Thursday, August 28, 2014

A Question or Two


Crystal and I drove to Payson, AZ and visited with our friends Ernie and Diana.  We had a lovely visit and enjoyed the cooler temperatures and beautiful landscape.

Learned about the Mogollon Rim, that are high limestone and sandstone cliffs. It was formed by erosion and faulting, and dramatic canyons have been cut into it, including Fossil Creek Canyon and Pine Canyon. The name Mogollon comes from Don Juan Ignacio Flores Mogollón, the Spanish Governor of New Mexico from 1712 to 1715.


The Payson airport lays parallel to the rim and I was wondering, had we flown, would we have had to land at a different indicated airspeed (IAS) than at home in Avra Valley. 

Well, neither Crystal nor I are pilots, but we have talked about flying together.  She closes her eyes during landing, so I would land and she take off.  HL could sit on a pillow in the luggage area and teach us both at the same time.   Smile

Our drive was really pleasant we went back by way of Roosevelt Lake and Globe. Below are some shots as we drove along.

IMG_1962   IMG_1963   IMG_1964

My Question

I didn’t leave my question about landing at different elevations unasked for long and Ernie gave me a good explanation, when I explained it to Greg he added some more information.  Then I sat down at my computer and started searching and reading.  I think I’ve got it right:

Indicated airspeed (IAS) is driven by the pitot-static system.

Below are two different looking pitot-static tubes and on the right are pictures of installed tubes.


IMG_1978  IMG_1982  IMG_1983


The pitot-static system uses the difference between total pressure and static pressure to measure dynamic pressure. Dynamic pressure includes terms for both density and airspeed. Since the airspeed indicator cannot know density, it is by design calibrated to assume the sea level standard atmospheric density when calculating airspeed.

This was the same as Greg and Ernie had explained.  Ernie used an example of a box of oranges.


The oranges at the bottom of the box are more compact then at the top of the box, much like the air molecules at sea level relative to higher elevations.  The closer the air molecules the more lift a wing has, Greg added, and the more oxygen goes to the engine for increased power. The ideal performance would be at sea level, zero degrees and dry conditions.  The air would give optimal lift and increased engine power, as described below:

Air density is perhaps the single most important factor affecting aircraft performance. It has a direct bearing on:

  • The lift generated by the wings — reduction in air density reduces the wing's lift.
  • The efficiency of the propeller or rotor — which for a propeller (effectively an airfoil) behaves similarly to lift on wings.
  • The power output of the engine — power output depends on oxygen intake, so the engine output is reduced as the equivalent "dry air" density decreases and produces even less power as moisture displaces oxygen in more humid conditions.

Aircraft taking off from a "hot and high" airport such as the Quito Airport or Mexico City are at a significant aerodynamic disadvantage. The following effects result from a density altitude which is higher than the actual physical altitude.” 

  • The aircraft will accelerate slower on takeoff as a result of reduced power production.
  • The aircraft will need to achieve a higher true airspeed to attain the same lift - this implies both a longer takeoff roll and a higher true airspeed which must be maintained when airborne to avoid stalling.
  • The aircraft will climb slower as the result of reduced power production and lift.

Due to these performance issues, a plane's takeoff weight may need to be lowered or takeoffs may need to be scheduled for cooler times of the day. Wind direction and runway slope may need to be taken into account.  [Wikipedia, Density Altitude]

Note:    When the tower says,“density altitude”, there is an aerodynamic disadvantage for the take off.  I will let Crystal know, as she is in charge of take-offs.

The short answer to my question-I would use the same IAS going over the fence at Payson airport as I would at Geronimo Field, Avra Valley.  However, I might need a bit more runway due to true airspeed or ground speed increase from being on top of the oranges at Payson Airport.


What did the guys do while we were gone?


The Boss painted the paint booth and spent a couple hours pressure washing the floor.  The purpose was to have more light reflections from the white walls and less trash (paint flakes from the floor) in the air during painting.  I want to clearly state that he does a far better job on the planes than on this!

 Landing Lights vs. Recognition Lights

I was taking pictures of the parts that are ready for primer paint when I had another question.

IMG_1971         IMG_1968

Why are LSA being fitted with landing lights?  Good question, huh?  LSA don’t fly at night. 

IMG_1974                 IMG_1975

The Boss then corrected me and said that they are “recognition lights”.  Not the first time that I have experienced something being called different in the shop than what the Boss said it is.  However, the Boss then said that a tower will request that a pilot turn on landing lights for recognition.  Hum….just so everyone knows what LSA lights on the front edge of the wing is for recognition only. 

Bob’s Plane

Bob’s plane has some parts, lain out on the console, ready to be installed that will support the instruments behind the panel.  Those round vents are for airflow into the cabin. The supports are installed in the middle picture and the engine wires are ready to connect with the instruments.

IMG_1973    IMG_1981      IMG_1984


Ron and Al’s Planes

Ron is making arrangements with Ted for inspection sometime next week. 

Al and Colby are giving us time to get the paint on then they will be returning for final assembly.