Can you guess a Fighter jets envelope?

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jessmo112

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Unread post17 Nov 2020, 02:08

This article today on warzone gave me an interesting thought.

https://www.thedrive.com/the-war-zone/3 ... first-time

You will notice how in the article that the U.S. demonstrated a augmented reality fight using a AI J-20.
My question is, is it possible to guage a planes characteristics by using available data.

For instance the Engine the J-20 uses is the one being used in the Su-27 family for years its a know quanity.


So if the Engine =y
And the aircrafts weights=z
Can we make a guess on drag and other parameters?
Can we guess basic flight data?
Even if the weight is off slightly you should be able to guess things like ITR. And sustained turn.
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sprstdlyscottsmn

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Unread post17 Nov 2020, 02:48

Anyone can guess. With the right background one can even make a good guess. I do this all the time.
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linkomart

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Unread post17 Nov 2020, 08:40

sprstdlyscottsmn wrote:Anyone can guess. With the right background one can even make a good guess. I do this all the time.


And some good tools help as well.
If you are interested on how to do it:
Daniel P Raymers: Aircraft conceptual design book works gives some guidelines.
John D Anderson: Introduction to flight gives some insights as well.
Dr Jan Roskam: all books are interesting, but be aware, they are a handful.
I have been recommended
Leland M Nicolai: Fundamentals of Aircraft and airship design but I have not studied it in detail.

my 5 cent.
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spad_s.xiii

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Unread post17 Nov 2020, 23:49

linkomart wrote:
sprstdlyscottsmn wrote:Anyone can guess. With the right background one can even make a good guess. I do this all the time.


And some good tools help as well.
If you are interested on how to do it:
Daniel P Raymers: Aircraft conceptual design book works gives some guidelines.
John D Anderson: Introduction to flight gives some insights as well.
Dr Jan Roskam: all books are interesting, but be aware, they are a handful.
I have been recommended
Leland M Nicolai: Fundamentals of Aircraft and airship design but I have not studied it in detail.

my 5 cent.

Depending who you are, but if you are a government, you can do a much better guess than you get from conceptual design. I did participate in a EU-project once, where we developed a software for conceptual design and the methods for aerodynamic calculations weren't too sofisticated, but fully functional for that purpose. You don't need too many pictures in different angles to make a resonably good 3D-model of an aircraft, then run it through a much more accurate CFD-software and get a better aerodynamic model.
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jessmo112

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Unread post18 Nov 2020, 00:22

So basically because the U.S. onows the Su-27 engine very well. They can do a very accurate simulation.
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mmm

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Unread post18 Nov 2020, 03:42

Until you guessed center of gravity wrong and everything has to be thrown out. :doh:
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linkomart

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Unread post18 Nov 2020, 08:18

spad_s.xiii wrote:Depending who you are, but if you are a government, you can do a much better guess than you get from conceptual design. I did participate in a EU-project once, where we developed a software for conceptual design and the methods for aerodynamic calculations weren't too sofisticated, but fully functional for that purpose. You don't need too many pictures in different angles to make a resonably good 3D-model of an aircraft, then run it through a much more accurate CFD-software and get a better aerodynamic model.


The software for conceptual design you describe runs the formulas described in the books I mentioned, and they give you a very accurate estimation of the performance of the aircrafts from a few key parameters.
If you can find good data of the engine then you have a very good model with a small error.

Then you can create a 3d model and run CFD on that.
There is just one risk with that, imho, that is that you run high fidelity analysis on a low fidelity data.
CFD is very easy today, and you can make huge batch calculations on a vast dataset. The problem with doing CFD on a reasonably cad model is that the fine tuning going in to the design is lost.

With the hand book methods the empirical data is used to see the performance that can be achieved from a properly fine tuned design.

my 5 cent.
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linkomart

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Unread post18 Nov 2020, 08:21

mmm wrote:Until you guessed center of gravity wrong and everything has to be thrown out. :doh:


The equations in conceptual design seldom takes cg in to account, it is assumed to be good. If the airplane fly, it usually is. So you don't need it to estimate the performance of a enemy aircraft.

But I agree, in the design process, you constantly need to have razor sharp focus on the cg.

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