Official FAR Craft Repository

[smunisto]

I seem to be falling through the cracks regarding the whole transonic flight theory.

From what I get, the large volume of air going through the engine, the more thrust it should have.

However I am unable to get the following craft past ~ Mach 1.2.

I will try flying it with the stock intakes oriented with the opening down, however unlike of a reason that seems...

Here's the gallery, I know the curves are not amazing, but I doubt that's the problem. Maybe it's too heavy?

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https://bg3.biz/cloud/index.php/s/bovgIyO9L3YF0wx

That is the craft file. It uses stock, the latest B9 dev version, the B9 Proc Wings, SpaceY's Heavy Lifter 1.25m rocket engiens and the Adjustable Landing Gear.

Edited June 28, 2015 by smunisto

[tetryds]

I seem to be falling through the cracks regarding the whole transonic flight theory.

From what I get, the large volume of air going through the engine, the more thrust it should have.

However I am unable to get the following craft past ~ Mach 1.2.

I will try flying it with the stock intakes oriented with the opening down, however unlike of a reason that seems...

Here's the gallery, I know the curves are not amazing, but I doubt that's the problem. Maybe it's too heavy?

http://imgur.com/a/Gom4F

https://bg3.biz/cloud/index.php/s/bovgIyO9L3YF0wx

That is the craft file. It uses stock, the latest B9 dev version, the B9 Proc Wings, SpaceY's Heavy Lifter 1.25m rocket engiens and the Adjustable Landing Gear.

You should try to keep the yellow graph as close to zero as possible.

What is killing your transonic efficiency is a very high wave drag area, 4.05m² is a lot.

Aim for something smaller than 1.2m² at first, with time you will get the hang of it.

A low-power transonic design is recommended to have transonic wave drag area of less than 0.8m².

[FourGreenFields]

What he said. Wave drag is very high.

Also, weight has nearly no impact on top speed.

I'd try lengthening those side-engine things, so they reach the canards (or at least almost). All my other changes would include changes on the wings, so I have no idea wether it would lead to major issues changing that.

Best shape of the green graph (or actually your plane, but a plane like that'll be useless) would be something like this https://upload.wikimedia.org/wikipedia/commons/3/33/Sears-Haack.png (just ignore that that thing isn't horizontal). Try to get as close as possible to that when placing importand stuff (like engines, wings, fuel tanks, etc.), and then smoothen it out using less importand stuff (goo canisters, small fuel tanks, chutes, airbrakes)

EDIT: However, a clean cut-off at the end is usually better than a way-too-steep rear.

Edited June 29, 2015 by FourGreenFields

[smunisto]

I tinkered it a bit in the morning(without elongating the "side-engine things", which I will do tonight), but the best I could get the wave drag area to was about 2.2. And that is with a completely non-functional wing design resembling the gross baby of an SR-71 and Su-47.

Even without any wings, canards and tails, the main body of the aircraft itself gives a wave drag area of 2.7. I guess I have to try an redesign it from scratch.

Thank you for the advices, I will be sure to ask again should I have any trouble.

[tetryds]

I tinkered it a bit in the morning(without elongating the "side-engine things", which I will do tonight), but the best I could get the wave drag area to was about 2.2. And that is with a completely non-functional wing design resembling the gross baby of an SR-71 and Su-47.

Even without any wings, canards and tails, the main body of the aircraft itself gives a wave drag area of 2.7. I guess I have to try an redesign it from scratch.

Thank you for the advices, I will be sure to ask again should I have any trouble.

No problem.

Also, it does not really matter if its high before you place the wings, area ruling is a tweak that you make when the design is about to be complete.

Adding things doesn't mean it will get worse, you often add things to improve it.

Check stock FAR Blitzableiter and FAR Colibri.

[capi3101]

I seem to be falling through the cracks regarding the whole transonic flight theory.

From what I get, the large volume of air going through the engine, the more thrust it should have.

However I am unable to get the following craft past ~ Mach 1.2.

You've gotten good advice from tetryds and FourGreenFields already, so I'll be brief. I'd start by moving the nacelle and main wings forward if you can do so without compromising the stability of your craft - you want to start by trying to smooth out the green curve there between the end of the cockpit and the leading edge of the wing. If that makes your craft unstable, I might suggest losing the Cessna Starship wingtips; it looks like you've got plenty of tail as is. You might also try adding a bit of strake from behind the cockpit up to the leading edge of the wing, something that will give you a bit of cranked arrow. Finally, since you're using B9, I'll ask what you're doing with the wing thickness. If you've left it as default, I might suggest leaving it thicker at the root but thinning it out towards the tip (you'd have to adjust the control surfaces to match as closely as possible). You'd be amazed at how much just doing that will reduce your wave drag area.

