Hence Why,
 

hitherto: "On page 270 on Google books too, you may find a more detailed treatment of load factors with different velocity, wind gusts:

ngust= Lgust/W= 1/2 rho (V+-u)^2 SCl/W considers an horizontal gust."

Keep up the discussion...:8

jcbmack

I can find reference to An introduction to aircraft performance by Mario Asselin on google books but it wont let me read the section you suggest. I am not familiar with the google books site is there something I need to do to be able to download this?

Nigel

nigelisom,
unfortunately you cannot download the book, but you can sign up for Google books library and save the given book too. You can also scroll down to the pertinent chapter and you will find page 269 which begins flight in weather. If you scroll down fast, you will not be able to load the pages well, if at all, so scroll down slow.

Also if you google on scholar and google books, principles of flight, you will find many good selections, and the FAA provides many publications online for free. The pilot's handbook of aeronatutical knowledge link I gave you does work and it is also free to download each chapter.

John Tullamarine also has great suggested websites as does checkboard among others, please see these links via tech log.
http://www.pprune.org/tech-log/66205...eferences.html

So the long and short of it is if you want to read it you got to buy it.
I don't have a problem with that, however I am not sure that I wish to spend 65 dollars getting a further explanation on an exam I have already done. Unless I have failed it of course and need to do a resit!
Thanks again to you all for your imput and lets hope I don't need to buy the book.
Nigel

NO!!!
 

It is free to read most of the book on Google books!!! Page 269, 270 and thereafter are all available for free on Google Books.:bored:, Not sure how you read into my post that you had to purchase it to read that information at all; if I miscommunicated to you, I apologize... the links I gave you for all the information from PPRUNE are free and the handbook is free too. You do not have to pay to see the references fromm google books I gave you.:ugh:

?$?$?$
 

All of the information you need to for this aforementioned test and future tests are available online for free or via mail order for around 12 bucks.:eek: Amazon.com, Payhalf.com, Ebay, Craig's list have examples of such materials for sale. However, flying is expensive business which can end very fast with a stall, a crash onto the runway (like with windshear, or all engines out, if one is not prepared; even some who are prepared) or a deep spiral dive. If you are truly training to become a pilot, then you know there is nevere too much you can know or know how to do regarding your aircraft.:ooh:
Leave nothing to chance, my young friend. We are not just discussing one exam, but rather, we are discussing your lifetime process of assimilating and accomodating knowledge/skill sets, so that you do not end up pitch down into a @*$%^&! sand dune.:ouch:

http://www.pprune.org/tech-log/66205...eferences.html

http://www.pprune.org/private-flying...-approach.html

just to add a little,... it is important to remember a few circumscribing facts, since it is possible to encounter conditions outside of the part 25 gust envelope because
the theoretical model of the 'gust' considered is an alleviated sharp-edged gust modeled on a bell-shaped curve
it assumes that the gust steadily increases to a maximum then dies out likewise---however if a real sharp edged gust is encountered [severe CAT ] then a much higher load factor than computed will ensue possible leading to ultimate loading from the instantaneous increase in AoA without alleviation
and the value of the bell-shaped gust likewise decreases with with increased speed
going from Vb [max gust instensity] Vc [design cruise] Vd [design dive]
lastly, the the TAS value of the gust is rightly decreased with altitude [thinner air] but don't get a false sense of security from this fact either

so although far 25 offers a great deal of protections it does have its limitations the does not preclude the real possibility of structural failure if real life conditions are encountered beyonded the certificated envelope as is a very real possibility in real life even at the VTP/VRA

so always respect turbulence and slow down!

this may be considered controversial:ouch: but one should slow to the computed Va [based on weight/stall speed] if severe gusts are really encountered ---don't worry about the stall you wont exceed design limit loading and if equipped/necessary you'll have stick pusher protection or the stall would be a better option than structural failure: so if really caught out; slow way way down and remember that since maximal wing loading i.e. weight to surface area loading occurs at the stall
Va will thus be dependent on Vs [as previously described by Keith Williams]
and Vs is a function of weight the Higher the Vs the Higher the Va will be hence you will have a Higher Va at a Heavier weights,...FAR 25 is comprehensive but there are several large Gaps that can kill those caught unaware of the limitations of the design envelope

Actually, the whole picture is quite complex:\

PA:)

PA

Quite complex? More like very complex. Would you please elaborate on "maximal wing loading i.e. weight to surface area loading occurs at the stall"

Dick

sorry DW I could have said that in a simpler manner meaning that that maximum weight to be carried by the wing[mainly] is the weight [in terms of total load factor] that the wing carries at the stall i.e the ratio of W/S is increased to a maximum; this gives rise to the fact that a stall at 1Vs loads the wing with a maximum 1 'g' however at 2Vs an accelerated stall g of 4 g based on the relation ship Vsn = Vs[n [load factor]^1/2

Va is computed similarly except that n [any load factor] is replaced by the design limit load N therefore Va represents the speed that if a stall occurs the wing loading will not exceed design limit loads,...this is a mathematical certainty at odds a bit with the somewhat artificial/ statistical world of design standards [as JT always says 'a line in the sand'] in both cases the Change in Load factor DeltaN i= q*delta AoA but....

in FAR 25. [340???] the worst gust assumed [Uref] to impact the airframe are alleviated i.e statistically assumed to build up gradually reach maximal intensity then decay gradually but in reality in extreme turbulence the gust may be sharpedged and result in an instantaneous increases in AOA this will result in higher than assumed load factors ---hence Vra/Tp becomes very very artificial and only speeds near Va can protect you,...in reality for Extreme turbulence it may just be better to stall

and in my opinion the original question is very poorly worded and should remain off of the exam

I hope I didn't mess anything up:\

PA
 

Thank you for such an enlightening treatment of the subject.

