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  #11  
Old 08-11-2015, 02:57 PM
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vfrazier vfrazier is offline
 
Join Date: Jan 2007
Location: Mount Vernon, IN
Posts: 1,031
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Russ is correct. If you've got the tailwheel in trail and locked, you'd have to shear the pin to get it to unlock if the system is in proper working condition.

It is a common, but completely incorrect, assumption that the spring somehow regulates the tailwheel breakout force. There is no such thing. The spring simply pushes the pin into the locking notch. The groove inside the mount (aka the ramp) is what unlocks the pin, and ONLY at a deflection that is beyond anything normally seen on the runway. The system is designed to unlock only when making a tight turn to park, or when rotating the tailwheel around to push the plane into a hangar.

The standard Van's control arm, pin, and the ramp mentioned are typically in a less than optimal condition for the task... even when new.

We deepen the notch in our control arms, make the groove deeper, and the pin a wee bit more blunt to give a more optimal lock to the system.

You can modify Van's stuff to work better if you understand what it's doing. You'll likely need a milling machine to really do it right.

Seriously guys, these parts are dragged through mud, dirt, water, and grass and you're asking a 1/4" square pin to last the life of your aircraft! That's insane. If you're having a problem back there.... fix it!

Bottom line: if your tailwheel is unlocking at the wrong time, buy new parts. We have them. JD Air has them. Van's has them. They are all a heckuva lot cheaper than taking out a runway light!!!
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F1 Rocket and F4 Raider components
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RV and Rocket Accessories, Tailwheels, Tools, & More
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Last edited by vfrazier : 08-11-2015 at 03:02 PM.
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  #12  
Old 08-11-2015, 10:47 PM
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mach25 mach25 is offline
 
Join Date: Apr 2007
Location: Houston
Posts: 26
Default 3 point

Tim,
When the wind is really cross I always do 3 point rather than wheel landings. Learned this from experience flying Pitts and Christen Eagles that it is better to get that sea anchor dragging in the back for stability.
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  #13  
Old 08-12-2015, 11:09 AM
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smokyray smokyray is offline
 
Join Date: Jan 2005
Location: TX32
Posts: 1,620
Default Fork it over!

Quote:
Originally Posted by riobison View Post
Gents,

I'm looking to replace my Vans Tail wheel fork with something that will take a little more force to unlock it).

As well as NOT raise the rear of my RV4 any higher than what it is. (Its the shorter gear version of the RV4 that I have)

I could possible put a longer spring in with the key might help but a slightly different design might be better.

Any suggestions?

Thanks
Tim
Tim,
I operated my RV4, Harmon Rocket and RVX on less than improved landing surfaces for 25 years. I found quickly the Van's tailwheel fork and many of the aftermarket TW forks were inferior to what I required for off airport operations with an RV. I finally found a great product made by API (aviation products Inc). Their dual fork TW has the perfect amount of breakout force for crosswinds and handles my forays in The Bush with aplomb. There are other good products out there, Vince's Fly Boy accessories and the Bell which both look good. The API however, has stood the test of adversity and time with zero failures and great product support from a small company.
Highly recommended...
http://www.apitailwheels.com/products/

V/R
Smokey



PS: I too prefer wheels landings. Why? Better visibility, rudder authority (the fuse blocks the rudder in 3 pt in a 4) and ground clearance from the prop on rough unimproved surfaces. The addition of 380X150X5 tires improves ground handling and soft field performance significantly.

Last edited by smokyray : 08-12-2015 at 01:38 PM.
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  #14  
Old 08-12-2015, 12:49 PM
Berchmans Berchmans is offline
 
Join Date: Nov 2009
Location: Anchorage, Alaska
Posts: 388
Default TW Maitenance

Tim in his write up and Vince in his reply hit the nail on the head here. If the tail wheel breakout is not satisfactory then by all means address it per Vince. If you are however relying on the TW to overcome significant cross winds then you are likely headed for a ground loop. Tim notes not exceeding 15 knots of cross wind in the future and that is probably the key...my math shows the crosswind component at between 17.7 and 21.7 knots if a 25 knot gust is assumed at between 45 and 60 degrees. I have lots of TW experience off airport (not
in an RV) and really never rely on it's locking ability, sometimes it acts more like a skid than anything. The best thing to do when wind is not your friend is find someplace else to land.
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  #15  
Old 08-12-2015, 01:03 PM
riobison riobison is offline
 
Join Date: Jul 2011
Location: Oliver BC & Red Deer Alberta Canada
Posts: 308
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Hello Smokey,

I'm in the process of changing the arm, key and spring out. They old ones seem to fit ok and look good but until I can compare them to "Brand New" I won't know for sure. I've been taking that wheel apart and cleaning it every 25 hrs or so but obviously something is still not quite right.

I've been shimming the socket onto the stinger but now that I have dug deeper I see that some of the guys have gone with the tapered pin fix so that's slated to do as well. In short when I'm done it will be better than new.

I wasn't aware of the API product so will look at them. Being a short legged 4, I don't wish to raise the tail anymore than it is so maybe API is a better option.

Jeff,

With all of my old Citabrias and Decathalons, that is all I did was 3 pts with the occasional 2 pt. But for me, this RV4 is a lot easier and safer to fly it on with a wheel landing. I do get the odd good 3 pt but most of the time they are horrible.

But I'm still practicing the 3 pt.

