FSDreamTeam forum
General Category => Unofficial F/A-18 Acceleration Pack board => Topic started by: neutrino on September 05, 2009, 07:49:37 pm
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Hi, guys. I did some flight testing with the Acceleration Hornet to test which speed gives the approach AOA of 8.1 degrees at different weights. It seems that the FSX Hornet approach speed (8.1 AOA) is about 9 knots higher than the real world Hornet. For example, at 30,000 lbs gross weight, the FSX Hornet is at 8.1 AOA at 139 knots, but the real Hornet is at 130 knots. At max trap weight (34,000 lbs) the real hornet lands at 139 kts and the FSX Hornet at 148 kts. This means that we are landing at much higher speeds in the simulator. It's not such a big deal but I wonder if anyone else has noticed that? I am sure whoever modelled the aircraft had some good data to work with, and yet 9 kts is strange difference.
Edit (September 08, 2009): OK, I found the answer to the problem. It is very interesting. The Hornet appoach speed (8.1 degrees AOA) in the simulator is higher than the speed of the real Hornet (by 9 knots), simply because it does not land with the flaps fully extended. You can visually check the flaps in the sim at approach speeds and you will see that they are extended only about 50% of their full limit (45 degrees). This is even if you have pressed F8 and the 'FULL' flaps light is on. So the plane is actually very accurately modelled. If the real Hornet were to land with half flaps its speed at 8.1 AOA will match that of the Hornet in the simulation.
Why are the flaps not fully extended? Because of the Auto-flaps system the ACES has introduced in the Acceleration. The auto-flaps system has a logic that controls the position of the flaps depending on speed and AOA. It is always working in the background and you can know it is changing the flaps position each time the amber light 'FLAPS' goes on. It is a generic flight model system applicable to all aircraft in the simulator and can be turned on and off by the property 'maneuvering_flaps' in the aircraft.cfg file. If you put maneuvering_flaps=1 in the Cessna aircraft.cfg it will have auto-flaps just like the Hornet.
Unfortunatelly, because the system is not specific to the Hornet, it does a poor job of controlling the flaps in this particular aircraft. In the real Hornet the flaps are controlled by the flight control system based on airspeed and AOA, just like in the FSX system, but if you are in 'FULL' flaps mode, the logic will fully extend (45 degrees) the flaps at approach speeds. The FSX system however extends the flaps fully at speeds below 95 knots for the Hornet. I checked how the auto-flaps work in the Cessna, and they work fine - fully extended below 65 kts (approach speed) and fully retracted above 100 kts (cruise speed).
So you have a choice here, to leave the default <maneuvering_flaps=1> for the Hornet and enjoy the auto-flaps system, which works almost like in the real Hornet at high speeds, but at appoach speeds your flaps will not be fully extended as they are in the real Hornet. This will put an additional 9 kts to your approach speed and your nose is certain to hit the deck of the carrier if you land at close to your maximum weight. Also your VSI will be higher. The F5 to F8 keys in this mode only control the maximum deflection of the flaps and the lights 'HALF' and 'FULL' should not be used as an indication of flap position.
The other choice is to set <maneuvering_flaps=0> (for both leading edge and trailing edge flaps - [flaps.0] and [flaps.1] respectively) and manually control the position of the flaps. Make sure you are not at FULL flaps above 160 kts, and at HALF flaps above 200 kts. Switching off the auto-flaps system by changing a line in a file looks like tinkering, but in the real Hornet you can also turn off the FCS control of the flaps if you put the GAIN switch on the FCS panel (behind the throttle) in "ORIDE" instead of "NORMAL". Unfortunatelly this is not impleneted in the FSX Hornet, so feel free to change it in the aircraft.cfg :)
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What happens if you drop the FSX Hornet down to the real world speeds? With full flaps, you should be able to match the real Hornet speed of 139 knots, which to me seems slow for a supersonic aircraft. A Boeing 737 comes in hotter than that.
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What happens if you drop the FSX Hornet down to the real world speeds? With full flaps, you should be able to match the real Hornet speed of 139 knots, which to me seems slow for a supersonic aircraft. A Boeing 737 comes in hotter than that.
You can do that, but the AOA will have to increase to 9.1 degrees, to support the aircraft at the lower speed, which is 1 degree more than the recommended value. You will be landing at a speed closer to your stall speed which is of course more dangerous and will make the aircraft more difficult to control. Also in carrier landings, the hook touch down point will move aft by about 4-5 feet.
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neutrino, I would be interested to know where the data is for the Hornet Optimum AoA please. Often this information is in a NATOPS graph but I do not have one for the Hornet. Thanks.
As a complete generalisation, having used in FSX only this Hornet and Dino Cattaneo's freeware Goshawk T-45C and Tomcat F-14D it would seem that it is difficult to get the Optimum AoA parameters correct (comparing sim to real world). For example (if memory serves well) the Dino Goshawk is about 5 to 10 knots KIAS slower at Optimum AoA compared to real world. HOWEVER... the aircraft performs it seems (without having flown it real world) as it should and I think same applies to Tomcat by Dino. He works on this issue though.
Another future FSX naval aircraft will be the RNZAF KAHU Skyhawk which probably will have a similar issue with Optimum AoA / KIAS matchup but for the moment it seems to fly well (with other issues yet to be solved).
I would suggest that flying at the indicated Optimum AoA on the indexer is the only way to do it in the sim with the aircraft below max. landing weight and properly configured dirty (full flap, speedbrakes out, gear down).
As noted by neutrino it is vital to approach and land at Optimum AoA for not only NOT exceeding the maximum arrest speed for the gear but possibility of breaking the aircraft and also as noted the 'hook to ramp' distance (raising or lowering hook). The mirror/fresnel lens glidepath is calibrated for the pilot eyeline at Optimum Angle of Attack. Flying outside any of the parameters required for a carrier landing is fraught (real world). In the sim one may get away with changes however my suggestion would be to stick with what is there and fly at the indexer indicated Optimum Angle of Attack below the Max. Landing Weight.
Without knowing how the Hornet specs were modelled in FSX, perhaps what is there is optimised for the model. To my knowledge from the KAHU model maker for example there are many limitations in the sim that have to be fudged to get close to real world modelling. Perhaps the difference in KIAS to Optimum Angle of Attack for the Hornet in FSX is one of those examples of compromise?
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neutrino, I would be interested to know where the data is for the Hornet Optimum AoA please. Often this information is in a NATOPS graph but I do not have one for the Hornet. Thanks.
Yes, it is from NATOPS.
I would suggest that flying at the indicated Optimum AoA on the indexer is the only way to do it in the sim with the aircraft below max. landing weight and properly configured dirty (full flap, speedbrakes out, gear down).
Why the speedbrakes? I thought at least in the groove you don't use speedbrakes...
Flying outside any of the parameters required for a carrier landing is fraught (real world).
I like that statement ;D
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neutrino, Would you do me a big favour please and make a screengrab or scan of the relevant Optimum or AoA info pages please? TIA. Here is the LSO NATOPS info for the Hornet. This LSO manual used to be online same place as the Hornet NATOPS but sadly now taken offline. Neutrino drop me an e-mail for more info.
Question about speedbrakes: AFAIK it is standard operating procedure (SOP) to have S/Bs out, full flap since about the 1960s with the early Skyhawks and then for all jets. It was discovered then that for a few extra pounds of fuel with slightly higher drag (S/Bs don't have that much effect at slow speed) the extra engine RPM required to be at optimum parameters meant faster engine response (to full power especially) which is a good thing when needed. Perhaps now in individual aircraft cases this may no longer be the case; but I have not researched this aspect for the Hornet / Super Hornet. I will do that later.
