169th_TweetPuke

This is a fairly common feature of US military aircraft. I assume it iscommon to most military aircraft but I don't really know. Typically, flight at less than zero G is limited to a minute or less. The fuel pumps in the feed tank for each engine are surrounded by a bell shaped chamber. There is a "donkey dick" fuel pickup that can swing around under negative G to the "top" of the chamber to pick up whatever amount of fuel is trapped there. When the fuel is consumed from the chamber it gets very, very quiet and the pilot gets demoted to test pilot so he can verify the crowbar-like gliding qualities of high wing loaded jets. Engine oil systems (in older jets anyway since I don't know about more current ones) often have similar, or less, negative G capability as well. This isn't really too restricting as there is very little use for negative G flight beyond a short duration "bunt" unless the aircraft is used for display purposes. It can then be modified to meet those requirements. It's all about the real reason airplanes fly: $$$$$$

Thanks for the info Shepski. A CG that is close to the location of the main gear would in fact contribute to a low weight on the nose gear and reduce the traction the nosewheel can generate. This would account for the "twitchiness" while taxiing. I still don't see this as a particularly big deal. It's as simple as watching your speed while taxiing and not getting into high speed turns. However, I would expect an aft CG to have an entirely different effect on pitch stability and control. Let me explain. The CG in most aircraft without computers to maintain pitch stability is forward of the center of lift. This configuration requires the horizontal tail to generate a "down" force to zero the sum of forces and maintain level flight. A pitch increase is created by raising the aft edge of the elevator or horizontal slab which decreases the angle of attack of the horizontal tail generating additional down force on the tail which raises the nose. It's all very much like a seesaw. The distance between the CG and the center of lift is critical to pitch stability. A greater the distance requires more down force to be generated by the horizontal tail to effect a pitch increase. The result is greater pitch stability as the horizontal stab will have to generate higher loads to make even small pitch movements. The closer the center of lift is to the CG the less the pitch stability. Small movements of the horizontal stab can now generate large pitch moments. This relaxed pitch stability is what makes possible the tremendous maneuverability of recent generations of fighter aircraft. Advanced computer flight control systems are absolutely necessary since mechanical systems and a pilot cannot keep up with the greater sensitivity. So there's my problem with the aft CG answer. An aft CG would increase pitch sensitivity and stick forces would be lighter if everything else is equal. It also shouldn't affect buffet as buffet is a function of the lift characteristics of the wing and/or, possibly, horizontal tail positioning relative to the wing or external stores. The onset of buffet is quicker for heavier loading and higher drag indexes but those are really still a function of the lift characteristics of the wing. Also, the buffet seems to be programmed to occur only with the onset of stall. I'm sure it's a limitation of the FM and isn't an error. I'd just like to see these jets buffet the way they do when you load up the G in real life, without the loss of lift due to stall. But then we wouldn't ahve anything else to hope for in the future. Shepski, the best information you had is that the -25T has to be flown in real life like it does in the sim. That's the best indicator of how good the simulation and FM really is. I can accept that. I'm just thankful I don't have to take this hog into real combat with it's bad habits.

I'm the other guy Cobra discussed the flight model with in that session in the -25T where he had so much trouble with tires. I never had the problem of blowing tires but I do have some concerns about the flight model or, possibly, the handling characteristics of this beast. Much of my initial dissatisfaction was due to stick setup. I have a FSSB mod Cougar that used to have a curve built into the stick and another slight curve in game to refine the feel. Many problems were resolved by removing both curves. It makes every other aircraft in LO a bit twitchy but that's not a bad thing once I got used to it. Still, there's something not exactly right. It's very hard to say without having flown the aircraft whether it's FM or handling qualities. The areas I'm not sure about are: 1. Takeoff - Several people have mentioned the high stick forces necessary to rotate. I agree that they are a bit high but I don't think this is necessarily wrong. It's not unusual to require high stick forces to get the nose off of the ground. This can even be a design feature of an underpowered, high wing loaded aircraft like the -25T. My technique follows real life and manual/tutorial suggestions: rotate to pitot tubes on the horizon at about 250 kph and allowing it to fly off. That usually occurs at 280-300 kph for me. I think the problem many people have is in maintaining that attitude, especially if holding crosswind controls at the same time. This is partially a function of the limitations of our control syatems but may also point to experience with a higher fidelity FM. 2. Roll - There is a tremendous amount of inertia in the roll axis and not very much roll authority to the flight controls. It takes a lot of stick to get a roll going and stopped. It rolls slowly even with high stick pressures. I like the implementation of inertia. While I think it may be a bit too high, it is well done. The main complaint I have is in control authority, it's poor. A heavy 747 has a similar roll rate. That's fine in an airlines but is unsatisfactory in an attack aircraft. The fairly high stick forces further exaggerate the effect. Now, this may be how the real jet flies. If so, I can't believe it ever made it out of flight test. 3. Pitch - I have similar comments to those I made about the roll problem. At first, I thought it handled much like a mechanical control system but I understand the elevator is hydraulically boosted. That seemed very strange again. It didn't make sense to me until I thought about this being an underpowered, high wing loaded aircraft. This could be a design characteristic to temper the effect of a hamfist pilot. I can accept it this way but, again, I find it hard to believe an air force would accept such poor pitch authority in an attack aircraft. Here's an example of why I think something is not right. I like making weapons passes fast. That's a no brainer. When I come off the target and plan a reattack I have to reposition. I use a whifferdill to do this. The idea is to run out of the target area a short distance (stay within visual range of the target, threats permitting) ease the nose up to bleed speed and decrease turn radius and increase turn rate in the reposition maneuver. As the speed gets below ~450 kph I roll into 90-135 degrees of bank and add backpressure to get the nose below the horizon so I don't slow to less that 370-400 kph while pulling it around through 180 degrees of turn. I come out of the turn nose low with building airspeed for another pass. It's a great technique that retains energy and keeps your speed up in the pass. It also is difficult to do in the -25T. There is a fairly limited airspeed range between low speed stall and high speed buffet which acts similarly to a stall (I don't think this is right at all). This limits the pitch attitude you can get before you run out of airspeed and then the turn rate is abysmal as you're always right on the edge of low speed or an accelerated stall. I've tried several different airspeeds, pitch, and bank variations with pretty similar results. 4. Airspeed envelope - I'm not too concerned that a heavily loaded, underpowered -25T can't go faster than 450-500 kph (242-270 knots which is slower than a loaded A-10!)although I find it curious. I do find it very strange that it maxes out at around 700 kph (378 knots) and that when it does it buffets and acts like it is in a stall. That doesn't make aerodynamic sense. I could accept that it buffets or that it hits a sudden drag increase that prevents it from going any faster. It's the loss of pitch and/or roll control authority that I doubt. The causes of these behaviors can be many. Thrust, drag, inertia, control authority, or stall modeling could each have a part in it. Or it could be this aircraft truly just barks and bays at the moon. Past Soviet designs have been notorious for horrendous handling characteristics and control quality. (The MiG-19 comes to mind as the best example.) So, it's definitely possible in my opinion. Now, all of the criticism aside. I think this is by far the best flight model I've seen in a desktop sim. I think the stall modeling is still weak, too computerish ie only on or off, but everything else is top drawer. Like I said earlier I also think much of the criticism of how this thing flies can be laid at the feet of our stick and rudder systems. I'm very interested in any explanations you testers might have.