[1.3.1] Ferram Aerospace Research: v0.15.9.1 "Liepmann" 4/2/18

[cantab]

When it takes my underpowered spaceplane something like 20 minutes to get to the altitude where I light the rockets...yeah, trial and error becomes a bit less appealing.

[thorfinn]

The matter is quite complicated... here is a document I found that I don't have time to read in full at the moment: http://www.dept.aoe.vt.edu/~lutze/AOE3104/climb.pdf

It seems that the exact solution depends on the characteristics of engines and wings. What I know is that there are two different attitudes for best rate of climb and best angle of climb: the second condition happens at a slower speed, but how much slower I don't know in general (All I remember is that for light planes at takeoff there can be a very significant difference)

Edited March 14, 2015 by thorfinn

[Van Disaster]

It's even more complicated for spaceplanes by us needing to be going at max jet velocity by the time we arrive at whatever height we run out of jet acceleration, but going too fast too low brings dynamic pressure too high & burns excessive fuel up through drag loss...

For lower powered stuff I usually just leave it at 11-12 deg pitch angle until about 15km - any more than that usually just increases AoA rather than any noticeable change in rate of ascent - and then reduce it to 8 until it stops climbing, and then gradually go back up to 12-13 & transition when I can't get any more out of jets.

[tetryds]

Yes it is very complicated, if you are going to orbit I suggest the following (totally empirical) method:

Note: This is a method for "underpowered" spacecraft.

Fly as fast and as low as you can, I suggest about 500m, then nose up 20 degrees and hold, note your speed and total climb time when you reach 2km (can be "nonexistent" if you can't make it that high)

Do the same, but now pointing 10 degrees up.

Then, reach 2km altitude, repeat above procedure and mark for 4km and 6km.

If you feel like doing it, you can try that for higher altitudes, always aim for 2 or 4km climb.

Tips:

Always have two different angles at which the plane can reach the desired target altitude, example 20 and 10, 10 and 5, 5 and 2.5, etc.

If your plane does not do it to the aimed altitude, do it for half of it, but always try to have as high climb angle as you can.

Take screenshots right before you start the climb and when you reach the altitude goal (always hold the angle), you can analyze them later.

Now on KSP you can quicksave while on the atmosphere, make several quicksaves and tag them with the situation so you can test more later if you want.

To guesstimate a good climb, measure how fast you are climbing, and how much speed you are losing.

pick the altitude difference and divide it by the time you took to reach it, and the speed before and after the climb.

Do that for both different climb rates, and different altitudes.

Now compare the speed loss with the time it takes to reach such altitude.

Two points for each "shot" will be enough to draw two lines on a graph (you can use excel to quickly do that), from this graph you can estimate the optimal climb angle of your aircaft.

Edit: cross a line speed x time, separate for horizontal and vertical speeds, remember starting vertical speed is zero and final vertical speed = altitude / time

You can do a lot with it, for instance, the point where both lines cross mean your thrust is being wasted only on atmospheric drag, the point where your speed loss is zero is the one where your thrust is being equally divided between atmospheric and gravity drags.

Using the different curves for the different speeds, you can guesstimate the best climb profile for your plane, always be biased towards the fastest possible climb, you will notice that sometimes its worth to suffer a bit to get a bit higher then pick up speed from there and climb again.

But again, this is a lot of work, if your design is underpowered I would seriously consider boosting it to higher altitudes or adding more engines.

This is also empirical and HAS FLAWS (nothing is actually linear, etc, etc.), but it's a good way to understand your aircraft.

Edit: that is for gaining speed, after you are already high and want to shoot to orbit that is a whole different story, but I would recommend diving a bit to gain speed then pull up as much as you can to get as big arch as you can.

Edited March 15, 2015 by tetryds

[Van Disaster]

That sort of thing sounds like it could be kOS automated ( I can't remember if kOS programs can write to seperate files, if not then maybe one of the not-kOS automatons can ).

Zoom-climbing at powerplant transition implies you can actually zoom climb, I am usually too edge of flight envelope to be doing radical stuff by then

[Wanderfound]

Best rate of climb is not the same thing as best route to orbit, however.

