Mach Calculations with RAS

[Sqwark2004]

Simple question and simple calculations, but for the life of me I can't recall how to do 'em.

I have the Instruments and Nav. Aids exam coming up and have found a couple of questions that give RAS, Temp and FL, then ask/tell you to work out the Mach and/or LSS

ie. RAS 290kts
Temp ISA-2
FL 290

What is (i) Mach and (ii) LSS

If anyone can point out the obvious (or at least where to find it), it would be much appreciated.

Cheers

S2K4

[swh]

Should give your M0.75, 442 KTAS, LSS = 588 KT

Mach No = TAS/LSS where
LSS = Local Speed of Sound = 38.94 * SQRT(Air Temp in Kelvins).

Sea level (15'C) = 288 K
ISA 29000 = 15-(29x2) = 15-58 = -43 deg C ISA
ISA -2 = -45 deg C
Kelvin = 273 - 45 = 228
LSS = 38.94*SQRT(228) = 588 KTAS

If you want to go into all the details you could look at this early NACA report (http://naca.larc.nasa.gov/digidoc/report/tr/37/NACA-TR-837.PDF)

[gaunty]

swh amazing isn't it I had that page and some others like it bookmarked for yonks, if only to remind myself that they had all the problems of supersonic and hi altitude flight sussed waaaaaaaaaaaaaaay back then they just didn't have the technology or grunt to implement it.

As a boy I grew up at the time late fifities early sixties when they were really on the edge of it with all the early jets and supersonic flight and farnborough was likely to have at least 2 new and highly experimental types in the flying display. Geoffrey de Havilland Jr actually "bought it" in full view of the world at one.

Looking back at the movies and newsreels then it seems so primitive as we now routinely cross the continent supping fine food :rolleyes: and sipping fine wines :E at speeds with which they were then seriously struggling.

[swh]

gaunty,

Took NACA/NASA etc a while to learn the tools that mathematicians of the likes of stokes, green, kutter, and guass gave us. Those mathematician/physicists' abstract thinking still blows me away when people find new ways of using their tools in today’s society, even if its taken us a couple of hundred of years to understand their tools. Computers are still catching up to calculate the formulas these guys gave us giving us incremental performance and structural optimisation.

Maybe when we fully understand what einstein gave us, and how to use quarks, quavers and other sub-atomic particles, in 50-100 years maybe we will fly without the use of a jet/ramjet engines, I guess all that knowledge will be redundant then.

:ok:

[The Messiah]

Gaunty

I thought that according to Blackjack Walker, Geoffrey DH Junior was lost to the West of Bankstown doing a flight test in a narrow fused Mosquito called a 'Hornet'. Blackjack was the last to see him from the cockpit of a Nene engined model Vampire that he was heading out in to do Vne tests in.

The memory is vague however so I am willing to accept any corrections you may have.

[OpsNormal]

I'll sit here and dispute any claim by anyone that VH-RAS is even capable of achieving anything remotely resembling a Mach number..... ;)

Sorry kids, it was there to be said.;)

OpsN:}

[gaunty]

The Messiah

I may well be confusuing the John Derry DH110 accident in this context, I thought there was a de Havilland killed at Farnborough but my memory is getting crankier. Must go and have a look.

They eventually became a remarkable aircraft with a couple still flying.

http://www.ukskies.co.uk/D/images/De%20Havilland%20-%20DH110%20Sea%20Vixen.jpg

Why nobody thought of the Derry turn as a perfectly elegant means of reversing direction, before escapes me and whilst it may well have been waiting for turbine grunt, there were plenty of piston fighters capable of it.

Should have googled it in the first place.

During a practice flight (DH108) on 27th September, 1946, the aircraft's structure failed at around Mach. 0.9, and it broke up, falling into Egypt Bay, near Gravesend, Kent. The pilot, Geoffrey de Havilland, died in the accident.

There were only three built all crashed but one was the first Mach 1 flight with John Derry at the controls.
http://tanks45.tripod.com/Jets45/Histories/DH108/DH-108_1.jpg