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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?

8th Apr 2015, 20:02

Join Date: Sep 2014
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How far will an aircraft travel in 2-1/2 minutes with a groundspeed of 98 knots?

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

I understand the answer is 4.08NM

But I want to know how one would calculate the answer?
8th Apr 2015, 20:15

Join Date: Oct 2002
Location: ireland
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(98/60)*2.5
8th Apr 2015, 20:20

Join Date: Mar 2011
Location: Norway
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2,5 minutes equals 0.04167 hours. 2.5/60

98 knots is 98 nautical miles per hour.

0.04167 hours times 98 nautical miles per hour equals 4.083 nm

(you should know this from kindergarten)
8th Apr 2015, 21:26

Join Date: Aug 2011
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I'm hoping he meant an easy way to calculate it in his head... There are 60 minutes in an hour. So 98kts is just a little over 1.6kts per minute x 2 then add .5 which equals 4. Close enough for doing the calculations in your head.
8th Apr 2015, 22:29

Join Date: Feb 2002
Location: Sunny Solihull
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This is a late April Fools question?

You'll find I am more than happy to answer serious ATPL level questions on this forum but this is beyond a joke. Others have answered your question.
9th Apr 2015, 21:50

Join Date: Jan 2011
Location: England
Posts: 643
The profile for Spencer indicates that he is currently working towards his PPL so we should not be too surprised that he is asking this type of question.

1 knot is 1 nautical mile per hour.

This means that 98 knots is 98 nautical miles per hour.

There are 60 minutes in an hour so if we divide 98 by 60 we will convert 98 nautical miles per hour into 1.633 nautical miles per minute.

If we then multiply this by 2.5 minutes we will get the number of nautical miles flown in 2.5 minutes. 2.5 X 1.633 is 4.0825
9th Apr 2015, 22:19

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Assuming there is no wind?
10th Apr 2015, 07:15

Join Date: May 1999
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I just thought 2½ min at 1½ mi/min plus 10% would be near enough...

So, in my head, that's 3+¾, i.e. 3.75, plus .37 is a tadge over 4 nm.
10th Apr 2015, 08:40

Join Date: Sep 2014
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I appreciate the help. As Keith said I've just begun my PPL.
10th Apr 2015, 09:44

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It should be fairly obvious from the replies above, for a no wind day - but wind will completely change the situation - hence the infamous 'whizz wheel' where you can graphically add the wind vector and then derive groundspeed.
10th Apr 2015, 09:58

Join Date: Aug 2005
Location: Glens o' Angus by way of LA
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It should be fairly obvious from the replies above, for a no wind day - but wind will completely change the situation - hence the infamous 'whizz wheel' where you can graphically add the wind vector and then derive groundspeed.
Or you could ball park it with the wind direction degrees of beam, i use the "6" method ie. if the wind is 30 degrees of beam its 3/6 (half) the wind speed decducted from the GS, if its anything more than 60 degrees (6, 6's) deduct the full wind speed.

If I have this wrong I will gladly be corrected.
10th Apr 2015, 10:34

Join Date: Mar 2014
Location: The World
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How far will an aircraft travel in 2-1/2 minutes with a groundspeed of 98 knots?

I understand the answer is 4.08NM

But I want to know how one would calculate the answer?

On the ground, real calculation -> 98 knots equal 98 nautical miles per 1 hour equal 60 minutes, so the 2.5/60 fraction of 98 nautical miles = (2.5/60)*98 = 4.083 nauticals

In the air, head calculation -> 98 knots is almost 90 knots +10% and 90 knots is 1.5 nauticals per minute, 1.5 times 2.5 is 3.75 plus 10% roughly equals 4.1 nauticals - good enough
10th Apr 2015, 12:28

Join Date: Jan 2008
Posts: 602
The most memorable math class I ever had in school saw a surprise test. It was simple math, but big, awkward numbers, and lots of them. The teacher told us that we would not have time to calculate them all (and calculators - to be honest, had not been invented yet). He told us that nearly all the math we would ever do in life would be used to make a decision. The result would direct us to a "yes" or a "no". So, if we were pressed for time, a close guess would probably result in the correct decision. The purpose of the test was for us to guess at the answer. If our guess was within 10% of the correct answer, we would get the mark.

