Primarily for general aviation discussion, but other aviation topics are also welcome.
User avatar
By PaulB
#1718901
brucehumblehand wrote:
PaulB wrote:Does Foreflight use the CAA factors?


What are CAA factors?

EDIT: Just researched this, and it seems that yes, Foreflight does indeed use the same factors for calculating performance. The nice thing about it is that it pulls all the required weather, runway and aircraft data automatically. All you have top do is tell it which aircraft and runway you wish to use. Very quick and very accurate.


I don't recall see any mention of safety factors here



and not mentioned here

https://www.foreflight.com/products/for ... rformance/

That said, it's clearly a powerful feature though seemingly US based (mentions ADSB weather which isn't available here)

There's a massive library of aircraft profiles here

https://foreflight.com/products/perform ... ctory/#/_/

Make no wonder that this feature is only available on the most expensive subscription.
#1718915
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).
bookworm, ivanmia, TheFarmer and 2 others liked this
#1718956
What are these “exact airframe” settings and differences then? Last time I looked, the performance figures for each variant of most types were identical published POH charts?
neilmurg liked this
#1718962
Balliol wrote:Somewhat surprised at some of the views so far to be honest. Calculating performance figures for your aircraft is a key licensing skill, and conceptually it gives you an idea of whether your intended runway/loading is suitable for the conditions - additional factors will always make it more conservative on top.

I agree @Balliol, however @TheFarmer has it right in my view.

Here's why; when it comes to using such an app how does one determine the definition for long grass and do airfields keep records of the grass type and how well drained it is,? And how does one determine just exactly how wet it is? Similar with snow, how wet is it, how slippy is it?

Of course there are factors in the POH, as well as apps which do the calcs, however, by definition, they are based on particular conditions, an independent judgement is still required as to how closely the actual conditions match the conditions used in calculating the factors.

Irrespective of whether the pilot uses the POH or an app a judgement is required.

The POH and apps have value, of course they do. I don't think anyone is questioning their value, however to blindly rely on them alone is risky.
kanga liked this
#1718963
Ok, so you’re sitting at the end of a grass runway..

Compared to last week, the temperature is the same, as are your passengers weights, but...

1. The ground is softer after three inches of rain.

2. Two of your tyres are softer because they’ve got slow punctures.

3. Your spats are full of fresh grass cuttings.

4. Your oil isn’t as warm as when you last took off because you’re rushing a bit.

5. Your headwind is slightly less constant.

6. Your MOGAS is a lower rating this week.

The above, amongst lots of other factors, could cumulatively add a 20% negative factor to your takeoff roll.

As you hit the trees at the far end, will your last words be “well, it was ok last Wednesday, and my App said it would be fine’.

App’s are great, but they seem to be squeezing themselves towards taking over from airmanship and solid decision making. I despaired when I saw the LAA advocating a SkyDemon rectangular ‘hold’ over Pitsford. If we are now going to rely on our iPads to tell us if we will get airborne, I’m glad I’m not a junior and inheritance-expectant relative of Bob Bevan!!
#1718969
But Shirley
Many of us take off and land from familiar airfields and over time, because the aircraft loads are less than MAUW and the runways are more than we require, we (well, you, I'm perfect) can get complacent. Part of the purpose of the calculation is to remind us to think about the variables so we don't do something stupid because we haven't thought about it. Like taking off with a slight tailwind in an unfamiliar plane on a marginal length runway, just because it avoided a backtrack and it was a downhill slope... like I did.
I worry that 'that worries me' isn't useful, it's just negativity, rather than useful advice; there is a lot of useful advice in TF's post
Balliol, Flyin'Dutch' liked this
#1718977
If we are supposed to a.) do the “complicated method” using the POH tables and charts and pencil and ruler, and then b.) apply various numeric adjustment factors (e.g. CAA) and then c.) use common sense and judgement on top of that, how is that different from using a Magic App which does a.) and b.) much quicker and allows us to focus on c.)?

I would suggest plenty of people routinely skip to their version of c.) without doing a.) and b.) at all because it’s too cumbersome, and I’ll bet it frequently contains mistakes.

Common sense and judgement need to used, but why not make the purely factual piece easier to get to as a starting point?
Balliol, ChrisT, neilmurg and 1 others liked this
#1718997
All that is being suggested is an app which does electronically what this does in a steam driven world?

Image

And then gives the option to apply the additional factors the CAA suggests you might? To give a result with the same reliability (and liability) and use AND ANSWER as a manually calculated figure?

Except in extremis I wouldn't use it to give me a routine go/no-go assessment of a marginal strip (I always want 50% more!) but i would use it to assess the suitability of a distant airfield as a stopping point.
Flyin'Dutch', PaulB liked this
#1718999
Uptimist wrote:If we are supposed to a.) do the “complicated method” using the POH tables and charts and pencil and ruler, and then b.) apply various numeric adjustment factors (e.g. CAA) and then c.) use common sense and judgement on top of that, how is that different from using a Magic App which does a.) and b.) much quicker and allows us to focus on c.)?

I would suggest plenty of people routinely skip to their version of c.) without doing a.) and b.) at all because it’s too cumbersome, and I’ll bet it frequently contains mistakes.

Common sense and judgement need to used, but why not make the purely factual piece easier to get to as a starting point?


This! Thank you for a far better explanation of my thoughts than I could say! :thumleft:
#1719005
I agree, @JAFO, it has been established apps do exist to give rough calcs. I thought the discussion had gone on.

By definition, when the difference between what the POH (or app) and factual becomes significant I'd suggest it's too close for comfort and therefore of little use,

An analogy may be VFR minimums, the actuals are of little use to me, since I'll never intentionally come anywhere near having to use them to remain legal. I'll have made the no fly decision well before. I'd suggest that's what happens with questionable strips. As @matthew_w100 says, his requirements render the actuals of limited use.

How many LAA aircraft are flying without such info, even in a POH and manage fine?

I think @PaulB is looking for a solution to a problem that doesn't exist. Especially when you factor in the (in)consistency of the pilot. :D
#1719011
Tim Dawson wrote: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?

:scratch: