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Plane Not Capable of Takeoff - can't taxi straight.

#1
Hi friends,

I can't seem to get my custom plane off the ground. Here's a video of what I get when I try to accelerate it:

I have taken previous advice, including widening the wheelbase and giving slight "toe-in" on the wheels, and yet I still have issues. Even when I go as slow as possible, eventually the whole thing just spins out and stops. Can anyone help me solve this? I'm very sad to be having this experience where I can't even get the dang thing anywhere close to airborne.

Thanks.
 

Keno

Well-known member
#2
There are two things you can do to solve this and that is to add some right thrust to your motor mount. A simple shim in your motor mount on the left side should help you out. On a trail dragger you need to be aware that you need to apply right rudder when you see it taking a left turn. The cause of this is known as motor tork related to the prop movement counter clockwise. I am sure others can explain tork to you better than I can and also how to spell tork.
 
#3
There are two things you can do to solve this and that is to add some right thrust to your motor mount. A simple shim in your motor mount on the left side should help you out. On a trail dragger you need to be aware that you need to apply right rudder when you see it taking a left turn. The cause of this is known as motor tork related to the prop movement counter clockwise. I am sure others can explain tork to you better than I can and also how to spell tork.
But we can see it spin out in both directions. Sometimes it cranks left, sometimes right. It seems like angling the motor right would counteract if it was systematically turning left, but with it going either way, it seems like your solution would just mean that the spin-out would be always to the right, which isn't much of an improvement.
 

DamoRC

Well-known member
Mentor
#5
But we can see it spin out in both directions. Sometimes it cranks left, sometimes right. It seems like angling the motor right would counteract if it was systematically turning left, but with it going either way, it seems like your solution would just mean that the spin-out would be always to the right, which isn't much of an improvement.
I didn't count them by 90% of the spins outs are to the left. You should have a little down and right anyway to help the plane fly correctly once it is airborne.

Do you have the rear wheel attached to the rudder (you can steer it with rudder input)? Or is it free to turn on its own.

Either way I would suggest removing the wheel as it doesn't have enough sideways grip on that surface so it can't effectively counteract the tendency to spin. Make it a true tail dragger!

And if you just want to get in the air, hand launch it.

DamoRC
 
#6
Do you have the rear wheel attached to the rudder (you can steer it with rudder input)? Or is it free to turn on its own.

Either way I would suggest removing the wheel as it doesn't have enough sideways grip on that surface so it can't effectively counteract the tendency to spin. Make it a true tail dragger!
It's already a tail dragger, no rear wheel.

I'm just a little scared of hand launching due to the risk of not being able to sustain flight. I don't want to faceplant immediately. But I guess hand launching might be the only possibility.
 

SlingShot

Maneuvering With Purpose
#9
You need to HOLD right rudder and steer with small inputs. It looks to me as though the plane is doing great. Is there an experienced pilot to help you there?
 

Hai-Lee

Old and Bold RC PILOT
#10
One thing you can try which improved one of my designs for a particular customer who wanted a high power motor installation and then couldn't get it to take off was to put an extension, (Strake??), from the vertical fin forwards to the rear upper fuselage deck. I also suggested that he increase the rudder deflection and area.

This was done in conjunction with increased right thrust on the motor.

The problem seems most often to occur the moment the tail starts to lift. Try holding the elevator to MAX up to keep the tail planted until the plane gains enough speed for the rudder to function properly! DO not use the full up elevator when travelling too fast though or the plane will lift off, Point to the sky, and slam into the ground breaking into a large number of pieces!

Just what works for me!

Have fun!
 
#11
You need to HOLD right rudder and steer with small inputs. It looks to me as though the plane is doing great. Is there an experienced pilot to help you there?
I've tried everything I can steering. The moment I start to see it drift left, I slam rudder full to the right, but it still spins left. The moment I start to see it drift right, I slam rudder full to the left, but it still spins right.

I'm not even sure if I'm going fast enough to get any control authority from the air hitting the rudder at the point that it "dies".

I don't know any other pilots, unfortunately.
 

SlingShot

Maneuvering With Purpose
#12
I've tried everything I can steering. The moment I start to see it drift left, I slam rudder full to the right, but it still spins left. The moment I start to see it drift right, I slam rudder full to the left, but it still spins right.

I'm not even sure if I'm going fast enough to get any control authority from the air hitting the rudder at the point that it "dies".

I don't know any other pilots, unfortunately.
I see. Well, tail draggers are tough especially tiny ones. There is a reason airplanes evolved to tricycle gear. It's easier for everyone. You should just hand launch it to avoid the headache. I see above about the fear thing. You need to get over that! Besides, trust me when I say lifting off of from the ground is not going to make any difference in that respect. It would be better to be over grass if you can manage it.
 

d8veh

Well-known member
#13
Nearly all planes do that. You need to learn to deal with it. You should just give it full throttle and steer it sraight with the rudder. As the plane starts to move, you need a lot of rudder, then you gradually release it as the plane speeds up until you have more or less no or very little rudder at the point of take off. If you hold the rudder on too much for too long, the plane will flip the other way.
 

