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  #31  
Old 11-01-2012, 07:21 AM
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Ironflight Ironflight is offline
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Quote:
Originally Posted by flyenforfun View Post
Side question, does the rocket link make the tail wheel noticeably more touchy? Because I really want one..
I'd have to say yes - when you touch the rudder pedals, you get a response from the tail wheel immediately - not after you get the slack out of the chains (if you had chains). Now personally, I like tight chains, so I like the links...but for many, it is an acquired taste, and many never acquire it. It's a trade between sensitivity and "stability", and you have to pick where you live on that spectrum.

Fortunately, it is not hard to switch back if you don't like it - and you can probably even find someone willing to buy it from you if you go back to chains.
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  #32  
Old 11-01-2012, 08:14 AM
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RV7Guy RV7Guy is offline
 
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Default Check a few things

I think it is important for you to check a few things that are simple to do before going crazy checking toe in/toe out details.

We at JDair have sold hundreds of our tail links and have learned a few things in the course of interacting with pilots. (I'm sure Vince will echo some of the same things)

1) It is important to regularly service your tail wheel assembly. I do mine every 25 hours during my oil changes. I have a small saw horse and lift the tail during oil changes. I take my tail wheel assembly off, clean, inspect, regrease and reassemble. Pay attention to the locking pin. Check for burrs in both the pin and the notch. File out as necessary. After reassembly, make sure the tailwheel will break free easily before putting the link back on.

This is the most common problem we have discovered. In many cases pilots do not know when the last service was performed. Do this regularly. It is a 20 minute process.

2) While you have it apart, check that the tail wheel assembly is true with the rudder. Adjust the link as needed to get it centered with the rudder. WE have heard some have pre loaded some right tailwheel to counter act torque. Well, when you land, you don't have that torque anymore. So if you've preloaded right, guess where it is going to go?

3) Yes, the steering link will add considerable sensitivity to steering, (regardless of brand) especially if your are coming from a plane with chains. Once you become accustomed to this you'll be fine. It is easy to get behind when you are not accustomed to this increased control authority. Minimize unnecessary control inputs. Avoid "happy feet."

4) Finally, if all of the above have failed you could analyze the toe in/toe out integrity. I seriously doubt this is the problem. With thousands of RV's flying out there I think this would have reared its ugly head more often. Possible, but unlikely.

Good luck and I hope this helps. Please keep us posted so everyone can glean some knowledge from your experience.
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  #33  
Old 11-01-2012, 09:12 AM
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vfrazier vfrazier is offline
 
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Darwin is correct. Keep the stuff back there occasionally maintained and you'll wonder what all the fuss is about since you'll never have any of the problems mentioned.

We have a tailwheel and steering link tech sheet that I will gladly email anyone who asks for it. No charge. It has everything you'll ever want to know about these things and more.

Please email me directly at vincefrazier@gmail.com if you want a copy.
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  #34  
Old 11-01-2012, 10:22 AM
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vfrazier vfrazier is offline
 
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Oh gawd.... here we go again..... I think there are still some misconceptions out there about this topic.

The toe in/toe out question was thrashed mercilessly on the F1 forum a couple years ago.

IMHO, there are a few things that apply to RV, Wittman trailing rod type gear:
1) toe in and toe out are equally squirrelly. Think of it this way: both wheels are crooked regardless of whether they are toed in or out. Imagine if you could swap the wheels, they'd still be crooked!
2) applying the brakes will cause the wheels to TOE OUT. This is the reason that I say you should set the tires to toe in slightly if they can't be made perfectly zero toe.
3) it is impossible to get the tires to be perfect at all attitudes because when the tail comes up, the tires will TOE OUT. Another reason for slight toe in on this type of gear.

RocketBob is correct. Set the toe (if you can set it!) in the 3-point attitude, at typical flying weight, i.e. one pilot, full fuel, etc. Use sandbags if you're doing this during construction.

Most of the above also applies to any other type of landing gear, except #3 may not be valid for RV-8 gear (and others) where the wheels/lower gear legs are effectively (mostly) parallel to each other regardless of attitude.

An easy way to tell if you've got an alignment problem is to roll your airplane across a SMOOTH, SHINY hangar floor. If the tires squeal and squeak continually it is because they are misaligned. Fix the alignment and the squeaking magically disappears.

Also, crooked tires wear out MUCH more quickly. If your tires are shot in less than 100 hours, you might have a problem. Your choice is to fix it OR simply buy tires more often!

YMMV. What I've said above requires some thoughtful reflection so PLEASE don't go cutting off your gear legs without complete understanding of the issues involved.
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  #35  
Old 11-01-2012, 11:29 AM
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The -8 is unique among "thousands of RV's flying....".

All other tailwheel RV's have tapered rod legs swept rearward. When loaded, the gear legs spread outward. They also twist torsionally.

