X-plane as educational program

It seems that X-plane educates aerodynamics, what to expect and think about different things. I was originally saying that I am not so interested in transonic region but rather interested in high altitude. I have been reading about these, but some little things like tinkering with X-plane can cause heureka moments.

And here is what happened:
I have a model of my twin concept in X-plane simulator (obviously, why wouldn’t I). So I set in the latest incarnation the engine critical altitude to 50000 ft (which is feasible with two turbos in cascade plus the mentioned electric turbo compounding). I used 110 hp per side (equivalent of Rotax 912ULS equipped with two turbos doing turbo normalization plus intercooler and after cooler).

I was reading Roskam couple of days ago and noticed that the transonic drag is not a problem if the speed is mach 0.2 or below or not that much above that, e.g. 0.3-0.4 is still quite fine. So I was thinking that maybe it doesn’t get that high that it would become a consideration.

So so obviously, I put the plane model to climb to 55000 ft with autopilot. I had previously added the mach meter to the hud. I came back checking how it flies after couple of tens of minutes. And oops: mach 0.56 when level at 55000 ft. The IAS was barely 100 kts. TAS was a quite a bit higher.

Then, I was thinking what happens to the Reynolds number. Indeed it gets smaller with altitude increasing. But interesting thing is what really happens, to which number it gets. I verified with atmosphere calculator, that indeed, the interesting Re range for this kind of concept with the AR=14 wing, it becomes 600000 – 1600000. That is _very_ low for an aircraft, which is full size and not a RC-model. So the low Re becomes after all a major consideration.

How a plane with AR=14 flies at 55000 ft? It requires _full_ trim aft (meaning nose high) to get the plane keep level – in this model. It became quite apparent that indeed, the tail volume coefficient is a more major concern at high altitude than at low altitude. And the control authority that felt fine at low altitude was not so fine at high altitude.

So this is what we have:
– High performance low Re airfoil is very necessary
– Cd at high lift coefficient is an important design point, the airfoil needs to be designed so that it gives high L/D at high lift coefficient rather than at low lift coefficient like for example NLF414F is targeting.
– A big tail with long enough moment arm
– Propeller with large diameter and possibly more blades than usual, e.g. 5 blades
– And of course, two turbos, intercooler, aftercooler, generator, battery, electric motor and a shaft between the prop and the engine.

Btw, my model is not yet available for download because it is not perfect, and it has couple of problems. It is very hard to get the splines right with straight sections edited by hand, and e.g. engine nacelles look really terrible at the moment. Anyway, it is a fun way for trying out things in practice.

Advertisements
    • dodlithr
    • January 29th, 2009

    X-Plane, yes, I have some ?free? version of that also and know that it was used for example in Rutan’s Space Ship One simulator. It should be some environment to do testing with hypothetical planes. Haven’t have the time to do so…. maybe soon.

    But if it was used in Rutan’s Space Ship One simulator, it should give reasonable results for high altitude flying also!!??

    http://www.scaled.com/projects/tierone/data_sheets/PDF/Posterboard%20-%20Simulator.pdf

    Usually low cost game simulators are not too realiable sources of flying qualities, but X-plane might be different? All is in the physics engine. If it is well done, it should give fair results.

    • dodlithr
    • January 29th, 2009

    X-Plane, yes, I have some ?free? version of that also and know that it was used for example in Rutan’s Space Ship One simulator. It should be some environment to do testing with hypothetical planes. Haven’t have the time to do so…. maybe soon.

    But if it was used in Rutan’s Space Ship One simulator, it should give reasonable results for high altitude flying also!!??

    http://www.scaled.com/projects/tierone/data_sheets/PDF/Posterboard%20-%20Simulator.pdf

    Usually low cost game simulators are not too realiable sources of flying qualities, but X-plane might be different? All is in the physics engine. If it is well done, it should give fair results.

    • dodlithr
    • January 29th, 2009

    naah…. after checking the Space Ship One prochyre it says:

    “The vehicle’s position and attitude are sent over a network to 12 display computers which utilize commercial graphic software to generate outside views.”

    So the X-Plane program is just generating the outside views ?? The actual simulator program is maybe different. But nice simulator, what so ever, 12 windows views at the same time.

    • dodlithr
    • January 29th, 2009

    naah…. after checking the Space Ship One prochyre it says:

    “The vehicle’s position and attitude are sent over a network to 12 display computers which utilize commercial graphic software to generate outside views.”

    So the X-Plane program is just generating the outside views ?? The actual simulator program is maybe different. But nice simulator, what so ever, 12 windows views at the same time.

    • Karoliina Salminen
    • January 29th, 2009

    The SpaceShipOne sim to my understanding is the commercial sim there. X-plane works so that you can put a network of 12 computers to render individual windows if you like. However, I can not be sure, because the link you showed is the all information I have about the matter.

    You can see what X-plane calculates from here:
    http://www.katix.org/karoliina/packages/twinconceptcycledump.txt

    • Karoliina Salminen
    • January 29th, 2009

    The SpaceShipOne sim to my understanding is the commercial sim there. X-plane works so that you can put a network of 12 computers to render individual windows if you like. However, I can not be sure, because the link you showed is the all information I have about the matter.

    You can see what X-plane calculates from here:
    http://www.katix.org/karoliina/packages/twinconceptcycledump.txt

    • Karoliina Salminen
    • January 29th, 2009

    The above copy-paste from the cycle dump is just a short moment of the plane flying. X-plane handles these calculations couple of times per second.

    • Karoliina Salminen
    • January 29th, 2009

    The above copy-paste from the cycle dump is just a short moment of the plane flying. X-plane handles these calculations couple of times per second.

    • Karoliina Salminen
    • January 29th, 2009

    One more addition still:
    The difference on X-plane and Microsoft Flight Simulator is that X-plane calculates aerodynamic calculations and uses real values there to get the results. It is all real thing. It is not 100% accurate and there are known shortcomings to its model. X-plane started from a some kind of aircraft design software and ended up being a sim.

    However, in comparison: MS Flight simulator does not calculate these things, but it only simulates with a parametrized model of something flying but it really does not fly, but is just a sophisticated arcade type of simulation. MS Flight sim started from a game, not a airplane design program.

    • Karoliina Salminen
    • January 29th, 2009

    One more addition still:
    The difference on X-plane and Microsoft Flight Simulator is that X-plane calculates aerodynamic calculations and uses real values there to get the results. It is all real thing. It is not 100% accurate and there are known shortcomings to its model. X-plane started from a some kind of aircraft design software and ended up being a sim.

    However, in comparison: MS Flight simulator does not calculate these things, but it only simulates with a parametrized model of something flying but it really does not fly, but is just a sophisticated arcade type of simulation. MS Flight sim started from a game, not a airplane design program.

    • dodlithr
    • January 30th, 2009

    Space Ship One simulator uses X-Plane. Check next link ->

    "Scaled Composites: Now these are
    the guys that built Spaceship One. They used X-plane for the visualization of their Spaceship One simulator: they'd be seeing X-plane graphics out the windows."

    http://forum.macologist.org/showthread.php?t=1676

    But for the physics they must use their own creations, I belive. The jump to the space is so much outside the normal airplane simulation and also the several phases of the full flight that it demands special programming.

    BTW: If you need a good physics core for airplane simulation, I have one available (source code) which does excellent simulation. I did some work to dig it up. It is originally the NASA LaRCSim.

    http://albatross-uav.org/index.php/LaRCSim_Architecture

    One could use it with the X-Plane, so that X-plane generated the views and the xxxSim did all the calculations. If you need extra to X-Plane.

    The sim core is not very large program. I think most of the code in a full simulator is due to the graphics.

    • dodlithr
    • January 30th, 2009

    Space Ship One simulator uses X-Plane. Check next link ->

    "Scaled Composites: Now these are
    the guys that built Spaceship One. They used X-plane for the visualization of their Spaceship One simulator: they'd be seeing X-plane graphics out the windows."

    http://forum.macologist.org/showthread.php?t=1676

    But for the physics they must use their own creations, I belive. The jump to the space is so much outside the normal airplane simulation and also the several phases of the full flight that it demands special programming.

    BTW: If you need a good physics core for airplane simulation, I have one available (source code) which does excellent simulation. I did some work to dig it up. It is originally the NASA LaRCSim.

    http://albatross-uav.org/index.php/LaRCSim_Architecture

    One could use it with the X-Plane, so that X-plane generated the views and the xxxSim did all the calculations. If you need extra to X-Plane.

    The sim core is not very large program. I think most of the code in a full simulator is due to the graphics.

    • Kestenan
    • January 31st, 2009

    dodlithr, X-plane is an exceptional program, and is designed to simulate flight from the surface of earth (or mars for that matter) into pure vacuum. Space simulation is FAR simpler than atmospheric flight, so you need to be suprised to know that x-plane can do it.

    • Kestenan
    • January 31st, 2009

    dodlithr, X-plane is an exceptional program, and is designed to simulate flight from the surface of earth (or mars for that matter) into pure vacuum. Space simulation is FAR simpler than atmospheric flight, so you need to be suprised to know that x-plane can do it.

  1. No trackbacks yet.

You must be logged in to post a comment.
%d bloggers like this: