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Ja3k_Frost

Any tips or tricks for making hypersonic planes?

Question

Ja3k_Frost    2

Background:

A while back I remember a fun challenge I picked up that involved BD Armory and delivering a bomb to a target about a third of the way around Kerbin in the fastest possible time, it was fun and all but I really wanted to break a barrier I saw in Kerbin speed possibilities. I wanted Jeb to go faster, farther, and more efficiently, then any Kerbal before him and thats when I began looking up real world hypersonic craft and became really interested in this subject area.

What I have discovered already:

There doesn't seem to be a lot of info regarding people who are building craft meant to travel in excess of 1300 m/s and above 20 kilometers, most of this is due to where the stock Whiplash engines cut out around 1300 m/s and 20,000 m, you might as well just use rocket engines and insert yourself in orbit at that point anyway. To go above and beyond this I picked up the X43 Hyperblast Scramjet Engine from the wonderful MK2 expansion pack (aptly named after its real world vehicle). It's kinda hard to use as it wont start until you are close to 1250 m/s at 20,000 so the whiplash acts as a good stepping stone to using it on your vehicle. Also, while looking for a design to start from, the real world X43 fills exactly what im trying to. A successful knockoff of its design produced a craft capable of breaking 2000 m/s at 33,000 meters in game. I fully realize that once you start getting into using modded engines, tweakscale and other mods that asking about game mechanics regarding them becomes magnitudes more difficult. So im just curious about general design, and if anyone else has tried to tackle this or something similar before

Actual Question:

Are there any tips/tricks or for building vehicles that travel in atmosphere at speeds between 13-2000 m/s? Why is the real world X43 designed the way it is; flat front vs pointy, smaller control surfaces vs larger, and flat topped body vs circular fuselage?

Also would it be helpful to add a pic of the craft I already have so it can be critiqued, etc?

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fourfa    795

You might be interested in this thread, particularly towards the end:

In which people play with how to stay at the ultimate top speed of the RAPIER (~1751m/s) for circumnavigation racing.  Lots of thermal problems to navigate.  Loads of creative designs.

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FancyMouse    362
Posted (edited)

I've used it once, and my conclusion is X43 isn't well suited for Kerbin operation. Kerbin's orbital velocity is so low, you even need to push the nose down in order to get air for the engine, and it's not uncommon that you can push your apoapsis to hundreds of km by X43 alone. For Kerbin surface operations, you might as well just go to orbit and in vacuum you need zero fuel to move around, saving the trouble of diving to gain speed (the trajectory with X43 is similar to how a low TWR spaceplane breaks sound barrier, except it's now diving from 20km to about 15km breaking ~4.5 mach "barrier"). I would imagine if you're using some modded planet, which is huge, whose atmosphere has oxygen (like Earth), then X43 might be super useful.

Edited by FancyMouse

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bewing    1273
1 hour ago, Ja3k_Frost said:

and flat topped body vs circular fuselage?

It's called a supersonic lifting body.

In real world aerodynamics, below the speed of sound, a well-designed wing shape is rounded on the top (from front to back), and basically flat (or maybe a little concave) on the bottom.

When you go supersonic, however, this gets reversed. Best lift with lowest drag means flat on the top, and curved on the bottom. Best to google it, because there's a lot of info.

Stock KSP does not model aerodynamics in this amount of detail. I don't even think FAR does. You can model the hypersonic scramjet engine, but that's the only part that can be moderately accururate in KSP.

The reason the X43 has little control surfaces is that it is not meant to steer. It is meant to go in a dead straight line for testing purposes. The control surfaces are just for micro adjustments to keep it straight.

As FancyMouse said -- scramjets can make a big difference on a large planet with an escape velocity in the 7km/s range -- but on Kerbin, once you light a scramjet, you're basically on your way to the Mun anyway.

 

 

 

 

 

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Wanderfound    1198

High speed atmospheric flight in KSP is primarily about drag reduction (minimise radially-attached junk, use wing incidence to minimise fuselage drag, neither too little nor too much wing) and heat resistance (a fuel tank between the nose and the cockpit helps a lot with this).

A demonstrator that can hold 1,600m/s+ long enough to circumnavigate Kerbin:

 

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Urses    536
Posted (edited)

@bewing

If i understand your information right the best way to fly a scramjet in realistic atmosphere is to build a normal supersonic plane, go for the targeted hight light the scramjet and flip the plane upsidedown for best aerodynamiks?

Funny Kabooms 

Urses 

Edited by Urses

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Spricigo    431
7 hours ago, Urses said:

@bewing

If i understand your information right the best way to fly a scramjet in realistic atmosphere is to build a normal supersonic plane, go for the targeted hight light the scramjet and flip the plane upsidedown for best aerodynamiks?

Funny Kabooms 

Urses 

more like normal subsonic, at supersonic speed turn upsidedwon, reduce wing incidence and sweep wings backwards, at hypersonic speed drop almost all wings .

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Urses    536
2 hours ago, Spricigo said:

more like normal subsonic, at supersonic speed turn upsidedwon, reduce wing incidence and sweep wings backwards, at hypersonic speed drop almost all wings .

Yes sweep wings would be real nice. One addition would be a rotation able Cockpit and you have a Beast of a plane... what we will need to build something like this at KSP...

Maybe something like KSP3+:D

Urses 

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