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New historically realistic Sopwith Camel JSBSim FDM released

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New historically realistic Sopwith Camel JSBSim FDM released

Postby flug » Sun Mar 31, 2013 5:33 am

I've released a new JSBSim FDM for the Sopwith Camel that is as historically realistic as I can make it. Download the current version here:

https://github.com/bhugh/SopwithCamel-J ... 0delta.zip [ver 2.0gamma, 2017/03/19]

HELP GETTING STARTED WITH THE JSBSIM SOPWITH CAMEL
JSBSim Sopwith Camel Page on the FlightGear Wiki here - for help getting started with the JSBSim Camel, PLEASE READ the Wiki article and/or the aircraft help file ('?" in FlightGear). Both have basically the same information--and you WILL need it. You probably won't be able to get off the ground unless you read the instructions first!

This is the Version 2.0delta version--the (hopefully!) final ver. 2.0 release candidate.

You can also download the full Bombable package, which includes the 2.0gamma JSBSim Camel as well as much more:

https://github.com/bhugh/Bombable/archive/4.6delta.zip

- Choose the JSBSim version of the Camel, which is called "sopwithCamel-Bombable/JSBSim" in FGRun. The JSBSim FDM is my contribution to this project.

- A YASim version is included in the package for convenience and comparison, but it does not incorporate any of the historically realistic features that the JSBSim FDM includes. The YASim version flies much like a modern aircraft would.

BACKGROUND - REASONS FOR A NEW FLIGHT DYNAMICS MODEL FOR THE SOPWITH CAMEL

In flying the existing Sopwith Camel flight models in Flightgear with Bombable in simulated combat situations, the shortcomings of these flight models became apparent to me. Flightgear flight models are typically designed and optimized for flying aircraft well within their design envelopes, as a commercial airline pilot does (and for good reason!). The FDMs work very well in those situations.

However, combat aircraft are often operated near the limits--or even over the limits--of their documented capabilities. Particularly for an aircraft like the Camel, working with and against the quirks of its design was an integral part of operating the aircraft in both everyday operations and in combat. These operational quirks were openly exploited by combat pilots.

As one writer said:

I enjoyed flying the Camel, but its vices of control instability, extreme control sensitivity and pronounced gyroscopic effects all combined to create the impression of balancing an egg on the point of a needle rather than flying an aircraft . . .

It was never forced into manoeuvres - they were executed by light pressure on the controls and subsequently relaxing, or sometimes reversing, the pressure once the desired rate of response was attained.


In flying the Camel in FlightGear/Bombable, I became curious about the real historical experience of flying a Camel. What about the famous strong gyroscopic effect that causes the nose to rise in a LH and drop in a RH turn? It's commented on by most every pilot who writes about flying the Camel, but (it turns out) impossible to implement in YASim. What about the famous sensitivity to the controls, the quick turns (especially to the right), and propensity to fall into spins, and all the rest?

JSBSIM SOPWITH CAMEL - WHAT'S INCLUDED AND WHAT'S NEW IN EACH VERSION
Version 1.3
I set out to create a flight model of the Camel that would incorporate as many of the documented combat flight characteristics of the Camel as possible, and in as realistic a way as possible. In addition, as of ver 1.3 it includes:

- More historically accurate lift/drag profile
- Historically accurate modelling of gyroscopic moment of engine and prop, which has very noticeable effects on turns and other maneuvers.
- More realistic start sequence
- Engine starves of fuel and stops in inverted/negative-G flight, just as in historical Camel; restarts when positive G flight resumes.
- Option of manual mixture control (fiddly engine controls are an often-mentioned feature of the Camel)

Version 1.6
- Tweaked controls that better fit historic descriptions--but are far different (and generally, weaker and less effective) than controls on modern aircraft we are more familiar with. Particularly:

- Weak rudder, too weak to completely counter engines gyroscopic moment in fast turns.
- Ailerons have a vast amount of adverse yaw, a high amount of drag, and generally far less effective in inducing roll than you would expect from four such large barn-door-like affairs.
- Elevator is more powerful than the rudder or ailerons but still relatively weaker than in previous versions.

- First really convincing demonstration of the faster right/slower left turn characteristic cause by the gyroscopic moment of the rotary engine together with that other control characteristics of the aircraft. (Most obvious in sustained, constant speed, level turns at about 60-65 knots.)
- Generally smoother and
- Improved stall and spin response compared with ver. 1.3.
- Tweaked overall weight, center of gravity, fuel tanks, and a few other items mentioned by people who posted on this thread (THANK YOU!)

