PSA: F-14 Performance/FM Development Status + Guided Discussion

[Noctrach]

1 hour ago, Victory205 said:

Theoretical Question-

Two identical aircraft are flying in formation at the same steady state speed and altitude, only difference is one is 20% heavier than the other.
 

Both simultaneously pull into a vertical climb at same angle, no changes to thrust. 
 

Which aircraft climbs quicker and attains the greater height?

Fun question. I'd say these should reach the same altitude because at a steady-state starting point that means their thrust-to-drag is equal, making the comparison a purely ballistic one if thrust is unchanged. There'd be some AoA-related shenanigans involved due to difference in lift force needed, but I have no idea how it'll affect the outcome so I'm gonna assume it evens out somewhere... (more drag in the pull, but bigger reduction as lift vector aligns with thrust... something like that)

It's not directly applicable to this situation because while both aircraft begin with the same start, plugging the burners does mean there is a thrust change affecting the outcome. The question would be how significant the thrust difference has to be for it to be measureable in seconds on a hand-flown test scenario.

Edited October 28, 2021 by Noctrach

[maxsin72]

25 minutes ago, Golo said:

F-14A NATOPS manual.

F-14A can definitely launch at mil.

 

But it is risky in case of one engine failure so not possible for safety and in any case not possible at max weight.

Edited October 28, 2021 by maxsin72

[maxsin72]

1 hour ago, fat creason said:

There's no reason to be testing stuff right now, wait til we let you know the FM done or close enough in certain regimes to test... Better yet, I'll test things and post results here when I have the time.

Just about the only thing I'd test right now is level flight acceleration and top speed, which is an indicator of excess power (Ps), but even that is being refined to be closer. After that, more tuning will be done to get sustained turns closer. Then we'll check climbs and all kinds of other stuff... 

 

Good to know, thx

Not having read your answer before, I did the same tests after the last patch and in fact the situation has not changed.

Both A and B with the same gross weight (46600 lbs), A with 4000 lbs fuel, B with 2000 lbs fuel.

F14BAFTERPATCH.zip.acmi F14AAFTERPATCH.zip.acmi

Edited October 28, 2021 by maxsin72

[Baz000]

2 hours ago, Victory205 said:

Theoretical Question-

Two identical aircraft are flying in formation at the same steady state speed and altitude, only difference is one is 20% heavier than the other.
 

Both simultaneously pull into a vertical climb at same angle, no changes to thrust. 
 

Which aircraft climbs quicker and attains the greater height?

The one 20% lighter than the other because of more thrust vs. weight. Even though they powered into the climb at the same angle and didn't change thrust.(they both don't have the same starting thrust tho... One needs more thrust to maintain formation) The one that is heavier has more force to overcome against vs his thrust output in his thrust to weight ratio.

Also the earlier steady state they were in, it isn't possible for both planes to fly in formation together at the same thrust output.

The plane that is 20% heavier needs to have more thrust applied and thus burn more fuel to maintain level flight in formation if the leader is the lighter plane.

If the leader is the heavy plane, the wingman needs less thrust than leader to maintain formation.

 

That being said, the heavier aircraft at the start of the climb had to have had more thrust to maintain formation, so entering into the climb the lighter plane has less thrust than the heavy guy.

The lighter aircraft- final answer Regis

Edited October 28, 2021 by Baz000

[eatthis]

1st answer in my head is the lighter 1 because thrust to weight, if its vertical then aoa is out of the equation isnt it? because youd be at 0 aoa?

[Baz000]

If you want the most simple way of arriving at an answer, think of them in a dive in his same exact conditions and parameters... Who dives faster and gets to the deck first?

Then just think of the reverse effect in relation to a climb.

[Noctrach]

This is the situation:

• Both aircraft are identical, flying the same altitude and speed, meaning:
• Coefficient, density and velocity squared is identical for both aircraft
• Mass is 20% higher on one aircraft

20% mass increase will lead to 20% increase in gravity component, requiring 20% more lift to offset (maintain level flight).
Since all components of the lift formula are identical, the only way to increase lift is to increase effective wing area by 20%.
The only way to increase wing area by 20% is to increase the AoA on the wing by 20%.
This in turn increases the drag of the wing by 20%.
Finally, 20% more thrust is needed to offset the drag and reach the same steady-state speed.

