Issues still need tobe addressed in BOS

[unreasonable]

Did a little test.

 

Two Yak-1, one with 40 liters of fuel, the other with 408 liters.

 

Engines off, dived from 2500m at 200km/h... once at sea level, the lighter Yak-1 was 10km/h slower than the heavier (which reached ~635km/h).

 

In their climbs, the heaviest finished higher, by 150m (1000m vs 850m) at 200km/h.

 

So if 190 is underperforming Yak in your original test, it must be down to it's power or drag characteristics? The weight effect is in there as you would expect.

[ZachariasX]

Wow. 1% in weight differnence are 10 km/h in speed difference. So, 10 % weight difference would then be 100 km/h and 100% would be...

Edited June 25, 2015 by ZachariasX

[JG13_opcode]

Did a little test.

 

Two Yak-1, one with 40 liters of fuel, the other with 408 liters.

 

Engines off, dived from 2500m at 200km/h... once at sea level, the lighter Yak-1 was 10km/h slower than the heavier (which reached ~635km/h).

 

In their climbs, the heaviest finished higher, by 150m (1000m vs 850m) at 200km/h.

What was the repeatability of your test?  How can you be sure you flew the exact same course in each aircraft?

[Dr_Molenbeek]

So if 190 is underperforming Yak in your original test, it must be down to it's power or drag characteristics? The weight effect is in there as you would expect.

 

Sure, better aerodynamic will "minimize" the advantages of the 190 (better climb rate, better power-to-weight ratio, 1 ton heavier), but i simply can't believe it will make such a high difference, to the point of turning the situation.

 

You also forgot the 109s, which retain their energy less efficiently at high speed than the 190, both in high speed climb and straight line... So the Yak-1 outperforms the 109s in this way because of drag characteristics (we no longer talk about a radial plane, but about 109s) ? To you to tell me... 

 

 

"What was the repeatability of your test?  How can you be sure you flew the exact same course in each aircraft?"

 

"Did a little test", i made it 2 times only, with same results.

 

You're not satisfied ? You have the game, you're free to do it yourself.

[JG13_opcode]

Not really correct. It would be a very bad and underpowered aircraft that you are describing.

Please check your understanding. I assure you, if you increase the weight of the aircraft but change nothing else, you also increase the induced drag. For reference, aerodynamic theory lets us calculate the induced drag coefficient:

 

Cdi = Cl^2 / pi * e * AR

Where Cdi is the induced drag coefficient, Cl is the lift coefficient, e is the efficiency factor, and AR is the aspect ratio. This is basic undergraduate stuff.

 

In reality, IF (you normally can) you can go faster, the added lift will offset the downforce added by the additional weight. An example for this: A regular sailplane (the planes where drag is especially undesired) I can load with about an added 40% of its "dry" weight in the form of water ballast. Why would I do that? When I want speed. What it does, it increases the sink rate as well as the airspeed, making me slide down the same triangle, but just faster. If I had a drag penalty, then I would slide don a steeper slope. So I'm not losing out on the gliding angle. I'm just driving faster. Added drag through the speed increase is, in todays sailplanes, shockingly small.

Nothing in this paragraph contradicts what I wrote. Your ballast does increase your glider's induced drag coefficient.

 

Adding weigh is bad, when it forces me to fly at an unfavorable AoA, because the wing area/airspeed combination is not sufficient. At slow speed, this becomes apparent. But let's look at cruise speed. The aerodynamics of the airframe and airfoils decide how "slippery" it is. If I load a plane with say, 100 kg more fuel (like an added 5% of the empty weight or so), then all I need is to be able to fly just a little faster, I guess maybe 5 km/h (just an example), to get the most favorable AoA again. Now, How much of a penalty in fuel consumption do I get? Now, at max. speed. the wing of any plane can lift way more than it could structurally support (at lower altitudes). Thus, just an increase of 1/100th degree would give you huge additional lift. The difference in AoA at max speed between a fully loaded plane and a lightly loaded plane (like the ones with big wings such as we have them here) is almost nil.

 

Where the AoA comes into play, is in the ability to accellerate from very slow speed to full speed. At slow speed, you get lots of drag from the higher AoA (wing PLUS airframe) and you have to overcome that. A heavyier loaded plane should not really be slower, but accellerate slower.

 

Extreme cases, such as airliners that fly with the bare minimum of wing area (more creates more drag) at cruise altitude are more sensible to this. There, from one side of the Atlantic to the other it is around 5% of throttle setting that you can reduce for the same speed while your 100 tons (!) of fuel burn up, making a reduction of >50% of the dry weight of the aircraft. Not ~5% as in the Yak et. al.

 

Max speed is almost exclusively decided by the effective forward thrist and the aerodynamic drag of the airframe. That one doesn not really change as AoA at high speed is for practical purposes unaffected by the weight you can load.

 

1, 2 or 3 km/h in ultimate top speed difference are not the reason why you would lose a fight. Opening a window can do that too. You lost because you blew it in the first place.

This all seems mostly irrelevant so I will not bother responding.

 

I find it quite charming how obsessed people here are with max. speed alone. All the other "speeds" don't seem to matter. Like the Bf-109's disappointing cruise speed. Or the Spitfires cruise speed. A Tempest approaches for landing at these speeds. (Tempest pilots could always piss of Spit drivers with that "terminal" remark.) But hey, here, we keep the throttle firewalled and almost exclusively comment how it flies that way. Sit in a Cessna and do that.

