Aerodynamics and Performance

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First some Abbreviations straight from OOAAA:
Term
Definition
TASTrue Air Speed = Speed over the earth with nil wind
IASIndicated Air Speed = number of molecules hitting you per unit time
Vs Stall Speed = When you stop flying and start falling. When you hear buffet ease off the stick IMMEDIATELY
RoTRate of Turn = The fastest way to point your weapons at the bad guy = GOOD THING also see Vc and Vcs
TRRadius of Turn = smallest sircle possible but not necessarily best RoT
AoBAngle of Bank = The angle between the wings and the horizon. Can be seen on Artificial Horizon in instrument panel.
RhoDensity of teh Air and used by really smart folks to work out all kinds of stuff
BRoCBest Rate of Climb Speed = Maximum Altitude change per unit time. Should be shown as IAS or TAS
GGravity = 9.8 m/s/s = what we feel when sitting down having a beer
VcCorner Velocity, Instantaneous = Best RoT Speed and what you can do as you lose Energy wihout ripping the wings off
VcsCorner Velocity, Sustained = Best RoT that you can maintain and what you never go below in a fight!
PsSpecific Excess Power = Your ability to add Energy to your airframe, by either climbing or accelerating


This is a list of some Aeronautical Formulae and will perhaps show you some of the science behind what we do and why we do it:

 The G required to maintain a Level Turn = The inverse of the Cosine of the AoB
(Note Speed and Weight are NOT factors)

Vs at Any G is found by Vs@desiredG = Vs@1G*Square Root of desiredG
Once we know our Max sustainable G we can work out the Speed to fly to get it. So if you are above Vc and need to turn tight then pull till you 'just' feel the buffet! When you get to Vcs then hold that.

RoT (degrees/sec) = 111*G*TanAoB/TAS
We want this at a Max of course so once we know how much G we can pull the rest is easy.
TR = TAS/RoT*60*Pi
and also
TR = TAS Squared/3.782*G*TanAoB
This is not as interesting to us in Fighters unless we are using Dissimilar Aircraft Tactics.

Specific Excess Power = Change in Height or Speed / Time Squared {Dependent on what Units you want to use}
Comes from good old Kinetic Energy = .5*Mass*Velocity Squared and Velocity = Initial Velocity + Acceleration * Time
This is why we do Level Acceleration Tests and tell us what G we can sustain to give us Vcs


Here are links to many interesting pages for the aspiring Boffin.
 NASA Flight Testing where we get our test formats
What do these E-M and V-n Charts all mean to Simmers?
Aerodynamics. Pages below all hang off this site as well
Lift
Drag
Climb Performance
Stall Speed
Want to know how to reduce drag?
What is Best Rate of Climb Speed and how do I use my superb knowldge of aircraft performance to defeat the hordes with consumate skill and ease?

OK. If there is one thing I have noticed when flying online it is that many people complain that this or that aeroplane is a slug, won't climb, is too slow etc. I regularly lead formation flights and Sections in combat and many people find they just can't keep up. Unfortunately for most of us a sim doesn't teach you all the stuff that a real pilot learns in the ab initio stage of training and indeed delves deeper into as his career progresses. Flying is all a matter of mathematics with lots of graphs and curves and equations. The Best Rate of Climb Speed is that speed at which you have Maximum Excess Power. This means that the lower your Drag and the higher your engines Power the faster you will climb. This couple of diagrams (which I pinched gratuitously from These fine people) give you a hint.

ExcessPower.gif - 37800 Bytes Excess Power - Prop Aircraft The THP available for a propeller aircraft is shown in red in the diagram to the left (THP = ? x BHP.) The excess is power is determined by subtracting required power from available power.

Excess_Power2.gif - 5710 Bytes The speed at which the maximum excess power (Px) occurs will be Vy (best rate of climb speed.) This can be any speed, depending on the propeller chosen for the aircraft. Usually it is fairly close to the L/Dmax speed. In other words Vy is fairly close to the maximum range speed

Excess_power3.gif - 5070 Bytes The Excess Power vs. Velocity graph always looks like the one shown to the left. It rises from zero at a low speed to a maximum excess power at Vy. It then drops off to be zero at the maximum level flight speed, i.e. the speed at which full power is just enough for level flight.

Rather than torture you all further I will try and just give you the esssence and result of all that study. But if you really are a masochist then go to NASA Flight Testing and click on the Sawtooth Climb Test. There is all the info you need and more. Good Luck and I say to you Well Done! Il2 is without question the best PC sim I have ever flown and these tests are directly applicable such is the fidelity of this sim. Thanks Oleg!
Here is a site that will make it all quite clear why I say there is ONE and ONLY ONE speed for Vy = Best Rate of Climb Climb Performance Tutorial (Technical)l

So my little chickens of the sky it is this simple: There is one and only ONE speed at which you will get the best RATE of climb in a certain configuration ie with flaps out etc. Configurations other than clean (gear and flap up) are of no concern here. There are two basic methods to determine what is your particular aircrafts best rate of climb speed is.

1. Trim aircraft out at different speeds and ensure it is stable at that speed ( = no control inputs required to maintain a set attitude) and allow the speed and Rate of Climb to stabilise. Make a not of these two readings from your cockpit instruments and then try another speed say 10KMH different.. YES! it is that sensitive!

2. Get your trusty stopwatch out and again trim for a set speed and time the interval taken to climb by 2000M or so. Shorter time = better climb performance. Note that this method can have problems as the Best RoC Speed changes with altitude and is hard to do without paper and stopwatch, descents and climbs. This method however is more meaningful to real world Interceptor pilots.Here is how it works Check Climb

So I suggest you jump into your favourite aeroplane and get flying. This is a simple exercise and I have included a track file for you to see the effect of correct trimming. You will also see that the speed you thought was giving you a good rate of climb is waaaay low. This is why ppl have trouble keeping up with realworld pilots in IL2. So do what we do.. keep an eye on the VSI (Vertical Speed Indicator) after takeoff and ensure you pick a climb speed that sees it at a maximum.. what no VSI you say?.. and you wonder why I like to fly a P39 and always climb at 300-330kmh! Now there's a hint. Now what we need is man the calibre of Iddons of Warbirds fame to spend the awesome amount of time it would take to test and tabulate the data from all the aircraft available to us in IL2

I think as a basic intro this should be enough for you to start. Any questions please just ask.

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