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Options for a higher breakout force on tail wheel?

riobison

Well Known Member
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
 
Is it possible that your existing locking key is worn? I recently had the situation where my tailwheel would lock to the right but not to the left. I removed the key and spring attach arm and both were worn. I replaced the key and turned the arm upside down and got back to very strong locking force.
 
This is very common when the slot in the arm gets worn - check it carefully to see if the edge of the "U" slot is rounded or sharp - they aren't very costly to replace. Temporarily, you might be able to flip the arm over - they generally wear asymmetrically (top to bottom).
 
So my lesson from this is

Hello Chris and Paul

I have it apart again and looking at it and its still clean, the key and spring looks good , the arm does show a little wear so it needs to be changed for sure. On the mounting socket the brass bushing needs to be replaced as the tail wheel fork has a tiny bit of play in there when its bolted together. As well there is a small bit of movement where it bolts onto the stinger.

I have the Vans set up on my RV4 with 600 hrs on it. It appears to be stock except for the tire that I put on a 100 hrs ago.

The wheel locks and releases as normal. But when I think about it, the wheel has not taken as much brake these days to unlock it to swing it around.

On Saturday when doing a cross wind landing with a lot of gusts to 25 knots with an average of 45 to 60 degs off the run way heading I could keep it straight until I slowed down and let my tail down. As soon as the tail touched the plane immediately weather vaned into the wind and off the run way and into the Alf alpha on the side of the runway. (no damage:)) I know my cross wind component was around 20 knots or maybe even more with the gusts. But the little wheel felt to me as well as my girl friend riding shot gun in the back that it had unlocked as soon as it started taking a load. I had full rudder and then got some brake on it as well but there was no changing its course. The skids marks are still there from the braking and the tire locking and letting go on the pavement, through the gravel and into the alp alpha.

So my lesson from this is that there is more than sufficient rudder while doing the approach and side slipping in and during the touchdown.

But when the plane gets slowed down and the tail is coming down there is not enough rudder with or without the brake to keep it straight at least on my RV4 especially if the little guy comes unlocked.

So I need to restore the little wheel to like new or better.

And above all not tackle anything much over 15 knots direct cross wind component. Next time I might not be so lucky.

Do any of the aftermarket set ups offer a higher breakout force? Or is the factory one sufficient when its like new? I could possibly add a little longer spring to put a little more tension on the pin. That would be another option.

Thanks
Tim
 
?force? is not what is intended to release the key from the steering arm, I think all the manufactures use the same method, the key climbs a ramp inside the yoke as the fork is deflected, the ramp pushes the key back disengaging it from the steering arm, if the fork has not been deflected sufficiently to cause the key to be pushed out of the steering arm then it should not disengage regardless what the force is, if it is disengaging without being deflected then the arm or key or both are worn out
 
What material is your steering arm made out of?

The early ones were made out of aluminum and didn't hold up well (corners of notch got rounded off as described by Paul).

It was changed to being made out of steel about 15 years ago.
 
?force? is not what is intended to release the key from the steering arm, I think all the manufactures use the same method, the key climbs a ramp inside the yoke as the fork is deflected, the ramp pushes the key back disengaging it from the steering arm, if the fork has not been deflected sufficiently to cause the key to be pushed out of the steering arm then it should not disengage regardless what the force is, if it is disengaging without being deflected then the arm or key or both are worn out

Russ is correct, but if the notch in the arm begins to get worn, the tail wheel will start to release at a smaller deflection angle than is intended, because the ramp is no longer needed for it to happen.
 
Just to address one comment you have made twice, I would not use a longer spring. Stiffer maybe but longer may prevent the key from retracting all the way.
 
If it is a STEEL arm, some have used a round file to clean up the slot and make it deeper by a couple thousands. One of the aftermarket venders has recommended this and it seems to work very well. Larry
 
I'll change out the arm as there is a small bit of wear (still not sure what is acceptable wear) put in a new spring and key as they are cheap and should be good to go.

I take it that if everything is like new then the design is good and sufficient to do its job even in strong cross winds.

I lifted the tail off the ground and put a scale on the trailing edge of the wheel and it took 3 1/2 to 4 pounds of pull to disengage the little guy in either direction. I used a small scale to measure the pull. Not overly scientific not overly accurate but it is a bench mark.

Will compare the measurement with the new parts installed.

Thanks
Tim
 
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!!! :eek:
 
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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.
 
Fork it over!

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.
 
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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.
 
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.:eek:

Thanks guys

Tim
 
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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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
 
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.
 
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.

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).
 
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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Tail wheel locking options

Gents

After changing parts and evaluating everything I'm sure my tail wheel is and was working properly. The tail wheel and parts have consistently been inspected, cleaned, lightly oiled and function tested every 25 to 30 hrs. I have religiously followed this procedure as it has been posted for the last 3 yrs that I have owned the plane. I have the screen door style chains and they are set with a good 3/4"slack with the tail wheel on the ground. With the wheel in the air and with almost full rudder deflection it WILL Disengage the wheel. (that is the design that I have) If I maintain this much rudder while side slipping in and trying to keep the plane lined up, the wheel will be in a free castering mode and the plane will weathervane and take off like a lawn dart into the wind as soon as the wheel touches down. The only real way around that is that I would need to relax the rudder somewhat to get the wheel to lock in before setting the tail wheel down. With a real strong cross wind that would be for the most part would be impossible to do in the majority of cases.

Some of the options that I'm seeing would be to cut the groove back a bit as Vince suggests but there are pros and cons to this with probably minimal gains. With full rudder deflection the end result would probably be very similar. A mechanical style locking tail wheel like on the Harvard or maybe with an electric solenoid and pin.............................Or I will probably accept my direct cross wind component with this plane as being around the 15 knot mark.

Thanks

Tim
 
Tim,

If you cut the groove all of the way around the inside of the housing (please don't!) then your tailwheel would never unlock. So, there is also some point along that groove where your tailwheel won't unlock with rudder deflection under normal conditions. It sounds like your groove wasn't cut sufficiently around the inside of the housing. It's easy enough to fix. A 5/8" end mill will do the trick.

This ain't my first rodeo.... if you want to pop the top off of your tailwheel assembly and shoot me a photo or two, I might be able to spot the problem. Something sure seems amiss.

send to [email protected]
 
Tailwheel breakout rudder angle angle

Hi All,
I installed my tailwheel chains today on my JD tailwheel assembly, maintaining approximately 1/2" slack (hard to adjust with the adjustments being one whole link) on both sides when centered. When checking the rudder throw, I noticed that the tailwheel would unlock about 5 degrees before the rudder would hit the stops. The stops are precisely shaped so that the rudder meets the required 1 1/8" inch clearance from the elevators on both sides.
Should this be the case, or do I need to slacken the chains further? My concern with slackening the chains further is that it could make the thing interesting, as the next link makes the chains super loose.
To fully demonstrate my lack of tailwheel understanding, at what angle should the tailwheel be disconnecting, if at all (unless of course you stand on a brake to purposely unlock it)? During the 9 hours training I have spent in a tailwheel RV, for much of it the tailwheel was not working correctly as the locking mechanism had failed, so I don't have a lot of practical experience to go by.
Tom.
 
Hi All,
When checking the rudder throw, I noticed that the tailwheel would unlock about 5 degrees before the rudder would hit the stops.

This is an undesirable action and should be corrected before flying in my opinion.

Adding even more slack to the chains is not a good way of resolving the issue.
Reworking the tail wheel for full throw without releasing would be the correct fix.
I am not familiar with the inner mechanics of the JD tail wheel so I can't recommend how to adjust it.
 
How to fix it...move the attach points inboard on the rudder horn to change the ratio. And get all the slack out of the chains. Preload the springs a bit as necessary to make the connections. Remember, the release pin retracts based on yoke angle, not rudder angle. Given a sideways push, slack just allows more yoke angle for any given rudder angle.

The eyebolts drop the attach point lower, so the chains/cables/rods/whatever don't scratch the bottom rudder cap

 
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Thanks Scott and Dan.

Dan a further two questions for you. First, are the castellated nuts on the AN115 cable shackles fully tightened up with the pivot point being between the cable shackle and the spring, or are they just pinned loose so they can swivel in the tail wheel holes? Secondly, I presume that you can move your rudder to both stops by hand without the tailwheel unlocking using the new bolt positions in the rudder horn, so is the only way you can unlock your tail by standing on one brake?

Thanks.

Tom.
 
First, are the castellated nuts on the AN115 cable shackles fully tightened up with the pivot point being between the cable shackle and the spring, or are they just pinned loose so they can swivel in the tail wheel holes?

Pinned

Secondly, I presume that you can move your rudder to both stops by hand without the tailwheel unlocking using the new bolt positions in the rudder horn, so is the only way you can unlock your tail by standing on one brake?

I should probably put the tail in the air and check fine details of rudder travel, etc before offering a transferable absolute. Frankly I've never paid much attention to exactly how much side force it takes. I just swing into a parking space with a brake, and it works. Pretty sure doesn't unlock if I merely taxi slow with the rudder against the stops.
 
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Tailwheel

If you cant keep the airplane on the runway with full rudder deflection and brake application the tailwheel which probably has less than 45lbs of weight on it will probably just skid the same as your main tire did anyway.

If you ever had the non full swivel tailwheel you may have experienced this...

Cm
 
I presume that you can move your rudder to both stops by hand without the tailwheel unlocking using the new bolt positions in the rudder horn, so is the only way you can unlock your tail by standing on one brake?

Tom, amazingly enough, I actually remembered to check...

If I stand behind the slowly rolling airplane and move the rudder to the stops, the yoke remains locked. However, if I add some lateral force (i.e. shove the tail sideways), enough to stretch a spring, the additional angular deflection of the yoke will allow it to pop into full swivel.

Note two possible adjustments. Moving the rudder arm connection points inboard decreases yoke deflection for any given rudder deflection. Set that ratio so full rudder deflection doesn't deflect the yoke quite far enough to reach its unlock angle. Now, the additional lateral force necessary to unlock is a function of spring stiffness.
 
Thanks for checking Dan. I also remembered to give Jason at JD Air Parts a call and ask him for his position on things, given that there must be hundreds of these setups out there with the with the prescribed drilling positions. He said that what ends up happening is because the contact point of the tailwheel is aft of the pivot point, the tail wheel tends to pull straight a little even at full rudder deflection, so he said it would probably still be necessary to stamp on a brake to get the thing to unlock. He also said the internal geometry setup was almost identical to the Van's tailwheel, so the unlock angles should be similar, however my thoughts now are that this will only apply in the unloaded condition or if the arm length between the contact point and pivot point center are the same, and of course only when the tailwheel is on the ground. In a nutshell, I'm going to give it a crack as it is for now. If I don't like it during taxi tests, I'll drill that next hole inboard. I'll let the guy who is performing the initial test flight know what the deal is and if he wants either the chain length adjusting or another hole inboard drilling, I'll have the gear ready to do it.
Cheers,
Tom.
 
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