Originally published at: http://www.mudspike.com/flight-factor-a320-ultimate/
One of our resident real world Airbus A320 pilots takes the recently released Flight Factor A320 Ultimate for a test flight, wringing it out in ways only an actual Airbus pilot could think of…. So. Here we are. Flight Factor’s A320. I was in two minds about getting it, to start with, in much the…
Originally published at: http://www.mudspike.com/flight-factor-a320-ultimate/
oops! I see I wrote my little float down memory lane in the wrong spot. Great write-up @Cygon_Parrot. And by all accounts an amazing module.
What are the opinions on its current state? It’s currently on sale, but still priced pretty steeply at $81.
Yeah. I still haven’t pulled the trigger on it just because at that level of entry point, I feel I’d need to really dedicate some time to learning it properly.
Probably answered further up in the thread…but anyone try it in VR and is it pretty operable?
true that. Although if a plane is fun to fly, the hours come easily. I watched some vids and it seems to be in a good spot. I may have had a few hours for myself to spend simming anyway, so…
Had a bit of time this evening…
Subject for today. Flexing…
No, no, Miss. Not that sort of flexing. Flexing with the Airbus.
So, asks @Sryan, how do we calculate a Flexible Take Off assumed temperature for an Airbus A-320? Well, the short answer is…
As a pilot, you do not.
You read it off the RTOW (Regulatory Take Off Weight) tables, provided for you by your airline’s Operations Engineering Department, prepared using approved Airbus Industrie methods and tools. I HAVE to say this, please understand, before the fun starts.
This basically boils down to an application called the FOVE (Flight Operations Versatile Environment). With FOVE, you input certain parameters, such as QNH, wind, runway, aircraft configuration, and TOW, among others. FOVE crunches this up, and spits out your V1/Vr/V2 and Flex Temperature for the given conditions. Now, pilots do not actually have FOVE. It is, as mentioned, and Operations Engineering tool, and the RTOW, produced by Opertaions Engineering using such resources as FOVE, is the pilot’s tool. Here’s an example of an RTOW…
I saw, used and was trained on the FOVE tool exactly once; at the Initial A-320 course. They show it to you to allow you to know how this data is produced for the A-320. Then it ceases to be your concern. I have still got the training manual for the FOVE tool. Here is a random picture of a page from it, to give you an idea…
You see, Airbus is very cagey about their data getting out in any great detail, because their competitors could use it for any number of… erm… “strategies”.
But this is the sim world, right? There is a way, hidden in the FCOM, and not some site that gives you the numbers as mysteriously as the RTOW. You get to do some work.
Some Preliminary Stuff…
Let us establish some things, first. This is going to be for the CFM 56-5B4. Now, @Sryan, you probably know a lot of this already, but I have to be reasonably complete. With that said, I might also have a slightly unorthodox approach to explaining this, as I will be trimming of a bit of the “blinding science” padding that surrounds this topic in order to be practical. Text book learners, please be tolerant.
Like most high-bypass turbines these days, the CFM has (at least, for now) a couple of limitations. The first of these is something called a Flat Rating, and then there is the thermal limitation. Let us expand…
Any such engine has mechanical (physical) limitations. Let us face it, it is a bunch of metal flying around an axis, and if it goes around too fast, it will begin to shed parts through material failure under centrifigal force. Just to give you these book limitation numbers (which include a margin to actual material failure), they are;
N1 - 104% = 5,200 rpm.
N2 - 105% = 15,180 rpm.
On an ISA day, sea level, the engine will produce 12,010 dekaNewtons of force at these figures, roughly equal to 27,000 lbf, which is the book thrust of the CFM 56-5B4. Even if atmospheric temperature (lower) conditions would allow the engine to run at higher rpm than this, without infringing on the thermal limitation and consequently producing more power, it should not be done. Therefore, this is the Flat Rating. Now, just to confuse matters a bit, engineers express the Flat Rating as a temperature. They are not wrong in a sense, of course, but for the sake of simplicity, this explanation initially gets the point across effectively and reasonably accurately.
In Airbus jargon, the Flat Rating is known as T-Ref. For the CFM 56-5B4, it is equal to ISA + 29º C. Now, here is why it can be considered a temperature rating.
Gas turbines, like the core of the CFM that drives the fan, are susceptible to the temperature of the air they intake for the combustion. There are some physics laws that describe this, but to stay simple, if you intake air at a given temperature and thrust setting (max rated), you will get a reasonably predictable higher temperature at the exhaust, through compression and combustion. If you only increase the temperature of the air being taken in, the exhaust temperature will also rise. If you keep increasing the air temperature going into the engine, you will eventually get to a point where the resultant exhaust temperature causes damage to the hot end of the engine.
