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New historically realistic Sopwith Camel JSBSim FDM released

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Re: New historically realistic Sopwith Camel JSBSim FDM rele

Postby LesterBoffo » Sat Apr 01, 2017 12:57 pm

flug wrote in Thu Mar 16, 2017 4:45 pm:
....................

FWIW I seem to recall that one of the issues early on with this model was inconsistent ground reactions, and that part of the solution was moving to 120 hz FDM rate and also making some other adjustments.

One of the issues with a model like this is that the original aircraft didn't really have any suspension per se. It's just a hard rubber tire mounted to a wheel, the wheel to an axle, the axle to some bracing, and the bracing directly to the aircraft fuselage.

So it's not like any more modern landing gear where there is likely to be some kind of damped spring arrangement that has X inches (or even feet) of compliance built into it.

Rather, with an aircraft like the Camel they were depending on the 'natural' inherent spring of the entire system--tire, wheel, axle, bracing, fuselage, etc--to absorb any forces. This is hard to get your head around modelling but more to the point of JSBSim, the entire system seems to act pretty much like a very short, stiff spring with quite a bit of damping and that is the very type of thing that JSBSim with its relatively slow modeling rate is going to have the most difficult time with.


..................................




It amazes me that you have spent so much time and effort in getting this plane's FDM historically accurate, and yet you can't bother researching further about WWI aircraft landing gear suspension.

All WWI planes had some sort of sprung suspension, be it either shock cords, coils springs or torsion bars or shock corded Oleo struts, no exceptions. These planes all flew off of rough grass fields and the technology for landing gear suspension was already available long before the Guns of August. You only need to load up Helijah's Bleriot XI and watch the castoring and shock absorbing complex of struts and wheels while it taxis across a grass strip. These early suspensions did not have much if any damping, so they were quite active and bouncy on rougher fields. So take that into consideration when adjusting your FDM.

Another thing: WWI aircraft tires (tyres) where pneumatically inflated, just like bicycle, car and motorcycle tires of their day, and used latex rubber and fine threaded cotton or linen casings/treads. They were meant to be very light. Hard rubber tires are really heavy.

Not having suspension on any aircraft that has to taxi up to a take-off speed approaching 40 to 50 mph is asking for a lot of damage to the airframe if the ground is really rough. The 'natural give' of the airfarme will never give enough without some kind of failure.

Image

The Bleriot XI was first flown in 1909, with a working wheel suspension. In fact there were very few pioneering aircraft that did not have some sort of rudimentary L/G suspension. The Camel had a pair of V struts tied at their bottoms with an elaborate weldment, supporting two axles wrapped in shock cording at their pass through holes in the bottom of the V struts. You could have easily found this out by registering at the Aerodrome Forum and asked a few questions. There's a number of people around the world that restore original and build replica WWI aircraft, they might even be kind enough to send you images of their own work.
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Re: New historically realistic Sopwith Camel JSBSim FDM rele

Postby Bomber » Sat Apr 01, 2017 11:00 pm

It's an interesting plane....I've just done the coefficients for it's airfoil and it stalls out at 6 degs AoA.... now as the bottom wing has an incidence of 3 degrees, this means that when the aero/alpha-deg is at 0 degrees the wing is seeing 3 degree and at an aero/alpha-deg of 3 degrees the wing is stalling out...That's going to result in a not very forgiving plane, if you're flying close to 42knots.

It's an accident waiting to happen.
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Re: New historically realistic Sopwith Camel JSBSim FDM rele

Postby Alant » Sun Apr 02, 2017 9:45 pm

Please check your sources.

I have this for wing incidence https://www.flightglobal.com/FlightPDFArchive/1918/1918%20-%201019.PDF, which gives the rigging for both upper and lower wings.

With a biplane layout the airflow of each wing is strongly affected by the other wing. How have you taken these effects into account?

Alan

PS

The Camel, whilst being the most successful British fighter in combat, also suffered by far the highest number of non-combat and training fatalities. The handling was difficult to master

Alan
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Re: New historically realistic Sopwith Camel JSBSim FDM rele

Postby Bomber » Mon Apr 03, 2017 12:06 pm

Thanks Alan that agrees with what I wrote.... the wing has an incidence of 3 degrees...

I've not seen that page before and it does help with the weight of the fuel tanks although confused as it seems to imply that both the pressure and gravity fuel tanks are behind the pilot....when I'd expect the gravity tank to have been more local to the engine, somewhere near where the oil tank is located.

As for your question about the interference of the wings on each other... I've yet to come up with something satisfactory, in other words I'm ignoring it at present and will come up with some working method in time, maybe along the same lines as I've resolved ground effect.

regards

Simon
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Re: New historically realistic Sopwith Camel JSBSim FDM rele

Postby Alant » Mon Apr 03, 2017 4:13 pm

You only specified the bottom wing. The page I sent you says the top wing is rigged 2 degrees at the centre and 3 degrees at the wing tip.

