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-   -   How far will an aircraft travel in 2-1/2 minutes with a groundspeed of 98 knots? (https://www.pprune.org/private-flying/559557-how-far-will-aircraft-travel-2-1-2-minutes-groundspeed-98-knots.html)

 sspencer1248 8th Apr 2015 20:02

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?

 confused atco 8th Apr 2015 20:15

(98/60)*2.5

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) :=

 highflyer40 8th Apr 2015 21:26

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.

 RichardH 8th Apr 2015 22:29

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.

 keith williams 9th Apr 2015 21:50

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

 yotty 9th Apr 2015 22:19

Assuming there is no wind?:cool:

 BEagle 10th Apr 2015 07:15

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.

 sspencer1248 10th Apr 2015 08:40

I appreciate the help. As Keith said I've just begun my PPL.

 gasax 10th Apr 2015 09:44

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.

 piperboy84 10th Apr 2015 09:58

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.

 ChickenHouse 10th Apr 2015 10:34

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

 9 lives 10th Apr 2015 12:28

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!

 Crash one 10th Apr 2015 12:54

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.

 fastjet45 10th Apr 2015 15:49

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 ?

 thing 10th Apr 2015 15:55

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!

 Pirke 10th Apr 2015 16:27

I'm missing some crucial information: is the aircraft going in circles or in a straight line? :ugh:

 ChickenHouse 10th Apr 2015 16:52

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 ... :ugh::ugh::ugh:

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