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How far will an aircraft travel in 2-1/2 minutes with a groundspeed of 98 knots?

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How far will an aircraft travel in 2-1/2 minutes with a groundspeed of 98 knots?

19th Apr 2015, 11:21

Join Date: Sep 2006
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Actually half an inch and .5 inch are technically the same, it is the precision of the dimension that matters, for instance, (no offence meant) a builder / bricklayer may build a wall to an accuracy of +/- 1/8 of an inch and consider it perfect, the toolmaker will cut and grind a piece of steel to an accuracy of +/- .ooo1" before being satisfied, .001" under half inch could be scrap in certain circumstances.
19th Apr 2015, 11:39

Join Date: Apr 2009
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98 is pretty close to 100.

There are twenty four 2.5s in sixty.

24 is pretty much 25

divide 100 by 25 = 4
19th Apr 2015, 15:13

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Actually half an inch and .5 inch are technically the same, it is the precision of the dimension that matters
The "half an inch" or ".5 inch" is the precision of the dimension, and can mean that those two expressions of the dimension could represent quite different values.

"Half an inch" suggests a precision of +- "one quarter inch", because greater precision than one quarter inch either side of the value is not expressed. So something expressed as "half an inch" with no further statement of precision, would be acceptable if it was greater (just) than one quarter inch, and less than three quarters of an inch. If "half an inch, plus or minus one sixteenth of an inch" is expressed, then things are different.

".5 inch" is a much more precise dimension, and suggests a precision of +- .05". Therefore, without a further statement of precision, ".5" would be interpreted as .45" to .54", which is much more precise than the .25" to .74" which is conveyed by the word expression of "half".

To take it further, .001" means a dimension from .0995" to .0014". Parts in your engine are made and maintained to greater precision than that. If you accepted a Lycoming cylinder, with a valve guide dimensioned at "half an inch", you'd be a fool!

In aviation, this does not matter much in inches, unless you're building or maintaining the plane. But, think of it in "tanks". Would you be content to have a "half tank" of fuel put in, based upon reading the fuel quantity indicator in the instrument panel? Or, would you feel more comfortable ordering .5 of 100 liters, knowing that in doing so, you must be pumped between 45 and 54 liters. Or, request .50 of 100 liters, and you'll have to be pumped between 49.5 and 50.4 liters.....
19th Apr 2015, 15:43

Join Date: Sep 2006
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Step:

I know where you're coming from with your statement about accuracy but in reality if you asked for .50 of a hundred litres they would probably cart you off to the local asylum.... I think we all know if we ask for a hundred litres it's understood that we'll get a hundred litres. Unless you want to start a debate about the accuracy of the bowser meter. Which in fact would be a valid point. I flew a 172 for nearly two hours the other week and put in 37 litres of fuel to full afterwards. According to the bowser.
19th Apr 2015, 15:52

Join Date: Sep 2006
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Arguing over the precision of a part in the engineering business used to be the norm, years ago, a tenth (.0001") often disputed depending on ones "feel" with a micrometer, now with digital comparators and all manner of technology the doubt is removed down to parts of a micron. But even then absolute yes or no is debateable . Depending on the application, one man's perfection is another man's piece of shrapnel.
I thought I had retired from this stuff!
Wasn't there an engineer a while ago remarked "the fit between the cylinder and piston was so close you couldn't get a shilling piece between them"?
19th Apr 2015, 16:40

Join Date: Jan 2008
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The important point is that math, like English, is a language, and it is important that you use it with the precision you intend, to convey what you need to. Clarity can be vitally important, to assure that one thing works as intended with the next....

If the tower cleared you to land on runway "E", you'd expect a final approach heading somewhere between 045 to 134 degrees. Landing on runway 09, conveys much greater precision of heading. Runways aren't "090", cause no GA heading indicator is that good!
20th Apr 2015, 07:15

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Forget the PPL, this is a high school type question.
Actually this is a primary school question for a 10 year old.

I downloaded a past GCSE Maths paper for my 15 year old son for some revision and the first question was:

A picture of a clock with the big hand on the 9 and the little hand approaching the 3:

"Write down the time shown on the clock"..

