How do propellers throttle?

[catloaf]

This is a simple question, but I know very little about how these things work. My question is how do propellers throttle? I can't imagine they use blade pitch like in ksp. I have seen many things propeller planes and most don't appear to have propellers that can change pitch. Also, in rl I have flown drones that can definitely throttle and definitely don't have pitching propellers. This is also how planes behave in simulators like real flight 9. My best guess as to why this is not true is that ksp's physics engine cannot simulate rpm's high enough for propellers to throttle by changing rpm like my drone appears to. 

Edited July 13, 2020 by catloaf

[mikegarrison]

17 minutes ago, catloaf said:

This is a simple question, but I know very little about how these things work. My question is how do propellers throttle? I can't imagine they use blade pitch like in ksp. I have seen many things propeller planes and most don't appear to have propellers that can change pitch. Also, in rl I have flown drones that can definitely throttle and definitely don't have pitching propellers. This is also how planes behave in simulators like real flight 9. My best guess as to why this is not true is that ksp's physics engine cannot simulate rpm's high enough for propellers to throttle by changing rpm like my drone appears to. 

Actually, most propellers do use blade pitch. Very simple setups change rotational speed, but other than that propellers are usually run at constant speed and change the amount of power they put into the air by changing pitch. The reason for this is because tip speed is an extremely important design parameter, and it's easier to design the propeller for constant tip speed than to avoid variable pitch.

Of course, engine power also needs to be adjusted to match, because the power that the propeller puts into the air has to come from somewhere.

Edited July 13, 2020 by mikegarrison

[Kerbart]

Actually most propeller planes, especially the larger ones, do have variable pitch. You can also change the RPM of the engine, that's how drones do it.

Throttle usually is power while you can think of pitch as the gear you're in. While cruising you want a "high gear" but you don't want to rev the engine, just like you'd do on a bike (compared to, say, climbing)

[catloaf]

20 minutes ago, Kerbart said:

Actually most propeller planes, especially the larger ones, do have variable pitch. You can also change the RPM of the engine, that's how drones do it.

Throttle usually is power while you can think of pitch as the gear you're in. While cruising you want a "high gear" but you don't want to rev the engine, just like you'd do on a bike (compared to, say, climbing)

Thanks for the analogy, that is what flying a plane in ksp feels like. Changing blade pitch appears to change the speed just like changing years on a bike, not the rate of acceleration like pedaling harder. I also have another question: how should you fly a propeller plane in ksp. Should you ever turn down the rpm on your engine while flying, or should you change your speed only with blade pitch? Also, assuming that you do change engine rpm, how do pilots change their speed? Do they have two throttles or is it automated in some way.

Edited July 13, 2020 by catloaf

[Kerbart]

9 minutes ago, catloaf said:

Thanks for the analogy, that is what flying a plane in ksp feels like. Changing blade pitch appears to change the speed just like changing years on a bike, not the rate of acceleration like pedaling harder. I also have another question: how should you fly a propeller plane in ksp. Should you ever turn down the rpm on your engine while flying, or should you change your speed only with blade pitch? Also, assuming that you do change engine rpm, how do pilots change their speed? Do they have two throttles or is it automated in some way.

The problem with KSP's control model is that effectively you control RPM, not throttle.

In most internal combustion airplanes you'll have (sets of) three levers; from left to right: throttle, pitch, mixture.

Throttle is just that - how much fuel is going to the engine. Add more fuel, and the engine will work harder. Cut back on fuel, on the engine will work less hard.

Pitch we discussed - it's the "gear" of your propeller.  High pitch gets you high velocity, but also high resistance. Low pitch gives you low velocity.

Throttle up at low pitch, and the engine's RPM will increase until the resistance of the air beating the propeller matches the engine's power. To make the "game" more difficult, usually your engine will proved more power at high RPM's, but that also heats up the engine a lot. So when you're done climbing to a desired altitude you usually can cut down on RPM (less power needed) but increase the pitch to maintain velocity.

Finally as most small ("general aviation") airplanes are self-balancing, the controls work reverse of what you'd expect. Increase throttle will indeed increase speed at first, but that will result in more lift and the plane starts to climb, losing speed again. In a similar fashion, pulling the stick will pull the nose up, increases lift, plane climbs, loses speed. Increase throttle and your plane will usually "settle" for the same velocity but with a higher rate of climb; pull the stick and your plane tends to stick to the same rate of climb but with a lower velocity.