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Some random pages here from a Google book online may help answer questions but because of random nature of pages presented there does not seem to be info about the Hornet S/B issues: http://books.google.com/books?id=D-ctX2Q-CSIC&pg=PA196&lpg=PA196&dq=Hornet+Speedbrake+out+for+carrier+approach&source=bl&ots=sf9w2DV2zw&sig=edwtvgnRGgKA8bOTWJyCGtWYYds&hl=en&ei=eP2iSozwOILYsQPEsYiNDw&sa=X&oi=book_result&ct=result&resnum=1#v=onepage&q=&f=false
Good discussion here (which may not be totally accurate regarding S/Bs and other stuff but...): http://fsxproblueangels.com/phpBB3/viewtopic.php?f=15&t=224
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Good stories here about Hornet Ops in USN, specific quote about the break and dirty up on downwind (no mention of putting the S/Bs back in):
http://www.neptunuslex.com/2005/10/18/rhythms-part-xxxiv/
"After counting off 19 seconds from the lead’s break turn to downwind, the wingman started his own left break- much less aggressively than his lead, but still a good turn, the g-forces pulling at his head, his forearms, pushing him down in his seat. He brings the throttles smoothly back aft to flight idle, thumbing the speedbrake out. Under the combination of idle power, high “g” and speedbrake deployment, the jet rapidly decelerates, and at 250 kts he lowers the landing gear and flaps. The landing gear make abrupt hydraulic coughs and grinding sounds in their transition, the sound instantly overcome by the wind noise as they fall into the windstream while the flaps cause the jet to pitch bobble up a bit. Gear down and locked and the sound goes to a reduced, but still elevated pitch from normal flight. With the gear down and verified locked, and the flaps down, he must continuously trim the jet’s nose back up as she slows down to approach speed.
Established now on downwind now the timeline seems to accelerate, and the wingman races to complete his landing checklist, dial his radar altimeter warning bug down to 400 feet (the LSO warning: “Never go below 400 feet without a ball” flits in his head). His abeam distance is 1.3 nm – a little tight – and he drops the right wing for a moment to build some separation before reversing back to the left to start his descending approach turn as the carrier’s fantail goes by, this time in the opposite direction." CONTINUED HERE: http://www.neptunuslex.com/2005/10/23/rhythms-part-iiiv/
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Apologies for incorrect assumption regarding Hornet S/B use. Always pays to ask a Hornet pilot! Here is the response to my question: "Does a Hornet use S/Bs for a carrier approach"?
"By no means, in fact the speedbrakes automatically retract when the
gear or flaps are lowered. They have to be manually thumbed out and
held out in those cases. They disrupt the airflow over and around the
rudders.
As you may know, in the Super Hornet there are no speedbrakes per se,
but rather the ailerons, flaps and rudders feather in opposition to
one another."
Not having a Hornet NATOPS to refer to is just sad. ;D Often I have seen reference to the S/Bs being deployed for the break into a carrier circuit (SOP) but then no mention of them again during the subsquent carrier approach. Oh well. ::)
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Nothing like a good NATOPS diagram. [The colour text is my amendment + title.] I believe this one is from an appropriate model NATOPS (awaiting a confirmation from former Hornet pilot). Anyway the online PDF is pretty good for the Falcon 4 sim Hornet C model. However having nothing to compare it with I have no idea about accuracy but it looks appropriate, especially the injunction to select S/Bs in going downwind (after S/Bs out - optional for the break): http://www.cockpits.net/files/FA-18Cv3.0_MANUAL.pdf (1.2Mb)
Here is comment from a former Hornet pilot about the diagram (I guess the diagram we see has been modified for the Falcon 4 sim settings required): (I had asked: Is this diagram close to 'real thing' from NATOPS)
"Pretty close. I think that downwind level power was closer to 85-87%,
maybe 82-83% in the approach turn. Whatever got you 300FPM rate of
descent to the 90, increasing to 500FPM to the 45 and 750 or so in the
groove. Which looked more like "right wingtip of the velocity vector
on the zero pitch line" for the first part of the turn, gradually
increasing to 3 degree negative pitch on final. And as I mentioned,
the speedbrake retract was an automatic function, not a checklist
item. Unless you were really hauling the chilly (>400kts, e.g.) you
wouldn't even use it. She bled down readily at idle power with any
kind of g on. We also used 25-27 degrees AOB from the 180 rather than
30. If you were at 30 degrees AOB (especially in autothrottles) you'd
practically be guaranteed a wrapped up, fast nose down start, or (in
manual) an angling approach."
