ED新消息——DCS：P-51D

F风

Our lead flight model programmer has put together a few developer note articles that discuss some of the more interesting features of both the real and the virtual DCS P-51D. We will be releasing these over the course of the the next couple of weeks.

The first and probably most lengthy article overviews some of the principles behind the Manifold Pressure Indicator in the cockpit.

Enjoy!


Quote:
Manifold Pressure

Given that the Manifold Pressure (MP) indicator will quickly become one of the primary cockpit instruments used when flying the Mustang, a discussion of some of the principles behind its indication is worthwhile. Before we begin, remember that manifold pressure is measured in inches of Mercury (in.Hg).

First, let’s review the general airflow through the induction system of the P-51D Merlin engine, equipped with a carburetor and a two-stage, two-speed supercharger. Initially air is ingested through the air intake(s) (of a couple of possible types, which we’ll discuss in another note) and flows past a throttle valve that controls airflow volume into the carburetor. Here, fuel is added to create a fuel-air mixture of a specific ratio. The mixture is then passed through the supercharger, where it is highly compressed, becoming significantly hotter in the process. To prevent the compressed and very hot mixture from causing detonation, as well as to allow more of it to be “packed” into the cylinders, it is cooled twice – by the intercooler between the first and second supercharger stages and by the aftercooler just prior to entering the manifold. Finally, the mixture is passed into the manifold for induction into the cylinders. The manifold itself is a very strong structure surrounded by about 8 mm of aluminium alloy – a necessity given that pressures attained here may be as high as two atmospheres.

Cooling of the fuel-air mixture is performed by the aftercooling system, which is completely separate from the engine cooling system and circulates as much as 36 gallons of coolant per minute under peak performance conditions. The radiator of the aftercooling system is installed as a single unit with the engine coolant radiator in the aft section of the air scoop underneath the fuselage, although they are functionally independent from each other. To protect the manifold from backfires, it is equipped with flame traps - essentially metal filters designed to prevent flames from expanding throughout the entire manifold.

If we get rid of everything, except the throttle valve, carburetor and the manifold, we are left with a conventional, naturally aspirated engine. Let’s consider what happens with pressure in the manifold as we open and close the throttle valve while maintaining a constant engine speed (RPM). With the throttle completely open, air flows freely and manifold pressure equals ambient atmospheric pressure. As the throttle valve is closed, the cylinder pistons begin to “suck” air through a limited opening, creating a partial vacuum in the manifold and a corresponding drop in manifold pressure.

Similarly, when the throttle valve is partly open while engine RPM is increased, manifold pressure drops, because with increased RPM the cylinder pistons must “suck” more air into the manifold through the same narrow throttle opening. The same effect can be witnessed when bumping the throttle up from idle power. Initially the RPM are kept down by low engine power output, but as power output increases when the throttle is moved forward, an initial boost in manifold pressure takes a dip as RPM begin to catch up.

Let’s now return everything we removed earlier and take another look at how RPM affect manifold pressure. Pressure increase (boost) levels in the supercharger have a very non-linear relationship with engine RPM. Thus, under relatively low RPM (60-75%) and throttle settings, typically manifold pressure will drop as RPM is increased, similarly to the situation described above. Under high RPM settings, however, supercharger boost levels significantly outweigh the pressure drop immediately past the throttle valve, resulting in increased manifold pressure.

In the Merlin engine, things are even more interesting, thanks to an automatic manifold pressure regulator installed to help ease the pilot’s workload. For any given throttle setting, manifold pressure can change dramatically as flight conditions change (in particular as air density changes with altitude). The automatic regulator tries to maintain the manifold pressure set by the pilot's throttle lever, minimizing any additional throttle “jockeying” required to hold this setting in flight. The automatic regulator does not work throughout the entire performance envelope of the engine. In the V-1650-7 model engine featured in DCS Mustang, it begins to function at 40 in.Hg. Below this value, manifold pressure is controlled exclusively using the throttle handle and all of the effects described above can be witnessed. At 40 inches and up, however, the throttle handle sets the desired pressure value and the automatic regulator attempts to maintain it by adjusting the throttle valve opening as necessary.

Operation of the automatic regulator consists of the following primary elements. An aneroid sensor coupled to a piston valve moves vertically in reaction to pressure changes, closing and opening vent lines leading to a relay piston. The relay piston moves horizontally in response to pressure differentials created by the aneroid piston valve to maintain equal pressure to either side inside a cylinder. As the relay piston moves forward or back, it opens or closes the throttle valve until pressure equilibrium is re-established, returning the aneroid piston valve to a neutral position and stabilizing the relay piston in place, which may be forward or back from its original position. The relay piston is connected to the throttle valve via a differential linkage system with the throttle handle in the cockpit. Within the operating range of the automatic regulator, the sum movements of the throttle handle and the relay piston determine the actual position of the throttle valve at any given time.

Let’s consider an example. We’ll assume the engine is driven to 3,000 RPM on the ground and the throttle is advanced fully forward. Under these conditions, the supercharger is capable of producing much higher pressure in the manifold than the maximum permissible pressure of 61 in.Hg. The regulator’s purpose is to limit pressure to 61 inches and maintain it there as long as the throttle handle is in the full forward position. As soon as engine RPM reaches levels at which pressure climbs above 61 inches, the aneroid becomes unbalanced, shifting the relay piston to close the throttle valve. The regulator operates in the same fashion throughout the manifold pressure range of 40 – 61 in.Hg.

In practical terms, what this means is that the pilot uses the throttle handle to set his desired manifold pressure and the regulator operates the relay piston to open or close the throttle valve to maintain this setting. As altitude increases and air density decreases, resulting in lower pressure, the regulator opens the throttle valve to maintain manifold pressure. Conversely, as altitude decreases and air density increases, the regulator closes the throttle to maintain manifold pressure.

In the above example of 61 inches of MP, when critical altitude for maintaining this pressure is reached, the relay piston and the throttle handle are both fully advanced, and the throttle valve is fully open. When manifold pressure is set substantially lower than maximum, for example the Maximum Continuous setting of 46 inches at 2,700 RPM, the regulator will attempt to maintain pressure as altitude increases, but will eventually hit the fully open position of the relay piston, even though the throttle valve is only partly open, because the throttle handle in the cockpit is not fully advanced. In this case, it will become necessary to move the throttle handle up to further open the throttle valve in order to maintain manifold pressure, because the automatic regulator will have no further authority due to having reached the relay piston’s limit of range of motion. As critical altitude for this pressure setting is reached, the throttle handle will have to be all the way forward to maintain it. Here, we have to remember that the supercharger is a two-speed system and switches into high blower mode somewhere around 19,000 feet. When this happens, manifold pressure increases dramatically and the throttle handle has to be moved back, otherwise resulting in a climb at 61 in.Hg at 2,700 RPM. Not deadly, especially using quality gasoline, but not recommended, either.

As you may have deduced, 61 inches at 3,000 RPM is full Military, or Takeoff power, nominally limited to 15 minutes. Let’s take a brief look at War Emergency Power (WEP) mode, nominally limited to 5 minutes of operation. WEP can be mechanically implemented in a number of ways. The first option is to artificially lower the pressure acting on the aneroid by opening an escape line, resulting in an opening of the throttle valve by the regulator so as to “maintain” pressure - while in fact boosting it beyond the value set by the throttle handle. This method was used on early Mustangs, which featured a special control handle in the cockpit to engage WEP. Another option is to design the throttle linkage assembly such that the relay piston is in the fully closed position when the throttle handle is set to full military power. The pilot would then push the throttle handle past this setting into the WEP position, further opening the throttle valve and the relay piston would be unable to act upon it to close it. And the final option is to design the linkage system such that the throttle handle position past full military power would produce manifold pressure up to 67 or even 75 in.Hg.

Given the limitations of most HOTAS controllers used by virtual pilots, DCS Mustang will model the first method. This allows us to avoid having to rely on throttle detents or limit their range of movement in the pre-WEP range. As such, we will have a dedicated input command to engage WEP as a simulation of a cockpit control handle.  
http://forums.eagle.ru/showthread.php?t=87065

Black-Angel

貌似讲p51真飞机的东西，看不懂技术性问题，也没兴趣，不如去看p51真飞机手册。

Regulus

看上去不错，ms还模拟了军推和紧急推力的可用时间

黄震楠

对ED已经失去信心，它的东西不再关注

heoly

google下

F风

歧管压力

考虑到多方面的压力(MP)指标将会很快就成为主要座舱飞行时使用的测量仪器的野马,讨论的一些原则背后的指示是值得的。在我们开始之前,记住歧管压力是以英寸的汞in.Hg)。

首先,让我们回顾一下一般气流通过感应系统的P-51D梅林发动机,配备了化油器和一个两阶段,双速增压器。最初的空气通过空气吸入摄入(s)(一群可能类型,我们将讨论在另一张便条)和流过一个节流阀控制空气流量进入化油器。在这里,燃料添加到燃气混合创造一个特定的比率。然后通过混合增压器,在那里它是高度压缩,成为明显的热的过程。为了防止压缩和非常热的混合物引起爆炸,并让更多的“包装”进缸,它是由冷器冷却两次——在第一、二次增压器和aftercooler阶段进入之前在静听着的松林之间。最后,通过混合相对应的感应到汽缸。相对应的本身是一个非常大的建筑,周围环绕着约8毫米的铝合金-必要性假设压力达到这里可能会高达两大气压。

燃气混合的冷却系统进行aftercooling,是完全独立于发动机冷却系统和循环高达每分钟36加仑的冷却液在山峰性能的条件。散热器的aftercooling系统作为一个单位安装引擎冷却剂散热器)在船尾的部分机身下方空气铲子,虽然他们都是功能独立于彼此。从保护歧管事与愿违,它装备火焰陷阱——本质上金属过滤器旨在防止火焰扩展在整个在静听着的松林之间。

如果我们摆脱一切,除了节流阀、化油器和相对应的,我们就与常规,自然吸气发动机。让我们考虑一下发生了什么和压力歧管内我们开启和关闭节流阀同时保持发动机的恒定转速(RPM)。完全开放的油门,空气自由流动和多方面的压力等于周围的大气压力。当节流阀是关闭的,缸活塞开始“吸”空气通过有限的开通,创造一个局部真空歧管内和相应的掉在多方面的压力。

同样的,当节流阀部分开放而引擎转速提高,多方面的压力下降,因为增加气缸活塞转速必须“吸”更多的空气进入流形通过狭小的油门开放。同样的效果可能会遭遇冲撞着油门从闲置的力量。最初是压低转速发动机输出功率低,但作为输出功率增加油的前移,一个初始的提高歧管压力以作为转速下降开始迎头赶上。

让我们现在还早,一切去再看看转速影响多方面的压力。压力升高(刺激)水平在增压器有一个非常复杂的非线性关系,引擎转速。因此,在相对较低的转速(60 - 75%)和油门的设置,通常是多方面的压力会减少每分钟转速增加,类似于上面所描述的情况。在高转速设置,然而,增压器提高水平显著大于压降立即过去节气门开度,因而在增加多方面的压力。

在梅林引擎,事情更有趣,多亏了自动调节阀安装多方面的压力,以帮助缓解飞行员的工作量。对于任意给定的油门设置、歧管压力能够改变飞行条件显著变化(尤其是这样空气密度变化随海拔高度)。自动调节阀试图保持歧管压力所定的飞行员的油门杆、减少任何额外的油门须持有“阴”这个设置逃跑。自动调节阀不工作,整个性能的发动机。信封在V - 1650 - 7发动机模型的特色在DCS野马,它开始在40 in.Hg功能。低于此值,无数的压力控制油门手柄,专门使用上述所有的影响可以看到的一幕。在40英寸,然而,油门手柄集所需的压力值和自动调节阀试图维护它通过调整节流阀打开是必要的。

