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3 point vs. wheel landing?

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3 point vs. wheel landing?

Old 01-04-2014, 11:12 AM
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vertical grimmace
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Default 3 point vs. wheel landing?

What is the opinion on whether a 3 point landing is preferred over a wheel landing on a tail dragger? I am of the opinion the wing needs to be at the positive angle of attack to stall properly and at the right time that the 3 point position affords. I understand in full scale it is sometimes preferred to wheel land for visibility reasons. I would like to keep this discussion relative to models though. I have noticed many of the lighter warbirds in our club bouncing their landings, while the pilots do not agree that a 3 point would help them.
Old 01-04-2014, 12:58 PM
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Rodney
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In my mind, nothing looks nicer than a three point landing with a tail dragger. Problem is, it is very difficult to always do. Just the opposite is true with a trike gear, a wheels landing there is the way to go. This requires that you touch down on the verge of a stall which takes lots of practice and familiarity with that plane.
Old 01-04-2014, 01:07 PM
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vertical grimmace
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From my book "Stick and Rudder", the 3 point landing was (is) part of the design parameters as it pertains to the length of the landing gear struts. So the length of the struts will be relative to the angle needed to stall properly at a given airspeed. Now none of this would be easy to know or execute with a model as we do not have access to the instruments. But as it relates to bounced landings, To me it seems the 3 point would help some of these pilots. That and understanding the stall and getting their planes to the proper airspeed before attempting to land.
Old 01-04-2014, 01:11 PM
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hugger-4641
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A lot depends on the surface you are landing on also. If you are on rough grass with a tail dragger, getting the tail down at or immediately after touch down is vital to preventing a nose over. But I will touch down mains first if my speed is a little too high for a full stall rather than force a stall before the plane is ready, which will usually lead to bouncing or nose overs.
Old 01-04-2014, 02:04 PM
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Originally Posted by vertical grimmace View Post
What is the opinion on whether a 3 point landing is preferred over a wheel landing on a tail dragger? I am of the opinion the wing needs to be at the positive angle of attack to stall properly and at the right time that the 3 point position affords. I understand in full scale it is sometimes preferred to wheel land for visibility reasons. I would like to keep this discussion relative to models though. I have noticed many of the lighter warbirds in our club bouncing their landings, while the pilots do not agree that a 3 point would help them.
Landing on the main wheels:
-The forward speed of the model must be high, so it can fly with small AOA (more or less horizontal attitude).
-After touch down, the CG will continue falling down, inducing a pitch up rotation, inducing a higher AOA, inducing lifting up again.
-Irregularities of the terrain will have similar effect as described above: a bump will make the model pitch up.
-In order to avoid the above, very slow descend and/or opportune coordination for pinning the wheels down (counter-act CG descend) via down elevator is needed.

Landing on three points:
-The forward speed of the model must be low, so it can fly with high AOA (tail-down attitude).
-After touch down, the CG remains level, inducing no pitch rotation (if all wheels touch down simultaneously).
-Irregularities of the terrain should not have much effect on pitch changes, unless a bump gets combined with much elevator-up input, making the plane lift-up again.
-Careful management of energy is needed, in order to reach the ground before the wing stalls; stretching the touch-down moment can be dangerous.
Old 01-04-2014, 04:25 PM
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Consider too that full size aircraft have much higher stall angles of attack than the same design as a model. That old Reynolds number issue again. So if you want a model to be at the stall angle when in a flat 3 point attitude you need to flatten the angle. Models up to around 4 foot span will stall at around 7'ish degrees AoA. The big gas engine models of over 15 lbs and at 100 inch span and bigger will stall at a more full size angle of up around 10'ish degrees. Meanwhile the full size stall angles are likely up around 15 or more degrees. That's why we see airliners "gliding" in at around a 10 to 15 degree glide slope even with their nose well up in the air. For that size and at that sort of Reynolds number the stall angle is way up well over 15 degrees. We simply can't match that with our models.

So in the end if we can land a Spitfire or Mustang model of modest to medium wing span with a nice 3 point landing it's likely that we timed the stall to the landing "just so". The model was in the process of stopping and pitching down just as the wheels touched down. But a landing without this sort of well time aggressive stall for a model will need to be a rolling landing. We just can't NOT end up with a lot of bouncing otherwise other than by sheerest luck.

