Some EM notes for Future F4 drivers from my old notes

[DHenriques_]

" Some notes on the energy approach to flying fighters for the sim pilot"
{Just for general information}
Dudley Henriques
President Emeritus
International Fighter Pilots Fellowship


"Before 1966, we had little in the way of comparison info between

any two fighters save for the personal experiences of combat

pilots and the information that they provided. Thanks to the work

done by Col. John Boyd USAF, Tom Christie a civilian math genius;

and E.S. Rutowski of McDonnell Douglas, all whiz kids with numbers, we

developed a way to compare fighter performance throughout each

aircraft's flight envelope. Using energy conversion against known

aircraft characteristics, we could now construct a maneuver

diagram that showed areas of advantage and disadvantage of each

aircraft through overlay. The concept was called "energy

maneuverability", and it changed the way we looked at combat, and

indeed all aircraft performance in the air. The first practical

application of EM concepts was used to compare the F4 to the

MIG21 in an effort to explain what had been observed in SEA and

to try and provide a game plan for F4 crews.

Keep in mind that EM is only one way to compare fighters. It

can't stand alone without other comparison techniques; it does

however provide a scientific basis for maneuvering tactics.

Total energy is potential energy+ kinetic energy. or WH+1/2MVsq. [sub for mass

and v] TE=WH+Wvtsq/2g.

Total energy however is a bad way to compare aircraft. Example: a

747 with a large w when flown high and fast would beat an F5

every time on total energy....ah but....would it win the fight?

Specific energy[Es] units in feet, is defined as total energy

divided by aircraft weight. Es=TE/W [Es=

WH/W+WVtsq/W2g][=H+Vtsq/2g]


F4 v Mig 21 . Both at 15K 450kts and combat weight. Es is equal

dispite the fact that the F4 has higher TOTAL energy.

Now put the F4 at 20K at 0kts and put the Mig at 0ft at 675 kts.

Ignore compressibility!!! and other factors. Theoretically BOTH

have the same Es: 20,000ft. Or in other words BOTH aircraft have

an EQUAL energy STATE.The Mig could theoretically zoom with

engine at idle and reach 0 airspeed at 20K. Likewise the F4 could

fall ballistic ally and accelerate to 675kts due to gravity. It

becomes evident that the specific energy of an aircraft or any

object is entirely the result of it's velocity and altitude. The

characteristics of the aircraft are not a factor. Even so, Es is

important as a measure of an aircraft's energy state,ie. ability

to zoom or conversely, trade altitude for airspeed.

Now for Ps.

If we know the energy state of an aircraft, the ability to CHANGE

that energy state would be important to us in developing a game

plan.

Enter EXCESS POWER!!!!!!

Defined as the change in specific energy with time. Units are

ft/sec. Ps=DEs/DT or[DH/DT V/g DV/DT] Ps= V{T-D}/W assumes

level flight. So Ps is a function of the aircraft's excess thrust

[T-D] at a given airspeed/altitude.

Steady state conditions are when Ps=0=V{T-D/W}This special case

is sometimes refereed to as "sustained" performance in that the

aircraft's energy state is not changing. For instance an F14 at

710KCAS, sea level, in burner. Parasite drag has increased with

speed until T-D=0. 710KCAS is Vmax [Q limit} at sea level. Ps=0.

An F4 at 290KCAS, 48K in military. At this altitude thrust has

decreased until T-D=0 and Ps=0. This means 48K is the military

service ceiling in military.

An F14 at 420 KCAS, 15K, in a level turn at military. As the g is

increased, drag increases as it's square. At about 5.5g, induced

drag has increased by a factor of 25. At this point, T-D=0 and

Ps=0. If g is decreased the F14 will accelerate. If we pull

harder, airspeed will drop off.

This brings me to a point. Ps can be either positive or negative

depending on whether or not we are adding energy or bleeding it

off.

As well as a measure of an aircraft's ability to climb, Ps can

ALSO be used to demonstrate the aircraft's ability to ACCELERATE

OR DECELERATE, and PULL G. An aircraft with a Ps of +600ft/sec

could theoretically climb at TWICE the rate of one with a Ps of

300ft/sec. Conversely, negative Ps values could be used to

compare rates of decent.

Ps values can not be directly equated to climb/dive rates like

those indicated on the cockpit VSI. i.e.. where Ps= -1000

ft/sec, the aircraft is NOT descending at 1000 ft/sec.



HM diagrams are great stuff. God knows I've seen enough of them

in my time. Knowing energy is fine. Knowing angles is fine. It's

a great tool".

Dudley Henriques

[Snuffy]

Thank you Sir!

[VulcanB2]

I completely agree! Great energy management makes all the difference.

You may be interested to know the F-16 can pull a sustained level +9 g turn at 600 kts below 15000 ft.

Best regards,
Robin.

[mattgn]

Thankyou for posting that information, extremely interesting.
Now I know these forums are full of people with tons of aviation knowledge, so a question I've been pondering and one which I hope will be answered by you most learned fellows, is this : how accurately does FSX actually model the changes in the energy state?
Further to that question: have you folks at A2A had to remodel (from the stock FSX) the way in which the energy state is calculated for the Accusim A/C?
I only ask the second question because Lewis had mentioned in the Spitfire update, that there were some generic FSX features that had been re-written by you folks at A2A, or was that purely in relation to the engine modelling?

I look forward to any and all answers !

Regards
Matt

[VulcanB2]

how accurately does FSX actually model the changes in the energy state?

Not very. There are all kinds of oddities in the flight model that prevent it accurately modeling much beyond straight and level.

The AoA model is FUBAR so most aircraft won't even stall correctly at altitude, and accelerated stalls aren't possible in the stock FSX engine (from what I read only the CFS flight models had this ability, though A2A found a way!). If that isn't bad enough, the drag from a shutdown engine is far too high, and the aircraft don't seem able to carry inertia as they should, either. This affects maneuvers such as loops. Gravity is another strange thing, and the reason aircraft don't fly well upside down.

If you want to do aerobatics with accurate flight physics, then MSFS isn't really the platform for it, unless you're flying A2A aircraft such as the Cub or Spitfire.

Best regards,
Robin.