Reach for orbit with an ion glider!

[MarvinKitFox]

One other thing to note. Extraneous solar panels and such do create more drag on the craft.

There really should be a "center of drag" button like center of mass/thrust/lift and such.

My favorite space plane design has all the intakes well behind the center of mass as they have huge drag, It makes it sooo much more stable, almost like flying with a parachute deployed. Spinout recovery is simple if your center of drag is behind your center of mass.

Agree on the center of drag display.

But solar panels (at least the single-panel ones) are completely exempt from physics. No mass, No inertia, no drag.

As are cubic octagonal structure, struts, radial batteries, rcs ports, and a host of others..

[MarvinKitFox]

Nedal, I can take your craft, launch it from a somewhat higher tower, and land(crash) it into the island runway.

After buzzing the control tower twice.

With your xenon tank on empty all the time.

[Nedal]

LOL

So I turned the control surfaces back on and abused infiniglide to see how quick i could make orbit.

Not much faster but i saved a crapton of fuel.

Enough to go to minmus.. land.. then fly back to ksc, and land. XD

Just so damn tedious to sit there pitching up and down constantly to infiniglide.

Lost a few parts on the landing at ksc but oh well... hehe craft recoverable!

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Edited April 20, 2014 by Nedal

[Nedal]

Agree on the center of drag display.

But solar panels (at least the single-panel ones) are completely exempt from physics. No mass, No inertia, no drag.

As are cubic octagonal structure, struts, radial batteries, rcs ports, and a host of others..

That's what I've heard too. But while messing around with this challenge I did notice a center of gravity shift after placing a bar of octagonal struts with solar panels on it. Also an earlier design i was using had a similar structure, a bar of octagonal struts up front with all the panels on it. and the wings behind that directly inline with the center of lift/mass however the thing always wanted to pitch up after accumulating any reasonable speed. Pretty sure it was the drag, as moving half the panels to the rear of the center of mass fixed it.

[Nedal]

Nedal, I can take your craft, launch it from a somewhat higher tower, and land(crash) it into the island runway.

After buzzing the control tower twice.

With your xenon tank on empty all the time.

But you couldn't fly across the whole daylight time, like with infiniglide. What you describe is a really good glider.. XD

[Nedal]

Shaved a little time off by using the angles more efficiently, and turning the craft upsidedown to take advantage of more solar panels when coming close to the darkside while making the proofs for the microssto challenge.

So heres updated img, with updated craft

Same craft just has landing gear on it. I suppose its true, landing gears really have no effect. Is that new?

craft: https://www./?s82wpn14c9toshf

[MarvinKitFox]

But you couldn't fly across the whole daylight time, like with infiniglide. What you describe is a really good glider.. XD

yeh, such a good glider that it can go from 100m alt at 25m/s to 800m alt at 125m/s

glider, yeh. right.

[SSSPutnik]

My entry (for now).

Altitude: 23673

Orbital speed: 755.8

Score: 1939.4

Ran out of fuel, but think was near limit anyway, speed was increasing, but altitude gain was dropping fast.

[Pyranz]

Looking at some of these makes me wonder how much of a factor Kerbin's sharp curvature contributes to horizontal speed being tranfered to upward speed. Could launch height have a major impact on how easy it is to get there? Also, can we use the thrust given by decouplers?

[donfede]

I've no entry to submit yet (and am surprised there's not a FAR leader-board); regardless, below are my current attempts at preparatory math and data points for this challenge with stock KSP v0.23.5:

# Review of the forces we are working with: weight, thrust, lift, drag

NASA review of Wright 1903 Flyer and the forces that affect it (and our ion 'gliders'):

# Weight

Weight is dependent on 'surface' gravity at various Kerbin altitudes, and can be calculated with:

Force of weight = mass * 'surface' gravity

We'll focus on the 'surface' gravity for now. Pic with graph:

Pic with equation, reference, and sample data points (apologies, I didn't have the patience to enter these into forum tables):

Note the gravity values at 30km and 70km, 8.8m/s^2 and 7.8m/s^2 respectively.

# Thrust

Force of thrust = 2kN x <count of ion engines>

I found it worth re-noting that 1N = 1kg*m/s^2.

# TWR of PB-ION (source KSP wiki)

[table=width: 500, class: grid]

[tr]

[td]part[/td]

[td]mass[/td]

[td]thrust[/td]

[td]isp[/td]

[td]TWR (Kerbin)[/td]

[td]ellect/s[/td]

[/tr]

[tr]

[td]PB-ION[v0.23.5][/td]

[td]0.25[/td]

[td]2[/td]

[td]4200[/td]

[td]0.815[/td]

[td]8.729[/td]

[/tr]

[tr]

[td]PB-ION[<=v0.23.0][/td]

[td]0.25[/td]

[td]0.5[/td]

[td]4200[/td]

[td]0.204[/td]

[td]14.5476[/td]

[/tr]

[/table]

However, TWR of a PB-ION is an incomplete picture. It's also worth reviewing the TWR of a PB-ION combined with its required energy source, and any additional mass for it to propel.

# TWR and ion engine count, with necessary energy source (solar panels)

source: reddit post by /u/Stinger771; note: his updated equation is slightly wrong (incorrect solar panel mass), but I only lurk reddit, so cannot contact him.

From his work, we can get the number of ion engines (n) required for a TWR > 1, with various parameters:

n = (m * g) / (T - i * g - s * g)

n - number of ion engines required for positive TWR

m - mass of other ship parts (ex: wings, command pod, xenon fuel)

g - 'surface' gravity <see above>

T – thrust of an engine; 2N as noted above

i – ion engine mass; 0.25t for PB-ION [stock]

s – solar panel mass <see table below; mass numX>

Unfortunately, in our case this equation is still not complete, as the Force of lift from the wings allow craft with TWR < 1 to fly. Still, it provides a good starting point, and it confirms that ion craft cannot propel themselves against Kerbin's gravity until they are ~250km above the surface.

# Solar panel review (given PB-ION electric draw of 8.729)

The table below looks at the solar panels available, with their corresponding energy/mass ratios, and the count required to support an ion engine. While the OX-S static solar panels have the best energy/mass ratio, they (obviously ) have the drawback that they cannot move and track the light source. For our ion flyers they are a requirement, as we're contending with the Force of drag in the atmosphere, which breaks off extendible solar panels. The most important detail from this table is that we need a dozen OX-S panels to support one engine WITH optimal light, so designers must adjust appropriately.

[table=width: 700, class: grid]

[tr]

[td]part[/td]

[td]mass[/td]

[td]electric[/td]

[td]m/e[/td]

[td]e/m[/td]

[td]num for ion[/td]

[td]num for ion (int)[/td]

[td]mass numX[/td]

[td]difference[/td]

[td]mass numX2 (Jool/Eeloo)[/td]

[/tr]

[tr]

[td]Gigantor XL[/td]

[td]0.350[/td]

[td]18.00[/td]

[td]0.019[/td]

[td]51.429[/td]

[td]0.485[/td]

[td]1[/td]

[td]0.35[/td]

[td][/td]

[td]0.35[/td]

[/tr]

[tr]

[td]OX-4L[/td]

[td]0.018[/td]

[td]2.00[/td]

[td]0.009[/td]

[td]114.286[/td]

[td]4.365[/td]

[td]5[/td]

[td]0.088[/td]

[td]0.263[/td]

[td]0.175[/td]

[/tr]

[tr]

[td]OX-Stat[/td]

[td]0.005[/td]

[td]0.75[/td]

[td]0.007[/td]

[td]150.00[/td]

[td]11.639[/td]

[td]12[/td]

[td]0.060[/td]

[td]0.290[/td]

[td]0.120[/td]

[/tr]

[/table]

# Lift

Pic of table summarizing wing lift:

As others have noted earlier in this thread, the small control surfaces have incredible lift/mass ratios compared to the other parts. Similarly, the swept wings appear to be more efficient than the delta wings.

I'm currently exploring how to convert the lift figures above into a Force of lift value. This KSP forum post by ChevronTango suggests the following equation may work (quoting his post):

Flift = CrossProduct(velocity, wingRight) * Cos(UpvAoA) * (1 - Abs(Cos(UpvAoA))) * Cos(AoA) * deflectionLiftCoeff * StaticAirPressure;

where AoA is the angle between the velocity and the forward vector of the wing,

and UpvAoA is the angle between the velocity and the upward vector of the wing,

wingRight is the vector to the right of the wing as placed, or can be thought of as the cross product of the wings up and forward vectors

DeflectionLiftCoeff is the lift value listed in the VAB

StaticAirPressure <see below, at drag calculations>

I've not yet worked numbers through this equation successfully, and thus do not yet have a good figure for Force of lift.

# Drag

The drag model in KSP is limited, but from their wiki we can see that the following equation can help us calculate its force:

Fd = 0.5 Pv^2dA

Pic of table with various drag calculations from test-flights:

# Current and next steps

As shown above, ion engines have a TWR > 1, only when gravity is less than ~5.5. But, gravity is not that low around Kerbin until one reaches ~250km altitude (clearly after wings are useful, as the flyable-atmosphere ends around 30km).(The variance is due to different possibilities, depending on solar panel type used.)

My current questions include how much drag can the ion flyer craft overcome, and how high will the wings lift the craft, thus I'm pushing on improving those equations. In addition I may have some unit (or magnitude) issues above which I'm polishing.

kdonfede

--

"Adding k to every word..."

[Nedal]

yeh, such a good glider that it can go from 100m alt at 25m/s to 800m alt at 125m/s

glider, yeh. right.

I can't seem to achieve this with the control surfaces disabled. Is there some kinda a tricky way to pilot it to do this?

Can anyone else attest to it?

[ihtoit]

question: given enough ion engines, is it not possible to use a small fission reactor rather than loads of static solar panels or RTGs? There's the weight issue, sure, but is there a point where that makes up for the reduction in drag? Also consider that with a nuke, you don't need batteries, hence the part count is also reduced... and yes, there is a way to pitch without control surfaces: use ASAS gyros.

[Nedal]

# Current and next steps

As shown above, ion engines have a TWR > 1, only when gravity is less than ~5.5. But, gravity is not that low around Kerbin until one reaches ~250km altitude (clearly after wings are useful, as the flyable-atmosphere ends around 30km).(The variance is due to different possibilities, depending on solar panel type used.)

My current questions include how much drag can the ion flyer craft overcome, and how high will the wings lift the craft, thus I'm pushing on improving those equations. In addition I may have some unit (or magnitude) issues above which I'm polishing.

kdonfede

--

"Adding k to every word..."

Awesome stuff!

The trick is to get horizontal velocity high enough in the thin but still flyable atmo that you launch out to a high enough orbit on the other side.

My lil ship starts losing lift around the 30km zone like you say, so you have to kinda keep "bouncing" off the atmo gaining some more horizontal velocity each time to reach the speed required.

[Nedal]

question: given enough ion engines, is it not possible to use a small fission reactor rather than loads of static solar panels or RTGs? There's the weight issue, sure, but is there a point where that makes up for the reduction in drag? Also consider that with a nuke, you don't need batteries, hence the part count is also reduced... and yes, there is a way to pitch without control surfaces: use ASAS gyros.

Im not sure. Im just finding out that a lot of parts are now massless.. If that includes the thermoelectric generators idk. They would be hella OP if they are.

If your ASAS gyro comment was geared toward me, I know. That was the whole design philosophy of the ship. But he's trying to say that it's an infiniglider even with the control surfaces disabled. And I can't seem to replicate his results.

[Nedal]

Looking at some of these makes me wonder how much of a factor Kerbin's sharp curvature contributes to horizontal speed being tranfered to upward speed. Could launch height have a major impact on how easy it is to get there? Also, can we use the thrust given by decouplers?

Good question, Setting up a huge decoupler launch would be interesting, potentially saving tons of time to orbit.

but yes, the curvature of the planet is instrumental in achieving orbit with something that has a twr <1

[ihtoit]

hmmm... well, runway tests confirm that locking the control surfaces in any position has direct effects on ground speed, for example my single-ion overweight topped out at 30m/s when I wasn't touching the pitch, ASAS turned off and it wouldn't take off. Pitching up increased top speed to 38.5m/s and the thing rotated. Go figure. Hardlocking small control surfaces and using ASAS gyro pitch control had pretty much the same effect: pitching up increased top ground speed causing the aircraft to rotate. So locking control surfaces doesn't result in a loss of lift. Can you infiniglide with locked control surfaces? Given enough of them, I'd say certainly. Have I tried it? Not as such, but my early ion powered planes (before I discovered wing control surfaces!) had a good go. One of my .18 planes actually made it to LKO on 5 of the old stock ions.

(this was my first to use control surfaces, just the one pair, and someone claimed the only reason it made orbit was because of the control surfaces. Truth of it is, I used them to rotate at something like 24m/s and then locked my pitch angle, hit ASAS and let it go. Yes, this is before batteries went massless!)

[totalitor]

New record for me: 36007 m and 1573 m/s. I gave up multiple engines and I used only one. The trick is leave so early that there is barely enough light to sun panels. Then climbing up - I used about 25 degrees. I still had fuel but panels did not had light. I used 55 minutes to reach that altitude. That is too much.

My score is 36007/20+1573=3373

[Nedal]

entry withdrawn, i cannot compete with infinigliders

:<

I was going back to see who made the awesome huge complicated ion glider.

Don't withdraw that thing! it's a friggin marvel of engineering.

[Nedal]

New record for me: 36007 m and 1573 m/s. I gave up multiple engines and I used only one. The trick is leave so early that there is barely enough light to sun panels. Then climbing up - I used about 25 degrees. I still had fuel but panels did not had light. I used 55 minutes to reach that altitude. That is too much.

Precisely. You don't always need full power on the drive. Take off as early as possible, try pitching up as much as your twr will allow you to climb without stalling, keeping your ground speed down as you climb saves you daylight for your final orbital burn. Also perhaps try putting a pair of panels that face the rear to give you that last push when you're toward the dark side. You're so close!

[SSSPutnik]

You can't use part mods or any other form of propulsion, so no decoupler launches or fission plants.

[Comma_dose]

Tried to do the same as this dude, but made it more like a reusable SSTO.

Ran out of fuel at 39,748 meters and final velocity was at 1550.9 m/s

Here's a link to the timelapse video

Edited April 21, 2014 by Comma_dose
Added link to timelapse video

[Visari]

seeing as how this is essentially a plane challenge, would it make sense to allow FAR with a separate scoreboard?

[SSSPutnik]

I think FAR is allowed, but probably harder.

[Nedal]

Yeah, im working on one with FAR now. It's a whole lot different.. Getting used to how it all works. Pretty cool. So far i've managed to make an ion plane that will fly stable and climb.. but .. no where near orbital yet. Still much testing to do.

[Visari]

Not just harder, likely impossible.

Best speed I've attained in FAR using stock and pwings in 23.5 is mach 1.75 at about 25-30km.

If using all other realism mods, even taking off becomes impossible due to the power requirement and supply tweaks from RO, creating the need for more than 8000 fixed solar panels per ion engine.