AV-8B flight model discussion

[MAD_MIKE]

IMHO Harriers FM looks like UFOFM.

Rocket climb rate, its possible?

 

Where the sideslip? Why he rolling without sideslip?

 

Roll, where are you from? Track file pleasehttps://dropmefiles.com/i5Kdy

 

Finally explain this?

Edited June 28, 2018 by MAD_MIKE

[jojo]

Roll, where are you from? Track file pleasehttps://dropmefiles.com/i5Kdy

 

 

At least for this one I think this is "induced roll".

You're activating rudder with high yaw rate.

Your wing external to the turn is taking more speed and lift than the one inside the turn, so the roll.

 

 

You can also experience this flying glider with large wingspan :smilewink:

[MAD_MIKE]

At least for this one I think this is "induced roll".

You're activating rudder with high yaw rate.

Your wing external to the turn is taking more speed and lift than the one inside the turn, so the roll.

 

 

You can also experience this flying glider with large wingspan :smilewink:

 

It's not glider;)

[Tobi1304]

But it‘s still a plane.

[MAD_MIKE]

But it‘s still a plane.

 

At these speeds(40-60 km/h)? Seriously?:megalol: Maybe you should read some of aerodynamic tutorials? No better school physics.

[jmijnen]

At these speeds(40-60 km/h)? Seriously?:megalol: Maybe you should read some of aerodynamic tutorials? No better school physics.

 

He named the aerodynamic effect causing your aircraft's behaviour there bud, why shut him down?

[MAD_MIKE]

He named the aerodynamic effect causing your aircraft's behaviour there bud, why shut him down?

 

Do you know exactly what forces causing sideslip induced roll and these amount at 40 kph? Do you can explain why Harrier have sweptback negative-V wing. I dont know english aerodynamic terminology. Tell me averege speed of large wingspan glider.

[TheSkipjack95]

100km/h

 

Source : I fly gliders

 

As for the anhedral, it is to reduce "pendulum effect" and decrease stability, ie make the plane more maneuverable.

You should get a bit of rolling motion with yaw even at near zero forward speed because you get angular airspeed, and as such the wing will create some lift anyway, pushing it upwards and creating roll.

[MAD_MIKE]

100km/h

 

Source : I fly gliders

 

As for the anhedral, it is to reduce "pendulum effect" and decrease stability, ie make the plane more maneuverable.

You should get a bit of rolling motion with yaw even at near zero forward speed because you get angular airspeed, and as such the wing will create some lift anyway, pushing it upwards and creating roll.

 

I know, but look at the AOA. Its negative AOA isnt? So if aerodynamic surfaces are effective at 50 kph, wings generates down force like spoilers, and if push the pedal and tail pneumo nozle do yaw spin, outer wing generates more down force then before yaw and then inner wing. Obviously while sideslipping with negative AOA inner wing generates little bit lifting force, and outer(forward) wing generates down force, it causes right roll when pressed left pedal. Also pay attension on big negative pith. With this high position of rudder we also have right roll with left pedal.;) Anyway at these speeds aerodynamic surfaces of this heavy speedy plane not effective at all.

[Katmandu]

To concentrate on the most obvious, what about the rocket climb to 9km? This is on par with F-15 and Su-27 full afterburner efforts.

Edited June 28, 2018 by Katmandu

[Kirkey_badgers]

Maybe others can share their experience too. But in a VTOL loadout (empty) I seem to struggle to get it to hover, even in some scenarios I'm at full power 90-100% RPM, but she still wants to drop. Nozzles tend to be around 80 degrees. Makes landing rather tricky.

[jojo]

I know, but look at the AOA. Its negative AOA isnt? So if aerodynamic surfaces are effective at 50 kph, wings generates down force like spoilers, and if push the pedal and tail pneumo nozle do yaw spin, outer wing generates more down force then before yaw and then inner wing. Obviously while sideslipping with negative AOA inner wing generates little bit lifting force, and outer(forward) wing generates down force, it causes right roll when pressed left pedal. Also pay attension on big negative pith. With this high position of rudder we also have right roll with left pedal.;) Anyway at these speeds aerodynamic surfaces of this heavy speedy plane not effective at all.

 

 

You're mistaking negative AoA and pitch down.

 

 

When he pitches down, at the start he has some negative AoA, but as the plane start to dive the negative AoA is reduced or cancelled when he made his rudder input.

