Jump to content

TWR Jet engines KER


Recommended Posts

I use a jet engine on my VAB and KER tells me my rocket has 3.12 TWR. Then i Launch, it starts gaining thrust, and i left go the arm, and my ship goes down! KER is showing 3+ TWR. Is it a mistake from KER or am I understanding something wrong here?

Spoiler

dU0cK0G.jpg

 

Edited by Agustin
Link to comment
Share on other sites

Takes a bit of time to jets 'get to speed'. Try to start the engines and afer a few secounds release the launch clamps (as in: use more than one to help with stability)

There's also the issue of how much air the intake can provide but I think is just the spool up time.

 

Link to comment
Share on other sites

30 minutes ago, Spricigo said:

There's also the issue of how much air the intake can provide

I believe intake air is binary.  The jet works fine if it has enough air, or it flames out and stops working out it does not.   So that should not be responsible for lower than expected (but nonzero) thrust.   Are you getting any flameout symptons?

Link to comment
Share on other sites

10 minutes ago, Aegolius13 said:

I believe intake air is binary.  The jet works fine if it has enough air, or it flames out and stops working out it does not.   So that should not be responsible for lower than expected (but nonzero) thrust.   Are you getting any flameout symptons?

I really don't know. But what I 'got' from the people explaining it is:

-jet engines only take air from one intake. One intake can feed multiple engines.

-without enough air jet flame out.

-how much air is enough for the jet is based on ¿stuff? 

-how much air an intake can produce is based on atmospheric pressure,  air speed and ¿things?

I can't really point a 'source'  and is not resulting of my own testings. Just assumptions, but good enough for my uses.  I let for people with better knowledge to answer if that is correct and fill the details.

 

Link to comment
Share on other sites

No, intake air is not binary. The thrust of an engine can be limited by the amount of intake air -- down to a bottom limit, where it flames out.

However, that large circular intake always delivers plenty at 0 speed.

I suspect that the KER calculation is using Max Thrust, though. Which happens at mach 1.5 or something for the wheesley.

 

Edited by bewing
Link to comment
Share on other sites

It's simply just not enough intake. Even a large circular intake cannot supply a Wheesley at stationary. For planes it works fine because you can still pick up speed, and intake immediately grab more air because you have a nonzero air speed, and that's a positive feedback that drives intake usage to 100%. However this one critically relies on an initial TWR>1 to lift off.

To bust previous theories:

During spooling up, KER will show TWR to be like 0.8/2.6, i.e. the first number will be smaller, which is not the case here.

In flight KER picks up realtime thrust/weight data, so it has nothing to do with theoretical max thrust or anything like that.

Link to comment
Share on other sites

This thread is quite old. Please consider starting a new thread rather than reviving this one.

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...