either of you believe the buffet is related to the wing root treatment, or the airframe dimensions and horizontal stab placement?

Click to expand...

I'd say no, but Van is the authority on this one.

buffett ??

I haven't tried to really horse it around at the stall. Maybe I could get it to break if I tried hard enough. That said, The 4's stall is barely perceptible. Below 70mph (75 with a pax) you get behind the power curve and it develops some sink. At and after the stall, the sink is a little more pronounced but that's about it.

In fact, the first time I stalled it, I didn't immediately realize that's what happened .

I haven't done any stalls with a pax. Maybe it would behave differently ?

John

P.S. I've got small fglass wing root fairings.....

RV-4 Acro

My Rv-4 has the old fibreglass fillet fairings. I don't get any tail shake at the stall, and not much pre-stall buffet. It doesn't stall viciously but it is easy to pull right through the stall if you aren't aware of where you have the stick.

A light RV-4 with the CG in the right spot walks through Sportsman sequences at half power. I've commented on this before , if you search you will find expanded comments. Intermediate competition sequences are also possisble, but you must be willing to flick your aircraft. The big gotchas are speed buildup - be prepared to pull the power on downlines, don't fly it like a Pitts at max blat the whole time.

RV-4 VH-PIO 250+hrs
O-360-A1A w.FP
Current Australian Sportsman Aerobatic Champion