600km/h dive test

[Dr_Molenbeek]

So, i calculated the time that BoS fighters take to pass from 2000m to 1000m while keeping 600km/h IAS constant.

 

Full fuel to all planes.

 

 

German fighters:

 

Bf 109F-4 (1.3 ata/2500 RPM)..... 104s

 

Bf 109G-2 (1.3 ata/2600 RPM)..... 90s

 

Fw 190A-3 (1.32 ata/2400 RPM)..... 111s

 

Note: outboard cannons removed on Fw 190, headrest removed on Bf 109s, and i left kommandogerät take care of radiators on Bf 109s.

 

 

Russian fighters:

 

Yak-1 (full power, radiators 25%)..... 90s

 

LaGG-3 (full power, radiators 25%)..... 72s

 

La-5 (full power w/o Forza, radiators 25%)..... 66s

 

 

Of course, these numbers are not 100% accurate, but they give an idea.

[6./ZG26_5tuka]

Honestly I can't see this being any usefull for evaluation...never heared of dive tests with constant IAS.

 

Do you want to compare aerodynamics or performance of the planes?

Edited July 21, 2015 by Stab/JG26_5tuka

[III/JG2Gustav05]

That means to get the 600IAS constant speed German planes need go with more shallow dive, that's why take more time to reach the same altitude? longer is better? if thing is like that G2 is supposed to take longer than F4 to finish it.

Edited July 21, 2015 by III/JG2Gustav05

[6./ZG26_5tuka]

 The only thing it says is that at that particular speed the plane with longer timeframe upon reaching the low level altitude has the better glide ratio. The Why relies on various factors though and it open for speculation.

[III/JG2Gustav05]

So we can see YAK is as good as G2 on maintaining 600km/h IAS shallow dive. 

[RydnDirty]

This is interesting and original test. Now if we can just figure out what it means?!? lol

 

I guess it has a lot to do with the drag in a dive the BUT you didn't tell us if you used the throttle to maintain IAS or used the angle of descent and left the throttle constant.

 

Assuming you left the throttle constant  and used the steepness to maintain speed then I might think the lower number means steeper dive lower acceleration due to aerodynamic drag.

 

But I have my doubts that I know what I am talking about. Nice Test ! 

[Finkeren]

Actually he did say that. The engine settings are given as constants for each plane.

 

Looks like the Bf 109 G2 has gotten the raw end of the deal. Otherwise the results are pretty much in line with what you'd expect.

 

EDIT: Sorry. Didn't read the ladt result correctly. Somethings definately wrong in the case of the La-5.

Edited July 24, 2015 by Finkeren

[unreasonable]

 

 

I found this a bit hard to understand in the original format so I tried to remember some geometry - took me ages since my Open office spreadsheet uses radians instead of degrees, Grrr!

[TP_Jacko]

Hairy angles.png

 

 

I found this a bit hard to understand in the original format so I tried to remember some geometry - took me ages since my Open office spreadsheet uses radians instead of degrees, Grrr!

Hi unreasonable how did you get the angle and horizontal distance is there some sort of report generated in the game

[III/JG2Gustav05]

Hairy angles.png

 

 

I found this a bit hard to understand in the original format so I tried to remember some geometry - took me ages since my Open office spreadsheet uses radians instead of degrees, Grrr!

I think Hairy did a good test to show us something interesting. 

Unreasonable, your calculation is based on IAS or TAS, TAS changes as altitude changes.

[unreasonable]

I think Hairy did a good test to show us something interesting. 

Unreasonable, your calculation is based on IAS or TAS, TAS changes as altitude changes.

 

I thought about the IAS/TAS issue, but I am much too lazy (and probably incompetent) to try to factor that in, so I just used IAS as per Hairy's test as an approximation to calculate straight line distance travelled, since:

 

1) The altitude change is only 1000m

2) All the planes are showing the same IAS throughout.

 

You could

rerun the numbers using an average IAS>TAS conversion and get a different glide angle, but I suspect that it is the difference between the angles that has meaning (if any) not their actual numbers.

 

Obviously I am also assuming that the aircraft all travel in a straight line, which is almost certainly also not exactly true.

 

However, although Hairy's elapsed time numbers are not subject to these approximations, they are also rather hard to make any sense of. So I thought than an approximate average glide angle would be more intuitively helpful in discovering what these tests are designed to illustrate. Not that I am sure what that is....

