I have said that I would do up an article explaining what Apache Havoc does both right and wrong when it comes to the flight model, so here it is. I will say up front that this isn't a list of things that should be fixed in Apache Havo, rather it is for those who asked for a comparison of the simulated model to real helo flight. (A good starting point to make it more realistic to fly would be to run at 2X game speed, Ctrl+ .)

Apache Havoc is in my opinion the best helicopter flight model on the PC. For me, this (and other things) makes it hands down the best helo sim out there. While I want to talk only about the flight model here, you need to know where I am coming from. I am a huge Apache Havoc fan and Todd Gibbs has done a super job with his work on this sim. (So has the rest of the team, but Todd has done some very special stuff.)

Some of the things that are going to get better when 1.1e is installed: torque will go the right direction for the helos now. Torque is now a dynamic variable that is dependent on how much collective is pulled (the more collective pulled the more torque you will have to deal with). Tail rotor use will no longer kill your ability to gain forward airspeed (this will have to be done through a command line addition).

In addition, there will be some other command line additions I will talk about that I have used to tweak the flight model to make it a bit better. Many thanks go to Richard (Flexman) Hawley for his great command line list for this sim that can be found on his site: Chapter 8.

Here is how I have my game set up: wind is on, cross coupling is off and retreating blade stalls are on. The command line additions I use to tweak the flight model are as follows:
/drv:2 /dra:5 /drd:0.5 /dtrd:0.0 /drbs:1.5. I also use a few other options that tweak other parts of the game. Just check out Richard's site and decide for yourself what you want to add. There you will also find an explanation as to what I have tweaked on the flight model (FM). Some of the listed commands will not work until you have the 1.1e patch.

From Lift Off Forward

I will start from the time of lift off and move from there. The first problem is well known and you see it the moment that you start to lift off; the total lack of ground handling. It is of course not right that your helo sticks to the ground until you are airborne. This is one of the things that we helo pilots use to be sure that we have not snagged on anything or to pack down snow that is being landed in.

A rolling or sliding take-off is also used in a helo that is loaded to maximum weight, especially if you are at a high density altitude. The same can be said for landing a helo, there are times when sliding on landing can be very useful. Needless to say this is one item that I hope is fixed for Comanche Hokum.

New for 1.1e Patch

New for 1.1e the helicopters will now perform correctly when they are lifted off the ground. The nose will now swing opposite to the main rotor direction and you will have to work the pedals much harder to keep the helicopter going where you want it. The pedals can no longer be put in one spot and held there until you are ready to let them off all together.

I found the climb rate of the helicopters to be excessive in the hover as most helos get a best rate of climb at 45-60kts. This is not the case in A-H; rather you lose ability to gain altitude as you speed up.

Here are the real numbers for the AH-64D Longbow. Maximum rate of climb vertical in average conditions 1255 feet per minute, maximum rate of climb 2370 feet per minute. As you can see there is a gain of over 1000 fpm (almost double!) by being at the Apache's optimum climb speed instead of a climbing hover. These numbers are the official ones coming from its makers so they are probably taken without a weapons load so that they look good. I would expect normal performance to be under these numbers by a bit.

Apache-Havoc seems to get climb rates right when moving, I got just over 2000 fpm with full load at 60 knots and about 1850 fpm at 75 knots. Things go very wrong, however, when you stop and try the same climb. I was hitting climb rates of 3000 fpm in a hover, more then double the actual numbers. I have included a picture of a common power chart for helicopters. It may not perfectly match the Apache or the Havoc but it is an average across most helos.

As I see it A-H gets the climb rates right once beyond 50 knots, but if you go much below that, things are not right. I would have given the same examples for the Havoc but I can't find the numbers for that bird. Keep in mind that all speeds I talk about are actual airspeeds, since wind has a big effect on flying.

The wind has some very noticeable effects on the helicopter when in the hover. These effects are very toned down in A-H to what a real helo pilot sees, but we can just assume that it is not very windy. Your helo will get blown around by the wind with both gusts and a steady wind. It will cause weather cocking in heavy wind and it has even been know to put guys into a tail rotor vortex spin. The only problem with the wind in A-H is that it doesn't have enough effect on the helicopter when in normal cruise flight. More on that later.

In the real world when you put the helicopter in transition to forward flight you should need a little extra power to hold your altitude depending on how far you tip the helo forward. As you hit 15-20 knots airspeed the helo will hit translation, where you gain lift. At this stage the nose should kick up while you should need a drop in power to not gain unwanted altitude. Through all this movement pedal adjustment will be needed to keep the nose of your helo in the right direction. There is a noticeable movement to the pedals when translation is hit, the tail rotor acquires translational lift gains just as the main rotor does.

Most of this isn't modeled in Apache Havoc. As I mentioned, however, with 1.1e you will no longer have a problem with the tail rotor causing odd drag that keeps your helo from going over 90kts while it is in use. This helps with the transition to forward flight and is more realistic. The power required to make the transition and the changes in pedal movement are very well done, except for when translation should occur.

Another place where things depart from realism in Apache Havoc is flight to either side. It is very hard to pick up any speed while moving the helicopter sideways. In a real helo I have flown sideways at 80 knots. A helo will pick up speed in this direction just as they do in forward flight.

This is one of the big things about helo flight; it doesn't matter what direction you move the cyclic the helo will respond basically the same as if you pushed forward to accelerate. The only difference in response for sideways movement is that the air is being encountered in a less aerodynamic manner.