 

 

And yes, 50 km/h do generate some lift.

That's why aircraft take off with head wing. And on short runway even a little amount of head wind can dramatically improve your take off weight.

 

 

Harrier uses Rolling Vertical Take Off/ Landing to increase payload over vertical landing/ take off.

 

 

A speed of 50kt gives +2300lbs over vertical landing weight. (source NATOPS)

So 50 km/h won't give as much, but it can surely roll the wing in case yaw.

 

 

Go to a real airfield, have a real flight and play with controls, it will be an eye opener :smilewink:

[monkie]

How much fuel do you have on board when you are trying to hover? Try with only 2000 lbs and about 82 degress and you should do fine. Also make sure you are in VTOL flap mode, and yes it takes a lot of thrust, close to 100% RPM to keep the harrier in hover.

 

As to the OP, I am thinking that trying to have a sim such as DCS mimic both VTOL and high speed flight dynamics is a near impossible task. Even multi-million dollar simulators used for training real world pilots don't properly simulate true aircraft dynamics. It's just 1's and 0's, there isn't real air going over that airfoil in DCS so they have to do they're best to simulate that.

 

Your VTOL example with the aircraft rolling right with forward stick, would be good to see your control inputs. During vertical hover any small amount of in change of the lift vector and the Harrier is going to get a bit unstable and require correction quickly. I for one have never had an issue with the aircraft rolling right as I transition from hover to forward flight so maybe it's a controller issue? What were your nozzle positions and what was the weight during your maneuver?

[MAD_MIKE]

You're mistaking negative AoA and pitch down.

 

 

When he pitches down, at the start he has some negative AoA, but as the plane start to dive the negative AoA is reduced or cancelled when he made his rudder input.

 

 

And yes, 50 km/h do generate some lift.

That's why aircraft take off with head wing. And on short runway even a little amount of head wind can dramatically improve your take off weight.

 

 

Harrier uses Rolling Vertical Take Off/ Landing to increase payload over vertical landing/ take off.

 

 

A speed of 50kt gives +2300lbs over vertical landing weight. (source NATOPS)

So 50 km/h won't give as much, but it can surely roll the wing in case yaw.

 

 

Go to a real airfield, have a real flight and play with controls, it will be an eye opener :smilewink:

Rolling VTO gives not only extra airflow on wings, its also gives more effectiveness to jetstreams and this gives much more lift than wings at 50 km/h. Jetstreams gain more new clean air...

How much fuel do you have on board when you are trying to hover? Try with only 2000 lbs and about 82 degress and you should do fine. Also make sure you are in VTOL flap mode, and yes it takes a lot of thrust, close to 100% RPM to keep the harrier in hover.

 

As to the OP, I am thinking that trying to have a sim such as DCS mimic both VTOL and high speed flight dynamics is a near impossible task. Even multi-million dollar simulators used for training real world pilots don't properly simulate true aircraft dynamics. It's just 1's and 0's, there isn't real air going over that airfoil in DCS so they have to do they're best to simulate that.

 

Your VTOL example with the aircraft rolling right with forward stick, would be good to see your control inputs. During vertical hover any small amount of in change of the lift vector and the Harrier is going to get a bit unstable and require correction quickly. I for one have never had an issue with the aircraft rolling right as I transition from hover to forward flight so maybe it's a controller issue? What were your nozzle positions and what was the weight during your maneuver?

Do you see trackfile?

Edited June 28, 2018 by MAD_MIKE

[monkie]

no I'm not looking at the track file, I just know that if I push the stick forward from a hover with only 2500 lbs of fuel and 82 degrees of nozzle I don't get a uncontrolled rolling motion as you show.

 

in hover I have to use slight movements of the stick to the left and the right to keep any roll motion from continuing, but I don't think that is abnormal at all.

 

Maybe I'm not understanding.

[MAD_MIKE]

You're mistaking negative AoA and pitch down.

 

 

When he pitches down, at the start he has some negative AoA, but as the plane start to dive the negative AoA is reduced or cancelled when he made his rudder input.

 

 

And yes, 50 km/h do generate some lift.

That's why aircraft take off with head wing. And on short runway even a little amount of head wind can dramatically improve your take off weight.

 

 

Harrier uses Rolling Vertical Take Off/ Landing to increase payload over vertical landing/ take off.