Therefore:

Thrust to weight is identical and both aircraft reach the same altitude.

Edit: also this means it very much is applicable to the current situation, thanks @Victory205 for showing us the light

Edit: Unless I'm overlooking something super obvious ofc in which case please do show me the light.

Edited October 28, 2021 by Noctrach

[Baz000]

How can thrust to weight be equal if both aircraft are identical except one has 20% more weight (I'm guessing has more internal fuel load)

And the force of gravity is an equal constant on earth so each plane has the same force of gravity applied to it

They both have the same drag, they are identical except for weight so they have same external configuration.

Edited October 28, 2021 by Baz000

[Noctrach]

10 minutes ago, Baz000 said:

How can thrust to weight be equal if both aircraft are identical except one has 20% more weight (I'm guessing has more internal fuel load)

And the force of gravity is an equal constant on earth so each plane has the same force of gravity applied to it

They both have the same drag, they are identical except for weight so they have same external configuration.

 

Force = mass * acceleration
You correclty assert that acceleration by gravity is equal, therefore
F_gravity = m * g
Therefore, if m increases by 20%, F_gravity increases by 20%

Meaning the gravity component in th picture I posted is 20% larger, therefore 20% more lift is needed to keep the airplane flying.

The rest I have explained in my post

 

[Baz000]

Each aircraft does not accelerate or decelerate the same rate.

Okay, there are many ways to skin a cat... When I look at a problem I attack it from many different angles to arrive at a solution.

let's simplify things a bit... Two F-16s are flying back home, same exact aircraft conditions and configurations except one has 3,000 lbs of fuel and the other 3,600 lbs. They both start a decent... Who dives quicker and gets the lowest? (in this theoretical example let's say they never hit the ground)

Now, when you get the answer to that, do the inverse and that is how you arrive at your climb answer.

Edited October 28, 2021 by Baz000

[Katj]

This is the situation:

• Both aircraft are identical, flying the same altitude and speed, meaning:
• Coefficient, density and velocity squared is identical for both aircraft
• Mass is 20% higher on one aircraft

20% mass increase will lead to 20% increase in gravity component, requiring 20% more lift to offset (maintain level flight).
Since all components of the lift formula are identical, the only way to increase lift is to increase effective wing area by 20%.
The only way to increase wing area by 20% is to increase the AoA on the wing by 20%.
This in turn increases the drag of the wing by 20%.
Finally, 20% more thrust is needed to offset the drag and reach the same steady-state speed.
Therefore:
Thrust to weight is identical and both aircraft reach the same altitude.
Edit: also this means it very much is applicable to the current situation, thanks @Victory205 for showing us the light
Edit: Unless I'm overlooking something super obvious ofc in which case please do show me the light.

Well, you overlooked both the parasitic drag and the fact that the drag will increase more for the heavier aircraft as they pull into the vertical, while thrust will (initially) remain the same.

[Baz000]

Thrust can't be the same tho at the start of the climb because in order for the guy heavier to remain in formation at the start, he had to apply more power to compensate for his additional weight to remain stabilized in formation.

What he said is they both keep the same thrust levels they had, as flying in formation, IE: they don't touch the throttles entering into and while in the climb.

So, at the get-go one guy already has more thrust than the other (he is running his engines at a higher rpm and fuel flow)

But they are stabilized in formation? What gives? Why aren't they sucked? Or acute? It is because all of those forces are balancing out to provide the same net result in level flight, in a climb or a dive that changes.

 

[Noctrach]

27 minutes ago, Katj said:

 

 

Well, you overlooked both the parasitic drag and the fact that the drag will increase more for the heavier aircraft as they pull into the vertical, while thrust will (initially) remain the same.

Yeah very good point. So if the drag coefficient scales non-linearly with the lift coefficient, the answer becomes "it depends on where we are on the drag curve" right?

Considering drag curves seem to be pretty exponential, while the lift curve is linear (right up to the stall area) the heavier aircraft might have a significantly higher thrust-to-weight to overcome induced drag. Then again it also bleeds more in the initial pull I still think it'll be about equal

Parasitic drag would be equal I think though, since both aircraft are the same shape and velocity.

Edited October 28, 2021 by Noctrach

[Baz000]

Wouldn't the heavier aircraft stall first because he has more "baggage" to overcome?

 https://www.grc.nasa.gov/www/k-12/airplane/weight1.html

https://www.grc.nasa.gov/www/k-12/airplane/wteq.html

"Since the gravitational constant (g) depends on the square of the distance from the center of the earth, the weight of an object decreases with altitude.

Let's do a test problem to see how much the weight of an airplane changes with altitude. If an airplane is flying at 35000 feet (about 7 miles) the distance to the center of the earth is about 4007 miles. We can calculate the ratio of the gravitational constant to the value at the surface of the earth as the square of (4000/4007) which equals .9983*.9983 = .9965. If the airplane weighs 10000 pounds on the surface of the earth, it weighs 9965 pounds at 35000 feet; it has lost 35 pounds, a very small amount compared to 10000 pounds.

Let's do another problem and compute the weight of the Space Shuttle in low earth orbit. On the ground, the orbiter weighs about 250,000 pounds. In orbit, the shuttle is about 200 miles above the surface of the earth. As before, the gravitational constant ratio is the square of (4000/4200) which equals .9523*.9523 = .907. On orbit, the shuttle weighs 250,000 * .907 = 226,757 pounds. Notice: the weight is not zero. The shuttle is not weightless in orbit. "Weightlessness" is caused by the speed of the shuttle in orbit. The shuttle is pulled towards the earth because of gravity. But the high orbital speed, tangent to the surface of the earth, causes the fall towards the surface to be exactly matched by the curvature of the earth away from the shuttle. In essence, the shuttle is constantly falling all around the earth."

Since you guys seem to wanna do some rocket science, here is some.

https://www.grc.nasa.gov/www/k-12/airplane/density.html

"This explains why airplanes have a flight ceiling, an altitude above which it cannot fly. As an airplane ascends, a point is eventually reached where there just isn't enough air mass to generate enough lift to overcome the airplane's weight. The relation between altitude and density is a fairly complex exponential that has been determined by measurements in the atmosphere."

^^ so if one airplane starts 20% heavier, who will climb quicker and be ending up higher?

Edited October 28, 2021 by Baz000

[captain_dalan]

9 hours ago, fat creason said:

There's no reason to be testing stuff right now, wait til we let you know the FM is done or close enough in certain regimes to test... Better yet, I'll test things and post results here when I have the time.

Just about the only thing I'd test right now is level flight acceleration and top speed, which is an indicator of excess power (Ps), but even that is being refined to be closer. After that, more tuning will be done to get sustained turns closer. Then we'll check climbs and all kinds of other stuff... 

 

Got it. I just did some quick runs at low altitude and I'll keep testing for my own personal tactical use only, but there are some minor improvements in the areas that were most off before. All in all, it seems the transonic area is the most contentious one.  The top speed for the A in 4x4 appears to be only slightly above the published figures. 10 to 15 knots or there about. 

Will be waiting for your posts! Keep up the great work and thanks for all the efforts!   

Edited October 29, 2021 by captain_dalan

[Snappy]

7 hours ago, Noctrach said:

This is the situation:

• Both aircraft are identical, flying the same altitude and speed, meaning:
• Coefficient, density and velocity squared is identical for both aircraft
• Mass is 20% higher on one aircraft

20% mass increase will lead to 20% increase in gravity component, requiring 20% more lift to offset (maintain level flight).
Since all components of the lift formula are identical, the only way to increase lift is to increase effective wing area by 20%.
The only way to increase wing area by 20% is to increase the AoA on the wing by 20%.
This in turn increases the drag of the wing by 20%.
Finally, 20% more thrust is needed to offset the drag and reach the same steady-state speed.

Therefore:

Thrust to weight is identical and both aircraft reach the same altitude.

Edit: also this means it very much is applicable to the current situation, thanks @Victory205 for showing us the light

Edit: Unless I'm overlooking something super obvious ofc in which case please do show me the light.

 

Assuming your „end state“ picture on the right is supposed to show the aircraft in pure vertical attitude, please explain why the lift vector is pointing straight up?

I really don’t get this. 
 

Depending on airspeed and actual AOA the wing may or may not be still generating lift, but in vertical attitude I’m pretty sure that lift would not be generated upwards in direction of flight.

