G loading ?

[Aerodynamisist]

If you are flying straight and level and hit turbulence the aircraft the aircraft gets accelerated to say 2g for a few seconds.

If you are carrying out an aerobatic manoeuvre at say 4g and hit the same pocket of turbulence that had you at 2g straight and level, will you now be accelerated to 6g or 8g ?

[Horatio Leafblower]

I thought G-loading was what made young women's jeans sit halfway down their hips and it was only the G-string that held them up... ?

...or have I got that wrong?

[Giles Tuwotu]

Very unlikely that turbulance would be experienced for "a few seconds"... most turb acceleration (g) only last a fraction of a second!!

[djpil]

Roughly, increase in g results from gusts at right angles to the flight path so in straight and level an increase in g results from a vertical gust. Answer is yes if pulling that 4 g while flying horizontally.
Doesn't matter how short a time, the extra g can break something.

[ops_guy]

I think the question could be read a couple of ways. Here's my take on and corresponding answer for it:

Smooth Air Straight and Level : 1G
Turbulent Air Striaght and Level (oxymoron?) 1G + 1G = 2G

So, the turbulence is actually adding an additional 1G to the normal straight and level G-Loading.

Therefore, if we were pulling in to a manoeuvre with a 4G load and experienced the original turbulence we'd have: 4G + 1G = 5G

Hope this helps :8

[djpil]

Yes ops_guy, I was never very good at arithmetic.

[Obidiah]

There is more to this, and the formula used takes into consideration;


The lift curve slope - plan form aspect ratio
Air density - increased TAS reduces effective gust angle, < R/angles
Wing loading - A/C ability to react to the gust
Other things - leading edge radius, IAS
If the scenario were pulling out of a dive at 4g the effective wing loading is 4 times at this moment. Therefore the same gust would create less vertical deflection of the flight path and the pilot/g meter would sense lower g increase than for a lower wing loading. However the bending moment on the wings would still exist commensurate with the lift curve slope, ie strong slope for high aspect ratio and lesser slope for delta form.

So perhaps when at 4g and you encounter the previous gust that created a 2g increase, in this circumstance it may be slightly less, 4+ 1.5g for example.

For the long and complex answer see pg. 332 of Naval Aviators.

Good question.

[Aerodynamisist]

That makes sense Obidiah. hence the higher Turbulence penetration speeds at higher weights on many aircraft.

[Sunfish]

And if I am inverted in the middle of a loop? Or inverted in a barrel roll? DjPl? Mr. Robson?

[T28D]

At the speed you would be inverted in a loop or barrel roll the ability to get an overstress through "G" is impossible.

Maybe a bit of real aerobatics instruction would be a good idea.

[Obidiah]

And if I am inverted in the middle of a loop? Or inverted in a barrel roll?


Dunno....wake up and gets some clean dry sheets.....

Sorry, couldn't resist.

[Obidiah]

Aerodynamisist

hence the higher Turbulence penetration speeds at higher weights on many aircraft.

All aircraft.

Manoeuvre/turb speed = stall speed x the square root of the limit load factor.

[Old Akro]

Turbulence comes from moving through different parcels of air. Aerobatics takes place in a relatively small volume of air (1km x 1km x 2,000ft), so its less likely to involve turbulence from moving through different air parcels. Often a sequence will be done over a single paddock. T28D also reminds that a large amount of the time aerobatics is done at low speed.

A long cruise descent poses the biggest risk from turbulence.

[Sunfish]

T28D:

At the speed you would be inverted in a loop or barrel roll the ability to get an overstress through "G" is impossible.

Maybe a bit of real aerobatics instruction would be a good idea.

1. Don't EVER challenge the Sunfish ability to do something impossibly stupid and break an aircraft.

2, I don't need more encouragement to do aerobatic instruction. I love it. Its addicitive. I just need more time and opportunity to finish the endorsement/rating.

Merry Christmas to all.

[MakeItHappenCaptain]

And on that topic, here's today's challenge.

Is aerobatics/acrobatics performed under an endorsement or a rating?

References please, & no "I was told" or "I thought" answers permitted.;)

[djpil]

Sunfish, if you are inverted at the top of something then consider that, as some-one else mentioned, you won't break anything at low speed so what's the worst that can happen? Just like "normal" flying. Not pleasant anyway.
If you have the inclination then I have the time to finish your ... whatever it is.

[Ultralights]

whats the worse that can happen?

G Stall just as your in the middle of a roll off the top. :{ damn, rolling G..

[Aerodynamisist]

Endorsement

I don't have a reference for you though, I read the rule book but didn't memorise the page numbers.

[Steve888]

'Tis an endorsement.

CAO 40.0 Subsection 2
2.2 The holder of an aeroplane pilot licence must not, while flying an aeroplane as
pilot in command, or co-pilot, deliberately put the aeroplane into an upright
spin unless:
(a) an authorised flight instructor who gave the holder spinning training is
satisfied that the holder can safely recover an aeroplane from a fully
developed upright spin; and
(b) the instructor has made an entry to that effect in the holder’s personal log
book

2.4 Subject to paragraph 2.5, the holder of an aeroplane pilot licence must not,
while flying an aeroplane as pilot in command, carry out acrobatic flight
unless:
(a) an entry mentioned in subparagraph 2.2 (b) has been made in the holder’s
personal log book; and
(b) an authorised flight instructor, or an approved person, who gave the
holder training in acrobatic flight is satisfied the holder can safely carry
out acrobatic flight; and
(c) the instructor, or person, has made an entry to that effect in the holder’s
personal log book; and
(d) an entry mentioned in subparagraph 2.5 (g) has been made in the holder’s
personal log book in relation to each manoeuvre mentioned in paragraph 2.5.

