Best hyper-sonic nose cone?

[ajburges]

I finally got Rapiers in my career game so I'm now playing with SSTO designs flying level past Mach 5. A new problem emerged due to this: any nose with a heat tolerance less than 2300 K will fail during the speed run! This eliminates both the Adv. Nose Cones and Tail Connectors as nose pieces. A quick (and moderately good looking) workaround was to conically shield the Tail Connector with a Small Nose Cone Stack (Radially attached stack of Small Nose Cones and Mk0 tanks).

Modeling experiments off of Luch Kot's videos I compared my workaround against bot a Shock Cone Intake and a NCS adapter on mass controlled SRBs (0 mass difference). It was slightly worse (a couple rocket lengths) than the other two which were tied.

Does anyone know of a less draggy hyper-sonic nose cone (1.25 m) than the Shock Cone or NCS + Small Nose Cone? I know from a previous experiment that the Ramp Intake is higher drag. I guess a fairing might work, but I don't like the thought of abusing the fairing as a nose cone.

[bewing]

Well, you may want to rethink a little bit. The main question is whether you want the nose to be built to manage heat, or to decrease drag. Your plane is already going mach 5 -- so if you make it your aim to decrease drag, you may actually manage to increase your top speed by 1.5 or 2 whole m/s. But (especially if you eliminate fairings out-of-hand) you already have tested your only real choices.

If, instead, you decide to say to yourself, "my plane already goes fast enough, now I want to keep the nose from melting." That takes you on an entirely different path. You can try the antenna trick. Or, you can go the opposite direction from trying to reduce drag, and go with a blunt nose -- to take advantage of the detached shockwave phenomenon.

So, to provide a completely stupid answer to your nosecone question: maybe try the small science container. Lightweight, unbelievable temp resistance, useful, size 0 for a small front profile, and blunt.

 

 

Edited January 30, 2017 by bewing

[Jarin]

Shock Cone and a couple others I can't recall are currently tied for least draggy mk1 endcap. It can still have heat issues, but only at the edge of the hypersonic flight envelope. What atmospheric performance are you looking to reach?

Edited January 30, 2017 by Jarin

[Wanderfound]

See above; if you don't want to get cheaty with heatshields and fairings, the shock cone or NCS is the best option at 1.25m.

Why the 1.25m, though? The Mk2 parts have higher heat tolerances, and although they're draggy if you use them wrong, they can be very slick if you build right.

 

 

The key is to set your wing incidence such that the fuselage holds a 0° AoA at cruising speed.

 

Edited January 30, 2017 by Wanderfound

[fourfa]

I don't see why the fairing is abuse.  I like to use it to cover a relay antenna - kinda looks like a radar dish does on real planes.  And it's high heat, low drag, and flexible to a few different form factors for aesthetics.

In fact I've been playing with circumnavigation challenge planes lately, and the easiest way to survive 40+ minutes of 1751.2m/s (ultimate top speed of RAPIER before flameout) is to just stuff the entire plane (aside from wings and engine) inside a fairing.  

Edited January 31, 2017 by fourfa
typo

[AeroGav]

3 hours ago, ajburges said:

A quick (and moderately good looking) workaround was to conically shield the Tail Connector with a Small Nose Cone Stack (Radially attached stack of Small Nose Cones and Mk0 tanks).

Er what?  If I'm reading that correctly, you're surrounding the tail connector with a stack of mk0 fuselages to protect it, thereby getting the drag of multiple mk 0 stacks as well as the nose cone for your mk1 core stack?

My preferred solution is the small nose cone + ncs adapter combination.   These are both 2400k parts and good enough unless perhaps you want to re-enter on Eve.  They hold a bit of fuel and the drag increase over the advanced nose cone is negligible,  especially considering the vehicle as a whole.  Swap small nose cone for fly by wire hub if  you want to increase separation distance of bow wave from the cockpit, but it's a bit heavier.   

The next step up is the procedural fairing, but that has significantly higher drag than advanced nose cone or even the basic aerodynamic nose cone.   

Also, what altitude are you conducting the speed run at?

