PPRuNe Forums - View Single Post - Flying a small plane over water, from Northern Ireland to Scotland?
Old 6th Oct 2019, 07:16
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Originally Posted by owenc

Thank you. The distance to Mainland Scotland is 21 Statute miles from outside Larne, where did I say 28? (I know that Kintyre is 12 miles but that would involve a lot of island hopping to get to the true mainland)

Where are you getting the 60 Knots figure from? If we were cruising along at 150 knots and had an engine failure would this not be a starting point?

Weather on that crossing is my main concern. I know from experience that it is difficult to get a time with decent weather over the North Channel.

It’s not rare for there to be fog in the North Channel in a High Pressure situation. In fact, often it is the case where you can see the Mull of Kintyre from our NE coast on a cloudy day, but not on a sunny, calm day. So clear conditions are rare.

Perhaps as a trial run we could try going out 5-10 miles and turning around just to see what the conditions are like and what we would be setting ourselves in for.
i got the 60 knots (best glide speed) and the 500 fpm rate of descent from nowhere, hence the ‘assume’. Both will come from the pilot operating manual which we are taught to look in, your father will have and which I don’t.

if your engine fails at 150 knots you’re right that is the starting point, but the aircraft won’t keep moving at that speed without a prop turning - think about a car when the engine stops. The difference with a plane is that a pilot can keep it moving forwards using gravity-trading height for speed.

(Very simply Gravity wants the plane to fall from the sky, the wings give lift to counteract that. Drag (air friction) wants the plane to stop moving forwards and there’s no longer an engine to overcome drag. If the plane isn’t moving through the air the wings stop producing lift. So you angle the plane downwards, the airspeed created by the plane ‘falling’ gives lift which means you keep flying forwards but downwards. The pilot holds the plane at the angle that returns best glide speed)

Somebody has done the sums for you in stating best glide speed which is the optimum speed to fly at without the engine working. It’s different for every model of plane and a pilot should know these numbers before taking off so that in a situation they instantly know what to fly at.

Sorry about the 28 mile reference, if the distance is only 21 then the minimum height can be lower.

incidentally, did you really mean that you’ve never been more than 30 miles from base ? At 150 mph cruise you cover 2.5 miles per minute so that makes your longest flight has been 12 minutes long ?

I’m sure your father knows all this, he will have studied it in getting his licence which I’m guessing wasn’t all that long ago.


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