Version 1.8
- Incorporated many suggestions made by users when the historically accurate Camel was Aircraft of the Month in May 2013.
- Improved spin characteristics--now it doesn't get 'stuck' in certain situations and just float straight down without getting into a spin.
- Improved realism of the control surfaces further, which further makes the difference in speed between left and right turns obvious
- Generally, further refinements to FDM and realism.

Version 2.0
- Ground contact effects, ground shadow (in ALS mode - highly recommended)
- Rembrandt-ready
- Greatly improved sound design, ground contact, engine, and air effects
- Much improved and refined Flight Dynamics Model, closer to actual Camel performance in a large number of measurable ways
- Greatly improved engine and 'blip' simulation, far closer to engine & magneto operation of the historical Sopwith Camel
- Updated documentation and in-game help for takeoff, landing, taxiing, etc, including several new historical documents and first-hand accounts of flying the Camel
- Minimal HUDs (install in your Huds directory & add to preferences.xml) ideal for WWI-era aircraft
- Crash and damage effects

The new JSBSim FDM is my first try at accomplishing this--any feedback appreciated. It is included as part of the Bombable FG add-on package, but it also works as a free-standing aircraft (and installs alongside the existing Sopwith Camel, so it doesn't over-write anything.)

If this new FDM works for people, I'd like to see it included in the next FG release. I think it would be a simple drop-in addition to the existing FG 2.10 UIUC and YASim Sopwith Camel versions.

Image
Last edited by flug on Sun Mar 19, 2017 11:46 pm, edited 13 times in total.
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Re: New historically realistic Sopwith Camel JSBSim FDM rele

Postby flug » Sun Mar 31, 2013 5:54 am

FYI, here is an example of how the new Sopwith Camel JSBSim FDM matches up with the historical Camel:

Image

And it's not like it was hand-tweaked to match those values, either . . . the engine, drag, lift, and a variety of specific details were built into the JSBSim model based on published specs and information, and then those values were tweaked to match published speed in level flight at various RPMs, etc. When I ran across the historical 1917 Camel climb/speed chart today I thought it would be a great test to see whether that approach was giving realistic results or not--and it looks like it's working pretty well.

The fit isn't perfect, but it's pretty darn good--especially note how the JSBSim graph is very similar to the Camel graph below (the green graph highlighted below is the source of data for the red graph above), but not so similar to any of the other WWI-era aircraft also graphed below:

Image

Graph/info source is http://home.comcast.net/~clipper-108/AI ... 05-119.pdf
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Re: New historically realistic Sopwith Camel JSBSim FDM rele

Postby flug » Sun Mar 31, 2013 6:31 am

Some of the Camel's characteristics I worked to include in this FDM:

* Quick/light response to controls

* The gyroscopic effect causes the nose to rise in a left-hand turn (moreso that most other similar aircraft)

* The gyroscopic effect causes nose to drop in a right-hand turn

* Fairly large amounts of left rudder were needed in both L & R turns to correct the above gyroscopic effects

* Sluggish in left turns. Quicker through 270 degrees to the right than 90 degrees to the left.

* Sensitive in a turn, if the turn were tightened just a little, it was likely to whip into a tight spin.

* Accelerating the aircraft caused the nose to climb, and swing to the left.

* Able to land and take off in a very short distance--just a few aircraft lengths. See interesting demo here: http://www.youtube.com/watch?v=VT9wtDNiKaI

With a 15 mph headwind, JSBSim Camel now matches this takeoff almost exactly.

* Match published speeds, rate of climb, etc.

* Very quick half-roll (a touch of left rudder for a half roll, then a quick half-loop was a often-used maneuver to reverse direction).

* Historically accurate armament.
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Re: New historically realistic Sopwith Camel JSBSim FDM rele

Postby DFaber » Sun Mar 31, 2013 10:55 am

Hi flug,

flug wrote in Sun Mar 31, 2013 5:33 am:However, combat aircraft are often operated near the limits--or even over the limits--of their documented capabilities.


