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YST對航空基礎面的誤解和他的面子之15 - 對Tu-95的補充
2007/01/25 11:08:53瀏覽1213|回應0|推薦3

我在之10當中對於YST不知道在哪裡找的的Tu-95的最高速度的數字,提供了比較完整的比較供各位參考,他對於蘇聯在研發渦輪噴射轟炸機之後又回頭生產一架螺旋槳的興趣很高,只是很遺憾的有些概念與史時不符合。我這邊以其他網路上的資料作一點簡單的整理。

原文請參考:YST 對航空專家的最後幾句話


但是,不論是SEAL還是mustang都不能對YST提出的兩個例子,野馬戰鬥機和熊式轟炸機,提出任何的反駁。說了一大堆,都是不相干的話。我不知道是誰為了面子而避重就輕。

YST幾次提到Tu-95使用螺旋槳的事情,而我也提出一些資料來向各位說明蘇聯當初受限於渦輪噴射發動機的效率,無法達到預計的航程,而蘇聯需要這些轟炸機對赴美國本土,這是在洲際彈道飛彈還沒有開始取代轟炸機的年代,而蘇聯的空中加油技術起步又較慢(目前大家熟悉的兩種空中加油技術,飛錨和飛衍,前者是英國技術美國資金,後者是純美國技術和資金),所以圖波列夫才會否定繼續用純噴射發動機,以滿足航程的需求。在技術上看起來像是走回頭路,不過在之前的M-4設計已經是讓蘇聯高層非常的不高興,加上M-4體積大航程還是遠遠不足,要是再不滿足,難保不會出現逆向工程研發Tu-4時期的狀況:做不到要被槍斃。

為了讓各位有一些參考資料能夠比較我的解釋,首先,我引用FAS網站上的說明,在研發的部分有這樣一段解釋:

Development of the TU-95 intercontinental bomber began in the early 1950s after series production of the medium-range TU-4 started.. Initially, several designs were considered, including a modification of the TU-4 and production of a new aircraft with piston engines. Prototypes of these aircraft were developed and tested from 1949 through 1951, it was concluded that bombers with piston engines could not provide adequate performance for the intercontinental attack mission. In March 1951 development of the T-4 intercontinental jet bomber began. However, KB Tupolev did not support the development of a bomber with turbojet engines, believing that the proposed AM-3 jet engines would not provide for the required range of more than 10,000 km. As an alternative, KB Tupolev proposed an aircraft with four turbo-prop engines that would provide a range of more than 13,000 km and speeds of more than 800 km/h at altitudes of 10,000 meters. The aircraft-design was designated as "95".

我就不翻譯這一段,只將有關航程需求的描述加粗,各位可以自行參考,有需要解釋的請提出來。

同樣在FAS這個網頁當中有列出多個Tu-95的飛行數字,其中並沒有YST所使用的超過1000公里/時的證據,而是和我所提到的數字接近,因此比B-52還快之說是否存在,各位也可以自行判斷。

此外,在一個俄國的網頁中的討論裡面,也有提到Tu-95的螺旋槳的相對氣流速度:

The Tu-95 propellers  reach transonic speeds (in the order of M1.05) when it
flies at its maximum speed (M0.83) and when it flies at max. cruising speed
above 11 000 metres (36 000 ft). The rest of the time they are subsonic
despite their large diameter (5.6m , 18ft 4in). This is due to their very low
constant rotational speed, which is around 800 rpm( "plus/minus one mile") 8:}D
This can be observed in all Tu-95 in-flight pictures. In most of them even the
de-icing boots can be clearly seen. In static conditions the tips reach about
M0.74.

Those tips are in fact supersonic airfoils (1952/3 vintage. Remember this
aircraft was shown in public for the first time in 1955), very thin and with a
sharply diminishing chord that reduces to zero at the apex.

請各位看一下我所加粗的部分,他說這個螺旋槳葉片是超音速翼剖面,也就是說這種翼剖面和二戰時期螺旋槳使用的大不相同,因此將Tu-95使用螺旋槳的事情和螺旋槳本身,尤其是在二戰時期的狀況畫上等號其實並不恰當。

同一個網頁,另外一位發表的文字當中對於Tu-95的噪音和一般螺旋槳的現象提出說明:

I have spoken with several F-15, F-16 and F-106 pilots who have
intercepted Bears.  They all said that they could clearly hear the noise
of the Tu's props over the sound of their own engine(s), even with their
helmets on.  Thomas' comments about the tip speed are all valid;
however, he apparently missed the fact that the propeller blade itself
need not be travelling at supersonic speed in order to generate shock
waves.  When the tip velocity approaches high subsonic Mach numbers, the
local velocity over the blades becomes supersonic, and shockwaves are
generated.
  Even supersonic airfoils have this characteristic behavior. 
The exact Mach number at which shockwaves will appear is dependent on
airfoil and angle-of-attack.

YST以為臨界馬赫數是我發明的,其實那只是用來說明高速飛行下物體表面氣流會先到達音速的現象,也就是上文中的Local Velocity所指出的地方。

總結來說,Tu-95回頭去使用螺旋槳是因為距離的需求,當俄國繼續發展下去的時候我們可以看到螺旋槳並未出現在後續的機種上,而這些新機種都是可以超音速的。

其次,Tu-95飛行速度很高,但是也沒有超過音速,同時也比B-52要慢。

第三需要注意的地方是Tu-95採用的螺旋槳設計是二戰時期完全沒有的,而同軸反轉的設計也是我提到多次,可以繼續維持螺旋槳在效率巔峰下工作的一個設計方式,只是不見得每個設計師都願意採用,而且,能夠拿掉螺旋槳這個阻力也不小的機構,何樂而不為?

從這些資料整合起來,加上二戰末期已經有4000匹馬力的活塞發動機服役,要說活塞發動機出力不夠而影響螺旋槳的使用,和實際上的情況是有不小的差距。

如果各位有需要對其中某個部分加以解釋,敬請提出指教。謝謝。

( 知識學習科學百科 )
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