• There seems to be an uptick in Political comments in recent months. Those of us who are long time members of the site know that Political and Religious content has been banned for years. Nothing has changed. Please leave all political and religious comments out of the forums.

    If you recently joined the forums you were not presented with this restriction in the terms of service. This was due to a conversion error when we went from vBulletin to Xenforo. We have updated our terms of service to reflect these corrections.

    Please note any post refering to a politician will be considered political even if it is intended to be humor. Our experience is these topics have a way of dividing the forums and causing deep resentment among members. It is a poison to the community. We appreciate compliance with the rules.

    The Staff of SOH

  • Server side Maintenance is done. We still have an update to the forum software to run but that one will have to wait for a better time.

Flight Dynamic Problems

The way I work... is like some politicos. If I have a prop table that is pretty close and my HP vrs Altitude curves as right as I can get, then I will adjust the CDO drag value in the Primary aerodynamics tab in the .AIR file to get the proper airspeeds. If the CDO value is a reasonable one then everything is good under the heavens, or about as good as it will get.

Props vrs airspeed and RPM can be a bit interesting, even for constant speed versions. They will be optimized for a particular airspeed, altidude and advance ratio depending on the type of aircraft. Also it should be noted that the prop is connected to an aero engine which may or may not put out it's maximum torque or horsepower at mximum RPM. The R2800 C series gained a couple of hundred HP over the B series through improvement of the oil scavenging system, reducing the HP list internally from splashing oil around!

The addon Aircraft Airfile Manager is a good utility as you can see every one of the prop tables as a series of curves which are easy to edit.

Cheers: T
 
As I understand it, drag is a 'number' used in calculations and not a curve. So if I alter drag to achieve hi altitude speed lower altitude speeds are going to change (which is what I'm trying to avoid). I did find the prop beta range in FDWB so I can alter the calculation range the workbook is cooking up, so back to the labs tonight. I actually do all my editing in aired while reading the data from AAM, save the edits from aired then reload the model into airwrench to see what it comes up with. Airwrench has crippled many A/C simply by turning on the edit function and making NO changes, so I'm afraid to use it.
 
MK:

Drag is indeed a number, however the absolute value varies with the air density. For WWII fighters (and I ahve done a bunch of them), if I get the SL: and critical altitude HP values right, usually the SL and critical altitude TAS values will be very close if I adjust the drag to fit either.

Yes Airwrench does a complete search and destroy with the entered values. Usually Jerry's utility does a very good job on calculating prop parameters. Ya can steal them from a dummy airfile if you want to do that and paste them into your handmade file.

Cheers: T
 
Thanks Fliger, thats exactly what I did. FDWB gave me a 'limp' version of what I already had, but I took the FDWB generated sec 511 and 512 tables and inserted them into the original air files and presto- about 14 kts more top speed at 21k ft. As I compare the original tables with FDWB's tables I see an identical sec.512, but 511 has all the curves starting .5 below the originals. Seems lower power coefficients work better than higher efficiency numbers. Still alot of testing to go, but I think I may be on the right track. My beta has stabilized right around 16 instead of the original 20 or so, and the prop is turning 2100 instead of 1600 to get that speed. Still alot to learn, but I'm getting closer to what was published.
 
A slick plane like a Spitfire might havce a CDO somewher around 30. A fairly draggy plane perhaps 50. Just from a look? 38-41 might be in the ballpark.

Cheers: T
 
At max alt (21k) and max weight (10300), max speed (105 kias/145 TAS) CDo is .028, CD is .0479, l/d 12.48, cdp is .0364. This is Alex Nicolsons FM for Amelia Earharts FSDB Lockheed Electra L-10E, with my new prop tables. The old tables netted about 90 KIAS, the orig FSDB tables got in the 125ish range.
 
Did this plane have a real constant speed prop or adjustable ones lik the early Spitfire ones which could have two pitch angle selected. A CDO of .28 seems pretty low.

Cheers: T
 
According to Lockheeds docs it was equipped with a fixxed prop (1:1 ratio) but a constant speed prop was offered as an option. This model is equipped with the constand speed variety with a beta range of 9-23. The FSDB model came with a range of 12-40 IIRC.
 
Hello Folks,

Didn't think anything was really happening in this thread, so I missed the last few weeks of discussion.

Napamule,
The problem here is that I am actually still tweaking AIR files for CFS1. There aren't any useful variables in the CFG file.

Mr. Shupe,
I don't disagree with the tools helping understanding, but in this case, I was working on an "AIR" file for a ground vehicle, so a basic understanding of the relationships and calculations was all I was looking for. There really ISN'T a real world match to what I am doing. As it turns out, I pretty much got the effect I was looking for except for the engine lugging. I would like to set up a reverse thrust deal, but don't know enough to do it or even whether it is possible in CFS.

MaddogK, Fliger747,
I only mess with CFS flight models, so newer versions may have different tweaks, but here goes:
There IS a supercharger / turbo charger boost setting which can be tuned for better high altitude performance. Even the effect of that boost setting can be altered slightly by adjusting the torque percentages at each RPM and the Friction loss at each RPM. I use it to bring the engine power UP at medium altitudes and reduce power to bring the service ceiling down. It has worked the couple times I have tried it. I currently have a Ki-61-Ic that has a service ceiling just over 40,000 feet that needs this treatment.

Besides the standard CD0, there is also the Mach Drag tables which can be used rather creatively. I use it to limit the terminal velocity for planes I build, but it is just a value for each speed range up to about Mach 3.2, so you can change the lower values and leave the upper values at zero if you wish to add some drag at the lower speed ranges. I use it to create a Sound Barrier and then have the values past Mach 1 slightly lower but high enough so that there isn't enough thrust even in a power dive to make the plane go faster.

Hope this helps.
- Ivan.
 
For the plane he was working on there was a negligible mach effect, however with faster WWII aircraft, capable of infringing on the transonic area, it is possible to adjust the mach drag values. More importantly the mach pitch effects can also be adjusted as well as loss of control effectiveness.

Most planes do not achieve max altitude at maximum weight! For example thre max certified altitude on the 747-400 is 45,100 feet. I have had it up to FL 450 on a number of ocassions, but you have to be pretty light. At max weight (about 870,000 lbs) the low thirties is about max.

Cheers: T
 
Hi Fliger747,
I agree with you that the Lockheed Electra didn't REALLY have to contend with Mach effects. I was just describing how the Mach Drag tables can be used to create arbitrary non-linear drag through the speed range. In fact, I used the Mach Drag to limit the terminal velocity of a Fokker E.III Eindecker to around 200 mph which is no where close to Transonic. It is also how I am limiting the dive speed of a A6M2 Zero. The plane has structural limitations which can not be implemented in CFS1.

- Ivan.


Supercharger Settings:
[505]
9=34,BOOL,Turbo/Supercharged
10=38,double,Manifold Pressure Max (in)
11=40,double,*Supercharger Low Altitude Boost Related ?
11h=Usually 1.0000 if Turbocharged|Large values (~100000) Inc MP/HP at SL
12=48,double,*Boost Gain
12h=Maximum MP/Ambient Air Pressure|Sets max speed/max altitude factor

The two tables below allow adjustments for service ceiling. This may not be the right way to do it, but it seems to have the effects I am looking for.
[508]
1=00,int32,No. of Table Pairs
2=04,double,RPM 1
3=0C,double,Torque Fact 1
4=14,double,RPM 2
5=1C,double,Torque Fact 2
6=24,double,RPM 3
7=2C,double,Torque Fact 3
8=34,double,RPM 4
9=3C,double,Torque Fact 4
10=44,double,RPM 5
11=4C,double,Torque Fact 5

[509]
1=00,int32,No. of Table Pairs
2=04,double,RPM 1
3=0C,double,Torque 1 (ft-lb)
4=14,double,RPM 2
5=1C,double,Torque 2 (ft-lb)
6=24,double,RPM 3
7=2C,double,Torque 3 (ft-lb)
8=34,double,RPM 4
9=3C,double,Torque 4 (ft-lb)
 
Thanks Ivan (Nice to see you again), will give it a look, as the 'official' Lockheed certified docs state " Airplane performance @ full gross weight" 10100 lbs, service ceiling=21,150 ft, absolute ceiling=23,200, simply NOT achievable with the updated FM, but the original FM is overkill (near 25k ft) so all I wanted to do is increase the updated FM ceiling a bit as it's barely achievable EMPTY but the lower alt speeds are nearly spot on. To clarify I'm trying to get somewhere between two Fm's created by other peeps. So far with the prop table edits I've gotten the FM ceiling 21,100 @ 115 KIAS (somewhere in between the other 2) so I cant complain- it's BETTER. Still have to compare the published data (210 MPH @ 5000 ft) with my edits, but the data is from the L-10A, not the 10E with bigger engines, my tests shows about 10% faster as I think it should be so I'm content with it as-is. May have to play with fuel consumption a bit as it seems a tad low tho.
 
Hi MaddogK,
It sounds to me like you would want to increase the value for "Boost Gain" for record 505. Try small increases. A little goes a long way. Do you also have a "Full throttle height" for the aircraft? What altitude does it achieve maximum speed? Just changing the "Boost Gain" doesn't affect low level performance at all.

What I generally do when trying to tune altitude performance is to set the aircraft on autopilot to maintain altitude and warp it to various altitudes and note the engine power. From this VERY quick check, you can pretty much figure out where the maximum speed will be achieved and after one max ceiling climb test, you can figure out what power is required at the ceiling. (Note the fuel load because it is the one factor that is constantly changing.) You can then adjust boost to get the same power output at the new altitude you want to be the new ceiling. It isn't perfectly precise, but gets you there pretty quick.

I am also trying to affect fuel consumption in a CFS1 aircraft (B-25C) but am not sure how. The value that is labeled Fuel Flow Scalar seems to do nothing, and I don't have a value in a CFG file to tweak. If anyone here has some insight, please let me know.

- Ivan.
 
Hi Fliger747,

3D terrain is fun! I find that I crash into it a lot. =-)
Actually what might be even more scary is that I still do most of my development on a Pentium 233 MMX. Every other computer in the house is faster including this laptop I am using for Internet access, but the old Pentium is sufficient. I have installations of CFS2, CFS3, IL2, and a bunch of non-shooters, but I find I really only stay with CFS.

Originally I started building planes for CFS to prove that a decent looking plane could be built within the limitations of AF99 and Aircraft Animator. I believe I have pretty much hit the limit of what can be accomplished with these tools. IMHO, the B-25C looks pretty fair. I have seen a couple payware B-25s that have much more detail but the basic shapes are not right.

Check out a couple screenshots here:
http://www.sim-outhouse.com/sohforums/showthread.php?t=27511&page=4

- Ivan.
 
You must log in or register to reply here.
Back
Top