Merv

Well-known member
#14
Got a link to the parts you use for that? I couldn't find any good tiny wheels online.
Here are some pictures of my tailwheel. Start with a soft wire & make your self a template, to get the bends correct. Then make your gear with a hard wire, music wire or similar. You only get one chance to bend the music wire, then it will break. I use the wire from a marking flag, you can get 100 for about $10 from big box store, Lowe’s. If you live in farm country, the farm store will sell tile marker flags. The same wire, just longer. Any size wheel from 3/4 to 1-1/4 inch will work (16-30mm) something like this one . I use part of a tongue depressor (large craft stick) & pop sickle to mount, just hot glue the wire to the rudder. My push rods are also made from this flag wire.
 

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Hai-Lee

Old and Bold RC PILOT
#15
Just one final thing that you could try! DO NOT try to taxi slowly! Use the throttle as they did in WWI full on/off in pulses to get it moving and use the rudder to keep it straight. For take off, (assuming that the right thrust angle is adequate), just open the throttle to max and get the tail up and use the rudder for direction control immediately..

At full throttle the rudder will be most effective whereas low throttle settings as you try to build up speed will give little or NO effective rudder until the speed is quite high!

Just a thought!

Have fun!
 

quorneng

Well-known member
#16
One other thing, where is the planes balance point?
Any tail dragger is directionally unstable taxiing on the ground as the centre of gravity is behind the main wheels. This means that as soon as it starts to swerve in either direction it will just get worse. The further the balance point is behind the main wheels the worse this effect gets.
Your plane has a very short nose which suggests its balance point could be too far back. If it is further back than 1/4 of the wing width from the leading edge it probably wont be controllable in the air either!
Once you have the balance point in the right place for aerodynamics a tail dragger works best with the main wheels set so the tail wheel/skid is carrying as little weight as possible just enough so it does no nose over too easily. A 'light' tail load means the tail will lift quickly allowing the fin to be the controlling influence at even quite low speed. The plane may still swerve a bit but it will be stable so it will not get worse.

Notice how quickly this Tiger Moth tail lifts on take off. The tail fin along with small rudder inputs is the only thing keeping it straight for virtually the whole take run.
 

PoorManRC

Well-known member
#17
Everyone, of course, has given great pieces of Advice! I'll just add one to Merv's....
His Tail Wheel is already like this, but make sure if you're going through the process of adding Tail Gear, that you make sure you get a spongy Rubber Tire.
If nothing else, you can overcome that mad spinout with sheer Traction. That might just get you in the Air!!

...... You may also want to revisit your CG Balance. ;)
 

makattack

Winter is coming
Moderator
Mentor
#18
Hi there. Do you have a smaller prop, by any chance? Looking at some still frames of your video, it looks like as soon as your tail will lift up, and the wings become level / parallel with the ground, your prop will end up striking the ground. I suspect that plane might be a bit of a handful to fly inside the small space of the MIT "Winter bubble" tennis courts... you may want to try flying it on a soft grass field and trying some simple "all up weight" (e.g. with battery, etc mounted) glide tests to see if it'll fly well.

I'm in Boston if you need suggestions for where. Heck, the grass and turf fields around the track or along Vassar St might be good candidates for glide testing. I just wouldn't try powered flight as it's too crowded an area for that. If you're willing to travel to a good flying field with folks who might be able to help with instructional flight, Davis Field in Sudbury is great. I'm a member of the CRRC and if you're under 19, membership is free!

If you don't have a smaller prop, I probably do and can donate it to your effort!
 
#19
I suspect that plane might be a bit of a handful to fly inside the small space of the MIT "Winter bubble" tennis courts
Thanks for the advice! This is actually inside the Johnson Indoor Track, which is a very large space with a history of RC planes flying inside. I'd say it's about 150 by 300 feet. I'm also concerned about flying outdoors on a grass field just due to FAA stuff. Being near Logan Airport makes me afraid of accidentally breaking some laws.

I also don't have any form of transportation, so I'm really limited to MIT campus. Can't really get out to Sudbury.

I don't think my prop should strike the ground. It's a 10 inch prop, and from the prop shaft down to the wheel axle is 6 inches. Add another inch for the wheel radius and that makes for a 2 inch gap between the prop and the ground.
 

makattack

Winter is coming
Moderator
Mentor
#20
Well, I can help with the transportation, if it's on the weekend. I live a few miles from MIT (in Jamaica Plain) and can offer a ride to Davis Field -- where a few MIT alum are also members (including former member Dr. Mark Drela: http://www.charlesriverrc.org/articles/bubbledancer/markdrela-bubbledancer-3m.htm)
http://aeroastro.mit.edu/faculty-research/faculty-list/mark-drela

Alternatively, for something closer, I do some of my flight tests in the Brookline Larz Anderson Park or Boston's Franklin Park areas. Davis is a 45 min drive from Boston, while Franklin Park is probably about 20 minutes from the MIT campus (and also T accessible, but will take longer and might be awkward with a bulky plane).

What motor do you have driving that big 10" prop? What's the pitch on the prop? If it's not a low KV motor, I suspect it'll be really hard to overcome the torque of that prop unless you have a far longer runway in order to smoothly accelerate without a large / rapid throttle increase.

Also, glide tests won't run you afoul of any FAA regulations. The problem with MIT isn't so much just Logan (MIT is within 5 miles), but it's also all the helipads nearby with the hospitals. If you look at the restricted airspace map: http://knowbeforeyoufly.org/air-space-map/ most of our area is covered, but that doesn't mean people don't fly within it.
 
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