A few years back I did some design work to put tapered legs on a custom biplane....truss, sockets, and new legs, which I had Langair machine. Here's a screen grab approximating the load deflection case. Note how much the contact patch moves in relation to the socket axis (long red line). It is inboard of the torsional axis in flight, but moves outboard at 1G and way out at the 3.7G bounce limit. The distance from the contact patch to the torsional axis (blue line) is an arm:



If the plane of the gear leg is perpendicular to the earth while deflecting as above, there will be no torsional twist. If the leg is swept rearward (like the RV4, 6, 7), the torsional twist will result in toe out. If the leg is swept forward the torsional twist will result in toe in.

A swerve is similar to a drop, with a subtle difference. Consider an RV7 beginning a swerve to the right. Inertia rolls the aircraft to the outside; the left leg is loaded (toe out) while the right leg is unloaded and remains more or less neutral toe. This is an anti-swerve reaction.

I have not examined RV8 leg/tire geometry in detail, but we can safely assume it is similar to taper leg geometry in the way the torsional arm increases with load deflection. The primary difference is sweep; with the tail on the ground the gear sweeps forward. With load the torsional deflection results in toe-in...pro-swerve geometry.

Or so it looks to me
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Last edited by DanH : 11-01-2012 at 11:55 AM.
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  #36  
Old 11-01-2012, 11:40 AM
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Quote:
Originally Posted by DanH View Post
A swerve is similar to a drop, with a subtle difference. Consider an RV7 beginning a swerve to the right. Inertia rolls the aircraft to the outside; the left leg is loaded (toe out) while the right leg is unloaded and remains more or less neutral toe. This is an anti-swerve reaction.
Exactly right and why I set my Rocket up with a small amount of toe-out when loaded for a typical flight condition. In that condition the outboard wheel will begin to skip/bounce and so toe out in that scenario helps stabilize the airplane. All one has to do is observe the active runway from the flightline for a couple of hours at OSH and watch all the saved ground loops that happen.
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Last edited by rocketbob : 11-01-2012 at 11:44 AM.
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  #37  
Old 11-01-2012, 12:49 PM
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Quote:
Originally Posted by rocketbob View Post
Exactly right and why I set my Rocket up with a small amount of toe-out when loaded for a typical flight condition. In that condition the outboard wheel will begin to skip/bounce and so toe out in that scenario helps stabilize the airplane. All one has to do is observe the active runway from the flightline for a couple of hours at OSH and watch all the saved ground loops that happen.
I've learned alot of stuff while building this plane and I've read alot of opinions. One thing I learned through all of it is it always worked out best for me when I just did what Van's told me to do. And thats what I did and I haven't had a problem.
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  #38  
Old 11-01-2012, 12:56 PM
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Quote:
Originally Posted by flyenforfun View Post
I've learned alot of stuff while building this plane and I've read alot of opinions. One thing I learned through all of it is it always worked out best for me when I just did what Van's told me to do. And thats what I did and I haven't had a problem.
I've learned over nearly 20 years of being around Van's airplanes that not everything they come up with is optimal and there's always room for improvement. I can name a few things that were face-palm fails in my book of things Van's designed. Like the revisions of the alternate air door on the FAB box.

In this case if Van's used a socket at the lower axle on the tapered-gear airplanes like the Rocket does tire wear can be reduced to zero and the airplane can be made more stable by being able to fine-tune toe.
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N9187P PA-24-260B Comanche, flying
N678X F1 Rocket, under const.
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  #39  
Old 11-02-2012, 01:56 PM
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Bob, perhaps I'm reading Dan H's post incorrectly, but according to how I understand it, and in sync with my observations, there aren't any likely scenarios that will cause the RV trailing rod gear to suddenly toe in. OTOH, there are several factors that will cause additional toe-out.

So, explain to me again using small words, why would anyone want to intentionally build toe-out into this system? In other words, if a swerve, brake application, extra weight, or raising the tail all cause additional toe-out, why add any to begin with?
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Last edited by vfrazier : 11-02-2012 at 02:00 PM.
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  #40  
Old 11-02-2012, 02:59 PM
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Because in a ground loop or where the gear is misaligned the outside leg is loaded, the loads are applied to that wheel in a direction far off perpendicular to the wheel. If one straightened that wheel towards the vector of the load (toed it out) the force disappears, hence the skipping disappears, hence the airplane will tend to steer itself out of misalignment. You ever see the crosswind gear on a Cessna 195? Thats exactly what it does. Toeing it in in this situation will only make it worse.

If you watch an airplane ground loop (I've seen three up close) and if said ground loop fails one of the gear its always the outside gear that fails. Forget the gear on the inside of the turn because there's no load on it for it to do anything.

About three years ago I witnessed a known poor taildragger pilot ground loop and total a L-19 on a paved runway, in fact we were watching the landing because we knew how this guy lack some fundamental skills (he was taught to let go of the controls if something went wrong, no kidding...and he's damaged three airplanes). The gear failed exactly as I described.

In any situation where the airplane is misaligned on the runway, the wheel with the most load on it is going to be stabilized with toe-out.
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N9187P PA-24-260B Comanche, flying
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N244BJ RV-6 "victim of SNF tornado" 1200+ hrs, rebuilding
N8155F C150 flying
N7925P PA-24-250 Comanche, restoring
Not a thing I own is stock.

Last edited by rocketbob : 11-02-2012 at 03:07 PM.
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