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


ferram4

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@B15HOP_xmen

I boosted the elevator controls to shorten the takeoff roll, by way of 'negative flaps'. IIRC some modern fly by wire aircraft also flip their tail feathers to induce pitch up, then revert to normal control ranges once airborne. F-35 is one of them.

Once you rotate, immediately revert elevators to normal position by hitting the '2' key twice or visually inspecting the ailerons. Accelerate to transonic at medium altitude, and you can then turn off SAS and fly with trim controls or gentle stick input.

Also see notes on DPCR in the craft description. It will indeed rip itself to pieces without DPCR since I needed to make the plane responsive all across its flight envelope.

Well if I could video it... it could be made to work :)

Ok my mistake, you managed to include proper flaps and I didn't take note until I flew it the way it was intended. And yes now it flies well...

One thing though. Why do you have a negative angle of attack? The nose of the plane is pointing down by 5 to 10 degrees but it stays level. I've been trying to achieve this with some of my SSTO's but so far the best I've done is manage to get a zero AoA at say 20km altitude vs yours which literally points slightly down and still doesn't descend. I'm going to do some more research into this. The nose of the plane destroyed itself on initial lift off but I'm unsure as to why.

So yes a good design. =) I try base my designs off the SR71 or there about. To me the SR71 is a bullet proof design at even mach 6. Now that the game has friction heat (deadly re-entry) I probably won't be doing all the magical cool stuff that I could achieve before. I'll have to try new techniques. Not to mention that the B9 Sabre M engine will probably vanish in v6 of B9 pack.

Edit:

@pandoras kitten

One issue also was that your plane tends to explode at >700km/h at low altitude. If I drop flaps (key: 2,2) before takeoff and just get upto 500km/h then lift off. Not long after the plane blows up. I'm not sure if it's just me or what. :(

Edit 2:

I just realised that enabling SAS causes dramas because stability assist tries to level the plane based on prograde. So SAS flips the plane upside down. :huh:

Edited by B15HOP_xmen
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Found it thanks!

I sort of understand what I need to do, but now the only problem I'm getting is that when I place wings on the plane the CoL actually goes FORWARD making it impossible to get it behind the CoM :(

No problem.

Don't worry that much about the COL position itself, the graphs and stability derivatives are much more reliable than an indicator.

While I agree it should be removed, lots of people would report that as a bug, and it serves well when you want to just fly, or have no idea how to read the graphs.

Make sure you update your FAR, by the way, it fixed the COL positions a bit.

The bad part about it is that it moves around, depending both on speed and AoA, so it's hard to define it like that.

And it's not even a COL, it's a Center of Pressure.

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Under NuFAR, I'm finding it easy to extract extreme speed from sleek, single fuselage ships, but very very difficult (good!) to get anything multi-fuselage (AKA "hot dog") up to speed. I'd be interested in seeing if anyone's managed to get a larger ship working yet.

I'll eventually get one of my huge planes a shot. I might need to wait for B9 v6 though because I rely on sabre engines to get up to mach 5 before I rocket out into space.

Here is my old SSTO from v0.9 KSP style FAR. (pre voxel) The thing flips out at mach 2 for no apparent reason. Even with crazy amounts of RCS and 4 huge control wheels. My guess is that B9 is screwed up. But that's my fault. haha =)

B6B9BC7A7958730658284CAFD6DAFC2496242AA1

Edited by B15HOP_xmen
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Hi, i'm new to tinkering with nuFAR transonic designs and i'm hoping someone could help me with my SSTO design.

The idea was a huge SSTO with integrated full science payload and ore processing for offworld refueling. I'm using tweakscale to get stock parts in the correct sizes.

vv6Irvz.jpg

Vi3QSry.jpg

hFsPUeI.jpg

UVntSSz.jpg

p7ckNrZ.jpg

Now, that plane flies well enough, but when i try to get it to orbit, problems arise. As far i can tell with nuFAR you have to jet to around 17,18 km height, achieve whatever speed you can, then burn upwards to orbit.

The plane gets to that height, i level out and accelerate. Around 800 m/s the nose starts pulling to the left hard (SAS and FAR stabilizers enabled), the plane starts to tumble, and aerodynamic pressure tears it to pieces.