Flying with full throttle controls in MS Flight Simulator or X-Plane (or in a real aircraft) is a fun exercise that comes fairly natural after a little while but it's very different from how you control planes in KSP.

[WestAir]

Most small 4 seat single engine planes have just a throttle and mixture (fuel-air ratio) lever. 

Most multi engine propeller planes have another lever for propeller pitch. Some planes automatically "feather" the propellers if the engine quits.

I don't know how helicopters work.

[Entropian]

1 minute ago, WestAir said:

I don't know how helicopters work.

https://en.wikipedia.org/wiki/Helicopter_flight_controls#Collective

[Shpaget]

Helicopters are especially reliant on pitch control since they need it for up/down, but also left/right and front/back movement.

Up/down, or more precisely, total thrust, is controlled by collective pitch where all the blades change their pitch in unison.

Forward/backward and left/right movement is achieved by cyclic pitch, which changes pitch depending on where each blade is currently, relative to the helicopter body, so blades generate more lift on one side of the helicopter and less on the opposite. Cyclic pitch gives opposite blades opposite pitch adjustment. Of course, collective pitch is added to the cyclic pitch so there is no negative thrust (well there could be if the pilot so chooses and the mechanics allow it, that's how model helicopters can achieve those insane aerobatics).

This model helicopter has the same controls as a full size helicopter (probably greater range of pitch control, but same type).

The tail rotor on conventional helicopter is only used to counter the torque of the main rotor and prevent the entire helicopter from spinning in place. Other than that it has no purpose, which is evident from different configurations, such as two rotors on Chinook, or coaxial rotor on Ka-50. Those don't have tail rotors.

Edited July 13, 2020 by Shpaget

[mikegarrison]

20 minutes ago, Kerbart said:

Finally as most small ("general aviation") airplanes are self-balancing, the controls work reverse of what you'd expect. Increase throttle will indeed increase speed at first, but that will result in more lift and the plane starts to climb, losing speed again. In a similar fashion, pulling the stick will pull the nose up, increases lift, plane climbs, loses speed. Increase throttle and your plane will usually "settle" for the same velocity but with a higher rate of climb; pull the stick and your plane tends to stick to the same rate of climb but with a lower velocity.

This is how all airplanes work in cruise. (It's different for direct thrusting climb, like a rocket or a fighter climbing straight up with T>W).

The general situation for steady-state flight:

• Lift = Weight
• Thrust = Drag
• Lift = (L/D) * Drag
• Lift coefficient is proportional to angle of attack
• Lift = 1/2 * density * airspeed^2 * wing area * lift coefficient

L/D is generally a fairly constant number based on aspect ratio and other factors. So that means lift is directly proportional to drag, and thus to thrust. So increasing thrust increases lift. When lift increases, the plane climbs.

Therefore: to make a plane climb, increase thrust.

What about if you pitch up? Well, that changes your angle of attack. That makes your lift coefficient increase. But if you don't increase your thrust, then your total lift stays the same. So if total lift stays the same, density stays the same, wing area stays the same, then if lift coefficient increases then airspeed must decrease.

So angle of attack controls airspeed, and thrust controls climb/descent. (All this assumes quasi steady state lifting cruise.)

[Guest]

Actually, the part about pitching up changing the angle of attack isn't exactly true. You got it backwards. Changing pitch decreases the horizontal thrust (because part of it is now used to raise the altitude) and that causes an airspeed drop, resulting in increased AoA, which in turns increases drag and slows you down even further.

In theory, throttling up to climb works, but you'll pick up a lot of speed doing that. In practice (at least, the way I've heard it), you only control climb/descent with throttle during landing, where you use the throttle to control angle of attack, which is directly related to your angle of descent. In all other regimes, you use throttle and elevator in coordination in order to keep your airspeed more or less constant. Autopilots sometimes include an airspeed hold that does this automatically (you throttle up, it pitches up to maintain the desired airspeed). If you try to accelerate in straight line without stick input, the plane will climb, but that's because it'll be out of trim for the new airspeed, and in most airliners, thrust will induce an additional pitching moment, because the engines are below the wings (An-72 will push the nose down with increased thrust because of this).

Edited July 13, 2020 by Guest

[StrandedonEarth]

My 3 cents: (2 cents adjusted for inflation): Large multi-engine propeller-driven airliners and especially bombers had the ability to feather the propellers in case the engine quit or was shut down. This prevented the propeller from windmilling the engine, reducing drag and preventing further damage to the engine (which could also damage the airframe). So pitch control was a given.

[catloaf]

Ok, so here's what I have absorbed: increasing throttle changes how hard the engine will work to try and work to raise its rpm, so once your at the desired rpm you can throttle down. Ksp does not stimulate this correctly because you can control rpm, not how hard the engine working. Changing blade pitch changes how much you will accelerate, as well as what speeds you can reach. However, higher pitch puts more strain an the engine, meaning it needs to work harder, thus you may need to throttle up when you increase pitch until you reach the max speed for that pitch where you can throttle down again. 

Edited July 13, 2020 by catloaf
Once again I'm probably wrong.

[WestAir]

Go to a Delta crew room full of reserve pilots and ask if you pitch for speed or altitude.

You'll get more answers than words in the dictionary. I used to be in the biz, and my answer was always "both," because using both stick and throttle usually got me into whatever config I wanted and made check airmen happy. 

The truth is: I think a lot of 5k hour pilots and aeronautical degree students don't know as much as they think they know. God knows I didn't.

[K^2]

33 minutes ago, Dragon01 said:

Actually, the part about pitching up changing the angle of attack isn't exactly true. You got it backwards. Changing pitch decreases the horizontal thrust (because part of it is now used to raise the altitude) and that causes an airspeed drop, resulting in increased AoA, which in turns increases drag and slows you down even further.

In theory, throttling up to climb works, but you'll pick up a lot of speed doing that. In practice (at least, the way I've heard it), you only control climb/descent with throttle during landing, where you use the throttle to control angle of attack, which is directly related to your angle of descent. In all other regimes, you use throttle and elevator in coordination in order to keep your airspeed more or less constant. Autopilots sometimes include an airspeed hold that does this automatically (you throttle up, it pitches up to maintain the desired airspeed). If you try to accelerate in straight line without stick input, the plane will climb, but that's because it'll be out of trim for the new airspeed, and in most airliners, thrust will induce an additional pitching moment, because the engines are below the wings (An-72 will push the nose down with increased thrust because of this).

You are getting yourself confused somewhere. When you throttle down, in steady state, AoA stays constant, air speed stays constant, and you descend. Your pitch angle changes, because your relative wind now has vertical component, so the same AoA means a more nose-down attitude. Likewise, if you throttle up, the nose goes up and you start climbing, but again, AoA and air speed stay pretty much constant.

And the reason is that airplanes are intentionally built this way. The CoP of the main wing is behind CoG, which means that with no other forces, the only direction a plane would be going is a vertical dive. But the horizontal stabilizer on the tail is built for negative lift and is way behind the CoG. The net CoP is balanced on CoG in level flight. Now, if you apply external force to force a plane to pitch up, AoA on both the wing and stabilizer increases, which increases lift on the wing and decreases negative lift on the tail. This shifts CoP back and causes the plane to pitch forward. Likewise, trying to force the plane to pitch down results in CoP shifting forward and plane pitching up. Assuming all other factors impact your wing and stabilizer the same way, AoA is fixed in steady state and depends only on position of elevators. And because "neutral" position of elevators depends on your trim settings, when you trim your aircraft, what you're really trimming for is specific AoA.

And as pointed out, if AoA is fixed, so is the air speed. Once airplane settles down to your adjustments, all forces and torques are balanced. (That's definition of steady state.) That means Lift + Weight + Drag + Thrust = 0. And unless you're doing something really drastic, Lift and Weight are roughly opposed and Drag and Thrust are roughly opposed.

With this in mind, what @mikegarrison wrote should make more sense. If you keep your trim settings and throttle down, the AoA can't change, because your elevators didn't move. The lift hasn't changed, or you'd be accelerating down. And so the only thing a plane can do is continue at the same air speed, descending gradually, trading gravitational potential energy to substitute for reduced power from the engine.