 

Edited October 29, 2021 by Snappy

[Katj]

Yeah very good point. So if the drag coefficient scales non-linearly with the lift coefficient, the answer becomes "it depends on where we are on the drag curve" right?
Considering drag curves seem to be pretty exponential, while the lift curve is linear (right up to the stall area) the heavier aircraft might have a significantly higher thrust-to-weight to overcome induced drag. Then again it also bleeds more in the initial pull I still think it'll be about equal
Parasitic drag would be equal I think though, since both aircraft are the same shape and velocity.

The whole point of having a wing is that it gives you more lift than drag. How could the heavier aircraft have a higher twr? The only way this could happen is if the heavier aircraft has a stalled wing.

[Noctrach]

4 hours ago, Snappy said:

Assuming your „end state“ picture on the right is supposed to show the aircraft in pure vertical attitude, please explain why the lift vector is pointing straight up?

I really don’t get this. 
 

Depending on airspeed and actual AOA the wing may or may not be still generating lift, but in vertical attitude I’m pretty sure that lift would not be generated upwards in direction of flight.

 

 

Yeah my point was to illustrate that in the end-state the only contributing factor to lift is thrust, i.e. the scenario described goes from being about thrust-to-drag to being about thrust-to-weight. It would be more correct to remove the lift vector and make the drag vector very very tiny, but ehhh

 

3 hours ago, Katj said:

 

The whole point of having a wing is that it gives you more lift than drag. How could the heavier aircraft have a higher twr? The only way this could happen is if the heavier aircraft has a stalled wing.

I'm not saying drag is greater than lift do I? I'm saying the drag coefficient increases more quickly as a factor of AoA than the lift coefficient. Since increasing AoA is the only way to create more lift with the same wing at the same speed, the heavier aircaft is going to have to exponentially modulate its thrust setting to maintain steady-state formation.

I.e. a 20% increase in AoA, will generate a 20% increase in lift, but a greater or smaller than 20% increase in drag, depending on whether we are right or left of L/D_max

Image courtesy of wiki.

If we want to be entirely correct then the answer becomes "It depends where we are on the L/D curve".

Edited October 29, 2021 by Noctrach

[Baz000]

The air density plays a large part here too guys, as both planes climb thrust output as well as drag decrease... Remember, they are flying inside of a fluid medium. As they climb, the air gets less dense for their wings to "bite" into. And because of the molecules of air hitting their wings being less dense, the wings produce less lift.

So, who out of the two might have a harder time climbing faster and reaching a higher peak altitude?

I love how metaphorically speaking @Victory205 throws a hand grenade in here.

Edited October 29, 2021 by Baz000

[Noctrach]

I wouldn't be surprised if his point is nothing more than "don't pretend you can prove anything based on arbitrary, imperfect scenarios"

Personally, I just enjoy physics discussions, since that invariably means learning a thing or two.

[Baz000]

I think the point he was trying to make was KISS (keep it simple st*pid)

Us human beings have a nasty tendency to overcomplicate simple things.

[Katj]

I'm not saying drag is greater than lift do I? I'm saying the drag coefficient increases more quickly as a factor of AoA than the lift coefficient. Since increasing AoA is the only way to create more lift with the same wing at the same speed, the heavier aircaft is going to have to exponentially modulate its thrust setting to maintain steady-state formation.
I.e. a 20% increase in AoA, will generate a 20% increase in lift, but a greater or smaller than 20% increase in drag, depending on whether we are right or left of L/D_max

Image courtesy of wiki.
If we want to be entirely correct then the answer becomes "It depends where we are on the L/D curve".

Yes, this checks out and my previous statement was incorrect!

[eatthis]

so whats the actual bloody answer lol

 

[Noctrach]

12 minutes ago, eatthis said:

so whats the actual bloody answer lol

 

"It depends" xD

But all things combined it'll be about equal unless we go to the extremes.

Edited October 29, 2021 by Noctrach

[Baz000]

Man! "it depends" is the typical fighter pilot answer lol

28 minutes ago, Noctrach said:

"It depends" xD

But all things combined it'll be about equal unless we go to the extremes.

 

Honestly, I do disagree with you... If you turn it around and say it is a dive... Who gets to the ground faster and gets there first? I think the same principle applies but in reverse for a climb.