The Rapier's thrust declines more slowly than drag up to 22km, so the best altitude for top speed in level flight is 22km, provided you have enough wing area to hold level flight with the nose less than 5 degrees above prograde (if the wings are angled, and have built in incidence, then your body AoA should be even lower).     Conducting the speedrun at lower altitudes than this increases thermal stress.

Bear in mind too, that if you're getting mach 5 airbreathing, you're already doing well. 

By mach 5.5 the engine isn't producing any more thrust than it is at mach 1 - and a design optimised for delta v/payload fraction won't have any more engine than absolutely necessary in order to pass mach 1.  So realistically mach 5.5 is about as good as it gets .  By mach 6, thrust is at zero.

Heat can be more of an issue on interplanetary spaceplanes using NERV power to get to orbit rather than rapiers in oxidizer mode, because the nerv burn from mach 5 to orbit lasts about 4 minutes rather than 45 seconds.    If I'm overheating here however, i think it's best to add more wing area, than go to draggy 2600k procedural fairings.   More wing area means you'll gain altitude faster once you pitch up out of the speed run, so things won't be so hot, and with plenty of wing area you can do that while still keeping the angle of attack at a low drag value like 5 degrees or less.  Also the big S wings and strakes hold plenty of LF for your NERVs, and flying higher also has the advantage of lowering drag from the fuselage , which you won't get if you instead go the "more heat tolerant" approach.

Again, if you're in a rapier only ship just punch it and go.

Edited January 30, 2017 by AeroGav

[GoSlash27]

A little food for thought:

 

@Jarin is using a clever combination of radiators and shrouds to stay alive. You should pick his brain.

Best,
-Slashy

[Jarin]

4 hours ago, GoSlash27 said:

@Jarin is using a clever combination abomination of radiators and shrouds to stay alive

ftfy

[ajburges]

23 hours ago, Wanderfound said:

See above; if you don't want to get cheaty with heatshields and fairings, the shock cone or NCS is the best option at 1.25m.

Why the 1.25m, though? The Mk2 parts have higher heat tolerances, and although they're draggy if you use them wrong, they can be very slick if you build right.

The design that started me on this investigation was a Mk3 Lifter. Termination to 1.25 m was obvious (fuel adapters), The 1.25 m termination was not obvious because of the greater variety of choices. At the Mk3 scale, 80 units of liquid fuel is less impressive sounding because it is only 1% or less of fuel.

Currently I have nothing but hate for the Mk2 parts. Their drag and low wet mass puts them at too much of a disadvantage against Mk1 stacks. Mk3 just makes for a more flexible cargo ship once you get Rapiers. The best results I've gotten in pursuit of a Mk2 lifter is longer than my Mk3 lifter because I've limited it to one stack. That ship uses a Shock Cone to feed a pair of Rapiers.

 

21 hours ago, AeroGav said:

Er what?  If I'm reading that correctly, you're surrounding the tail connector with a stack of mk0 fuselages to protect it, thereby getting the drag of multiple mk 0 stacks as well as the nose cone for your mk1 core stack?

Tail connector with a single size 0 stack clipped on the end as a fat aerospike. 2 Mk0 tanks make for an elegant transition and a nose cone to fill the end node. It does add an additional stack, but the minimal drag from the tail cone almost completely offsets the penalty. Experimental observations were that there was more side drift between the Shock Cone and NCS than lagging of the mentioned nose. So it's not the best, but it is pretty good (and is more aesthetically pleasing than the NCS on the 2.5 m adapter tank).

 

21 hours ago, AeroGav said:

Also, what altitude are you conducting the speed run at?

The Rapier's thrust declines more slowly than drag up to 22km, so the best altitude for top speed in level flight is 22km, provided you have enough wing area to hold level flight with the nose less than 5 degrees above prograde (if the wings are angled, and have built in incidence, then your body AoA should be even lower).     Conducting the speedrun at lower altitudes than this increases thermal stress.

Altitude is somewhere between 18 and 21 km. I likely don't have enough wing (2 pairs of big-s + 1 pair big-s "tail" @ 4 degrees I believe) but I have trouble slapping on more wing in a style I like.

