What, if anything, is 'energy retention'?

[AndyJWest]

From the Wikipedia article on the Me 262:

Quote

As many pilots soon found out, the Me 262's clean design... meant that it, like all jets, held its speed in tight turns much better than conventional propeller-driven fighters, which was a great potential advantage in a dogfight as it meant better energy retention in maneuvers.

https://en.wikipedia.org/w/index.php?title=Messerschmitt_Me_262&oldid=877758751

 

The article cites two sources, neither of which uses the term 'energy retention':

https://www.hq.nasa.gov/pao/History/SP-468/ch11-2.htm

http://zenoswarbirdvideos.com/Images/Me262/ME262PILOTDEBRIEF.pdf (Wikipedia doesn't actually include a link to this document, but I don't think it is hosted elsewhere)

 

As for the general merits of the Wikipedia Me 262 article, or of Wikipedia coverage of WW2 topics in general, I'm not proposing to start a discussion here. What I am interested in however is why the article uses a term ('energy retention') which is not only absent from the sources cited, but which appears not to be in general usage in aviation. Indeed, from what I can find on Google, usage of the term (as far as aviation goes) is almost entirely confined to a single context: discussion of air combat simulations/games. About the only exception to this I can find is a discussion on a RC aircraft forum, in relation to gliders. This is the first post in the thread:

Quote

Not sure if the power fliers will have heard the term, but anybody who flies slope gliders should be familiar with it. Slope heads typically talk about a glider having "good energy retention" when describing a ship that doesn't scrub off too much speed during the turns, and holds speed well coming out of a dive (or pulling up on a vertical line).

It really seems to be a slope head euphemism for "Goes really fast and keeps going fast" but from what I can tell it it's just a synonym for "low drag". Am I missing something? Is there anything other than low drag that would lead to describing a glider as having good energy retention?

There also seems to be a generally-held belief that heavier gliders have better energy retention. Ignoring for the moment that I haven't come up with an exact definition of energy retention yet  why would this be the case? Certainly a heavier glider will be able to penetrate in high wind better, but why would it help it "hold energy" any better than the same glider at a lighter weight?

Just trying to sort out exactly what the term means, or if it even has a concrete definition...

https://www.rcgroups.com/forums/showthread.php?624426-What-does-energy-retention-*really*-mean

 

The thread goes on to discuss further, and I'd recommend reading it, since it seems to be discussing much the same thing as combat simmers mean by the term. Ultimately, it seems to come to two sort-of-conclusions: that 'energy retention' is higher for heavier aircraft, and that otherwise it is a function of low drag at high angles of attack and control deflection angles. Beyond that, it doesn't actually arrive at any real definition. As the thread correctly states though, a glider can only hold two forms of useful energy: gravitational potential energy, and kinetic energy. A powered aircraft will of course also hold chemical potential energy, in the form of fuel which can be converted to thrust via the engine etc. Either way, whether discussing gliders or powered aircraft, it seems to me that the phrase lacks anything in the way of a concrete definition, and seems to be an amalgam of at least two, and possibly three, different things, all of which can, at least in theory, be measured: the mass of an aircraft, the drag under specific conditions (e.g. a turn at specific G), and arguably (except for gliders) excess power available beyond that to sustain a turn, if any. Now there is no particular problem with using undefined terms in general conversation, but doing so in an encyclopaedia article isn't particularly helpful (not least because most readers are unlikely to be combat simmers or RC aircraft enthusiasts), and I will suggest is actually unhelpful when trying to make objective comparisons between aircraft.

 