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EVERYTHING YOU MAY WANT TO KNOW ABOUT WHYs and WHEREFOREs of CARRIER LANDINGS PDF ;D
http://www.robertheffley.com/docs/HQs/NAVAIR_2002_71.pdf (3Mb)
"4.4.10 SPEED BRAKES page 75 (of 220)
Many historic Navy aircraft extended speed brakes on CV approach. This provided several benefits.
First, the increased drag of the speed brakes moved the bottom of the drag bucket to a lower speed,
moving the Vpa closer to the frontside of the power-required curve, and thus improving the
flightpath stability. Next, the additional drag necessitated a higher mean power setting, with two
consequent benefits. A higher mean power point enabled faster, more linear thrust response, thereby
improving GS tracking. Furthermore, the higher mean power setting permitted a quicker transition to
full power in the event of either bolter or waveoff. This, together with simultaneous stowage of the
speed brakes, permitted more rapid achievement of the maximum excess power. While not deployed
by the F/A-18A-D models on approach, speed brakes remain a viable means of improving the
handling and performance on approach (e.g., operationally deployed EA-6B and F-14)."
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Thanks SpazSinbad for the airbrake info!
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neutrino, no thank you for the graphic below (I guess this is OK with you?). IT is interesting to find out these things that otherwise I had assumed were the case (that use of S/Bs was standard, except with the Super Hornet and I have a NATOPS for that). Maybe one day there will be a Super Hornet for FSX? Anyway it is a big learning curve for me also. The graphic shows the Optimum Angle of Attack for different AUW and dirty conditions for the F/A-18C (from NATOPS?) keep in mind the different limitations of arrestor gear (if needed - as per the LSO NATOPS info).
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Neutrino, Missed your 'amendment at top of page'. Many thanks for figuring out what is happening with the FLAPs.
Yes at first I was puzzled by the 'look' of the flaps in the Hornet when they were supposed to be at FULL. Then I forgot about it (because I had the speedbrake out). :-) Because this is a simulator - try using the speedbrake as well to see how that affects the Optimum Angle of Attack, as well as your 'FULL FLAP workaround'. We can see that already the FSX Hornet has a lot of compromises in the implementation. Personally I prefer to land at slower KIAS so I don't get KILLED. ::)
A good example of this would be the Freeware Goshawk T-45C by Dino Cattaneo. This bird lands slower (also slower than real speed) so it is a nice introduction to carrier landings and using the AoA indexer at Optimum.
Remember it will always be best to land at the minimum airspeed possible for the AUW. The arrestor gear has limits (what they are in the sim I do not know). To enable surviving a marginal carrier landing would not it be best to minimise the energy expended on the flight deck at arrest?
Another reason when on land doing FCLP to have the strongest wind possible down the runway (without low level turbulence by the way) to help get that slow groundspeed approach.
The LSO NATOPS manuals have graphs showing the effect of WOD (Wind Over the Deck) on the glideslope. How the effective glideslope is changed by the WOD and how there is an ideal WOD. I'll not try to describe here what the diagram shows. It'll appear here soonish.
