Show off your B9 Designs!

[Van Disaster]

There's many things that contribute to drag; general cross-section, length vs cross-section, blunt areas etc... but there are dynamic considerations like AoA. If you find yourself running high AoA a lot you either don't have enough wing area, it's not the right shape, or your ascent profile is too steep ( or maybe all of those at once ). If your Q figure is going up alarmingly, you're not steep enough. If you've got high AoA *and* high Q, you definitely don't have enough wing.

Not terribly good at explaining things today, so I just did an annotated ascent in one of my not terribly optimized HL craft. Note you're never going to get the cD of a fighter in a fat thing like this...

Javascript is disabled. View full album

Edited November 28, 2014 by Van Disaster
sigh imgur

[PCanas]

So I made a little update to the craft: had to add another cargo bay segment (the smallest) so I can fit those orange tanks inside. Obviously, I also had to reasemble the wings (still the same shape and size) and engines (in the same place, but with a single precooler), because of the CoM and CoL.

I managed to takeoff (with the orange tank) as easily as before (it needs a bit more runway and speed) and it flies as it did before. It still wants to pitch down on its own, but I managed to "lock" it in a certain position with SAS (no woble) and FAR flight aids (Yaw). Didn't made it to orbit, but didn't aimed there anyway. The purpose of the test flight was to see how the craft behaved, and it's pratically the same as the smaller version. Didn't try to land.

Managed a CD value of 0.025 a few seconds after takeoff

If possible, I'll tweak as much as possible to make as good as I can, and I'll then post the craft file tonight, so you experts can take it for a ride

[Hodo]

There's many things that contribute to drag; general cross-section, length vs cross-section, blunt areas etc... but there are dynamic considerations like AoA. If you find yourself running high AoA a lot you either don't have enough wing area, it's not the right shape, or your ascent profile is too steep ( or maybe all of those at once ). If your Q figure is going up alarmingly, you're not steep enough. If you've got high AoA *and* high Q, you definitely don't have enough wing.

Not terribly good at explaining things today, so I just did an annotated ascent in one of my not terribly optimized HL craft. Note you're never going to get the cD of a fighter in a fat thing like this...

http://imgur.com/a/UI5VR

Are you talking about the Q number in the flight FAR screen? If so that is the pressure on the exteriour of the craft. That number should go down the higher you go if you maintain a steady speed. If you are up around 10km and pushing mach 1+ you will get high Q numbers, generaly around 45-55kpa.

You may actually have a bit more success with your spaceplane designs if you went with a bit more wing width or just more wing area. Right now you have a large thin wing which is great for planes like the U-2 which pretty much are powered high alt gliders. But on the upside your thin wings wont generate a whole bunch of drag.

[Van Disaster]

Yep: Q is more important than straight up cD ( well, it's a product of cD and other things ), you can use it as a rough check if your design has enough wing or your flight profile is off.

My thin wings also mean less mach tuck - I do increase chord length at the root, but the tips are a bit limited by having an engine stuck on there most of the time. More span would be an option but then we start running out of runway width honestly not really worried about the time it takes to orbit, the real problem I have is high landing speed which is the result of high wing loading, but if I get the right flap design that will mitigate a lot - that's still a work in progress.

We *want* to concentrate on high altitude performance, really - the higher we can get without going fully ballistic means the less fuel we have to spend pointing upwards.

Edited December 3, 2014 by Van Disaster

[Hodo]

Yep: Q is more important than straight up cD ( well, it's a product of cD and other things ) - but you can use it as a rough check if your design has enough wing.

My thin wings also mean less mach tuck - I do increase chord length at the root, but the tips are a bit limited by having an engine stuck on there most of the time. More span would be an option but then we start running out of runway width honestly not really worried about the time it takes to orbit, the real problem I have is high landing speed which is the result of high wing loading, but if I get the right flap design that will mitigate a lot - that's still a work in progress.

We *want* to concentrate on high altitude performance, really - the higher we can get without going fully ballistic means the less fuel we have to spend pointing upwards.

