Hello hd764jvgd843,
First off, thanks for taking the time to provide such an in-depth evaluation and review of the Hornet! Second, although Sludge was the creator of this thread, he is not the creator or author of this jet. That person would be me
. I believe he has another thread for those interested in his variant of the F/A-18. And third....let's dig in and answer some of your questions!
;Moments of inertia values, including reference_datum_position and empty_weight_CG_position:
I noticed that these values have been changed from the original ones. Are the new ones correct or just best guess? A short explanation would be nice.
These values have been changed and are probably not accurate to the physical model. Some "cheats" have been made throughout the design of this jet, so that the flight control system that I have designed can complement the actual control of the jet. Great example would be the pitch control. If I implement the raw physics of the pitch control on the hornet, I could easily pull upwards of 12 Gs, which would be unrealistic due to the fact that the hornet has a limiter set to 8.5 and +33% with limiter off. The max that the gauges in FSX will refresh is 17 times per second. Using the raw physics model will quickly saturate the limiter that I have designed and would still allow for the jet to easily get to 12+ Gs. So I have to adjust certain parameters so that they "play well together". This is done in real life with the jet's Flight Control System. It takes the "raw jet" and waters it down to something manageable to fly and fight with....
[Turbine EngineData]
Static_thrust: I have found the following values to be correct, for the F404-GE-400 10600 Lbs and for the F404-GE-402 11950 Lbs.
Agreed. Throttle and thrust curves have been the bane of my existence here. I used a few things here. First I opened the .air file and adjust and tweaked the engines based on performance data from an actual Hornet Driver. In the document he provided, he gave different air speeds attained, at certain altitudes and certain fuel flows. The aircraft was clean. From there I used the formula for Thrust Specific Fuel Flow, and thrust vs. altitude, to derive how much thrust each engine was producing given the said conditions. Once I had the thrust curves correct, I adjusted drag and lift values to match the speed that the pilot had documented. Then there's a condition within FSX that has to be accounted for to have the engines actually provide more thrust at altitude (35,000 MSL) instead of diminishing it like most default jets in FSX do. Finally, I worked on matching the acceleration curves that was provided where the time was measure how long it took for the jet to accelerate from one airspeed to another. That's how the numbers fell once I accomplished that. Agreed, it's not perfect, but it's what I have for now.
Afterburner_available: number of AB states of 6 seems to be correct.
I was looking for the number of Afterburner stages in the NATOPS, but couldn't find it. If you could help me out and tell me where I can find it that would be awesome! Setting 20 stages provided more controllability while in afterburner.
Afterburner_throttle_threshold: I have found no actual references here, but for my personal gusto I assumed 0.70 (70%)
A lot of the testing and use of this jet is done by the FSX Blue Angels. Since most of us have some form of the Saitek X52 Flight Stick/Throttle, we decided on 80% since that is where the throttle detent is located on the actual throttle quadrant. It made it easy for us to distinguish between MIL and AB.
ThrustSpecificFuelConsumption: I have found the following values to be correct, for the F404-GE-400 0.85 and for the F404-GE-402 0.67
AfterburnThrustSpecificFuelConsumption: I have found the following values to be correct, for the F404-GE-400 1.85 and for the F404-GE-402 1.74
Notice: F404-GE-400 is the old engine which was replaced by the F404-GE-402 upgrades to all C/D Hornets in service today. Some NASA prototypes not to be included being A/B versions.
See reply to first question.
[Contact_points]
Impact damage thresholds: Are these values really that high? I find it almost impossible to crash the aircraft during a landing, even when fully loaded.
Feasible. If you can provide me with some accurate data to go by, I will adjust.
Static_cg_height:
I noticed that these values have been changed from the original ones. Are the new ones correct or just best guess? A short explanation would be nice.
This was adjust to compliment the FCS system designed for the jet. Mainly for the pith auto-trim system. Please remember that jets like the Hornet do not get its flight handling solely as a result of its physical characteristics. The control logic used to move control surfaces provided from the FCS and engine control, produce a jet that handles differently than what is displayed on paper. Good example is the way the Hornet's FCS uses the flight stick to control different things based on the speed of the aircraft. On the ground, the stick directly controls stabilator position in relation to the amount of pull or push. In the slow speed, landing, or high alpha region, the stick directly commands the jet to hold a certain angle of attack, and not stab position. At medium speeds, moving the stick commands pitch rate, or how fast the nose raises or lowers. At high speeds, G is commanded by the stick. My point is... you can't use "Cessna Logic" on the Hornet to get a realistic flying jet. Just plugging in the physical dimensions and power outputs of the jet into the CFG will not yield you a high fidelity, realistic flying jet. Matching the FCS's output and characteristics are what you have to chase after with this.
Toe_brakes_scale: Value seems much too high. Could almost land on a carrier without cables. A suggested value like 0.7 (brake balance) looks more realistic to me.
Agreed. The flip side of this is that the brakes on the hornet should be able to hold the jet on the ground while at a certain throttle setting. 80% N2 is a pretty common throttle setting for most Hornet drivers while doing run-ups just prior to releasing the brakes for the takeoff run. I found that difficult to do with 0.7. But I agree, the brakes are pretty aggressive. I will dive back into this one.
[Flaps]: positions & values. I noticed that these have been changed from the original ones. Are the new ones correct or just best guess? A short explanation would be nice.