The beast is probably overpowered; it uses 8 Rapiers because 6 Rapiers was insufficient for take-off. It always wound up in the water after 1 km. Its cargo bay can only hold 1.5 orange tanks and has over 600 m/s after circurlarization. I could probably extend the cargo bay, but anything I make longer than 5 Mk3 segments tends to be too large for a cargo bay regardless. I will likely use the air frame for a fuel tanker by replacing the cargo bay with 1-2 4 segment tank and a short bay for the 2 reaction wheels, EC, and probe core.

I have yet to actually configure a stick to play, so I still fly using the keyboard. This leads to difficulty adding fine input and I find I have the most success doing the speed run at whatever altitude the craft can maintain while following prograde. It will rise some during the speed run so I use occasional inversions to create negative lift avoid entering a yo-yo. At the end (when horizontal speed gain stalls out), I allow the increasing lift and pitch at the end to feed into the zoom when I enter closed cycle mode. If I find myself in a (shallow) dive, I engage flaps for more lift/pitch and ride it out. Such a dive can take me below 18 km, but tends to feed into a better horizontal angle for the zoom which helps the closed cycle burn.

 

11 hours ago, GoSlash27 said:

A little food for thought:

 

@Jarin is using a clever combination of radiators and shrouds to stay alive. You should pick his brain.

Best,
-Slashy

I must admit, I never thought of using aerodynamically shielded radiators to manage heat; I thought shielding prevented radiators from working.

I think I'll pass though; seeing physics cry in the corner makes me feel bad. I don't plan on going fast enough to need measures that extreme. I imagine milking air breathing for that long just wastes fuel and mass budget for an SSTO.

[Jarin]

48 minutes ago, ajburges said:

I think I'll pass though; seeing physics cry in the corner makes me feel bad.

There's a reason I call it an abomination.

I typically just use the "heat spike" of sticking a collapsed whip antenna on the nose. Functional, and looks realistic. Granted, that's just for Mk1/2. Mk3s are already snowplowing through the air, so those just get more engines to kill drag.

Edited January 31, 2017 by Jarin

[AeroGav]

19 minutes ago, ajburges said:

I have yet to actually configure a stick to play, so I still fly using the keyboard. This leads to difficulty adding fine input and I find I have the most success doing the speed run at whatever altitude the craft can maintain while following prograde. It will rise some during the speed run so I use occasional inversions to create negative lift avoid entering a yo-yo. At the end (when horizontal speed gain stalls out), I allow the increasing lift and pitch at the end to feed into the zoom when I enter closed cycle mode. If I find myself in a (shallow) dive, I engage flaps for more lift/pitch and ride it out. Such a dive can take me below 18 km, but tends to feed into a better horizontal angle for the zoom which helps the closed cycle burn.

Yeah fair enough - at these really high speeds a tiny deviation leads to a gain or loss of several km,  and getting into up/down oscillations (phugoids, i think they are called) is pretty much a given when you're on air breathing engines whose thrust constantly changes and tends to feed back into the cycle.

I have tried using the analog bit of an xbox 360 controller and this 10 year old usb saitek joystick ,  but even with sensitivity tweaked down as far as it will go, you can only control pitch to within 3 degrees of what is intended which is far too coarse for what we need, and my wrists start to ache within a minute or two - holding that all the way to orbit would not be fun.

I could go out an buy a top of the line flight sim stick and hope to get enough accuracy but if the problem is the game's joystick calibration sw then i'd just be wasting my money.

So, I basically have two ways of doing it -

1) in airplanes where the wings are angled up to make lift even when the fuselage is pointing at prograde, i just set SAS to follow prograde and allow the up/down oscillations to do their thing.    Example here -

2) With non-angled wings,  I turn SAS off,  and control pitch by making adjustments to pitch trim.  Requires positive pitch stability and that you've tuned out thrust induced torque by either keeping engines in line with centre of thrust of by adjusting them to point up/down slightly.    Also made easier if  you've designed the craft in such a way as to not have changes in CG as the fuel burns off.

 

[foamyesque]

On 2017-01-30 at 1:26 AM, AeroGav said:

The Rapier's thrust declines more slowly than drag up to 22km, so the best altitude for top speed in level flight is 22km, provided you have enough wing area to hold level flight with the nose less than 5 degrees above prograde (if the wings are angled, and have built in incidence, then your body AoA should be even lower).

