Safety Device for Antique Aircraft - Mixture Control

Engine "Backfire" - Leaning the Mixture

If you have ever experienced a sudden power loss due to carburetor icing this technique will improve your chances of landing safely with power.

Lycoming and Continental engines in conventional carburetor equipped aircraft experience carburetor icing. The carburetor can cool below the freezing point of water quickly. The use of carburetor heat and idling the engine can keep the temperature of the carburetor system above 32 degrees F. On take off, when power is applied, the amount of fuel vaporized is increased and that vaporization absorbs heat from the carburetor and lowers its temperature.

Humidity plays a important part whether the moisture in the air can freeze the water onto the surface of the venturi of the carburetor. Greater the humidity the greater the chance for the moisture in the air to form ice.

This is directly related to the dewpoint of the air at the time of your flight. The dewpoint is that temperature where the water in the air begins to form water droplets. (like fog and clouds, for example) If the dew point is 68 degrees F on a nice clear summer day where the ground temperature is 90 degrees F you would not think of icing on a day like that.

THe adiabatic lapse rate for air is 4.5 degrees F per 1000 feet of altitude. This means if the aircraft reaches an altitude of approximately 5000 feet the temperature is 68 degrees F. The plane can begin to form ice in the carburetor at this altitude. 

I spent some time in a normally aspirated Cessna 182. Several times a year it would develop ice in the carb! I would try the normal procedures for melting the ice but an effective technique is to reduce power and lean out the mixture. The engine will back-fire and blow out the ice formed in the carburetor. Its effective.

In flight when the throttle is reduced too rapidly the fuel/air mixture goes with it, but the fuel valve does not react as fast as the air reduction. Therefore the fuel left behind explodes.
For it to be heard it must be done in one of the cylinders exhaust stroke. There is no spark at the exhaust stroke so the little fuel or un-burnt carbon is heated to its flash point from the hot cylinders. Its ignited by the severe heat when the fuel is reduced (the fuel keeps the CHT cool, reducing it makes less fuel so less mass to be superheated in a very short time). Overal the fuel did not finish its complete burn before the exhaust and comes out as a "pop of flames".

On the ground this "Back fire" will also happen if the fuel/air is reduced to rapidly and then the un-burnt fuel is left to reach its flash point.

During the run-up the leaner the mixture the more backfire you will have. This is also because the fuel is too lean for the air mixture making it burn at very high temperatures. This increases the CHT, EGT, OIL Temp to where the fuel can also get to its lash point and explode uncontrollably.

The freezing that occurs in fuel-injected engines is when ice forms on the intake screen of the air source for the fuel before it enters the engine. 

New To Unusual Attitudes - Newly minted IFR Pilot!

Instrument Nostalgia for Newly Minted IFR Pilots

In instrument conditions, the attention of the pilot should be on flying the plane. With newly minted IFR pilots sometimes our attention fixates on lesser duties.

Such was the case with me flying the Bonanza near Capitol City Airport in the vicinity of three major towers soaring more than 1000 feet each above the ground. They are formidable in VFR conditions.

Checking the IFR Center instructions I failed to direct my attention to the attitude of the Bonanza, a high performance plane that can quickly get away from you if you don't pay attention to what you are doing.

This time the warning that something was amiss came from my sense of smell! Yes, sense of smell! The distinct smell of dust in the cockpit air. Whoa! Forward on the yolk immediately! A spilt second later and it would be my first experience of recovering from a loop in IFR conditions with high towers nearby.

The return to piloting the plane and recovering from the entrance into a loop cost me several hundred feet of altitude. The danger was not over until I had sufficient altitude to clear the radio towers in the immediate area. Climb mode, rechecking position, attitude and altitude confirmed that I was okay. Not so my sensibilities and fright from a close call.

This flight had important lessons that are obvious to many. One sense, that saved me, was the sense of smell. My reaction time to that information prevented a tragic accident from happening because my priorities were not with flying the plane.

Yep! Like many pilots I made my fair share of dumb moves. But I learned from them!

PreFlight - A Missing Cotter Key on a SeaBee

The Importance of a Cotter Key


Much of my earlier years were in the right seat of a Republic Aviation well constructed but underpowered Republic SeaBee. The amphibian received its nickname, "The Flying Rock" from its tendency to fall 'like a rock' once the power was reduced. The Piper TriPacer with the shortened Lippert Reed modification of the basic Piper Cub wing was a close second. They both landed where you pointed them.

Dick Marsh of Hughes Aircraft Service at Capital City Airport in Lansing, Michigan has first hand experience with the "Flying Rock!" I am sure Mr. Marsh has passed on to the great airport in the heavens but he lived to recount the manufacturing expertise of Republic Aviations' SeaBee.

Harvey Hughes' Cessna Dealership did a 100 Hour Inspection of our SeaBee and Dick took the SeaBee up for the check-flight.

The check-ride went well until the cotter key that didn't have the lock pin in it worked loose from the reversing mechanism for the prop.

At approximately 500 feet over the airport, on its return from the check-ride, the prop went into reverse/neutral. The SeaBee fluttered down like a leaf in the Fall, hit on the keel of the hull, bounced up and settled down on the dirt.

The force of the unintended landing popped several rivets on the hull, destroyed the right pontoon, caused the pusher propeller to cut a nice slice out of the fuselage between the cabin and tail, but the engine was still running after the crash.

