Hello Remi,
Yes, the airspeed axis on page 15 Figure 1 is labelled "VEASKTS", standing
for Equivalent Airspeed in knots, which is a more technically precise term
than Indicated Airspeed for aerodynamicist's calculations. For practical
purposes, they may be treated as equal for the flight envelope of the
Europa.
The reason why you need more horsepower at altitude for a given IAS is that,
for a given efficiency, the engine is providing thrust to equal the same
drag (which is dependent on IAS) but the True Airspeed is greater, so the
actual distance moved in a given time is greater. Work = Force x Distance;
Power = Work/time. The engine is therefore having to do more work in a
given time at the same IAS at altitude, but this is more than offset by the
gain in TAS, so cruising at a given TAS requires less horsepower at
altitude.
I do not believe Don Dykins is wrong, and I do not agree that it is nonsense
to talk about performance in terms of indicated airspeed. As I understand
it, he is showing his calculations of aerodynamic performance and comparing
them with the results of flight tests, where IAS is measured.
It would be interesting to know how the latest VP propellers compare in
efficiency with his working assumption of 80%.
Best regards
Mike
_____
From: owner-europa-list-server@matronics.com
[mailto:owner-europa-list-server@matronics.com] On Behalf Of Remi Guerner
Sent: 30 January 2008 08:12
Subject: Europa-List: Don Dykins book
Hi all,
I have just read Don Dykins book < Understanding the aerodynamics of your
Europa aircraft > and I am puzzled by what I read in the "Prototype flight
test performance" section.
Figure 1 on page 15 shows that you need more power to fly at a given
airspeed at altitude than at sea level. I first thought it was a typo, but
page 18 confirms this assertion: "more HP is required to fly at a given
speed at 10,000ft than at sea level".
The typical light aircraft cruises about 5 to 10 percent faster at 10000 ft
than at sea level using the same power, and you can verify this with your
own Europa as well.
So Don Dykins is wrong. Unless he is talking about indicated airspeed. In
that case, talking about performance, this is nonsense.
I cannot believe someone who has contributed to the design of such a
wonderful aircraft can be so wrong. Am I missing something?
Please comment.
Remi Guerner
|