You have reached the thermal (EGT) limit. If the outside air temperature rises above that of T-Ref (ISA + 29), we would need to reduce thrust to avoid going through that thermal limit. This does not mean the engine cannot be run (or the aircraft operated) above a real OAT that exceeds T-Ref, however, only that it cannot be run at its maximum thrust rating anymore. For all intents and purposes, the power the engine produces can be reduced up to 40% (for the -5B4) while adhering to the thermal limitation, and the aircraft still be operable (even considering a One Engine Inoperative scenario), with a corresponding TOW penalty.
In a nutshell, the Flat Rating temperature is the point along the scale of increase of OAT where the mechanical limitation meets the thermal limitation, beyond (higher OAT) which power must be reduced.
There is a limit to how high the OAT can be. The engine (-5B4) reaches the 40% reduction limit at approximately ISA + 40º C. That is called T-Max, in Airbus jargon. At sea level, T-Max is 55º C OAT. If it gets to be that hot, the aircraft should not fly.
Now, what is Flex?
Assumed temperature thrust reduction. As we have stated, the aircraft can safely take off with quite a bit less than full thrust, if its real TOW is below MTOW for the conditions. In other words, it could take off at a given real TOW even if the OAT were much higher. So, why not pretend we are at the MTOW for a higher OAT? The engine would use less fuel, and would not be straining against max rated thrust. We just need to feed the engine the temperature data so that the FADEC will not violate the temperature limits for the “assumed” temperature of that MTOW limit.
Now, because weight is a factor in this, the Flex temperature we can give the FADEC can be higher, even, than T-Max, if the aircraft is light enough. The limit of how much more than T-Max we can give the FADEC is known as T-MaxFlex, again, in Airbus jargon. It can be as high as ISA + 70º C (that is, up to 85º of Flex, at sea level).
Remember, the higher the Flex Temperature, the less thrust the engine is limited to produce.
So. How do we know how high we can take a Flex Temperature to reduce power? That is down to the TOW, which translates into how low we can get the V speeds (V1, Vr and V2) for a given TOW while increasing the Flex, from conservative values, until we either hit a VMC, VMU, or T-MaxFlex limit. It is a special case, though. We might see that in action some other time.
Those are the limits to keep in mind. Here they are, again, in brief;
T-Ref = ISA + 29
T-Max = ISA + 40
T-MaxFlex = ISA + 70
Flex temperature must never be lower than T-Ref.
Flex temperature must never be lower than the actual OAT.
Flex must never be used if the take off is performed from a contaminated runway (standing water, slush, snow, ice).
Finally, NEVER believe you are obligated to remain at Flex power once you have started a take off using it. If conditions require, for example if there are indications of wind shear and you are passed V1, you ALWAYS have TOGA thrust available to save the day. If there are doubts, FIREWALL the sucker if you are over V1, or REJECT if below V1 or VMCG. And NEVER take off on the assumption you are going to have both engines all the way. Flex power is actually enough to get you through a One Engine Inoperative scenario rotation if it occurs during a take off, yes, but if you are using extreme values, it is probably better to be safe than sorry. Do not forget the second segment gradient, there.
Now, Let the Fun Begin…
As we do not have any RTOW for sims, there is a table way to establish Flex Temp, V1, Vr, V2 provided in the FCOM. It is there for situations when you might have had to divert to a airport for which you do not have RTOW, to get you out of a corner. It is a bit rudimentary and limited, compared to the RTOW, but it works just fine. That is what we will use here for a couple of examples.
First, let us assert a simple scenario. We will not be doing too much interpolation for this one.
TOW = 68.4 tonnes
Flap Config 2
Elevation = Sea level
Length = 8,000 ft
Slope = 0.7% uphill
Wind = 10 knot head wind
QNH = 29.92
Temperature = 30º C
Now, let us look at these tables…
They establish the Minimum Control Speeds (VMC) for V1, Vr, and V2. Good to know, because you may never assign these speeds any lower than these under any circumstance. Get them, for a sea level airport, CONF 2.
V1 = 113, Vr = 117, V2 = 121
Now let’s look at this table…
It establishes the minimum (VMU / VMCA) V2 for a given TOW, CONF 2. Find the closest weight to our TOW (65 t) at SL.
V2 = 134
What this means. If, when we do the calculation, our V2 comes out lower than 134 KIAS, we must use 134 as our V2.
Now for the Runway Correction. Have a look at this table…
Start with the wind. We have an 8,000 ft long runway with a 10 knot head wind. You will see the correction is to add 31 feet for each knot of head wind. With 10 knots HW, that means 310 ft, right? Add that to the original runway length…
8,000 ft + 310 = 8,310 ft.
