Take Offs Part 1

//Take Offs Part 1

Take Offs Part 1

It’s a beautiful day and you decide that you want to go fly your Stearman. So you go out to the airport, roll it out of the hangar, crank it up and taxi out to the runway. There you line it up, cobb the power to it and launch yourself into the sky. Nothing to it, right? Wrong! There is much more than that to a successful take-off that should serve as the starting point of a proficient and competent flight and set the tone for the remainder of that flight to follow. There are several concepts and elements of the environment that affect the operation of a tailwheel airplane that may influence the quality of a take-off maneuver. I would like to examine each of these and discuss how they all may directly apply to flying a Stearman and specifically to the take-off. The four most important components of the flight environment are as follows:

  1. Torque and P-Factor
  2. Wind
  3. Runway Surface
  4. Airplane Characteristics

Each of these above listed factors deserves a detailed discussion because each of these areas are often ignored by many pilots. Those pilots may have subsequently developed some bad habits which in a tailwheel airplane such as the Stearman can bring sudden grief. Until these factors are thoroughly understood and mastered there is little reason to discuss take-offs any further.

In most American built piston engine airplanes the engine crankshaft and the propeller turn counter-clockwise as viewed from the front of the airplane. The word “torque” is the generally accepted term used to describe the tendency of the entire airplane to rotate to the left. There are several different components of torque which affect this left turning tendency which is particularly apparent in a tailwheel airplane.

To counteract this left rolling tendency an aircraft’s left wing often is rigged at a higher angle of incidence than the right wing (“washed in”). Thus it provides slightly more lift than the right wing. But this also produces more drag and causes the airplane’s nose to yaw to the left. For this reason in many aircraft the leading edge of the vertical fin may be off-set to the left to counteract the yawing tendency to the left. An example of this is the North American AT-6 “Texan” whose vertical stabilizer is off set 1 ½ degrees to the left. In the case of our beloved Stearman a manually ground adjustable trim tab is installed on the rudder which will deflect the entire rudder which produces the same effect.

The slipstream from the rotating propeller as it flows rearward back over the airplane follows a spiraling or corkscrew path around the fuselage. When it reaches the tail assembly it is spiraling upward on the left side and impacts the left side of the vertical stabilizer. Conversely, on the right side of the fuselage the slipstream is spiraling downwards and thus misses the vertical stabilizer completely. The net result of all this is that the tail is forced to the right causing the nose to yaw to the left. The angular offset of the vertical fin, or in the Stearman’s case, the rudder deflection caused by the trim tab, tends to compensate for this effect since it is more nearly aligned with the actual direction of the slipstream as it passes over the tail section.

But since the amount of torque varies as power and airspeed changes it is obvious that built-in corrections cannot adequately compensate for all flight conditions. Most often aircraft designers chose to correct for the most common flight regime – cruising power and airspeed. The result is that for all power settings and airspeeds other than for cruise flight these corrections are either too large or too small and the pilot is required to input his own corrections.

With higher power settings and low airspeeds, as in the take-off and climb, the built-in torque corrections are insufficient and the airplane tends to yaw to the left. The pilot must input right rudder to compensate for this. Conversely, with low power settings and high airspeeds as in a dive, the built-in corrections are too much. There is less torque effect than with cruise power, yet the amount of built-in correction has not changed. Thus the nose tends to yaw to the right and the pilot will need to hold left rudder to maintain the aircraft in proper flight trim.

In almost all flight regimes other than steady state cruise flight, you will notice the effects of torque. But as experience is gained the pilot will automatically compensate for these changes in flight without really being conscious of doing so. The take-off phase of flight is where the effects of torque are most noticeable and most likely to present the pilot with control problems. In more advanced airplanes that have adjustable rudder trim tabs the torque effect can be more easily corrected and the rudder trimmed for any combination of power settings and airspeeds.