I agree that top speed alone is not the only relevant metric. Unfortunately people who lack technical training/understanding tend to get caught up in sensationalist claims like "Aircraft X is superior" which they take to mean "I cannot lose if I fly aircraft X".

 

----

 

"What was the repeatability of your test?  How can you be sure you flew the exact same course in each aircraft?"

 

"Did a little test", i made it 2 times only, with same results.

 

You're not satisfied ? You have the game, you're free to do it yourself.

I'm not interested in doing such tests myself because they are not repeatable and therefore don't tell us much of value. You have no way of knowing if your dives were at the same angle. Or your climbs. You have no way of knowing that you did identical pull-outs.

 

A small difference such as yours (~16%) can easily be attributed to flying a different path. I am not trying to be insulting; I am just pointing out that drawing conclusions from your little test should be done with caution.

 

There is a user on these boards who used to go by the alias Tagert, and he had an autopilot for il2 1946 using the devicelink interface. It was completely repeatable in that you could script the inputs to the aircraft's controls and it would perform exactly the same maneuver every single time.

 

Human error should always be eliminated when possible!

Edited June 25, 2015 by 13GIAP_opcode

[unreasonable]

Wow. 1% in weight differnence are 10 km/h in speed difference. So, 10 % weight difference would then be 100 km/h and 100% would be...

 

? How much does 368 litres of aviation fuel weigh? If specific gravity was 0.7, and Yak is 2900kg, I make the difference about 9%.

 

So to double the speed you would need about 4000 litres extra. ( Alert! This is also a joke ! )

[unreasonable]

 

You also forgot the 109s, which retain their energy less efficiently at high speed than the 190, both in high speed climb and straight line... So the Yak-1 outperforms the 109s in this way because of drag characteristics (we no longer talk about a radial plane, but about 109s) ? To you to tell me... 

 

 

I'm a bit confused, is that a misprint? If the 109's "retain energy" less efficiently than 190s, and the Yaks win vs 190s in your dive-zoom tests, you would expect Yaks to win that test vs 109s, right?  Question is why is the dive-zoom result the opposite of the fast climb result you mention.

 

Anyway, I could not test anything myself, I have nothing like test pilot accuracy to get anything comparable from one run to another in one plane, let alone hopping from one type to another.

 

Someone eventually might be able to write a utility to check in game data so that tests can be seen to be systematic. Somehow I doubt that 1CGS will release anything even if they actually have it: state secrets and all that.  Jason is asking for test pilots to generate performance data for the new manual: maybe the job comes with some access to inside tech that will give new insight.

[Dr_Molenbeek]

I'm a bit confused, is that a misprint? If the 109's "retain energy" less efficiently than 190s, and the Yaks win vs 190s in your dive-zoom tests, you would expect Yaks to win that test vs 109s, right?  Question is why is the dive-zoom result the opposite of the fast climb result you mention.

 

I actually made a typo in my post, thanks for noticing !

 

I talk about "109s" when i only tested the G-2 (because according the people on the forum, the F-4 is OP).

 

And yes, you understood what i mean !

 

As i did yesterday, the test is from 700km/h to 500km/h, starting at 200m.

 

The 109G-2 at full power reaches 400m at 600km/h and 800m at 500km/h.

 

The 190 at full power reaches 500m at 600km/h and 1000m at 500km/h.

 

Now at combat power (1.32 ata 2400RPM), the 190 reaches 450m at 600km/h and 900m at 500km/h.

 

The results of the 190 are the same with or without the outboard cannons.

 

And here's the Yak-1, at full power with radiators 25%... it reaches 550m at 600km/h and 1050m at 500km/h.

 

What do you think, unreasonable ?

 

Should i make a video ?

[unreasonable]

What do you think, unreasonable ?

 

Should i make a video ?

 

I have to be careful about saying what I think, otherwise I might get banned

 

So normally I just ask questions to see if I understand what other people are saying, at least on the topic of aircraft performance....

 

Earlier post of yours said:

 

"Also did a high speed climb like for 109s and 190, 500km/h, from 200m to 1200m.

 

Here the Yak-1 is behind the 109s, which are behind the 190 (as it should)."

 

So if I understand you right you are saying that at a fairly fast climb you get the results you expected (190 best, then 109, Yak worst)

But at the above top speed climb you get Yak best, then 190 then 109.

 

So as you stated much earlier on, Yak looks strange inside the very high speed area. Another way of putting it would be, once you have got a Yak going really fast, it does not want to slow down as much as the others. (edit: I know I am repeating stuff here I just want to get it clear in my head).

 

Is this not possible if the aerodynamics are slicker? I think the Spitfire shared this feature, IIRC (from books, not the tests) Spitfires were used to try to get close to the sound barrier in dive tests for this reason, rather than Tempests, but this could be a false memory.

 

Anyway thank you for a stimulating discussion. You could make a video and tabulate the results for the devs if you think it would do any good....

Edited June 25, 2015 by unreasonable

[ZachariasX]

 

 

Please check your understanding. I assure you, if you increase the weight of the aircraft but change nothing else, you also increase the induced drag. For reference, aerodynamic theory lets us calculate the induced drag coefficient:

 

Yes, but how much is that for practical purposes in a plane? If done within the planes specifications, the penalty is very small. And your formula will tell you that as well. My point is no other than that.

 

It helps if an undergraduate boards a real plane to get a practical understanding of a formula.

[ZachariasX]

? How much does 368 litres of aviation fuel weigh? If specific gravity was 0.7, and Yak is 2900kg, I make the difference about 9%.

