@lionel all I can say is “oh come on” of course you czn fly a VPT accurately there are so many guides. As for the.rate 1 turn the VPT needs to be flown under 160knts which gives you a bank angle of 24°. At 90knts your bank angle would be 14°. There would not be a huge difference in the radius especially as you have a check point at A over the motoway junction which will give you a guide whether to tighten or loosen your turn. B is between 2 hills.
I don’t see the problem, really. What about others on here that fly to Cannes regularly?
gallois wrote:
There would not be a huge difference in the radius
The radius of a constant rate turn is proportional to the TAS, so at 90 KTAS, the radius is a bit more than half that at 160 KTAS. To me that’s a huge difference.
You think the difference in radius between 24° and 14° would be huge? I don’t think so especially when there is a check at mid way. It is not much different to doing a check on the base turn of a NDB approach or hippodrome turning from outbound to inbound.
As for TAS at 90kts at 2000ft you would be doing 93kts at 160kts IAS you would be at 165kts it doesn’t make much difference to the bank angle. You would at Cannes to be more likely to be concentrating on your ground speed at this time, anyway and throttling back as you descend so less noise.
gallois wrote:
As for the.rate 1 turn the VPT needs to be flown under 160knts which gives you a bank angle of 24°. At 90knts your bank angle would be 14°. There would not be a huge difference in the radius
At 160 kts the radious would be 78% larger than at 90 kts. It is quite simple, it is is proportional to the speed.
gallois wrote:
especially as you have a check point at A over the motoway junction which will give you a guide whether to tighten or loosen your turn.
You are saying one should “tighten or loosen your turn”; so now not rate 1? “Obviously” that is the correct answer, relying on rate 1 doesn’t make sense; fast aircraft will have to do tighter than rate 1, and slower aircraft less than rate 1. I’m trying to show you that your “just use rate 1 from A” just doesn’t work across any range of speeds, and just happens to be valid by happenstance at one specific speed. Maybe that speed just happens to be the one of the Robin’s and/or PA28 that the local airclubs fly, and so they teach it that way, for their aircraft, at a specific speed.
It is quite simple, it is is proportional to the speed.
Actually turn radius is a function of the SQUARE of speed. So at 160 the turn radius (160/90)^2 larger than at 90, i.e. 3.16. Relying on that to keep out of nimby range will not end at all well.
As for flying visually – at Point A the “traffic circle” is to the right just not quite under the aircraft. Flying from the right seat, it is impossible to see. Ditto the white tent.
And that’s in my TB20. In something like a Lear the “comne of invisibility” under the aircraft is much larger.
The ONLY way to fly this safely – in terms of keeping your license – is to have some in-cockpit guidance. Which the DGAC won’t let you have.
gallois wrote:
all I can say is “oh come on” of course you czn fly a VPT accurately there are so many guides.
No, there are many inherent errors; one of them is parallax (you are sitting left, sometimes right, of the centerline); the other is that when overflying, frankly it is basically impossible to see if one is straight above a point or 5° off or even 10° or 15° off. As long as point disappears “below the cabin” and is not visible left or right below the wing (or in front of / behind the wing for a low wing aircraft), the pilot will have believed he has overflown it; a radar view on the other hand will show a lateral deviation.
5° lateral deviation at 2000ft is 55m; that’s the difference between “over the road” and “behind the backyard of the house”. 15° is 160m that’ the difference between “over the road” and “over the house two or three streets away from the road”.
Visual navigation is inherently very imprecise. I mean visual navigation, not using a GNSS on a moving map.
And that’s when flying straight. In a turn, well, the airplane will be banked. So frankly, to know what is just below you and/or what you will overfly exactly? Not possible visually.
johnh wrote:
Actually turn radius is a function of the SQUARE of speed.
No, I think you mean the turn radius at fixed bank angle is proportional to the square of the speed. Here, we were discussing a fixed rate turn; that will be a different bank angle depending on speed, and radius will be proportional. See it like that (assuming no wind):
So at 90 knots that is 885 m and at 160 knots 1575 m (with some rounding).
Using a ruler on the map with the reference that CMD-PIBON is 3 nmi gives an expected radius of about 1675 m. Looks like a rate 1 turn will be too tight for any plane given the maximum 160 kts (which I don’t see on the approach chart, but taking gallois’ word for it).
I just looked on Google earth. The ICAO-standard “big white tent” isn’t there any more!
Oh dear are you saying you cannot overfly identifiable landmarks at 2000ft in.VMC conditions without GNSS. Where on earth were you trained.
So what you are saying is that the more you bank the aircraft has no effect on the radius of the turn? If that is the case why does the majority of IFR turns based on rate1. Approximately 15% of TAS.
Lets look at Cannes. Firstly there are co-ordinates for the VPT read the AIP text.
Secondly you are descending on the final approach for 35 and at 2.3NM from threshold to 35 or 3NM from CMD you turn right onto 025°
look up and right on the nose where the sea meets the coast and where the railway line also touches the coast there. You head directly for that point. But staying south and west of Iles de Lérins, another obvious landmark.
But just in case you can’t its 500m east of Rochers de la Bocca which is a pretty obvious landmark. But just in case you need it in your GPS , the coordinates according to the AIP can be found in Enr 4.4.
You now turn North in clean configuration tracking to PIBON which is 1km West of the village of Vieux village de Mougins. We all know what part of our wing to look at to judge 1km don’t we? But if we don’t there are co-ordinates Enr 4.4. It is also 3Nm from CMD.
It also says to avoid villages shown on IAC AD2 LFMD ENV 01 but easy to spot and avoid.
Start descent at PIBON fly over A which is the roundabout of the Pénétrante Cannes -Grasse its pretty big. Continue the turn to point B which is on the final approach which you can stick on your OBS but.its between the hills and lines up with the runway axis.
In IFR it is normal to set up any 180° or any turn for that matter as a rate 1. If I need to reassess during the turn due to eg wind . Rate 1 being more to do with a time and what bank rate you need to take to turn 3° a second at the speed you are travelling. Under VFR that’s not strictly necessary but the VPT shows a curved base and you wont be far off rate 1 and there are several points where you can tighten or loosen a turn.
Dear me, I can see why the British half of the Concorde investigation had such a hard time. Dare to suggest that anything isn’t perfect in France and the establishment descends on you, with more spurious and irrelevant arguments than you can shake a baguette at.
Firstly there are co-ordinates for the VPT read the AIP text.
For LUXUS and PIBON, sure. They’re in the Garmin, too. But for points A and B, they aren’t, and as I was told by the airport this morning, the DGAC will not give them out. It’s not THAT hard to figure them out given modern tools, but they are not officially available. And the one piece of guidance they do give – the famous white tent – isn’t there any more.
In IFR it is normal to set up any 180° or any turn for that matter as a rate 1.
While this is absolutely true, it is also totally irrelevant. A rate 1 turn at 100 knots starting at point B will put you very firmly in nimby land. In our planes it has to be flown as roughly a half-standard rate turn.
Given you’re VFR and not limited to standard rate etc, I guess you could set up the runway on the OBS and just pull a 60 degree bank when it starts to line up. Though I think having some better guidance is probably safer.
