Hello All :
Mr. Topspeed asked :
Your estimate is based on ...what ?
Basic math. If you know the top speed of an aircraft with a given horsepower, it is fairly
easy to compute how fast it will go with an increase or decrease in power, assuming the
static and dynamic coefficients of drag do not change, ie, that you are not significantly
increasing or decreasing the frontal area, wetted surface, or lift-drag coefficients of
You can find this Online, and if you want, there is an Aeronautical Engineer named 'Greg',
who has a site on YouTube called Greg's Airplanes and Automobiles
, which has
numerous videos, all well done, which can talk you through how to do some of these
calculations. I highly recomend his site if you want an Engineer's perspective on how
things work on an airplane.
Paul R. Ward
P.S. - For years, I had seen figures quoted regarding the Heinkel He 219's top speed,
giving it a figure on the order of 420 MPH.
I doubted this very much, considering
the crude surface finish of the aircraft, the ' suitcase ' design of the fuselage, the high
drag shape of the tail, and the built in headwind of the frontal radar antenna.
So, I spent a few days, did a lot of math, and came up with a figure of about 360 MPH
as a top speed, assuming both engines are working up to snuff and there were no
technical issues with the aircraft.
So, where did the figure of 420 MPH ( which you can find in Wikipedia ! )
come from ?
Well, the post war Allied evaluations of several captured He 219s gave top speeds,
using American gasoline, of about 365 MPH.
At some point, someone apparently
translated that figure into Metric, ( MPH to KPH ), but, instead of using the statute
miles conversion, used the Nautical Miles Conversion
, increasing the speed
by a factor of about 1.15.
Then, someone else converted that metric KPH back into MPH, and used the statute miles
, and, voila, 365 MPH became 365 KnPH, which became 675 KPH,
which became 419.3 MPH !
And that's where the 420 MPH figure came from - sloppy
conversion - probably done by a history major.....
Do you want to know why Engineers use the Metric System ? Well, if you are measuring
liquids using the non-metric English System, then :
2 Cups make a Pint
2 Pints make a Quart
4 Quarts make a Gallon
4.5 Gallons make a PIn
2 Pins make a Firkin
2 Firkins make a Kildirkin
2 Kildirkins make a Barrel
1.5 Barrels make a Hogshead
2 Hogsheads make a Butt,
and 2 Butts make a TUN
Or, you could just stick with Liters......