 

 

Hi unreasonable how did you get the angle and horizontal distance is there some sort of report generated in the game

 

 

No it is just me calculating an approximate geometry using the timings, speeds, Pythagoras and some cos/sin/tan tables.

[6./ZG26_5tuka]

I think Hairy did a good test to show us something interesting.

Which is the glide ratio only. The only interesting bit to find in here to me is that the la-5 has a way worse glide ratio than the Lagg-3 although having higher wing loading.

The G-2 also has a worse glide ratio than the G-2 but that may be due to human error. Everything else seems unevaluable to me and more "nice to know" (no bad judment).

[unreasonable]

Which is the glide ratio only. The only interesting bit to find in here to me is that the la-5 has a way worse glide ratio than the Lagg-3 although having higher wing loading.

The G-2 also has a worse glide ratio than the G-2 but that may be due to human error. Everything else seems unevaluable to me and more "nice to know" (no bad judment).

 

Is that not what you would expect, given that they are flying at the same speed, have almost the same wing (I think) and the la-5 is much heavier. To stay on the Lagg3 glide angle the la5 would have to either speed up or/and increase AoA. Given that speed is constant, issue then is if the extra power of the la-5 is enough to keep the thing going at the constant 600kph, at a high enough AoA to maintain the glide slope? Seems not in the tests anyway.

 

Similar to the 109 F and G comparison: G is heavier so it has to create more lift to stay on same glide angle. With lift from speed ruled out that would mean higher AoA, which generates more drag. So extra power of 109 G is insufficient, it has to have a slightly steeper angle.

 

That is just how I interpret this anyway.

[6./ZG26_5tuka]

Heavier wing loading means that the optimum gliding speed is sifted to a higher airspeed. Thats why glider pilots for example use to fill their planes with water to acchieve higher ranges in competitions.

 

Given both planes share their basic construction (especially the airfoils) their glide number at equal weight should be theoreticly very similar. At combat weight the La-5 exeeds the Lagg-3, thus has the higher wing loading and with it a better glide ratio at high airspeeds.

Example: (W/S = Wing loading)

[unreasonable]

Glide slopes for gliders are just about the optimum L/D ratio, but the OP's test concerns powered flight at a set speed. These are not really "glide slopes" at all, just the angle of flight at which the OP could maintain 600kph at a fixed engine setting. 

To stay on the same slope as the Lagg at the same speed as defined by the test, it must generate an additional vertical vector from somewhere to offset it's extra weight, since at a set speed and AoA the Lagg and the La are generating identical lift, having the same wing. This can only come from:

1) Lift generated by having a higher AoA than the Lagg

and/or 2) The vertical vector of additional thrust.

 

These are the only way you can make L-W-T-D sum to zero. Put it another way, if a Lagg and an La were to fly wingtip to wingtip in formation the same speed, the La is always going to have to have a slightly higher AoA.

 

The question is when you increase AoA to achieve 1 and/or 2 does the extra drag you create prevent the La from maintaining the predefined speed target, or do you have enough extra Thrust to power through?

[6./ZG26_5tuka]

Yes their AoAs differ so does the generated lift. Thats why - if you want to test drag force as example - planes should be compared at a fixed dive angle. Thats why I initially asked what kind of valuable data this test is meant to offer.

[unreasonable]

Yes their AoAs differ so does the generated lift. Thats why - if you want to test drag force as example - planes should be compared at a fixed dive angle. Thats why I initially asked what kind of valuable data this test is meant to offer.

OK I think we are agreeing then, close enough. I am not sure how to interpret it either!

[JtD]

Well, for practical purposes it shows you how much relative energy you gain in a shallow descent, like an escape scenario. For instance, the La-5 as tested will have lost 1000m while the Fw190, going at the same speed, will only have lost 600m, thus having gained 400m of altitude. If the La-5 pilot choses to match altitude, the distance between the aircraft will increase. Bottom line it shows that at this test set-up, the Fw190 outruns all other aircraft in a shallow dive.

 

The La-5 in this test shows that it produces a lot of parasitic drag, which is also evident from my flaps test. It's a little fishy, to say the least.

 

unreasonable, please note that in a dive, aircraft weight effectively adds power to overcome the drag. So looking at LaGG-3 and La-5, assuming 3t for the -3 and 3.5t for the -5, the -5 adds about 500kW to the engine power due to the descend, whereas the -3, being lighter and diving at a shallower angle, adds only about 400kW. 100kW at those speeds is easily enough to overcome the higher induced drag (11kW) due to the higher weight. Which is also why, going to steep dives, the heavy aircraft will reach a higher terminal velocity than the light aircraft of the same type.