Now, all of this works to first order. Yes, real planes are more complex. L/D is not constant. It's a factor of absolutely every variable mentioned and a few that weren't. The wing and stabilizer do not respond the same way to air speed changes, because they aren't the same shape and there is air stream interference. If your climb/descent rate are significant, then your lift and weight vectors are not colinear. All of that means that in a realistic scenario, if you adjust one thing, you have to adjust all the others. It's not as bad as flying a helicopter, but you still have to coordinate your inputs. Nonetheless, if you want to descend, you reduce throttle and then correct everything else. If you want to slow down you pitch up, correct everything else, then trim if you're happy with the new speed. The intention is still tied to a specific input, with other inputs being corrective. Mentally, think of it as a difference between making small adjustments to the steering wheel in a car when you're hit by sudden gust of side wind vs making deliberate turn. You're turning the steering wheel in both cases, but intention and how you process it are very different.

Disclamer: I don't have significant air time on anything larger than a C172. So this might not strictly apply to airliners, but I haven't heard anything that implies it shouldn't.

[mikegarrison]

I believe the issue here is that we're talking about simplifications in the physics. As I mentioned, what I wrote applies to quasi steady state level cruise. Obviously if you change something, it's no longer exactly steady state. And yeah, it's a simplification to say that thrust has no relationship to speed or that pitch only controls speed.

There are also differences in the level of the analysis. The simplified description I wrote up doesn't explicitly consider things like the cosine losses to lift as you change body angle. This level of detail is unimportant to the big picture, although it still is real.

The big picture is that thrust is how you add energy to the airplane. Energy can be used for speed or altitude. You can use thrust to speed up, and you can climb by pitching to convert your speed to altitude. But generally speaking, mainly you (or your autopilot) climb by adding thrust, and mainly you (or your autopilot) control speed by changing the pitch.

(There is always a most efficient trim for your airplane to be in, and if you change away from that you will obviously lose efficiency, which means adding energy, which means adding thrust. So you can't just speed up or slow down by changing pitch without having some other effects. When an airline crew decides they need to make up time and therefore fly a little faster, the autopilot will lower the lift coefficient in order to match the increased airspeed. But it's also going to have to bump the thrust up a bit because the airplane is now in a less efficient trim.)

Edited July 14, 2020 by mikegarrison

[Guest]

9 hours ago, K^2 said:

You are getting yourself confused somewhere. When you throttle down, in steady state, AoA stays constant, air speed stays constant, and you descend. Your pitch angle changes, because your relative wind now has vertical component, so the same AoA means a more nose-down attitude. Likewise, if you throttle up, the nose goes up and you start climbing, but again, AoA and air speed stay pretty much constant.

Airspeed certainly does increase if you throttle up, even if you don't retrim the aircraft. I just checked that with C172 in X-plane, by trimming it for level flight and then firewalling the throttle. It does go out of trim and start to pitch up, and if you don't do anything it'll eventually start slowing down (right up to the point where it enters a dive). Either way, the throttle is not an effective way of controlling altitude, unless you have an autopilot to handle the elevator for you. 

9 hours ago, K^2 said:

And the reason is that airplanes are intentionally built this way. The CoP of the main wing is behind CoG, which means that with no other forces, the only direction a plane would be going is a vertical dive. But the horizontal stabilizer on the tail is built for negative lift and is way behind the CoG. The net CoP is balanced on CoG in level flight. Now, if you apply external force to force a plane to pitch up, AoA on both the wing and stabilizer increases, which increases lift on the wing and decreases negative lift on the tail. This shifts CoP back and causes the plane to pitch forward. Likewise, trying to force the plane to pitch down results in CoP shifting forward and plane pitching up. Assuming all other factors impact your wing and stabilizer the same way, AoA is fixed in steady state and depends only on position of elevators. And because "neutral" position of elevators depends on your trim settings, when you trim your aircraft, what you're really trimming for is specific AoA.

The AoA increase only comes into play during the pitch up. All that applies only to the situation when you're actually deflecting the control surfaces. After you release the stick pressure, the airplane will return to close to its previous AoA (disregarding the airspeed drop from increased drag during the maneuver), only it will be flying at an angle to the ground. As this period is relatively short in practice, I disregarded it. 

