SSTO engines

[Val]

I recreated Slashy's craft as best as I could, with the wings mounted with no incidence.

To me, the line of the wing surface intersecting the crew compartments, is exactly the same as on Slashy's. So in my opinion: No, the wings don't appear to be angled on Slashy's craft.

[Geschosskopf]

This is carrying way more cargo to LKO than a single RAPIER would normally do. wing Cl/ mass is a little under 1/2 on this one.

Nice design. I'm going to steal it .

I'm kinda surprised you got this to work with just 1 engine and the shuttle wings. I was really excited when the shuttle wings appeared--lots of lift for fewer wing parts, plus they can hold fuel. But after using them a lot, I fell out of love with them. Their airfoil cross-section makes it hard to attach landing gear under them, but more to the point, they're thick and blunt. Thus, seem to produce more drag than a flat panel wing with the same lift rating. I had great difficulty getting low-powered SSTOs to orbit with them so eventually stopped using them and went back to flat panels.

However, I do agree with your basic point about wing loadings, and have used it myself many times. The more TWR you have, the less wing area you need and vice versa. But there is a definite limit to what you can do with wing area as a substitute for TWR. More wing means more drag, so eventually it will overpower whatever thrust you have. Also, the low acceleration caused by low thrust and higher drag means the engine must run for a longer time to reach any given speed, so you end up needing more fuel.

The result, it seems to me, is that a low-thrust, big-wing design only really works for SSTOs about the size you show here. If they're any smaller, you have a higher TWR so don't need the extra wing. If they're much bigger, the factors noted above will eventually keep it from reaching orbit.

[Starhawk]

I recreated Slashy's craft as best as I could, with the wings mounted with no incidence.

http://i.imgur.com/31Dkxkn.png

To me, the line of the wing surface intersecting the crew compartments, is exactly the same as on Slashy's. So in my opinion: No, the wings don't appear to be angled on Slashy's craft.

You are right. It's the fatness of the wet wings that threw me off. Sorry 'bout that.

Happy landings!

[GoSlash27]

All,

Val is correct about the benefit of adding incidence and also correct that the design I've shown here doesn't employ it.

Geschosskopf is talking about the same thing I am; when dealing with low t/w, it's important to *not* jump to the conclusion that reducing wing area (or incidence) will help.

Adding wing area or incidence can actually reduce drag.

Here's a bigger one incorporating 3° incidence to further reduce drag:

Best,

-Slashy

Edited August 30, 2015 by GoSlash27

[Val]

...

Geschosskopf is talking about the same thing I am; when dealing with low t/w, it's important to *not* jump to the conclusion that reducing wing area (or incidence) will help.

Adding wing area or incidence can actually reduce drag.

Best,

-Slashy

Ah. Now I get what you are saying. You are of course right.

[Geschosskopf]

Here's a bigger one incorporating 3° incidence to further reduce drag

You reminded me why I hate low-TWR spaceplanes. They take FOREVER to get to space . I built a copy of yours here and needed like 20 minutes for it to work.

[Stoney3K]

Also keep in mind that the RAPIER does not have an alternator while the jets do. It's kind of embarassing to see your spacecraft go dark right in the middle of a climb.

[panzer1b]

All,

Val is correct about the benefit of adding incidence and also correct that the design I've shown here doesn't employ it.

Geschosskopf is talking about the same thing I am; when dealing with low t/w, it's important to *not* jump to the conclusion that reducing wing area (or incidence) will help.

Adding wing area or incidence can actually reduce drag.

Here's a bigger one incorporating 3° incidence to further reduce drag:

http://i52.photobucket.com/albums/g13/GoSlash27/CamachoII_zpsxstt1iyy.jpg

Best,

-Slashy

For whatever reason MK2 parts seem to create excessive drag, in the case of all my new SSTLs, they use between 3-5 degrees AOI, which helps ALOT when you have no bloody MK2 fuselage drag to worry about.

My latest working craft uses this concept, although its buggy (and gets 5.4K dV in LKO with weapons and RCS gear stripped out).

Im not going to pretent this is without any abuse (i did clip alot of fuel inside the cargo bay, no drag and well, it has like 3000 fuel inside total (its ~27 tons on takeoff), single nuclear-rapier drive, which has worked very well for me sofar.

[GoSlash27]

For whatever reason MK2 parts seem to create excessive drag, in the case of all my new SSTLs, they use between 3-5 degrees AOI, which helps ALOT when you have no bloody MK2 fuselage drag to worry about.

My latest working craft uses this concept, although its buggy (and gets 5.4K dV in LKO with weapons and RCS gear stripped out).

http://i.imgur.com/YL0naaa.png

Im not going to pretent this is without any abuse (i did clip alot of fuel inside the cargo bay, no drag and well, it has like 3000 fuel inside total (its ~27 tons on takeoff), single nuclear-rapier drive, which has worked very well for me sofar.