Why is it unhelpful though? Because, I have to conclude, the factors involved may well be directly contradictory in the context that simmers use the term, making any general assertion about aircraft X having more 'energy retention' than aircraft Y more or less meaningless. Higher mass clearly relates to higher kinetic energy, but all other things being equal also equates to higher drag during manoeuvres (and in level flight for that matter), given the need to generate higher lift, either through increased AOA or through increased speed - which can only be achieved through a reduction in gravitational potential energy (i.e. by losing height) or through the utilisation of chemical energy in the form of excess power. Consider three very different aircraft, and then decide which has the best 'energy retention'. Firstly, an advanced sailplane with high-aspect-ratio laminar flow wings, and minimal parasitic drag. Properly flown, it will 'retain energy' very well if put into a shallow dive to accelerate, and then placed into a zoom climb until it returns to its initial airspeed. To be sure, it will of necessity (in still air) end up losing some height, but the losses should be small in comparison to most aircraft. For contrast, consider a Sopwith Camel, turning on a sixpence in the sort of combat it seems best suited to.  Properly flown (not easy...) it should be able to sustain altitude and airspeed almost indefinitely, while out-turning almost anything but a Fokker Dr1. Again, there are losses: in this case chemical energy in terms of burnt fuel. Otherwise, this is as good as you can get for 'energy retention'. You aren't losing any, despite the abysmal drag characteristics of a Camel in comparison to almost any aircraft of a few decades later. And finally, consider the Me 262, as described by Wikipedia. What exactly are they referring to here? It seems most like the Camel, in that they are apparently describing its performance in 'tight turns'. But 'tight' in comparison to what? And under what conditions? As test pilot Hans Fay suggests in the second  of the sources Wikipedia cites, the Me 262, being a jet, has flight characteristics notably different from a typical piston-engined fighter. In particular, the engine performance (delivering relatively high power at high airspeeds, and low power at low airspeeds) means that its best sustained turn rate will be found at higher airspeeds than with  prop fighters. Note though, that this is a function of high engine thrust, rather than low drag. The Me 262 has good 'energy retention' because it converts chemical energy most efficiently at high speeds. Our three examples than all demonstrate good 'energy retention': but only if you define it differently for the three cases.

 

I'll conclude then by suggesting that Wikipedia shouldn't be using the term 'energy retention' at all, since it doesn't define it. And that it would probably be for the best if combat simmers didn't use it either. It isn't 'a thing' at all. It is a confused amalgam of several different factors, all of which can be described more accurately. Lift-drag characteristics etc of high-performance gliders have been analysed to the Nth degree. The turn performance of the Sopwith Camel less so, but at least in principle all factors can be accounted for. Likewise, we know enough about the general characteristics of jet engines to make useful comments about the turning ability of the Me 262 under different conditions. In no case is anything useful added by vague references to 'energy retention'. Under all circumstances, all aircraft are 'losing energy' one way or another, and if they are losing it more or less under specific conditions, it is because of specific characteristics. Not because of some mythical property only found on simmer forums. If I'm wrong about this, I'd like the following questions answered: what are the appropriate units to measure 'energy retention' in, and how do you measure it, in a way that can make comparisons between different aircraft in different circumstances meaningful?

[HagarTheHorrible]

Energy retention is simply the energy retained by the aircraft once chemical energy stops being a factor.  I doubt energy retention has anything to do with how well an aircraft turns, that is power to weight and wingloading

[Gambit21]

Fighters don't out-turn each other, they "out conserve energy" one another.

That's right for a fighter pilot's mouth, and well said from what I can tell.

 

 

[6./ZG26_Klaus_Mann]

This is energy retention: 

 

[AndyJWest]

Well, if 'energy retention' is an actual thing that some aircraft have more of than others, it should be measurable. So I'll ask again, how do you measure it, and what units do you measure it in?

Edited January 20, 2019 by AndyJWest

[6./ZG26_Klaus_Mann]

A Polar Graph like this, giving a Potential Energy gain (Altitude) per Unit of Time, for any given Speed. Now, with a Motorplane like a Bf109G-2 for example this Graph at Sea Level would show negative Values below 150kph, no gain at 150km/h, 21m/s gain at 270km/h, no gain at 529km/h, and negative gain above 529km/h. 

 

Now, the Aircraft that at any given Speed has the better Climb/Sink Rate is the one that decelerates less, which means it retains its Energy better. 

 

 

Take for example these two, and you will see which one retains Energy better than the other, given the ASW-15/18 to maintain 150km/h decends at only 0.8m/s, while the K-13, an old Wood and Canvas Plane, has to decend at 3m/s to maintain 150, meaning a rather steep dive, compared to the ASW-15 which is going pretty much straigh ahead. The required loss of Altitude is basically your Energy Bleed, the lower your Bleed and Drag, the better the Energy Retention.

 

 

 

Edited January 21, 2019 by 6./ZG26_Klaus_Mann

[AndyJWest]

How would this relate to the statement in the Wikipedia article that the Me 262 showed "better energy retention in maneuvers" due to it being a jet?

[6./ZG26_Klaus_Mann]

Well, your Aircraft has a Total Energy, which is your Kinetic and Potential Energy combined. 

Now lets we talk about a 70° Bank Turn, which is about 3G, and slightly above 25 Seconds for the 360, at a certain Speed, lets say 400km/h. If you have Plane A fly that Manouver without loosing Altitude, it hasn't lost any TE in that Turn.

Plane B looses about 25m of Alt in that Turn, lowering it's TE, it has worse Energy retention than Plane A

Plane C gains Alt, about 25m in that Turn, meaning it has not only retained its Energy, but gained some. 

 

 

Now, go back to the K-13 and the ASW-27 Graph above. Now, lets say the K-13 is a Spitfire and the ASW is a 262. Now, if they Dive on the same Slope, lets say, falling 1 in 25, the 13/Spitfire will fall at about 80km/h, while the 262/ASW27 will outrun it, being able to do 1:25 at well over 200km/h. 

That of course Means, that on the Bottom of the Dive, the 262 can convert 200km/h into Manouvering or Zoom Climbing, while the Spit has to start with 80. 

And then of course, to climb again the Spit has to go a lot slower again, as the 262 can still Climb at well over the Zero Climb(=Top Speed) of the Spitfire. 

Motorplanes are just Gliders with Artificial Energy Sources, a permanent Thermal or Upwind stuck to them, which they can convert at their Ease into whatever necessary. 

[AndyJWest]

So what unit is 'energy retention' measured in?

[Vig]

I always thought that energy retention was what happened when you stayed high, kept your speed up, and didn't pull the stich too hard.

 

[AndyJWest]

9 minutes ago, Vig said:

I always thought that energy retention was what happened when you stayed high, kept your speed up, and didn't pull the stich too hard.

 

 

That would be a consequence of the pilot's behaviour, not a property of the aircraft.

[Vig]

Ah.  I see.  I wonder what kind of energy retention a BF-109 has compared to a F-105?  It would seem to depend on the flight mode. 

[unreasonable]

50 minutes ago, AndyJWest said:

 

That would be a consequence of the pilot's behaviour, not a property of the aircraft.

 

It could be, but if you took two aircraft with the same mass, traveling at the same speed, they would have the same KE. At the same height, the same PE too.

If each then changed AoA by the same amount, they might, depending on the design, end up with a different speed and height. That would be down to the property of the aircraft, presumably something to do with how the L/D ratio changes with AoA depending on wing design etc, but I leave that to the experts.

 

In practical terms I have always thought of "energy retention" in terms of how quickly a plane will slow down when you attempt a given turn without changing your power output. Klaus_Mann is just extending that to include the vertical component which makes perfect sense to me.

 

I agree with your more general point that this often comes up in flight sim forums in a rather vague way; but then again almost everything in flight sim forums is usually treated in a rather vague way.  

 

 

[ZachariasX]

5 hours ago, AndyJWest said:

How would this relate to the statement in the Wikipedia article that the Me 262 showed "better energy retention in maneuvers" due to it being a jet?

As Klaus said, but in the context of that quote, it also reflects that jet engines are more efficient at higher speeds. At, say, 600 km/h the jet engine can deliver still a lot of its power into forward accelleration, whereas a piston engine starts to bleed energy by losing propulsion efficiency. This extra power you can use to have you pushed through maneuvers without similar loss in speed.

 

This means that, conversely, at low speeds the tables are in fact turned, the prop gaining advantage by being more efficient. Hence, speeds below 500 km/h are not suitable for the 262.

Edited January 21, 2019 by ZachariasX

[AndyJWest]

16 minutes ago, ZachariasX said:

As Klaus said, but in the context of that quote, it also reflects that jet engines are more efficient at higher speeds. At, say, 600 km/h the jet engine can deliver still a lot of its power into forward accelleration, whereas a piston engine starts to bleed energy by losing propulsion efficiency. This extra power you can use to have you pushed through maneuvers without similar loss in speed.

 

This means that, conversely, at low speeds the tables are in fact turned, the prop gaining advantage by being more efficient. Hence, speeds below 500 km/h are not suitable for the 262.

 

This rather illustrates the point I made when I started this thread. Klaus posted a video which very well illustrated one form of 'energy retention' in the context of a high-performance glider, and went on to provide graphs illustrating what he took the term to mean.  Discussions of 'energy retention' concerning the Me 262 in contrast seem to concern the high performance of its engines  (compared to likely opponents) at high speeds. If 'energy retention' is something exhibited by gliders, how can it be attributed to the engines in the case of the Me 262? Nothing I've seen so far convinces me that discussions of relative aircraft performance are made easier by the usage of a term which seems to mean different things depending on the context.

[ZachariasX]

55 minutes ago, AndyJWest said:

If 'energy retention' is something exhibited by gliders, how can it be attributed to the engines in the case of the Me 262?

Klaus posted something that IMHO is as important as it is overlooked. But it does remain a factor about why plane A is a better „boomer & zoomer“ than the other, not just the engine.

 

You have two factors: one is how likely an aircraft is bleeding energy upon doing X, and the other is how well can this aircraft compenate for the energy bled performing X.

