Letters To The Editor
All letters will be carefully considered; those of general interest will be used. Send to Model Aviation, 1810 Samuel Morse Dr., Reston, VA 22090.
Quetzalcoatlus Northropi
This was a quite well-done article on a significant engineering endeavor that has been, unfortunately, overshadowed by the public failure at Andrews AFB. I hope the "bad press" doesn't influence Dr. MacCready's backers to the extent his work will not be completed.
One thing I noticed in this article and other reports is a lack of mention of a theory that pterodactyls were not capable of actual flight in the same sense as present-day birds. This theory holds that they were capable of gliding down from a height to pounce on prey, but were not able to climb on muscle power above the starting perch. This same theory also explains the rather strong bone and claw structure on the wing leading edge as climbing aids which allowed the creature to climb to the heights needed for descent to prey.
From the standpoint of that theory, Quetzalcoatlus northropi is well represented by Dr. MacCready's model. I look forward to reports on MacCready's continuing efforts to produce the version that will fly independently. I wish him success.
Jim Coffin Annandale, VA
I enjoyed reading about Quetzalcoatlus northropi in the August 1986 issue. Dr. Paul MacCready has performed an outstanding engineering feat.
The article said that the pterodactyls lived on the edge of physical impossibility and that the laws of aerodynamics have remained constant. True enough. However, there is a possibility that the physical properties of the atmosphere have drastically changed.
Dr. Joseph Dillow, in his book The Waters Above, addresses the question of the existence of the pterodactyls as a natural consequence of his theories. Dr. Dillow believes that, recently, Earth had a water-vapor canopy that increased the atmospheric pressure to over twice what it is today. If this were true, then the flight envelope of the creature would have been stretched to accommodate a more realistic upper and lower boundary. The weather under the canopy would have been conducive to a stable atmosphere, which would have provided a more favorable environment for flying. Perhaps, more importantly, the increase in the partial pressure of oxygen would have supercharged the bird's muscles, giving it the efficiency necessary for flight.
Jim Hassinger Hagerstown, MD
Vertical Tx Antennas
Some time ago I thought that a strap-held box for my transmitter would be a good thing, so I built one and tried it. I noticed that the plane seemed to be getting a weaker signal, especially when some distance away and near the ground.
Then it hit me. The gain of a rod-type antenna is maximum at right angles to its length and minimum parallel to the length. Having been involved in antenna design years ago, I should have known that the gain off the end of the antenna is essentially zero.
Having finally discovered my oversight, I now hold my antenna vertically and thus have no similar problems.
Marion E. Gilliland Lehigh, IA
We have noticed that transmitters designed for use with strap-held trays have the antennas located so they are vertical, or nearly so, when in the flight position.
Glow Start Sans Power
I read with interest the "Safety Comes First" column in the July issue. Preston Streson discusses the fact that glow-plug engines can start without benefit of electric power being applied to the glow plug. This can occur because the glow-plug igniter can act as a catalyst to produce ignition of the fuel. This principle was used in cigarette lighters during World War II in areas where an open flame was not allowed. It is also used in today's catalytic converters on many cars.
If the platinum igniter is clean and the wire is free from soot, it is not necessary to have the plug red hot to produce spontaneous ignition. It doesn't occur if the igniter is contaminated or if the wire is so massive that the small amount of heat developed cannot raise the temperature to the ignition point. Just after a run the glow plug is clean, since it has been hot and burned off contaminants. If the plug is near its end of life, parts of the wire may be very small in diameter. Under these circumstances, when a proper mixture of oxygen and fuel is present, the glow-plug wire may glow low without any electrical power being applied. It's somewhat chancy, but the possibility is always there.
Old glow plugs are normally contaminated with lubricant, and sometimes it's hard to get them hot enough even with a battery.
I am an independent RC sailplane enthusiast. I thank you for all the work that goes into each month's publication of Model Aviation. Here's to more fields to fly from.
Lloyd F. Hlavka Palo Alto, CA
Transcribed from original scans by AI. Minor OCR errors may remain.