You want to get out of the lower atmosphere soup quickly, but gaining just enough horizontal speed to continue to enable stable level flight at the increasing altitude. This is not necessarily the same pitch as best rate of climb; too much climb will see you in a ballistic trajectory, unable to maintain altitude after it peaks.

Once you get to the point where your air supply starts to run short, then you want to level off and crank up the speed before switching again to a very steep climb after engaging the rockets (to minimise drag losses after engine shutdown).

[silentdeth]

Is there a way to turn off FAR automatically setting the flaps at take off?

[futrtrubl]

How does FAR treat parts with PhysicsSignificance = 1 ?

[plasmeus]

Question: is there a way to automatically dampen controls in physics time warp to prevent planes from pulling huge g's and and their corresponding "Spontaneous Unplanned Disassembly"?

[Van Disaster]

Plasmeus: I think the best way to solve that would be to make sure there's as little oscillation as possible in 1x time, to be honest. You could try using an alternate control damper like Pilot Assistant also.

Silentdeth: I wish...

[dbmorpher]

I'm trying to make a replica of the Avro Vulcan and I'm having some trouble

Whenever I try to do a banked turn the plane yaws in the opposite direction and I lose control

Most of the fuel tanks are empty

Javascript is disabled. View full album

Any thoughts on how I could make the vehicle more stable?

Tips on maneuverability would be appreciated also

[cantab]

From experience the L-Beta derivative is fixed on subsonic aircraft by adding dihedral to the wings or their tips. It's hard to see to what extent the original Vulcan had that. It's possible your inner wing segments, curved over the fuselage, are being treated as lifting by FAR and that could make things worse.

You could also try sweeping the wing trailing edges back a bit. The Vulcan *did* have such a sweep, and on my Vulcan-inspired spaceplane I found it helped sort the L-Beta derivative in the transonic region, though I didn't alter it independently of the leading edge sweep so I can't be sure what was important.

Your AoA chart also looks on the edge of stability, I'd be minded to nudge the wings just a shade back.

[tetryds]

@dbmorpher: Yep, just increasing your dihedral angle may fix most of your issues.

You can add the angle to the entire wing as well as the wing tips, but that will have some different effects.

Also remember that adding dihedral decreases lift a bit, and check if it will not go past the COM afterwards.

You also need more tail, but there is a chance that if you angle the wings right you won't need to add more tail.

It's very likely that you have to.

[Wanderfound]

1: Yaw problems = moar tailfin.

2: Don't use wing pieces as structural/aesthetic elements. They'll mess up your aero.

3: You need to set the speed when running an AoA sweep: the one you've shown has you at Mach 0.2, which is much slower than typical flight speeds.

4: Ditto for the stability analysis. Run it at Mach 0.5 with the altitude set to 5km and you'll get a better picture of what's actually happening in flight.

And, to clarify: when you try to turn by banking over and pulling up, the nose yaws away from the ground?

- - - Updated - - -

Is there a way to turn off FAR automatically setting the flaps at take off?

Not that I know of, but I'd love it if there was.

[Hodo]

1: Yaw problems = moar tailfin.

Not always the case. Sometimes it is the placement of the tail. If it is to close to the CoM it will not have the needed force to keep the craft straight.

It also depends on the wing design also and the speeds the craft was designed to operate at.

I know I have sacrificed low speed Yaw stability for high speed stability on some craft.

[Wanderfound]

Not always the case. Sometimes it is the placement of the tail. If it is to close to the CoM it will not have the needed force to keep the craft straight.

It also depends on the wing design also and the speeds the craft was designed to operate at.

I know I have sacrificed low speed Yaw stability for high speed stability on some craft.

Yeah; I was simplifying a bit due to the context.

Yaw is trickier to sort than pitch and roll problems, IME. Moar tailfin usually helps, but you also get weird interactions with other factors. I have no idea why, but I often find that shifting purely horizontal surfaces (canards etc.) can make the difference between red and green. And while shifting CoM forwards usually helps, this morning I had one that was reversing this; I ended up needing to shift weight backwards to sort it. Very strange.

[Van Disaster]

From experience the L-Beta derivative is fixed on subsonic aircraft by adding dihedral to the wings or their tips. It's hard to see to what extent the original Vulcan had that.

