Controllable pitch propeller and radio failure inquiries

11 Answers

1. 
   

   
   

   Brian on Apr 26, 2013

   If a constant speed propeller, most likely not. Although I’ve flown older aircraft whose rpm would change if the pilot passed gas.

   Question two, sure why not? That’s what light gun signals are for. Something to note with this question, if I had no other emergency and it was a nice clear day, or I knew I could fly to an area of VFR weather, I don’t consider an electrical failure an emergency. My j3 doesn’t have an electrical system and I’ve not killed myself on a single flight yet!

   In other words, don’t rush to land, just think it through and land safely. You’re plane will fly till it’s out of gas (except the new fadec birds) even without an electrical system.

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2. 
   

   
   

   Wes Beard on Apr 26, 2013

   Scenario one:

   If the winds are gusty enough to affect the propeller (which I highly doubt), the RPM will change, the constant speed prop will sense the change via flyweights and speeder springs and correct the changed RPM to maintain a constant RPM. This is what it does anyways. If the airplane climbs, the prop will naturally slow down with a slower airspeed, the constant speed prop changes the angle of attack to keep the speed constant. The only thing you may notice is a change in manifold pressure but I highly doubt you will even see that. It is more of an interesting question to see if you understand the system.

   Scenario Two:
   In the interview, they would be looking to see if you know what the regulations state about entering the airspace without a radio failure. It could also be used as an exercise in interpreting the regulations. 91.129 is operations in Class D airspace. 91.130 and 91.131 is operations in Class C and B airspace.

   The first thing 91.130 and 91.131 state is that 91.129 (Class D operations) rules apply to Class C and D.

   Reading the communication failure procedure (91.129(d)), the words “in a Class D” airspace stick out meaning this section is only applicable to Class D and not Class C or B airspace.

   The answer is I can land under a Class D airport but should not enter Class C or B airspace with a radio failure. As Brian stated, a radio communication failure is not an emergency.

   It should go without stating that this procedure is for VMC conditions. If you are in IMC conditions 91.185 applies.

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   JJ on Apr 26, 2013

   You have my deep respect guys (Brain & wes) for your quick answers and comments.

   -What about the proper way to enter or join a controlled airport pattern under radio failure situation.

   -A friend of mine been asked about the following scenario:
   During the climb out phase after take off engine failure occurred while strong left cross wind were existed, which engine you would rather to fail.

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4. 
   

   
   

   Gregory Weglewski on Apr 26, 2013

   JJ – To the first question: You may not enter any airspace where a control tower exists until establishing two-way communication with the ATCT. If you have a comm. failure prior to making contact, you should find an uncontrolled field. If you have already established communication and you experience comm. failure subsequently, tower/approach may have given some guidance as to which runway to approach as well as how to approach. Follow those guidelines if applicable. If, however, the only radio contact you make is to give your position report, and they reply with a tail number and offer no guidance, I would recommend entering the pattern on a 45 degree entry to left downwind as you would at any uncontrolled airport (provided RP is not published for that runway). As to which runway, ATIS generally provides the landing runway. Hope this helps!
   P.S. This is my interpretation of the AIM Chapter 4-3-2. If someone can add guidance as to if it is legal to enter airspace with a CT without two-way communications, I would love to see that.

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5. 
   

   
   

   Gregory Weglewski on Apr 26, 2013

   As to the engine failure question, are we operating a conventional light twin or do we have counter-rotating props? I certainly would prefer to have the critical engine operating if the former is the case. If not, may I assume the aircraft has sufficient thrust to continue climb-out and return to land? If so, I would prefer the leeward (downwind) engine to be failed, as it is usually easier to land with the windward (upwind) engine operating. It should not affect the flight characteristics of the aircraft during climb-out, as the aircraft should already have weathervaned after rotation.

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6. 
   

   
   

   Bob Watson on Apr 27, 2013

   re: “During the climb out phase after take off engine failure occurred while strong left cross wind were existed, which engine you would rather to fail.”

   That’s easy. Neither.

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7. 
   

   
   

   Brian on Apr 27, 2013

   -A friend of mine been asked about the following scenario:
   During the climb out phase after take off engine failure occurred while strong left cross wind were existed, which engine you would rather to fail.

   The airplane could care less, once it’s wheels leave the ground the wind (gusts and sheer aside) mean nothing to the airplane. The only person the winds matter to is the improperly educated pilot.

   This question goes right along with the “if you turn from upwind to downwind are you at risk of stalling the airplane?” The answer is no, but if you ask a room of pilots I guarantee you at least some of them will argue adamantly that you lose airspeed because you’re now going downwind instead of upwind.