操作的自动调节阀由以下主要元素。一个双刻度传感器耦合到一个活塞阀门垂直移动反应压力变化、关闭和开启排气线导致继电器活塞。火炬接力活塞运动水平在回应压差由双刻度活塞阀门保持两边相等的压力在钢瓶。当活塞运动前进或回传递,它会打开或关闭节流阀直到压平衡重建,回复,双刻度活塞阀门,一个中立的位置,和稳定传递活塞的地方,可以从前进或回原来的位置。火炬接力活塞连接到节流阀通过微分联动系统与油门手柄在驾驶舱。经营范围内自动调节阀,增资额动作的油门手柄,继电器活塞决定实际的位置的节流阀在任何特定时间。

让我们考虑一下,一个例子。我们将承担发动机驱动至3000每分钟转速在地上和先进的全油的前进。在这种情况下,增压器能生产高得多的压力比最大允许歧管压力为61 in.Hg。监管机构的目的是为了限制61英寸的压力和维护那里只要油门手柄位于完全的前沿阵地。当引擎转速达到层级的压力超过61英寸爬,双刻度变得不平衡,将传递活塞关闭节流阀。调节阀运行在相同的时尚在多方面的压力范围的40 - 61 in.Hg。

实际上,这意味着飞行员使用节流阀把手可使他渴望的多方面的压力和调节器操作继电器活塞在节气门开启或关闭维护这个设置。作为高度增加,空气密度降低,导致较低的压力时,调节阀打开节流阀保持多方面的压力。相反地,海拔高度增加而降低空气密度,调节阀关闭油门保持多方面的压力。

在上面的例子中61英寸的MP,当临界高度,维护这个压力时,火炬接力活塞和油门手柄都充分发达,节流阀门处于开启状态。当歧管压力设置显著低于最大值,例如最大持续设置46英寸2700转/分,监管机构将试图保持高度的压力增加,但将会达到全开的位置继电活塞,即使节流阀仅是部分开放,因为油门手柄在驾驶舱不能充分先进。在这种情况下,它将成为必要将油门手柄向上进一步打开节流阀以维持多方面的压力,因为自动调节阀将没有进一步的权威由于有达到传递活塞的运动的范围的限制。重要的高度,这压力设定值时,油门手柄将所有前进的道路来维护它。在这里,我们必须记住增压器双速鼓风机系统和开关模式高19000英尺左右。当这一切发生的时候,多方面的压力显著增加和油门手柄要搬回来,否则导致61 in.Hg爬在2700转/分钟。不致命,特别是采用优质汽油,但不鼓励,也。

就如你所推断的,61英寸3000每分钟转速的全部军事,起飞和力量,名义上局限于15分钟。让我们简要地看一看战争应急电源(WEP)模式,名义上限于5分钟之内的运作。WEP可以透过机械执行在一些方面。第一个方法是人工降低压力作用于双刻度线开一个逃脱,造成一个打开节流阀的调节器,“保养”的压力,但事实上它超过设定的值增加的油门手柄。该方法应用于早期的野马,其特色是一个特殊的控制手柄在驾驶舱进行WEP。另一种选择是设计节流连杆总成,继电器活塞处于完全关闭位置时将满油门手柄军事力量。飞行员将把油门处理过这安置进入WEP地位,进一步打开节流阀和火炬接力活塞将无法按照它要把它关闭。和最后的选择是设计的联动机制,例如油门手柄位置过去成就的军事力量的多方面的压力将会产生67甚至75 in.Hg。

大多数的限制下使用操纵杆控制虚拟飞行员、DCS野马来塑造的第一个方法。这让我们避免过度依赖油门制动器实现静电接地或限制他们的活动范围在pre-WEP范围。这样,我们将有一个专门从事输入命令的WEP模拟座舱操纵手柄。

F风

自动翻译和蛋疼，不过要速度只能这样了

Regulus

坑爹的gg翻译。。。

305L7

虽然看不懂外文，但是机器翻译得更蛋疼

F风

305L7 发表于 2012-4-17 11:24
虽然看不懂外文，但是机器翻译得更蛋疼

去过巴黎的人还不懂外文........卖萌啊

foxwxl

机翻党自重……- -

F风

foxwxl 发表于 2012-4-17 12:36
机翻党自重……- -

有人说我发这种帖子没中文，木办法啊

xiaominhua

在dcs系列中，不太适应二战类机型，感到很另类。

Regulus

新图一张

qq562317994

还是喜欢喷气机