Jacko wrote:
Sorry if this is a daft question, but why do you want to fly that fast in poor viz under low cloud? Is 120 kt really the slowest your airplane can fly?
Why not slow down to 1.3 Vso, with flap?
I didnt say I wanted to. It was, I thought a good way to emphasise that really, for VFR flying, the rules allow way worse vis for flying than you would actually want to do.
I would counter, do you really want to be flying at 1.3Vso whilst seriously distracted by the poor conditions? As I recall my workload on the couple of occasions I REALLY wanted to get on the ground due to the visibility dropping, was through the roof…
Regards, SD..
skydriller wrote:
I would counter, do you really want to be flying at 1.3Vso whilst seriously distracted by the poor conditions?
Yes, I would rather be going at 1.3Vso than full bore in low viz. I try to practice slow flight pretty frequently and find it certainly gives you far more time to think about what you’re doing and what you may wish to do if you’re not happy.
Some types 1.3 Vs produces quite a high nose attitude and requires power in a turn. Flaps 20-25 will improve visibility and the engine will be at a higher power setting.
Some types lend themselves naturally to slow flight, others less so.
I would counter, do you really want to be flying at 1.3Vso whilst seriously distracted by the poor conditions?
I certainly can’t think of a reason to fly faster in any moderately well-behaved airplane. Far from high workload, it is very relaxing.
A properly rigged airplane should be comfortable to fly much slower than that. Power off, flap lever and yoke back all the way, and steer gently with feet. If a wing drops, just catch it with some opposite rudder. Practice at safe altitude until it’s second nature.
But I do see your point. If I never bothered to practice slow flight, I could more easily work myself into a lather when faced with reduced visibility.
For avoidance of doubt, I agree categorically that it’s a bad idea to plan to go scud-running. But just like VFR into IMC (exercise 19?), it is part of the PPL syllabus for a very good reason – and therefore we ought to practice it.
It’s funny, when we think about it: to get a PPL, our first milestone on the way to being a pilot, we have to learn a whole bunch of rules and regulations. Then we have to learn to do something which is plainly illegal…
I think the key is to fly the speed that needs minimum power for level flight and manoeuvring with flap/gear configuration, that should give the best view and best available manoeuvrability, I am sure it is not around VS0 nor above 2*VS0, it always sits around 1.2-1.5*VS0 for any SEP unless it has a junky power curve and wired ending/flaps or MEP with dead engine, no need to get very accurate flight testing, no one will be able to fly that accurately at 500ft agl with no horizon, so about 1.3*VS0 & TakeOff flaps as Jacko said will do, anything else will have lot of IFs vs flight/terrain/cloud envelope and is type specific
The power curve of a typical SEP is infinity at stall speed (yes you need infinite power to fly level at VS0 like a hyperbola) and grows to 100% at max cruise speeds (like a quadratic function), so about 1.3*VS0 you can fly level with minimum power with the aircraft taking care of itself, why fly level on minim power in low visibility and keep your landing/climb performance nearby? I think everybody should know the answer 
Also, you can turn 45deg in IMC at that “minimum power regime”, you will be in a slow decent not stalling, spinning or spiral diving, the old French PPL syllabus recommends that 45deg for decent though cloud layers followed by precautionary landing, it is also the kind of speeds one flies for approach hand off and the one one use for low level flying and ground reference manoeuvres, or the speed one has to fly when they have no clue on aircraft POH or what they are doing…
Of course, I am not suggesting 45deg at 150kts on 100% power or at 60kts on 0% power those are not smart moves near IMC or terrain but there its a middle point, if one can’t find it they better stick to Rate1 turns above MSA or published IAP…
RobertL18C wrote:
Some types lend themselves naturally to slow flight, others less so.
I’m looking forward to getting our Rallye 235E after “spring break”. It really is a forte of the Rallye, a scud running aeroplane par excellence. Also, VG’s on an aeroplane give a nice improvement for this scenario. A seaplane in the right place is a natural candidate too.
30 years ago at my local airfield EIAB. The local procedure was to track RTE radio mast as an NDB to Athlone, descend on a heading to cloud break over the lake and then follow the river Inny at low level to Abbeyshrule. It was done all time with the planes full of duty-free cigarettes, booze and fuel coming back from IOM and Dublin.
Vs increase by 1.2x in a 45 degree bank level turn, so 1.3 x Vs gives minimal gust protection
During my PPL training I had one instructor, who had a “reputation” for all sorts of things, especially involving very young female students, and who did all sorts of what most would regard as cowboy stuff e.g. stopping the engine at 2000-3000ft and gliding the C152 for a bit, but actually he was a very good instructor. One of the lessons involved slow flight in ~ OVC008 / 1000m, between the Sussex hills. Of course he knew every sheep in the fields below by its first name, so he wasn’t going to get lost. He pointed at a hill emerging from the mist and said “this is what death looks like”.
And this is one of the challenges. You do need total awareness of the terrain ahead, and you need this even if your Plan B is to climb straight up into IMC – because there could be a hill ahead which will exceed your best climb gradient.
Peter wrote:
And this is one of the challenges. You do need total awareness of the terrain ahead, and you need this even if your Plan B is to climb straight up into IMC – because there could be a hill ahead which will exceed your best climb gradient.
Indeed. You need to know your exact position all the time in relation to the terrain. The problem is you don’t see the terrain with 1.5 km visibility, except a tiny little “bubble”.
RobertL18C wrote:
Vs increase by 1.2x in a 45 degree bank level turn, so 1.3 x Vs gives minimal gust protection
Is there a requirement to keep it level? accepting a bit of height loss can keep the gust protection and keep a tight turn
