飛行最美--輕航機世界

認識空速表,來看這張圖很清楚的可以知道空速表的運作概念,這個空速表對於我們在飛輕航機的時候可是最重要的參考指標ㄋ,不論是起飛滾行時帶桿時機的參考,或是大玻度轉彎時加油門的依據,最重要是落地時最常的參考儀表之一,(參考圖)當沖壓空氣(ram air)進入了導引管(pilot tube)再進入了膈膜片,進而帶動了各項機構槓桿推動指針,原理很簡單,但是他所指示出的意義就有分很多種了,我來依序的介紹空速表的說明種類,細分有下列四種 (IAS), (CAS), (EAS), (TAS). 所謂(IAS)就是Indicated Airspeed.就是指示空速,是未經過儀器修正或是系統校準的空速,此外(CAS) Calibrated Airspeed (校準過後的空速),換言之它是利用飛機在移動時透過速度及空氣密度，再經由對IAS作儀器方面所發生的錯誤數據進行校正。(EAS)Equivalent Airspeed 這是透過校準皮託管內部的儲存空壓後的數據,簡單的說在海平面的時候CAS與EAS應該理論上是相同的,當空氣速度與壓力高度增加時,CAS數據就會變得比較高,假設在剛起飛(海平面)CAS指示100浬,EAS也是100浬..但是當高度飛到10000FT的時候CAS指示100浬,但是真實的EAS可能只有80浬了,最後一項(TAS) True Airspeed,很簡單的說就是對溫度跟高度(所謂的大氣壓力)做修正後的數據,種種而論這些空速意義種類對於我們有什麼幫助呢?就拿實際的例子來說當在30000FT的時候看著空速表只有250海浬的指示空速,但是在參考一下馬赫表ㄌ?哇賽 地速已經飆到400多海浬了,根據柏努力定律靜壓+動壓1/2ρV平方==總壓 (ρ=空氣密度)計算大略可以推斷出當你飛機高度在5000FT的時候 IAS是100浬(實際要+8%)TAS就變成了108浬…10000ft的時候IAS100浬 TAS很可能就變成了117浬這是大略估算,…話說回來輕航機平常並沒有飛的這麼高所以大部分都可以參考GPS的地速,就可以相呼應的比較數據,在高空的時候隨時注意GPS地速避免你參考IAS造成飛機超速的窘境.但是如果在夏天非常高溫的氣候之下,或是飛到海拔高度較高的機場,起飛滾行加速的時候就要小心了,因為你習慣參考IAS的空速來帶桿,那數據可就有差別了,因為空氣密度變低氣溫變高,相對的螺旋槳的效率也會降低,你有可能會使用到更長的跑道才能讓飛機離地起飛,此時你若再參考未經過修正的IAS空速數據會讓你太早帶桿,造成飛機未達起飛條件,卻帶著仰角在滾行加速,那是阻力而不是助力,輕航機推力原本就比較小,建議大家在夏季氣溫高的時候可以順便參考一下GPS的地速來決定起飛帶桿的時機~~

Types of Airspeed

Just as there are several types of altitude, there are multiple types of airspeed: Indicated Airspeed (IAS), Calibrated Airspeed (CAS), Equivalent Airspeed (EAS), and True Airspeed (TAS).Indicated Airspeed (IAS) IAS is shown on the dial of the instrument, uncorrected for instrument or system errors.

Calibrated Airspeed (CAS)

CAS is the speed at which the aircraft is moving through the air, which is found by correcting IAS for instrument and position errors. The POH/AFM has a chart or graph to correct IAS for these errors and provide the correct CAS for the various fl ap and landing gear confi gurations.

Equivalent Airspeed (EAS)

EAS is CAS corrected for compression of the air inside the pitot tube. EAS is the same as CAS in standard atmosphere at sea level. As the airspeed and pressure altitude increase,the CAS becomes higher than it should be, and a correction for compression must be subtracted from the CAS.

True Airspeed (TAS)

TAS is CAS corrected for nonstandard pressure and temperature. TAS and CAS are the same in standard atmosphere at sea level. Under nonstandard conditions, TAS is found by applying a correction for pressure altitude and temperature to the CAS. Some aircraft are equipped with true ASIs that have a temperature-compensated aneroid bellows inside the instrument case. This bellows modifi es the movement of the rocking shaft inside the instrument case so the pointer shows the actual TAS.