Another major component of the torque equation which greatly adds to the left turning tendency is asymmetric loading of the propeller, commonly called P-Factor. This is normally present anytime the engine is producing power and the aircraft is not moving directly in the direction that its longitudinal axis is pointed, provided of course, that the airplane has some forward speed. Note that there is no P-Factor whenever the airplane is not in motion. For example, while doing an engine run-up, holding the brakes and running the engine up to check the mags, there is no P-Factor because the airplane is stationary. P-Factor is developed because the downward moving propeller blade which is on the right side of the fuselage as seen by the pilot in the cockpit has a higher angle of attack than the upward moving blade on the left side of the airplane. The downward rotating propeller blade also has a slightly higher relative velocity with respect to the air. Aerodynamic theory shows that the higher speed and higher angle of attack of the downward moving blade both result in producing more lift, or in this case, more thrust. The ultimate result of all this is that the descending blade on the right develops more thrust than the ascending blade on the left. The final effect of all this being that the airplane wants to turn to the left.

The asymmetric thrust is a temporary condition that is primarily present only during the take-off roll portion of the flight when the tail is down. It also is present during the climb and in airborne maneuvers such as slow flight. Since most airplanes do not have any type of compensation for this built in, the pilot must rectify the situation with right rudder input.

A third factor contributing to the left turning phenomenon is the gyroscopic precession of the propeller. The prop spinning at an appreciable speed acts like a giant sized gyroscope. If a force is exerted against the side of a gyroscope, it reacts as if that force had actually been exerted in the same direction at a point 90 degrees in the direction of rotation. The disk produced by a turning propeller makes a good gyro wheel. Precession affects an airplane only during attitude changes. For example, you will encounter precession in a tailwheel airplane when you attempt to force the tail up quickly on a take-off roll. The airplane will try to get away from you as it suddenly yaws to the left. This is because the propeller is in a certain rotational plane and you are also fighting all the other previously mentioned torque effects as well. When you push the stick forward and the tail rises, the airplane reacts as though the force was exerted on the right side of the propeller disk from the rear. The result is a quick swing to the left.

All these components contribute to what we pilots call torque. This is what causes your flight instructor to utter the most often heard phrase that you hear whenever you might be receiving any type of dual instruction in your Stearman – “Right rudder, right rudder, RIGHT RUDDER!” In summation of all of this, if the airplane turns in either direction (left or right) on takeoff, correct it with opposite rudder input. But remember, whatever rudder input you put in as a correction must quickly be removed to maintain a straight path and to avoid over controlling and swerving from side to side.

Wind is forever with us. Very seldom over the course of a flying season do we enjoy the benefits of a calm day. There almost always is a wind of some sort present and more than likely it will be a crosswind. Analyzing the wind conditions should be a primary concern of any tailwheel pilot and especially those who are privileged to fly Stearmans. The wind should be monitored throughout the flight and decisions made according to its velocity and direction and your ability to handle your airplane under varied wind conditions.

Control usage during taxi in winds is very important and especially in our Stearmans. The Stearman is a fairly large biplane with a high center of gravity, narrow tracked landing gear, a large side area and a tendency to try to get away from you in a crosswind. Generally speaking the correct control inputs while taxiing are: controls into the wind while going into a headwind and controls away from the wind while taxiing downwind.

So if you are taxiing directly into a headwind the stick should be full aft to give full up elevator to help keep the tail on the ground. If you have a crosswind add in up aileron into the wind to help keep the wings level. When taxiing directly downwind the stick should be forward to give down elevator. The tailwind hitting the down elevator will help keep the tailwheel on the ground. If you have a crosswind add in opposite aileron so that the upwind aileron is down. In this case the tailwind striking the down aileron will help keep those wings down and maintain a wings level attitude. Whenever making a turn crosswind to the opposite direction of taxiing smoothly make the changes in control positions to their appropriate positions as the wind requires.

A runway is a runway! Well, not always. The runway surface and condition as well as the directional alignment with the wind are major considerations. A narrow 50 foot wide paved runway certainly will give a Stearman pilot a lot more of a challenge than a 100 or 150 foot wide one that you might find at a larger municipal airport. The surface might be concrete, blacktop, oiled rock, pea gravel, dirt or grass and it might have a gradient, sloped uphill or downhill, or might be a bit roly-poly. All have their special concerns and benefits. Just remember – grass is the great equalizer! But there could be hazards on a grass field too – chuck holes, gradients and tall grass could require special attention. But a nice grass field is a Stearman’s best friend.