Just on the remote chance that anyone has the slightest interest, I am happy to say despite my lack of knowledge of this area I managed to pass my PoF exam along with AGK and OP.
So just 6 to go, back to the books for me.
Nigel

Nigel, congrats man!!!:ok: Keep up the good work, and never stop learning.

I really wish the JAA would quit trying to have everybody find the square root of things, rather than just applying common sense, which is - slow down in turbulence. Plain and simple. I too passed PoF, but not without a great deal of eye-rolling and mumbled cursing.....

Oh I forgot to write---

you must add 1g to the Nz because your already in sustained 1g flight:
for example if you compute delta N to be 50000lbs and the plane weighs 25000lbs then the load factor would be 2+1g =3g

PA

Gust load factor and altitude
 

Keith,

Do you think we could use the same reasoning to answer the following question:

Is the Gust load increasing or decreasing when altitude increases (IAS and all other factors of importance constant) ?

I assume vertical gust.

Altitude 1 < Altitude 2
IAS1 = IAS2

Using your argumentation I get this formula :

L2/W = gust load = Rho2 (TAS2)² / Rho1 (TAS1)²

If IAS constant, when altitude increases TAS increases too. However air density decreases much more thus gust load decreases.

Could that be a good explication ?

Thanks for your answer Keith.

Have a good day,
Emmanuel Cordier.

In order to produce the Indicated Airspeed (IAS) our Airspeed Indicator measures the dynamic pressure, then produces an indication that is determined by the value of that dynamic pressure.

So if we are climbing at constant IAS then we must be climbing at constant dynamic pressure.

This means that as we climb 1/2Rho2 (TAS2)² must be equal to = 1/2Rho1 (TAS1)²

This in turn means that if we are to have constant lift to match our (assumed to be) constant weight, then our angle of attack must also be constant.

If we hit an upward vertical gust this will increase our angle of attack, which will in turn increase our lift and our load factor.

The increased load factor in the gust is proportional to the amount by which the gust increases the angle of attack.

The increase in angle of attack is determined by the relative magnitudes of the TAS and the vertical speed of the gust.

If we climb at constant IAS we will have a gradually increasing TAS.

If we assume that we meet a series of gusts of a constant vertical upward TAS while climbing at constant IAS, then in each case we will have a constant upward TAS (the gust) being added to an increasing horizontal TAS.

This means that the relative magnitudes of the Gust and the aircraft TAS will gradually decrease. This will cause the change in angle of attack to gradually decrease. This in turn will cause the gust load factor to decrease.

So the gradual decrease in gust load factor as altitude increases at constant IAS, is caused by the gradual reduction in the relative magnitudes of the (constant) upward TAS of the gust, and the (increasing) forward TAS of the aeroplane.

The only part in all of this that is played by the reducing air density is that this causes the aircraft TAS to increase in our constant IAS climb.

All of the above is of course a simplification of the situation, because the addition of the gust to the aeroplane TAS will also change the dynamic pressure acting on the aeroplane.

Thanks again Kieth for your very complete and logical explanation, as always.

But I do have a problem,... following your argumentation, it leads me to think that the fastest you fly, the longest is the aircraft TAS vector in comparison to the vertical gust vector, then the least sensitive to gust would be the aircraft. However we know that it is not the case since we always have to slow down to Vb (outside yellow arc for C152) while flying through turbulent air.

How can you explain this contradiction ?

Thanks again for your help Kieth,
Emmanuel Cordier.

Principles of flight, stick force & manoeuvre stability
 

Have a look at that question:

The manoeuvre stability of a large jet transport aeroplane is 280 N/g. What stick force is required, if the aeroplane is pulled to the limit manoeuvring load factor from a trimmed horizontal straight and steady flight? (cruise configuration)

I suppose that the limit manoeuvering load factor that wee need is 2,5.
Well at least with that load factor I get the right answer which is : 420 N

Could someone give us all the limit load factor we need to know for small and light aircraft, and for large transport jet that we need to know for the JAA ATPL exam ?

Thanks a lot
Emmanuel Cordier.

I think that you are mixing up two very different situations.

Situation 1 Increasing IAS at constant altitude.

As we go faster the dynamic pressure increases with the square of TAS so the angle of attack and CL both decrease to maintain constant lift for level flight.

Because the CL and angle of attack are decreasing, the sudden increase in angle of caused by an upward gust will represent a greater proportional incease in CL, lift and load factor. So if we go fast enough a gust that was no problem at low speed (when the angle of attack and CL were high) will tear the aircraft apart.

So acceleration at constant altitude increases gust response, so we must not go too fast in gusty conditions.


Situation 2 Increasing altitude at constant IAS.

As we go higher at constant IAS the dynamic pressure, angle of attack and CL are constant, but our TAS increases. So any given upward gust velocity produces a smaller increase in angle of attack CL and load factor.

So climbing at constant IAS decreases gust load factor.