I'm afraid this is a myth.
No Combat pilot over Enemy Territory, in unclear weather or uncertain altitude is going to try fancy Aerobatic manouvers which may lead to loss of control or disintegration of his Aircraft. Lots of WW2 Aircraft Manuals prohibit such manouvers in Combat and the major part of current day Combat Jet Manuals consists of Diagrams to give the Pilot an Idea of how not to leave the envelope and risk an expensive Airplane.
Apart from that, the main advantage of a Fighter Pilot is Altitude and Speed, a situation well within the envelope.

No sane Pilot who is aware how far he has to walk home will intentionally leave the safe margins of his Aircraft.

It's commented on by most every pilot who writes about flying the Camel, but (it turns out) impossible to implement in YASim.


It sure is possible. If you prefer JSBSim that's perfectly alright, but please don't do YaSim Bashing.

Greetings
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http://flightgear-de.net

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Re: New historically realistic Sopwith Camel JSBSim FDM rele

Postby Johan G » Sun Mar 31, 2013 2:05 pm

I've seen this YouTube video before, but I had quite forgotten the details about the engine. It has no carburettor(!), and therefore no throttle. It instead have more magneto settings:



Quite an alarming engine sound, would it had been a modern engine. :?
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Re: New historically realistic Sopwith Camel JSBSim FDM rele

Postby flug » Sun Mar 31, 2013 2:19 pm

DFaber wrote in Sun Mar 31, 2013 10:55 am:Hi flug,

It's commented on by most every pilot who writes about flying the Camel, but (it turns out) impossible to implement in YASim.


It sure is possible. If you prefer JSBSim that's perfectly alright, but please don't do YaSim Bashing.

Greetings


Aha--let's rephrase that to say that I first tried to implement this via YaSim and couldn't figure out how to do so. So very possibly a reflection on me rather than YaSim. In fact it would be an interesting and useful addition to the Camel YaSim model if it can be done.

Do you know how or can you point me to any examples or tutorials about how to do this using YaSim?

Thanks!
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Re: New historically realistic Sopwith Camel JSBSim FDM rele

Postby Hooray » Sun Mar 31, 2013 2:27 pm

added the good news to the upcoming newsletter and the bombable article (wiki).
It would be great if screen shots and/our youtube videos could be added, too (volunteers ?).
Please don't send support requests by PM, instead post your questions on the forum so that all users can contribute and benefit
Thanks & all the best,
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Re: New historically realistic Sopwith Camel JSBSim FDM rele

Postby flug » Sun Mar 31, 2013 8:07 pm

DFaber wrote in Sun Mar 31, 2013 10:55 am:Hi flug,

flug wrote in Sun Mar 31, 2013 5:33 am:However, combat aircraft are often operated near the limits--or even over the limits--of their documented capabilities.


I'm afraid this is a myth.
No Combat pilot over Enemy Territory, in unclear weather or uncertain altitude is going to try fancy Aerobatic manouvers which may lead to loss of control or disintegration of his Aircraft.


I probably need to phrase this a bit better.

But just for example, Camel pilots would sometimes use the propensity of the AC to drop into a spin during a turn, to deliberately induce a spin as a way of escaping opponents.

As another example:

"The same with the half-roll. Nothing would half-roll like a Camel. A twitch
of the stick and flick of the rudder and you were on your back. The nose
dropped at once and you pulled out having made a complete reversal of
direction in the least possible time.

Thomson, the squadron stunt expert told him that it (half-roll) was just the
first half of a roll followed by the second half of a loop; the only stunt
useful in fighting. If you were going the wrong way, it was the quickest known
method of returning in your slipstream."

http://www.theaerodrome.com/forum/aircr ... yth-6.html


My point is, neither of these are maneuvers you are likely to try if you are simply navigating from airport to airport or flying around a bit checking the scenery. (Not that there is anything wrong with either of those activities! They are just a different type of flying.)

If you're doing that type of airport-to-airport type flying you might be perfectly satisfied with an FDM that hits the basics of the AC's profile for speed, lift, drag, etc.

But if you're doing the snap rolls, the fast turns, the half rolls, the strafing runs, the dive bombing, or whatever else combat pilots did do, you're just in a different part of the AC's performance envelope and you're likely to notice different things missing in the FDM or want certain things to 'work right'--things you just wouldn't care about too much if your main interest in is flying in a different style altogether.

That was my motivation for trying to put together a FDM for the Camel that hit more of these performance characteristics.

Now whether I've hit the target or not--that is a different question entirely!
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Re: New historically realistic Sopwith Camel JSBSim FDM rele

Postby LesterBoffo » Sun Mar 31, 2013 8:36 pm

I'd say it's pretty close, the gyro precession and it's attendant aero-forces seem a bit 'notchy' if I can use that term. I'm also wondering about the airfoil lift and drag tables you used, as most WWI airfoils ran in narrow AoA' lift and drag coefficients. The Camel's Bombable/JSB airfoil tables seem somewhat generic which might explain why it seems to toggle between mild and wild in the precession with varying degrees of rudder and elevator.
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Re: New historically realistic Sopwith Camel JSBSim FDM rele

Postby daveculp » Sun Mar 31, 2013 10:09 pm

Thanks for making that, flug. The pilot's notes in the config file are fascinating! I'm looking through the JSBSim code, chasing the wires to find the gyroscopic force. This may take a while :)
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Re: New historically realistic Sopwith Camel JSBSim FDM rele

Postby jonsberndt » Mon Apr 01, 2013 12:26 pm

daveculp wrote in Sun Mar 31, 2013 10:09 pm:I'm looking through the JSBSim code, chasing the wires to find the gyroscopic force.


Hi Dave!

As I recall, the gyroscopic force is determined by the moment of inertia in the engine/propeller. At one time that was calculated in FGAircraft, but it got moved somewhere, I think.

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Re: New historically realistic Sopwith Camel JSBSim FDM rele

Postby flug » Tue Apr 02, 2013 7:04 am

Aha, I think you're onto a couple of interesting items.

LesterBoffo wrote in Sun Mar 31, 2013 8:36 pm:I'd say it's pretty close, the gyro precession and it's attendant aero-forces seem a bit 'notchy' if I can use that term.


I experimented a little and I think much/most of this is due to the method I used to compensate for the reversed gyroscopic effect in JSBSim. It basically takes the gyroscopic moment, multiplies it by -2 and adds it back in as a control moment. But maybe there is a little delay or something--it acts like there is a little feedback problem to me.

So for now I'm just going to go with the JSBSim gyroscopic forces, even though they are reversed.

I'm also wondering about the airfoil lift and drag tables you used, as most WWI airfoils ran in narrow AoA' lift and drag coefficients. The Camel's Bombable/JSB airfoil tables seem somewhat generic which might explain why it seems to toggle between mild and wild in the precession with varying degrees of rudder and elevator.


This is a good point as well. I actually put most of this together a couple of years ago, so some of the details are fuzzy. But I think I started with a basic Aeromatic profile to get things close and then used some other JSBSim aircraft as models.

But it looks like I was thinking of basically a 22.5 degree critical angle of attack whereas for the Camel it probably should be more like 14 degrees? (Stall speed is 48 MPH.)

I've got a new version worked up with those adjustments and I think it is moving in the right direction.
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Re: New historically realistic Sopwith Camel JSBSim FDM rele

Postby Buckaroo » Tue Apr 02, 2013 5:39 pm

Lester's likely right. I think the Camel used an R.A.F 14 airfoil, and if so critical stall would be around 14 degrees, 15 tops. I saw it once in a NACA report, but now the danged NASA technical reports server isn't available to the public due to some danged reaction to some danged alleged Chinese espionage so I can't call it up again. @#$%!

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Re: New historically realistic Sopwith Camel JSBSim FDM rele

Postby Johan G » Tue Apr 02, 2013 6:02 pm

Buckaroo wrote in Tue Apr 02, 2013 5:39 pm:..the danged NASA technical reports server isn't available to the public due to some danged reaction to some danged alleged Chinese espionage so I can't call it up again. @#$%!

:evil:
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Re: New historically realistic Sopwith Camel JSBSim FDM rele

Postby AndersG » Tue Apr 02, 2013 6:09 pm

Buckaroo wrote in Tue Apr 02, 2013 5:39 pm:I saw it once in a NACA report, but now the danged NASA technical reports server isn't available to the public due to some danged reaction to some danged alleged Chinese espionage so I can't call it up again. @#$%!


Fortunately, the British have a copy of the NACA archive... :) http://naca.central.cranfield.ac.uk/

Nice work, btw!

Have you checked the propeller/engine <sense> element for setting the direction of the gyroscopic effects? (I think it ought to affect them.)

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