 

So to double the speed you would need about 4000 litres extra. ( Alert! This is also a joke ! )

 

You are right 368 litres of AvGas weigh approx. 276 kg. I overread his line. Mea culpa. So we have 10 km/h speed difference at max. speed. between a 10% wight difference of total weight. This a bit more than expected but is still reasonable by all means.

 

It would be interessting to see the fuel efficiency at cruise speed between the different laodings. This would give you a more accurate idea of how much you burden the design than the max. speed attained.

[Dr_Molenbeek]

I have to be careful about saying what I think, otherwise I might get banned

 

Aw... i only hope that's not because of me. 

 

So if I understand you right you are saying that at a fairly fast climb you get the results you expected (190 best, then 109, Yak worst)

But at the above top speed climb you get Yak best, then 190 then 109.

 

Yes ! You have perfectly understood... Below the top speed, all seems right, and once above that speed, there's a situation reversal, when what should happen is a bigger difference (but as you pointed, there's a aerodynamic part !).

 

So as you stated much earlier on, Yak looks strange inside the very high speed area. Another way of putting it would be, once you have got a Yak going really fast, it does not want to slow down as much as the others. (edit: I know I am repeating stuff here I just want to get it clear in my head).

 

You read my thoughts. 

 

Is this not possible if the aerodynamics are slicker? I think the Spitfire shared this feature, IIRC (from books, not the tests) Spitfires were used to try to get close to the sound barrier in dive tests for this reason, rather than Tempests, but this could be a false memory.

 

And here i let the experts to clarify things.

 

Is the aerodynamic a factor that is able to "create" such a big difference (note again that now 109G-2 is also concerned) ? I confess i do not know at all.

[ZachariasX]

Is this not possible if the aerodynamics are slicker? I think the Spitfire shared this feature, IIRC (from books, not the tests) Spitfires were used to try to get close to the sound barrier in dive tests for this reason, rather than Tempests, but this could be a false memory.

 

The Spitfire has the highest Mach number of those planes due to its thin wing profile. So you can go fastest before the Mach-tuck makes your try to pull out of the dive an impossibility. Having a high Mach number doesn't mean you can still effectively control the aircraft at that speed, it just means if you go faster, then the controls are aerodynamically not able anymore to make you pull out of the dive. The highest speed in a prop plane was reaches in a PR Spit AFAIK (and it lost the prop in the dive due to overrev, almost killing the pilot). High Mach number has no relation to "slickyness" of any sort.

[unreasonable]

Ah I see - thin wing > less airflow acceleration over top of wing > less movement in centre of lift > less tuck. A different issue. I learn something new today!

 

But there must be something in the Yak FM which is giving it this "reversal" feature vs the 190/109, assuming that Ze_Hairy's tests are essentially correct even if they cannot be exactly measured.

 

For the time being I will think of it as "slickyness" for want of anything better.

 

Perhaps the soviet planes used for the tests the 1CGS data was drawn from were highly polished? (Grasps at straws...)

[ZachariasX]

The Mach tuck is something that has specifically to be modelled for the planes. It does not come out of the sim engine when you enter profile values in it. You notice mach tuck in a dive, when through increasing speed you push the stick more and more forward to stay in the dive, at some point it just noses over pulling you into the dive even onto your back (you hit the farm by then) and pulling back won't work anymore. This is an effect that either happens when it is (extra modelled) or it just doesn't (when it's not). It has no influence on the speed that you are going.

 

Air pressure, density and humidity have an effect on when you will experience a Mach tuck. It is the wing profile that determines when this effect comes into play. You buld certain wings specifically for high Mach numbers, such as seen in airliners. The big bodies on the trailing section of the wing (often, but not always) containing the hinges for flap mouts are devices that push critical Mach further back. Polishing your wing won't help you at all. Although being tidy is not a bad thing.

 

See the Convair Coronado:

 

The big thingies on the wings are in fact empty, hollow. But they help making the Coronado among the fastest airliner of the era.

 

So: critical Mach is when God comes and pushes the nose of your aircraft down. Slippery or not.

 

I haven't tried dives in this sim to check for that, but you just got me motivated

[Dakpilot]

Two people jump into a server with identical A/C but one with full fuel and one with light fuel load, mix it up and see how you do..

 

The lighter aircraft will have the upper hand regardless of the extra 'potential  energy' of the heavier one  no need for graphs

 

Cheers Dakpilot

[JG13_opcode]

Yes, but how much is that for practical purposes in a plane? If done within the planes specifications, the penalty is very small. And your formula will tell you that as well. My point is no other than that.

 

It helps if an undergraduate boards a real plane to get a practical understanding of a formula.

I agree, but the entire point of my original post was to debunk the idea that you can have two aircraft that are identical in all characteristics but weight.

[unreasonable]

I agree, but the entire point of my original post was to debunk the idea that you can have two aircraft that are identical in all characteristics but weight.

But they are identical in intrinsic characteristics - just as two spheres of the same size, one containing a heavier core than the other, are identical except in one respect.

 

What your post states is that the behavior of the two otherwise identical aircraft may be affected by that single intrinsic difference in a way that forces us to look at a complex relationship, since we have a lift/drag variable to look at as well as an inertia/air resistance variable.

 

As it happens, Ze-Hairy's tests show that the Yak-Heavy beats the Yak-Light in a dive and zoom test, which corresponds to ZachariasX's assertion that the lift/drag penalty of extra weight is insignificant in the context of this test and also corresponds to (most peoples') intuitions.

