Laythe Plane (now with Flight Data questions)

[drakesdoom]

You may find you have better economy with only 1 intake. The only reason to have more than 1 per engine is to achieve orbit.

[Brotoro]

Surely laythe is too hilly for the rover wheels to be safe?

I don't think this plane will make a great rover (compared to the other one I'm sending), but I think I'll be able to get it places. I'll just have to be very careful about ground clearance for the plane when roving. I'll get back to you on whether its a sure thing or not.

[bsalis]

I like how your using rover wheels and put your ASAS cone on the tail.

As for Laythe. generally, any plane that works well on Kerbin works well, or better, on Laythe. The thinner atmo is offset by the lower gravity.

[loppnessmonsta]

Debug menu keybind is now just Right-Alt + F12.

Anyway, I really like your plane and refueling station. I am going to copy portions of your designs shamelessly!

[zarakon]

With 2 ram intakes and some throttle management, you should be able to get that up to almost 2000 m/s and circumnavigate Kerbin at 30+km altitude

When the engine flames out, immediately kill the throttle (x) then throttle it back up to slightly lower than it was when it flamed out. You can get a lot more speed and altitude by repeating this until you're running on nearly zero throttle

[RoboRay]

I spend a lot of time in planes, and I spend a lot of time on Laythe, and I think you've come up with a fantastic design. In fact, I will be copying it.

The avionics package is tricky with the Mk1 cockpit. I usually stick it out on the nose using a little truss, like this:

It never occurred to me to make a tail-pod for it, EA-6B style. I'm going to be trying that, too.

I think the regular jet engine would be better for a craft that's not going to trying to get back into space or make high-speed, high-altitude transits, though, and have limited refueling options... it's more fuel efficient.

Edited April 25, 2013 by RoboRay

[musicpenguin]

Looks great. When I get to laythe (I'm yet to get to mun/minmus) I will make a giant plane and have it drop a small base for future kerbals to inhabit. It will be a simple hab module with landing legs and paracutes to help descend and a small large fuel tank with a docking port for refueling. The large plane wil then scout out a little bit more than return to the station in orbit. After that a small fleet of landers with other parts of the base will descend and attach. A base will be made with a small runway made out of the weird wing things that are flat. Planes will land there and refuel. That is my extravagant plan. I am yet to land on the mun or minmus. Wow.

[Brotoro]

...I think the regular jet engine would be better for a craft that's not going to trying to get back into space or make high-speed, high-altitude transits, though, and have limited refueling options... it's more fuel efficient.

I think I may go that route, since the group of islands I'll be exploring aren't that far apart, and because the shorter jet engine will be less likely to get banged off the tail while roving around.

[Brotoro]

Boosting BirdDog

I finished testing the BirdDog plane/rover by launching it into orbit around Kerbin (with its refueling station) and then bringing them back down to the KSC. Below is the payload mounted on my Reusable Rocket launch vehicle. I thought at first I might mount the plane flat on its back on top to make the payload shorter, but that way lies death and destruction. So I mounted it pointing nose up with a radial decoupler and a girder and plate and several struts...and it was surprisingly stable. For this manned test flight, brave Aldner Kerman volunteered to fly the ship into orbit and back (but the plane does have a OKTO2 probe body mounted on the back of the Avionics package on the tail, so it can be flown unmanned).

The Reusable Rocket deposited the 22-tone payload (off in the distance behind the sustainer) into orbit with lots of fuel to spare, then the sustainer stage went on its merry way (eventually to return to the KSC itself). For the Laythe mission, the BirdDog/RefuelingStation payload would be docked at this point to a Standard Nuclear Tug for the push out to Laythe (it will go unmanned, since the kerbels will be riding in their spacious Laythe space station).

When the radial separator is fired, the two parts of the ship go tumbling apart. It looks a bit hairy, but they move apart fast enough that they are in no danger of collision.

I handled the reentry of the Refueling Station first, while Aldner waited in orbit so he would know where to land if the station ended up far off target. But I was using MechJeb's landing point prediction to target the station to the KSC, so there was no problem. The Refueling station has seven tanks of jet fuel on board (enough to completely refuel the BirdDog three and a half times...assuming it lasts that long). It also has twelve of the gold torroidal tanks for the fuel/oxidizer for the retro rockets, which are six 24-77 radial engines. There was a tendency for the station to yaw during retro burn because it is not perfectly balanced (I have added a gigantor solar array to the next version as a counterweight for the girder).

