Stick 40

HI,

I have the hanger 9 J3 ,.40 size cub with a saito .56 on it. Great plane and lots of power, but I have been having ground hanling problems. So I took the wheels off and bent the metal gear until I had some toe in.

But I can't remeber if the wheels are to be stright up and down or should there be some , I guess you would call it camber. I mean like vertical toe in????

sticks

Flyboy Dave

My Feedback: (21)

....yes. Tilt the tops of the wheels away from each other, and the fronts of the
wheels towards each other. The plane will track straight like this, instead of
wandering or ground looping.

FBD.

Stickbuilder

Since the main wheels don't steer, you don't need to introduce camber or even caster. About 1 degree of toe in (total) should be okay. Nose wheels and tailwheels do need a little caster to remain tracking straight ahead. Caster dictates that the wheel involved wants to roll straight ahead instead of wanting to swivel. You want the axle to be well behind the centerline of the gear strut. But again that's only on the wheels that actually are steerable. Some taildraggers, and some light private aircraft will appear to have a little positive camber in the air, but on the ground with the gear loaded, vertical is what you want. Look at a full scale cub flying. The gear is unloaded, and the wheels appear to tuck in at the bottom, while on the ground, they are straight up. The main thing is not to allow the tailwheel to have too much authority (movement). A little goes a long way.

Bill, AMA 4720
WACO Brotherhood #1

Stick 40

Hi guys,

Ya , it worked . The cub handled great tonite, its like a different plane. I finaly enjoyed a flying it tonite. The toe-in was the ticket.

OH, my trainie did his first take off , fly around , and land on his own!!!!!!

thanks
sticks

Rudolph Hart

Use the rudder more smoothly

airbusdrvr

I have a Hangar-9 J-3 and several other tail draggers. Flyboy Dave is absolutely correct. Do the wheels the way he says and your takeoffs will be much better. Also, do remember that there is generally no need for full power on takeoff. So come in slowly with the power keeping the plane lined up with the runway. Then lift off at a shallow climb angle until you have a good flying speed. Then keep the power coming in toward half to full power for the climb. This procedure will prevent wing tip stalls followed by the subsequent cart wheel on takeoff.

Bozarth

My Feedback: (15)

If you think using the rudder will prevent the inherent instability (static and dynamic) resulting from Toe-out, you will drive yourself crazy. Toe-in restores stability (a force diagram would explain it).

Kurt

Rudolph Hart

Hello kurt

I've read threads here arguing for both(toe in or out)and always thought it a bit academic to be polite.If you have the same wheel measurements on either side and a prop out front pulling...

Stick 40

I did not know there was a debate about toe-in and toe-out, but let me tell you, after adjusting that hanger 9 from toe-out to toe-in its like a new plane. Take offs are a pleasure and landings are the best. I agree on puttig the power on slow and not full power on takeoff, the plane just does not need much power to take off. In fact its hard to get it to come back down for a landing.

thanks
sticks

Stick 40

airbusdrvr,

you have your wheels tilted out at the top then??? What engine do you have on your hanger 9?

Bozarth

My Feedback: (15)

Hey Old Fart,

Friendly speaking, it's not academic. It's basic stability. It also doesn't matter if the thrust is in the front or in the back. Toe-in can drastically help a tail dragger:

Consider a model with toe-out. If and when the model turns a tad bit to the right, the right wheel is now pointing even more to the right while the left wheel is more in line with the centerline of the runway. The left wheel produces less drag while the right wheel produces more drag, causing the model to turn even further to the right, and so on and so on.

Now consider a model with toe in. If and when the model turns a tad bit to the right, the right wheel is now aligned more with the runway centerline and the left wheel is pointing too much to the right. The left wheel is now producing more drag than the right wheel, causing the model to turn back to the left. We are only talking about a few degrees here.

Toe-in produces stability (the concept that the model returns to it's initial position)
Toe-out provides instabiliy.
Parallel wheels provide neither, they are neutral. If and when the model turns a tad bit to the right, both wheels are pointing to the right and neither creates more drag, so the model will continue to go in that direction.

Fun stuff.