This logic is very prevalent in piloting. You'll need to make many decisions, most usually, do I have enough fuel to get there? The good guess, with a bit of conservatism, will be adequate.

I do not imagine a situation where based on the groundspeed of a GA aircraft, there is a need to know the distance covered to within 1/100 of a mile. For my experience the nearest mile, or 5% for greater distances has met the need every time. That said, during training and exams, the questions might force greater precision, as you choose the best of two possible multiple choice answers. Know the theory, but know when to apply it too!
10th Apr 2015, 12:54

Join Date: Sep 2006
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This depends on whether you need an absolute to the thou or a ball park guesstimate for navigation.
98 (nearly 100kts) which is 1.6 per min, times 2.5 = about 4.
10th Apr 2015, 15:49

Join Date: Jul 2008
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How far will an aircraft travel in 2-1/2 minutes with a groundspeed of 98 knots?
Some the answers / remarks given here fall in to the category of RTFQ, were does the wind come in to the calculation ?
10th Apr 2015, 15:55

Join Date: Sep 2006
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I'm not saying the OP should ball park it for his PPL studies but once in the real world just divide it up into multiples of 6.

90 kts=1.5 nm minute

96kts=1.6 nm minute

102kts= 1.7nm minute etc.

98 kts is nearest to 96 so just multiply 1.6 by 2.5 which equals 4.0. If you're feeling particularly anal bung a bit on for the wife and kids.

Piperboy: you don't have it wrong, I use the same method. It's just the sine of the wind angle. 60 degrees off would actually be 0.866 but it's near enough to one for me. I use the same method for xwind component on takeoff/landing, which is what your drift angle is anyway.

Some the answers / remarks given here fall in to the category of RTFQ, were does the wind come in to the calculation ?
Come on, wouldn't be Prune without people jumping in at the deep end!
10th Apr 2015, 16:27

Join Date: Mar 2014
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I'm missing some crucial information: is the aircraft going in circles or in a straight line?
10th Apr 2015, 16:52

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Location: The World
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Guys, keep it stupid simple ... lets take the easy road with ground meaning no wind, perpendicular to gravitational forces -> if it would be groundspeed along gravitational force the typical GA plane won't make 2.5 minutes ...
10th Apr 2015, 17:31

Join Date: Aug 2005
Location: Glens o' Angus by way of LA
Age: 56
Posts: 1,974
The most memorable math class I ever had in school saw a surprise test. It was simple math, but big, awkward numbers, and lots of them. The teacher told us that we would not have time to calculate them all (and calculators - to be honest, had not been invented yet). He told us that nearly all the math we would ever do in life would be used to make a decision. The result would direct us to a "yes" or a "no". So, if we were pressed for time, a close guess would probably result in the correct decision. The purpose of the test was for us to guess at the answer. If our guess was within 10% of the correct answer, we would get the mark
Many moons ago (before computer accounting software was available to small companies) I hired a lady who's primary job was to gather all the sales tax information for the different jobs and equipment sales we had done that month and compute the sales tax (VAT in UK) we had to remit to the government. At that time the company turnover was usually about \$100,000 per month,the sales tax rate was 8.25% and almost all our sales were sales tax eligible. After her first month she walked in and presented me with a check for approximtley \$84,000 to sign for mailing to the tax office. I asked her if we had had an unusally large sale that month (knowing we hadn't) to which she said no, revenue was just over \$100,000. I suggested she check her math and she threw a wobbler about me questioning her professionalism and how rude it was of me to doubt her numbers based on her many years of being a accounting dept sales tax expert.

Bottom line, I thought to myself, is she cant start out with a ballpark number in her head and then work the actual figures that will verify her "guesstimate" then she is going to bankrupt me sooner or later and out the door she went.

Always start out with a rough mental calculation before working out the exact number.
10th Apr 2015, 17:56
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