   If it helps you perceptually, imagine a subway car that could be on a perfectly smooth track. Riding on a cloud of air, as it were. The subway car represents a moving airmass, it’s moving along the ground at 50 mph, just like a 50 mph wind would. You are on board this subway car and are now operating within it, just as the airplane operates within the airmass. Is it any harder for you to walk in one direction than another? When walking in the direction the train is moving you decide to make 180 degree turn and walk the other way; do you think you’re speed relative to the subway car would change assuming you don’t decide to walk faster or slower?

   The airplane operates in the airmass exactly as you would within the subway car. Where we pilots get in trouble is with our tendency to reference the ground when looking to determine speed. This can be a dangerous and faulty way of quantifying this variable. Use your pitch attitude and airspeed indicator or AOA if you’ve one on board.

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8. 
   

   
   

   Wedge on Apr 27, 2013

   Brian, I agree with the beginning and end of your response. However, you do in fact lose airspeed if you quickly change direction in relation to the wind direction. An exaggerated example of this is windshear (as you kind of stated). The aircraft has substantial inertia and may not be able to adjust as quickly as the wind has shifted. When changing the wind velocity over the aircraft, it needs time to accelerate to adjust to the new wind environment. This is one of the reasons why it is generally accepted that in a SE airplane experiencing an engine failure after takeoff, you should not turn around until at least ~800′. Coupled with low airspeed and a steep bank angle, the quick change in relative wind will have detrimental effects.

   Thinking about your example, when you turn around in the subway, your walking speed must drop to zero before accelerating back to normal walking speed in the opposite direction, unless you make a wide turn, just as planes cannot simply stop and turn around.

   Perhaps a better example would be sitting on a motorcycle atop the subway (so we can go faster than the subway). When starting in the rear and riding forward, you don’t need to go fast to obtain a strong wind in your face (like a short takeoff roll). However, if you turn around and ride in the other direction, you would initially experience a tailwind until you accelerated past 50 mph. In an airplane, making this rapid heading change, we absolutely would stall unless making a wide enough turn to allow the aircraft to slowly accelerate into the airmass.

   Jump in a simulator with a strong headwind and turn around immediately after taking off… see what happens.

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9. 
   

   
   

   Brian on Apr 28, 2013

   “Brian, I agree with the beginning and end of your response. However, you do in fact lose airspeed if you quickly change direction in relation to the wind direction.”

   Within the moving airmass we are in the wind has not shifted. If you want proof take a plane up above a cloud deck and trim yourself out in a perfectly stabilized turn. Once stable and hands off (if able, use an auto pilot) just watch your airspeed. You’ll go round and round until your tanks run dry without the slightest variation in airspeed.

   Keep in mind, on your initial entry you’ve added drag that will likely rob you of a couple knots. This is often misinterpreted as a support for your argument when it isn’t. That’s why it’s important to stabilize the aircraft in a turn before referencing the airspeed indicator.

   Finally, wind sheer and gusts are another ballgame. They will cause changes in airspeed because they are characterized as disruptions to the steady state flow of the rest of the airmass. That same disruption to the airmass is also a disruption to anything in it’s path within the airmass.

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10. 
    

    
    

    John D. Collins on Apr 28, 2013

    Wedge,

    I agree with Brian’s analysis completely. Although there can be relatively fast changes in wind velocity in a gust that can change the relative wind, manipulating the controls does not induce anything near the forces that would be required to instantly change direction. In effect, the airplane uses the lift force of the wings as the force that turns the aircraft as it flies within the inertial air stream in which it immersed. Your example confuses measuring speed with respect to the air verses with respect to the train. In an aircraft, once airborne, all airspeed is measured with respect to the air and not to the ground. To determine ground speed, you need some indication from outside of the aircraft, such as actually seeing the ground or using a navigation device to measure ground speed. Without these visual or navigation tools, if you are on top of an overcast, there is no way to determine the direction of the wind. With the assignment to enter a 60 degree bank turn and point the airplane directly into the wind, there is no way of accomplishing the task without seeing the ground or using navigation equipment.

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11. 
    

    
    

    Brian on Apr 28, 2013

    “manipulating the controls does not induce anything near the forces that would be required to instantly change direction.”

    Just want to clear up one thing here John. I realize you probably know this and may have misspoke or I may have misread.

    Rate of directional change has no impact on the result. For instance, let’s consider taking a spinning top and placing it on a raft. Now float that raft down a perfectly calm river. The river represents a mass of air, the raft exists in the example only to keep the spinning top from sinking, and we should consider this experiment to happen in a vacuum. That is, there is no air. Atop our raft the top is continually, rapidly, changing direction and all the while the river (remember this is the airmass in our example) has no influence on it’s rotation.

    Examples like this work because they represent an object detached from the earth that are moving with a fluid mass. Keep in mind that air is considered to be a fluid.

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