Thanks guys

Tim
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  #16  
Old 08-14-2015, 08:33 PM
The Wizzard The Wizzard is offline
 
Join Date: Nov 2009
Location: Cincinnati, Ohio
Posts: 134
Default missing the point

If I am not mistaken early Vans aircraft had no steerable tailwheels. There are several airplanes other than vans that don't have steerable tail wheels as well.

Having said that I believe that it is pilot technique. I fly my RV-8 in crosswinds of 90 degrees at 25 kts (my personal limit, and I'm out of rudder pedal at that point as well!) and keep the tail off the ground until it won't any more. At that point my speed is very slow, maybe 30-40 knots at which point I plant the tail and control it's forward vector with the brakes very aggressively.

At the same time that I am "planting the tail the rudder has to be neutralized otherwise you will be a lawn dart to the upwind side of the runway! And that would be a great argument for not having a tail wheel that won't unlock freely. IF your rudder still has deflection towards the upwind side of the runway when the tail is planted you would want a tail wheel that lets free so the airplane tracks in a straight using differential braking.
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Last edited by The Wizzard : 08-14-2015 at 08:40 PM.
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  #17  
Old 08-16-2015, 08:38 PM
riobison riobison is offline
 
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Location: Oliver BC & Red Deer Alberta Canada
Posts: 308
Default Got the point

There was no visual wear between the old parts and new parts but I changed them anyway. The new arm was another 1 mm deeper and the spring was 5 mm longer but other wise to real wear or difference between the old and the new.

Break out force went from 4 pounds to 7 1//2 pds, surprisingly a small positive change.

But running the tail wheel through the full range of motion (up on blocks) I realized that with me using full Rudder on final and touchdown to keep it straight, the tail wheel will unlock itself at close to full rudder deflection. Obviously it wouldn't be able to lock again until the rudder is relaxed enough to almost straight and that can't happen when you are maxed out. Cleary explains why it weather vaned into the wind when I let the tail down and had no steering. I'm surprised I have missed this after all of these years. (Maybe with the Citabrias I ran out of control on final so never really got myself into this position)

I had full braking in effect with little effect (skid marks still there) When the tail is coming down, there is still some lift in the wings taking load off the gear reducing the braking action.

As we are an uncontrolled airport, all I can do is estimate the gust factor and quite possibly it was higher at the moment I was touching down.

Lots of control on final and when touching down but that's it. My personal limit on this plane won't be much over 15 knots for a direct X wind component.

Tim
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  #18  
Old 08-17-2015, 10:20 AM
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vfrazier vfrazier is offline
 
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Location: Mount Vernon, IN
Posts: 1,031
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Tim,

If your tailwheel is in trail, rudder too, then you should have to shear the 1/4" steel pin to unlock a properly working system. Obviously, that will require a lot more than 7 1/2 pounds of force. Something is still amiss with your system.

Others,
If your tailwheel is unlocking on the runway at full rudder deflection, then you may also need adjustments or repairs. The groove in the housing can be cut a bit further around the housing if necessary. There is a compromise between unlocking too soon and not having having it unlock soon enough to park easily. YMMV... all homebuilts are different.

Everyone,
Please don't neglect the tailwheel and ALL related parts. Take a look at it and try to understand how it works. Everything from your rudder stops on back to the tire itself will have an effect.
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F1 Rocket and F4 Raider components
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RV and Rocket Accessories, Tailwheels, Tools, & More
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  #19  
Old 08-17-2015, 01:03 PM
rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
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Quote:
Originally Posted by The Wizzard View Post
If I am not mistaken early Vans aircraft had no steerable tailwheels.
RV plans and kits have always specified a steerable tail wheel.
What was not the norm in the beginning was a full swivel steerable tail wheel. The tail wheel only turned as far as the rudder deflection would allow.

Quote:
Originally Posted by riobison View Post
But running the tail wheel through the full range of motion (up on blocks) I realized that with me using full Rudder on final and touchdown to keep it straight, the tail wheel will unlock itself at close to full rudder deflection.
Are you using one of the push/pull rod links instead of springs and chains?
This will happen when using one of the links, but with chains / springs the rudder usually wont deflect the tail wheel far enough for it to unlock (at least that is how it designed to operate).
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  #20  
Old 08-17-2015, 01:39 PM
SHIPCHIEF SHIPCHIEF is offline
 
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Location: Seattle
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If you use full rudder deflection for a cross wind landing, you will have released the tail wheel lock pin.
I'm thinking it is possible that you did not have a failure at all.
As another poster indicated, you need to quickly re-center the rudder over whatever position the tail wheel is.
This can be effected by the lubrication of the tail wheel king pin. If the greased is old and stiff, the tail wheel tends to stick, and needs some force to move. You can feel that when taxiing. Also, a dirty or dry tail wheel lock pin will stick in the retracted position. This sometimes happens in cold weather too, especially if some water is in the pin socket.
I always try to park my RV-8 with the tail wheel in trail and locked to the rudder. This prevents aborted take offs due to a tail wheel that won't lock.
The 'repair' is easy. Set the tail wheel spring up on a block, remove the top nut and rotate the tail wheel to disengage the pin. Then pull the assembly out thru the bottom. Inspect / clean / lubricate. Reassemble and go fly 30 minutes later than you planned.
I usually do this at least once between condition inspections, partly because we fly off a grass strip where more wheel and brake maintenance is required.
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Last edited by SHIPCHIEF : 08-17-2015 at 01:46 PM. Reason: sp
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