I was asking which Q you are talking about? The one in the FAR Flight Data screen when flying or the one in the graph in the SPH?

The Q is a VERY important line and number to pay attention to in the SPH, but in flight Q is just air pressure on the craft at that speed and altitude. And that is not that important, not as much as your L/D or any of the other numbers.

"Mach tuck" can be overcome by proper balance of the craft for those speeds or shifting your fuel load around, which is what I do. As the craft goes faster and the CoL shifts back I shift fuel towards the rear of the craft to keep the CoL and CoM where I want them. I usually design most of my craft with a partially empty tank for this very reason. Which is how some modern supersonic aircraft do it.

As for your flap issue, that is a pretty simple one.

You will want your flaps to be inline with your CoL or as close as you can get them to it, this will help to generate lift and not push the nose down. I found that you can also add leading edge slats for thin wings that help also. I used them on one of my delta wing designs a while ago and got the landing speed down to 60m/s an take off around 65m/s. On a craft that was about 30tons and would handle up to 11G maneuvers and still achieve orbit.

Edited December 3, 2014 by Hodo

[Van Disaster]

I was talking about dynamics, so in-flight Q in that case - which is a function of speed & air pressure, and I mentioned why I was talking about it in relation to AoA.

Supersonic CoL shift can be mitigated by fuel shift yes, and I used to do that - but reducing chord length is valid also, and large span wings currently don't seem to have any real drag penalty. Given the amount of time a spaceplane spends in the lower atmosphere and what it's doing there, I'm of the opinion that's not as big a deal as it would be for say, an airliner anyway. You want to get to the upper atmosphere where drag isn't such a big deal, and only then go really fast - and in relative terms a few minutes later you're in zero drag. On the way down again all you're doing is an extended approach to land, and extra drag is a bonus given you're coming from orbital speeds.

[Hodo]

I was talking about dynamics, so in-flight Q in that case - which is a function of speed & air pressure, and I mentioned why I was talking about it in relation to AoA.

Supersonic CoL shift can be mitigated by fuel shift yes, and I used to do that - but reducing chord length is valid also, and large span wings currently don't seem to have any real drag penalty. Given the amount of time a spaceplane spends in the lower atmosphere and what it's doing there, I'm of the opinion that's not as big a deal as it would be for say, an airliner anyway. You want to get to the upper atmosphere where drag isn't such a big deal, and only then go really fast - and in relative terms a few minutes later you're in zero drag. On the way down again all you're doing is an extended approach to land, and extra drag is a bonus given you're coming from orbital speeds.

Ok so we are talking about the same area. That number is just the pressure on the outside of the craft at that time, or the dynamic pressure. While that CL and CD will give you your current paresitic loss for the craft at that speed and altitude. It is not one of the most important numbers in that chart. Overall I am most concerned with the C/D if that number is to high it is like pushing a house through the air.

There is a reason why some wing designs work well and others dont. I know on my heavy lifters the delta wing is the way to go for them, and even then it isn't a true delta wing, I took a book out of the Russian aero designs. I have compound delta wings that have verying sweep angles to provide lift at different speeds.

Edited December 3, 2014 by Hodo

[PCanas]

So, I finally managed to get into orbit. It's the first time I've got into orbit on an SSTO designed by me (craft file)

As I've mentioned before, I had to alongate the cargo bay to fit the orange tank. This of course changed the CoL and CoM, so I also had to relocate the wings and engine.

Anyway, it flies well* to about 40km high, then, just before the engines switch to rocket mode, it begins to fall into a limbo state, where you never know when you're going to completely lose control. It remains in that state for a while, probably for the next 10km up (didn't check, was too busy trying to keep it flying straight). Once out of the atmosphere, it's like any other rocket.

* "well" means it flies straing ahead, but it's always pitching down, so it needs constant adjustments to pitch.

As you can see, the test was made with a full orange tank in the bay. The craft, when empty, takes off at about half way the runway. With the tank, it takes off a few meters before the end of the runway.