 

Obviously the question of Yak vs 190 comparison involves loads of intrinsic differences including weight. The problem is finding one or more that could account for the reversal of results at very high speed.

 

My suggestion about polish was not entirely frivolous. I cannot find the reference, but I have somewhere a photo of a very shiny 109. The text remarked that the pilot and his black-men polished the entire surface of the standard paintwork, which gave a significant increase in top speed. I have in mind 30kmh? I wonder if that sort of effect would be disproportionately effective at very high speeds?

 

We can say, that since there might be errors of technique in Ze_Hairy's tests, we should simply ignore the results. But his results are less about the precise numerical outcomes and more about the ordering, which is much more robust. My estimate would be that if someone could use some software that ensured dive angles etc were all replicated exactly, the reversal result would still hold.

 

Or, we could simply say that, whatever it is that is creating this counter-intuitive result, the developers know what they are doing, so it is probably right, so we should just stop talking about it and play the game.

 

But it seems to me that it is useful to know, if you are flying in BoS, that a Yak will beat the LW fighters in this particular very high speed situation and that this is not some paranoid "luftwhining" figment of the imagination brought on because the LW pilot mistook the Yak's energy state.

 

Then there is the line of thought that says it is all terribly complicated so why bother.

 

Well this is a matter of personal taste: I find it interesting to ask, as a purely intellectual exercise, if this effect is a true reflection of reality, which it well may be, how and why it arises: or even how could it possibly arise?

[Dakpilot]

If at a reasonable altitude I have an engine failure, am I in a better position for gliding to a safe field if I am in a heavier aircraft? due to the fact it has higher potential energy/momentum?

 

don't think so

 

Cheers Dakpilot

[JG13_opcode]

If at a reasonable altitude I have an engine failure, am I in a better position for gliding to a safe field if I am in a heavier aircraft? due to the fact it has higher potential energy/momentum?

 

don't think so

 

Cheers Dakpilot

Agree. The force of gravity is greater on the heavier aircraft so it decelerates faster in a zoom climb. Glider pilots add ballast to increase their sink rate which lets them fly faster, because a heavier aircraft's best L/D ratio is at a faster speed than a lighter aircraft's.

[Dr_Molenbeek]

Take a look at this.

 

http://www.spitfireperformance.com/spit14afdu.html

 

Maximum Climb
26. The Tempest is not in the same class as the Spitfire XIV. The Tempest V however, has a considerably better zoom climb, holding a higher speed thoughout the manoeuvre. If the climb is prolonged until climbing speed is reached then, of course, the Spitfire XIV will begin to catch up and pull ahead.

 

Need i remind gentlemen that the Tempest is heavier about over a ton (3800kg vs +5000kg) ?

Edited June 26, 2015 by Ze_Hairy

[unreasonable]

Agree. The force of gravity is greater on the heavier aircraft so it decelerates faster in a zoom climb. Glider pilots add ballast to increase their sink rate which lets them fly faster, because a heavier aircraft's best L/D ratio is at a faster speed than a lighter aircraft's.

 

This first statement is totally incorrect. The force of gravity is exactly the same for every object - one g. The issues are 1) the effect of weight on overcoming air resistance and 2) the additional drag effect (if any) created by the requirement to provide lift equal to the extra weight in order to keep the planes on the same flight-path.  As ZachariasX pointed out earlier, additional lift is generated by the extra speed the heavy plane attains on the same flight path.

 

In BoS the Yak-Heavy zooms higher (ie decelerates more slowly) than the Yak-Light. Are you saying this is wrong?

 

Dakpilot's points about the advantages of being lighter in other regimes of flight are completely irrelevant to the issue Ze_Hairy raised. We all know that in some situations being lighter is an advantage. The issue raised by Ze_Hairy's tests pertains to one specific set of circumstances in which the results seem counter-intuitive.

 

I am sure he would be as open as I am to any suggestions as to what could be causing this result.

[JG13_opcode]

But they are identical in intrinsic characteristics - just as two spheres of the same size, one containing a heavier core than the other, are identical except in one respect.

 

What your post states is that the behavior of the two otherwise identical aircraft may be affected by that single intrinsic difference in a way that forces us to look at a complex relationship, since we have a lift/drag variable to look at as well as an inertia/air resistance variable.

 

As it happens, Ze-Hairy's tests show that the Yak-Heavy beats the Yak-Light in a dive and zoom test, which corresponds to ZachariasX's assertion that the lift/drag penalty of extra weight is insignificant in the context of this test and also corresponds to (most peoples') intuitions.

 

Obviously the question of Yak vs 190 comparison involves loads of intrinsic differences including weight. The problem is finding one or more that could account for the reversal of results at very high speed.

 

My suggestion about polish was not entirely frivolous. I cannot find the reference, but I have somewhere a photo of a very shiny 109. The text remarked that the pilot and his black-men polished the entire surface of the standard paintwork, which gave a significant increase in top speed. I have in mind 30kmh? I wonder if that sort of effect would be disproportionately effective at very high speeds?

 

We can say, that since there might be errors of technique in Ze_Hairy's tests, we should simply ignore the results. But his results are less about the precise numerical outcomes and more about the ordering, which is much more robust. My estimate would be that if someone could use some software that ensured dive angles etc were all replicated exactly, the reversal result would still hold.

 

Or, we could simply say that, whatever it is that is creating this counter-intuitive result, the developers know what they are doing, so it is probably right, so we should just stop talking about it and play the game.

