jcagle
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Posts posted by jcagle
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Thank you for the kind words. This is probably the most rewarding accomplishment that I could hope to achieve as a developer. I hope it continues to live up to your standards, and please don't hesitate to throw out some suggestions (particularly related to the flight mechanics) if they arise.
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Nice! Beautiful shots!
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I'm sorry I was wasn't clear, I meant you should read it now. I'm awful about reading manuals for any product I buy.
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Landing can be a bit challenging, especially is you drop below the recommended final approach speed of 100KIAS. You should definitely read the threads pinned at the top of this forum about some of the unusual flight characteristics of the Bronco.
Low-Speed
Adverse and pro-verse yaw
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Greetings Alvaro and fdm79,
I was the flight modeler for this project and might be able to give a little more insight into the topic of fuel flow.
For a gas turbine engine in FSX, the active Fuel flow is determined by the flowing equation:
Fuel Flow = Engine Thrust * Thrust Specific Fuel Consumption (TSFC)
I put in a significant amount effort to give an accurate thrust profile throughout the entire flight envelope. This involved creating engine tables from scratch by combining published performance data (see here) with known engine specifications as inputs and boundary conditions for a computer aided engineering program (CAE) which performs cycle analysis on gas turbine engines. (See Attached for raw data output imported to Excel) If you have any software which can edit .air files, I would suggest that you dump the Airbus's flight model and compare tables 1502-1506 with default MSFS to see what I am talking about.
While one has a significant amount of control over engine thrust, TSFC is a static variable in FSX. This is a somewhat reasonable assumption for a low bypass ratio turbofan or a turbojet, however, for a high bypass ratio turbo fan the TSFC is quite dynamic and primarily a function of: Altitude, Mach, and percentage of Maximum thrust. The difference between ground static and a cruise flight of M0.78 at FL350 is a factor of approximately 1.5. This makes it quite difficult to nail down a single value for use in the simulation. In this case, range was given priority over appropriate fuel flow for a single flight condition, and this was used as the standard from which the simulation TSFC was derived. Hopefully that answers your questions!
Kindest Regards,
John
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Looking at discrete trends is a good place to start with the subject of stopping an aircraft. A-10A charts happen to be within arms reach, it's a light aircraft relative to medium/large airliners, and it has huge drag surfaces; so I'll use it as an example. At 50,000lbs; a clean A-10 requires ~2,150ft to stop on a dry runway with flaps and speed brakes fully extended. At an identical Landing Index; with flaps and speed brakes fully retracted, the distance is only increased to ~2,800ft (~30% increase). A couple of reasons for this, and a good place to start is drag force. In the world Aeronautics, we're used to looking at coefficients since they are a great point of comparison between aerodynamic bodies (similar to BMEP in internal combustion engines). But, we're presently concerned with Newton's Second Law, so force is the order of the day. When air is the only fluid involved, Drag force is defined as:
Fd = 0.5*Air_Density*Cross_sectional_Area*Cd*Velocity^2
You can quickly see that the only two dynamic variables during a single landing run are Cd and Velocity. At approach/landing speeds, Cd is primarily a function of Reynolds Number; which is used to quantitatively establish the ratio between pressure and viscous forces on an object traveling through a fluid. It is defined as:
Rn = Air_Density*Characteristic_Length*Velocity/Absolute_Air_Viscosity
Trends based on Reynolds number tend vary by order of magnitude (10^1, 10^2, .... , 10^N) and between 20kts & 150kts, there's not going to be much change. So, Drag Force is heavily dependent on velocity. This makes drag devices relatively effective at high speed, but exponentially worse as speed decreases. This is where ground interaction comes into play..and where the physics gets really complex. But, the good news is that we all have a qualitative understanding of weather conditions on vehicle performance....hopefully not too many cars were smashed in the process.
In brief; empirical data and the associated physics (causality) tend to support the notion that drag devices provide a relatively large contribution initially, but stopping power is primarily dependent on surface/wheel interaction.
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Thanks Adam, I will take a hard look at theses and see what can be done.
