Dave Patrick Models Extra 330L
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Posts: 1284
Joined: 10/27/2002 From: St. Charles, MO, USA Status: offline
There is a big discussion of Rn in another thread. It is worth reading. Your Profili will let you calculate it. The larger it is the "better" the device in question will behave. If you calculate it for several wing chords and velocities you can get a feel for the Rn that gliders fly at, TOC airplanes, Delta Darts, etc. The only reason it is important is that a lot of aero characteristics vary with its magnitude.
Posts: 404
Joined: 6/14/2002 From: San Diego, CA, USA Status: offline
I had a looong read tonight. It was a juicy thread in more ways than one. I liked the scientific explanations and got a good feel for what Re is all about. Thanks, again!
I've included a CpX plot of my lifting body (it has many airfoil shapes over it's width, of which this is just one). XFoil misbehaved whenever it got the chance. I'm utterly exhausted from trying to get something out of it. I wish people would stop writing programs that use FORTRAN (as XFoil does). If you know what a "dusty deck" is you are not only a VERY seasoned computer scientist, but also someone who knows the evils of old FORTRAN libraries.
-Q.
[QUOTE]Originally posted by Ben Lanterman There is a big discussion of Rn in another thread. It is worth reading. Your Profili will let you calculate it. The larger it is the "better" the device in question will behave. If you calculate it for several wing chords and velocities you can get a feel for the Rn that gliders fly at, TOC airplanes, Delta Darts, etc. The only reason it is important is that a lot of aero characteristics vary with its magnitude. [/QUOTE]
Posts: 404
Joined: 6/14/2002 From: San Diego, CA, USA Status: offline
...and here is a polar plot of the lifting body section. Notice that the lifting body stalls way below the 11 degrees AoA of the airfoil data presented previously. I'm not sure this is a good thing. I'm gonna need to fly it to see. I suspect that AoA above 5 or 6 degrees will introduce a lot of drag and slow the plane down. I guess this is what happens to delta wings and flying wings?
Posts: 1284
Joined: 10/27/2002 From: St. Charles, MO, USA Status: offline
I hate Fortran in any form it came in. At one time to run our six-degree-of-freedom airplane response program just the data took 3 of those big fortran card boxes. We had to carry them to the input area and hopefully pick up the output later. Just one mispunch and it was cussing time. Or the immense joy of showing up and the operator confessing that he dropped some of the cards and they are now all mixed up. It was a time of wailing and tears. It was better than computing by hand but not by much! End of Rant.
I am a beginner at running the Profili/Xfoil program and I am still learning its independent streak. It is a great tool though and the price is unbeatable. For someone that likes things aerodynamic it is a lot of fun.
I am looking forward to seeing the final machine and flight test reports. You might consider carving a little one out of foam in the GWSelectric motor size to check out initial CG and control location, etc.
Posts: 4662
Joined: 6/23/2002 From: Palmdale,
CA, USA Status: offline
[QUOTE]Originally posted by Ben Lanterman I hate Fortran in any form it came in. At one time to run our six-degree-of-freedom airplane response program just the data took 3 of those big fortran card boxes. We had to carry them to the input area and hopefully pick up the output later. Just one mispunch and it was cussing time. Or the immense joy of showing up and the operator confessing that he dropped some of the cards and they are now all mixed up. It was a time of wailing and tears. It was better than computing by hand but not by much! End of Rant. .... [/QUOTE] . We had to punch up our own cards! And lick the street dry with our tongues... . I recall in the early Tristar design at the simulator in Rye Canyon one of the test pilots complaining about the way the simulator handled relatve to what he expected.. The old-hand simulator engineers scoffed and laughed.. "Old pilot, what does he know?" That lunch period I went thru all the aero data on the digital part of our hydrid computer, and found one Cd number for one Mach condition input with the decimal point one place off. This made the drag at that flight condition 10x what it should be. You could fly the simulator all around that area and never notice, but this guy flew right into it... (I don't recall if the plane's tail went up or down). I corrected that point, and all was lovely. And red faces among the "old hands". Loved it!
Posts: 1284
Joined: 10/27/2002 From: St. Charles, MO, USA Status: offline
I did mine walking backwards in the snow........
Enough!
Banktoturn, I haven't been able to find a source of the program that will run on a Mac which is also my primary computer. I guess we have to live with it until the world becomes enlightened.
I enjoy toys so recently bought a Compaq PC to run RealFlight on and also some other PC only programs. With RealFlight and Profili it is almost worth it.
Thanks for the info about the Mac version, or lack thereof. I have been thinking about getting a copy of VirtualPC, but for $200, I could almost have a cheap PC. I guess I'll mull it over for a while, or get my hands on a compiler and work on building it myself.
Posts: 87
Joined: 11/20/2002 From: Lancaster, CA, Status: offline
Q- the airfoil that you ran through XFOIL, is that the cross section of your entire fuselage? Unfortunelty, since you've said this is not a conventional airplane, I can't really comment on what might happen if the lifting body stalls. Also, I'm not sure XFOIL's results will be accurate or even apply in this situation. Lifting bodies are very different from conventional airfoils; they're basically very very low aspect ratio wings, and practically all their lift and drag comes from 3-D effects. Guess you'll have to fly it and see.
heh heh, fortran. They don't even teach fortran programming anymore. I think I was in one of the last classes that was offered. Kind of a shame, actually, as they replaced it with a MATLAB class that barely goes into programming. Still, when those guys hit their first hard core programming class, it's good for a Damn-I'm-Glad-I'm-Not-You laugh.
Welcome to the wonderful world of X-FOIL, where the program convergence depends on the airfoil, the Reynolds number, AoA, time of day, phase of the moon, and sunspot activity.
Posts: 404
Joined: 6/14/2002 From: San Diego, CA, USA Status: offline
Yes, the airfoil I ran was a total cross section of the fuse at a point slightly more than half way from the center. The center is a little thicker. I've attached a CpX plot of a section slightly less than half way from the center of the fuselage. You need to keep in mind that the body is flat and wide. It has about a 1:2.3 aspect ratio i.e. span:cord. The wing span to body span ratio is 5.8:1. The aspect ratio of the wing is 6.1:1. The wing area to body area is 2:1. I'm sure these figures only serve to intrigue you more, but the point is that the body should play a sygnificant part in the lift of the plane since it's area is half that of the wing.
I'm currently cutting and gluing like crazy to get it finished for you to see. Hang in there. It woun't be long now.
-Q.
[QUOTE]Originally posted by Daniel Nelson Q- the airfoil that you ran through XFOIL, is that the cross section of your entire fuselage? Unfortunelty, since you've said this is not a conventional airplane, I can't really comment on what might happen if the lifting body stalls. Also, I'm not sure XFOIL's results will be accurate or even apply in this situation. Lifting bodies are very different from conventional airfoils; they're basically very very low aspect ratio wings, and practically all their lift and drag comes from 3-D effects. Guess you'll have to fly it and see.
heh heh, fortran. They don't even teach fortran programming anymore. I think I was in one of the last classes that was offered. Kind of a shame, actually, as they replaced it with a MATLAB class that barely goes into programming. Still, when those guys hit their first hard core programming class, it's good for a Damn-I'm-Glad-I'm-Not-You laugh.
Welcome to the wonderful world of X-FOIL, where the program convergence depends on the airfoil, the Reynolds number, AoA, time of day, phase of the moon, and sunspot activity. [/QUOTE]
< Message edited by a088008 -- Feb 4 2003 8:27AM >
Posts: 63
Joined: 1/27/2003 From: Noordbrug, SOUTH AFRICA Status: offline
hi guys,
Xtr gives you the transition point where the flow changes form laminar to turbulent. You can set a trip position in Xfoil, or you can leave it for natural transition.
At the low Rey number we are looking at the transition is normally a laminar transition bubble. This means the flow separates laminarly from the surface of the wing and reataches turbulent. You can safe some drag by tripping the flow turbulent before it goes naturally.
A transition bubble can be seen when the Visc and Invisc pressure distributions results are compared. The visc pressure deviates virst above and then below the invisc pressure line on the upper side of the airfoil wher the pressure recovery starts.
We have use xfoil extensively to design airfoil sections for a fullsize glider.
Posts: 404
Joined: 6/14/2002 From: San Diego, CA, USA Status: offline
In case you were reading this thread and wondering where the plane is. It's completed and has flow successfully. It's called the "Adrenaline". Look out for it's own thread in this and the Electric forums.
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All Forums >> RC Airplanes >> Aerodynamics >> XFoil and airfoil data 
XFoil and airfoil data - 
I liked the scientific explanations and got a good feel for what Re is all about. Thanks, again! 
An update for those who have not made the correlation -