A few of things here… First, the default "autoflap" system for FSX does not provide accurate flap settings for the Hornet base on what NATOPS documents. So I decided not to "fully" use it. Second, there is a chart in NATOPS that shows the flap scheduling of both the leading edge and trailing edge flaps. For the most part, both are based on angle of attack (AOA), but how they behave as AOA increases is not the same. The leading edge flaps deploy linearly as AOA increases to their maximum extension. The trailing edge flaps, however, follow more of a plateau, initially extending as AOA increases, then retracting as AOA increases past a certain AOA (28 deg. I think, will have to verify). FSX default auto flaps work on the same logic I stated for the leading edge flaps. So for the leading edge flaps, I opted to use the FSX autoflaps. To recreate the logic for the trailing edge flaps, I had to create a gauge to do so. One problem I encountered is that you can only designate 10 definite flap positions in FSX. Take 3 away for up, takeoff and landing flap angles that leaves me with 7 flaps positions that I can use for autoflaps. I turned to the NATOPS to determine the flap travel range while flaps are in the auto mode, and divided by 6 flap positions since that was an easy round number that I could divide by. This gave me an autoflap range to move the flaps in 3 degree increments to replicate the Hornet's trailing edge auto flaps characteristics.
[Airplane_geomentry]
Wing_span: Depending on what sources you look at, values like 40.4 ft or 37.5 ft are found. I believe neither of them to be correct for the simulator’s definition of wing_span. If you subtract from a width of 40.4 ft (with Aim9’s) the weapons (do not forget the weapons winglets), then the correct value here should be something like 38.7 ft. This roughly corresponds with the value I found on the Wikipedia website for the X-53 overall wing span (without weapons) of 38.5 ft. Have a look at the diagram I provided below.
Easy. Will adjust to accurately reflect.
Wing_twist: This is somewhat of a compromise. The original value of -1.5 degrees seems to be definitely wrong. When you look at actual FA-18C/D pictures, you can easily see that it is much more. I found a source stating that it actually is slightly more than 4 degrees, which seems to correspond with the visual appearance. The simulator can show wing twist only but does not alter the actual flight behavior. The FA-18C/D has a relatively flat and flexible wing, which bends under g loads (you can find several NASA test videos on the subject). So, from an estimated -4.1 degrees as the actual value my best guess as a compromise for actual flight behavior in the simulator would be something like -3.5 degrees.
I'll check this out. Played with it a bit a while back, but did not notice an impact.
Oswald_efficiency_factor: I tend to stick with the original 0.8 value here, because the FA-18C/D’s have relatively flat wings, thus limiting the lift efficiency (unlike the FA-18E/F’s which have much thicker wings, which can contain more fuel, too). An Oswald factor of 0.95 would be that of a high performance sail plane, which I find quite unrealistic here. When you compare the 0.8 value with that of several other calculated oswald values for other fighter aircraft, 0.8 as lift efficiency seems to be quite ok.
Not saying that the F/A-18 is anything near a sail plane, but does that 0.8 also take into effect the LEXs?
Wing_sweep: The original value of 20 degrees seems to be obviously wrong, because several sources state the FA-18C/D wing sweep to be 26.7 degrees, which can be easily visually confirmed. Have a look at the screen shot below.
You're
obviously right. I'll change it.
Wing_pos_apex_lon: Have you changed this value due to changed moments of inertia values? A short explanation would be nice?
Htail_area: 88.26 square feet seem to be correct, considered in relation to other values, too. See references.
Vtail_area: 104.2 square feet seem to be correct, considered in relation to other values, too. See references.
Elevator_area: 88.26 square feet seem to be correct, considered in relation to other values, too. See references. (for FA-18 elevator_area = htail_area)
Aileron_area: 24.4 square feet seem to be correct, considered in relation to other values, too. See references.
Rudder_area: 15.6 square feet seem to be correct, considered in relation to other values, too. See references.
You're probably right on all of these. I had to keep in consideration a few things like this jet has stabilators vs. elevators. V-Tail rudders and LEXs also assist in certain characteristics that normally would be absent in most aircraft. FSX doesn't necessarily account for all of these things. I have tweaked a few things to these areas to compensate.
Elevator_up/down_limit: I noticed that these values have been changed from the original ones. I have myself used similar ones, because the original ones seemed to be quite unrealistic. Are the new ones correct or just best guess? A short explanation would be nice.
Positive/Negative_g_limit_xxx: I noticed that these values have been changed from the original ones. I have myself used similar ones, because the original ones seemed to be quite unrealistic. Are the new ones correct or just best guess? A short explanation would be nice.
Thought I grabbed the values from NATOPS. Pretty sure it was 8.5 positive and -3.0 negative. There is a positive bump of G to about 10 G with override on. There is a decrease to 5.5 beyond a certain weight. Will double check and correct if needed.
.air: Concerning changes in the .air file, I noticed that flight behavior of the FA-18 at slow speed is quite sluggish (e.g. ability to roll), and not what
can be observed at several air show videos, which show a quite good maneuverability even at slow speeds. I noticed that some values have been changed here
from the original ones. Are the new ones correct or just best guess? A short explanation would be nice.
From several air show videos that I have observed, I noticed that the Hornet isn't quite as maneuverable at slow speeds as the default acceleration Hornet (i.e. full roll authority/capability at 30 KIAS) so I decided to change it. After viewing more Blue Angels airshows that I'd like to count, I decided to use their roll characteristics based off of certain maneuvers they have demonstrated in their air shows. Easy to change though…
Whew!!! That was a lot. Hopefully I've provided some reasonable explanations to some/all of your questions. As stated before, the jet is a work in progress and is by no means perfect. I'll keep working at it. Big take-away from this is, I am making changes to certain things to mimic the Flight Control System's control of the jet, and not pure physics (Cessna Logic). I have to do this due to my knowledge of coding within FSX. Until I can figure out/learn how to inject coding between IO input (physical control stick) and simulator output (FSX), and get all of the FCS logic used in the actual F/A-18 C (good luck with that...), I will have to continue using the technique that I have been using for the past few years.
Thanks again.
-Jimi
