by Harold Green
Copyright 2021. All rights reserved!
Published in Midwest Flyer Magazine June/July 2021
In the last column I promised to complete the landing discussion, so here goes. When last we discussed the issue, we were on short final preparing to actually land the beast. Remember, the goal is that after the landing both the airplane and the occupants should be reusable. That means we have to manage the round out, touchdown, rollout, taxi and tiedown.
In order to achieve a smooth touchdown, we need to make sure the energy level of the airplane is appropriate.
There are two forms of energy involved. The first is “potential energy.” The amount of potential energy is determined by how far above the ground the airplane is. This is traded off for “kinetic energy,” which translates to speed, the amount of which is a function of the weight1 of the airplane times the square of the velocity. That means any change in velocity has a greater effect on the airplane’s performance, than the percentage change in velocity would indicate.
For example, the difference between 65 and 75 knots is 15% in speed, but 33% in energy. This explains why both constant and correct airspeed are so important. Since, in the final analysis we will need to get rid of this energy through drag before we touch down, having the correct airspeed is critical.
Now what is correct for your airplane? That obviously depends not only on the airplane, but also on how long you wish to float just above the runway while slowing down to landing speed, also taking into account ground effect. This speed in a tail dragger performing a three-point landing is the “stall speed” of the airplane. In one with the training wheel up front, there is a little more leeway, but it would be nice to be at stall speed at touchdown.
For the tailwheel folks, a wheel landing can be performed at most any speed, but it would be really nice to be at or below approach speed, but above stall speed. Yes, Virginia, you can land a trike faster than stall speed and sometimes in a strong crosswind this may even be desirable. However, in general practice, there is no point in wearing out tires and – oh yeah – putting the airplane in a position in which control can be a challenge unless there is a reason to do so.
Next, we need to decide when and how fast rotation should occur.
The novice almost always asks, “How high should I be when I rotate?” The usual answer in a typical training airplane is about 10 to 15 feet above the ground. The trouble with this answer is that no one is going out there with a tape measure to determine height. While this advice is probably appropriate, the final answer comes from demonstration and experience. Each person develops his or her own sense of when to rotate to begin slowing the airplane. The really critical part here is the rate of rotation because rotating too fast will cause the airplane to convert kinetic energy back into potential energy and up we go again. Therefore, it is important to pace the rotation rate to the speed of the plane and the height above ground. No, there is usually no set of numbers to provide guidance. This is just by feel folks. (Remember, we are talking about the usual single-engine general aviation light aircraft here, not something like an F-15.) If you have performed this operation properly holding the airplane off, trying to keep it from doing what it is eventually going to do, the plane will continue to gradually settle onto the runway without a thump or a bounce. When this happens, the elevator ideally should be up. This is definitely true for the tailwheel folks.
For them, if the elevator is not all the way up, decreasing the backpressure can cause the plane to reduce pitch, even through relaxing the tailwheel spring, and lo and behold, you are airborne again. Not good because you wanted to land. Typical reaction is to pitch down, bounce and then, pull back, then bounce again and awaayy we go! Also, not good.
Porposing can happen in a trike also. In this case it is usually caused by one of two things: First, landing on the nose-wheel first and correcting too rapidly, or touching down with too much speed and at a high angle of attack, bounce and again awaayy we go! Frankly anything that causes the plane to increase angle of attack with too much speed for the configuration of the plane can cause this.
The cure? Very simple: For the novice, “go around.” Do it now and at full power. With sufficient experience, you can tell if the situation is recoverable, but by all means, the safest thing is to go around.
While there is much more that could be said, we have covered the basics, so let’s now go to the roll out. The goal here is to keep the airplane solidly on the ground, rolling straight ahead and firmly under the pilot’s control.
For both tailwheel and tricycle, the directional procedure is the same…focus down the runway and keep the nose pointing straight ahead with reference to some ground object and keep the airplane from becoming airborne again until speed is lowered well below stall speed.
For the tricycle, simply by keeping the power out and looking over the cowling, this is relatively easy.
For the tailwheel, life gets more complicated by two things: First sometimes one can’t see the runway over the cowling, so straight ahead means keeping the runway edges, or other appropriate object, in the same relative position with respect to the airplane’s movement. Equally important in the tailwheel aircraft is to keep the elevators at full up pitch to prevent gusts, etc., from re-launching you. In a tricycle aircraft, with heavy or gusty winds, it may be desirable to use down elevator to keep the plane glued to the runway. However, in this case be careful not to become a wheelbarrow. Tailwheel drivers doing wheel-landings keep the tail up as long as possible to maintain directional control. For both wheel configurations in a crosswind, the landing rollout should end with ailerons full into the wind. Now it is time to consider using brakes to slow down. Be careful to ensure the wheels don’t lock up on slippery pavement. Here is where I am going to express a personal opinion.
