Variation of thrust with speed

[Paulo]

Hi

The basics, Page 2.2

states that if speed was the only factor, thrust would increase as speed, specifically Mach number, increases.

It is is also mentioned in the following paragraphs to do with momentum drag, and it states that momentum drag increases slightly but steadily above M0.4

Can some please help, I think my problem I have is related to mis-understanding of a previous chapter in POF

regards Paulo

[colin]

Hi Paulo
As you say you have misunderstood the notes! Read them again and you will find its says " thrust on low by pass engines reduces initially because of intake momentum drag and then (the thrust) increases slightly but steadily above M0.4 with improved mass flow."

Colin

[Paulo]

Hi Colin

I have found an explanation in a subject Ive not read yet (following the BGS program of study) in the AGK engines section, "factors effecting thrust"

have I missed something more fundamental else where?

many thanks Paulo

[colin]

No, they both say the same thing.
As speed increases there is an interaction between the air entering the engine and the air by passing the intake, it's called intake momentum drag and it initially causes a loss of thrust. Around 300kts, M0.4, where the air becomes compressed the ram effect of the air entering the engine overcomes the intake momentum drag and the thrust level recovers.

Colin

[Paulo]

cheers Colin

Its good to be on track

thanks again Paulo