Introduction

Recently Eric Marlow was conversing with Zero_G on the topic of helo sims in the industry, in particular focusing on the flight model (FM). Here is part of that conversation. Watch for more from Zero_G soon!

Current Helo Sims:

• Apache (Digital Integration)
• Apache Havoc (Empire Interactive)
• Team Apache (SIMIS)
• Comanche 3 (Novalogic)
• Longbow Gold (Janes)
• Longbow II (Janes)

Coming Soon:

• Ka52 Team Alligator (SIMIS)
• Comanche-Hokum (Empire Interactive)
• Longbow III

By leaving out many important FM aspects developers miss a big part of that system. Here are my own top ten:

1) Torque effects. This can be the nasty little thing that bites you in the ass. To run the pedals in a helo is constant work when at slow speed and somthing that needs attention at higher speeds. They even need to advance from Apache Havoc the more collective you pull the more torque you have thus the more pedal you need. Quick pulls of the collective can be a terrible problem: more so with a heavy load on the helo. This needs to be modeled.

When I was training I was learning how to come out of translation to a hover. I was coming in high to my spot of landing so I thought I would just let the collective down and fall a little faster. My big concern was not getting into a vortex ring state so I watched my rate of descent very closely.

Once you come out of translation the helicopter needs more power to stay up. I never caught the need to pull collective for a moment till I was droping quite fast. Instinct tells you to pull collective, lots of it and fast, so I did.

That is why they have an instructor in the helo with you, the helicopter snapped around so fast that I just froze for 1-2 seconds. That would have been enough for me to get into an almost unrecoverable spin [for someone with low hours] Let's just say I owe my instructor a big one, he reacted very fast to stop the problem then right away made me finish my landing. One quick practical lesson on torque and all the class room speechs about it made perfect sense.) This leads us to #2.

2) Translation. Translational lift is what happens when a helo gets an airspeed of 15-20 mph.The rotor becomes much more effective since it is getting clean air to cut.This makes the helo do a strange kick backwards when moving forward into translation and the helo will want to start to climb. It also makes you need more power when slowing to a hover this addition of power along with the reduced airflow past the helicopters body is why you need to add pedal when slowing and hovering.This is very important to flying but it my be out of reach with todays computer power.

3) Weight. The Apache is rated to carry just over 6000 pounds. This doesn't mean that with a full load like this it can just up and take off. Most helicopters when loaded to full weight must either do a rolling take off much like a plane (the Hind does this for most missions) or they push forward and stay under 6-8 inches in the air until they get translational lift.

If a helicopter is is allowed to slow down while it is loaded heavily it can do a thing called settling with power. This just means that you are too heavy for the helo to hold itself up and it will sink untill it hits something.

This causes many helo crashes when combined with wind. When a pilot is looking for a place to set down, or in the case of a gunship a place to stop and peek over a hill, if all the pilot watches is his\her speed and not airspeed they can get below translation when they have a tail wind. The same happens to pilots moving slowly who then turn down wind. If the wind speed takes their airspeed below translation they can sink into the trees/buildings/rocks below. Doing a proper weight model is very important.

4) Wind. Wind can be a big help if used right and it can kill if you don't pay attention to it. For a better post on some things that wind can do read the post in the Choppers forum called "Odd Apache-Havoc FM Quirk." Though my thoughts on why it wasn't in A/H turned out to be wrong I now am pretty sure some of this is modeled in A/H. Don't forget what wind did to the Apache pilots in the gulf war: it blew them off course enough to make the first kills a friendly APC. Wind is a must have in sim modeling.

5) Vortex ring state. Sadly this was in Apache Havoc but at the request of beta testers it was removed. This is a big must as far as I am concerned.

The reason it was killing so many beta testers is that it is just that dangerous.The rules to avoid this problem are simple and if it happens with enough altitude the escape rules are simple enough also.

What happens is this. If when flying you bring your helo into a slow enough speed, usually 20 mph or less, and you have a sink rate of 500 feet per minute or more you get the helicopter into its own wake and down wash. This makes the helo drop fast and the worst part is the more collective you pull the faster you fall. It may sound like alot to have a 500 fpm sink rate but it isn't: most guys flying helo sims do it all the time.

I have watched helicopter pilot instructors encounter the vortex ring state in sims because they are doing somthing that seems more important. Remember the first rule of flying is to pay attention to that task above all else. The only way out of this mess if you get into it is to lower the collective and push forward to add airspeed. If you are too low for that then you must lower the collective to the bottom and enter autorotation and hope you don't hit too hard.

6) Blade stalls. There are three types of these: retreating blade tip, reverse flow and compressibility stall. For the most part only the retreating blade tip stall will have an effect on normal helos and pilots. I will have to see how it is fixed in Apache Havoc 1.1d. It didn't seem to work at all in 1.1c. It should make the helo vibrate when it first starts then if the helo is allowed to speed up it should pitch nose up and roll over causing a massive loss of control. This also is a must.

7) Throttle. I would kill for a helo sim that lets you control the throttle. It would allow for proper start ups which are easy to mess up and if done wrong you can burn out a turbine in just a few seconds. Proper throttle modeling also allows for autorotations if a clutch is modeled. These are two wishes a bit lower in priority though.

8) Dynamic roll over. I see no reason why it isn't present in todays sims. What happens is as you lift off or land you dig a skid into the ground because of an uneven attitude. Because of the way a rotor moves air as the helo tilts the rotor starts pulling over in that direction. There comes a point when there isn't enough cyclic movement to correct this and the helo rolls over. The only way to correct this is to lower collective and let the helo resettle on the ground and start over.

9) Ground resonance. This happens when a helo on wheels is set down fairly hard and at an uneven attitude. Spin a quarter on end and watch what happens when it runs out of energy. That funny roll around its outside edge is the same thing that will happen to a helo: it can pull the machine apart in a very short time. The best way to fix this is to get it back up in the air. If enough power isn't there to allow lift off then the helo should be shut down right away. This is another thing that is lower on the wish list.

10) I almost forgot about tail rotor failures. They can be controlled if they happen in flight and they made for some of my most sweat filled training. This could only be done if they add in throttle and autorotation controls.