I kid you not..... (When I did O level Maths I was doing calculus at 14...WTF...)
20th Apr 2015, 08:22

Join Date: Jul 2008
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I'm clear about the precision expressed by 0.5 implying between 0.45 and 0.55, just as 0.50 implies between 0.495 and 0.505. However, I don't understand why 1/2 inch means between 1/4 and 3/4. I don't think that it would be normal in the imperial system to specify a higher level of precision by stating a dimension as, say, 2/4", or perhaps 32/64". I studied engineering as the SI system was becoming the standard, partly, I thought, because it removed some of the many uncertainties in the former systems of units. If I order a 1/2", or indeed, a 5/16" bolt, I think I would need to refer to some sort of standards document or manufacturer's spec sheet to find out the relevant tolerances. I don't think it could be inferred from the description. Actually, I guess the same is true when specifying an M10 bolt - but perhaps that's why it is described as an M10 bolt, not a 10mm bolt...

And I'm not sure about Step Turn's runway 'E'. If a nautical helmsman was told to steer E, I think he would be in trouble if he went anywhere close to NE or SE. I think it would rather depend on the number of points marked on the compass. Which, of course, is not necessarily linked to the precision, or the accuracy, of the compass!
20th Apr 2015, 12:06

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You'll find I am more than happy to answer serious ATPL level questions on this forum but this is beyond a joke
Why would private pilots ask serious ATPL questions here?

CG
20th Apr 2015, 17:24

Join Date: Aug 2012
Location: Wales
Posts: 541
Well Guys, the ATPL question is.....

'How far will an aircraft travel in 2-1/2 hours with a ground speed of 380 knots?'
.
20th Apr 2015, 17:50

Join Date: May 2005
Location: Yorkshire
Posts: 1,085
Well, the method you would use would depend on the spread of alternative answers.

If the alternative answers were:

a) 2

b) 4

c) 6

d) 8

a TLAR method would be quite adequate.

If they were:

a) 4.06

b) 4.07

c) 4.08

d) 4.09

something more accurate is required.

MJ

Ps. I've come to this a bit late. Have I missed something, or has this thread gone on far too long?
28th Apr 2015, 20:40

Join Date: May 2010
Location: Yorkshire, England
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By my reckoning, 950 NM?
29th Apr 2015, 18:56

Join Date: Jan 2007
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Clearly you lot on here need my book, Diversion Planning.....!! Got a few useful things about speed, distance and time. Near as need be, groundspeed is 100 kts, which is 5/3 of a mile per min.....multiply by the number of minutes and theres your answer. (25/6 miles or approx 4 and 1/6 miles, the approximation coming from the round up from 98 to 100 kts. In a light aeroplane you wont want to be this accurate, for the most part!! 5/3 per min is 10/6 per min, and 2.5 times this is 25/6. See, no calculator!)
29th Apr 2015, 19:54

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Location: Scotland
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What about: one aircraft leaves Goodwood heading for Edinburgh at 90 knots, another leaves Edinburgh at the same time at 120 knots heading for Goodwood, same altitude, disregarding airspace, both calculate for a wind of 290/20. Where will the crash site be?
1st May 2015, 14:54

Join Date: Feb 2014
Location: Crawley
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10-up

When gliding I always think vertically in terms of hundreds of feet per minute, as that is what the variometers display your climb rate in. 1-up is 100' per minute, which is almost exactly 1 knot. Thus 1000' per minute is close to 10 knots, so about 4 miles in 2-2.5 mins.
1st May 2015, 16:08

Join Date: Jan 2008
Posts: 602
Where will the crash site be?
At either Goodwood or Edinburgh, during a botched landing. Because both aircraft will have dutifully flown at the altitude appropriate for the direction of flight, and passed safely!
1st May 2015, 17:56

Join Date: Jul 2013
Location: Here for now
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Well, the 1/2" vs 0.5" thing depends a lot on context.
if you ask for affaninch, then 1/4"-3/4" might be an acceptable thing.

As a math/engineering nerd, i read 0.5, 0.50, 0.500 etc as different tolerances unless otherwise stated. I read 1/2 to be the same number but with perfect precision- you can write 0.499 as 0.5 but not as 1/2 (well, you can. but it aint right.).

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