Re: [Flightgear-devel] Help with B-29
Hi guys I guess the only thing that needs to be remembered is the prop tip must never become supersonic so work out the prop dia and what rpm keeps it near supersonic and that will be close to the prop rpm. Cheers Innis From: Arnt Karlsen [EMAIL PROTECTED] Reply-To: FlightGear developers discussions flightgear-devel@flightgear.org To: FlightGear developers discussions flightgear-devel@flightgear.org Subject: Re: [Flightgear-devel] Help with B-29 Date: Sat, 19 Mar 2005 06:24:26 +0100 On Fri, 18 Mar 2005 11:14:45 -0800, Andy wrote in message [EMAIL PROTECTED]: Josh Babcock wrote: OK, here's the file: http://home.comcast.net/~jrbabcock/superfort/b29-yasim.xml Some random notes, before I start running it: The inbord and outboard engines don't match. Your inbord ones are defined to produce 2200 HP at 1000 RPM (which is *monster* engine), while your outboard ones get 2200 at 2900 RPM (a little over 1/3 the power of the others). The inboard ones look typoed to me. I see that all your propellers have a gear-ratio=0.35 setting. This is almost certainly wrong. The B-29 used big cylinder radials, and as far as I know no one ever made one of these with with a gearing system ..no? Those late and post WWII big ass corncobs were all geared, to stay as small as possible. ;o) (no point, as pistons that size can't be made to move much faster). Note also that this doesn't match your (outboard) engine settings. You have a propeller that wants to sink 1800 HP at 2200 RPM. But at that speed the engine would be turning at a shaft-melting 6285 RPM. The props also have buggy settings for their controller levers. The are power-calibrated at 2200 RPM, which matches the engine settings you have. But the max-rpm value is only 1200, so the governor will never allow them to turn that fast. ..those B-29 props was spun at 910 rpm by 2200 T/O and military ponies spinning the crank shaft at 2600 rpm. http://www.wpafb.af.mil/museum/research/bombers/b3-30.htm http://www.google.com/search?num=100q=B-29+R-3350+rpm+%22gear+ratio%22ie=UTF-8oe=UTF-8 I'll try these changes as soon as I get a chance and see what happens. Andy ___ Flightgear-devel mailing list Flightgear-devel@flightgear.org http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d -- ..med vennlig hilsen = with Kind Regards from Arnt... ;o) ...with a number of polar bear hunters in his ancestry... Scenarios always come in sets of three: best case, worst case, and just in case. ___ Flightgear-devel mailing list Flightgear-devel@flightgear.org http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d ___ Flightgear-devel mailing list Flightgear-devel@flightgear.org http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Help with B-29
Arnt Karlsen wrote: ..what had me wondering is the eng-rpm in the turbine-engine section, where these word of wisdom appears: ;o) And what would you propose? Turbine RPM is almost never quoted in real units, but in percentages. Where is appropriate, the documentation tells you to specify engine RPM. Where it is not appropriate, it tells you to use shaft RPM. It even explains why. Seriously, if you want a change, ask for it. All you are doing right now is nitpicking and pissing me off. So, let me ask this just once, nicely, before I start yelling: is there an *actual* change to the YASim parser or documentation that you would like to see? Andy ___ Flightgear-devel mailing list Flightgear-devel@flightgear.org http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Help with B-29
Jim Wilson wrote: From: Josh Babcock snip Yeah, I'm still messing around and I don't really understand what I'm doing. The .35 gear ratio came straight out of the POH, and I think I recall seeing a cutaway photo of this engine with a gearbox behind the propeller. The engine rpms should be 2900, I'm not sure how that 1000 got in there. The weird controller lever setting are me grasping at straws. Should the prop rpm figures be in prop rpm or engine rpm? I took some of the engine figures and multiplied by .35 whet I set some of those. Hi Josh, I'm not sure what Andy is talking about, which may not mean he's wrong. What I can say for certain, is that if the props are indeed 16.25' in diameter, then 1000 rpm or so would have to be the max. That would make the gear ratio of 0.35 about right. In short, assuming the data you've provided is accurate (it sounds right), your max-rpm under engine should be 2900. Your gear ratio 0.35. And the prop max-rpm should be 1015 (2900 * 0.35). I haven't tried the file yet, this is just based on a quick look at it and the dicussion so far. Best regards, Jim Wilson ___ Flightgear-devel mailing list Flightgear-devel@flightgear.org http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d Yeah, I have been reviewing this, and I think I understand how the definition works. I'm getting pretty much the same numbers based on the 2900 and .35 which I got out of the POH and several internet sources on the cyclone engines. I have a more appropriate yasim file now, but I still can't get it to solve, so I wonder if there is another problem somewhere else? Maybe I have screwed up the aero data and it is producing way too much drag. Here's the latest: http://home.comcast.net/~jrbabcock/superfort/b29-yasim.2.xml Everyone, thanks for all the help so far, it is very appreciated, Josh ___ Flightgear-devel mailing list Flightgear-devel@flightgear.org http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Help with B-29
Yeah, I have been reviewing this, and I think I understand how the definition works. I'm getting pretty much the same numbers based on the 2900 and .35 which I got out of the POH and several internet sources on the cyclone engines. I have a more appropriate yasim file now, but I still can't get it to solve, so I wonder if there is another problem somewhere else? Maybe I have screwed up the aero data and it is producing way too much drag. Here's the latest: http://home.comcast.net/~jrbabcock/superfort/b29-yasim.2.xml Everyone, thanks for all the help so far, it is very appreciated, Josh Not sure if I started with the latest or not, but this one solves: http://www.spiderbark.com/fgfs/b29-yasim.xml This is what I changed: 1) Added fuselage length. 2) Increased wing length to something closer to correct length. 3) Probably adjusted a couple other less significant numbers that seemed wrong (wing sweep angle maybe?). 4) Fixed rpm/power numbers under the prop tags. They need to be scaled back according to the gear ratio. Someone with a better understanding of mech engineering might be able to explain why the BHP on the prop shaft is reduced by a factor of 0.35 when that's the gear ratio, or maybe that is wrong and there is something going on in the YASim calcs. It seems that is what you have to do to get a solution that works. In any case YASim should at least do some sanity checking here to avoid the endless loop thing. Solution results: Iterations: 1220 Drag Coefficient: 3.398360 Lift Ratio: 417.065216 Cruise AoA: 1.252508 Tail Incidence: 3.132050 Approach Elevator: 0.268476 CG: -10.439, 0.000, -0.137 This solution isn't quite right. I had to knock down your cruise speed and altitude, but at least you've got something to go back to while tweaking. BTW I don't know much about the B-29, but did you do that airspeed in KIAS? 365 @ 25000 sounds a bit high. Best regards, Jim Wilson ___ Flightgear-devel mailing list Flightgear-devel@flightgear.org http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Help with B-29
Jim Wilson wrote: Yeah, I have been reviewing this, and I think I understand how the definition works. I'm getting pretty much the same numbers based on the 2900 and .35 which I got out of the POH and several internet sources on the cyclone engines. I have a more appropriate yasim file now, but I still can't get it to solve, so I wonder if there is another problem somewhere else? Maybe I have screwed up the aero data and it is producing way too much drag. Here's the latest: http://home.comcast.net/~jrbabcock/superfort/b29-yasim.2.xml Everyone, thanks for all the help so far, it is very appreciated, Josh Not sure if I started with the latest or not, but this one solves: http://www.spiderbark.com/fgfs/b29-yasim.xml This is what I changed: 1) Added fuselage length. 2) Increased wing length to something closer to correct length. 3) Probably adjusted a couple other less significant numbers that seemed wrong (wing sweep angle maybe?). 4) Fixed rpm/power numbers under the prop tags. They need to be scaled back according to the gear ratio. Someone with a better understanding of mech engineering might be able to explain why the BHP on the prop shaft is reduced by a factor of 0.35 when that's the gear ratio, or maybe that is wrong and there is something going on in the YASim calcs. It seems that is what you have to do to get a solution that works. In any case YASim should at least do some sanity checking here to avoid the endless loop thing. Solution results: Iterations: 1220 Drag Coefficient: 3.398360 Lift Ratio: 417.065216 Cruise AoA: 1.252508 Tail Incidence: 3.132050 Approach Elevator: 0.268476 CG: -10.439, 0.000, -0.137 This solution isn't quite right. I had to knock down your cruise speed and altitude, but at least you've got something to go back to while tweaking. BTW I don't know much about the B-29, but did you do that airspeed in KIAS? 365 @ 25000 sounds a bit high. Best regards, Jim Wilson ___ Flightgear-devel mailing list Flightgear-devel@flightgear.org http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d Many thanks, I will make these changes (I already caught the fuse snafu, I put that in by accident recently) As for the figures, they are the same ones that I keep seeing everywhere. Actually, the max altitude is more like 32000. Part of the reason that we beat Japan so badly once we got in range is that they simply didn't have anything that could catch and/or reach the superfort. Josh ___ Flightgear-devel mailing list Flightgear-devel@flightgear.org http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Help with B-29
Jim Wilson wrote: Yeah, I have been reviewing this, and I think I understand how the definition works. I'm getting pretty much the same numbers based on the 2900 and .35 which I got out of the POH and several internet sources on the cyclone engines. I have a more appropriate yasim file now, but I still can't get it to solve, so I wonder if there is another problem somewhere else? Maybe I have screwed up the aero data and it is producing way too much drag. Here's the latest: http://home.comcast.net/~jrbabcock/superfort/b29-yasim.2.xml Everyone, thanks for all the help so far, it is very appreciated, Josh Not sure if I started with the latest or not, but this one solves: http://www.spiderbark.com/fgfs/b29-yasim.xml This is what I changed: 1) Added fuselage length. 2) Increased wing length to something closer to correct length. 3) Probably adjusted a couple other less significant numbers that seemed wrong (wing sweep angle maybe?). 4) Fixed rpm/power numbers under the prop tags. They need to be scaled back according to the gear ratio. Someone with a better understanding of mech engineering might be able to explain why the BHP on the prop shaft is reduced by a factor of 0.35 when that's the gear ratio, or maybe that is wrong and there is something going on in the YASim calcs. It seems that is what you have to do to get a solution that works. In any case YASim should at least do some sanity checking here to avoid the endless loop thing. Solution results: Iterations: 1220 Drag Coefficient: 3.398360 Lift Ratio: 417.065216 Cruise AoA: 1.252508 Tail Incidence: 3.132050 Approach Elevator: 0.268476 CG: -10.439, 0.000, -0.137 This solution isn't quite right. I had to knock down your cruise speed and altitude, but at least you've got something to go back to while tweaking. BTW I don't know much about the B-29, but did you do that airspeed in KIAS? 365 @ 25000 sounds a bit high. Best regards, Jim Wilson ___ Flightgear-devel mailing list Flightgear-devel@flightgear.org http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d Is the sweep supposed to be the LE or the .25% chord? Josh ___ Flightgear-devel mailing list Flightgear-devel@flightgear.org http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Help with B-29
Josh Babcock wrote: Jim Wilson wrote: Yeah, I have been reviewing this, and I think I understand how the definition works. I'm getting pretty much the same numbers based on the 2900 and .35 which I got out of the POH and several internet sources on the cyclone engines. I have a more appropriate yasim file now, but I still can't get it to solve, so I wonder if there is another problem somewhere else? Maybe I have screwed up the aero data and it is producing way too much drag. Here's the latest: http://home.comcast.net/~jrbabcock/superfort/b29-yasim.2.xml Everyone, thanks for all the help so far, it is very appreciated, Josh Not sure if I started with the latest or not, but this one solves: http://www.spiderbark.com/fgfs/b29-yasim.xml This is what I changed: 1) Added fuselage length. 2) Increased wing length to something closer to correct length. 3) Probably adjusted a couple other less significant numbers that seemed wrong (wing sweep angle maybe?). 4) Fixed rpm/power numbers under the prop tags. They need to be scaled back according to the gear ratio. Someone with a better understanding of mech engineering might be able to explain why the BHP on the prop shaft is reduced by a factor of 0.35 when that's the gear ratio, or maybe that is wrong and there is something going on in the YASim calcs. It seems that is what you have to do to get a solution that works. In any case YASim should at least do some sanity checking here to avoid the endless loop thing. Solution results: Iterations: 1220 Drag Coefficient: 3.398360 Lift Ratio: 417.065216 Cruise AoA: 1.252508 Tail Incidence: 3.132050 Approach Elevator: 0.268476 CG: -10.439, 0.000, -0.137 This solution isn't quite right. I had to knock down your cruise speed and altitude, but at least you've got something to go back to while tweaking. BTW I don't know much about the B-29, but did you do that airspeed in KIAS? 365 @ 25000 sounds a bit high. Best regards, Jim Wilson ___ Flightgear-devel mailing list Flightgear-devel@flightgear.org http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d Is the sweep supposed to be the LE or the .25% chord? Josh ___ Flightgear-devel mailing list Flightgear-devel@flightgear.org http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d OK, it solves with this line: control-input axis=/controls/engines/engine[3]/propeller-pitch control=ADVANCE/ but not this one: control-input axis=/controls/engines/engine[3]/propeller-pitch control=PROPPITCH/ Does ADVANCE mean prop pitch here? Josh ___ Flightgear-devel mailing list Flightgear-devel@flightgear.org http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
Re: [Flightgear-devel] Help with B-29
Josh Babcock wrote:
Josh Babcock wrote:
Jim Wilson wrote:
Yeah, I have been reviewing this, and I think I understand how the
definition works. I'm getting pretty much the same numbers based on
the 2900 and .35 which I got out of the POH and several internet
sources on the cyclone engines. I have a more appropriate yasim file
now, but I still can't get it to solve, so I wonder if there is
another problem somewhere else? Maybe I have screwed up the aero
data and it is producing way too much drag.
Here's the latest:
http://home.comcast.net/~jrbabcock/superfort/b29-yasim.2.xml
Everyone, thanks for all the help so far, it is very appreciated,
Josh
Not sure if I started with the latest or not, but this one solves:
http://www.spiderbark.com/fgfs/b29-yasim.xml
This is what I changed:
1) Added fuselage length.
2) Increased wing length to something closer to correct length. 3)
Probably adjusted a couple other less significant numbers that seemed
wrong (wing sweep angle maybe?).
4) Fixed rpm/power numbers under the prop tags. They need to be
scaled back according to the gear ratio. Someone with a better
understanding of mech engineering might be able to explain why the
BHP on the prop shaft is reduced by a factor of 0.35 when that's the
gear ratio, or maybe that is wrong and there is something going on
in the YASim calcs. It seems that is what you have to do to get a
solution that works. In any case YASim should at least do some
sanity checking here to avoid the endless loop thing.
Solution results: Iterations: 1220
Drag Coefficient: 3.398360
Lift Ratio: 417.065216
Cruise AoA: 1.252508
Tail Incidence: 3.132050
Approach Elevator: 0.268476
CG: -10.439, 0.000, -0.137
This solution isn't quite right. I had to knock down your cruise
speed and altitude, but at least you've got something to go back to
while tweaking. BTW I don't know much about the B-29, but did you do
that airspeed in KIAS? 365 @ 25000 sounds a bit high.
Best regards,
Jim Wilson
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Is the sweep supposed to be the LE or the .25% chord?
Josh
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OK, it solves with this line:
control-input axis=/controls/engines/engine[3]/propeller-pitch
control=ADVANCE/
but not this one:
control-input axis=/controls/engines/engine[3]/propeller-pitch
control=PROPPITCH/
Does ADVANCE mean prop pitch here?
Josh
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OK, looks good in yasim, but in fgfs I get this:
[snip]
open(/usr/local/share/FlightGear/data/Aircraft/b29/jim.xml, O_RDONLY) = 15
fstat64(15, {st_mode=S_IFREG|0644, st_size=10371, ...}) = 0
mmap2(NULL, 131072, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) =
0xa53da000
read(15, ?xml version=\1.0\?\n!-- Tacti..., 131072) = 10371
read(15, , 131072)= 0
read(15, , 131072)= 0
close(15) = 0
munmap(0xa53da000, 131072) = 0
--- SIGSEGV (Segmentation fault) @ 0 (0) ---
+++ killed by SIGSEGV +++
Oh woe is me, what's up with the segfaults? Let me know if anyone wants the
whole strace. This looks suspiciously like what the jsbsim one was doing, but my
b29-magic works fine, and the only difference is the fdm file.
Josh
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Re: [Flightgear-devel] Help with B-29
On Sat, 19 Mar 2005 07:45:07 -0800, Andy wrote in message [EMAIL PROTECTED]: Arnt Karlsen wrote: ..what had me wondering is the eng-rpm in the turbine-engine section, where these word of wisdom appears: ;o) And what would you propose? Turbine RPM is almost never quoted in real units, but in percentages. Where is appropriate, the documentation tells you to specify engine RPM. Where it is not appropriate, it tells you to use shaft RPM. It even explains why. ..ah, missed that pie. I agree %'s are more appropriate here, however I feel the 100% rpm figures (that the %'s are calculated from), as such will become useful as we start playing with shaft torque calculations to make things like turbos from shaft driven superchargers and power recovery turbines. Seriously, if you want a change, ask for it. All you are doing right now is nitpicking and pissing me off. So, let me ask this just once, nicely, before I start yelling: is there an *actual* change to the YASim parser or documentation that you would like to see? ..not yet, the docs and source first needs a read, and I some more sleep so the reading gets productive, it's been a while. (Never ever accept round-da-clock-to-meet-everlasting-deadlines just to get your business going.) I stand firm on the B29's R-3350 .35 gear ratio, though. ;o) ..the other change I would like to see in YASim (and the other FDM's too), is running independently like JSBSim can do, so we can simulate one plane with several different networked FDM's to see how they differ in responding to gusts, ice, vortices etc., should help debugging and build better data on modelling new planes. By independently, I mean running YASim, LaRCSim, -UIUC etc outside of FlightGear, I see no need to drag along dead weight, the graphics _is_ the heavy part of FG. -- ..med vennlig hilsen = with Kind Regards from Arnt... ;o) ...with a number of polar bear hunters in his ancestry... Scenarios always come in sets of three: best case, worst case, and just in case. ___ Flightgear-devel mailing list Flightgear-devel@flightgear.org http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