BTW not sure what you mean by "...if you land at close to your maximum weight. Also your VSI will be higher." I think you misunderstand but maybe I misunderstand what you are saying here. Anyway it is always best initially to land at a minimum realistic AUW rather than at the maximum because at the lowest AUW your KIAS will be lower and your energy at arrest will be much lower (groundspeed slower multiplied by lower AUW) to cause a problem if any other variable is dodgy.
Neutrino, thanks again for figuring out the FLAP thing.
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This is a worthwhile PDF download (4.1Mb) because the data is around the time of the Hornet (rather than later similar LSO NATOPS manuals). However the information remains at its most basic the same. Here are some graphs from this PDF:
NATOPS LANDING SIGNAL OFFICER MANUAL NAVAIR 00-80T-104 dated 1 Nov 1997
http://www.robertheffley.com/docs/CV_environ/00-80T-104--LSO%20NATOPS.pdf
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Amazing background info to Whys and Wherefors for USN Carrier Landings PDF:
http://www.robertheffley.com/docs/HQs/NAVAIR_2002_71.pdf (2.8Mb)
OR
http://www.aoe.vt.edu/~durham/2002-71.pdf
Info in graphic perhaps is not easy to understand without reading part of the PDF but I'll post it here anyway to encourage those interested to download the PDF for themselves.
NB: the max trap weight chart (last column) for 'ideal landing speed' - don't misread this as something to aim for. It is only a nominal value. The Optimum Angle of Attack for any given All Up Weight (below maximum) is the way to determine the landing speed (which is irrelevant if you are monitoring the Optimum Angle of Attack). Also the last paragraph mentions that 'the rate at which the pilot monitors GS (glideslope), lineup and Optimum AoA' is the only way to get a good approach. In other words don't wait until you see a large deviation to make a change back to ideal. Try to anticipate once a trend starts - to correct that trend back to ideal. Perhaps this is really difficult in the FSX environment (due to not being able to see the mirror from any reasonable distance and then to see it with minute accuracy on a monitor) but it is something to keep in mind for your flying carrier approaches in FSX. Happy Landings. ;D
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BTW not sure what you mean by "...if you land at close to your maximum weight. Also your VSI will be higher." I think you misunderstand but maybe I misunderstand what you are saying here. Anyway it is always best initially to land at a minimum realistic AUW rather than at the maximum because at the lowest AUW your KIAS will be lower and your energy at arrest will be much lower (groundspeed slower multiplied by lower AUW) to cause a problem if any other variable is dodgy.
Some interesting stuff in these documents, SpazSinbad. What I meant was that if you are faster on approach and want to maintain the same effective glideslope angle (angle of descent), naturally your vertical speed (VSI) will be proportionately higher. So you are both havier and faster and as you point your kinetic energy will be higher (not good for landing gear and arresting gear). In real life you may have to dump fuel to lower your weight below max trap weight. For the Hornet this is 34,000 lbs, which is a clean configuration + 87% fuel in the internal tanks. So in the simulator if you land at 100% fuel (as the Carrier Practice mission is designed) and have the default auto-flaps, you will have to land at about 150 knots and about 750 fpm and hit the deck really hard. I personally find that not realistic so before finding out about the autoflaps I usually set my fuel to 50%. I am posting the fuel destribution in the tanks I am using to preserve the CG position. The Left tip and Right tip tanks feed the Left and Right Aux. tanks, so they must be empty first. The Left and Right tanks feed the engine so they must be emptied last.
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Neutrino said: "...if you are faster on approach and want to maintain the same effective glideslope angle (angle of descent), naturally your vertical speed (VSI) will be proportionately higher." Don't worry about anything other than what the mirror/IFLOLS is showing you. There is no other thing to consider apart from lineup and Optimum Angle of Attack - below maximum landing weight and of course the GS (glideslope shown via mirror). A carrier pilot is not concerned with 'other variables'. Other people (the LSO and Airboss and people on or below deck) concern themselves with these 'other variables' to ensure that the WOD and the arrestor gear are correct and that the deck is not 'foul'. The pilot himself can only know about these things if he is told, otherwise he assumes that all is within acceptable limits. There is NO effective glideslope angle to be maintained - unless one speaks about a visual landing ashore on a runway without any landing aids. Even then a carrier pilot will instinctively maintain a constant glideslope to the best of his ability. Otherwise the carrier pilot is not trying to maintain a visual carrier landing by looking at the deck (deck spotting). The mirror is the only guide for glideslope information.