 

Bottom line of that is, nothing can beat the 262 as long as it stays fast while it should actually be easy to stay very fast.

 

This is also a difference between the Tempest and the latest 109 variants (beside the formes better handling at high speeds): Once fast, the Tempest loses less speed in maneuvering. This is illustated by getting more altitude in a zoom climb than the 109 despite on average lower substained climb rate. It essentially negates the 109‘s main ability of being a good „hit and run“ figher (certanly better than most of the Spit IX) and force it into a maneuvering fight, where it performs less well, but still good enough to be a match for a Tempest silly enough picking up on a slow affair.

 

The Spit IX on the other hand had to drag the 109 in a slow fight. The 109 has to remain fast. But staying fast gives the pilot less leeway for maneuvering while not slowing down as a Tempest pilot has.

[Ehret]

3 hours ago, unreasonable said:

In practical terms I have always thought of "energy retention" in terms of how quickly a plane will slow down when you attempt a given turn without changing your power output. Klaus_Mann is just extending that to include the vertical component which makes perfect sense to me.

 

My other "practical" interpretation is: if we assume that there are two planes and they are in a fairly step dive and once they level (at the same altitude and velocity) then the one which is decelerating slower has a better energy retention.

 

In the Thunderbolt you should be able to out-loop the Spitfire after initiating a similar maneuver; is it case in the sim?

In the Mustang the radiator gains efficiency with velocity; the faster you go the lower the cooling drag should be; will we get it?

[6./ZG26_Klaus_Mann]

The unit would be m/s and the Unit your Total Energy, as in a Glider. m/s gained is Energy gained, m/s lost is Energy lost.

https://en.wikipedia.org/wiki/Variometer#Total_energy_compensation

[unreasonable]

1 hour ago, Ehret said:

 

My other "practical" interpretation is: if we assume that there are two planes and they are in a fairly step dive and once they level (at the same altitude and velocity) then the one which is decelerating slower has a better energy retention.

 

In the Thunderbolt you should be able to out-loop the Spitfire after initiating a similar maneuver; is it case in the sim?

In the Mustang the radiator gains efficiency with velocity; the faster you go the lower the cooling drag should be; will we get it?

 

On the Mustang point, apparently not. IIRC, Jason mentioned at some point that the Meredith effect would not be modeled explicitly, so I suppose there will have to be an approximation to total drag to make the top speeds align with the reference data, in which case the P-51 may be a little too slick when  slow, but who knows, the developers may be able to tweak their numbers to get the right outcomes somehow.

 

The problem in discussing specific examples of relative energy retention - like Thunderbolts out looping Spitfires - is that you are hardly ever controlling for other variables. The Thunderbolt is much heavier: at equal speeds it will always have a higher energy than a co-alt Spitfire. Since it is heavier it much also take more energy to change direction (?), so "energy retention" comparisons between different planes would have to take that into account. You have to be clear whether you are talking about total energy (Joules) or specific energy (J/kg).

 

 

 

 

 

[AndyJWest]

Ignoring specific energy for now, measuring energy in Joules makes more sense than trying to measure it in metres per second, I think. The trouble is we aren't trying to measure energy, but 'energy retention' - which to me suggests that what we are actually trying to measure is energy loss over time. For which the logical unit would seem to me to be the Watt - a Watt being 1 Joule per second. Now this is at least in theory measurable, in that total energy loss over time must equate to the difference between the sum of kinetic energy plus gravitational potential energy plus chemical potential energy (i.e. usable energy content of fuel remaining) between the start of the time period and the end. The snag with that is that it implies that an aircraft with a less fuel-efficient engine has lower 'energy retention', which seems to have little relationship with the way the phrase has been used so far. And I think that it is certain that even at a constant power output, energy loss isn't going to be constant over time, while manoeuvring. Even if you could arrive at a figure in Watts (or possibly Watts per kilogram?) it would only apply under specific conditions. So really, I'm not sure that either Joules nor Watts (or W/kg for that matter) are actually something you can really use as a direct unit of 'energy retention'. Under specific conditions, when making direct comparisons, you may be able to arrive at directly comparable figures,  but under the same conditions you can compare the more obvious results anyway,  without resorting to complex maths. Which still implies to me that 'energy retention' as some sort of inherent measurable general property of aircraft, isn't a very useful concept. Which may be why the aviation industry doesn't use it, or anything quite like it as far as I'm aware.

[6./ZG26_Klaus_Mann]

You are making it entirely too complicated. Fuel Consumption is irrelevant, even Engine Type. The Polar Curve of your Aircraft is the only thing that really matters in determining where and wether you have better Energy Retention at any Speed. 

