Taildragger with steerable main wheels.

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captarmour

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I have thought for a long time that a taildragger with steerable main wheels should not have ground loop tendencies and should be very easy for crosswind landings as it could actually touch down crabbing with no need to kick it straight just prior touchdown. It would need a tiller to maintain its crab on the ground but steering with rudder pedals would automatically straighten it when the wheels are lined up just like we all do in a xwind landing.

Well I see now Plane Driven has done exactly that with their road able aircraft.

Would a tail wheel endorsement still be needed?
 

captarmour

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I didn't mention it because it is a mono wheel but now u mention it makes a lot of sense. A tricycle with the nose wheel the main wheel. The twin nose wheels will be more stable though.
 

Toobuilder

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The main problem with taildraggers is the fact that the CG of the vehicle is behind the main tire contact patch (high traction). The configuration is inherently unstable, and having the front wheels steerable will not change that.
 

saini flyer

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I didn't mention it because it is a mono wheel but now u mention it makes a lot of sense. A tricycle with the nose wheel the main wheel. The twin nose wheels will be more stable though.
Are you suggesting that the two mains are on the nose and the third one on the tail?
 

captarmour

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Just another way of saying taildragger in this context, sorry.

Toobuilder,

agreed, main wheels behind CG may be more stable.

the difference with steerable versus non steerable 'ahead of cg' mainwheels, is that if its steerable it can turn to keep the aircraft tracking straight even if the aircraft is sideways.
Normally when a taildragger starts to turn off runway heading it starts tracking in the direction the wheel(s) is pointing and then the whole thing comes around.
With steerable, ahead of CG, main wheel(s) when the rudder pedal is pushed, the rudder and wheel(s) will counter the turn.
If for example the steering is actuated by a tiller and the rudder not used to correct, the airplane can track the center line up to the same angle as maximum steering angle.
 

Toobuilder

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...the difference with steerable versus non steerable 'ahead of cg' mainwheels, is that if its steerable it can turn to keep the aircraft tracking straight even if the aircraft is sideways...
Understood, but you need to remember that as long as the CG is behind the wheels with all the traction (mains) the entire vehicle is unstable, so any upset will tend to get worse. Also keep in mind that the tailwheel on most airplanes is minimally effective due to a significant lack of traction. At speeds above taxi, the rudder is doing most of the work. A steerable main gear might be somewhat easier, but physics dictates that you still need to have active feet to keep it from coming around on you. In the end, the weight and complexity might not buy you any more stability than a well set up conventional (rear steer) taildragger.

If you want an example of the dynamics of this, take your car out on a dirt road sometime and lock the rear wheels with the emergency brake. the front wheels are free to roll and steer (high traction), but the rear wheels have almost zero traction - just like an airplane tailwheel. Is it easy to keep straight? Sure, as long as there is no swerve. ...But once that back end starts to come around, you better catch it quick!
 

bmcj

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Toobuilder is right on the points he makes.

I'd like to add that a steerable main gear on a taildragger has the potential to arrest a swing at the beginning of a ground loop, but it will do so by matching the direction of the swing and cause the whole airplane move sideway away from the centerline.

Another potential problem is that the dynamics of a steerable main gear and the rudder differ. With a steerable tailwheel, the rudder and the tailwheel try to push the tail in the same direction. As weight transitions on or off the tailwheel, the transition of the truning forces are congruous. With a steerable maingear and right rudder input (for example), the force will transition from a pull to the right at the front of the plane to a pull to the left at the tail. Force changes like these can be undesirable at the critical moments of takeoff and landing.
 
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Dana

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A solution in search of a problem... like the nosewheel... :)

There were a number of tailwheel aircraft that had spring loaded castering main gear. I believe the Cessna 195 was one of these, along with some larger aircraft. The idea was to make crosswind landings safer, but it made crosswind taxiing difficult. Many of these aircraft now have conventional rigid gear.

-Dana

The Bill of Rights goes too far--it should have stopped at "Congress shall make no law".
 