 

But it seems to me that it is useful to know, if you are flying in BoS, that a Yak will beat the LW fighters in this particular very high speed situation and that this is not some paranoid "luftwhining" figment of the imagination brought on because the LW pilot mistook the Yak's energy state.

 

Then there is the line of thought that says it is all terribly complicated so why bother.

 

Well this is a matter of personal taste: I find it interesting to ask, as a purely intellectual exercise, if this effect is a true reflection of reality, which it well may be, how and why it arises: or even how could it possibly arise?

All right, let's put this to bed once and for all. In a zoom climb we have three main forces. Thrust, Drag, and Gravity. Doing a force balance for a zoom climb at some arbitrary angle Theta looks like this:

 

 T - D - m*g*sin(Theta) = m*a

Let's agree that the better-zooming aircraft decelerates more slowly in the climb. Let's also say that g = 10 instead of 9.8 because I don't want to get out my calculator. It doesn't matter because as you astutely put it, we're interested in the general trend.

 

Let's say Yak A masses 1000kg and Yak B masses only 100kg. That is to say A is 10x more massive than B. It's 10 times heavier.

 

Let's say A and B are both flying at 0m (sea level) at 100m/s and they both initiate a zoom climb at the same angle. Let's say the angle is 90 degrees (straight up) to make the math nice.

 

sin(90) = 1, so for Yak A it looks like this:

 

T - D - m*g*sin(Theta) = m*a
T - D - W              = m*a
(T-D)/m - W/m          = a
(T-D)/m - g            = a

Let's say D = 5, T = 10.

 

For aircraft A

(10-5)/1000 - 10 = a
-9.995 = a

For aircraft B

(10-5)/100 - 10 = a
-9.95 = a

A deceleration of 9.995 is greater than a deceleration of 9.95, thus the heavier aircraft decelerates faster.

 

Okay that's all well and good but what does it mean? It means the heavier aircraft should dive first and *then* zoom, because it will accelerate faster in the dive, and then the two aircraft will not be zooming from the same speed or altitude. I think most 190 pilots already do this instinctively.

 

This first statement is totally incorrect. The force of gravity is exactly the same for every object - one g.

No. No no no no no. Gravity exerts a force proportional to the object's mass. That is literally the definition of weight. I strongly urge you to go review your physics.

Edited June 26, 2015 by 13GIAP_opcode

[unreasonable]

I do not need to review my physics when I have you here to explain it in nice simple terms.  

 

I expect that you are right that I am sloppy with terms of physics - well I would not be alone in that, .

 

What I do know (I think) is: 

 

1) That the acceleration of a body due to gravity in a vacuum is independent from weight  - or mass or whatever.

 

2) The air resistance encountered by a body is a function of it's shape and its speed, not it's mass.

 

3) If two identically shaped bodies follow the same path through a resisting medium at the same initial speed, the light body will come to a halt first.

 

4) Therefore (unless there is another factor I have missed) to take a slightly different example, if you could fire two identically shaped projectiles vertically at the same initial velocity, the heavier one will reach a higher altitude.

 

Are any of these points incorrect?

[JG13_opcode]

 

Take a look at this.

 

http://www.spitfireperformance.com/spit14afdu.html

 

Maximum Climb

26. The Tempest is not in the same class as the Spitfire XIV. The Tempest V however, has a considerably better zoom climb, holding a higher speed thoughout the manoeuvre. If the climb is prolonged until climbing speed is reached then, of course, the Spitfire XIV will begin to catch up and pull ahead.[/size]

 

Need i remind gentlemen that the Tempest is heavier about over a ton (3800kg vs +5000kg) ?

It should be obvious that there are more differences between the Spitfire and the Tempest than just weight. For starters, the Tempest V incorporates a laminar-flow wing which considerably reduces drag.

[JG13_opcode]

I do not need to review my physics when I have you here to explain it in nice simple terms.  

 

I expect that you are right that I am sloppy with terms of physics - well I would not be alone in that, .

 

What I do know (I think) is: 

 

1) That the acceleration of a body due to gravity in a vacuum is independent from weight  - or mass or whatever.

 

2) The air resistance encountered by a body is a function of it's shape and its speed, not it's mass.

 

3) If two identically shaped bodies follow the same path through a resisting medium at the same initial speed, the light body will come to a halt first.

 

4) Therefore (unless there is another factor I have missed) to take a slightly different example, if you could fire two identically shaped projectiles vertically at the same initial velocity, the heavier one will reach a higher altitude.

 

Are any of these points incorrect?

1) This is technically correct, but gravity is not the only force in our little aircraft example. Also make sure that you are not confusing "1 G-force" (which is not actually a force) or "acceleration due to gravity" with "the force of gravity".

 

2) The drag on a lifting body (i.e. a wing) is indirectly a function of its mass (recall lift-induced drag).

 

3) Only if the two identical bodies are not subject to any other forces such as thrust.

 

4) This is true, but aircraft are not ballistic projectiles since they have engines and wings

Edited June 26, 2015 by 13GIAP_opcode

[Dr_Molenbeek]

It should be obvious that there are more differences between the Spitfire and the Tempest than just weight. For starters, the Tempest V incorporates a laminar-flow wing which considerably reduces drag.

 

Of course opcode, i agree.

 

That was just to answer to those i've seen say "the plane is heavier, i do not see why it should zoom climb better" without seeing further.

[JG13_opcode]

Of course opcode, i agree.

 

That was just to answer to those i've seen say "the plane is heavier, i do not see why it should zoom climb better" without seeing further.

Right on

[unreasonable]

1) This is technically correct, but gravity is not the only force in our little aircraft example. Also make sure that you are not confusing "1 G-force" (which is not actually a force) or "acceleration due to gravity" with "the force of gravity".

 

2) The drag on a lifting body (i.e. a wing) is indirectly a function of its mass (recall lift-induced drag).

 

3) Only if the two identical bodies are not subject to any other forces such as thrust.

 

4) This is true, but aircraft are not ballistic projectiles since they have engines and wings

 

Thank for coming back and your patience: as per 3 and part of 4, this is why I suggested engine off tests; anyway in a Yak-H vs Yak-L test the engine and thrust are the same.

 

On the wings issue (2-4), the idea of a vertical dive or zoom is to minimize the requirement to generate lift to stay on a path, hence I had hoped, minimizing that problem. Although I understand that the wing is still generating lift).

 

There is something else about your formula that bothers me but I will have to worry about it later  - RL distraction just come up, just when I was getting interested!

 

Meanwhile, the other point of my longer post, which was about why there is an apparent reversal of performance order, is still out there, even if I accept your assertion/calculation that, other things being equal, a heavier aircraft will finish it's zoom lower. (With which I am not quite there, but that is not your problem of course....)

[JG13_opcode]

Meanwhile, the other point of my longer post, which was about why there is an apparent reversal of performance order, is still out there, even if I accept your assertion/calculation that, other things being equal, a heavier aircraft will finish it's zoom lower. (With which I am not quite there, but that is not your problem of course....)

I think I worded my posts poorly and kind of got lost in a tangent in this conversation

 

What I'm saying is that thrust to weight ratio, propeller design and drag are far more important than weight, since the propeller delivers our thrust and form drag scales with the square of the velocity, which becomes a huge problem at high speed (like the speeds you start a zoom at).

 

Not having actually crunched any numbers, I can't say for sure whether the 190 should outzoom the Yak-1 or not. It obviously depends on speed and altitude.

 

Intuition tells me that for any speed less than or equal to the Yak's top speed at that altitude, the Fw 190 does not have a significant advantage in zoom climbs.

Edited June 26, 2015 by 13GIAP_opcode

[unreasonable]

I think I worded my posts poorly and kind of got lost in a tangent in this conversation

 

What I'm saying is that thrust to weight ratio, propeller design and drag are far more important than weight, since the propeller delivers our thrust and form drag scales with the square of the velocity, which becomes a huge problem at high speed (like the speeds you start a zoom at).

 

Not having actually crunched any numbers, I can't say for sure whether the 190 should outzoom the Yak-1 or not. It obviously depends on speed and altitude.

 

Intuition tells me that for any speed less than or equal to the Yak's top speed at that altitude, the Fw 190 does not have a significant advantage in zoom climbs.

 

That is OK, it is an interesting tangent that I am about to make even more bizarre.

 

First of all I completely agree that the other variables are likely to be more important in the RL case.

 

Second, though, the interesting thing about Ze_Hairy's tests is that the Yak suffers a disadvantage upto to top level speed (approx.) but an advantage over it - as after a long zoom. That is the conundrum. 

 

Going back to the pure weight point, I have a thought experiment for you:

 

You have said that my conclusion that the heavier object will get higher if both are fired vertically is correct for a ballistic object, ie artillery shell. But, you say, Yaks have wings, and your formula seems to reverse this finding.

 

But suppose you took Yak_H and Yak_L and took the wings off, then fired them, engines off, vertically out of a giant cannon such that they had the same muzzle velocity.

 

Would you agree that Yak_H would reach a higher altitude? I think that this is inescapable.

 

Suppose that you now fixed tiny little hand-sized wings to each Yak and repeated the experiment. Surely Yak_H is still higher?

 

If your assertion that the life size winged Yak_L would actually get higher is correct, there must be some size or characteristic of the wing at which the two would reach the same height and after that the lighter one would get higher. But why? They have the same wing in each case, and are producing the same lift at a given speed since the flight path (or at least flight vector) is vertical.

 

I am puzzled as to how your equation deals with that?

[unreasonable]

Using that formula in a variety of scenarios in which a heavy and light Yak have the same T and D I get:

 

1) Whenever T>D, the lighter Yak will decelerate more slowly in a vertical climb, as per your illustrated example, but will also accelerate faster in a vertical dive. ((T-D)/m)+g =a

 

That is OK, the planes are using their engines to accelerate their masses since T>D, same T-D, less mass, get more acceleration to supplement g.

 

2) If T=D, weight is irrelevant, everyone accelerates (decelerates) at g. (T-D)/m = 0

 

So the bigger the difference between T and D in case 1), the bigger the advantage to the lighter Yak.

 

3) If T<D the heavier Yak accelerates faster in the dive and decelerates more slowly in the climb. The excess drag is trying to slow the aircraft down, but it takes more to slow down the heavy Yak than the light Yak.  Again the larger the difference between T and D the bigger the advantage to the heavy Yak. 

 

I assume that at speeds above normal top speed Drag is greater than Thrust. (? otherwise it could speed up?) Then according to your formula, a heavy aircraft is indeed at an advantage throughout the period of a dive and zoom in which speed is above normal top speed.