 

For example 109E v P-40. Both have the same Stall and Top Speed and best Climb Speed, but differing Climb Rates. The Climb Rate indicates Energy gain when climbing, and Energy Loss when sinking. 
At the same Time then, these Curves also indicate Acceleration in a Straight Line, as every Rate of Climb corresponds with exactly one Rate of Acceleration in a Straight Line at any given Speed. 

Same with Deceleration. In this case for example, the 109 shows that is Aerodynamically inferior to the P-40, but the Superior P/W Ratio allows it to outclass the P-40 at Speeds below 500. 

Above 500, the cleaner P-40 will however Come out ahead due to its lower Drag. 

 

In a 2g Manouver you take this Curve, but shift it Down, to a Stall Speed of around 1.4 times higher.

 

[ZachariasX]

1 hour ago, AndyJWest said:

Ignoring specific energy for now, measuring energy in Joules makes more sense than trying to measure it in metres per second, I think.

Klaus‘ formula (as I understand it) shows the differen amount of tow force required to remain at given speed. m/s is downward movement, meaning the higher the number, the more (potential) energy you lose to remain at the speed desired.

 

Using w = m*g*h, this translates directly in the investment in Watts required.

 

This means the aircraft not only has to be sleek, it must also be in a flight configuration that is still efficient to not start bleeding energy on top of lost by sheer drag.

 

This is very evident in comparison of required time to altitude. A Zero will be rather good at that, as long as you are relatively slow. It has both good lift and efficient pull making most of his power at slower speed. If you drag it now in a shallow, fast climb behind a Mustang, it will bleed so much energy by going fast that there is little remaining for the climb. The Mustang on the other hand can go fast without bleeding much energy and still has a lot of power left for the climb. This means the Mustang can convert altitude in speed and vice versa with far less loss in energy. A Zero cannot trade much altitdude in direct speed gain, as it will not be controllable anymore. Any altitude invested in a dive beyond combat speed is wasted and lost. The higher combat speed along woth a sleek airframe can give the better the trade off and the more energy your aircraft will retain when trading speed for altitude again.

 

Energy retention is you not losing that much energy (Watts invested) by converting potential to kinetic energy and vice versa.

Edited January 21, 2019 by ZachariasX

[HagarTheHorrible]

This is all way too complicated.

 

Forget the engines, they aren't a factor,  there are only two things that count, lift and drag (not as in queen).  Try and imagine two gliders dukeing it out.

 

The only way, I can imagine that an aircraft can have better energy retention coming out of a turn is if it uses something like Kerrs, from F1.  An aircraft with a higher wing loading will always have to expend more energy to proscribe a circle of a certain diameter than an aircraft of a lower wingloading, it is always going to have to trade more energy just to retain enough energy to keep flying.  As far as I'm aware a swept wing isn't as efficent at producing lift, we know this because the 262 had a high take off and landing speed.

 

The only thing I can think the debate might center on is that something like the 262 could possibly go around the circle faster rather than tighter, thus retaining more kinetic energy but, of course, that isn't specific to the 262 just any aircraft with a large speed difference. The problem for the 262 is that because of low acceleration, once it has lost energy it's up shits creek and we know this because this is when Allied aircraft chose to attack it, during take off and landing.

 

YO-YO's are a good example of energy retention because it's fairly simple to see how it's possible to convert, or retain, one type of energy by storing it up as another, but again that only works if you have an excess, compared to your opponent,  to start with.

 

So, to summerize, a much faster aircraft can potentially reach the same point by flying a bigger circle, faster, than a slower, tighter turning aircraft, thus RETAINING more potential energy to trade in when the need arises.

 

As pointed out earlier BFM is all about conserving energy and spending it as efficiently and as effectively as possible.

 

 

Edited January 21, 2019 by HagarTheHorrible

[AndyJWest]

@Klaus: If 'energy retention' equates to rate of climb at a given speed (or rate of descent for a glider), why do we need another, less clear, term for it?

 

As I understand it (anyone feel free to correct me if I'm wrong), rate of climb at a given speed correlates more or less directly with excess power available compared to that needed to maintain level flight at the same speed. And the same correlation applies to acceleration. Which means, if I'm correct about the correlation, and if Klaus's definition is also the correct one, that 'energy retention' isn't about retaining anything, it is about having enough of something to spare that you can make use of it. Thoroughly misleading terminology.

[unreasonable]

In a fight the main time I worry about this is when I am behind someone and trying to get enough deflection for a shot: sometimes you know that you can increase AoA (or yaw for that matter)  just enough to get a shot but it will scrub off so much speed that you will now be much more vulnerable.  I find the German crates particularly hard to judge for this, since they can pull the highest AoAs for a short time, but it is generally better not to give in to the temptation. So it is not only a matter of trading KE for PE - sometimes you are spending KE for a change of orientation.

[AndyJWest]

22 minutes ago, unreasonable said:

In a fight the main time I worry about this is when I am behind someone and trying to get enough deflection for a shot: sometimes you know that you can increase AoA (or yaw for that matter)  just enough to get a shot but it will scrub off so much speed that you will now be much more vulnerable.  I find the German crates particularly hard to judge for this, since they can pull the highest AoAs for a short time, but it is generally better not to give in to the temptation. So it is not only a matter of trading KE for PE - sometimes you are spending KE for a change of orientation.

 

Isn't this the situation where you are supposed to use a high yo-yo:

Quote

The high Yo-Yo is a very effective maneuver, and very difficult to counter. The maneuver is used to slow the approach of a fast moving attacker while conserving the airspeed energy. The maneuver is performed by reducing the angle at which the aircraft is banking during a turn, and pulling back on the stick, bringing the fighter up into a new plane of travel. The attacker then rolls into a steeper pitch turn, climbing above the defender. The trade-off between airspeed and altitude provides the fighter with a burst of increased maneuverability. This allows the attacker to make a smaller turn, correcting an overshoot, and to pull in behind the defender. Then, by returning to the defenders plane, the attacker restores the lost speed while maintaining energy.

 https://en.wikipedia.org/wiki/Basic_fighter_maneuvers#High_Yo-Yo

[Ehret]

3 hours ago, unreasonable said:

On the Mustang point, apparently not. IIRC, Jason mentioned at some point that the Meredith effect would not be modeled explicitly, so I suppose there will have to be an approximation to total drag to make the top speeds align with the reference data, in which case the P-51 may be a little too slick when  slow, but who knows, the developers may be able to tweak their numbers to get the right outcomes somehow.

 

That's my fear... we already have the "Thunderspit" and if would get "Zerostang" next then... no, please, no!

[unreasonable]

 

2 minutes ago, AndyJWest said:

 

Isn't this the situation where you are supposed to use a high yo-yo:

 https://en.wikipedia.org/wiki/Basic_fighter_maneuvers#High_Yo-Yo

 

Yes it is: the problem though is that sometimes (I am really talking about Career mode here) the fights are very low to start with so there is little margin for error when you are diving on a target. The best solution is still to gain some height and come back at another angle: but sometimes I just cannot resist taking the shot.... 

4 minutes ago, Ehret said:

 

That's my fear... we already have the "Thunderspit" and if would get "Zerostang" next then... no, please, no!

 

Thunderspit?

[Ehret]

Just now, unreasonable said:

Thunderspit?

 

Yes - the Thunderspit - in the sim Thunderbolt with 30-60% flaps and WEP which can out-turn everything. When you increase flaps to 100% then it becomes a helicopter...

Edited January 21, 2019 by Ehret

[unreasonable]

Oh yes: people doing things that no sane WW2 pilot would ever do or dream of doing and then complaining that the results are not simulated correctly. I am not impressed. If the performance over the normal operational envelope is fairly well represented I am content with that.

[AndyJWest]

20 minutes ago, unreasonable said:

Yes it is: the problem though is that sometimes (I am really talking about Career mode here) the fights are very low to start with so there is little margin for error when you are diving on a target. The best solution is still to gain some height and come back at another angle: but sometimes I just cannot resist taking the shot.... 

 

Yup. I have the same problem sometimes. Lack of patience is never good.

[=WoVi=cercataa]

On 1/17/2019 at 8:47 PM, AndyJWest said:

The article cites two sources, neither of which uses the term 'energy retention':

 

I think it's just a matter of terminology, they use "drag", and thats loosing energy, the contrary of retaining it.

Sometimes you can read "drift", that is also some kind of drag.

[AndyJWest]

7 minutes ago, =SFF=_cercataa said:

 

I think it's just a matter of terminology, they use "drag", and thats loosing energy, the contrary of retaining it.

Sometimes you can read "drift", that is also some kind of drag.

 

Clearly it's a matter of terminology, since I'm asking what 'energy retention' is supposed to mean. As this thread clearly illustrates, there doesn't seem to be any sort of consensus here though. If one thread contributor equates it with rate of climb, and another says it is a synonym for drag, I think that rather than trying to arrive at a conclusion, we probably need to accept that there really isn't one. And stop using the phrase...

[unreasonable]

55 minutes ago, AndyJWest said:

 

Clearly it's a matter of terminology, since I'm asking what 'energy retention' is supposed to mean. As this thread clearly illustrates, there doesn't seem to be any sort of consensus here though. If one thread contributor equates it with rate of climb, and another says it is a synonym for drag, I think that rather than trying to arrive at a conclusion, we probably need to accept that there really isn't one. And stop using the phrase...

 

Perhaps we should come up with a list of forbidden terms - it seems to be all the rage nowadays.

 

I propose we add the term "arcade" to the prohibited list. It always starts fights.  Another good one would be "mineshell" which seems to send some people into a posting frenzy, especially if you voice any scepticism about it's magical powers.   

 

I am sure there are more simulation related words and phrases better left unsaid...

[JtD]

Energy retention is energy retention. You look at an aircrafts mechanical energy at time 1 (E1), and then again at time 2 (E2), and the difference is what can be labelled - given that in terms of armchair piloting is often used for situations where supposedly E1 > E2 - energy retention. The amount of energy you retain through a manoeuvre. The unit is of course J, because it's energy.

 

Feel free to try out Tacview to look at the energy charts. Make a quick 180° level turn and see how energy changes. Do the same thing in a number of aircraft and the retention term gets a meaning. Which by the way is how you easily measure it.

Edited January 21, 2019 by JtD

[AndyJWest]

If everyone could agree that 'energy retention' was whatever Tacview measures, we might be getting somewhere. Except that Tacview doesn't give any sort of general result. The answer you get depends on the manoeuvre you test. Enter a level turn at speed X, turn Y degrees at rate Z and measure the speed at the end of the turn. Calculate mechanical energy at the beginning and end of it - or get Tacview to do it for you. You will have a result. A result only valid for inputs X,Y and Z though. Change the parameters and the result will be different. So given that their doesn't seem to be any agreed test (and I can't see how a fair one could be arrived at, given the widely-differing best-performance parameters of different aircraft) this isn't a method for arriving at any general means to compare different aircraft with each other.

 

Real aircraft performance figures can be set out in tables. Like this:

Maximum speed: ~440 mph (383 kn, 708 km/h) at 25,000 ft (7,600 m)
Cruise speed: 362 mph (315 kn, 583 km/h)
Stall speed: 100 mph (87 kn, 160 km/h)
Range: 1,650 mi (1,434 nautical miles (2,656 kilometres)) with external tanks
Service ceiling: 41,900 ft (12,800 m)
Rate of climb: 3,200 ft/min (16.3 m/s)
Wing loading: 39 lb/sqft (192 kg/m²)
Power/mass: 0.18 hp/lb (300 W/kg)
Lift-to-drag ratio: 14.6
Recommended Mach limit 0.8

 

Adding 'Energy retention 500 Joules' or whatever to that would be ridiculous. It would be meaningless without specifying the test being carried out. And given that there is no consensus in this thread as to what 'energy retention' is, never mind how you measure it, I can't see us arriving at one.

 

'Energy retention' as some sort of measurable general characteristic isn't a property of aircraft. Change in energy state during specific manoeuvres clearly is. You can measure the latter. But you don't have to invent some entirely unnecessary property in order to describe it. And you can't state that aircraft X has more of it than aircraft Y, without describing very precisely the specific manoeuvre being carried out. And then the results are valid only for that test.

 

I asked in my first post what units 'energy retention' could be measured in. And asked how it could be measured. Neither question seems to have been answered in any consistent way. Instead we have a mess of contradictory definitions, and nothing approaching an agreed method to arrive at any sort of measurable and consistent value. Because it isn't 'a thing', it is a vague phrase thrown about on simmer forums.

 

 

 

 

 

[JtD]

11 minutes ago, AndyJWest said:

A result only valid for inputs X,Y and Z though. Change the parameters and the result will be different.

 

Exactly. Energy retention is aircraft and manoeuvre specific. You can make a generalisation, just like you can say "this aircraft is faster", "... climbs better", "... turns better", but as with those statements, a generalisation might not cover all conditions. That can hardly be surprising.

[HagarTheHorrible]

NOT WRITTEN BY ME;

 

Energy retention is currently very often missinterpreted.

 

The most blatent exemple is "Yak-3 energy retention is totally OP". Which is wrong and I'll explain why.

 

Actually, we are talking here of energy flux. Don't be afraid, I'll explain that.

 

Without taking into account the vertical of the plane (lift / gravity), we basically have 2 forces: thrust and drag.

Thrust is your energy production, drag is your energy dissipation.

 

Energy retention, in WT, is like I said "abused" in the way that we are actually talking about energy flux (production - dissipation).