Best of luck.

[gary85]

ye it did work but it burned all the fuel like normal engine . Back in 0.25 i run it to moho and back with 1 tank .

now it bured all liquid hydrogen in min before i even reach orbit idk what im doing wrong now.

[blowfish]

Engines have much closer to real life Isp now (i.e. much lower). This has nothing to do with FAR. You will need more fuel than in previous versions.

[gary85]

this sux.

but no way it dont even have enough juice to go to kerbal orbit? ... happen this was like most efficient engine.

[kcs123]

Probably it is left unnoticed, but I have used small porions of B9PW to add some more crosssection area on strategic places on hull, where it was needed to flat out that yelow line.

Good thing about it that it could be filled with fuel, so it is not dead weight and offers posibility to create nice custom aerodynamic fuel tanks.

[blowfish]

this sux.

but no way it dont even have enough juice to go to kerbal orbit? ... happen this was like most efficient engine.

I will add that rocket Isp was also needed somewhat (this time perhaps not so realistic). But it shouldn't be expected that craft from an earlier version will still work as they did.

[Hodo]

So thanks to a challenge I saw I made this....

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XF-149 STOVL fighter.

[smunisto]

A new report(text-only for now, screens in about 2 hours):

Based on the recommendations given, a lot of try and error and some reading of basic information sources such as wikipedia, I was able to get my craft down to between 1.60 and 2.10 m² wave drag area.

I guess that due to the body shape and the limits in part adapters I am unable to fall down under 1.6 m².

My considerations for this are: the S2 is not the most aerodynamic cockpit and the lack of 4 engine S2 adapter force me to use side nacelles for 2 of the engines that don't fit in with the overall aircraft shape and force me to compromise the wing shape due to esthetics and possible wing root placement.

I have made a lot of FAR SSTOs, but that was back in the 0.20 days, where "intake spam" was a thing. I remember that it was quite possible to build an SSTO without RAPIERS and Sabres and with almost any shape whatsoever.

Nowadays with area ruling being a component of FAR, it seems a lot harder and more satisfying to actually create an SSTO, however limited the part choice in B9 is when it comes to making something without the aforementioned dual-mode engines.

Back to my actual craft: In the multiple versions of it I produced, I moved and elongated the side-engine nacelles, offset the canards back, attached the wings to the main body, elongated them and swept them back a bit, thinned them to be 0.120 at the root and 0.40 at the tip, removed the trailing edges where ailerons/elevons are present and conformed these and all other changes with the Stability graphs.

Now I am able to consistently reach between Mach 2.4 and Mach 3 at 15-20 km, however at this point all my designs start losing yaw stability and shortly after this, as speed and height increase, the craft rapidly veers off the prograde vector and stalls. Some of them tend to roll left ever since I launch, some of them start to exhibit this around 15km and > Mach 2.5. I wonder if I need more "wing", more engine "oomph", or some sort of anti-roll wing strakes.

I did experiment with strakes under the tail, but they raised the wave drag area too much and I gave up on the concept.

Please, do provide more suggestions when I post screens of the craft(s) in question.

[capi3101]

Loss of yaw stability is generally a sign that you need more tail, but I'll defer offering that up as advice until I see the revised design; I seem to recall saying something about "having enough tail" in just my last post...which, since you're now having yaw issues, is kinda embarrassing.

Stability analysis then - do a set of graphs and derivatives for Mach 2.5 at 17.5 k. Also run a simulation once you've got your numbers, plugging in "5" as your initial value for beta for the same altitude and speed. Post the results as screenies; let's see what's going on. Make sure to run the numbers wheels up.

[FourGreenFields]

For stability it depends on how desperate you are.

If you are very desperate add wieght to nose and bottom, or drag to the tail.

You can also add wings to the rear.

My personal favorite is high wing sweep though. Adds both yaw and roll stability. Other than that just make sure you got loads of pitch stability and you should be good.

[tetryds]

As you go faster your wings start to become less effective.

What happens then is that you have too little tail and too little control to compensate for that.

It's weird to imagine wings getting worse with speed, but that's super/hypersonic, it's not meant to be very intuitive.

@FGF: That is a delicated thing to suggest, as I said before, if you have too much dihedral effect it will overcompensate and can become unstable, esp. on small crafts.

[FourGreenFields]

@FGF: That is a delicated thing to suggest, as I said before, if you have too much dihedral effect it will overcompensate and can become unstable, esp. on small crafts.

Mounting the tail fin below the CoM would easily make up for that though.

[tetryds]

Mounting the tail fin below the CoM would easily make up for that though.

But that decreases roll stability, check what happened to the X-15.

[FourGreenFields]

But that decreases roll stability, check what happened to the X-15.

Which is just what we were trying to fix though... right? Dihedral effect adds alot to roll stability.

[tetryds]

Which is just what we were trying to fix though... right? Dihedral effect adds alot to roll stability.

Problem is, you get a lot of of dihedral effect from wing sweep when you are fast, but not when you are slower, so it can be dangerous if you fly the craft at different situations than what it was designed to be stable at.

[smunisto]

Here is one of the variants with which I manage to reach Mach 2.7-2.9 before it becomes too hard t control it.

It is interesting that at the given speeds and altitude it shows all green(and I am using TAC Fuel Balancer in order to keep the CoM stationary during atmo flight), but in actual flight, with some

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I just edited it and added a second wing section, basically to give the wings the inverted gull shape (Ju-87 style). I doubt that is very good for supersonic craft though. Will test that too and if it does not work, maybe I will just try dihedral by 5 degrees from the mid-line.

[tetryds]

Here is one of the variants with which I manage to reach Mach 2.7-2.9 before it becomes too hard t control it.

It is interesting that at the given speeds and altitude it shows all green(and I am using TAC Fuel Balancer in order to keep the CoM stationary during atmo flight), but in actual flight, with some

http://imgur.com/a/s2pYT

I just edited it and added a second wing section, basically to give the wings the inverted gull shape (Ju-87 style). I doubt that is very good for supersonic craft though. Will test that too and if it does not work, maybe I will just try dihedral by 5 degrees from the mid-line.

Did you use the rotation gizmo on absolute mode with swap to angle enabled to make sure the V tail is perfectly straight?

[smunisto]

Did you use the rotation gizmo on absolute mode with swap to angle enabled to make sure the V tail is perfectly straight?

Nope, I recently got back to actively playing KSP and still don't put the new editor tools to their full potential.

The rotation gizmo is the xyz spherical-looking gadget, ok, but could you guide me as to the rest of the process you described?

I was actually kinda pissed since forever at Bac9 for making these impossible-for-perfect-straight-alignment-on-surface-attach-parts-tail adapters. And you just told me there is a way to fix that.

And back on topic for the craft - I put a 5 degree(If memory serves, 1 step is 5 degrees) dihedral angle to the second iteration of the craft I just posted in addition to the already mentioned second elongating section.

It feels like it's flying much more stable at super/hypersonic speeds, but I found out two other design flaws of my craft - Not enough oxidizer for a circularization burn, I ignited the rocket engine at Mach 3 and 19km Ap, because the moment I hit Mach 3 the jet engines' temps skyrocketed(using stock heating while waiting for DRE's update). I guess one thing leads to another and I will have to swap the side nacelle-like tanks from LF only to LFO and add some of the newly implemented radiator parts.

[tetryds]

Nope, I recently got back to actively playing KSP and still don't put the new editor tools to their full potential.

The rotation gizmo is the xyz spherical-looking gadget, ok, but could you guide me as to the rest of the process you described?

I was actually kinda pissed since forever at Bac9 for making these impossible-for-perfect-straight-alignment-on-surface-attach-parts-tail adapters. And you just told me there is a way to fix that.

Yes, select rotation gizmo, click on the part you want, press F, turn on angle snap.

Then, click on any direction of the gizmo, it will snap to the nearby global snap angle.

Just move it around a bit and it will align perfectly with the SPH.

Now you can align anything, anywhere.

Good for landing gears

Edited July 1, 2015 by tetryds

[FourGreenFields]

Problem is, you get a lot of of dihedral effect from wing sweep when you are fast, but not when you are slower, so it can be dangerous if you fly the craft at different situations than what it was designed to be stable at.

Wouldn't realy call minor roll instability dangerous though (EDIT: At low speeds that is EDIT END; ). At least not while paying attention and keeping the roll assist on. Unless ofcourse your landing gear is very, very narrow... in which case you can always use chutes deployed just before touchdown to pull your tail back.

And btw: I gotta try what you said in the above post... chances are it'll be very usefull.

Edited June 30, 2015 by FourGreenFields