I assume because the wings are too wide for a transonic design? Should i try a different ascent profile, just jet straight up? TWR is high enough. I just dont know if the LVNs can get me into an orbit. Don't think so, really.

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Hi, i'm new to tinkering with nuFAR transonic designs and i'm hoping someone could help me with my SSTO design.

The idea was a huge SSTO with integrated full science payload and ore processing for offworld refueling. I'm using tweakscale to get stock parts in the correct sizes.

http://i.imgur.com/vv6Irvz.jpg

http://i.imgur.com/Vi3QSry.jpg

http://i.imgur.com/hFsPUeI.jpg

http://i.imgur.com/UVntSSz.jpg

http://i.imgur.com/p7ckNrZ.jpg

Now, that plane flies well enough, but when i try to get it to orbit, problems arise. As far i can tell with nuFAR you have to jet to around 17,18 km height, achieve whatever speed you can, then burn upwards to orbit.

The plane gets to that height, i level out and accelerate. Around 800 m/s the nose starts pulling to the left hard (SAS and FAR stabilizers enabled), the plane starts to tumble, and aerodynamic pressure tears it to pieces.

I assume because the wings are too wide for a transonic design? Should i try a different ascent profile, just jet straight up? TWR is high enough. I just dont know if the LVNs can get me into an orbit. Don't think so, really.

Use "stabalisers" instead of "winglets." They provide more control at high speed.

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I'm finding that rocket designs that worked on 0.90 FAR are having too much drunken-like wobble now. I could usually fix that by having less authority on my winglets, but now I'm having to set them as low as 1 or 1.5, which means my gravity turn is taking forever and is not very efficient.

Is this expected behavior? I aim for around 1.3-1.6 (vacuum) TWR on the pad, but both the thrust and launch profile seem so much more finnicky than before.

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@6.forty: Looks like it happens when something breaks in B9 proc wings in setting up the wingtip, which probably causes everything to fall apart from then on. I'd take it over to the proc wings thread and see if they can help.

@tetryds: No, if it were a center of pressure it would tend to fly off into infinity as lift heads to 0. It's pretty close to an actual aerodynamic center now, though I still hate the damn thing with a passion.

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Hello, guys! Someone can explain me meaning of drag and area ruling selector? By default, it switched to "Moderate Drag, Moderate Area Ruling", but after selection "Full Drag, Strict Area Ruling" the rocketflip is gone. Which mode is more realistic accurate?

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Easy. No sudden changes in cross reference area from nose to tail and cross reference area can be wide.

http://i.imgur.com/YlWxRmy.jpg

I guess I don't really understand fully :/

Is it because my wings are really thin compared to my fuselage? How is it that massive tail on the back of your plane doesn't make everything crazy while the mild tail on mine creates the Valles Marineris XD

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I guess I don't really understand fully :/

Is it because my wings are really thin compared to my fuselage? How is it that massive tail on the back of your plane doesn't make everything crazy while the mild tail on mine creates the Valles Marineris XD

On kcs123's plane, the big tail surfaces begin right where the fuselage starts tapering. So the area is flowing smoothly from the fuselage into the tail.

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Farram, you're trying to determine what parts of the voxel mesh are wings, correct? Is there a field on the voxel data that could represent "this voxel was generated from the geometry of a part xxxxxxx"? If do, could certain parts be flagged as "wing" parts (such as, well, wing parts) and that flag would be transferred to the voxel metadata? The problem then would be identifying which parts deserve the "wing part" flag. Maybe metadata could be added to known parts using module manager (or by mod creators for their own parts), and an educated guess could be made based on certain .cfg file values if such a yes/no flag isn't present?

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I guess I don't really understand fully :/

Is it because my wings are really thin compared to my fuselage? How is it that massive tail on the back of your plane doesn't make everything crazy while the mild tail on mine creates the Valles Marineris XD

If you'd cut through your plane from above (right angle compared to the direction you want to fly towards) you get the cross section.

The area of that cross section needs to increase/decrease steadily.

If the yellow graph is too high, add more cross section = add more parts, or move parts there. If it is too low, move parts away, or make them clip into each other.

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I've increased my number of tail fins to 3 and it doesn't spin out anymore. The problem with getting to orbit remained, it was not enough thrust after all. I replaced the 3 LVN with a single mainsail (had to replace the main liquid fuel tank with rocket fuel) and i just managed to get a 130 km suborbital flight. On reentry, the mk1 fuselages exploded due to overheating, so i have to somehow fix that. Putting all of them above the wings perhaps? Also i have the distinct feeling the mk3 Monoprop tank is wayyyy to much. Or i need bigger monoprop engines.

@Bishop

Are stabilizers stock parts? I only see winglets. And no, i don't use winglets. The small front wings are tweakscaled S-Delta Wing and S-Elevon One's.

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So dreadfully I'm back with more tests, for the sake of science.

This time I did some trickery with MM to get the right mass, the main issue was surely that the cockpit is pretty heavy.

I taken to compare the Cessna 208 Caravan as its more popular and easier to find information on.

The Cessna Caravan

Wing Area: 25,95m²

Empty Weight: 2550 Kg

Cl and Cd: ?¿

Glide ratio: 1:14

Glide speed: 95 kias (48m/s)

Stall speed clean: 63 kias (33m/s)

Stall full flaps: 50 kias (26m/s)

I still couldn't find the coefficients for lift and drag, but foun the glide ratio and speed, which we derive it from, also the airfoil profile 'NACA 23017.424'.

References and additional info:

http://www.aopa.org/News-and-Video/All-News/2009/March/1/Turbine-Pilot-Cessna-Caravan-Sky-Truck

http://en.wikipedia.org/wiki/Cessna_208_Caravan

http://m-selig.ae.illinois.edu/ads/aircraft.html

=0.3&MNaca5DigitForm[posKey]=15_0&MNaca5DigitForm[thick]=17&MNaca5DigitForm[numPoints]=81&MNaca5DigitForm[cosSpace]=0&MNaca5DigitForm[cosSpace]=1&MNaca5DigitForm[closeTe]=0&yt0=Plot"]http://airfoiltools.com/airfoil/naca5digit?MNaca5DigitForm

screenshot_2015_05_11_14_26_14.png screenshot_2015_05_11_14_45_14.png

Area ref with only main wings place, which is the used as before. At first I tried the trickery to get the air intake to work as an engine. However it seems that the thrust pulling the plane was also pushing it :P.

screenshot_2015_05_11_14_49_39.png screenshot_2015_05_11_14_50_25.png

Stability data for the full craft, empty weight of 2534, main wing area of 25,3. This is indeed as close as I can get for comparison, reported stable minimum speed 51m/s. The wings mass have been strongly tuned down to accommodate the weight requirements.

screenshot_2015_05_11_14_56_39.png screenshot_2015_05_11_14_56_52.png

It smoothly rolls out at 45m/s, but thats mainly because of wrong incidence angle for the tail elevator. I'm also using EAS, as it must be indicating relative wing speed to the longitudinal axis, right?

screenshot_2015_05_11_14_59_04.png screenshot_2015_05_11_14_59_45.png screenshot_2015_05_11_15_00_10.png screenshot_2015_05_11_15_00_27.png screenshot_2015_05_11_15_00_40.png

Time for level flights, assistant to hold on altitude and heading. From the first picture throttling off, from 141,9m/s to 61,9m/s takes 1:10 minutes.

screenshot_2015_05_11_15_01_08.png screenshot_2015_05_11_15_02_06.png

Then I just try to maintain level to horizon to figure my glide ratio. 60 m/s but starts getting speed.

screenshot_2015_05_11_15_05_15.png screenshot_2015_05_11_15_05_22.png screenshot_2015_05_11_15_05_29.png

Now for the stall test, it happened around the 30m/s and took a bigger plunge this time, so its nearly ok.

screenshot_2015_05_11_15_08_48.png screenshot_2015_05_11_15_11_43.png

Now of powered level flight, minimum speed I could achieve, 65m/s clean and 45m/s flaps, a bit too high as this should be closer to a stall.

screenshot_2015_05_11_15_14_53.png screenshot_2015_05_11_15_15_46.png screenshot_2015_05_11_15_16_15.png screenshot_2015_05_11_15_16_33.png screenshot_2015_05_11_15_17_04.png

screenshot_2015_05_11_15_17_13.png screenshot_2015_05_11_15_17_23.png screenshot_2015_05_11_15_17_34.png screenshot_2015_05_11_15_17_37.png screenshot_2015_05_11_15_17_51.png

Now for another landing, not much scientific but fun. Came in on more or less expect glide scope but still took to long to slow down and flare, all powered off.

screenshot_2015_05_11_15_23_52.png screenshot_2015_05_11_15_24_22.png screenshot_2015_05_11_15_25_04.png screenshot_2015_05_11_15_26_03.png

My second attempt at landing with lower speed, coming from a much lower glide scope now. Ended up under estimating and plunged to a crash XD.

Conclusions

Lift to drag ratio seems close enough, speeds are lower, but considering that the plane in comparison has much efficient airfoil and FAR considers a symmetrical airfoil, it makes sense and is expected behavior.

Still it seems to glide a bit much, maybe the symmetrical airfoil should have a bit lower L/D ratio.

Considering the L/D ratio is ok, both coefficients could have a small tune up, eg, this will allow for the same gliding but more longitudinal braking, it would also make stalls more aggressive.

Another strong possibility is that surface drag is a bit week. Since the biggest symptom is the relative longitudinal speed gaining and not losing. maybe some test with objects without wings.

Finally, now I hope I've made some useful comparison. Let me know what you think.

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If you are flying on any sort of downslope, then it is perfectly normal to take a long time to slow. With sufficient downslope, you will be able maintain speed or even speed up (to a point, of course). Also, minutes is hardly a long time.

I suggest a visit to your local airport to watch a few planes land. Note how they come in low and slow (and that 50m/s is 180km/h) and consider that they have been slowing for some time. And next time you're on a plane, get a window seat over the wing and watch the flaps and spoilers. The spoilers don't come on "hard" until the plane is on the ground.

Subsonic drag is not too low for you. Your expectations of subsonic drag are too high. Remember that planes are designed to have high lift and low drag.

:D I didn't made myself clear :D Sorry I thx for the explanation but I'm a pilot and have a pretty good understanding of this, I juts didn't want to go t too deep, but here we go.

My concern is that I made a with a pretty high cross section and I got a glide ratio of 12 (L/D ratio in glide with optimal AoE). This is good (http://en.wikipedia.org/wiki/Lift-to-drag_ratio) but I don't think my design is as efficient as a 767, from the looks of my aircraft it should have the glide ratio of about 10 or less (its a damn brick :D ). This is just my personal guess, but since at landings I have trouble dropping speed, I say I'm about right.

This is what I mean with "Subsonic drag seems like too low for me". BUT this is minor! I'm not complaining , Loving the mod!

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I have a progress report on the wierdness that I've found out happenes when using nuFAR with TweakScale. I had posted earlier (page 890 thereabouts) that when scaling and moving parts sometimes the game would glitch and nuFAR wouldn't calculate the correct values and work correctly.

The trigger is using CTRL + Z to revert some changes done to the craft. After that all scaled parts are displayed with the correct visual mesh and the stats are correct, but the lift calculation works on the part being at 100% scale. It also seems to go wierd overall. I've built 20t aircraft without scaled part on them and 100m^2 wing surface area. It needed to go 120m/s at 10° AoA to get off the runway...

The bug is gone after I reload the game. If I open any craft with bugged wings it persists. FAR works together well with B9 pWings (havent tested the other variety pWings, couldn't get them to work). I use the up to date version of Tweak Scale.

I don't know whether this can be fixed from your side Ferram4, the developer of Tweak Scale (Pellinor) says that from his side using the scaling function it should return the correct size of mesh and visual mesh to the game for FAR to work with.

I have posted on this on the tweak scale thread too.

Thank you for looking into this.

4plains

Edit:

If KSP is not closed and reopened the bug gets progessivly worse with calculating lift. I know how to reproduce the bug, but I'm at a loss which part of the code it would come from. What kind of variable are you using for storing the value for lift in your code Ferram4? Integer or Floating point number? Could that be caused by a variable overflow?

Bug is gone as of updating to nuFAR 15.1 "Fanno". Good Job Ferram4

Edited by 4plains
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While working on a shuttle orbiter, I noticed that placing the engines moved the center of lift forward considerably. Here's one shot of the craft with the engines mounted, which shows the CoL roughly in the center of the craft, and another without the engines. I've also included a screenshot showing how the engines are mounted. They're attached to a tri-coupler that's offset into the shuttle.

y6XColt.jpg

Da6qWGK.jpg

Uh3zNr8.jpg

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