I managed to detach the tank in orbit (easy...) but I forgot to add RCS ports to the rear of the craft, so it was tricky to get away from the tank lol

when coming back home, I had to change fuel back and forth to keep the plane stable, wich was obviously expected, since the CoL was designed having in mind the CoM WITH the orange tank.

I also managed to land at KSC... kind of...

Javascript is disabled. View full album

[Hodo]

PCanas, your pitching issue is pretty normal at those altitudes and speeds. It is because the CoL shifts back towards the rear of the wing of the craft shifting the balance to become more nose heavy at those speeds. At higher altitudes you don't have enough airflow to overcome the shift. The easiest fix for this is to shift your fuel load back towards the rear of your craft.

I personally use TAC fuel balancer so I can manually do this quickly. Others like PWB fuel pumps, both work.

Oh one more thing... looks like your FAR is out of date, you may want to update it, I think FAR is up to 14.4+

[Van Disaster]

FAR is at 0.14.4, Mechjeb is at 2.4 I think, and I'd seriously recommend Pilot Assistant.

What sort of drag are you getting out of the derivatives tab for your latest heavy lifters, Hodo?

[Hodo]

FAR is at 0.14.4, Mechjeb is at 2.4 I think, and I'd seriously recommend Pilot Assistant.

What sort of drag are you getting out of the derivatives tab for your latest heavy lifters, Hodo?

I don't have any recent pics of that, I will take some of the FAR derivatives tab for three of my larger lifters that I use currently when I get home. It will be a while, possibly tommarrow.

I think those three are the three I am currently using for all my lifting into orbit. Mostly the first one, I dont need a super heavy lifter yet.

[PCanas]

PCanas, your pitching issue is pretty normal at those altitudes and speeds. It is because the CoL shifts back towards the rear of the wing of the craft shifting the balance to become more nose heavy at those speeds. At higher altitudes you don't have enough airflow to overcome the shift. The easiest fix for this is to shift your fuel load back towards the rear of your craft.

I personally use TAC fuel balancer so I can manually do this quickly. Others like PWB fuel pumps, both work.

Oh one more thing... looks like your FAR is out of date, you may want to update it, I think FAR is up to 14.4+

The pitching down problem is constant, from the moment you leave the runway all the way up to space. What happened at about 40km looks like a yaw problem instead of a pitch/roll problem, since the plane started to deviate from it's heading (and prograde marker)

Can you try to fly it, and check if the same happens with you?

[Hodo]

The pitching down problem is constant, from the moment you leave the runway all the way up to space. What happened at about 40km looks like a yaw problem instead of a pitch/roll problem, since the plane started to deviate from it's heading (and prograde marker)

Can you try to fly it, and check if the same happens with you?

I will check it out tonight when I get home. It could also be an issue of not having enough lift or having your CoL shift rearward on the craft.

[PCanas]

Meanwhile I've tried a new design:

Javascript is disabled. View full album

Flies even better than the previous design. It can be a bit unstable at the begining, but after you manage to stabelize it, you can activate SAS and it stays there. The first attemp I used those big airplane-like wings, but the craft got too unstable. Maybe it had too much lift. So I redesigned to wings in the same fashion as the previous craft. Contrary to previous craft, this one tends to pitch up.

Problems detected:

- Be carefull at take off: you don't need to pitch much to a tail strike...

- Center engine overheats (air breathing mode) and shuts down at about 20km up. Can be reactivated a moment later as rocket mode.

- Smaller engine change to rocket mode much sooner than the bigger engine.

- Either I did it wrong (I'd bet on this one) or it really lacks bracking power: when trying to land at KSC, I ended up flying by it, at about 15.000m high and almost 2000m/s. Tried to turn around, but failed. Good thing I had an escape system

Craft File - don't mind group keys, except 4 and 5: they operate those chutes in the wings (wich were air intakes). They are there as an experiment: to add extra drag to slow down the plane. They're set with default settings, so be sure to cut them (5) before you are at 500m high.

[Van Disaster]

Meanwhile I've tried a new design:

More wing area, much better

- Either I did it wrong (I'd bet on this one) or it really lacks bracking power: when trying to land at KSC, I ended up flying by it, at about 15.000m high and almost 2000m/s. Tried to turn around, but failed. Good thing I had an escape system

Way too high to attempt to land, really - point the nose up & just go completely round Kerbin again with that much speed ( or better, realise when you're higher up you're not going to manage an approach & go round a bit faster ). You can try some heavy banking turns but at that speed & height you're probably not going to do much turning...

[Hodo]

ok here is some of those pics I promised earlier.

Landing speed and take off speed.

Mach 1 at 10km

Mach 5 at 10km.

Granted I am never Mach 5 at 10km.

[Van Disaster]

Thanks, and nice. I'm going through mine trying to tweak in a bit more wing & get derivatives in the green at all speeds, getting there in a slow fashion. This is probably getting a bit esoteric for a craft display thread, but here's some major ones - 4 sabre heavy lifter, 2 sabre medium lifter, 2 sabre bulk lifter.

Javascript is disabled. View full album

Might be worth having a thread for technical discussion of heavy lift spaceplanes at some point. Also I notice your derivative page is subtly different, must check my FAR version...

[PCanas]

More wing area, much better

Way too high to attempt to land, really - point the nose up & just go completely round Kerbin again with that much speed ( or better, realise when you're higher up you're not going to manage an approach & go round a bit faster ). You can try some heavy banking turns but at that speed & height you're probably not going to do much turning...

When I made the reentry burn in orbit, I aimed slightly ahead of KSC, hoping the atmospheric drag would slow down the plane just enough to be able to land at KSC, or at least, to be able to make some maneuvers to slow it down even more. Apparently, it didn't slow down enough, and I went by so fast that the turning around was happening on top of that little round island east of the KSP (not the one with the 2nd runway).

I'll try again, but this time I will try 2 things:

1- I'll aim the reentry burn to be "behind" the KSC

2- I'll aim the reentry burn to be ahead the KSC, but I'll reentry the atmosphere in a more accentuated angle, more "brick-like"

[Van Disaster]

When I made the reentry burn in orbit, I aimed slightly ahead of KSC, hoping the atmospheric drag would slow down the plane just enough to be able to land at KSC, or at least, to be able to make some maneuvers to slow it down even more. Apparently, it didn't slow down enough, and I went by so fast that the turning around was happening on top of that little round island east of the KSP (not the one with the 2nd runway).

I'll try again, but this time I will try 2 things:

1- I'll aim the reentry burn to be "behind" the KSC

2- I'll aim the reentry burn to be ahead the KSC, but I'll reentry the atmosphere in a more accentuated angle, more "brick-like"

I tend to burn above or just past KSC with a 25km periapsis - once at periapsis I try and hold altitude while I bleed off speed, and then hopefully I can drop down to KSC gently. Depends how heavy the plane is, some do seem to want a couple of laps round the planet.

[PCanas]

I tend to burn above or just past KSC with a 25km periapsis - once at periapsis I try and hold altitude while I bleed off speed, and then hopefully I can drop down to KSC gently. Depends how heavy the plane is, some do seem to want a couple of laps round the planet.

I'm confused...

- you burn when you're orbiting above KSC until you get a periapsis of 25km, wich will be at the other side of the planet, and then you fly all the way to KSC?

or

- you aim the landing point to be above the KSC?

[Hodo]

I'm confused...

- you burn when you're orbiting above KSC until you get a periapsis of 25km, wich will be at the other side of the planet, and then you fly all the way to KSC?

or

- you aim the landing point to be above the KSC?

With DRE I try and set my PE about 5km over KSC from the otherside of the Kerbin. This way I am flying about halfway around the world in the atmosphere on re-entry it gives me plenty of time to slow down. The problems I have been having lately is my craft will overshoot slightly and have to turn around about 100km out and land west to east.

[Van Disaster]

I am at say, 250km when I do my re-entry burn. I aim my periapsis to be 25km, so yes that *is* mostly around the planet depending where I've done my burn - but I will be doing 2k m/s or more at that point still. At that point I either hold 25km alt until I've dropped some speed, or hold 0 pitch and gently lose height. Your descent from that point depends on the craft, but usually once I'm used to how a craft behaves I can glide all the way to the runway from there.

It's not a capsule, don't try bombing it out of the atmosphere like one

"New" ( last played seriously with 0.22, they are still new ) ion engines are a major surprise - after launching a small mun lander with one out of a smaller spaceplane ( didn't want the hassle of designing a rocket ) I thought that seemed a rather excessive launcher, so I started removing things... and eventually arrived at something that can scrape a stable orbit if it's empty, but really all it needs to do is hop out of the atmosphere long enough to get rid of it's payload and give me enough time to get *that* into orbit.

Pretty cheap too ( just under 50k after the sat cost in the pic below is removed ), no idea what the upper payload limit is - if the payload is fairly heavy I could always add a tank in the bay anyway. I'd do it entirely with jet engines but I can't find any suitably big ramjets, and I haven't got round to doing a reaction engines Scimitar yet, no idea really how to make that perform & still fit in with all the other available engines.

Note periapsis in the last one, still plenty of time to get the payloads in stable orbits though.

[Hodo]

I am at say, 250km when I do my re-entry burn. I aim my periapsis to be 25km, so yes that *is* mostly around the planet depending where I've done my burn - but I will be doing 2k m/s or more at that point still. At that point I either hold 25km alt until I've dropped some speed, or hold 0 pitch and gently lose height. Your descent from that point depends on the craft, but usually once I'm used to how a craft behaves I can glide all the way to the runway from there.

It's not a capsule, don't try bombing it out of the atmosphere like one

"New" ( last played seriously with 0.22, they are still new ) ion engines are a major surprise - after launching a small mun lander with one out of a smaller spaceplane ( didn't want the hassle of designing a rocket ) I thought that seemed a rather excessive launcher, so I started removing things... and eventually arrived at something that can scrape a stable orbit if it's empty, but really all it needs to do is hop out of the atmosphere long enough to get rid of it's payload and give me enough time to get *that* into orbit.

Pretty cheap too ( just under 50k after the sat cost in the pic below is removed ), no idea what the upper payload limit is - if the payload is fairly heavy I could always add a tank in the bay anyway. I'd do it entirely with jet engines but I can't find any suitably big ramjets, and I haven't got round to doing a reaction engines Scimitar yet, no idea really how to make that perform & still fit in with all the other available engines.

https://farm8.staticflickr.com/7579/15803878740_88f7b2a717_b.jpg

https://farm9.staticflickr.com/8571/15368990634_aa04c9fe45_b.jpg

https://farm9.staticflickr.com/8605/15804053170_949ddf53fa_b.jpg

Note periapsis in the last one, still plenty of time to get the payloads in stable orbits though.

That craft is so light you could get away with almost half the wing you have there, and could get away with a little bit more fuel this would give it the ability to reach orbit on its own.

I know because I have a craft not to much bigger than that, that is my light cargo SSTO. It can haul about 20-25 tons into orbit.

Edited December 11, 2014 by Hodo

[Van Disaster]

I don't *want* it to be able to orbit - that was the point and yes it probably has a lot more wing than it needs empty ( 165m3 ), but that should hopefully give it the ability to lift considerable amounts more than I've tried so far - and using 10km alt/mach 2 as a benchmark, FAR is giving me a Cd of 0.018 so it's still a pretty slick ship. I did originally try it with less wing & no canards but it wasn't terribly well balanced. The only reason I'm using the small sabres is because I don't have any pure jets that will give me enough speed to hop out of the atmosphere on a useful trajectory.

[Hodo]

That is cool, I use the SABRE-S also. I love that thing one of the most versitile 1.25 engines out there. A bit long but still useful.

I find it odd that you dont want a craft that can actually achieve orbit just hop and return. But hey its your program and that is pretty cool.