9 hours ago, K^2 said:

Disclamer: I don't have significant air time on anything larger than a C172. So this might not strictly apply to airliners, but I haven't heard anything that implies it shouldn't.

I've yet to get a real pilot's license, but I've flown everything from warbirds to jumbo jets in flightsims. Quite a few of them (mostly fighters, but also some Russian airliners) are equipped with AoA indicators. Unless you're actively doing something with the controls, AoA depends only on your weight and airspeed. At extreme angles of climb, it gets more complicated, because a significant portion of your weight is supported by the engine and not by the wings, but in normal conditions this isn't noticeable.

[K^2]

7 hours ago, Dragon01 said:

Airspeed certainly does increase if you throttle up, even if you don't retrim the aircraft. I just checked that with C172 in X-plane, by trimming it for level flight and then firewalling the throttle. It does go out of trim and start to pitch up, and if you don't do anything it'll eventually start slowing down (right up to the point where it enters a dive). Either way, the throttle is not an effective way of controlling altitude, unless you have an autopilot to handle the elevator for you.

- "To change lanes, simply turn the steering wheel gently. The car will start to drift to adjacent lane without altering its speed."

- "I just tried this. I jammed the steering wheel all the way and the car span out of control and crashed."

That's not how you drive a car and it's not how you fly a plane.

7 hours ago, Dragon01 said:

AoA depends only on your weight and airspeed.

You're still getting that backwards. Airspeed depends on your AoA, and AoA depends on elevator settings. Yes, weight and balance will determine which elevator setting corresponds to what AoA.

Again, you can't change steady state airspeed of an aircraft without changing AoA by changing your control surface positions. If you go faster, lift exceeds weight, and you accelerate up. You can't endlessly accelerate up, so you will reach a new equilibrium at some climb rate. And your equilibrium AoA doesn't depend on your climb rate or air speed, because it's just a balance of torques. If you are no longer climbing and your AoA is the same, then your air speed settled back on its original value. What other options are there?

I can't help the fact that this contradicts your expectations. That never stops physics from working, I checked. And the rest is just confirmation bias, I'm afraid. Jamming inputs to the limits, watching plane do something erratic, and then divine some sort of pattern that matches your expectation is not the right way to check yourself. Trim an airplane for level flight at 70% throttle. Smoothly cut throttle to 60%. Wait for plane to settle. How much did the air speed change? How much did AoA change? What's your new glide angle?

Next exercise. Put a plane in slow level flight on approach to a runway. It should maintain altitude and heading on trim alone. 1,000 feet AGL at 60 knots for a 172 should be good for this. Now try to land the plane without touching the throttle until you are wheels down. Repeat, but this time, land without touching elevator controls or elevator trim. Was that easier or harder?

[Guest]

3 hours ago, K^2 said:

That's not how you drive a car and it's not how you fly a plane.

No, normally what you do is to adjust your throttle, your elevator and your trim whenever you want to do anything. If you want to correct your altitude by a handful of feet, then maybe minute throttle adjustments are the way to do that, but in the general case, elevator is very much used. In fact, during the initial climb, you use full throttle and adjust elevators to maintain optimal climb airspeed. This is true both in Cessna and in the F-16.

I admit, I am coming over from fighters, where "jamming inputs to the limits" is something you do quite often, especially in modern FBW birds. So I might be flying that Cessna a little rougher than it's usual. However, physics don't change between a Mustang and a C172, only engine power (that and the fact you can trim your ailerons in a Mustang). AoA depends on weight and airspeed. In fact, military planes usually don't have a landing speed specified, because their weight varies so much that it would be pointless. Rather, they have a specific AoA that you're supposed to hold. For civilian planes, it works the same physically, only instead of flying the AoA indicator, you have to calculate a landing airspeed which, incidentally, is the airspeed which would give you the proper AoA for landing.

It helps to think of what fighter pilots call "energy", and which in physical terms is the sum of kinetic and potential energy of the plane. Your engine gives you energy, which you can put into airspeed, or into altitude. By changing your pitch, you adjust how much of your thrust is going into either. Drag takes away your energy at a rate dependent on your airspeed and AoA, which is dependent on your airspeed and weight. Gs you're pulling (by actuating your elevators) factor into the latter, but most GA planes can't stray too far from 1G. Pitch itself doesn't, as long as you're not climbing or descending so steeply that it causes your G-load to change.