 

If the two Yaks start wingtip to wingtip at the maximum level flight speed of the heavy Yak, and enter a dive, there will be a (very) brief period while the light Yak gets ahead until it reaches the maximum level speed for its weight, at which D=T. From the point at which the planes reach and exceed D=T the heavy Yak will dive faster and zoom further, until the speed drops sufficiently that T>D, at which the advantage for the light Yak will emerge.

 

How am I doing in my physics homework?

 

As to my question about how the equation deals with my Yak cannon, the answer is that the scenario I have given you there is one in which D>T (since T=0), and your own formula predicts that the heavier Yak-shell will decelerate less.

Edited June 26, 2015 by unreasonable

[MK_RED13]

.... omg.. and the result is? Yak = U.F.O.  + flaps

[Dr_Molenbeek]

.... omg.. and the result is? Yak = U.F.O.  + flaps

 

I suspect the Bf 109F-4 to be touched by that "high speed drag" issue, as for the Yak-1.

 

This plane is known to be OP, but the only thing i've read is about high altitude speed.

 

Actually, it performs even better than the Yak-1 in term of 700km/h zoom climb...

 

I've already saw this issue in the past in others flight sim... One of the reasons (if not the only) that can be cited is when X plane do not reaches his requiered power (HP) BUT achieves proper performance (in term of speed)... the propeller becomes too efficient.

[ZachariasX]

I agree, but the entire point of my original post was to debunk the idea that you can have two aircraft that are identical in all characteristics but weight.

 

Ok, if that is what came across as a message, then I apologize, that was not the intention, because you are right in saying that they are “not equal” with different weights.

 

What I tried to point out is that the penalty incurred through additional load (within reasonable and certified limits) is not necessarily reflected in the attained max. speed of the aircraft.

 

Why is that, given the fact that the wing needs to carry more weight, has a higher AoA, as well as an increased induced drag?

 

The answer is: The wing is not the only part travelling through the air. You have the entire airframe plus the tail surfaces. When an aircraft is designed, the first thing you do is you set the chord of the wing and the cord of the fuselage at a certain angle depending on the wing area, shape and profile used, as well as the intended speed the aircraft is supposed to be travelling. This angle sets the trim and attitude of the fuselage in flight. Depending on the wing, the aircraft will pitch down more or less at higher speeds, as well as nose up at slower speeds. Now, for almost any aircraft, this design speed is NOT max. airspeed. No aircraft spends more than a tiny fraction of its flying time at that speed. For an interceptor of that era, the envisioned airspeed may be closer to the projected max. speed, but it will most likely never be max speed, even in the Bf 109 or the Spitfire, planes that had their DNA from racing planes (about the only planes where you set everything for max. airspeed).

 

In consequence, if you go faster than this designed speed, the aircraft will be flying more and more with a nose down attitude. This may seem good, because, after the formula mentioned, the drag of the wing is reducing even more, but as you look from the front, the tail will rise up more and more, increasing frontal surface significantly. So what you and up getting is a configuration in a situation of exponentially increasing aerodynamic drag, that the fuselage exposes more and more its dorsal section into the headwind.

 

The irony with added weight is now the following: If your plane is a bit heavier, you have to counter that with increased AoA of the wing, which in consequence lowers the tail again giving you in total a better aerodynamic situation. This is one aspect of the “mending by weight” that is applied in sailplanes (the example I was making). Sailplanes are like any other plane, just aerodynamics matter more than in any other plane and you do not have the effect of an engine to get confused even more.

 

Here is a graph showing what happens to an aircraft when you add weight (almost double it), in the case of an Antares glider:

 

The graph shows that increased weight just increases the speed of the best gliding angle. You make the aircraft go faster. It glides faster forward, and it sinks faster. The triangle however remains almost the same (this reduction illustrates the added penalty by induced drag because of the weight), even in the extreme case of almost doubling the weight of the plane. The change of the planes attitude is the main reason for this effect. A glider, designed to fly at 120 km/h has a pronounced nose down attitude when going at 200 km/h. Induced drag by the added weight is minimal compared to the drag added by the airframe. Flaps help to mend this issue. If you can move up (and reduce the angle of wing chord and fuselage chord) the chord of your profile, that helps a lot to go fast. A Yak has none of that. Neither do the rest of the planes. You can’t set those to negative. But an F-18 can.

This means: if I add weight to an aircraft, it likes to go faster and very much hates to go slower. How much this is depends on the load out, the wing and general aerodynamic property of the plane.

 

This is why increased weight not really mean that you max speed is slower but it depends.

 

Thus, everyone adds up to ~40% weight in ballast to make their glider like to go fast if they want to fly distance. They dump that when they have weak thermals and need to climb well (when sink rate is more important than speed). And I can repeat, a heavier and a lighter kind of the same aircraft DO NOT have the same flight characteristics. Whether they differ in max. speed and how much that is, that depends.

 

I hope this is more clear.

[JG13_opcode]

This is why increased weight not really mean that you max speed is slower but it depends.

I don't think I've been disagreeing with you on this point.

 

And I can repeat, a heavier and a lighter kind of the same aircraft DO NOT have the same flight characteristics. Whether they differ in max. speed and how much that is, that depends.

On this we definitely agree.

 

I assume that at speeds above normal top speed Drag is greater than Thrust. (? otherwise it could speed up?) Then according to your formula, a heavy aircraft is indeed at an advantage throughout the period of a dive and zoom in which speed is above normal top speed.

It's not "my formula", it's a widely accepted relation that describes the aircraft in any arbitrary climb.

