Modifying Air Files

[bub]

Hi All,
I realize this may be a silly question. I've been looking to modify the P-40b air file for Thorston's model to suit the P-40 II's flown by the Flying Tigers. I've found everything I need except the weight of the aircraft, empty, gross, max, etc. I'm more than likely just missing it. Using AirEd, where would I find those specs? Thanks in advance.
Bob

[No Dice]

Ivan in the CFS1 forum will know that info............

[bearcat241]

Empty weight is easily found in record 1101 Primary Aerodynamics -- adjust there. Keep in mind that any significant increase will effect take off power. Too much added empty weight and you'll need to add more horsepower to the engine data. However, there are no fixed records for Gross and Max weight. These two are more elusive and are actually an equation of calculated wing loading, lift and max take off thrust. The simplest approach is use trial and error to arrive at these by continuously increasing to the empty weight until she won't take off under max power anymore, then back it down until she barely gets airborne safely.

When you say "P-40 II's" are you referring to the P-40B which was the equivalent to the Tomahawk Mk.II export version used by the British?

[bub]

Thanks guys,
That would be the one BC. I found an article written by Erik Shilling, who stated that their aircraft had "better" performance due to differences from other models. Just trying to recreate it. I did look at that part of the air file. Just thought I was missing something. Thanks again.
Bob

[bearcat241]

What were the differences...did he offer any details?

[Thudman]

It has been said that the engines were cobbled together from rejected engines at the Curtiss/Allison factory for the AVG aircraft. The best parts were used after referring to factory specs. Basically the AVG engines were for all practical purposed "blueprint" engine and produces a little more horsepower when delivered.

[bub]

BC,
I remember from the article, can't find it in my files, that it was lighter due to not having the heavier armor required by the Air Corp along with different self-sealing fuel tanks. It also had no provisions for external tanks. Thudman is correct. Allison didn't have the required amount of engines. To meet the 100 for the contract they had to scour the part bins and put together the engines. They called them "Factory Fitted" engines. These had more horsepower, as they had a problem with burning out propeller reduction gears that were rated for the standard H.P. engine. Also, the roll rate at 260 m.p.h was 96 degrees per second. So, a conservative estimate of 20% more H.P. and 5% loss in weight should put it in the ballpark. I'll let you know how it turns out.
Bob

[bub]

BC,
Try these out. A little better, no drastic improvements. A little more H.P., a little less weight and a smidge better roll rate. 325 mph at 5000 ft. seems about right.
Bob

[bearcat241]

Not bad at all Bub, except for the minor detail of the lack of rudder authority at speed. You might want to bump that up a bit. Good for targeting. And also consider that almost all common flight dynamics tweaking in the community misses a critical hidden detail about the subject: the default number of propellers assumed by the *.air file is only two in all cases.

Strangely, there's nowhere in the air file to change this, so almost all performance mods are being based on a two-prop engine configuration - bad business for any model with more than two. I don't know if you're familiar with Airwrench or not, but if you have the program, it will confirm what i'm saying if you use it to look inside the air files one of the stock models.

You can mod this in the aircraft.cfg in the [propeller] section:

[propeller]
thrust_scalar = 1.0
propeller_blades= 3
rotation = 1

This is essential for achieving the best simulation of any model's engine thrust apart from raw horsepower. Imagine a two-bladed Corsair with 2800 hp versus a three-bladed Corsair with the same horsepower. Feel free to test this in your sim workshop.

[e.a.wicklund]

Love this airfile. This is just what I was looking for.


BC,
Try these out. A little better, no drastic improvements. A little more H.P., a little less weight and a smidge better roll rate. 325 mph at 5000 ft. seems about right.
Bob

[bub]

BC & e.a.,
Try this. I added the prop number line and bumped up the Rudder_Effectiveness from 1.0 t0 1.5 in the cfg. In the airfile, i increased the, in line 1101 Flight Dynamics, Rudder? from 14 to 22. It seems to have made an improvement. Not a lot, but enough. I may play with it a little more to fine tune it.
Bob

[bearcat241]

Works for me Bub...:encouragement: But i bumped the rudder to 5.5 for the extra tail "wag-ability". I like to carve tight doughnuts in the mud on strafing runs, not to mention the last second adjustments to line up my quarries just right.

[bub]

So you're saying to bump the rudder_effectiveness up to 5.5 in the cfg. I'll have to give it a try. Thanks for all your suggestions. If you think of anything else, let me know.
Bob