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Dswo
1) This is a two fold question. The outer wing panels begin to stall at 20.4 degrees AoA and every surface is stalled by 25.5 degrees AoA. However, the aerodynamics are such that the lift coefficient continually increases until 35 Degrees AoA (the absolute Maximum). So, the F-16 stalls very subtly in FSX. What purposes are you wanting to know stall, take-off and landing, or maneuvers?
Take-off Speed Range:
First off, these numbers are a little low compared to what's happening in FSX, especially on CAT-III models. Take-Off speeds coincide with slow speed performance and in order to achieve appropriate pitching capability in the air, the pitching ability on the groung (starting at a low AoA) was impeded. As far as I have been able to determine at this point, it's one of those FSX quirks, but I am actively seeking a solution (none found yet).
26,000lbs (Clean full fuel) : ~150 KIAS
39,000lbs (Loaded full fuel) : ~185-190 KIAS
Landing Speed Range:
20,000lbs (Clean near Empty fuel) - Final Approach: ~140 KIAS Touchdown: ~130 KIAS
28,000lbs (Loaded Near Empty fuel) - Final Approach: ~165 KIAS Touchdown: ~155 KIAS
If you are out on a short flight and try to land with full fuel stores, these numbers will go up quite a bit.
Maneuvering:
If you are trying to fly at the highest stable AoA (roughly 35 degrees), you should moving at ~80 KIAS.
2) I don't have an answer for you right away unfortunately. Engine performance was designed aroung constant altitude acceleration, so I have not been so motived to get high as quickly as possbile that I've broken out calculations. However, when I do want to get up quickly, I try to get up to ~550KCAS (Around Mach 0.95) and keep a roughly constant Calibrated Airspeed (which increases Mach number as you climb). This is by no means the official (military) or the optimal solution, for that I would send a PM to TAFKAM; he's been the hugely important practical resource I've tapped when lacking hard data.
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After watching the two videos....I would say the cause appears to be a lack of elevator control authority. At what speeds are you attempting this maneuver? Also, If you have the video saved on FS recorder, can you PM me and I"ll send you my email address?
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Where on earth do you find your rumours? :shock:
I picked up a phone and called Aerosoft Canada :wink:
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Rumour has the release period set for end of this month to begining of next, and a pre-order will get a copy sent to soon as soon as they come in the door
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neh when will this package be released?
I second; is the development within days, weeks, or months of being finished?
initial observation
in OV10 Bronco
Posted
While I can't speak for the other concerns, I can address the rate of climb. We did not use NASA data for anything related to thrust; that data was pulled directly from the flight manual (which was actually quite good). Unfortunately, I think this is a case where I can't confirm the problem. I tried to setup a similar flight, with centerline tank with a 50% total fuel load. This put the aircraft at a gross weight of 9,950lb. In the attached picture you'll see a bunch of numbers, and I'll do my best to point out the ones of interest.
(Yellow Box) - I have 237Gal of Fuel. Half of 252 Gal of internal fuel plus half of a 150Gal external tank would be 201Gal, so I'm running a little heavy,
(Magenta Box) - This tallies up for a gross weight of 9,943lbs
(Red Box) - You'll see my climb speed is 128KIAS. Climb matrix is this: Sea Level (0 Drag) 134KIAS, 5,000ft (0 Drag) 129; Sea Level (50 Drag) 127KIAS, 5,000ft (0 Drag) 123. I'm at roughly 2,350ft with centerline tank, which gives me a drag index of 14. Interpolating the above, and the recommended climb speed is 129KIAS. So I'm pretty close to where I should be (and undeniably nerdy).
(Blue Box) - I'm running at 1,713ft-lbs of torque on Engine 1 and a little more on Engine 2, but still less than the 1,878ft-lbs rated at military thrust.
(Red Box) - My climb speed is ~2,120ft/min
(Brown box) - I have a Newtonian (NET) thrust of 39lbs (Think F=m*a), which means I'm accelerating very, very slowly.
All added up; I'm a little heavy with the weight and little low on the power delivery, but still pretty close to your rated 2,300fpm. So, I would that hopefully all you need is a restart and the problem should heal itself. However, it is worth noting for the non OV-10 pilots reading this, that as the weight goes up with a full fuel load, this number will drop noticeably.