Best Air Temperature for Speed Records

[Mark]

I vaguely recall reading or someone mentioning the best air temperature for running Dyna-jet class engines to break official speed records. Does anyone know if very cold or hot or mild temperatures work best?

[dynajetjerry]

Mark,
I have no specifics but can make a few pertinent observations.
Static thrust of pjs seem to increase as air temperatures decrease, mostly because the air is more dense. At the same time, more dense air causes an increase in drag, perhaps negating the rise in thrust. I do recall that, in 1948, several Speed Jet practitioners set a new Jet Speed record in Minn. by flying indoors, in sub-zero weather. (That record has aroused many questions in modelers.)
Jerry

[Mark]

Thanks for that Jerry.

[Rocket Man]

I is a well know fact you can not change the laws of physics. Cold air contracts, an engine can suck in more oxygen in cold weather. More oxygen means the engine can burn more fuel. If you keep the fuel on ICE or DRY ICE this helps to super cool the intake air producing more power.

[Mark]

I remember seeing a post of all the metering jet sizes someone had for their Dyna-Jet, like a little drill bit set. I guess with all the different fuels and experimental combinations it's probably fun sorting out the right size for the weather conditions and fuel/air ratios. And too some fuel feeds probably have limits in how well they vaporize/handle the fuel. It would be funny to see someone control-line flying a Dynajet in minus 40 F/C in Antarctica. Maybe at that temperature everything would be thrown off, including the porportions of the engine for optimum thrust.
http://www.pilotfriend.com/training/fli ... t_perf.htm

[noclassmac1972]

Flying very low on a hot day to get the extra heat from the tarmac makes a little jump in speed. The Warmer the air the less work the engine has to do to warm it!!!! Colder or wet days are usually slower....

Metering jets in 1 thou steps make a difference even if you can get the 1/2 thou sizes makes for finer setting... Plus on the sidewinder models we can shim the engine out or in to alter the cyntrifical force on the fuel..

Robert

[dynajetjerry]

Mark & All,
D-J metering jets were made with standard US numbered drill bits starting with the smallest (#1 jet, .036 in. dia., #64 drill, and up to a #10 jet, .052 in. dia., #55 drill.) Because #56 and larger drill sizes are larger by more than .001 in. for each increment, there can be significant jumps in sizes. i.e., a #56 bit is .0035 in. larger than a #57; a #55 is .0055 in. larger than a #56; a #54 is .003 in. larger than a #55; etc.
It is possible that a few metric bits can fill in some of those gaps in sizes. Too, some drill bit mfrs. offer special sizes but at higher prices.
Also, there are tapered reamers that can be used to obtain non-standard openings.
Jerry