Kurt

airbusdrvr

OS 70 Surpass II

airbusdrvr

There is an old saying that "I've been rich and I've been poor and rich is better." I'v flown the H9 Cub with wheels towed in and wheels towed out and towed in is better. My H9 Cub has well over 200 flights. Over time the landing gear had spread and the wheels also had a "tow out" condition. During this slow progression with the gear I was having more difficulty with my takeoffs. I naturally attributed this difficulty to pilot skill. One day one of my fellow club members, who also had a cub, noticed my wheel alignment. He suggested the wheel correction Flyboy Dave suggests and immediately the Cub was back to its easy flying self.

Rudolph Hart

This sounds good if i learn something out of it.You are talking straight line takeoffs right? and you always measured your geometry accurately?or did your club member measure his..if so,how did he do that??

I'll bet a little money with you two on some results,if an accurate test has ever been done.Maybe someone out there has trod this ground before?? or i can google it maybe.

Rodney

Yep, toe in is a must for easy ground handling, especially on the J3 Cub with the narrow landing gear wheel spacing. Positive caster also helps but is not nearly so critical.

airbusdrvr

I think the solution to all this for for Stick40 to tow his wheels in and OldFart to tow his wheels out and everybody will be happy. Stick40's takeoffs will be better and OldFart"s rudder will get some use.

Flyboy Dave

My Feedback: (21)

I've been flying Cub's for over 35 years. They can be the hardest of all
planes to take-off if the wheels are not set correctly....it's just the way they are.

With the wheels set the way I described, they set up an equal amount of drag.
If you have ever taken a skiing lesson....the idea is the same as the "snow plow"
technique...where the skies are tilted and pointed inward to gain stability.

If you want to see a totally uncontrollable Cub....set the wheels perfectly straight "up",
then turn both wheels "out" just a tad....

....you will find out what a ground loop is all about.

Take-off tips I have been successful with:

Only use 1/2 throttle until you pull the plane off the ground, then apply more throttle.
Start the take-off roll out with 1/2 right rudder applied, and full up elevator for the first
15 or 20 feet. The "right rudder" and keeping the tail wheel on the ground will keep the
plane from veering to the left from th prop/engine torque. Some right thrust in the engine
is always desirable with a Cub as well.

Once the place rolls the 15 to 20 feet, release the elevator and allow the tail to come
off the ground. At this point you should have enough speed so the rudder will be effective.

Release the right rudder as the plane starts to move to the right...keep the right applied
until this happens. The trick is having the correct amount of steering (rudder) and the correct
amount of throttle to keep the plane going straight until the speed is right for take off.

Increase the throttle very gently as the plane lifts off...and don't lift off until you have some
decent speed.

I think one of the reasons I've always had a Cub is because they are challenging to fly. My
last one was a built up clipped wing Goldberg Anniversary Cub with a Magnum .91 four stroker
in it. I had it for about 15 years, and sold it to a friend who wanted it. It was built like a tank.

I have a new kit in the pile....I must build it soon.

FBD.

Rudolph Hart

Hey i'm cool..at my age and with a little help from gravity,lots of things are beginning to toe out

Years back i got quite involved in steering geometry so i'm interested in what you have to say.....Subjectively..

FBD's description of technique is a good one and thank you dave.

I repeat my question above.With equal measurements and geometry on either side of the aeroplane and an engine out front pulling your model..ok can i see a force diagram bozarth if you have one? and a brief explanation of it would be much appreciated too.I feel that not to many people are measuring what they are talking about but rather rely on assumptions.

Rudolph Hart

Boz i've just seen a reference to 'tail moment' in an aviaton mag i'm reading.They say it contributes the largest force you can apply to an aeroplane while it is still on the ground,whether the engine is running or not.What do you think?

Bozarth

My Feedback: (15)

OF (I wish I knew your name, my mom told me never to call someone an Old Fart!)

Elaborate more on the article.