Now that we have thoroughly covered the preliminaries, it is time to get down to the “nitty gritty” and examine the peculiar characteristics of a take-off in our favorite biplane, the Stearman. The Stearman has several design features that may influence the take-off which have already been mentioned in a previous paragraph. However, they again are: that it is a fairly large airplane which has a large concentration of weight in the fuel tank high in the center section which gives it a high center of gravity; a narrow tracked main landing gear with wheels that are slightly canted inboard; a large side area and a fairly powerful radial engine swinging a propeller of significant size. These all contribute to its ever present tendency to want to swap ends with you.

The take-off probably may be the biggest surprise to the pilot who is new to the Stearman. Most have probably heard the harrowing tales concerning how difficult landing a Stearman can be and all the grief that may be expected in the landing phase of flying the Stearman. I think this fear or maybe the development of a proper respect for the Stearman in the landing mode is what stays with most Stearman pilots even after they become experienced and proficient in it. (With good reason!)

However, the take-off in a Stearman can also lead to some very exciting moments if not properly performed. So it is very important that the Stearman pilot approach each and every take-off in a professional manner and give to the airplane the honor and respect that it so justly deserves.

As an example I might relate a story that a Stearman friend recently passed on to me during a telephone conversation. He had been flying with a new Stearman owner who was both a fairly low time pilot and also one with little or no tailwheel time. He had told the new owner that the checkout in his Stearman would take some length of time to prepare him to become a good, safe and competent Stearman pilot and to try not to become discouraged with his apparent slow progress. He especially counseled him not to get ahead of things and go fly his Stearman by himself. Well, for whatever reason, one day the owner decided he should just go ahead and go fly his Stearman solo. On the ensuing take-off he lost directional control and went careening off the side of the runway which culminated in considerable damage, not only to his Stearman, but to his pride as well.

So it is very important to develop a sense of respect for the Stearman starting with the take-off. For as my favorite philosopher, Forrest Gump, might say, “Lest it rise up and bite you in the buttocks!”

After a thorough pre-flight of the airplane the start of a good take-off in a Stearman is initiated when the pilot climbs into the cockpit. The pilot’s seat height and rudder pedal adjustments should be made at that time. The WW II U.S. Navy Flight Training Manual and the U.S. Navy training films both recommended that the seat height be adjusted to the highest point at which full rudder deflection was still possible. This height will provide the greatest amount of visibility during taxi. Just prior to the take-off the seat should then be lowered so that the pilot’s eyes are looking directly through the center of the windshield. The Navy designated this as the flight position. Personally, I find this recommended flight position just a bit too low for me. I prefer to sit higher than that for taxi, takeoff and landing. I like to sit as high as the seat will allow to obtain maximum visibility around the nose. But I usually lower the seat later after being established in the climb to place my head more behind the windshield.

Whatever seat height position you are comfortable with and are accustomed to using in your Stearman is what you should continue to employ. Don’t change it. But be sure to try to be consistent in your seat position so the sight picture will remain constant for each flight. Your feet position on the rudder pedals is also important. Your heels should rest on the floorboards with the balls of your feet on the lower portion of the rudder pedals. Don’t have them raised up high so as to get onto the brake portion of the pedals. While this appears to be very basic and unnecessary to comment upon, rest assured that you do not want to be dragging brakes while you are trying to accelerate on the take-off.

When beginning to taxi towards the take-off position the Stearman pilot should use only enough power to start the airplane moving and then retard the throttle to obtain a speed no greater than a fast walk. To taxi at a greater speed than that may require excessive use of the brakes and aggravate the airplane’s tendency to sway from side to side. Should the wheels hit any small bumps it also can lead to possible directional control problems, especially if you have any significant amount of crosswind.

