Aerospike producing too much drag?

[BabaYaga]

I've been experimenting with spaceplanes for the last few days as I'd unlocked the hypersonic tech in science mode. I had managed to get a spaceplane to LKO before but couldn't get it efficient enough to be usefull. Now I'd made a similar version using the ramjet and aerospike instead of the terrier and panther, and lo and behold: it was horrible. Could not even get upto mach 2. With some debugging and  using the aerodynamic forces overlay I found out that the aerospike engines where creating an absolutely devastating amount of drag at the speed of sound. Same exact plane can go mach 5+ and get into lko by just replacing them with terrier engines, but the low thrust meant that it does cost most of my fuel. Looking online the aerospikes are loved by most people for SSTO use, so I am not sure what I am doing wrong. What do you guys think? Thanks in advance!

[miklkit]

Is the aerospike engine centered in its mounting?  They can get offset which causes drag.   Also, a shroud can be installed on it to greatly reduce drag.  Take a small nosecone, rotate it 180 degrees, and then install it behind the aerospike.  Then move it forward until it is almost invisible. 

[Xheotris]

Miklkit's answer is a good one. Part clipping, a.k.a. using the move tool to slide one part into another, is frowned on by some, but it's necessary for some designs for realism. If that's annoying, you can always install FAR's aerodynamics mod, which gives a much more realistic simulation of drag.
 

 

[Lt_Duckweed]

The aerospike is a fairly aerodynamic engine when node attached, and shouldn't be creating large amounts of drag.  Are you sure it's actually node attached and not surface attached?  Hold alt while placing the aerospike to disable surface attachment.

[miklkit]

The devs are ok with using that nosecone trick to reduce drag as when it is done to the aerospike and nerv engines they get a shroud over them.

[BabaYaga]

It was surface attached, and node attaching it did in fact fix it! I did not know you could force node attach it like that haha. Kinda weird, I think this is the only type of engine that requires this. I did take special care in getting it perfectly centered but I guess the game doesn't care. Thanks for the suggestions!

[Streetwind]

19 hours ago, miklkit said:

Is the aerospike engine centered in its mounting?  They can get offset which causes drag.   Also, a shroud can be installed on it to greatly reduce drag.  Take a small nosecone, rotate it 180 degrees, and then install it behind the aerospike.  Then move it forward until it is almost invisible. 

Is this a trick limited to a select few engines, or is it supposed to work with all engines?

I was doing a silly thing on a lark where I was trying to get something into orbit with nuclear engines alone for propulsion, which is obviously tricky given that the LV-N alone without any fuel or other parts has something like 0.5 TWR at sea level. I got pretty far but felt like I had drag issues, so I tried the nosecone trick. Didn't work on the LV-N. Or rather, it might have worked if I could have flown, but I couldn't, because the nosecone blocked all thrust even when clipped deep into the nozzle.

Have you ever tried it with a LV-N?

[Lt_Duckweed]

4 hours ago, Streetwind said:

Is this a trick limited to a select few engines, or is it supposed to work with all engines?

I was doing a silly thing on a lark where I was trying to get something into orbit with nuclear engines alone for propulsion, which is obviously tricky given that the LV-N alone without any fuel or other parts has something like 0.5 TWR at sea level. I got pretty far but felt like I had drag issues, so I tried the nosecone trick. Didn't work on the LV-N. Or rather, it might have worked if I could have flown, but I couldn't, because the nosecone blocked all thrust even when clipped deep into the nozzle.

Have you ever tried it with a LV-N?

It works with the LVN, it sounds like you didn't offset far enough.  I use this trick on most of my spaceplanes (though it should be noted that this effect is not as large for the nerv as it is for some engines, like the rapier (rapier has an extremely blunt end so has high backface drag)

[swjr-swis]

6 hours ago, Streetwind said:

because the nosecone blocked all thrust even when clipped deep into the nozzle.

Make sure you offset the nosecone forward past the bottleneck of the nozzle. The Nerv is one of the few engines that checks exhaust blocking from inside its nozzle.

21 hours ago, Lt_Duckweed said:

Are you sure it's actually node attached and not surface attached?  Hold alt while placing the aerospike to disable surface attachment.

Quoting for relevance.

[miklkit]

As others have stated it works for all engines I have tried it on.  I have not tried the Whiplash or other rocket engines like the Wolfhound.  So far only the aerospike and nerv get shrouds.  Here is a look at nerv and Rapier engines with nose cones in them.  You can see the nose cone in the Rapiers but not the nerv.  Also, use the tiniest nose cone in the nerv and a larger one in the rapier.

Edited February 8, 2023 by miklkit
addition

[jimmymcgoochie]

Useful tip: hold Alt while placing a part to force it to node attach only, this ensures your parts don't just surface attach to whatever's under the cursor at the time.

[miklkit]

That is a tip that I did not know about until this thread.  The difference in a properly place piece and a badly placed part. is dramatic.  In this spaceplane the outer two rapiers were badly placed but looked good.  The difference in drag is dramatic.