First taxi, can't straighten after starting a turn.

[haribole]

I got my engine tuned and did my first taxiing yesterday. It was exhilarating to feel the plane move on its own power after sitting in pilot seat for over a decade and dreaming.

I was expecting it to go straight, initially it seemed to, but as soon as I tried to steer it with a gentle press on the left brake pedal, it did start turning left, but would not straighten up. Had to run back to the hangar to get the towbar and straighten the tailwheel.

Suspecting the right brake to be ineffective, I checked the fluids and even raised up the right gear and manually confirmed that the right brake was working fine. In spite of this, I am unable to straighten it out once I start turning. And it only turns left.

I have a tundra lite tailwheel with T3 dual shock suspension. This does not have any steering and is supposed to be steered with the brakes.

Here are things I checked so far:

Both wheels turn smoothly when jacked up, and both the brakes are working ok. The tailwheel also turns both ways without any interference.

I have never taxied on a free castering tail wheel before, not sure if I am doing this right.

Thanks
Hari

[jaredyates]

Congrats! The Bearhawk is very heavy on the tailwheel compared to most light taildraggers. Are the other guys running the t3 only steering with brakes? I haven't tried the T3, but taxiing with only brakes does require some finesse. And you might have to let it roll a little so that the wheel has time to come around, which means planning ahead more than you'd need to with direct steering.
When it wasn't working, was your right wheel still turning with full right brake pedal, or were you able to lock the wheel but still stuck? If the latter, try more of a tapping motion to let it roll some. If you weren't able to lock the wheel, cinsider the brake suspect.

[jim.mclaughlin924]

Do you have a parking brake?

[svyolo]

Left wheel nut may not be torqued enough, or one of the bearings might not be installed correctly. Turns OK with no weight on it, but bearings bind or the brake disk drags with weight on wheels?

Just an idea.

[haribole]

Congrats! The Bearhawk is very heavy on the tailwheel compared to most light taildraggers. Are the other guys running the t3 only steering with brakes? I haven't tried the T3, but taxiing with only brakes does require some finesse. And you might have to let it roll a little so that the wheel has time to come around, which means planning ahead more than you'd need to with direct steering.
When it wasn't working, was your right wheel still turning with full right brake pedal, or were you able to lock the wheel but still stuck? If the latter, try more of a tapping motion to let it roll some. If you weren't able to lock the wheel, cinsider the brake suspect.

Thanks Jared, will have someone observe the right wheel when I try this again.

jim.mclaughlin924 I do have a parking brake, haven't tested that yet.

svyolo Thanks, Will double check the torque on the wheel nuts. Wondering how to check if the bearings bind or disks are dragging with weight on the wheels.

[jim.mclaughlin924]

Check to see if your left brake is releasing right away when you release pressure on the pedal. Had this problem on another airplane when the valve in the parking brake was sticking.

[zkelley2]

This is one of the many reasons I dont run a parking brake on tailwheels.

[Battson]

Baby out with the bathwater...

[Bdflies]

The caster angle, or more correctly, swivel angle is quite important on a free castering wheel. If the swivel axis is tilted forward, the wheel will tend to self center. If it’s tilted aft, it would tend to remain turned when displaced. As Jared says, Bearhawks have heavy tails, which will exaggerate this.
I don’t know what adjustments are available on your system, but be sure the swivel is close to vertical.

Is this a flat spring or round installation? I understand the T-3, but slack in a round bar-to-fuselage joint would allow the unit to cock over in a turn.

Bill

[haribole]

Thanks Bill, that is what seems to be the issue here, coupled with some more issues in the wheel nut torque etc. I think this angle can be adjusted with some spacers at the mounting point.

Screenshot_20200609-124629.jpg

Screenshot_20200609-094811.jpg

[svyolo]

Can you take another picture of it from the side, tailwheel centered, level with the tailwheel?

[whee]

You have a very positive caster angle wish is good for preventing shimmy but can be challenging when running a big tw tire. With a positive caster angle the tail is raised a little when the tw is straight. With a big tw the fork is longer so the tail is raised more, there is a larger twisting force placed on the tail spring (long fork=longer lever) so it takes more aggressive braking and throttle to straighten out the tw. The natural resting position of the tw will be sideways. Running unchained makes this even more challenging.

[John Bickham]

Never thought about it till this post, the brake break in would be a challenge for me with a free castering tailwheel. I'd need a wide runway. I know the brake won't behave or have a lot of stopping power till broken in correctly. May be a little part of the issue?

[AZBearhawk272]

With respect to the T-3 tailwheel installation. There is a
situation that is problematic and prone to early failure.
One of the Bearhawk’s on the North Dakota Passport
challenge is equipped with the T-3 Tailwheel. We like the tailwheel. It works well. The point of failure is the
attachment of the Tailwheel to the aft saddle support below the tail post. The aft support cracked from the attach holes outboard and in the corner where the gussets are bent forming the attach plane where the
eyebolts connect the T-3 to the bracket. The concentrated point load applied through the eyebolt causes the plate to flex and crack out.

Situation fixed by Welding a solid block going crosswise
to the saddle plate below the tail post. This block has a hole running through crosswise. Block is sized to fit just inside the T-3 mounting plates and a single bolt goes horizontally securing the tailwheel assy to the spring saddle mounting plate.

Once you see the failure there is an AH Hah moment.
Heavy tail wheel loads, when turning, huge torsion moment being reacted through thin un supported plate...........

Stock tailwheel spring, the bolt hole ears only hold the clamp and NOT point load weight of the tail.

Kevin D
Bearhawk #272

[whee]

With respect to the T-3 tailwheel installation. There is a
situation that is problematic and prone to early failure.
One of the Bearhawk’s on the North Dakota Passport
challenge is equipped with the T-3 Tailwheel. We like the tailwheel. It works well. The point of failure is the
attachment of the Tailwheel to the aft saddle support below the tail post. The aft support cracked from the attach holes outboard and in the corner where the gussets are bent forming the attach plane where the
eyebolts connect the T-3 to the bracket. The concentrated point load applied through the eyebolt causes the plate to flex and crack out.

Situation fixed by Welding a solid block going crosswise
to the saddle plate below the tail post. This block has a hole running through crosswise. Block is sized to fit just inside the T-3 mounting plates and a single bolt goes horizontally securing the tailwheel assy to the spring saddle mounting plate.

Once you see the failure there is an AH Hah moment.
Heavy tail wheel loads, when turning, huge torsion moment being reacted through thin un supported plate...........

Stock tailwheel spring, the bolt hole ears only hold the clamp and NOT point load weight of the tail.

Kevin D
Bearhawk #272

Big tail wheels significantly increase the torsional force created by the tw when heavy and turning. Now that the tailwheel is solidly fixed to the saddle that torsional force is now a bending moment acting on the tail post. Watch it for cracking at the lower rudder hinge.

[AZBearhawk272]

True,

Been there, done that on a standard Bearhawk with leaf spring. The T-3 setup applies the loading in a non optimal manner. Devils in the details, got to keep an eye
on the hardware. The bigger the tail wheel the more vigilant one needs to be about ground handling.

Kevin D

[Battson]

With respect to the T-3 tailwheel installation. There is a
situation that is problematic and prone to early failure.
One of the Bearhawk’s on the North Dakota Passport
challenge is equipped with the T-3 Tailwheel. We like the tailwheel. It works well. The point of failure is the
attachment of the Tailwheel to the aft saddle support below the tail post. The aft support cracked from the attach holes outboard and in the corner where the gussets are bent forming the attach plane where the
eyebolts connect the T-3 to the bracket. The concentrated point load applied through the eyebolt causes the plate to flex and crack out.

Situation fixed by Welding a solid block going crosswise
to the saddle plate below the tail post. This block has a hole running through crosswise. Block is sized to fit just inside the T-3 mounting plates and a single bolt goes horizontally securing the tailwheel assy to the spring saddle mounting plate.

Once you see the failure there is an AH Hah moment.
Heavy tail wheel loads, when turning, huge torsion moment being reacted through thin un supported plate...........

Stock tailwheel spring, the bolt hole ears only hold the clamp and NOT point load weight of the tail.

Kevin D
Bearhawk #272

This is good information (above).

Having broken the tailwheel off a couple of times now, including breaking the spring, those bolts deal with a lot of stress. This shows that the T3 loads them up somewhat differently to the leaf spring. The leaf spring allows twisting and sliding which reduces the stresses on the airframe.

I don't understand the fix but it sounds concerning. If there's enough stress to break those attachment plates, strengthening the plate is only going to move the stress further into the airframe.

[yateselden]

I have the same situation as Hari. It's a T3 w/ Eric tundra setup. Bill is exactly right, when I turn the tailwheel 90 deg. It lowers the tail (demonstrated, turning by hand) and is difficult to get it back centered. (lots of power) Long fork leverage as Whee said. Not sure there's an easy fix, but wouldn't forward stick and getting the weight off the tailwheel help this situation? Landing would be different that's my concern

[svyolo]

To me that sounds like the tailwheel is statically unstable. As soon as it goes off center, it wants to go further off center due to gravity. And it takes a lot of force, fighting gravity, to get it back to center

[yateselden]

You have described it to a T. When the tailwheel is 180 deg. It actually works better when returning the plane to the hangar. I assume I will have shimmy, unless I change the king pin angle. All new to me

[Battson]

... when I turn the tailwheel 90 deg. It lowers the tail (demonstrated, turning by hand) and is difficult to get it back centered. (lots of power) Long fork leverage as Whee said. ...

This is true for any tailwheel with the king bolt at the correct angle.

As you add weight into the plane, the king bolt angle will start approaching vertical, and reducing the forces required to re-centre. It's a self-correcting system.

Are you guys using strong enough tailwheel steering springs??
You need a spring with a barrel about 1" diameter, and the spring steel needs to be at least 3mm in diameter. 2.6mm spring steel will not be strong enough to command the tailwheel without using brakes / power to help.

Bearhawk tailwheels can shimmy on hard surfaces, if you put a lot of weight on the tail while moving too fast. On grass, shimmy is never a problem in my experience.

[yateselden]

Thanks for the tip, I think my springs are smaller. My hanger mate and I were both surprised at how large the springs were for his C150

[yateselden]

I have the compression type of spring. Wire is heavy.