In real world a carrier can make too much WOD - more than ideal - for any given aircraft. Other LSO manuals have these figures if you are interested. There are many variations on the LSO NATOPS manual out there, some more recent with even more information than the one online at that URL given.
There is information about the rate of descent for any given angle of descent. However as the other charts suggest these things vary according to conditions. If a nominal ROD is 800 feet per minute then the aircraft is stressed to much more than that for ordinary operations because the ship moves up and down. If I remember correctly a one degree ship ramp/landing area movement up is an effective one degree steepening of the glideslope. For a carrier landing the many variables are relative as shown in the 'speed definition' diagram. There is a 5% factor noted, perhaps this 'factor' can be seen in the slightly higher approach airspeed due to the auto flap issue noted at beginning of this thread. You can see how some of the 'other variables' need to be considered (but not by the pilot at time of approach):
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SpazSinbad, I agree completely about not concerning yourself with anything other than ball, linup and AOA when in the groove. What I meant under "effective glideslope" is the angle of descent of the aircraft relative to the earth surface. If there is wind over deck this angle will be lower than the basic glideslope angle of the lens assembly (tipically 3.5 to 4.0 degrees). So my statement should read: "If you increase your speed and your angle of descent stays the same (your velocity vector is in the same position relative to the pitch ladder), then your descent rate (VSI) will also necessarily increase."
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Neutrino, OK - what is crucial is the non variable "relative to the earth's surface". So now you are referring to a runway landing. Remember for a carrier landing the ship is always moving away from you - unless it is stationary. This movement will decrease the angle. However all these issues for carrier landings are theoretical for thinking about - only when NOT carrier landing. The only thing to be concerned about when carrier landing are the three items. ;D Life is simple in that respect. ;D GlideSlope/Lineup/Optimum Angle of Attack.
Perhaps if someone is landing on a non-moving carrier then also the non-movement of the angle deck centreline makes that landing easier. In this case I would recommend making a strong WOD (straight down the angled deck centreline) without turbulence to help simulate carrier conditions (no point in having turbulence at low level except if you are a masochist). ;D With a stationary carrier with nil wind then it is more of an issue to be on the correct parameters - an unknown factor is the breaking point of the sim arrestor gear - so once again I would recommend that all carrier landings be done at a minimum fuel state (rather than maximum fuel state) YMMV.
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Hello fellas...
Just a quick two cents. I used neutrino's method but only enabled manual command of the FULL FLAPS position. This is done by only altering the [flaps.1] "maneuvering_flaps=0" rewrite to your "aircraft.cfg" file. You can use the half flaps as you please in their default AUTO mode, and then only use FULL FLAPS when you are below 160 and in a landing configuration. Using this mod is making the F-18 really fun to land on the carrier now.
Laterz
Sludge
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fgrimley32, good to know about the flap fix you have tried. Have not got around to that myself. Hope to do so later. Try having the speedbrake out also even though it is not 'kosher' for the Hornet - everything helps in my book (as per the olden days). ::)
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SPAZ...
OK, I think I was wrong in describing what my "flap fix" does. It allows manual command of the TRAILING EDGE flaps, not manual command of FULL FLAPS for both TRAILING AND LEADING EDGE. I guess the reason I got good results in that it still drops the trailing edge flaps to their optimum landing config of 45 degrees, when I selected full flaps.
When I get done with work today and head home, I will re-mod my "aircraft.cfg" file and set both to manual and see what difference that makes in landing.
Laterz,
Sludge