Archive for the ‘Homebuilt’ Category

I just updated the blog title and again just watched the page and the blurb.

It’s when we start working together that the real healing takes place, … It’s when we start spilling our sweat, and not our blood.

It’s a quote of David Hume, my favorite philosopher. I haven’t read his books though. I was reading a Finnish translation of one but it seemed so tedious with the language that I couldn’t bother. So me favouring him is based on the works of others about him.

The quote reminded me of the conflicts that I’m witnessing. The subject line matter needs to be done. At the moment many parts of climate software seem to be science software – written by people in a hurry with little planning, and code that has seen different people adding bits and pieces here and there, making it a big mess. Fortran and supercomputers and all that. Well, most software is a mess. Twenty man years, said MT. That’s a small amount of money considering how much is at stake and even compared to the amount of huffing and puffing efforts around the subject. I am available.

What else needs healing and sweat spilling? Well, quite many things. Including stuff in my personal life.

There are lots of old (sometimes Fortran) code packages hanging around. Nuclear stuff, rocket trajectory calculations, rocket engine chemical/thermodynamics performance… You name it, anything a young man is interested in seems to depend on these archaic pieces of software. So there’s a lot of potential work here but it seems so big for just a lone person to do much on their own free time.

The blog title picture is just some hinge flapped NACA foils simulated with the vortex lattice method in QFLR5. That actually IS a free software project, mostly by Andre Deperrois and uses Mark Drela’s XFOIL for 2D calcs. In the picture, the front wing has NACA 4415 with 6 m span, 1 m chord, 25% chord 15 degree full span flap, and the tail is a NACA 0012 with 2 m span 0.5 m chord, 40% flap or elevator at -15 degrees. Flying at 5 degrees AoA (plus 4 deg to the front wing) and 18.9 m/s, lifting about 2000 N. Absolutely no guarantees about the results.

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It seems the US is getting onto private aviation bashing. No trailerable aircraft to airports or automobile gasoline for the engines. The former could be seen to be motivated by trying to prevent building bombs into aircraft, the latter is a bit more obscure, probably having to do with ethanol additives that some aircraft engines (or fuel pipes and seals) can’t handle. But it’s peculiar to outright ban auto fuel. The people can deal with this themselves. Probably you could easily produce ethanol kits for most auto fuel engine systems.

I’m reminded of Finnish automobile laws which are probably the strictest in the world. You can’t do this or that and even if you do something out of the ordinary within the very narrow limits, your new vehicle will probably be taxed to death. Even ordinary new or used imported cars have high taxes in Finland and gasoline costs over 1.3 euros per liter. The roads take a lot of effort to build and maintain because the harsh winters cause the ground to freeze, causing bumps in anything but very deeply and thoroughly based roads, the snow has to be plowed and salt is dispensed to melt it, lots of streetlights are used since the winters are dark, frequent repaving is needed because of winter tires grinding the asphalt etc. This money has to be taken from somewhere. That I understand.

But try to bring a used car from say Germany to Finland. It’s a disaster. A friend of mine spent the summer in central Europe and bought a decent smallish German car for 1500 euros. He drove around Europe a few thousand kilometers with it with the temporary registration and everything worked fine. I was on a trip too and joined him in Poland and we drove the car to Finland. It was a well working machine with no problems whatsoever, I’ve driven worse perfectly legal vehicles in Finland. It even had air conditioning which made the trip nice. But when he arrived in Finland, the problems started piling. First lots of customs payments, then he had to bring the car for checkup so it could be registered in Finland. Just that exact model had not been imported to Finland. The inspector demanded some changes to be made at a repair shop (changes that would not affect the car’s function in any way, may I add!), to make the car resemble more its ordinary sibling model. Yet when some were made at a great cost, it was discovered by another inspector the changes were actually wrong. It was made clear that the car could not be registered. My friend contemplated a lawsuit, but here they take so many years and so much money. In the end the perfectly good drivable and safe car ended up to be crushed. All because of stupid overstrict laws and an incompetent inspection system. This is not protecting road safety, it’s protecting local car dealers.

Vehicle changes and registrations are really a complex world here. There’s a group of people working on an “open source hardware” electric conversion of Toyota Corolla, sähköautot.fi. Even the prime minister has promised tax exemptions for electric vehicles but I think at the moment they’re taxed as harshly as diesel vehicles (which is much more than gasoline, but the fuel is cheaper – but for electrics the fuel is cheaper anyway!). Same with a guy who has a home made biogas facility at his cow farm in central Finland. The overregulation is strangling innovation and experimentation. Meanwhile in Sweden they are experimenting with all kinds of alternative fuels and give perks like free parking to less polluting vehicles. The Finnish car factory in Uusikaupunki that used to do Porsche Boxters is now changing over to electric vehicles to be on the leading edge. And none of them will be on sale locally, all for export, because of the tax system and regulations. Someone should wake up!

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Someone was asking on ARocket about where to start with building a differentially throttled hovering vehicle. Lots of advice were given by various people. I’ll show some stuff I quickly sketched back in 2007 with Simulink. It’s such an easy to use and awesome software (especially compared to a recent short battling with LabView), that whipping up any control system or any process or system models are really quick jobs.

This is just some really trivial basics, it doesn’t take into account nearly enough things to produce a real hovering vehicle. I guess it’s just a way to show how things could be started.

So, here’s a pic of a simple one-dimensional rotational feedback system. Just tested some feedback coefficient values for the PD controller.

1) You can see the placeholder “guidance algorithm” output at the top left “scope” graph. This is the reference or target value of the angle where we want the vehicle to be. At the start it’s giving a desired angle of zero radians, then from 4 seconds onwards it suddenly wants 0.5 radians, then again zero after 6 seconds. This could be holding a tilt for a while for getting up some lateral velocity for a transverse move.

2)  Below that, you see Theta, the angle that the vehicle actually had during the simulation. It follows the desired angle quite nicely. Below Theta, there’s omega, the angular velocity.

3) The tilting is done by throttling the two thrusters. At top center and top right you can see the values of the throttles. Since this thing only concerns tilt and not stationary hovering, the throttles are at zero when the vehicle is at the right attitude (reference=Theta) and there’s no angular velocity. When the refence is moved, at 4 seconds, throttle 1 shoots up for a while and the vehicle starts tilting. At around 4.8 seconds the other thruster, throttle 2 shoots up to stop the rotation, since the vehicle is nearing the desired angle.

You can see from the block diagram how the error value, E = theta – reference is calculated. And also omega is used. From these the throttle values are calculated, simply by Throttle1 = E*Kp1 + omega*Kd1 and so on. By fiddling with the Kp and Kd values, called gains, one can tune the system. The values currently are just some I quickly tried back then.  This Simulink model actually has a bug, a sign error. The error signal’s difference calculation is backwards, hence Kp1 and Kd1 are negative. It should be the other way around.

You can tune the model. Basically, raising the proportional values makes the system faster (reach desired values quicker) but gives overshooting and can make the system oscillate unstably. Higher derivative gains remove the tendency to oscillate, but the system becomes more sensitive to noise (noise can after all have large derivatives). If the vehicle had problems of always staying some amount off from the final required attitude value, an error integrator could be added that would fine tune the vehicle a little (making it a PID controller). This is probably not needed here though – the guidance system could notice if the vehicle travels somewhere it doesn’t want it to go.

The MDL file for the above is available here.

This is just a very quick first brush analysis, there are much much more things to take into account. The other tilt axis, roll, the need  to actually stay airborne (altitude or vertical velocity feedback loop) that ties into the throttle values too. One could abstract this tilt in one axis to a single control block, and produce another similar block for altitude holding, then couple these blocks into a whole system of altitude and tilt holding (by mixing the throttle values). This should avoid clutter and enable one to isolate problems.

Also, one should add some noise to the sensed angle vs real angle as gyro noise seems to be a real issue for VTVL vehicles. One wouldn’t want to tune a PD controller’s values in a noiseless simulator and then find out it gets wildly out of control in the real world. Even when not simulating noise, one can be quite conservative with the tuning values, and that helps too. The throttles probably would be another source of errors as well, if one used ball valves like here. One could also use pulse width modulated solenoids (John Carmack is fond of those for quick work) and those should be modeled. Digital valves (for liquids) have also improved lately, and hydraulics uses are emerging.

I’ve only done real world PID stuff on lab experiments. But it’s still very cool to see it work. It can balance a ball on an unsteady position on a moving cart, which humans have trouble with using a joystick, and the math in the controller is not complex since linear approximations can be used for that problem.

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Xombie NOW

Live stream just went up at http://qik.com/video/312581

they should be flying at 45 past whatever hour it is now in your time zone. Now on the pad loading propellants and helium.


And they did it! Congratulations! Also great accuracy.

The live cellphone video of the second flight was shot from quite close: http://qik.com/video/3126566

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Armadillo finally won L2 already.

Masten and Unreasonable are still flying for second place I think (I’m not 100% clear on the rules) today!

Spacetransportnews is the place to watch all this. (Or it has the links collected.)

It’s historical in a sense. These rockets will serve as the basis for reusable sounding rockets, possibly high altitude tourist vehicles and later orbital system lower or upper stages. When the operations are routine and landings safe, the cost per flight goes down orders of magnitude, compared to ordinary rockets.

A new era for rocketry is dawning.


Update: This is the twitter account to follow: http://twitter.com/mastenspace

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If you use a fifties shape, active roll damping is a really good idea at subsonic speeds at least. Old NASA video of some wind tunnel flying models. (via Secret Projects forum)

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Self Sufficiency

Armed with logic and general knowledge, Rick Boozer built an FM radio meteor detector. It’s a cool story. I feel ashamed to be so lazy as to never do anything cool in my spare time. I guess the internet uses up so much of it. Maybe in general people create far less physical things nowadays.

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62 mile club has a writeup of a beta “customer qualification program” for XCOR’s Lynx suborbital craft. This highlights the differences and current state of play. Rocketships will not be as safe as airliners in the near future, and they don’t need to be. There are millions of things that are less safe than airliners – scuba diving, ballooning, general aviation, motorcycling, probably even driving a car. And yet people do those things because they have the judgement and can decide for themselves.

The key difference is an informed consent. The suborbital rocket traveler should be told of the risks truthfully so that they can decide for themselves if they want to do it or not. This, I gather, has always been XCOR’s principle.

Airlines are not directed at such customers because they are a mass means of travel – the customer is not briefed specially but is expecting reasonably good safety – and there are thus governmental and intergovernmental bodies regulating the airlines and trying to constantly improve safety.

It would not make the slightest sense to regulate suborbital passenger rockets at this time at airline level – there are only a few passengers and the companies should have the time and resources to screen and brief them very well on what it will be like and what the risks are. (This is a must though – you shouldn’t advertise the service as something as safe as airlines.)

There should be some very simple regulation of rocketships regarding the risk to the uninvolved public of course – most companies deal with this adequately by just flying from remote enough locations. And of course there’s environmental regulation – it’s not cool to put tonnes of methanol into the ground water for example. Yet these are small no brainer issues (I’ve heard stories of over-eager environmental protection agencies though).

Nontoxic (or those that quickly decompose to such in nature) fuels and oxidizers should help a lot in this regard. Suborbital rocketry is not that performance critical anyway – it is a great way to find the lowest investment and operating cost approaches to rocketry – and these drive towards “nice” systems. Safe, easy, nontoxic, nonhazardous, redundant.

Regeneratively cooled LOX-ethanol or LOX-methane engines could be good in this regard – propellant spills and dumps are not that horrible to the environment or to the public, and the engine could in theory run indefinitely without any parts replaced if it is just refuelled.

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Human powered submarines:

Rather conventional seeming solutions, but nice anyway.

This is a more out there attempt. A flapping submarine, like a ray. It doesn’t seem to go very much anywhere when one compares to the propeller ones:

Festo has built an Air Ray, a remote controlled helium balloon with air muscles for flapping its wings, and it works nicely:

One possibility for future aircraft is incorporating flexibility again for morphing to increase performance.

Lisa Akoya already has a stretchy skin that comes out with the flaps between them and the main wing to give more wing area that enables low speed landings so the craft can stay in the ultralight category:

Reusable launch vehicles as well very likely need changing geometry to land comfortably.

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This is something I’ve been toying with for a while. A homebuilt single seater. Must be under 300 kg and stall under 20 m/s to enter ultralight regulations in Finland. A HKS 700 engine with 44 kW power would be nice (it’s modern, which is rare in aero engines), though it is quite big and the design struggles to keep the requirements with it.

Modeling with Blender (no landing gear in these models, it will be fixed and tricycle)

Light Version

Light Version

Cruise Version

Cruise Version

One of the design goals is very basic construction. Another is STOL performance. Yet another is that a 190+ cm tall pilot should have comfortable seating.

Aero analysis (just basics, mostly the wings, not the Blender models) with XFLR5:


Wing Streamlines Near Flap End

I’ve also toyed with a basic glider “airchair” idea as a starter project and looked at new foils for it to minimize wing size (XFLR5 has inverse foil design which is nice):

Very High Lift Foil for A Low Speed Glider

Very High Lift Foil for A Low Speed Glider

I’ve been exchanging info with Karoliina. Mini-Sytky, KR-1, Cri-Cri, Luciole and MAG-01 serve as the closest examples of similar designs, though there are marked differences.

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