"Mxsmanic" wrote in message
...
Roy Smith writes:

That's a pretty good rule of thumb when the two aircraft are flying at
similar speeds. It doesn't work when (for example), you're a 172 and the
guy on final is a Cub going 10 or 20 kts slower than you.

Does this mean that you have to know how fast each aircraft can or
usually does go, or can you easily tell how fast it is moving just by
watching it?

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I think it is pretty common knowledge that if an airplane looks similar to
your airplane, it is probably going the same speed as you, if it is "sleeker
and sexier" than yours, it is probably going faster, if is not as "sleek and
sexy" probably slower... If it is bigger, it probably goes faster, if it is
smaller, probably goes slower. If it has more engines than you, probably
faster, less would be slower. If it burns high grade Kerosene (Jet A) and
you are buring 100LL, it is probably faster, reverse this for "slower".

But this isn't always true and requires judgement and knowledge on the
pilot's part. i.e. While a 150 and a 172 look similar (172 is slightly
"sexier" and a little "sleeker" and is bigger and generally flys a little
faster than the 150) it is possible to fly a 172 at 59 kts on final, while
flying a 150 at 75 knots on final... so if the 150 is behind the 172, the
150 pilot needs to realize he is going faster than the 172 and slow down
(not hard in a 150), which you judge by looking out the window and seeing if
the airplane is getting bigger or smaller (only works if you are going in
the same direction)

Being a 172 "driver", I know that anything that has more than one engine, or
a jet engine is going to be faster than me, also know most low wing aircraft
are going be faster than me (exceptions could be some Diamonds, some
experimentals, some Pipers like the Tomahawk, but these are typically
smaller than a 172). Most high wing aircraft are going to be right around
my speed range (182s are faster, 150s a little slower, taildraggers are
probably going to be slower because of their landing characteristics, but I
don't know much about taildraggers)