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toe in
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 |
RE: toe in
....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. :D |
RE: toe in
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 |
RE: toe in
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 |
RE: toe in
Use the rudder more smoothly:)
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RE: toe in
ORIGINAL: Flyboy Dave ....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. :D |
RE: toe in
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 |
RE: toe in
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... |
RE: toe in
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 |
RE: toe in
airbusdrvr,
you have your wheels tilted out at the top then??? What engine do you have on your hanger 9? |
RE: toe in
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 |
RE: toe in
ORIGINAL: Stick 40 airbusdrvr, you have your wheels tilted out at the top then??? What engine do you have on your hanger 9? |
RE: toe in
ORIGINAL: Old Fart 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... |
RE: toe in
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. |
RE: toe in
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.
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RE: toe in
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.
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RE: toe in
1 Attachment(s)
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. :D 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. :D |
RE: toe in
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. |
RE: toe in
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?
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RE: toe in
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 |
RE: toe in
ORIGINAL: Old Fart 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? 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. |
RE: toe in
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. |
RE: toe in
ORIGINAL: Old Fart Use the rudder more smoothly:) 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!!:D 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! |
RE: toe in
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:) |
RE: toe in
ORIGINAL: 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. |
RE: toe in
Forgot to add that in theory and practice for me toe out accentuates a nose down down tendency under takeoff power with the tail up.Not bad in windy conditions.
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RE: toe in
What happened??..did i fart??:)
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RE: toe in
1 Attachment(s)
ORIGINAL: Flyboy Dave 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. :D 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. :D I did some research and found that many full scale pilots recommend toe out for taildraggers too. They even mention that some cars have toe out too. http://www.mombu.com/aviation/aviato...n-1400001.html Post #8 in this thread http://www.rcuniverse.com/forum/m_48.../tm.htm#488183 said that toe out worked on his narrow geared spitfire. I don't think that the above analogy of a snowplowing skier is good because skiers can shift their weight around (fore and aft and left and right) thus changing the steering qualities of their "wheels" in a way that airplanes can't. The inward pointing of the skis is mainly done because the inward pointing skis force the knees against each other and requires less muscle strength to hold that position than outward pointing skis. As with my diagram below, the skier's direction is based on the ratio of weight on each ski. In a plow, the skier can go left by putting more weight on the right ski. |
RE: toe in
ITS ALIVE, ITS ALIVE again.
Hi thought this was dead, have not seen it for awhile. The cubs are the only RC plane I have had a problem with, as fare as the ground handleing and this toe-in vs. toe-out. It had been years sence I put a .40 size cub together and I overlooked the toe-out of the wheels. I could not do a run for take off without ground loops and the landings were no better. I found myself applying full power and pulling it off the ground as quick as I could. But after the input above and putting toe-in into the main gear, the plane turned into a great handleing plane on the ground. I even let it track with the tail in the air for 20 to 30 feet on landings without a problemI really started to enjoy flying it, and how others do it is of no matter to me. Like RC KEN said the cub was the hard to handle on the ground, and I have to agree. But if set up right they are not that bad. sticks |
RE: toe in
It's possible that the Cub is a special case where toe in is needed. That Spitfire in the link that I posted benefited from toe out, though. I don't know what the factor would between the Spit and the Cub that would make the difference. The biggest difference between the Cub and a Spitfire is the Cubs higher dihedral effect. Other comments in this thread suggested that toe in is always needed for every airplane. My experience with my H9 corsair and the full scale forum that I linked to tell me otherwise. So, I just thought I'd present the reasoning for possibly using toe out. I didn't mean to come across as telling you that you are wrong about your Cub. In the full scale forum there was a comment to the effect that toe angle can't fully compensate for bad technique. So, toe angle may be made irrelevant by poor technique in some cases. Also, there may be a gray area when toe angle preference may be entirely dependent on the pilot's technique habits. In other words, both toe in and toe out may have their plusses and minuses and the pilot uses whichever toe angle that they got comfortable with first.
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RE: toe in
I have always put toe-in into the mains of my taildraggers and trikes. I noted that the wire main gear tended to "wear" to give toe-out, so I would keep bending things to toe-in after many landings. My aluminum gear would likewise go to toe-out with usage. About 3 years ago I built a SPAD 72" WS J3-Cub with an OS46FX engine and 12X4 APC prop. It uses a carbon reinforced fiberglass gear that keeps the wheels neutral, ALWAYS. The angles do not change with usage. I have stopped worrying about the toe-in/toe-out problem. Maybe it is because it is NOT adjustable by bending the gear. I see nothing in the performance to indicate to me that toe-in/toe-out is needed. I am always amazed at how difficult the J3-Cub is to take off and land. That is probably why I like it so much. Do it perfect or it will let you know. I loved that carbon reinforced fiberglass gear so much that I used it to replace the 3/16 diameter wire gear I was using on my SPAD OS46FX size Pusher Canard. That plane lands hot on the mains and the new gear works perfect. So, neutral, if it stays neutral under load and usage, seems to work great for me. In my opinion, if toe-in or neutral goes to toe-out under load/usage, then there can be difficulties.
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