These days, the predominant procedure is to maintain flaps and other systems at landing configuration until clear of the runway. Apparently this is a result of training to prepare the student for heavy, complex aircraft. In that situation, it makes sense because with several hundred thousand pounds of airplane and many systems to configure, attention should be on controlling the airplane until it is clear of the runway or it has been brought to a near stop. The usual explanation for this in a light airplane is to prevent the pilot from inadvertently retracting the gear instead of the flaps.
In the first place in the bad old days, the knobs or control points tended to be little balls no matter their function. No longer true. Flaps feel like airfoil…landing gear feels like a wheel on edge.
In the second place, leaving those flaps out at slow speed tends to increase the lift more than the benefits of drag. Therefore, in my opinion, on wet, snowy or ice-covered runways, one is better off with the flaps up during roll out to increase brake effectiveness. I feel flaps should come up as soon as the pilot feels they are not producing significant drag. Pilots can always be trained later to wait until clear of the runway, and furthermore, most pilots will never fly a heavy complex aircraft. Hence, I believe pilots are better served by being taught how to get the most from the airplane’s they will be flying.
During the whole procedure, it is good to estimate the amount of distance required to stop versus the length of remaining runway. If it doesn’t look good, again, around we go!
At last, we are ready to turn onto a taxiway. Sometimes the taxiway comes up faster than the pilot or the controller expected. Typically, this results in locked brakes, burnt rubber and the danger of either ground-looping or running off the pavement. On a turf runway, a sideways slide can be entertaining for those watching.
The cure for this problem is very simple – don’t turn! Keep going. If at a controlled airport the controller may be snarky, but that’s alright. They are paid to solve problems like that. No matter the cause, it is better to put up with some snark-ness, than to have to explain to someone why your airplane is on its nose alongside the taxiway.
It is now “taxi time.” Normally this is a no-brainer. However, there are a couple of things to bear in mind. First, don’t be in a hurry. On a windy day, this is particularly important for both tricycle and tailwheels, but more so for tailwheels because of their ability to swivel on a dime. Tricycles can be tipped over in a high crosswind if proper aileron is not used. Second, if the taxiway is a snazzy one with centerlines, keep your airplane on the centerline to ensure avoidance with objects alongside the taxiway.
In a crosswind, remember to place ailerons into a headwind and away from a tailwind. If you have a gyrocompass with a heading bug, setting the heading bug to the wind direction will provide a guide to this as you taxi. If the heading bug is ahead of the 90-27 line, the wind is ahead of you, and if behind it, the wind is from your tail and the quadrant of the compass tells you which way to turn the ailerons. If you are taxiing downwind of hangar(s) or other major obstructions, expect turbulence and/or increased wind velocity as the venturi effect created by air moving in a restricted passage.
At the tie-down area, point your airplane into the prevailing wind if at all possible as this will avoid damage from wind moving over a control surface in a direction to bang them into the stops. Parking into the wind will also prevent your door from opening too abruptly and tearing off the hinges.
If your airplane has control locks, by all means use them, as this will prevent extensive damage should the wind come up while the plane is tied down. If control locks are not available, using the seatbelts through the control wheel or around the control stick can at least keep the ailerons and elevator from banging around in the wind.
The heavy wire locks inserted into the control column are really good, but leave the rudder unprotected. The latter is not particularly a problem if the wind is from the nose but can lead to damage if the wind is from the side or the tail.
Rudders, which are interconnected to the nose wheel, have at least some support, but using a rudder lock is even better.
It goes without saying that the airplane should be firmly attached to the ground if it is going to be left outside for any period of time or in strong winds.
So now we have completed the landing.
While we may have missed some things, I think most of your questions on this topic have been covered, at least until we hear from you otherwise.
Finally, this is also my tie-down point. After a decade of writing articles for this column on a regular basis, and many more decades training pilots, it is time to allow others the opportunity to shed light on topics not yet covered and me greater flexibility in submitting articles in the future as needed.
Therefore, until our next “go-around,” which may be sooner than we think, may all of your landings be safe ones!
DISCLAIMER: The information contained in this column is the expressed opinion of the author only, and readers are advised to seek the advice of their personal flight instructor and others, and refer to the Federal Aviation Regulations, FAA Aeronautical Information Manual and instructional materials before attempting any procedures discussed herein.