Dick Marsh sustained a sprained back, pushed the seat down about two to three inches into the floor of the cockpit and vowed never to fly the "Bee" again.

That crash was mute testimony to the well constructed SeaBee. It saved a life but never flew again.

I started with the end of the plane as a memory of a great plane that ended with a cotter key working loose. How little things like that can result in a near tragic accident and the total loss of a fine aircraft.

Cross Controls and Lose Control - A Spinning Story

Spin Recovery - Cross Controls and Angle of Attack

Remember those wonderful days when you knew everything at the old age of fifteen? I think I passed through that "era" when I was just learning to fly.

I was absolutely sure as long as the nose of my venerable Cessna 120 Trainer was pointed down below the horizon and my indicated airspeed was 70 mph I was as safe from stalling as anything in the world! Yes Sir! I knew it all! So confident I would prove it!

My Dad turned to Bob Nichols, then the Manager at Gaylord, Michigans local airport located about 75 miles South of Mackinaw City. ( Now there is a hugh suspension bridge that connects Michigans Lower Peninsula with the Upper Peninsula)

"Is it time Bob?" my venerable Dad inquired of Bob. "Yes it is, Perry!" he replied.

Supremely confident of my flying knowledge we went through the customary exterior Pre-Flight, climbed into the Cessna 120, and after the normal in-the-cockpit check-off fired her up and proceeded to taxi to the take-off runway.

After the take-off I proceeded to climb the Cessna to five thousand feet in a series of climbing turns. In the practice area Bob Nichols told me to turn on carburetor heat (This plane is considered an antique now - just as I am!) slow the plane to 70 mph (like in a landing mode). I did just that!

Checking with this lanky know-it-all that all was comfortable and well Bob inquired again that a plane wouldn't stall as long as the airspeed was well above the stall speed of the Cessna and the nose was below the horizon.

I replied, in my cock-sure clipped English of a Michigander, "Can't stall when were in this attitude!"

Bob calmly told me to tighten my seat belt and put in full right airleron and full left rudder. I just got out the word "See" when the plane was heading downward in a snap-stall spin (straight down)!!

Since I never experienced a spin before he calmly told me to stop the rotation, above my screams, first and then apply forward pressure on the yolk until the aircraft leveled out and cruising speed was achieved. The previous information keeps the plane from entering a secondary stall. Then, and only then relax the forward pressure on the yolk and slowly apply power while turning off the carburetor heat. Needless to say I was impressed. A small change in my informational database was altered - for my own good!

Wolfgang, from Stick and Rudder, explains "Angle of Attack" well and that was what I exceeded when I "Crossed Controls" in the Cessna 120. When the angle of attack is exceeded the plane enters a stall that can rapidly turn into a fatal spin if done at approach to landing altitudes.

Safety hint? If you encounter cross winds while landing make a co-ordinated turn into the wind to correct for drift from the runway. Straighten out with rudder control and slight wing-drop into the wind just as you are about to touch down. Happy Flying from a know-it-all!

Be sure to check with your own instructor and follow his advice. Things may have changed somewhat over the years. I am an old not so bold pilot now!

Jim

Here is a brief paragraph of rudder control.

Aircraft rudders

The tail of a Martin B-57E with rudder deflected to starboard. On an aircraft, the rudder is called a "control surface" along with the rudder-like elevator (attached to horizontal tail structure) and ailerons (attached to the wings) that control pitch and roll. The rudder is usually attached to the fin (or vertical stabilizer) which allows the pilot to control yaw in the vertical axis, i.e. change the horizontal direction in which the nose is pointing. The rudder's direction is manipulated with the movement of foot pedals by the pilot.

In practice, both aileron and rudder control input are used together to turn an aircraft, the ailerons imparting roll, the rudder imparting yaw, and also compensating for a phenomenon called adverse yaw. 

Adverse yaw is readily seen if the most simple type of ailerons alone are used for a turn. The downward moving aileron acts like a flap, generating more lift for one wing, and therefore more drag (though since the 1930s, many aircraft have used frise ailerons or differential ailerons, which compensate for the adverse yaw and require little or no rudder input in regular turns). 

Initially, this drag yaws the aircraft in the direction opposite to the desired course. A rudder alone will turn a conventional fixed wing aircraft, but much more slowly than if ailerons are also used in conjunction. 

Use of rudder and ailerons together produces co-ordinated turns, in which the longitudinal axis of the aircraft is in line with the arc of the turn, neither slipping (under-ruddered), nor skidding (over-ruddered). Improperly ruddered turns at low speed can precipitate a spin which can be dangerous at low altitudes. This can be clearly seen in the crash of United Airlines Flight 585 and USAir Flight 427, where the aircraft experienced a rudder hard-over at a low altitude.

Sometimes pilots may intentionally operate the rudder and ailerons in opposite directions in a maneuver called a forward slip. This may be done to overcome crosswinds and keep the fuselage in line with the runway, or to more rapidly lose altitude by increasing drag, or both. The pilots of the Air Canada Flight 143 used a similar technique to land the plane as it was too high above the glideslope.

Any aircraft rudder is subject to considerable forces that determine its position via a force or torque balance equation. In extreme cases these forces can lead to loss of rudder control or even destruction of the rudder. (The same principles also apply to water vessels, of course, but it is more important for aircraft because they have lower engineering margins.) The largest achievable angle of a rudder in flight is called its blowdown limit; it is achieved when the force from the air or blowdown equals the maximum available hydraulic pressure.