As we all are aware the visibility out of Stearman while taxiing is severely limited by the high position of the nose while the airplane is in a three point attitude. The engine, cabane struts for the center section and the lower wings all combine to make seeing directly ahead difficult. Throw into the picture another person in the front cockpit and it can become even worse. A front seat passenger, even if they also are a pilot, invariably will hang their elbows up on the cockpit combing and lean out to the side of the cockpit to try to see where you are going, usually to the same side of the cockpit that you are also looking out. This blocks your view even more. In my pre-flight briefing to a passenger I always emphasize that I would appreciate it if they would stay centered in the cockpit and not hang out the sides of it as it impedes my view. Usually once they are made aware of this situation most everyone will comply. Once you have your Stearman underway in the taxi it is imperative that you S-turn so you can see what is directly ahead of you. S-turns do not need to be a rapid zig-zagging from side to side, but should be a smooth serpentine type movement from one side of the taxiway to the other. It is also important while taxiing to maintain constant vigilance concerning the location of the tailwheel while S-turning, especially if the taxiway is narrow or if there are taxiway lights installed adjacent to the taxiway. As you turn look out the side of the cockpit opposite to the direction the airplane is turning so you can see what is ahead of you. As you reverse your S-turn look out the other side of the cockpit.

Finally, turns should not be made with one wheel locked up with the brakes, especially on a hard surface. This can place stress on the wheel and possibly cause damage to the wheel or tire. The wheel on the inside of the turn should always be allowed to rotate slightly, even if it rolls ahead a bit. A slightly rolling pivoting turn can turn the airplane almost as shortly as one with a locked wheel and won’t burn off a bunch of rubber on the tire either! Over the years I have observed many Stearman pilots, as well as other biplane pilots, both at my local airport and at many fly ins that I have attended, who do not S-turn while taxiing. They just taxi on a straight path, quite often at a fairly brisk pace, and for all practical purposes are oblivious to what lies ahead of them. This is a very dangerous habit and one that exhibits poor airmanship. I urge everyone to slow down, S-turn while taxiing and make it safer for everyone concerned. Another item of importance while taxiing the Stearman, or any other tailwheel airplane for that matter, is of course, the tailwheel. Most all of the Stearmans that we fly today are equipped with a steerable tailwheel which operates in conjunction with the rudder movement. This provides a very positive control feature and simplifies taxi, take-off and landings in the Stearman. However, some Stearmans were originally equipped with a full swivel locking tailwheel. In most cases many of these Stearmans flying today have been modified by installing a steerable tailwheel in its place. But for a few of us remaining purists, we still have the original locking tailwheel in our Stearmans.

I might digress here slightly and present a short historical discourse on Stearman tailwheels. All of the U.S Army Air Corps Stearmans were delivered with steerable tailwheels. The U.S. Navy Flight Training Manual states that all Stearmans up through the N2S-3 version were equipped with a full swivel locking tailwheel. However, that statement is not totally accurate. “Report No A75N1-9000”, dated January 6, 1941, “Instructions for the Erection and Maintenance of the Model N2S-1, N2S-2 and N2S-3 Airplanes” clarifies this matter further. On page 70 of this manual it describes the tailwheel arrangement of the different models and on the following pages there are photos of each type. Only the N2S-2 and N2S-3 had locking free swivel tailwheels while the N2S-1 had a steerable tailwheel. So the initial U.S. Navy order for 250 Model 75s, designated as the N2S-1, delivered from September, 1940 through February, 1941 were equipped with steerable tailwheels. It is of note that the accompanying photos show that all three of these N2S models had 8 inch smooth contour ties. Obviously this was before the Navy changed to the 10 inch tire.

For that matter, most all of the Navy’s single engine airplanes, trainers, scout planes, dive and torpedo bombers and fighters, etc., were also equipped with locking tailwheels. They didn’t need a steerable tailwheel since their primary purpose was to operate from aircraft carriers and there was very little taxiing involved. There were no crosswinds either as the ship was always headed into the wind for flight operations.

However, in 1942 the U.S. Navy found that it had an urgent need for more Stearman N2S trainers. It negotiated a deal with the U.S. Army Air Corps to obtain some Stearmans that the Army had contracted for that were on an earlier delivery schedule. So from June, 1942 through July, 1943 the Navy received a total of 526 PT- 17s, 521 from the Army contract and five from Bolivia. The Navy designated these airplanes as the N2S-4. The final model of the Stearman trainer that was built was the E75, designated as the PT-13D by the Army and as the N2S-5 by the Navy. These Stearmans were the first totally standardized airplanes delivered to both services. They were equipped with steerable tailwheels.