These departures from the real world made it very difficult to do some basic training moves in Apache Havoc. For instance, doing a circle around an object while keeping the nose of the helo facing it. This is a good training exercise to help control the helo in wind but it is very tough to do because of the way that Apache Havoc handles sideways flight. You should be able to input enough pedal while flying to cause the helo to fly way out of trim.

This brings me to what the wind really does to a helicopter in cruise flight. When flying in even a 10 or 15 knot wind you do not fly with the nose pointed right where you are going. To keep in trim you must use pedal input to keep the helo in trim and to keep traveling the direction you want to go. If you were to fly right down the compass heading required you would find yourself way off course.

Now I will admit that most players wouldn't want this in sims until a company will release proper pedals meant for helicopters. (These would have no spring return on them as helo pedals are very often left out of center while flying.) Apache Havoc really doesn't allow for the airframe to go off of the line you are flying, I assume for that very reason.

I will not even try to compare how either helicopter handles to its real life counter because I have never flown them. For general handling characteristics they handle as well as one could expect from a sim. If you want to talk about a real helo you have to have a joystick that doesn't center and a helicopter that would be much happier if its rotor was below the airframe. The reason a cyclic doesn't center is because the center changes as you fly.

This is one of the nice little features that is in Apache Havoc. You will notice as you gain speed that the cyclic must be moved off to the advancing blade side. You can trim this away just like you would in the real thing.

Retreating Blade Stalls

It is very nice to see a company put retreating blade stalls in a sim even though the crash caused by this is not modeled correctly in the game. I will give you the full explanation for RBS so you can see its real cause and effect for a single rotor helo.

The speed at which the retreating blade tip will stall is dependent on the total pitch of the blade. This pitch is the product of the collective setting as well as that of the cyclic. The collective setting will vary according to the load of the helo, the atmospheric density and the rotor RPM.

As speed of the helo is increased the cyclic requirements increase and retreating blade pitch is built up until finally the stalling angle is exceeded. Since the relative airflow meets the retreating blade at the steepest angle at the tip, it follows that the outer segment of the blade will be the first part to stall due to excessive pitch. The effects have shown to take place slightly aft of the lateral position. 90-degree phase-lag delays the maximum flap to just beyond the full rear position.

The pilot feels this stall as the nose pitches up and the helo has a tendency to roll towards the advancing blade. The roll can happen towards the retreating blade but it is fairly rare. None the less the roll will be vicious and could well be beyond control. If the pilot ignores the vibrations that lead up to this condition they must avoid trying to counter the nose pitching up by using the cyclic. This will increase the angle of attack and make the stall worse. If collective is lowered the blade will not have a sufficient AoA (angle of attack) to remain stalled.

In Apache Havoc RBS is not something that you can recover from, but in most cases you probably wouldn't anyway. Just keep a close eye on your speed and all should go well. Hopefully Comanche Hokum will allow you to lower the collective when you see the vibrations to keep the rotor from entering this state.

Apache Havoc does other things right, like the ground effect model. The ground effect is just the cushion of air through which your helo will acquire extra lift while it is close to the ground.

There are several different theories as to how high a helo may rise with ground effect still present, but it is generally one to one and a half rotor lengths from the ground. In A-H the effect from rising beyond ground effect is a little weak but it would have been right when this sim had vortex ring state in the flight model. (Most of you know that this was removed at the request of beta testers because it was killing them on a regular basis.)

On the other hand, the effect on the main rotor if you are to fly over a building is pretty well done but it really shouldn't happen when you fly over trees. This is an area that can be a problem for helicopter pilots. If you stop to hover above trees with a heavy helo you could easily sink into the trees because you will not have help from the ground effect.

Apache-Havoc also handles tail rotor failures very well; I only wish that there were a throttle modeled so that they could be handled with proper procedure. Many people may not know that it is possible to land a helicopter without the tail rotor but it is an emergency that we train for.

I bet a lot of you thought that a helo would lose control the moment a tail rotor failure happened. This is correct if you are in a hover, but as long as you have airspeed the airframe aerodynamics will prevent the helo from spinning out of control.

A real danger, however, would be that tail rotor failure might take a large section of the tail boom with it. This would cause a loss of balance and the pilot might not have enough movement in the cyclic to hold the helicopter from going over forwards. Any total failure of the tail rotor would have to be landed with what might be a very ugly autorotation.

The flight model in A-H handles combat maneuvers very nicely. Smooth, quick stops are fairly easy to pull off. (When a pilot wants to stop fast, the cyclic is pulled back and the collective is dropped so that the helo will stop without altitude gain. Collective is then reapplied along with pedals as needed so that the helicopter doesn't lose altitude or change heading.)

Steep turns can also be handled in A-H without loss or gain in altitude. Apache pilots are limited to 60 degree banks and + - 30 degrees forward \ rearward tilt. Pop-ups can be done with relative ease and terrain masking is no problem at all.

Descending from mountaintops can be done properly by lowering the collective, not by diving. That is a good way to get into a RBS situation.

Slowing down for a landing is very well done in A-H, and getting right above your set landing spot is as tough as it should be. Landing has the same ground handling problems as take off, but they are more obvious here in A-H because the helicopter will not fall so that all wheels are touching the ground. Again, this is stuff I hope to see fixed in Comanche-Hokum.

I am sure that there are parts of the flight model that I left out because they are just where they should be so I don't even think about them. If you see anything I missed let me know. Questions and comments are welcome as always, just post them in the COMBATSIM.COM™ forums or to Zero G.