Reentry fire surrounds the Refueling Station as it drops in over KSC. In a perfect world, there would be a nice heat shield under those tanks, and the booms would fold upward, but I didn't feel like putting that much effort into the refueling station. Although having hinges on those refueling booms would potentially make them more adjustable...so maybe I'll add some Damed Robotics fun to this ship as well.

Six parachutes bring the Refueling Station in at 7-point-something meters per second, which the lander gear handles fine.

I considered different ways of mounting retro rockets onto the BirdDog, but since I had that nice docking port sitting at the CG, I attached a retro pack consisting of five gold torroidal tanks and an LV-909 engine. There is also a flat OKTO2 probe body in there, too, to make lining up the burn easier. After the retro burn and targeting, there were still two full tanks in the retro pack. But I like to have extra fuel more than I like having not enough fuel. I'm funny that way.

Below the retro pack has been decoupled and Aldner has the BirdDog pointed nose to prograde. The plane has no RCS...but it's a small plane, and the torque of the cockpit is plenty strong to control it through reentry. The refueling station also has no RCS, and the probe body torque was just fine for controlling that as well.

That's one hot BirdDog! I presume that there is some fine ablative material protecting the surface of the plane (there are what appear to nice heat shield tiles on the bottom of the cockpit part). But the rover wheels looked kind of vulnerable hanging out in the breeze, so I placed some token reentry shields in front of them.

After the reentry effects abate, the rover wheel heat shield plates are jettisoned, and Aldner is free to fire up the jet engine. I replaced the TurboJet engine from my previous test flight version of the BirdDog with a regular jet engine because I think the regular jet engine will work fine at the lower altitudes I'll be mostly flying at on Laythe, but especially because it is shorter and therefore less likely to get damaged while roving across the surface.

Below, Aldner has the jet engine running at half throttle as he does a 180 after overshooting the KSC. I'm sure he didn't deliberately blast overhead just to rattle all the windows with his sonic boom. I don't find the rudder particularly useful when flying this plane...I mostly just fly with the canards to bank and pull turns.

Aldner lines up on the runway, thens sets the BirdDog down gently with no problems. I guess he has assured himself a seat on the upcoming Laythe mission.

Raising the nose gear of the BirdDog lowers the rover wheels to the ground. Aldner then drove it over to the Refueling Station and tried docking with each of the three refueling ports. Once the ports look to be aligned, the nose gear is lowered, lifting up the plane a little to make contact between the docking ports. Because the Refueling Station was not perfectly level, some of the ports were easier to dock with than others, but Aldner managed to successfully dock with all three. The docking ports on the ends of the refueling booms are tilted one notch because the BirdDog has a slight nose-up attitude when its front landing gear is down. I had previous tested and tweaked the boom positions to be sure the BirdDog would fit correctly.

Later, I used the retro engines on the Refueling Station to 'bump' the Station up and back down a little (a very tiny hop) to see if that could be done...and it worked well even in Kerbin's gravity. If none of the booms are lining up well, this is an option for jiggling their positions slightly (since the landing gear with shift a bit during the bump).

Now I just need to launch another BirdDog (unmanned) and dock it to a Nuclear Tug... and then another ship will be ready for the Laythe fleet (as we have to wait about a Kerbin year for the next Jool launch window).

[RawChicken]

No SAS? I would add SAS and ram air intakes

[Levelord]

This is my Laythe Plane all terrain vehicle. I really liked your refuel station and it looks like it's just the right height for my plane too. I'd love to use it when you eventually release it.

[RoboRay]

I would add SAS and ram air intakes

Ram intakes don't offer any advantage over others for a low-altitude aircraft. In fact, all of the other intakes are actually more effective down low. It's only in high-altitude hypersonic flight that the ram intakes are by far the best choice.

Edited April 26, 2013 by RoboRay

[Brotoro]

This is my Laythe Plane all terrain vehicle. I really liked your refuel station and it looks like it's just the right height for my plane too. I'd love to use it when you eventually release it.

Very cool ship! It reminds me of a snow speeder. How hard is it to fly? Do you run into balance problems as fuel is used up?

[Brotoro]

No SAS? I would add SAS and ram air intakes

The current version does have ram air intakes. What advantages would adding SAS give me? I have to admit that I haven't used SAS on any of my ships in a long time.

[Levelord]

Very cool ship! It reminds me of a snow speeder. How hard is it to fly? Do you run into balance problems as fuel is used up?

I've run the ship on almost empty before, but I've never run into balance problems in atmosphere because the lift of the wings help cancel it out. It gets a bit off balance when using VTOL in space (replace the jets with aerospikes), but I usually use the LV-909 engines in space, so that isn't an issue for me.

The ship drains fuel radially inwards, instead of draining from front to back, which means the center of mass doesn't shift around like in conventional planes. It also means that my plane doesn't flip over when transitioning into SSTO flight, because the weight is still distributed forwards.

[zarakon]

No SAS? I would add SAS and ram air intakes

Avionics nosecone is basically the same as ASAS, but without the I part of the PID controller. It resists change without trying to actually go back to its original position, so you can still steer the plane. On small planes, it's very effective at preventing oversteering

[Brotoro]

With 2 ram intakes and some throttle management, you should be able to get that up to almost 2000 m/s and circumnavigate Kerbin at 30+km altitude

When the engine flames out, immediately kill the throttle (x) then throttle it back up to slightly lower than it was when it flamed out. You can get a lot more speed and altitude by repeating this until you're running on nearly zero throttle

I stripped off all the rover parts, put the TurboJet back on, replaced one of the jet fuel tanks with a fuel/oxidizer tank, added four of the 24-77 rocket engines, and tried to fly the plane to space. I could get it up and flying at around 30K at around 1/4 throttle, but I couldn't seem to get it to keep going at a lower throttle unless I also kicked in the rocket engines. Once I got it up to 2,000 m/s over 30K, I throttled up to full on the rocket engines (and when the jet engines flamed out for the last time I shut them down and closed the air intakes). I didn't manage to make orbit, but I did get it into a trajectory that peaked a 75,000 meters and arced nearly halfway around the planet.

But with all fuel gone, I came back down to a very flat area at night. A very flat, wet area with no land in sight. And without the weight of the rover wheels and batteries up front, and the weight of those little rocket engines in back, the plane wanted to pitch up out of control if I was not very vigilant. Just before landing I let my speed drop too low and the plane began pitching way up and oscillating back down. Splashdown ripped the plane apart, but the cockpit and front landing gear (and Corfrey Kerman) survived.

You know what they say... "And landing you can swim away from..."

[Brotoro]

I tried a couple more times to fly the modified (stripped down) BirdDog to orbit... but I always came up a little short. The best I did was an apoapsis of 110 km and a periapsis of 47 km... and another splashdown in the ocean that required the Navy fish Corfrey out of the drink again. So, as much as I have come to distrust the immediate urge to add MOAR FUEL, I modified the plane by adding another half tank of fuel/oxidizer (which helped with the CG after using the fuel up as well). And...I got into orbit:

With 31 units of oxidizer left (and a bit more fuel), the ship had 204 m/s of delta-V left. So after a day in space, I fired the rocket engines again and brought the ship back (using up most of the oxidizer in the process).

Reentry heading toward KSC, which I passed over at about 14,000 meters.

I had a little jet fuel left to run the engines a little to help me line up on the runway, then landed without a problem.

Almost out of fuel, Corfrey Kerman has returned safely to KSC. So ends my first successful SSTO plane flight.

[bsalis]

So are you going to take that thing to Laythe now or what?

[Brotoro]

So are you going to take that thing to Laythe now or what?

Got sidetracked playing with planes. But all of the hardware has been boosted into orbit and attached to nuclear tugs, and the tugs have had their tanks topped off. The armada will consist of five ships:

Laythe Space Station and Kerbin-return crew module are docked to Nuke Tug 1.

Laythe Surface Base and Folding Rover are docked to Nuke Tug 2.

Extra Fuel tanks are docked to Nuke Tug 3.

BirdDog plane/rover and its Refueling Station are docked to Nuke Tug 5.

Nuke Tug 4b is currently docked to the Laythe Space Station awaiting the 4-kerbal crew to bring up the SSTO Crew Carrier (Laythe version). After it docks to the station, the crew will transfer to the station for the trip out, and the empty SSTO Crew Carrier will be attached to Nuke Tug 4b for the trip to Laythe.

...but I don't want to launch the crew until the Jool launch window is closer.

All of this is being done in "Armada Mode" rather than trying to build one gigantic ship because I've been launching the parts on my Reusable Rocket launch vehicle, which has limited payload capacity.

[tavert]

I think I may go that route, since the group of islands I'll be exploring aren't that far apart, and because the shorter jet engine will be less likely to get banged off the tail while roving around.

Here's some data from the part.cfg's to compare the two jet engines: http://i.imgur.com/iRkpRRv.jpg

The basic jet gives more thrust up to about 150 m/s (and it's lighter and more compact), and better Isp for atmospheric pressure higher than about 0.56 atm (below ~3 km altitude on Kerbin, ~1.5 km on Laythe).

[jdmgto]

I really like the avionics package on the tail. It reminds me a lot of the FB-111E. It's a very slick looking little plane overall.

[Brotoro]

I spent most of my free time this weekend sending hardware to Laythe. Let me tell you: Handling five interplanetary ships at once is not five times harder than handling one ship; maybe 5-squared times harder.

Anyway, among other payloads was the BirdDog and its Gas Station, which are now safely at Laythe Base. Below is the picture of Aldner (who flew down in the plane). That's not the Gas Station in the background...that's the main base habitat and lab. Aldner landed the plane a couple kilometers away (didn't want to hit anything valuable), then drove it over in rover mode. Soon comes the exploring...but I'm all kerballed out for now.

Edited April 29, 2013 by Brotoro

[Brotoro]

I have tested the BirdDog plane on Laythe by sending it on a flight to the north pole and back (from my base near the equator...mission report later). As long as I was doing this long, somewhat boring over-the-ocean flight, I tried to gather data to see if I could figure out the best cruising altitude for this plane on Laythe. All of the measurements below were taken with the throttle at 1/3 position.

I started out with a level flight at 3000 meters and took data (speed, engine Isp, fuel flow rate...you get the Isp and fuel flow rate by right-clicking on the jet engine). Then I went up to 4000 meters and repeated. Then 5000...6000...7000...8000...9000...10000. I was having to give more and more pitch-up trim to keep the plane flying level as the altitude increased, and at 11,000 meters the plane was getting close to the angle where it wants to violently pitch up, so I ended this test at 10,000 meters. But I went back down to 3000 meters to recheck the baseline data, then did 2000 and 1000 and back up to 3000 again. Here are the data:

So I have questions for you airplane guys:

I was surprised to see that the "Fuel Flow Rate" was changing with altitude. I figured the fuel flow rate would correlated with the throttle position. But it seems that the engine is using fuel faster at higher altitudes with the throttle setting unchanged. And the decreasing Isp follows this increase in fuel consumption. This adjustment of fuel flow rate is something the jet engine automatically does?

What the heck are the units of the Fuel Flow Rate?? It is listed as "Fuel Flow Rate U" as if U is some kind of unit, but what is that supposed to be? I would assume it would have to be something like liters/sec or kg/sec.

In either case, I presume I would maximize the range my plane can fly on a load of fuel by maximizing the Speed/FuelFlowRate, right? In which case it appears that my plane (which has a standard jet engine and two ram air intakes) is more efficient the higher it gets (up to the limit where I feel it is safe to control on long tedious flights where you may not be on top of controlling it every moment). Certainly the Isp of the engine is decreasing and the fuel flow rate is increasing with altitude, but the increased speed (due to decreased aerodynamic drag) more than compensates for this.

The other thing I noticed by rechecking my measurements at 3000 meters was that the plane was flying faster at a given altitude as time went on. This is not surprising, I suppose, since it is using fuel and becoming lighter. But it does mean that the measurements taken later are skewed a bit higher because they were taken when the plane was lighter. I did not take time data, but I think each of these measurements took roughly the same amount of time (get the plane to altitude, level off, get trimmed, be sure it's trimmed...then take data), so the measurements are roughly equally spaced in time. The increase in performance from the first measurement at 3000 meters to the last measurement at 3000 meters is about 5.7%, so if I assumed that that performance gain factor was increasing linearly over time, and I "adjusted" the Speed/FuelFlowRate results to reflect it... and the overall trend of the results does not change.

So does all this make sense?

[Levelord]

The other thing I noticed by rechecking my measurements at 3000 meters was that the plane was flying faster at a given altitude as time went on. This is not surprising, I suppose, since it is using fuel and becoming lighter. But it does mean that the measurements taken later are skewed a bit higher because they were taken when the plane was lighter.

You could enable infinite fuel to fix the fuel weight and perform the experiment again to see if the results are different I guess...