[GrahamB]

Who says an app has to prepackage aircraft profiles?

Surely one where you put in the basic figures for MAUW, sea level, zero slope, ISA, zero wind and then applies the various factors for the conditions on the day is only doing what you do manually. You can then apply whatever, ‘grass is a bit longer, humidity, flies on the leading edge’ to arrive at a judicious figure.

In today’s world, I sense more people are likely to actually perform a calculation that way than dig around in the POH to do it manually.

[Tim Dawson]

W&B calculations involve fewer variables and are much easier to digitise, with much smaller margin for error. They’re pretty simple to set up.

And most of our users have big difficulties doing so.

[Tim Dawson]

Graham, that sounds pretty reasonable. What we’ve always avoided is attempting to get the user to digitise the graphs in their PoH books.

We do already know the head or tailwind, runway surface, temperature and weight (if the user has bothered to do w&b) so there might be something we can do to help, I just don’t want people ever assuming we have done all their calculations and issued a go/no go decision for them.

[TheFarmer]

TheFarmer hits the nail on the head perfectly. Relying on an app for this sort of thing is asking for trouble, unless you have personally set it up for your exact airframe (NOT some pre-packaged profile).

But we are content to use an/the app for W&B?

I agree with Tim.

W&B tells you if the aircraft is within limits, how far within limits it is, and if it is balanced safely for flight. It’s pretty binary.

It’s the other 300* factors that determine if you end up in a hedge or get to your destination.

* made up number, but you get my point.

[Flyin'Dutch']

* made up number, but you get my point.

Of course.

I have 'used' the calculator devised by Cookie a few times, more out of curiosity rather than to make a go/no go decision.

Most of the time the performance limiting factor is me rather than the aeroplane and people, especially if they fly the same aeroplane all the time, should know really what their combo is capable off and what the performance is going to be.

To achieve that I play around with some figures when I am new on type, calculate those scenarios and see what the numbers are and will then know that, a long as I stay within those parameters (and don't eat too much cake!) I will be fine.

For field length I look at MAUW on grass to clear 50 feet and double that as strip length below which I will get the POH out.

A couple of SOPs - 80% of take-off speed at half the strip length, touch down no further than 1/3 in, no tailwind greater than 5 kts, has so far stood me in good stead.

And a timely reminder on here that high temperatures adversely affect our performance.

[Tim Dawson]

I agree with Tim.

I’m getting that framed and hanging it on the wall at SkyDemon HQ.

[Awful Charlie]

Why is there such a clamouring for an App for every slightly different problem these days? Do we need one app to add 2 to a number, and another app to add 3 to a number? Any reasonably modern spreadsheet can make calculations and produce graphs, Excel 2010 (and lots of others) can even put these on top of a POH picture


As so often has been pointed out, garbage in=garbage out, surely the PiC has to take the responsibility and whether using a spreadsheet/app/POH or whatever, if the numbers don't work/look unreasonable or odd, unknown or whatever, then has to go away to get sufficient information until such time that the amomolies are resolved?
Of course every aircraft model is going to be different, and I wouldn't expect Flyer to be the centre of worldwide aviation, maybe checking the owner groups/communities for the type of interest will find it, eg Mooney drivers can find a few models on Mooneyspace and doubtless others exist too. If there's not a suitable model for your type of interest, maybe you need to get your own finger out and put one together?

For those you must have an App over a spreadsheet, you can always try https://www.openasapp.net/home/

[NorthSouth]

Got to admit I've found the "use the numbers versus suck it and see" focus of this thread surprising. We've all been through training and have used the numbers in the POH, and passed exams to demonstrate our ability to use those numbers and to understand the various factors set out in the relevant AIC.

Two things that might be helpful:

1. The CAA recommended factors state that a 10% increase in weight causes a 20% increase in take-off distance. The trouble with this is that POHs only ever have figures for the MTOW, so what you really want to know is what effect a decrease in weight from MTOW has on take-off distance. I have put together a spreadsheet that does that calculation (as well as all the others). The arithmetic pendants among you will point out that a 20% distance increase for every 10% weight increase corresponds to a 20% decrease in TOD for every 9.1% reduction in weight from MTOW. In the spreadsheet I've rounded this up to 10% to be conservative.

2. In all the talk on this thread about how to account for soft tyres, old engines, tired props etc, no-one seems to have mentioned paragraph 3.2 of AIC 127/2006, which states:
"To ensure a high level of safety on public transport flights, there is a legal requirement to add specified safety factors to the
data. It is RECOMMENDED that at least the same factors be used for private flights."
Unfortunately the AIC doesn't say what those factors are, but for Performance Group E (covering most single pistons) they are x 1.33 for take-off and x 1.43 for landing. In my experience if you apply all the relevant environmental factors (slope, elevation, temp, wind etc) to your POH figure, then apply the public transport safety factor, you will ensure that you are always on the safe side of actual performance.

Hope this helps.

NS

[David Wood]

A friend of mine converted the Take off Graph for our group owned PA28-181 to an excel spreadsheet that works out the Take off Run and also the distance required to 50 ft.

I did the same for my Arrow and it isn't all that difficult, even for a maths biff like me. I ended up with a front end that looks like this.



It approximates the various lines on the various graphs in the POH and has served me well so far. It is for strictly private, non-official (guidance only) use, of course, since it is only an approximation of the POH. But I'd argue that in all practical senses it's no less accurate than drawing lines on dog-eared bits of paper.