Now, look at the slope effect. We have a 0.7% uphill runway. Each 1% of uphill will theoretically shorten the runway by 1,205 ft, for an 8,000 ft runway. As we only have half a percent, then the result will be…
1,205 ft x 0.7 = 843.5 ft (say, 844 ft)
Subtract that from our last runway length result…
8,310 ft - 844 ft = 7,466 ft
That was easy. Our apparent (corrected) runway, with its conditions considered, is now 7,466 ft long. We can now go ahead and see what MTOW limit this gives us. Check out this table…
Look at the TEMP column. Find 30º C down it. Move across to the 7,000 and 8,000 corrected runway columns (as our corrected runway length is between these to values, we will interpolate them). Find these values…
7,000 ft at 30º C box:
MTOW = 75.1 t
8,000 ft at 30º C box:
MTOW = 79.3 t
Lets interpolate. This one is easy. As the resultant corrected runway falls almost exactly between the tabulated values, we can just do a simple mean average (in reality, this case is rare)…
MTOW = (75.1 t + 79.3 t) / 2 = 77.2 t
So, what does this mean? At TOGA, you could theoretically get an aircraft weighing 77.2 t off the runway. As our aircraft’s TOW is only 68.4 t, we are away with weight to spare. Now we can use that extra weight in our favour to FLEX! Here is how we do it.
Look at this table again…
Look down the two columns under the 7,000 ft and 8,000 ft corrected runway until you find two MTOW values either side of our aircraft’s real TOW (68.4 t). Then move across to the temperature column. The row at 55º looks fair, right? The values are…
7,000 ft at 55º C box:
MTOW = 68.0 t
Limit Codes = 3/9 (ignore, for now)
V1/Vr/V2 = 133 / 135 / 138
8,000 ft at 55º C box:
MTOW = 71.1 t
Limit Codes = 2/3 (ignore)
V1/Vr/V2 = 139 / 139 / 143
Interpolate the speeds…
V1 = (133 + 139) / 2 = 136 KIAS
Vr = (135 + 139) / 2 = 137 KIAS
V2 = (138 + 143) / 2 = 141 KIAS (rounded up)
None af those speeds are below the VMU/VMC limits we calculated earlier, so we can use them. And our FLEX temperature, to answer the original question posted by @Sryan is;
That is, the row we found our real TOW in. Put all that in your MCDU Take Off Perf page, for CONF 2.
PS: @Sryan, I noticed you had a bit of trouble on that post actually setting the thrust levers to the FLEX position, and ended up taking off at TOGA. If you are using FLEX, only advance the levers to this detent…
Your FMA should look like this…
All the best!
The Official 4th Annual Mudspike Christmas Flight - 2018 Edition
Thanks for the post- but it started way better than it ended!
What? You mean that wasn’t the best bit of leisurely fun you’ve ever had?
But no worries; it was an answer to a member for a very specific curiosity. Much as I would like to say “yeah, it is easy, just guess a number between T-Ref and T-MaxFlex, and you are good”, it unfortunately does have a process, if you have to revert to doing it without the RTOW, for whatever reason. Actually, there is a lot more that could follow on, but I had already been typing for an hour.
Over on the Where are You photos thread there might be something a bit more interesting, in a moment.
Woah thanks a lot for that, @Cygon_Parrot! Looking forward to putting it to use on my next leg!
And yes, i have the throttles figured out First CLACK gives you climb, Second CLACK gives you flex/mct and the last one gives you TOGA. I was just mentioning some issues I had when I was first learning her.
That’s very interesting. So is the standard procedure for an engine failure to advance the throttle lever to TOGA on every V1 cut or climb scenario?
No. Flex is sufficient enough to handle a company specific EOSID (engine out sid ).
Though, if you got it (more power) why not use it? but its not a requirement.
That’s an article-worthy post! You guys are too good!
Exactly what @Bogusheadbox said.
I’m very glad you picked up on it, though, as it is a comment based on specific experience, and in part is the reason behind the triggering of this…
I do realize this is probably known generally on the forum, so I’ll be very condensed. OEI-SIDs conform to the four segments, which must guarantee the greater gradient of the regulatory minimum gradient one engine inoperative climb performance (as defined in FAR Part 25, for example) or at least a 35 foot clearance to terrain from the net gradient that may be along the path, if these obstacles impinge on the regulatory gradients. If the latter is an issue, then the MTOW must be reduced to assure the climb / clearance requirement. There are several charts (graphs) for it, which would have been part two of the original post directed at @Sryan.
Here is one, for close obstacles, at CONF 2. Everyone will get the idea just looking at it…
Generally, at an airport without any significant terrain, the regulatory gradients complied with give you plenty of room as you climb away on one engine, and you feel quite comfortable with FLEX. The story changes a bit at places like Quito, Bogotá, and La Paz, where there is significant terrain. Further to that, there are turns to be executed during the OEI-SID (on the first two mentioned) while you are still performing the second segment, followed by unavoidable proximity to terrain afterwards.
The difference between the comfort of being at 1,500 ft afe at a flat terrain airport, and at a minimum of 35 feet agl over surrounding terrain is worth living, at FLEX power, if you are an adrenaline junky. Then there are always considerations of katabatic winds and general thermal activity further eroding that 35 foot screen.
Therefore for us, at the mentioned airports, establishing TOGA as soon as possible to increase our terrain clearance, in the event of a One Engine Inoperative scenario, is mandatory.
Again, @BeachAV8R, thanks for picking up on it!
LOL! Thanks for the kind words!