From looking at drawings it looks like a few degrees of anhedral, if anything - or the wing underside is nominally flat and the wing is so thick that the upper surface has a good amount, anyway. In flight I guess they'd have bent up to be neutral-ish.

Jumping on the lack-of-vertical-stabiliser bandwagon, the real one's fin runs all the way up to the front area of the wings. Whatever the layout it needs to convert sideslip into a turning moment into the sideslip, so just fiddle with the vertical stabs with that in mind.

[tetryds]

The plane also has smaller sweep angle, at speed they create a dihedral effect, which can be very strong and end up requiring compensation by angling the wings down.

Your plane has much lower sweep angle than the original, which creates a smaller effect, but also those wings used as fuselage, as was already mentioned before, FAR does not like them.

But don't worry, your craft problems are not too major and can be fixed by tweaking.

Also remember that real airplanes have stability controls.

You can add positive %AoA on your rudders to help a bit (but don't overdo it).

[Hodo]

So odd bug with FAR but no output.log or errors in the game. But when I create a new craft and build it FAR does not let me open the FAR window in game or give me any information on the craft in flight. It is like FAR isnt even working for that craft. But I can load an older craft and it fly fine in FAR even get the FAR window and all of the information.

[GigaG]

With the new aerodynamics, do you plan to continue developing FAR? Are you just going to wait and see how similar the new aero system behaves to yours?

On another note, would you consider making a mod to restore the "souposphere" after 1.0 ?

[Hodo]

With the new aerodynamics, do you plan to continue developing FAR? Are you just going to wait and see how similar the new aero system behaves to yours?

On another note, would you consider making a mod to restore the "souposphere" after 1.0 ?

I doubt Ferram will make a mod that restores the stock atmo to the game, but I am sure someone will.... why I dont know but someone will.

[tetryds]

With the new aerodynamics, do you plan to continue developing FAR? Are you just going to wait and see how similar the new aero system behaves to yours?

On another note, would you consider making a mod to restore the "souposphere" after 1.0 ?

I don't think that ferram really cares about what will come on the new version regarding his mod other than the fact that it will be disableable.

Stock KSP cannot be as complete as this mod, that is too much for the stock game, IMO, and the next FAR update will change how things work very drastically.

@Hodo: Are you using the release or development version? Don't use the development version unless you are really testing it.

[Daze]

I have a question for you guys.

It's about (amybe 6-7 months?) that i use FAR daily, but only today i've wanted to know EXACTLY how many dV i need for an inline rocket, and the result was... 3.7km/s for a 85x85 orbit... It isn't too much?

Basically my ascent profile is that i start turning at 100m/s, than i try to reach 20km with an angle of 45-50 degree.

TWR at liftoff: 1.40

Here's a pic of my rocket:

Edited March 23, 2015 by Daze

[futrtrubl]

I have a question for you guys.

It's about (amybe 6-7 months?) that i use FAR daily, but only today i've wanted to know EXACTLY how many dV i need for an inline rocket, and the result was... 3.7km/s for a 85x85 orbit... It isn't too much?

Basically my ascent profile is that i start turning at 100m/s, than i try to reach 20km with an angle of 45-50 degree.

TWR at liftoff: 1.40

Here's a pic of my rocket:

http://i.imgur.com/yO8Ojas.png?1

That seems about right for FAR, much better than the ~4.5km/s for stock.

Optimal for me seems to be to start my turn at 0.1km, aiming roughly prograde and aiming to be horizontal by 50km. I find that keeping my acceleration at 23m/s2 is best though I usually start with a TWR about 1.6 and only throttle once I reach 23m/s2.

[Daze]

That seems about right for FAR, much better than the ~4.5km/s for stock.

Optimal for me seems to be to start my turn at 0.1km, aiming roughly prograde and aiming to be horizontal by 50km. I find that keeping my acceleration at 23m/s2 is best though I usually start with a TWR about 1.6 and only throttle once I reach 23m/s2.

Yes i know that it's better than stock, but how can people in this thread make orbit with 2.9km/s of dV?

For an inline rocket it's possible that the difference is 800 m/s?