I am a bit confused here. I found on wwikipedia that TtW ratio on MiG29 is 1.13, so as far as I know the plane should be able to fly straight up into the sky like a rocket. So why doesn`t it?

And to make matters more complicated, my own calculations predict that an empty plane should have TtW of 1.5! I used the data given to me on wikipedia, so I dont know what is wrong with my calculations. So any help would be very much apreciated.

Thrust to weight ratio doesn't take into account aerodynamic drag. No matter how aerodynamically efficient the airframe may be, it still needs to push all those little air molecules out of the way. Also, the higher up you climb, the thinner the air gets, producing (less) thrust, but the weight is still there!

that still doesn`t explain my miscaculation. By mine calculations an almost-emptly mig (300kg of fuel) could still fly straight up into the air, but it doesn`t.

That must be at peak performance .... and you get a specific peak performance at a specific speed, when the engine get enough air to "breath".

So if you want to go straight up don't start too slow, minimum is your corner velocity, as an indicator of the slowest speed at which your engine and cope with the highest G-load. And from there and faster the engine should be just fine. So 800km/h and more perhaps .....

But then the engines thrust gets less and less as altitude increases and you need to focus on accelerating and get more speed and get more and more into levell flight.

I usually test my theories by what I call the MAX-MIN cases .... I never think of the normal case. Sometimes both min and max cannot fall outside normal.

MIN case: Can you picture a jet engine functioning perfectly at sea-level..... yes you can.

MAX case: Can you picture a jet engine functioning perfectly half-way between the earth and the moon? ..... no cause there is no oxygene there ..... otherwise Lindberg or Yeager would have landed on the moon. I am not trying to be a wise ass here just trying to box in the problem ....

Is there a point in the atmosphere where the oxygene simply vanishes?

Is it possible instead, that the available oxygene diminshes slowly and gradually as altitude increases?

Could it be that engine thrust decreases faster than the earths gravity diminishes as distance/altitude from earth increases ... very probable ...

So at some altitude earth gravity will be stronger than the thrust from you engine. And I guess that you agree it definitely will be so near the the geostationary orbits cause there is no air there so the engine can not function.

So first .... at sea level .... pick up enough speed to give your engine air to breathe .... keep the speed .... more air .... be hungry ... pick up the nose and start climbing .... watch the IAS ..... and worry about providing your engine with air .... and as altitude increases you will have to fly more and more horizontally .... there is nothing else to do if you want to maintain IAS or the earth will pull you back down as your engine gets weaker ....

I bet you are using uninstalled engine thrust for your calculation. The very act of putting an engine into an airframe changes the thrust due to flow variation through intakes.

i am using the engine thrust provided on wikipedia.

quote:

Originally posted by gorkyporky:
i am using the engine thrust provided on wikipedia.

Which is the uninstalled engine thrust.