As I said, landing is one situation where you generally use your throttle for fine glideslope adjustments. However, that assumes you're close to glideslope in first place. It's pretty easy to correct three whites or three reds that way, but if you've got four whites or four reds, I'd adjust the elevators, too. Another example of precision flying, that is formations, doesn't do that, though. You control your vertical and horizontal position with the stick, your overtake with the throttle, because there you don't care much about AoA, but airspeed has to match pretty exactly. I've never flown formation in a Cessna, but warbirds (and real formation manuals) certainly do work like this.

Edited July 14, 2020 by Guest

[wizzlebippi]

Since no one really answered OP's question, here it is. Engines throttle and propellers govern RPM. A simple constant speed prop for a piston engine uses engine oil pressure to drive a hydraulic cylinder in the prop hub. The amount of oil it is fed is controlled by a centrifugal governor mounted to the side of the propeller shaft. When the engine is throttled up, it tries to increase RPM. This drives the governor to feed more oil into the hub, which increases the pitch of the blades. This increases the load on the engine, and prop RPM remains relatively constant. Likewise, when the engine is throttled down, the pitch on the blades is decreased and engine RPM remains about constant.

Multi engine aircraft have the ability to feather the prop, or turn the blades such that they are parallel to the air flow to minimize drag. I think they're supposed to automatically feather when oil pressure is lost, but don't quote me on that. The aircraft I work on have contained spinny things and I'm not multi-engine rated.

Turboprops are a more complicated beast with the ability to feather and reverse pitch, usually requiring multiple governors (I've heard that the venerable PT-6 uses 3).  Again, not sure how that works.

[K^2]

1 hour ago, Dragon01 said:

No, normally what you do is to adjust your throttle, your elevator and your trim whenever you want to do anything. If you want to correct your altitude by a handful of feet, then maybe minute throttle adjustments are the way to do that, but in the general case, elevator is very much used. In fact, during the initial climb, you use full throttle and adjust elevators to maintain optimal climb airspeed. This is true both in Cessna and in the F-16.

Yes, you adjust your elevators to set your air speed for V_Y or V_X as desired with balls to the wall. Because elevator is used to control your air speed, and at full throttle, your climb rate depends on your air speed. And there's a reason F16 is called a lawn dart.

Again, try landing a 172 in simulator using only a throttle. Set the trim for 60 knots and don't touch elevator controls at all. In fact, just unbind them. Might take you a few tries, but you'll be a better pilot with what you learned.

[Guest]

The F-104 was the Lawn Dart, we call the F-16 the Viper.  Though since every plane has an optimum climb airspeed, this part is the same for all of them, only the required angle changes. This only applies during the climb, though. In enroute configuration, throttle controls airspeed and you trim out any pitch up or down tendency, especially if you're flying formation.

Oh, and I've landed Hornets using only the throttle and the trim switch. On a carrier. So let's say I've got that part figured out.  In fact, if you have to make stick movements (except to enter turns, and even then it's only for banking) at any point in the pattern, you will almost certainly miss the wires. Then again, you've got no room error on the boat. A glideslope deviation that would give you three reds on an airfield is pretty much grounds for technique waveoff at sea, so there's no such thing as a "coarse correction" (not if you want to trap safely, at least).

[K^2]

2 hours ago, Dragon01 said:

The F-104 was the Lawn Dart, we call the F-16 the Viper.

Maybe if you're in AF. If you're a general aviation pilot, you know that any fighter jet is called a lawn dart, but especially the F-16.

2 hours ago, Dragon01 said:

Though since every plane has an optimum climb airspeed, this part is the same for all of them, only the required angle changes.

