Asian Aerospace 2006 - Singapore

Salman
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Post by Salman »

JCage wrote:Huh? If anything it implies that speed remains high & hence impacts range given more friction at sea level needs to be overcome to maintain the speed & more of the onboard energy (ie fuel) is used up in this manner.
I do not believe that there is a microcontroller in the Brahmos that accelerates the burning of fuel to maintain the speed of Mach 2.5+ when it encounters reduction of speed. Please note that almost all ramjet missiles do not exceed speeds of Mach 1 or 1.2 at sea-level.

Anyway, ramjet engines are self-sustaining. They only have to be catapulted at a threashold speed. After that they should go on accelerating till they reach the speed of light....theoretically.

But Brahmos is restricted to Mach 2.5 +. I dont think that is done by a microcontroller, but rather its fuel gets over by the time it reaches Mach 2.9.
rakall
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Post by rakall »

Salman wrote:I do not believe that there is a microcontroller in the Brahmos that accelerates the burning of fuel to maintain the speed of Mach 2.5+ when it encounters reduction of speed. Please note that almost all ramjet missiles do not exceed speeds of Mach 1 or 1.2 at sea-level.
Could you please explain that?

AFAIK, they are not efficient at SL, but there is nothing that limits the SL speed of Ramjet... on the contrary the ram effect is most efficient ~M1.2. Thats why you have a rocket booster to sling it to that speed before ramjet takes over.

But the aerodynamics drag associated with lower alt is too high for Ramjets to be used for efficient or sustained flight (as in planes or RLV's) at SL. But i see no problem pushing it with brute force in a missile if the tactical scenario demands a Lo-Lo profile.

It is just that becoz of high drag your acceleration is lower (than if you were at higher alt), assuming you are burning fuel at same rate.. so you gain speed slower.. and hence gain distance slower.. so when you run out of fuel you have reached a shorter distance... but you still got a high speed. You travel only 120km, but you still got M2.5-2.9 on you.
Dileep
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Post by Dileep »

I do not believe that there is a microcontroller in the Brahmos that accelerates the burning of fuel to maintain the speed of Mach 2.5
Why not? You have this wonderful nav computer. Why can't you control fuel flow too?
Salman
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Post by Salman »

rakall wrote:It is just that becoz of high drag your acceleration is lower (than if you were at higher alt), assuming you are burning fuel at same rate.. so you gain speed slower.. and hence gain distance slower.. so when you run out of fuel you have reached a shorter distance... but you still got a high speed. You travel only 120km, but you still got M2.5-2.9 on you.
My point was that speed decreases=> distance covered decreases.

Extra fuel is spent in fighting the friction/drag/resistance but that doesnt mean speed is kept constant like the 2 volts battery keeps voltage constant across 1 ohm resistance or 10,000 ohm resistance....only in 12th standard Physics books and NOT reality.

Also, microcontroller is not likely to be used in controlling fuel-flow as Brahmos is a ramjet engine rather than in a car engine. Ramjets are left alone once they reach the threshold speed.
Austin
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Post by Austin »

well consider this

Sunburn : Flight speed: Mach 3(at high altitude), mach 2.35 at low altitude and Mach 2.5 at terminal stage

Shipwreck (grandfather of Brahmos ) : Speed: high altitude cruise: Mach 2.5, low altitude: Mach 1.5, Terminal flight: Mach 2.0

Both are Ramjet Missile
vina
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Post by vina »

Anyway, ramjet engines are self-sustaining. They only have to be catapulted at a threashold speed. After that they should go on accelerating till they reach the speed of light....theoretically.
That is why they need to be throttled and they are..
But Brahmos is restricted to Mach 2.5 +. I dont think that is done by a microcontroller, but rather its fuel gets over by the time it reaches Mach 2.9.
Sustaining Mach 3 is very tough..Aluminum is not a good enough material for this kind of speed, starts to lose strength becuase of aerothermal heating. For that, you need to move to Titanium (SR-71, Mig 25 examples here) and the cost shoots up exponentially... So my guess is it would be restricted to mach 2.5 becuase of materials reasons.

Once Brahmos reaches the targeted mach number, the thrust will be throttled back to be just in a sustaining mode..The full thrust of the engine and max fuel consumption is during the initial acceleration phase after the rocket booster jettisons and maybe during the final phase when it drops to seal level to sustain the top speed.
It must be noted that the range of the Brahmos in low-low profile is only 120 kms, which is less than half of its usual range of 290 kms (when launched in hi-lo profile).

This means that its speed is reduced when it cruises at just above sea-level, and implies drastic reduction in speed.
Ok. Go to the basic physics of this .. The total energy available to the missile after the rocket booster falls off, is the kinetic energy at this point, plus the energy value of the fuel it carries(with its associated conversion
efficiency into thrust).. Now since the resistance is exponentially higher at sea level, vs high altitude, for the given energy content in the fuel, the distance traveled at sea level will be far less than at altitude if the speed of the missle will be same. This is intuitive and is borne out by your observation on range.

However, you assume that the flight time at low altitude for 120km and at altitude for 290km is the same , maybe thinking that the fuel burn rate has to be constant irrespective of the altitude. That is not true. At low altitude, the engine can be throttled approriately to get max possible range (which mind you could be still less than that possible at altitude).

Anyway , check out Ramjet in Wikipedia .. (Gosh, this Wikipedia is so awesome, so convenient, next best thing to sliced bread internetwise)
Raman
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Post by Raman »

I wonder why people speculate (often incorrectly) when a simple Google
search can yield the answer
in 0.26 seconds
Given sufficient initial flight velocity, a ramjet will be self-sustaining. Indeed, unless the vehicle drag is extremely high, the engine/airframe combination will tend to accelerate to higher and higher flight speeds, substantially increasing the air intake temperature. As this could have a detrimental effect on the integrity of the engine and/or airframe, the fuel control system must reduce engine fuel flow to stabilize the flight Mach number and, thereby, air intake temperature to sensible levels.
Sumeet
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Post by Sumeet »

Admins,

Can we move discussion on brahmos/land attack mode to Indian missile tech thread. I will respond to the ongoing discussion there. People are already discussing air launched land attack missile there and i think thats the right place to discuss all this.
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