The newsletter on Takeoff and Landing Calculations ( Navigraph ) mentions the word ‘gradient’ 4 times, yet it is not explained how this is really taken into account when calculations are made and what are limitations of SimBrief in this regards.
Most importantly, does Simbrief has a database of obstacles and does it take into account obstacle clearances when takeoff calculations are made? I guess no, and if so, all of these calculations are NOT really reliable, to say the least. Same goes about landing calculations (go-around gradient and obstacle clearance).
I understand it may be tricky to obtain and maintain DB of obstacles, if so, please at least provide users with a work-around of some sort, such as to allow users to input required gradient as input parameter or to input obstacles manually, like TOPCAT did.
Without this, these takeoff and landing calculations are not really usable, unless you operate in flat areas without any obstacles in vicinity of airfields, which is not the case in most cases, of course.
This is covered in the User Guide in more detail. But essentially, SimBrief ensures that the minimum climb gradient (2.4% for a twin-engine aircraft) is achieved during the second segment.
I don’t agree. Yes, in a perfect world we’d like to consider obstacles. But at the moment we don’t have an obstacle database, and haven’t found a useable or even remotely affordable source for one. We are still working on it and maybe this can be added in the future, but we decided this wasn’t something that should block the release of our tool. Here’s why:
The 2.4% second-segment climb gradient already covers many of the obstacles that exist around an airport. Because there are in fact regulations on how high an obstacle can be inside of a certain distance from the runway, there is a practical limit to how much obstacles can actually limit takeoff performance. No question, many airports do have obstacles that require a higher gradient than 2.4%, which will impact the takeoff calculation. But the impact is rarely large. In practical terms, you might see a reduction in MRTOW of 1-2 tons, or a reduction of a few degrees on the flex temperature. As with anything, there can be more extreme examples, but they are rare.
Obviously for a real-world operator, accounting for any obstacles (no matter how small) is critically important, as well as a regulatory requirement. But for flight simulator use, we need to temper our expectations a bit. A small weight penalty or slightly lower flex temperature isn’t going to make or break a takeoff in the simulator. Especially when you consider that these penalties are only needed to ensure obstacle clearance in case of an engine failure at V1 (which almost no simmers ever do), and that’s assuming the add-on you’re flying even has realistic single-engine climb performance to begin with (which many don’t).
In my opinion, it would be great to account for obstacles, and if we can do it at some point down the line we will! But I disagree that the lack of obstacles renders the calculations “unusable”. There are so many other sources of error in the simulator and potential inaccuracies in add-on performance that will have a much larger influence on the safety margins. Accounting for obstacles would be more of an immersion builder, rather than something that will actually be noticeable when taking off in the sim.
This is slightly different, SimBrief doesn’t currently calculate missed approach gradients at all, it’s a landing distance calculator only at the moment. Calculation of missed approach gradients is planned to be added at some point down the road.
Yes, this may come in a future update. The longest part is collecting the data and calculating the relationships between weight and climb gradient for each aircraft type, thrust setting, and flap setting. I’m sure you can appreciate the sheer amount of data we’ve already had to collect to develop the current calculations for over 100 aircraft types. This will take some time, but it’s being looked into.
Hey, just wanted to follow up with a related request (probably asked it before somewhere) - if I understand correctly, right now Simbrief does calculate the takeoff climb gradient to ensure the 2.4% required gradient is met. Would it be possible to, for now, provide the calculated gradient in the output? This wouldn’t require obstacle data, but would be very useful.