How much g-force is made on an ultralight during take off if its upward velocity of 2m/s?And what's the average g force experienced during takeoff on an ultralight?
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asked Apr 9, 2018 at 21:15
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$\begingroup$ about 1.2g? (9.8+2)/9.8 = ~1.2 ? $\endgroup$– user3528438Commented Apr 9, 2018 at 21:20
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1$\begingroup$ nope, g=9,8 (m/s²) is acceleration while 2 m/s is velocity. totally different things and cannot be summed together. $\endgroup$– szulatCommented Apr 9, 2018 at 21:50
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$\begingroup$ Assuming wings level takeoff (no 60 degree banked turns during takeoff), Average (over the course of entire takeoff), is probably very, very close to 1 g. (starts at 1 G, ends up at 1 G, so there must be periods where actual G-Loading is slightly above 1 G and periods where it is slightly below). But based on 2m/sec, (2 m/sec over a 5-10 sec takeoff period is what in acceleration? 0.2 to 0.4 m/sec/sec?) Maximum G-Load however, is different story. $\endgroup$– Charles BretanaCommented Apr 9, 2018 at 23:22
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$\begingroup$ ... and @szulat, acceleration is simply rate of change of velocity, so user3528438 is correct (although he makes incorrect assumption that takeoff period is only one second.) $\endgroup$– Charles BretanaCommented Apr 10, 2018 at 14:38
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$\begingroup$ @CharlesBretana exactly, it's the rate of change and in this case the rate was not specified so the g force can't be calculated. if the user35 said the assumed time is 1 s then it would be correct. adding acceleration and velocity numbers together and hoping it somehow lead to meaningful result without understanding what actually is being calculated is incorrect. $\endgroup$– szulatCommented Apr 10, 2018 at 14:51
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2 Answers
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I fly part 103, specifically a Hy-Tek Hurricane. I also have a G meter on board. It is a Dynon D2, which features an artificial horizon (attitude indicator) and also a G meter. The average G's on takeoff is pretty small, usually around 1.1 to 1.2 Gs. I can also tell you it is impossible to pull anything over 2 G's during takeoff. I actually performed this test in the air at 2000ft, straight and level at full throttle (simulated takeoff from 2000ft?) at about 55mph, then pulled the stick back all the way in about 1/4 of a second until I was nearly vertical. The highest recorded G reading during this maneuver was 1.8 Gs. Of course all ultralight aircraft are different. I would NOT recommend performing this test from an actual take-off from the surface. Also you should consider that by performing the test at 2000ft, I was not in any kind of ground effect, so you would have to factor in that little bit of extra lift cushion you would get from an actual takeoff from the surface, but I would guess the extra lift component is probably small, so that is why I estimated 2 Gs max.
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$\begingroup$ 55 mph is, however, way too fast for take off, isn't it? At take-off speed, you couldn't pull that much, because you would stall if you did. $\endgroup$ Commented Jun 15, 2018 at 18:54
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2$\begingroup$ Exactly Jan. Since normal take-off speed in my aircraft is lower than 55mph, I would never reach 1.8 Gs on takeoff. If I tried yanking the stick back on actual takeoff, I would possibly stall the wing immediately. I don't know for sure, but I am not going to try. $\endgroup$ Commented Jun 16, 2018 at 13:33
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$\begingroup$ Given that lift goes as the square of speed, at 35 mph, your maximum G would be around half what you pulled -- which is less than 1 G (i.e. you couldn't be off the ground yet). At the moment of takeoff, there's precious little extra lift above the takeoff weight (including pilot and fuel) -- so G figures in the 1.1 to 1.2 range are very reasonable. $\endgroup$ Commented Sep 5, 2018 at 15:41
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The answer depends on how quickly was this 2 m/s velocity reached.
Could be 2 g if it happened within 0,2 s (9,81m/s² + 2m/s / 0,2s)
Could be 1.1 g if we were accelerating for 2 seconds to get to 2 m/s (9,81m/s² + 2m/s / 2s)
Example accelerometer recordings taken during the Cessna 152 takeoff (not exactly ultralight, but also a small plane). The first noticeable spike was about 1.2g
(recorded on iphone, 30 measurements/second)
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1$\begingroup$ And 0.2 s is absurdly short—if you handle the controls gently and smoothly as you are taught, you will definitely not rotate in 0.2 s. $\endgroup$ Commented Jun 15, 2018 at 18:51