Technical stuff aside, that picture!

- - - Updated - - -

You reminded me why I hate low-TWR spaceplanes. They take FOREVER to get to space . I built a copy of yours here and needed like 20 minutes for it to work.

True, but it *did* work.

The point is that if you have a low t/w you shouldn't look to reducing wing area or incidence to help reduce drag. You should look to go the other way.

My most efficient designs at the moment work at higher t/w, but the original question was about low t/w spaceplanes.

Best,

-Slashy

[Stoney3K]

With low TWR planes, it does look like the induced drag from wing lift when compared to the fuselage drag is out of balance. The fuselages may be too draggy, meaning a massive wing with some camber could get you into orbit in a snap.

I built two test planes with the Mk2 fuselage, with a high AoA (5+ degrees) I had a really hard time fighting drag above Mach 2, meaning I was just wasting fuel. But when I cambered the wing by that amount, so I could keep a nose-forward attitude while climbing at 10 degrees, smooth sailing. Saved me about 200m/s of delta-V on the same plane design.

[Val]

With low TWR planes, it does look like the induced drag from wing lift when compared to the fuselage drag is out of balance. The fuselages may be too draggy, meaning a massive wing with some camber could get you into orbit in a snap.

I built two test planes with the Mk2 fuselage, with a high AoA (5+ degrees) I had a really hard time fighting drag above Mach 2, meaning I was just wasting fuel. But when I cambered the wing by that amount, so I could keep a nose-forward attitude while climbing at 10 degrees, smooth sailing. Saved me about 200m/s of delta-V on the same plane design.

According to my tests, a wing area to mass ratio between 1/5 (1 Lift Rating per 5 t) and 1/10 is optimal with 5 degrees AoI. (With low TWR you need a lower ratio, or you won't get off the runway with enough speed to avoid splashing into the sea)

Here's a ~1/6 ratio design that takes off at 64.9 t, with just 2 Rapiers.

Album + Craft file

[GoSlash27]

According to my tests, a wing area to mass ratio between 1/5 (1 Lift Rating per 5 t) and 1/10 is optimal with 5 degrees AoI. (With low TWR you need a lower ratio, or you won't get off the runway with enough speed to avoid splashing into the sea)

Here's a ~1/6 ratio design that takes off at 64.9 t, with just 2 Rapiers.

http://i.imgur.com/Iv7Iq6j.png

Album + Craft file

That's good stuff!

-Slashy

[Geschosskopf]

True, but it *did* work.

By the hardest.

The main problem I had with it (other than it just taking forever) was the severe adverse roll caused by the high-mounted rudder. Any slight tap of rudder caused significant opposite roll, really skewing the plane to the airstream and causing mucho drag. I recommend replacing the tail winglet with a fixed vertical fin for stability and mounting small rudders on the tips of the wing trailing edge, where they're on the centerline and far enough laterally from the CoM to still have good effect even if they're close fore-and-aft.

[Starhawk]

I recommend replacing the tail winglet with a fixed vertical fin for stability

AFAIK, Slashy always disables control action for the rudder, so it's just a static vertical stabilizer.

Happy landings!

[GoSlash27]

AFAIK, Slashy always disables control action for the rudder, so it's just a static vertical stabilizer.

Happy landings!

^ What Starhawk said. Mine actually has the fin locked.

Best,

-Slashy

[Geschosskopf]

^ What Starhawk said. Mine actually has the fin locked.

I figured you were going to say that, but then what do you use for yaw control? I find the Mk2 probe core alone has insufficient torque on that axis, at least when making landings.

[GoSlash27]

I figured you were going to say that, but then what do you use for yaw control? I find the Mk2 probe core alone has insufficient torque on that axis, at least when making landings.

Nothing. Most planes have sufficient yaw stability to obviate the need for active yaw control. Just bank it and the tail will keep it in line.

Best,

-Slashy

[panzer1b]

I figured you were going to say that, but then what do you use for yaw control? I find the Mk2 probe core alone has insufficient torque on that axis, at least when making landings.

Most of my SSTLs rely on roll+elevator, and the rudder is usually just for stability (although in cases where its near the center and doesnt induce too much yaw ill leave it enabled for yaw only, not roll since roll and rudder is annoying to no end). You dont need that much control btw, since most orbital craft are designed solely to go fast, and they shouldnt need too much control surfaces aside from trying to turn at low altitudes which most of my SSTLs are terrible at, bad TWR coupled with bad maneuverability is not a good combo for doing anything but go to orbit, return from orbit, or landing (apparently even at duna you can land somewhat safely).

[Stoney3K]

Ah, I can relate to that problem. All of my designs are basic delta wings with elevons on the back and they have a habit of picking a fight with my rudder on the vertical stabilizer.

When using stock SAS, not much of a problem unless you use massive control inputs, but when using MechJeb, I can't keep attitude and the plane just keeps oscillating on the yaw and roll axes.