You're neglecting the effect of the airspeed decline relative to Mach as you climb. The absolute top speed for RAPIER craft is achieved in the low atmosphere (although that is, admittedly, not particularly useful for flight to orbit).

On 2017-01-30 at 11:28 PM, ajburges said:

Tail connector with a single size 0 stack clipped on the end as a fat aerospike. 2 Mk0 tanks make for an elegant transition and a nose cone to fill the end node. It does add an additional stack, but the minimal drag from the tail cone almost completely offsets the penalty. Experimental observations were that there was more side drift between the Shock Cone and NCS than lagging of the mentioned nose. So it's not the best, but it is pretty good (and is more aesthetically pleasing than the NCS on the 2.5 m adapter tank).

Hey, I do that, too! I don't bother with the fuel tanks, though; I just attach one small nosecone as a tailcone radially to the tailcone I'm using as a nosecone, then attach another small nosecone as a nosecone to the small nosecone I'm using as a tailcone that's attached to the tailcone I'm using as a nosecone.

It provides a nice niche to hide RCS thrusters in, or to hook canards to, and by building from the back forwards you make the thermal transfer from the nose into more explodey parts take longer, hopefully getting you out of the peak thermal regions before you thermally soak and doom your Kerbs :v

[Raideur Ng]

The best nosecone I've encountered is a 1.25m fairing tapered as slim as possible. It has high heat resistance and can be very aerodynamic.

2600K Max Heat vs Shock Cone 2400k  as seen below.

[Jarin]

22 hours ago, foamyesque said:

You're neglecting the effect of the airspeed decline relative to Mach as you climb. The absolute top speed for RAPIER craft is achieved in the low atmosphere (although that is, admittedly, not particularly useful for flight to orbit).

While interesting, I've yet to see a craft that can actually reach rapier top-speed below 20km altitude. I'd love to see a functioning example, though.

22 hours ago, foamyesque said:

Hey, I do that, too! I don't bother with the fuel tanks, though; I just attach one small nosecone as a tailcone radially to the tailcone I'm using as a nosecone, then attach another small nosecone as a nosecone to the small nosecone I'm using as a tailcone that's attached to the tailcone I'm using as a nosecone.

 

... ow

[foamyesque]

1 hour ago, Jarin said:

While interesting, I've yet to see a craft that can actually reach rapier top-speed below 20km altitude. I'd love to see a functioning example, though.

 

If you look through the challenges forum, you can see examples; I've had trouble managing a craft that can sustain it (the RAPIERs themselves become a limiting factor, at only 2000K) but it's possible to get well north of 1800m/s if you're on the deck.

EDIT:

In fact, in the fastest aircraft challenge thread that you participated in, someone produced a design that was cruising at 2km/s+ at about 2km up IIRC. They had a heatshield for a nosecone and I believe clipping abuse to jam enough RAPIERs in behind it to make it happen :v

Edited February 3, 2017 by foamyesque

[Jarin]

1 hour ago, foamyesque said:

In fact, in the fastest aircraft challenge thread that you participated in, someone produced a design that was cruising at 2km/s+ at about 2km up IIRC. They had a heatshield for a nosecone and I believe clipping abuse to jam enough RAPIERs in behind it to make it happen :v

Huh, I somehow missed that. That just makes my findings with the thrust curves even weirder. The engines were cutting out at slower speeds as you drop below 20k, but I couldn't manage to reach the cutoff below 19. 

[Raideur Ng]

1.25m fairing will not explode due to Rapier thrust acceleration. You'd have to expose it to intense, re-entry speeds head on to cause a failure. The fairings are just that good.

[foamyesque]

3 hours ago, Jarin said:

Huh, I somehow missed that. That just makes my findings with the thrust curves even weirder. The engines were cutting out at slower speeds as you drop below 20k, but I couldn't manage to reach the cutoff below 19. 

Well, for example -- and I admit I abused clipping to stick ballast and my controls inside a fuel tank, but then again I also drained it of oxidizer, so I don't feel too bad -- I made this:

The problem on this design is keeping the wings from overheating. It'll break 1800m/s at lower altitudes -- I've had it up to 1837m/s--, but if it does then all the wings start exploding on me.