[unreasonable]

Well, for practical purposes it shows you how much relative energy you gain in a shallow descent, like an escape scenario. For instance, the La-5 as tested will have lost 1000m while the Fw190, going at the same speed, will only have lost 600m, thus having gained 400m of altitude. If the La-5 pilot choses to match altitude, the distance between the aircraft will increase. Bottom line it shows that at this test set-up, the Fw190 outruns all other aircraft in a shallow dive.

 

The La-5 in this test shows that it produces a lot of parasitic drag, which is also evident from my flaps test. It's a little fishy, to say the least.

 

unreasonable, please note that in a dive, aircraft weight effectively adds power to overcome the drag. So looking at LaGG-3 and La-5, assuming 3t for the -3 and 3.5t for the -5, the -5 adds about 500kW to the engine power due to the descend, whereas the -3, being lighter and diving at a shallower angle, adds only about 400kW. 100kW at those speeds is easily enough to overcome the higher induced drag (11kW) due to the higher weight. Which is also why, going to steep dives, the heavy aircraft will reach a higher terminal velocity than the light aircraft of the same type.

Yes I do understand that momentum from weight helps overcome deceleration from drag - indeed there was a long thread somewhere else on this topic where I had to insist that was the case in the face of strenuous opposition! In the case where the aircraft are unloaded (no lift, no induced drag) this would be most advantageous to a heavier plane, and in an escape dive this is what one might do.

 

The OP's test though is at constant speed, (and I assuming at a more or less constant glide slope), so that there is no acceleration. The vectors have to sum to zero. So if the OP was unable to keep the La5 on the Lagg's glide slope at that speed, it implies that in the game the engine power at the chosen settings is insufficient to compensate for the differences in weight (and drag) between the planes. (I am not sure that thinking in terms of "extra power" in a dive is very elegant: the power is what it is at a given setting and speed independently of the plane's orientation).

 

I have no idea if this seems to be incorrect or not, BTW, but it does seem odd.

Edited July 27, 2015 by unreasonable

[JtD]

At these speeds, the differences come from parasitic drag. It makes up about 95% of the total drag. Therefore, the lift induced drag just about 5%. In terms of drag, weight is near irrelevant. If you were to double the weight of the La-5 in that test, it would perform a lot better.

 

If you want to think vectors - if you put the aircraft on the nose, the weight of the aircraft goes the same way the thrust does, they add up to oppose drag. Now you're on a slope, and weight supports thrust with sin(angle of slope)*weight. At high speed, even at shallow angles, this extra force is far larger than the extra induced drag, opposing it. If you take a dive at a 2° angle in a 3t plane with a 10m wing span, already below 300km/h EAS, weight produces less induced drag than it produces a force supporting thrust.

[unreasonable]

Again I find your formulation  a bit puzzling. Take a glider for example. It has no thrust at all. You only need to add lift, weight and drag to see how it could glide down a slope at a constant speed. Obviously if you add ballast it has to go faster at a given glide slope to generate the extra lift and equalize the forces. But we are not talking about going faster, we are talking about two planes of different weight attempting to maintain the same speed.

 

I am not sure what you mean by "extra force". To keep the heavier plane on a given glide slope, there are only two forces that exert a vector upwards: lift and thrust from the engine, provided that the AoA is sufficient that the thrust vector is above the horizon. I imagine that in the case of these tests this is no longer the case?

 

Anyway, that aside, what I am trying to make sense of is the situation where the La5 has I believe, in game, a slightly higher level top speed than the Lagg3 in the altitude band 2-1 km, but according to Le-Hairy's tests it would seem that at the Lagg's 600kmh slope of 4.8 degrees or so the La must be slightly slower. It is hard to understand why this should be so.

 

It may simply be that the tests are not that accurate, with all due respect to the OP's flying: he has had to manually attempt to maintain a set IAS and the times/slopes are only a little different between the Lagg and the La.

[JtD]

...Obviously if you add ballast it has to go faster at a given glide slope to generate the extra lift and equalize the forces...

