FURTHER COMPARISONS

An important point has been made regarding the wisdom of pulling such high loads, you have seen how expensive that is in terms of lost energy, and that it is simply not worth the cost! Pilots who fly that way are said to have G for brains and they don't live long! But let's make further comparisons with the real world for a moment, you may be able to pull 12.2G in the sim' and you may bleed energy very rapidly if you do so, but 12.2G, that's got to hurt!

It has been demonstrated in a centrifuge that real pilots can endure loads of up to 10G for as long as two minutes. However there is little doubt that excursions into areas of the envelope involving 12G loads may occur, but they would need to be extremely brief in order to have anything other than disastrous results. The F-15A and B had a 7.33G restriction applied, while an overload warning system in the C and D models permitted the pilots of those versions to reach 9G, and you have to love those "Over G" warnings.

Even so, greater loads are possible by ignoring the warnings and applying greater stick force or flying CAS off. The F-15 has a dual flight control system, in effect a conventional hydromechanical system complete with push rods and hydraulic actuators that move the control surfaces, and a separate Control Augmentation System (CAS). The CAS system uses electrical wire to transmit signals to servomotors that operate the same hydraulic actuators as the mechanical system. The CAS system takes data from sensors that feed it all relevant information about the aircraft load and motion. That information, along with stick force sensors allows the control laws of the CAS fly-by-wire system to compute the optimum control surface deflections and modify them appropriately.

Stick forces greater than 3lb per G require the pilot to apply a stick force of around 20lb in a 6G turn and even greater forces are required to initiate a response to a control demand at higher load factors. Even though I too have 20lb springs in my flight control stick (FCS), in fairness, these things are absent from most simulations, along with typically weak physiological modelling that allows you to stay at higher loads for longer periods than is realistically possible.

That is slightly unfortunate because the ability to produce such high loads, with none of the real world constraints is no help to flight sim' pilots who in the heat of virtual air combat will already have difficulty controlling the urge to pull all the way back on the stick. Although you lack that physiological feedback, there is still something that can be done to assist energy management in Jane's F15. The answer lies in the joystick calibration. Basically, you can de-tune the calibration in order that you never receive more than a 9G load from full aft stick at any point across the entire envelope. You might think of this as being able to customise the control laws of the CAS. Doing that makes the EM diagram look quite different, as shown below.

What you notice immediately when you examine this new EM diagram is that the blue Ps=0 curve has not moved. That is as you would expect because altering the joystick calibration doesn't and shouldn't have an effect on either the thrust or drag on which that curve depends. What it has done however, is restricted the amount of G that can be achieved with full aft stick and thus reduced the rate at which you will lose energy in that situation. With the default calibration there was a 1250 feet per second negative Ps at 400kts, now that has reduced to 450 feet per second, less than 40% the rate of energy loss. You will also notice the lower corner speed at 325kts.

Before we move on, let's just look at the implications of flying at our best sustained turn rate. You will notice that the slope of the Ps=0 curve is very shallow. The turn rate between 200kts and 400kts changes by less than two degrees per second. However, the turn radius varies by more than 1000ft over the same speed range. So it seems from this curve that sustaining lower speeds is more advantageous due to the reduction in turn radius, than the small increase in turn rate.

However flying at lower speed has two distinct disadvantages. Firstly at speeds close to 300kts any slight increase in G can result in a stall with the sudden drop in turn rate associated with the sudden loss of lift. Also at such speeds, you are particularly vulnerable to other threats. So it would appear that the choice of an ideal combat speed is more difficult when energy considerations are brought into the equation, and that staying as fast as the situation permits against the computer pilots keeps your options open and reduces the risk from other threats.

Good advice would be to pull only as hard as required to make small gains, holding your energy just as preciously as your angles. In any event you should try to never allow your speed to drop below 300kts. At that speed you can sustain 5G (see screen shot 1) at 100% throttle, a little less if you are caught with a full fuel load, and a little more if you are light. Flight sim' pilots with experience in Su-27 will find these aspects of energy management are already familiar, because that is another simulation in which the flight modelling is such that good energy management is rewarded.

PUTTING IT INTO PRACTICE

An important point to make in closing is that having the information presented in the EM diagrams is valuable because it provides you with the information you need to fly in the best tactical region of the envelope under the circumstances. However, during a dogfight it is difficult enough, while flying in the padlock view, to maintain your grasp on the BFM requirements, let alone monitor your flight parameters. However there is a way you can do both at the same time.

Firstly though, pay attention to the overload warning, and unless you have a bandit pulling lead, ease up when you hear it. Secondly, and more importantly, you can maintain better situational awareness, and remain conscious of your flight parameters by making frequent use of the "Glance Forward" view (zero on the numeric keypad). That view works very nicely in padlock because it allows you to keep a tally on the bandit while providing you with a reference to where your nose is pointing and allowing you to check the Head Up Display (HUD).

While there has been no attempt in this article to discuss BFM as such, it is hoped that the advice and data provided will allow you to fly all of your BFM more successfully! In that I wish you good luck, and happy hunting!

Leon "Badboy" Smith