I'm still looking for a good applicable force diagram of the tail dragger layout online with no luck. Have you had a chance to google it too? I understand your question/concept regarding symetrically angled wheels having equal force regardless of toe-in or toe-out. I was hoping to find a good force diagram that showed the initial position of an aircraft during takeoff roll, then a plane altered from this position (from another force, such as from a side gust, torque, etc) and how the wheels produce different values of drag, depending whether they have toe-in or toe-out. This second position along with the new forces and the airplane's inertia should explain why toe-out is unstable and toe-in is stable. I'll keep searching. My aeronautical engineering studies ceased in 1988 when I graduated. I never needed to explain this stuff to anyone - I flew single seat aircraft.

Kurt

da Rock

Tail moment is different things to different people who build model airplanes. But to the aero industry, it's the force the tail has based on it's size and it's leverage. You figure out the area of the tail and multiply that by how far back it is, and you have a value to compare relative to other areasXdistances. And it's power is absolutely tied directly to the airspeed it sees. And in fact, there are two of them. There's the horizontal tail and the vertical tail. It's significant that there really isn't much written about the fin/rudder even having "tail moment". Why? Maybe because it's sort of an on and off thing. It is pretty worthless until it's up to its flying speed, and once there, is suddenly as effective as it needs to be. And has enough power from then on.

Keep in mind that those things have zero force unless there is air movement. And the force is relative to the airflow over the surface. So when a Cub for example starts to taxi, the tires start out with the possibility of causing extremely more effect than any of the surfaces and keep that edge until airspeed has been built up. If you look at the battle between the tires trying to yaw the model and the fin/rudder trying to keep the airplane straight, it's not a fair fight. A Cub's fin/rudder really don't come online until the airplane has some speed. And one wheel can hit a bump or hole and create almost absolute STOPPING force. Until the wing helps keep the wheels out of the holes that fin/rudder is a fairly lame force.

We get a lot of our taxi problems when the fin/rudder aren't really flying yet.

da Rock

There is also a problem with the relative differences between the vertical tail and the horizontal tail. Vertical areas are almost never the size of the horizontal. And in fact, the horizontal has two sides working, which counteracts some blanketing problems. The rudder/fin is often blanketed by the fuselage or the horizontal tail whenever the airplane is yawed or pitched. And that rudder/fin doesn't have "the other side" to work in clear air like the stab/elevator has.

You'll notice that some airplanes don't develop yaw stability at the same time their pitch stability starts to work. The tail on lots of tail draggers starts to rotate the airplane and yet the rudder is almost worthless for awhile yet. Why? The horizontal tail actually is seeing a lot of "good air" that's actually at a beneficial AOA, so that tail is actually in a bonus situation. And the vertical tail is still seeing garbage air and not at all able to do much with the minimal airspeed parts of it might be seeing.

And all this time, the tires are seeing 100% of whatever force they have with the ground's bumps and holes.

The most important thing in this whole discussion of take off problems really is how hard and fast you jam the throttle. Build up the speed of airplane slowly enough and 90% of your ground handling problems never happen. "Slowly enough" is the technique. And 95% of the time, all that means is don't firewall the sucker.

Yeah, toe-in helps and toe-out usually hurts, but throttle management is what almost always works.

Stick 40

tell ya what, go out and get a J3 cub and toe the wheels out and fly it. Then toe them in and try it!!

I have been there is the past (15 years ago) and just went through this again with a new plane. History repeats itself, I had forgot in the years that went by and had to learn this again.

You can't argue with results, a humming bird can't fly??? Try telling him that in mid air. And a Cub will track better with toe-in!

Rudolph Hart

Hi kurt and old fart is fine,peter if you prefer.It seems that there are a lot of old time full size pilots here so i'll own up to being a bit tongue in cheek re the toe in toe out thing.Anyone who has throttled up a full size taildragger on initial takeoff knows how exciting things can get for your instructer.No one has yet mentioned the incredible side thrust the prop exerts against a typically flat sided fuse,you know,advancing and retreating angles of blade pitch relative to the air it is gobbling up and rapidly drawing back down the sides of the fuse.It's rotating.Dealing with gyroscopic forces generated as the prop axis changes and the tail rises?? forget the elevator for a moment please.No one i know leaves the tail wheel on the ground any longer than needed.

Da rock i see heaps of people bending undercarriages back up,down,and sideways after a heavy landing or hairy takeoff

Rudolph Hart

Hi rodney,do you have any geometry specs for a ww2 spitfire?