No, it could go faster with the same AoA, it could go at the same speed and increase AoA a little bit instead, it could go slower and increase AoA even more. Three possibilities, even if the slope is given. We have case two, btw., but, at any rate - the slope is not given.

At high speed, the heaver plane will usually go as fast on a shallower slope than the light one. For simplicities sake, look at the chart in post #14 and assume all planes want to maintain 180 km/h. At this same speed, the heaviest loaded plane has the lowest sink rate and therefore the shallowest slope.

So we have the heavy aircraft going at a shallower slope with the same speed at a higher AoA than the light one.

[unreasonable]

No, it could go faster with the same AoA, it could go at the same speed and increase AoA a little bit instead, it could go slower and increase AoA even more. Three possibilities, even if the slope is given. We have case two, btw., but, at any rate - the slope is not given.

At high speed, the heaver plane will usually go as fast on a shallower slope than the light one. For simplicities sake, look at the chart in post #14 and assume all planes want to maintain 180 km/h. At this same speed, the heaviest loaded plane has the lowest sink rate and therefore the shallowest slope.

So we have the heavy aircraft going at a shallower slope with the same speed at a higher AoA than the light one.

 

I do not see what you are trying to argue with me here, the proposition you have made which I have boldened is exactly what I have been saying! The slope is not given, it is an outcome of the experiment.

 

It cannot go faster on the same slope in this case because the speed is defined as 600kph.  So it must have a higher AoA to stay on the same glide angle without accelerating. But in Hairy's tests he was seemingly unable to achieve this.  The question is why? You are saying that this cannot (or is not?) be because of induced drag, fine. I am not trying to claim that I know the answer, simply to formulate the question in a way that makes sense.

 

If it is just about additional parasitic drag then the question remains why the La apparently has a higher level flight top speed but a lower top speed at the Lagg's 600kmh slope? Is this possible?

 

Piloting error, something odd in the FM, or an accurate reflection of the real thing, surely that is the issue?

[Guest deleted@50488]

Excellent test Hairy, and Excel work unreasonable.

 

From a glider pilot perspective, it really tells me nothing very important... It's really not glide ratio we're seeing here, right ? Well, but it reveals to me something I wouldn't expect, like an La-5 taking almost half the time to get there compared to the fw190 A3....

 

Thx for posting this thread!

[JtD]

I do not see what you are trying to argue with me here, the proposition you have made which I have boldened is exactly what I have been saying! The slope is not given, it is an outcome of the experiment.

I'm trying to convey the part you were not bolding - that the heavy plane does not need extra thrust in a shallow high speed dive to overcome any additional drag resulting from the higher weight. Higher weight is benefitial in this case.

 

I've also stated several times that the La-5 has a very high parasitic drag in game, and that this is the reason it cannot keep up with the LaGG-3 in this test. Which is supposed to be the answer to what I see as your key question.

 

Everything else is just trying to clarify statement you found a bit puzzling, sorry if I fail here on occasion.

 

Same way I'm now trying to answer your last question:

Without boost, in level flight at sea level, the La-5 is just 2% faster than the LaGG-3, even though it has about 30% more power. This relation is what leads to the results of the test, where the La-5 trades about 25% more potential energy per time (i.e. adds power) than the LaGG-3 does, to maintain the same speed. If it was 25% heavier, it would have the same sink rate, but it is not that heavy, so it sinks faster.

I don't know for sure that in game the La-5 is indeed faster than the LaGG-3 between 1000 and 2000m, if so I'd assume it would be even less than the 2% at sea level. But at any rate, 2% is pretty much "as fast as".

[unreasonable]

So the problem is that the La is picking up so much more drag than the Lagg in acceleration from top level speed to 600kph, that the additional weight of the La is insufficient to prevent it slowing down unless it dives more steeply. Whereas if you just took two Laggs and loaded one of them up with extra internal weight the heavy one should be able to dive at 600 kph less steeply. 

 

I suppose this is just an empirical fact one way or the other about the comparative  dragginess of the two planes. 

 

@JtD  Anyway appreciate your Tutor Mode as always! 

[JtD]

Nothing to add really, but then I have Excel and put it all into a sheet. Mind you, I'm away from game and sources, so while plane 1 is supposed to resemble the LaGG-3 and plane 2 is supposed to resemble the La-5, the input figures certainly aren't spot on. Feel free to experiment a little.

Divingcheck.zip

[unreasonable]

I know those are a rough cut, but Le_Hairy's times for those are within a couple of seconds!