This 1933 NACA report http://naca.central.cranfield.ac.uk/reports/1934/naca-report-458.pdf may help you in estimating the interaction between the wings. You could also search for any of the reports given in the list of references.
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Re: New historically realistic Sopwith Camel JSBSim FDM rele

Postby Bomber » Mon Apr 03, 2017 5:09 pm

Well yeh I did, but the reason was because I wanted to get the point across that there wasn't a lot of 'play' in these wings as they're set to an incidence that's roughly half their max AoA angle...and for that I didn't need to explain that the top wing has an incidence of 2 to 3 degree......3 degrees was enough to get the point across..

I'll read this and other info and see what can be achieved with regards interference, The intention is to produce a better fdm that what exists in FG, As no plane does this, If I can match and surpass then adding interference is way beyond where I need to get to to be better.
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Re: New historically realistic Sopwith Camel JSBSim FDM rele

Postby Thorsten » Mon Apr 03, 2017 5:13 pm

As no plane does this,


There's plenty of planes which do that - all for which there's windtunnel data for the whole body of the aircraft. As I've told you before, the Shuttle FDM for instance includes interferences between elevon movements and the aft fuselage, i.e. extra suction effects. It's your particular technique of separating airfoils which has a problem which these kinds of effects, not JSBSim or FG in general.
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Re: New historically realistic Sopwith Camel JSBSim FDM rele

Postby Bomber » Mon Apr 03, 2017 5:56 pm

Oh really Thorsten quit posturing, we're talking about a 1917 bi-plane here.....
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Re: New historically realistic Sopwith Camel JSBSim FDM rele

Postby Alant » Mon Apr 03, 2017 6:53 pm

The wings are probably set at 3 degrees so that the fuselage is aproximately in line with the airflow when flying at "high" speed.

Do you have any way of checking your FDM against published performance and handling data?
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Re: New historically realistic Sopwith Camel JSBSim FDM rele

Postby Bomber » Mon Apr 03, 2017 7:08 pm

At high speed 98kts and zero AoA (airfoil seeing 3 degs of AoA) the wing airfoil generates a lot more lift than is needed to maintain level flight... a lot of h-stab is needed to to maintain level flight.

I can test this plane any which way...

static engine performance test producing power to alt graph
wind tunnel testing of the airframe
and full flight testing using the auto pilot functions 'straight out the box' with no tuning required.

Simon
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Re: New historically realistic Sopwith Camel JSBSim FDM rele

Postby Alant » Mon Apr 03, 2017 7:49 pm

Lack of tail trim , thus requiring lots of stick in level flight was a well known problem with the Camel. On a PC based simulator this is no big deal, but was not a good thing on a real aircraft. The pilot could not let go of the stick to refold a map or unjam his guns.

Have you any data against which you have checked your simulation?
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Re: New historically realistic Sopwith Camel JSBSim FDM rele

Postby Bomber » Mon Apr 03, 2017 9:35 pm

Luckily the Camel by flug comes with a lot of historic documentation..... some accurate, some not, some contradictory.
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Re: New historically realistic Sopwith Camel JSBSim FDM rele

Postby Alant » Mon Apr 03, 2017 10:10 pm

See this for some modern wind tunnel tests, and a weight analysis on a replicahttps://www.scribd.com/document/338633686/Sopwith-Camel-Stability-Analysis
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Re: New historically realistic Sopwith Camel JSBSim FDM rele

Postby Thorsten » Tue Apr 04, 2017 5:26 am

Oh really Thorsten quit posturing, we're talking about a 1917 bi-plane here.....


In fact you were not... You couldn't resist the opportunity to talk down on others' work outside this thread: As no plane (emphasis mine) does this, If I can match and surpass then adding interference is way beyond where I need to get to to be better. - to which I pointed out you have no reason to claim this.

That's not a judgement on whether your or any other version of the Camel is better (that I don't know), it's a statement on accuracy of other planes in the repository - a topic which you started. I trust you're able to appreciate that difference.

Having said that, I suggest we all get back to enjoying the topic here.
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Re: New historically realistic Sopwith Camel JSBSim FDM rele

Postby Bomber » Tue Apr 04, 2017 11:19 am

I don't think of your shuttle as a plane...

If you're looking for accuracy... "There's plenty of planes which do that "... this is not true.

WE are talking about a 1917 plane, so it's pretty reasonable to assume when asked about top/bottom wing interference I'm replying as if talking about planes that have a top and bottom wing and not a shuttle... and how to improve the flight models of said plane...

So..... wind your neck in..
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