The simplest solution is to use the elevons for pitch only and use reaction wheels for roll authority. Yaw isn't really needed unless you want to do landings with non-existent crosswind.

[Stoney3K]

Also, common wisdom holds that once the jets are completely offline you should toggle all your air intakes closed to shave off a little more drag, but last I heard the jury is still out on how effective this is in the new version.

According to the "Display Aerodynamics Data in Action Menus", closing or opening an intake has zero effect on the intake's drag.

[Wjolcz]

Hey OP, check my sig if you want a RAPIERless SSTO. I'm really proud of that thing.

[Stoney3K]

I tended to move away from RAPIERs more when building SSTOs, mainly because they have a lousy power band in the upper atmosphere above 17km, and the rocket engines have a terrible Isp when you switch over right at that time. Automatic switching won't kick in until over 25km, when you're already well on your way of slowing back down.

Whiplashes have a bigger power band starting at 10k over Mach 1 and ending at about 17km, at which point you can stage your rockets and have the jets and rockets work together from 17km up to 25km. Any higher and the jets will flame out by themselves, so you can continue on rocket power alone.

My strategy for fuel planning usually is to keep flying on jets until my LF/OX ratio reaches 10/11, so there's a slight excess of LF when I'm in orbit. This allows me to return to the KSC even when I miss my approach since you can just fly a go-around on jets or circle to land.

[fireblade274]

Don't forget about the return trip! Make sure its balanced well, especially if its large, or an MSTO. My all stock plane uses a 100 cargobay and can haul up a full unused Jumbo tank.

https://www.dropbox.com/s/0te1cfwxivvduf0/2015-09-01_00008.jpg?dl=0

https://www.dropbox.com/s/wid2yozrmd9e6w1/LTP%20Q1.craft?dl=0

I use 10 whiplashes and 6 aerospikes. Aerospikes do pretty good for large planes. Drop a pair of mk2 liquid fuel tanks on the underbelly when empty and my assent profile starts at 20degrees till i reach 8k, then nose down to 10-15degrees to build up horizontal velocity, staying at near my apoapsis. Nose picks up slowly over time (keep that in mind with your own assent profiles); once at 10k, I nose down to 10degrees, go really fast, and let my nose slowly pull up on its own to begin building more vertical speed. Once orbit speed starts dropping, I manually open up all tanks except the main, large tail fueltank and the "cargo" jumbo tank. Hit RCS to keep nose up, and activate my aerospikes. This is important as they have no thrust vectoring! I needed 2 Verner's under the nose. I drop 6 of my whiplashes then, even if they still have 50nt of thrust left, and I still gain 100-200Dv. Next I drop my external tanks under my wings as needed. I also usually open up my main tail fuel tank's liquid fuel to even out liquid and oxidizer in the tanks i'm dropping; this gives you more Dv too. Once even, I shut off the tail tank so the external ones are used first since they will be dropped. I reach 80km stable orbits everytime with fuel left for retroburn and runway return. (you may want to put some delta wings or canards on the front of the plane on de-couplers; they help when you have cargo going up, but if your returning with no cargo your ship may go nose up and spin out, so I drop those on empty landings.

I spent many hours perfecting the design and learned a lot about getting large planes into orbit. Hopefully something here helps you! Using planes is extremely cost effective. Although my ship costs 150k to launch, I have a small discount that makes it about 135k. Once the ship is returned, I get about 98k back making it cost just about 35k to put up a full unused jumbo. Is it time consuming? Yes, but its really fun and usually cost effective compared to rockets. Its also good to design your ship first for its max load; if i'm just sending up liquid fuel with the design, I can just take off 2 of the whiplashes and their respective tanks, making it even cheaper to launch, and I still get back about 98k since they would be dropped anyway.

Edited September 2, 2015 by fireblade274

[Wolf Baginski]

Ah, I can relate to that problem. All of my designs are basic delta wings with elevons on the back and they have a habit of picking a fight with my rudder on the vertical stabilizer.

When using stock SAS, not much of a problem unless you use massive control inputs, but when using MechJeb, I can't keep attitude and the plane just keeps oscillating on the yaw and roll axes.

MechJeb is useful, if only to ensure consistent flight for testing, but for Spaceplanes I am finding Pilot Assistant to be better.

Remember that you can stick a 1.25m reaction wheel unit behind an intake, or in front of a 1.25m engine such as the RAPIER.

I've taken a RAPIER-powered spaceplane to Mach 5.22 at 20,000mâ€â€that's just under 1600 m/sâ€â€and then started the climb to orbit and gained a little more speed before having to switch mode at about 23,000m.

It is possible to build an entirely stock single-RAPIER spaceplane. This one may have a bit too much wing.

It made orbit without the high-speed dash but I doubt I was using the optimum ascent profile