 

Above your max level speed, drag is obviously greater than thrust, else you'd be able to maintain that speed. If you dive down from 2000m to the deck, you won't be able to maintain that 800km/hr sprint. You have excess drag, or from another perspective you have a thrust deficit.

 

As soon as you pull the stick back, you begin to add some of your aircraft's weight to the drag term in that equation also.

Edited June 29, 2015 by 13GIAP_opcode

[Dakpilot]

I think now would be a great time for some Lift/weight/thrust/drag vector diagrams, helped me a lot in my basic training to understand theories, I was lucky to have Military style training from very experienced fighter pilots

 

However this was rather a long time ago and I would certainly make  a mess of trying to explain clearly

 

Cheers Dakpilot

[unreasonable]

I don't think I've been disagreeing with you on this point.

 

On this we definitely agree.

 

It's not "my formula", it's a widely accepted relation that describes the aircraft in any arbitrary climb.

 

Above your max level speed, drag is obviously greater than thrust, else you'd be able to maintain that speed. If you dive down from 2000m to the deck, you won't be able to maintain that 800km/hr sprint. You have excess drag, or from another perspective you have a thrust deficit.

 

As soon as you pull the stick back, you begin to add some of your aircraft's weight to the drag term in that equation also.

 

You used that formula in an attempt to "put this matter to bed" or words to that effect, after upbraiding my for my apparent lack of understanding of physics. You asserted that a lighter aircraft would decelerate less in a climb, gave an answer derived from the formula to support this statement, and then asserted in your text that the heavy aircraft would accelerate faster in a dive.

 

I put the formula into a spreadsheet - you could get the same results algebraically if you so desire. All the formula does is show that a given amount of excess thrust will accelerate a lighter body more than a heavy one, whatever the value for theta, which should be no great surprise.

 

So whether a lighter plane accelerates faster or more slowly than a faster one is a function of the term T-D.

 

The point about dives and zooms, especially long ones, is that for much of the flightpath D>T since you are above (some relevant) maximum speed, in which case weight is good. The planes will accelerate in the vertical far beyond the point at which D=T, because the vector for weight is greater than the vector for lift. 

 

If you think any of this is incorrect please specify, I am always willing to correct errors.

 

Further, the problem with using "the" formula more widely is that D is assumed. I think it is OK to assume T, since we are looking at a scenario of planes differentiated only by weight. But the real source of difficulty is the point that D for the heavier plane is greater due to induced drag.

 

This is be true, but the additional penalty to D from weight is a function of how much total force the wing is producing, and the direction of that total force.

 

As a pilot enters a dive he can push the stick forwards. This reduces the effective AoA of the wing, which reduces lift. If lift is reduced, so is induced drag: for any given glide slope, they are proportional. As he speeds up, he gets more lift for a given AoA, which increases induced drag again.

 

However if the plane is diving steeply, the vector for the total force generated by the wing is closer to parallel to the earth' surface. I would draw the vector diagram as Dakpilot suggests if my skill at drawing and posting Paint scribbles were better, but it should be obvious that if it were possible to get your total wing force vector parallel to the earth's surface, the induced drag would be zero. Obviously this is impossible in a real aircraft, but the geometry is the same.

 

So a real, heavy aircraft diving would want to get as close to vertical as possible while also reducing effective AoA as close to zero as possible, while maintaining controlability. This will minimize induced drag and make the aircraft as close to a ballistic object as possible.

 

The same applies in a climb, as long as D>T. At some point once T>D the plane can either use the excess T to top out his vertical zoom as high as possible or move to a sustainable climb slope.

Edited June 29, 2015 by unreasonable

[Marauder]

If you enter a 0-g dive (nose over gently into the vertical), there's no difference between the heavy and the light aircraft, because you create 0 lift. AoA is not that relevant for creating induced drag, all that matters is lift - you don't have to align AoA with the vertical or something, just fly at 0 g. Lift is not 0 at 0° AoA for any airfoil used on the wings of WW2 aircraft.

 

It should be noted that even when you fly at 0 g, induced drag isn't really 0, because different wing sections usually produce 0 lift at different AoA's, but at least 0 g gives you the same induced drag for the same aircraft no matter the weight.

 

Did you know that parasitic drag is not constant, but also varies with a lot of parameters, for instance, it changes with different AoA? It could even be that a heavy aircraft creates less total drag than a light one in a certain flight condition, because the penalty of higher parasitic drag is offset by the benefits of better aerodynamics qualities in terms of parasitic drag at the higher AoA required.

 

The last two points just so that you have more things to think about.

[unreasonable]

Did a little test.

 

Two Yak-1, one with 40 liters of fuel, the other with 408 liters.

 

Engines off, dived from 2500m at 200km/h... once at sea level, the lighter Yak-1 was 10km/h slower than the heavier (which reached ~635km/h).

 

In their climbs, the heaviest finished higher, by 150m (1000m vs 850m) at 200km/h.

I just want to re-quote this incase anyone is misunderstanding what I am saying: assuming that Ze-Hairy was reasonably careful in his tests, this result indicates that the FM does indeed take weight into account (of course) but also that the momentum advantage of weight outweighs induced drag penalties, over a sufficiently long dive. Which is exactly what I would expect.

 

Other things being equal the advantage on a long dive and zoom should go to the heavier plane, and the longer the dive (within limits) the more advantage it will have.

 

I have no doubt that there are many important differences between the Yak and 190 which may or may not explain Ze_Hairy's results, but the effects of induced drag is unlikely to be one of them.