Last edited by BMatthews; 01-04-2014 at 04:27 PM.
Old 01-04-2014, 04:54 PM
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vertical grimmace
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So you are saying that with a model,a wheel landing is less likely to bounce than a 3 point landing? I tend to 3 point my models most of the time unless it is a touch and go.

How about scale warbird? A light one? A heavy one? Using flaps? Many variables here. Our sport models are one thing, but this question is mainly geared toward more scale warbird type models.

Thanks for the opinions guys.
Old 01-04-2014, 04:59 PM
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I have discovered a little down elevator at the point of touch down stops any bouncing. And once learned is a much easier and smoother method.
Old 01-04-2014, 05:16 PM
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1320Fastback
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The full scale reason for wheel landings where stutural damage may occur by having the tail wheel touch first "one pointer" may transfer into our models. If you really get too slow and the tail wheel touches first it will then rotate and slam the mains down.
Old 01-04-2014, 06:59 PM
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Yep VG, that's what I'm suggesting. And on the tail draggers I've flown those with a more scale like angle at rest do tend to land consistently smoother when wheeled on than tail dragger MODEL designs that tend to sit at a lower angle on the ground.

Mind you keep in mind that when I say "wheeled landings" I'm not talking about pushing the model down and force the touchdown. I'm still doing this from a slow, nose high glide path that produces a nice predictable descent angle. But that angle is already fairly close to the stall angle. So if the model isn't at an attitude where the wheels are already in the 3 point positions then forcing a higher angle just before touchdown is going to stall the model. Which is fine if we can stall it right smack dab at touch down. Otherwise if we flare even a few inches too high and the drag produces a sharp descent the wheels slam to the ground, that kicks the nose up and we get a nice bounce or two.

So I stopped trying with a couple of my models. I just set up the slow but fairly steep glide path and just before touchdown I'll add a click or two of throttle to slow the descent and grease it on. Then I cut the throttle the rest of the way and ease in the up elevator as the model slows down to aid with holding the tail down on our usually bumpy grass field.

With that method my landings on even the most bouncy models look pro. The model hardly jostles until the weight comes onto the mains after the first 10 feet of rollout.

Of course so many other things enter into the picture. The distance of the gear in front of the CG is a major player and might even be considered as THE MAIN factor for the landing behaviour of any model.

I can't say one way or the other what flaps would do for this. My only two flapped models were sailplanes which didn't seem to care one way or the other that the flaps were down as to the angle that the fuselage touched down.

I suspect that the key is that the angle of the wings when in the 3 point attitude still needs to be at or below the stall angle. If it's not then you can't reach the 3 point angle of attack, the plane will stall first. If the angle needed for a 3 pointer is comfortably less than the stall angle then I'd say that you'd likely have a model that can 3 point nice and smooth. If not then it's going to be darn tough to get good bounce free landings.
Old 01-04-2014, 07:13 PM
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Didn't your mother ever tell you "don't get caught with your ***** in the air"?

Darrolair
Old 01-04-2014, 11:13 PM
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Generally speaking, I think many modelers land their airplanes too fast. The reason (which was touched on) is that we don't have airspeed information and there is the fear of stalling before the landing. What I like to do is find where the airplane stalls in flight. Some airplanes I have won't stall but rather mush around with full up elevator. This is important to know so you know how slow you can get when landing. On most of my models, if I'm applying around 50% up elevator on final approach I know I'm at a reasonable landing speed.
Old 01-05-2014, 01:53 AM
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bogbeagle
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I choose the wheeler when I need better control during touch-down ... such as in a cross-wind or bumpy conditions.

You eat more runway, of course. And, you generally need a flatter approach.

From the pilot's perspective, forward visibility is increased, as is the effectiveness of the flying controls. Braking ... not so much! You can lower the tail at your discretion, buying yourself time to identify/control any swing. And, just a whiff of power will allow you to fly off, if things look tricky.

Some aircraft, such as the Rapide, can only be safely landed using a wheeler ... 'cos the nasty taper incites a tip-stall.




In my experience, the wheeler calls for considerably greater levels of pilot' skill than does the 3-pointer ... which is a shame, 'cos you need the wheeler most when you are already under greater stress.