Over the years since WW II there has been some confusion among Stearman enthusiasts and historians as to what type of tailwheel was installed in the N2S-4. As mentioned previously, the U.S. Navy Flight Training Manual incorrectly stated that the Stearman trainers up through the N2S-3 were equipped with a free swivel locking tailwheel. That would infer that the N2S-4 had a steerable tailwheel, especially since it, in fact, was really an Army PT-17.

The Navy added more fuel to the fire of this controversy when they produced a small soft covered 60 page booklet titled, “Meet the N2S.” It was a little blue pictorial pamphlet that pointed out all the salient features of the N2S and was issued to cadets at the Navy Flight Preparatory Schools. You probably have seen this little booklet and it is on sale in the retail store at the National Stearman Fly In at Galesburg Illinois every year.

The airplane used in all the photos in this booklet is painted in a standard U.S. Army paint scheme with a blue fuselage and yellow wings and tail. U.S. Navy is painted on the sides of the fuselage and N2S-4 clearly is painted on the rudder. The booklet states that the N2S has a full swivel tailwheel and an interior cockpit photograph shows the tailwheel locking handle located on the right side. Why the Navy chose to use an Army colored N2S-4 (PT-17) in this booklet instead of a standard marked Navy N2S is a good question. And who knows if this N2S-4 was used for the interior photos or if another standard Navy N2S was utilized. Well, I suppose that whatever type tailwheel was originally installed in the N2S-4 really didn’t matter too much at the time. They just used what they had. I guess that in the big scheme of things today, it’s no big deal either. But it remains an interesting conundrum.

The locking tailwheel presents a bit more of a challenge in operation than the steerable tailwheel which provides positive control throughout the flight regime. While taxiing with the locking tailwheel unlocked, turns must be initiated by tapping the brakes. To stop a turn opposite brake must be applied. One advantage to the locking tailwheel is that when taxiing in a crosswind the tailwheel can be locked to help prevent weathervaning. The tailwheel is locked for take-off and while the airspeed is low at the beginning of the take-off roll and before the rudder has become effective, you may have to raise your feet up from the floorboards onto the brake portion of the rudder pedals in order to apply some braking to steer the Stearman. Similarly, on the landing rollout, once the airplane has slowed to the point where the rudder is no longer effective, brakes must be used to steer it. But this situation on the take-off is only a factor for a short period of time as the effectiveness of the rudder is quickly obtained. This leads to a final point concerning the free swivel locking tailwheel – you must have good brakes!

As most of us are aware the brakes on the Stearman historically have been the airplane’s weak point. The original Bendix brakes were a source of constant problems and were very typical of WW II era technology. They either were always grabbing or they faded away to nothing. It seems like they always required constant maintenance of some sort. When I bought my Stearman N2S back in 1969 it still had the original Bendix brakes but had been modified with automotive brake master cylinders. I later found out that they were from a 1949 Studebaker pick-up truck. That system worked OK but still required constant attention. Every few years or so I had to overhaul the master cylinders by honing them out and installing new overhaul kits of pistons and rubber seals. Later the Stearman brakes were improved somewhat by the Hayes brake system with BT-13 wheels. But with the advent of the Redline hydraulic disk brake modification, brake problems with the Stearman have been practically eliminated. Other than replacing the brake pucks whenever they are worn and the brake discs every so often, it is a maintenance free system that works great. They operate just as well as the brakes in a C-172 or a Bonanza or any other typical modern light airplane.

The Redline brake system certainly is not cheap, but it is the best modification I have ever made to my Stearman. It is worth every penny! If you have a Stearman with the locking tailwheel, you must have a dependable brake system. The Redline brakes will provide that.

By |2016-11-13T09:33:06+00:00August 18th, 2015|Flying-Wire|Comments Off on Take Offs Part 1

About the Author: