DC-8 Flight Tuning

[Herman]

Most aircraft cfg files including HJG aircraft have a section called [flight tuning].

However, the HJG DC-8's do not have this section as part of the aircraft cfg file.

Just curious as to why this section is not part of the DC-8 cfg

At times I have found it usefull to do a bit of tweeking, especially in the area of "pitch stability" and "roll stability" in order to make the controls feel somewhat more realistic, at least in my opinion. Most have a value of "1" and by increasing that to 1.5 or 2, the controls feel heavier.

Herman

[aerofoto - HJG Admin]

We're aware of this Herman

It came up .... about a year ago (believe it or not and after all this time .... some 10 years or so now) when someone reported a pitch attitude problem with a DC8-62.

I'm not sure why/how it happened .... BUT .... however/whyever it happened is before even I connection with HJG.

FT's are one of the things Mike MONCE and myself are currently looking at .... in respect of the DC8 FDE revisions .... which we started, again in earnest, a couple days ago, having now gotten some 2 years of simultaneous new HJG projects out of the way.

Apart from FT's .... there'll be some other modifications too .... such as weights for some of the aircraft .... BUT .... without getting overly radical due to time etc.

There's a lot of aircraft to look at .... including a number to be added too (sub types with weight variations between them) .... and each aircraft must be individually assessed too .... SO .... it's going to take us a while yet to get through everything.

Whilst doing this I also hope to prepare more thorough HANDLING NOTES as well.

I'll make the odd comment .... from time to time .... as we progress things

Mark C
AKL/NZ

[jimhalinda]

Well I for one am glad to see my favourite jetliner getting some attention!

Don't get me wrong, I'm enjoying the newer HJG birds too, but I've been hoping that the DC-8 might get some of the improvements that have been on the back burner until now.

The DC-8 seems to be the Douglas airliner that gets the least respect, and I like an underdog I guess! Plus there were plenty of them around here in Canada when I was a kid!

So, Mark/Mike/HJG, rest assured that you will make at least a few of us happy when you release these updates!

Regards,

Jim

[MKA742]

I agree, she deserves more attention. If only I knew some more about developing so I could actually contribute...

Can't wait for the updates!

[rpjkw11]

I have always added flight tuning sections to the HJG aircraft with positive results from fine tuning. It's easy to do and is a viable alternative until the fine folks here put together "official" sections.

Bob

[MKA742]

Couldn't agree more. I made a new .air file with nice results, if your interested PM me.

[Leo]

Yeah i made some changes myself on both AIR and CFG files of my DC8-62AF to meet the real deal, small adjustments. The AIR file was just to meet the CFG changes.

OEW
MTOW
Flue Flow Escalar
Fuel Flow Gain
N2 RPM
Wing Area
Wing Sweep
VTail Sweep
HTail Sweep
Autopilot
Brakes
Radios
Lights

[Mike Monce - HJG]

Those are all parameters we will be looking at. Be careful though. The weights, wing sweep(actually changes the CoG location), and wing area can greatly affect the stability; the control surface sweeps have relatively little effect.

FFS, FFG, N2 values obviously can throw the engine parameters away from the listed specs for that particular engine.

We do work off of real world values as closely as we can within the limitations of FS.

Mike

[louross]

"within limitations of FS."
I understand that very well- based on actual flying characteristics and/or a/c behaviors that can not be replicated in FS. Could you give at least a couple of examples of engine characteristcs that are limited by FS (other than the PT6a)?
thanks,
lr.

[Mike Monce - HJG]

In terms of engines, the jet engine model is actually pretty good. I have a feeling that's because they are in reality fairly simple devices. With proper cfg/air file values and thrust/N2/throttle curves, MSFS does a very good job on jets. The only kicker is making sure the panel gauges are also calibrated/matched to the engines.

Don't get me started on turboprops ! Ugghhhh! Remember the Tupolev about a year ago everyone was using? I tried to get it right in terms of the engines and gave up. If you look in the cfg/air file for the original package, so did the designers.... they made all the engines jets! ;D

FS is a mess with turboprops.

Mike

[christrott]

Turboprops CAN be a mess, but there are ways around it - through gauge coding only though. This is the only way decent turboprop behaviour. There are a couple that run the Allison T56/501 correctly because of this effort, but there are also a couple that suffer because the gauge programming wasn't done properly. Piston behavior is just as iffy with FS. It'll work GA engines fine, but it doesn't handle true turbocharging (not turbonormalizing which is what the TSIO-series of engines use) well, it doesn't handle supercharging at all, and really doesn't know how to handle radials or V-engines.

Direct aerodynamics - FS does just fine though. Most of the problems are simply from inability of the developers to decode or understand properly the "black magic" that the legacy FS code contains and use it to their advantage. Fraser Turner did wonders with the SGA DC-10 and A300 because he understood how it all worked together.

[George Carty - HJG]

Regarding aerodynamics, is FS aware of the difference between flaps (which work by increasing lift coefficient at a given angle of attack, while not affecting stalling angle) and slats (which increase stalling angle, but do not noticeably increase lift when used at an angle of attack below the slats-retracted stalling angle)?

This of course would require that FS's stall warning would activate at different angles depending on whether or not the slats were extended...

George

[christrott]

George, I think you have a misunderstanding of how a wing stalls. There is never a difference in "stalling angle" of a wing. The Critical AoA is always the same, only the speed changes due to addition of lift devices. Now, pitch angle of the entire airplane when the wing stalls may change, but that has nothing to do with when the wing stalls. FS's "stall warning" systems work off of critical AoA, just as the real thing does. As long as the wing is properly designed within the CFG and AIR files, it will stall just like the real thing and the stall warning will work correctly.

A better way to put it is -

Slats reduce the wing's angle of attack or offset the change in AoA by the flaps. The flaps can change the angle of attack with varying degrees depending on the type (which FS does recognize all of the major types of flaps and properly models their effect), can increase lift, and can increase drag, but the critical Angle of Attack at which the wing stalls never changes.

[Leo]

Oh i only did minor tweakings, but always tweaking the AIR file to match the CFG to avoid any problems, right now its working like a clock and i made so far 54 flight hours on IVAO in my DC8-62AF flying freighter flights all over Brazil just like the real DC8-62AF did a couple of years ago (2007). Unfortunatly we no longer see this bird in the air as he is abandoned over SBEG airport along with his mates DC8's and B707's.

I once saw this DC8 landing and i was at the threshold waiting for a couple of flights and unexpected found that loud noise coming in and when i looked for the plane it was a DC8 and he flew by i almost became deaf from such a loud noise those PW's make.

I can tell you guys, i am flying a dream, what an amazing aircraft and what an amazing job you guys did, thank you.