Dan Thomas

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A solution in search of a problem... like the nosewheel... :)

There were a number of tailwheel aircraft that had spring loaded castering main gear. I believe the Cessna 195 was one of these, along with some larger aircraft. The idea was to make crosswind landings safer, but it made crosswind taxiing difficult. Many of these aircraft now have conventional rigid gear.
The Cessna 170 had castering mains as an option. Way back in the late 1940s or early '50s. Wasn't too popular. The wheels had very large but light ball bearings for the wheel, and the inner races were on a casting that was pivoted vertically to the gear leg. The pivot was forward of center and had a spring-loaded detent in the straight-ahead position. The idea was that a pilot could land in a crab and the gear would pop out of the detent and track the direction of travel. The problem was that there was then no definite tracking direction and the wind could push the airplane sideways off the runway anyway. Limiting the pivot range just meant a ground loop once the travel limits were reached.

As Dana says, it a solution in search of a problem. If one wants an airplane easy to taxi, take off and land, he should limit himself to trikes. If one wants to learn some real skills, he should get the training that allows him to handle taildraggers in all conditions.

I would bet that as many trikes as taildraggers get bent due to inept handling. Maybe more. I've seen trikes run off runways in crosswinds, I've seen the upwind wing rise in a crosswind landing when the pilot thinks the flight is over and neutralizes the ailerons, I've seen trikes porpoising down the runway. Whatever you want to fly, learn all you can about it and get some good training from people who take it seriously, not from those just trying to build their own hours at your expense. Besides, it's not really that difficult to master the taildragger. There are just way too many myths about it that scare those who have never tried it. If you can learn to ride a bike, you should be able to learn it easily enough. Nobody suggests training wheels on bikes for adults to prevent falling over, do they?

Dan
 

saini flyer

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I do not think the quickie has mains where the nosewheel sits. They are exactly where the taildragger mains needs to be but I may be wrong. I think a better example is the Cierva C-30 gyrocopter where the mains are on the nose wheel but it is not a FW and I do not know much about gyro anyways. Also, I can learn a few things about the C-30 landing gear vs a standard taildragger if someone knows what gives?
cierva_c-30-s.gif
 

captarmour

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My initial thought was with a fixed tail wheel, thought I had said it, sorry.

Would be interesting with all wheels castoring, like flying on the ground. I have this vision of runway 9 wind from 180 at 10, start ground roll on hdg 140 and by rotation hdg about 110. Lock the wheels for taxi.

On a more serious note, the issue was not that it would be more stable than a tricycle but more stable than a taildragger. As we have said it has been tried before, didn't work. It would be nice to get feedback from Plane Driven to see how it works in their application.

on a different note, I have seen very experienced pilots, even factory test pilots put the wrong wing down on a xwind landing.
A few years ago I think I figured the psychology behind it. muscle memory might be taking over and we inadvertently turn to the runway with the yoke.
I used to train pilots on the dash8 300 to 'Step on the runway to center the runway', just like you step on the ball to center the ball. Always worked.

thanks for your thoughts, much appreciated.
 

captarmour

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Had a look, just about everything is covered there.

Just was reading about FAA making a settlement for pax and pilot for damages due to 737 being blown off the runway by 40 knot crosswind gust. The report did say that the crew had inadequate crosswind training and the captain did not use rudder to counteract the gust.

I wonder how effective a taildragger trainer, with castering main wheels/differential braking, would be in teaching crosswind rudder skills to students?

The big difference requiring transition training back to none castering landing gear would be the touchdown alignment, but would certainly teach rudder skills on takeoff. The take off roll in particular would teach the influence of crosswind to groundspeed ratio. Even taxi on a sloping runway would require crabbing. It would probably be the closest thing to flying while still on the ground.

one of the big mistakes I see on approaches is when, close to DA, on an ILS for example, the runway comes into view off to one side the pilot turns to the runway and promptly gets blown off the extended runway center line. It takes discipline to maintain the crab as it is counterintuitive.

As I say at a height of about 10% of rate of descent, start stepping on the runway (like we step on the turn and slip ball) to align for touchdown. Keeping that in mind prevents muscle memory from kicking in and causing a turn to the runway with the yoke. We tend to automatically turn to where we are looking, like riding a motorcycle for example, so its good to have a memory jog to keep us from instinctively making the wrong input.

...
 

delta

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This may be one solution for a roadable aircraft's gear. The steerable main wheels for the road with locked rear wheel, and the other way around for air operations. The ground angle of incidence would be adjusted by lowering the powered tail wheel.
 

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bmcj

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Sure. I've often advocated such a gear arrangement. Of the 3-wheel arrangements, this is by far the most stable and controllable in my opinion.
 
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