Retaining energy well implies that you have a small dissipation. Back to Yak-3: if you cut the throttle and look how fast it slows down, you'll notice that aside from A6M, nothing slows down as fast as a Yak-3. Its energy retention is poor.

However, the plane has a great energy production. It can actually overcomes the poor energy retention, and even more, it is so good at producing energy (especially below 450kmh) that it is one of the best energy producer of the game.

Technically, energy retention should mostly refer to the capacity of a plane to retain its speed past top speed (aka when drag > thrust, hence the plane decelerates). Otherwise, we should refer to energy balance, but that is nipticking.

 

That is what is important to understand with "energy retention" as people say here: Heavy planes are great at zooming maneuvers, and extended maneuvers. You are heavy, you have a bad thrust/mass ratio, but you dissipates less in exchange. In a light plane, you produce a lot, you are excellent at "burst" maneuver, but extended operation at high speed is not always in your favor. When fighting a lighter plane (and if possible with a slower max speed than you), idealy you want to go past your max speed, in order to make the lighter plane bleed more energy than you. (both will bleed, but your goal is to bleed less than him)

 

Back to your Sabre - MiG matter:

 

Sabre engine is better at producing energy than a MiG engine, especially above 800kmh. That's why, in a turn, starting at 1000kmh, Sabre will end up with more speed and energy: even though the heavier Sabre bled speed (dissipation), the thrust (production) was enough to overcome the loss, at least to a greater extent than the MiG, On the other hand, if you start a turn at 800kmh, you will see than MiG is likely to finish the turn with more energy than the Sabre. What changed ? The energy production of both plane has switched to the favor of the MiG.

 

A clearer exemple: Sabre Max speed is 1107kmh at S.L. MiG-15 is 1075 kmh at S.L. If both dive at the same speed, and both ended up at 1111kmh at S.L, (A) Sabre will slow down at a slower rate than MiG-15 because 1) its top speed is higher 2) its mass is heavier; (B) In a zoom climb @ 10°, Sabre will be able to zoom up high faster and longer than a MiG-15. The more vertical you go, the more you give MiG an advantage, because you go for "burst" maneuver instead of a "sustained maneuver".

 

Sabre energy balance at high speed is "better" than MiG, and since jet are often fast, that is what makes people say that Sabre energy retention is better.

Well, like I said, Sabre E-rentetion is better, but actually what people mean here is Sabre energy balance is better, since energy retention only shows past max speed, which is not that often, even in a jet fight.

 

EDIT: and as you can see, MagZ is a happy follower of the "energy retention abuse", giving a lovely theory about E-retention during E-transformation whatsoever. Fact is E-flux is a confusing subject, and when you are let's say "clear" with what it represent, you can only laugh at people that give fancy name to suit their explanation / own understanding.

They are notsaying something fundamentaly wrong, but calling a lion a cat because both are feline is not totally correct either.

Edited February 8, 2016 by Rapitor

 

 

How to test a plane's energy retention(?)

MEC/Testing

Looking for a plausible way to find an indication of two planes' energy retention when I don't feel like playing matches but want to waste time. Came up with one test method which I thought seemed reasonable:

Find out a plane's top cruise speed (in TAS) at a fixed altitude, radiators closed, 100% throttle, fuel load etc.

Count how many seconds it would take for the plane to decelerate to max cruise speed when it starts at 200km/h TAS above it (all whilst maintaining the fixed altitude).

Repeat at every 1000m altitude.

E.g. The F6F-5 and Bf109F-4's top cruise speed at 3000m with 45mins fuel are roughly the same (the F-4 is a tiny bit faster). So I get both planes to 200km/h TAS above cruise speed at 3000m, and count how many seconds until the speed reduces to their respective cruise speeds. Prelim test runs show that although the F6F-5 max cruise speed is a tiny bit slower, it takes about a full minute longer than the Bf109F-4 to return to its max cruise speed.

EDIT: to me, the F6F-5 has indicated a slight lower cruise speed but better energy retention, i.e. if you pull out of a dive and fly level with a Bf109F-4 in equal pursuit, you would in theory pull away for a short time before the German plane starts slowly catching up once both planes return to max cruise speed.

I thought this method was pretty good for comparison even where if you look at a completely different plane like the A6M3, you can see it has both a combination of lower max cruise speed AND a faster speed/energy bleed when starting 200km/h TAS above it.

Any thoughts, suggestions for improvement, feedback, etc?

 

All plundered from WT.

 

Edited January 21, 2019 by HagarTheHorrible

[HagarTheHorrible]

This was interesing;

 

What-does-energy-retention

[6./ZG26_Klaus_Mann]

So, Question answered?