Consider the following about Ramjet and Scramjet:
1. Ramjet engine works efficiently at hypersonic speeds while Scramjets at subsonic speeds.
2. Scramjet engine can produce thrust at zero velocity while a ramjet cannot.
3. The efficiency of Ramjet engines starts increasing with the increase in speed.

How many of the above statements is/are correct?
(a) Only one
(b) Only two
(c) All three
(d) None of the above

Question

Consider the following about Ramjet and Scramjet:
1. Ramjet engine works efficiently at hypersonic speeds while Scramjets at subsonic speeds.
2. Scramjet engine can produce thrust at zero velocity while a ramjet cannot.
3. The efficiency of Ramjet engines starts increasing with the increase in speed.

How many of the above statements is/are correct?
(a) Only one
(b) Only two
(c) All three
(d) None of the above

ONLiNE UPSC · Accepted Answer

Statement 1 is not correct: Ramjets are efficient at supersonic speeds (Mach 2&ndash;6) but become inefficient at hypersonic speeds (Mach 6+).
Scramjets are designed specifically for hypersonic speeds (Mach 6+), not subsonic speeds.
Scramjets do not work at subsonic speeds because they require supersonic airflow for combustion.

Statement 2 is not correct: Both ramjets and scramjets rely on high-speed airflow to compress incoming air. Neither can produce thrust at zero velocity because they require forward motion to compress incoming air before combustion. They need an initial boost (e.g., rocket or another propulsion system) to reach operating speeds.

Statement 3 is not correct: Ramjet efficiency peaks around Mach 3-4. As the speed increases beyond Mach 5-6, the efficiency drops due to excessive heating and increasing drag. This is why scramjets are preferred for hypersonic speeds instead of ramjets.

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M Question 1	⏱ 0
Consider the following about Ramjet and Scramjet: 1. Ramjet engine works efficiently at hypersonic speeds while Scramjets at subsonic speeds. 2. Scramjet engine can produce thrust at zero velocity while a ramjet cannot. 3. The efficiency of Ramjet engines starts increasing with the increase in speed. How many of the above statements is/are correct? (a) Only one (b) Only two (c) All three (d) None of the above