2.5 The holder of an aeroplane pilot licence may carry out:
(a) a barrel roll; or
(b) a loop; or
(c) a slow roll; or
(d) a roll off the top; or
(e) a stall turn;
if an authorised flight instructor, or an approved person, who gave the holder
flying training in the manoeuvre:
(f) is satisfied that the holder can safely perform the manoeuvre; and
(g) makes an entry to that effect in the holder’s personal log book.
Note If a pilot is approved to carry out more than 1 of these manoeuvres, he or she may carry
out combinations of those manoeuvres

[djpil]

Interesting that the note changed in recent years. If one has loop and slow roll in the logbook then a roll off the top can be performed without a specific logbook entry for it.

[T28D]

Wow ultralights G Stall just as your in the middle of a roll off the top. http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/boohoo.gif damn, rolling G..

What are you flying an English Electric Lightning ?????????

[Ultralights]

positve G at top of the loop. add in rolling G and more backstick at you roll past 90 deg, one wing stalls, and your suddenly upright a lot faster than you expected.

oh, in a Robin.

[Horatio Leafblower]

4G at the TOP of a loop???:uhoh:

I must be doing it rong!

Let me watch you doing a stall turn: :rolleyes: :8

[Ultralights]

actually over the top im not exactly sure what the G loading is, normal loop in at 4 G, competition loop, aim for 5 with relaxing the stick over the top. so probably -1 G over the top of a competition loop. but roll off the top sometimes is helped by the rolling G added in the roll when one wing stalls.
as for hammerheads, "stall turns" i have a few vids to edit yet. fallen out of a few early ones into a nice tailslides. still cant figure out why they are called stall turns.

[LeadSled]

Manoeuvre/turb speed = stall speed x the square root of the limit load factor.

Obidiah, (or anybody)

Would you care to elaborate on this "rule".

Firstly, manoeuvre speed (if you mean max manoeuvre speed) Va might be a particular regulatory minimum (~ 1.9Vs, 1G power off, or Vs1 times the square root of the limit load factor) , but to suggest that this should be the turbulence penetration speed is a highly questionable "recommendation".

Indeed, for years I have flown aircraft with a recommended turbulence speed fixed in a narrow IAS/MNo band, regardless of weight, with a proviso that you can safely reduce the IAS when below max landing weight by about 50 kt. --- as the manufacturer says:"To reduce stress on the airframe".

To fly at the certified maximum manoeuver speed in turbulence can easily lead you into breaking something, Va is designed for /demonstrated in smooth air with smooth application of control with no rapid control reversal. To fly at that speed in turbulence can seriously cause a problem that will ruin your whole day.

Another somewhat lighter aircraft that I fly has a maximum turbulence speed well below Va.

The turbulence speed for your aircraft is what the AFM says it is, and at lighter weight even slow from that, if control is adequate, and you want to reduce further the loads on the airframe.

To say that higher speeds at higher weights does not increase the stresses in turbulence is just (engineering-wise) loopy. And does not make any sense for practical flying purposes.

Tootle pip!!

[T28D]

Really 4 G in a Robin at the TOP of a loop, what is powering it ??????? a gas turbine.

In my T28 with 1400 HP I enter a loop at 4 G 230 Knots and arrive at the top at 110 if I get it right and just G positive , I must be doing something wrong, Maybe I need new knowledge on this Aeros stuff, but I certainly run out of energy at thetop of the loop, funny the Extra 300 I fly does the same thing, must be technique.

[Ultralights]

im not exactly sure of the G over the top,i have edited my initial post to reflect that, it was meant to illustrate my point of increased G load in a manoeuvre, combined with the added Rolling G combined to create a stall situation. G over the top isnt much, im not looking at the G meter then, im looking at the horizon and line feature but i have felt the g stall during the roll off the top numerous times. so i am pretty certain the added rolling G factor while rolling off the top is whats generating the stall of one wing. every other stall in the loop is simply exceeding critical AOA.
all on the topic of G loading.. but will consult my instructor for a more in depth explanation.

[Mark1234]

LeadSled - I'm not sure about a 'rule', but the principle is sane - according to Mr Newton, F=ma (and therefore a = F/m)

So as M gets bigger, the same force will produce a smaller A (or G loading) - the aircraft is somewhat less sensitive to gusts. Last time I checked, the POH for the oh-so-common Cessna 172 listed two Va values, one for MGW, and one for very light weight. I don't believe there is a specific turbulence penetration speed, Vno around 120something, Va 104(?), so Va is/was generally taken as a safe turbulence speed, at least as I was taught. (Caveat I've not flown a 172 for ages, hence being a bit vague)

Also of course as the a/c gets heavier, there's a practical limit to how much acceleration that the wing can produce without stalling - not that that's a particularly useful method of turbulence avoidance, and all of this is ignoring any secondary effects, other than immediate acceleration.

Ultralights - in my experience of the Robin, yes, it's easy to buffet the roll off the top, however the problem is more likely to be one of reaching the top somewhere around, or even a bit below the level flight stall speed. Certainly you're unlikely to be capable of getting 4G. For a straight loop, that's less of a problem as you tend to float it over around 0G, but rolling off the top it's pretty easy to roll straight into a buffet / stall etc. Been a while since I aerobatted one, but I seem to recall adding 20kts to the entry for a roll-off or avalanche.