 

 

A speed of 50kt gives +2300lbs over vertical landing weight. (source NATOPS)

So 50 km/h won't give as much, but it can surely roll the wing in case yaw.

 

 

Go to a real airfield, have a real flight and play with controls, it will be an eye opener :smilewink:

Explain this;) Do you see positive AoA?

[jojo]

Explain this;) Do you see positive AoA?

 

 

You're creating negative AoA by vertical thrust. Your wing in that configuration is rather a giant air brake. It won't create negative lift.

 

90°/ -90°ish is way past stall. :music_whistling:

 

Yet when you input full ruder, you're creating a flow parallel to the chord of your wings which isn't sensed by your AoA sensor which is on your nose.

Then your outboard wing is gaining some more lift than inboard wing.

Because outboard wing is going forward while inboard wing is going backward.

 

So inboard wing is doing a poor job at generating lift because it's travelling reversed.

 

Plus AoA isn't the only thing creating lift on wing: there is the airfoil profile.

 

But I don't know why I'm still loosing time with you. You made up your mind.

 

 

The only thing I see is that you should probably not recover from such bank angle...

Edited June 28, 2018 by jojo

[monkie]

Ok I have no idea what you are trying to demonstrate, I thought you were saying that there was a roling moment if you only put forward stick in during hover flight but now I see you are putting in full rudder.

Edited June 28, 2018 by monkie

[MAD_MIKE]

You're creating negative AoA by vertical thrust. Your wing in that configuration is rather a giant air brake. It won't create negative lift.

 

90°/ -90°ish is way past stall. :music_whistling:

 

 

Yet when you input full ruder, you're creating a flow parallel to the chord of your wings which isn't sensed by your AoA sensor which is on your nose.

Then your outboard wing is gaining some more lift than inboard wing.

Because outboard wing is going forward while inboard wing is going backward.

 

So inboard wing is doing a poor job at generating lift because it's travelling reversed.

 

 

 

Plus AoA isn't the only thing creating lift on wing: there is the airfoil profile.

 

 

But I don't know why I'm still loosing time with you. You made up your mind.

 

Whut?

[Pyroflash]

There's a more sinister effect going on here. You are hovering off the axis of RCS thrust. The yaw RCS thrusters are not in the same horizontal plane of motion as the CG of the airplane, resulting in a control coupled rolling moment.

 

 

And yes, a large yawing motion may result in some induced airflow over the wing, regardless of what your AoA indicator says, simply because the AoA indicator isn't measuring AoA in the same plane of motion as the tip of your wing. The same principle is at work during a spin. The inboard wing generates a higher AoA than the outboard wing, stalls out, rolls, then spins. The displayed AoA in this case is also somewhat different from what the wings are actually experiencing.

[monkie]

I'll agree and say that should result in a hull loss though, the flight model is a bit too forgiving. :)

 

No need for videos, you seem to just want to argue when people are trying to understand what your concerns are.

 

Done.

[ouPhrontis]

To concentrate on the most obvious, what about the rocket climb to 9km? This is on par with F-15 and Su-27 full afterburner efforts.

 

The Harrier's powerful Pegasus has it still holding the time-to-climb record up to I think it was between 10-15,000 ft from ground level, it out-climbs the F-15 up to that point, after which the F-15 beats it to somewhere around 51,000 or more.

[ouPhrontis]

If you're taking exception at the ability to nose up from a hover and climb vertically, yes; they really can do that, it was known as the Farley take-off, he often did it at airshows. In the video where you climbed vertically to almost 29,000ft in under 3 minutes, that time to climb is inline with earlier Harriers, like the GR.3.

[TLTeo]

The Harrier's powerful Pegasus has it still holding the time-to-climb record up to I think it was between 10-15,000 ft from ground level, it out-climbs the F-15 up to that point, after which the F-15 beats it to somewhere around 51,000 or more.

 

 

Yea I don't think the climb is completely wrong. By definition of VTOL a clean Harrier needs a thrust:weight ratio larger than one by a good bit. I don't know about the F15, but there are stories circulating around of Harriers easily outclimbing F104s, so what you showed doesn't seem to be completely insane to be honest.

[Katmandu]

In the video where you climbed vertically to almost 29,000ft in under 3 minutes, that time to climb is inline with earlier Harriers, like the GR.3.

 

I did not know that, could you share a link?