The new aerodynamics and fuel consumption of jet engines at various altitudes

[Gnullbegg]

Hi!

Sorry if this has been asked before but I did a search and couldn't find anything recent enough. With the new aerodynamics I am back trying to build an efficient long-range turbojet plane. I know fuel consumption varies with throttle (duh), altitude, speed and intake air. Generally you want turbojets to fly at higher altitudes than basic jets. This much hasn't changed with the new model I believe. But I found this this old thread on the forums and if you look at the set of graphs the user tavert posted on page 2, I was wondering if these are still reasonably accurate?

Also any other/new bit of information on this would be appreciated!

[n0xiety]

Those graphs doesn't look right at all. They show rapier giving less thrust at high speeds than turbojet which is not the case in 1.02 . Currently as i see it the most efficient engine is the rapier at altitude passing 25k and speed over 1500m/s. Allready managed to build a long range lightplane that completed 6 kerbin circumnavigations without any refueling or droptanks. Im guessing with droptanks it could even make 10 circumnavigations. Rapier only shines in efficiency when you pass 25k altitude tho. Before that yes it will use alot more than turbojet. My design currently uses 0.09 fuel/s while going 1500m/s at 27500m altitude. The fuel consumption drops rapidly as the fuel gets consumed. While i was using my last bits of fuel the consumption dropped to 0.04 at 28500m altitude still going 1500m/s. Don't know if there is a thrust curve graph for 1.02 but it seems to me that the rapier is the new best engine right now. Turborams are only good for picking up speed at low altitude enough to pass supersonic range where rapier struggles if your plane is too heavy.

Edited June 12, 2015 by n0xiety

[Gnullbegg]

I'm guessing you're using only 1 engine, a relatively low amount of fuel and loads of intakes? I just did a few quick tests of my current bi-coupler design switching the turbos with rapiers and it starts to either disintegrate at 16-18km or have flame-outs around 25-26km. This may be my flying ofc. Though I am probably carrying way too much fuel anyway. Current mass is ~22 tons.

Edited June 12, 2015 by Gnullbegg

[n0xiety]

Yes my lightweight plane only has 1 engine and about %75 of the fuel is in the wings. Using 2 shockcone and engine cooler. Now let me teach you a trick. You are probably wondering why shockcone right? Well shockcone has alot less drag than ram intake and has a bit more mass which means it overheats harder. Ram intakes high drag doesn't worth using for the extra %10 air gain. Now to the second trick. This trick is called Rapierspike. You place a shockcone behind the rapier and clip it untill you can't see the white part of the shockcone. Do not clip more it needs a really delecate balance. What this will do is to give you stability, reduced tail drag and a bit more air + it looks frikin cool. Try it and you will notice the performance difference.

Just so its clear while using 2 shockcones i actually only have one looking at the airflow. The other one is used for the rapierspike.

Edited June 12, 2015 by n0xiety