Yes. And for F-16 best rate of climb angle is 90° with enough thrust left over to be "free falling" straight up settling on modest transonic speeds. Meanwhile, F-15 and F/A-18 do actually need a bit of lift to get them off the ground, but so little that it can actually be entirely body lift, with Israeli F-15 infamously landing without a wing. The way these aircraft stay in the air has more in common with physics of skipping rocks than aerodynamics of an airliner, let alone a general aviation aircraft. Most crucially, they aren't stable, with flight computer actually responsible for turning pilot's inputs into movement of control surfaces that result in the sort of movement of the aircraft that makes intuitive sense. When you pull on the stick in a modern fighter, it doesn't translate into movement of elevators. It translates into movements of every single control surface throughout the aircraft. This is almost never simulated in flight sims. Instead, they fake a conventional aerodynamics model that resembles the flight dynamics of a fighter, but which is, in fact, stable. The virtual control surfaces that simulation uses usually have nothing to do with locations of real control surfaces on a jet. Building an actual aerodynamic model of a fighter jet would require writing a dedicated flight computer for every fighter, and that's almost never done. Stock X-Plane and Microsoft Flight Simulator X jets most certainly do not do that, as I have messed with modding these. There might be some modded aircraft out there that attempt to reproduce correct flight model and flight computer behavior, but since all of the originals are military secrets, it can only be an approximation.

Which is why bringing fighter piloting experience from a generic flight sim, not one built for military training, is just a tier above citing an action movie. They do replicate a lot of the flight characteristics, and some better ones even do a decent job in replicating the feel of flying such a plane. But they have almost nothing to do with physics of an actual fighter jet, because that's just not the sort of thing these games are built to simulate.

It's also why I keep telling you to load up the C172. One of the nicer things about that plane is that it has a very simple aerodynamic model. Outside of wind shear, the hardest thing to simulate on it is p-factors, and that's not very hard. I cannot overstate the difference that a real cockpit makes with all the movement, vibration, that feeling of seat pushing into you as your wing load increases, and how you can feel every shift of the wind on a small plane. But all of that aside, even older flight simulators tend to do a good job of simulating how a C172 actually responds to input and how it behaves in the air. So it's a good test case. You can learn almost everything you need to know about flying that plane from a sim. Though, it might not be clear why some good practices are good practices until you get into a real cockpit and try to land a real plane.

Oh, and don't get me started on tail draggers. No sim will EVER prepare you for experience of landing a tail dragger. 

[KerikBalm]

5 hours ago, K^2 said:

Yes. And for F-16 best rate of climb angle is 90° with enough thrust left over to be "free falling" straight up settling on modest transonic speeds.

Ummm, no no no. Gravity drag losses would be terrible.

Anyway, to the question, there's a lot of ways to control your "throttle". It also depends on the aircraft and how fast it will fly. Take a powered hangglider: The speed range of the aircraft is not significant compared to the speed of the blade tips - You can just control the engine throttle (and RPM) while using a fixed pitch blade. Look at WWI aircraft designs: fixed pitch blades.

You can see this in KSP as well, if you design a plane that flies at very low speeds, you can adjust speed with just engine power.

If the blade tips are going 100 m/s, and you are going 10m/s, and want to increase rpm/speed/blade tip velocity, their AoA doesn't change much. Say you throttle up, blade RPM increases to 200 m/s, and your speed increases to 20 m/s... your blades have the same AoA. When you increase engine power, and thus increase RPM, the AoA remains pretty much the same, but the forward lift from the blades increases.

Now, Imagine you have a 30 degree pitch, your blade tips are going 200 m/s. At zero airspeed, your blade AoA is 30 degrees. At 100 m/s airspeed, your blade AoA is 0 degrees. You have 2 options, increase rpm, and thus blade speed, or increase pitch. Increasing blade speed works fine at low speeds, but as the blade tips approach mach 1, that becomes a bad idea, and its better to increase pitch.

You also have to account for the inertia of the blades. Changing pitch gives a much faster response than changing the speed of the blades.

 

To the subject of airspeed, throttle, steady states, etc. As a hang-glider pilot that has never used an engine, the question of throttle doesn't come up really.... but... ever fixed wing aircraft has an optimum AoA that gives it the best L/D. Every fixed wing aircraft also has a minimum sink AoA that is a bit higher than best L/D. If you were to have an engine, its between these AoAs that you would want to fly to optimize range or climb rate.

For a glider, to fly slower, you raise your AoA (this will temporarily trade airspeed for altitude, until a steady state is reached) - as long as you don't exceed a critical AoA that results in a stall*.

To fly faster, you lower your AoA (this will temporarily trade a lot of altitude for airspeed, resulting in a steep dive that will get shallower as you pick up speed).