If you have a looooong runway, it can be useful to wheel on, then keep the tail up for a fast taxy right to the end; instead of landing on the numbers and blocking the runway for several minutes.

Flaps can make a 3-pointer difficult, in that some arrangements rob the elevator of authority. Obviously, they change the aeroplane's attitude at which it stalls, too.

No clear-cut answers to be had. As ever.

Last edited by bogbeagle; 01-05-2014 at 01:56 AM.
Old 01-05-2014, 07:19 AM
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bogbeagle is right about the choice with regard to crosswind landings. Done right you cross control to align with the runway putting the plane in asymmetric flight. Now you need more airspeed to avoid the stall 'cause a tip stall is what you will get. You also need more rudder authority to avoid ground looping. Wheel landings are on order. There is nothing sweeter looking than a 3-point when the conditions are right.

Bedford
Old 01-05-2014, 08:06 AM
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I understand to reasoning to prefer wheelers as stated above. It's hard to make a nice cross controlled landing without that "in the airplane" perspective. A couple of drawbacks to consider would be an increased tendency to flip over (esp in grass) and if you have stiff gear such as piano wire you will bounce more.
Old 01-05-2014, 08:42 AM
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Having flown warbird for the last 20 years, I try to make some sense of the question. Every plane is different, even the same models have different weight. Every plane has it unique flying characteristics, some don't mind a three point landing, some just are to close to stall to try a three point. It was said in a previous post that we don't have access to instruments, true and I makes judging speed tough. Although that is changing with telemetry. To sum 20 years of flying warbirds, each plane requires a lot of practices to get the landings to look good. I find even going from one of my warbirds to another causes me a little troubles some times.





Originally Posted by vertical grimmace View Post
So you are saying that with a model,a wheel landing is less likely to bounce than a 3 point landing? I tend to 3 point my models most of the time unless it is a touch and go.

How about scale warbird? A light one? A heavy one? Using flaps? Many variables here. Our sport models are one thing, but this question is mainly geared toward more scale warbird type models.

Thanks for the opinions guys.
Old 01-05-2014, 08:46 AM
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Almost forgot, throw in flaps wind direction, temperature, altitude, and any other variables and getting a really good landing gets even harder.


Next question to ask Rich is the takeoff. 99% of scale warbird pilot can't do a correct takeoff. Just slam the throttle and point it down the runway.

Ron
Old 01-05-2014, 09:24 AM
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Works every time.
Old 01-05-2014, 09:38 AM
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I agree with all 17 posts however in our models the real issues are rigidity of the landing gear and wheel assemblies. Low bounce tires and spring loaded struts will solve most if not all bouncing issues with a competent pilot at the controls. Talk with the modelers who fly heavy war birds' if you don't believe me.
Old 01-05-2014, 10:05 AM
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Consider also that, even on many so called "scale" planes, the mains and or/tail wheel are not in the correct place. Often the tailwheel extends farther below the fuse than it really should, which causes the AOA needed for a stall to be difficult to achieve before the mains touch down. My .40 sized Great Planes P-51 is a good example. I used the rudder-mounted tailwheel supplied with the kit, which probably extends the wheel at least an inch lower than a real "scale" tailwheel mounted in the correct place would.
Old 01-05-2014, 10:12 AM
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Yes, a soft undercarriage is the anti-dote to bouncy landings. Esp if it's well-damped and close to the CG.
Old 01-05-2014, 10:21 AM
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If the mains are too far forward of the CG it will promote bouncing. There are other great tips here too such as CG placement that will help.
Old 01-05-2014, 10:25 AM
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bogbeagle
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Originally Posted by hugger-4641 View Post

causes the AOA needed for a stall to be difficult to achieve before the mains touch down.

.
A very common error in design. Pattern ships are notorious for this.
Old 01-05-2014, 01:05 PM
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we had a gee bee that was a dog to land, the fix was to raise the height of the tailwheel reducing the angle of attack of the wings as the tail settled, worked for us.
Old 01-05-2014, 04:58 PM
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I've found that 3 point landings is not necessarily the best all around technique. The wheel landing provides the best overall control particularly in highly turbulent and crosswind conditions .. conditions under which you can do some real serious damage.

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