* In a hanglider, I think the landing flare is quite different from the flare of a GA plane, which brings the vertical descent speed to close to zero, but does not stall the plane. A hanglider on the other hand will get into ground effect, bring vertical speed to zero, and increase AoA to maintain altitude, and then punch the AoA as high as possible when the critical AoA is reached, to allow one's feet to serve as landing gear.

Spoiler

and just fun shots:

Spoiler

 

See the birdy in the pic below, on the right... dogfighting?

 

 

 

Edited July 15, 2020 by KerikBalm

[magnemoe]

7 hours ago, KerikBalm said:

Ummm, no no no. Gravity drag losses would be terrible.

Anyway, to the question, there's a lot of ways to control your "throttle". It also depends on the aircraft and how fast it will fly. Take a powered hangglider: The speed range of the aircraft is not significant compared to the speed of the blade tips - You can just control the engine throttle (and RPM) while using a fixed pitch blade. Look at WWI aircraft designs: fixed pitch blades.

You can see this in KSP as well, if you design a plane that flies at very low speeds, you can adjust speed with just engine power.

If the blade tips are going 100 m/s, and you are going 10m/s, and want to increase rpm/speed/blade tip velocity, their AoA doesn't change much. Say you throttle up, blade RPM increases to 200 m/s, and your speed increases to 20 m/s... your blades have the same AoA. When you increase engine power, and thus increase RPM, the AoA remains pretty much the same, but the forward lift from the blades increases.

Now, Imagine you have a 30 degree pitch, your blade tips are going 200 m/s. At zero airspeed, your blade AoA is 30 degrees. At 100 m/s airspeed, your blade AoA is 0 degrees. You have 2 options, increase rpm, and thus blade speed, or increase pitch. Increasing blade speed works fine at low speeds, but as the blade tips approach mach 1, that becomes a bad idea, and its better to increase pitch.

You also have to account for the inertia of the blades. Changing pitch gives a much faster response than changing the speed of the blades.

 

To the subject of airspeed, throttle, steady states, etc. As a hang-glider pilot that has never used an engine, the question of throttle doesn't come up really.... but... ever fixed wing aircraft has an optimum AoA that gives it the best L/D. Every fixed wing aircraft also has a minimum sink AoA that is a bit higher than best L/D. If you were to have an engine, its between these AoAs that you would want to fly to optimize range or climb rate.

For a glider, to fly slower, you raise your AoA (this will temporarily trade airspeed for altitude, until a steady state is reached) - as long as you don't exceed a critical AoA that results in a stall*.

To fly faster, you lower your AoA (this will temporarily trade a lot of altitude for airspeed, resulting in a steep dive that will get shallower as you pick up speed).

* In a hanglider, I think the landing flare is quite different from the flare of a GA plane, which brings the vertical descent speed to close to zero, but does not stall the plane. A hanglider on the other hand will get into ground effect, bring vertical speed to zero, and increase AoA to maintain altitude, and then punch the AoA as high as possible when the critical AoA is reached, to allow one's feet to serve as landing gear.

  Reveal hidden contents

and just fun shots:

  Reveal hidden contents

 

See the birdy in the pic below, on the right... dogfighting?

 

 

 

You have some excelent points, in an slow plane having variable pitch is less useful as as these tend to be cheap planes you just as well go with fixed pitch. 
Now for something fast like an turbo prop or an WW 2 fighter plane you need variable pitch, you also want the engine to run near optimal RPM and flying high should also demand more aggressive pitch. 
And as you say changing pitch is fast who is useful for an fighter. 

Know about the trading speed for attitude as an way to do slow landings in KSP, nice for rugged terrain landings, downside is that its hard to land accurate but you can always taxi afterwards. 
 

[mikegarrison]

12 minutes ago, magnemoe said:

You have some excelent points, in an slow plane having variable pitch is less useful as as these tend to be cheap planes you just as well go with fixed pitch.

I think maybe you missed the whole point. @KerikBalmwas not talking about cost, but about blade element theory. http://www.aerodynamics4students.com/propulsion/blade-element-propeller-theory.php

I will point back to my first post in this topic and say again that the main reason why most propeller-driven airplanes use constant-speed variable-pitch propellers is because propeller tip speed is a very important design parameter and it is easier/better to design a pitch adjustment mechanism than it is to try to design for a wide range of tip speeds.