Systems Jar exam yesterday

[Irish Flyer]

Anyone do yesterday´s Systems Jar paper find question two in the paper to be a bit strange. Have asked around but no one seems to be able to give a definite answer to it. Any ideas?

What causes torsion on a wing?

a) Positive sweep
b) Dihedral
c) Wing tip vortices
4) Propwash

[CAT3C AUTOLAND]

Personally I found that paper a bit of a sod, and I went for option C, purley from the fact a vortex has a twisting motion.

There is hope, even though I found it a little touch and go :).

Good Luck with your results.

[Mister Geezer]

Keep the chin up guys - I was convinced that I had failed my systems exam but I passed. It is a bit of a lottery but remember, if you thought a question was a bit odd then someone will probably complain to the CAA and if it is dodgy then everyone will be awarded a mark (or two if the question was worth that etc!)

Hope all goes well!

[CAT3C AUTOLAND]

Mister Geezer,

Thanks for the support, I took three exams yesterday, and to be quite honest I have no eye dear how it went! From experience of what is assessed, there appears to be so many questions designed to trip you up, I am not sure of how many RTFQ questions that caught me out!!:)

Anyway, like I said there is hope, take care.

[mad_jock]

I would say A is the right answer.

Sweep causes the wing tip to be out of plane with the wing root.

Therefor the Cp will be away from the root so there will be a moment caused by the force through the cp and distance between root and cp in the longitudinal. Which will give a torsional force. ie rotation in the pitch sense at the wing root.

MJ

[Duck-U-Suckerz]

I was there (wishing I wasn't)
I put 'c' my self,
If they had put 'wash in/out' I would of gone for that, not to sure about sweep Mad-Jock but you are frightening me with your case,
but even if your wrong (and you may be right) it sounds good bulls#it!;) but thinking about it you may well be right as air moving fast outwards from underneath will cause a bending moment :( (oh B@@@@llks) where did I put those CAA exam application forms?

[avrodamo]

I went for C too. Tried to reason it and that seemed about best.:confused:

[Alex Whittingham]

Er....... (a) and (c) and possibly (d). I think we'll appeal this.

Can anyone else who sat this paper please confirm the exact wording?

[Duck-U-Suckerz]

GO ALEX GO!
If you ask me, the wording in the first post is about right but answer 'a' might of been 'SWEEP BACK'
I'll speak to Geoff Bull at LGU tomorrow and see if they will second
your appeal.

But how dose this work? whats the drill?

My e.mail; [email protected]

[timzsta]

I did last months Systems exams (LGU DL student) and thought that was a bitch of a paper too. (Got 79% so jobs a goodun!). There were 7 questions on gear/wheel/brakes and 5 on magnetos. What is that all about? So go get them. Agree with Alex it could be any of the three he mentions. But what do we know, we just spent hundreds of hours reading the books!

[avrodamo]

Alex. As far as i remeber the exact wording was as it appears at the top of this thread.

[concordino]

I think the answer to that question is A the positive sweep for the same reason mentioned by mad_jock.
Prop wash only re-energizes airflow over the wing thus creating more lift…
But could be wrong.

[Dean Johnston]

As someone once said to me " you could take the text books into the exam, and still not answer the question" What chance have we got ?

D.J.

[mad_jock]

I don't think you will have much chance of an appeal

Its basic engineering

Dihedral in static flight is a stability issue for dutch roll. It moves the CP in the vertical plane not the horizontal in relation to the wing root. And we need movement in the longitudinal to cause torsion.

Wing tip vortices are a function of drag and are external to the wing ie they are in the same plane as flight. So no moment so no torsion. (yes i know there will be a moment but not in the plane we are looking at it will be in the yaw axis but will be balanced)

Propwash as said before gives increased air flow over a portion of wing. But if the cp is is in the same plane as the wing root it will not give a torsional moment. Only an increased bending moment around the roll axis

A is the only answer

MJ

[Flamgat]

I must differ.

Although the twisting moment found on swept wings, when they flex in flight, is by far the most powerful, it is not the only torsional stress applied to a wing in flight.

If you have a difference in pressures, between the top of the aerofoil section and the bottom, and their mean points of action are not co-incidental, then you will have a twisting moment about the aerodynamic center. This is more marked with a cambered aerofoil with changing alpha.

If you have large wing tip vortices (low aspect ratio) then you will have more induced downwash at the tips, and consequently a reduced local alpha.

If you have reduced the alpha at one section (the tip) and increased the alpha at another (the root) to provide the total lift required, then there must be different pressure patterns over the tip section and the root section.

Different pressure patterns, different twisting moments, and therefore a torsion stress applied to the wing. Granted, it is not as marked or powerful, as the twisting moment found with a swept wing when it flexes in flight, but it exists.

Just ask the designers that use “wing warping” for lateral control!

[mad_jock]

Fair point.

Yet another great question in the JAR question bank.

I seem to remember something similar in the OAT feedback questions and Steve Chesher saying always go for the most marked effect.

MJ

[Keith.Williams.]

I agree that this question is somewhat dubious (pretty dreadful actually), but I'm rather surpised that most contributors have ignored the torsional effects of dihedral. Dihedral causes the wing tips to be higher than the wing roots. So any drag acting at the tips tends to twist the wings leading edge up.

If we try hard enough we can find arguments that suggest that all four options are correct to some degree. But assuming all four factors apply to a given aircraft, then wing sweep is likely to be the most dominant in causing torsional loads on the wings. As stated in the previous post, if more than one option appears to be correct, students should pick that which they think is the most correct. In this case I'd go for sweep back.

[BritishGuy]

Thank God! Nobody had mentioned the answer B! Thats what I put down. I dunno if it's right but I have my theories!

[CAT3C AUTOLAND]

Well, I most certainly respect Mr Keith Williams opinion, as I know he knows his stuff, looks as if I got another question wrong!! Dam!!:eek:

[carbonfibre]

Mad_jock

Have to agreee with you there, although c would cause some torsional twisting due to pressure differential on the wing surfaces its not nearly as high as the sweep.

So in the eyes of the CAA, i think Alex you pointed this out to me once, whats the most appropriate.

If i remember correctly though this is most marked at lower speeds.?

If its wrong shoot me, its been 18 months since i did mine, if the plane aint stalling its still flying, besides im not getting much sweep on the PA44

:D

[Alex Whittingham]

This really shouldn't be about exam technique. The exam questions should be clear and unambiguous with one correct answer and three wrong ones.

The CAA are quite onside about this and they regularly edit out bad questions and adjust the marks as a result of appeals from both candidates and schools. We'll bounce it up to them and see what they say.

[NineEighteen]

Keith.Williams. wrote...I'm rather surpised that most contributors have ignored the torsional effects of dihedral. Dihedral causes the wing tips to be higher than the wing rootsKeith, this option crossed my mind, however, I sat this exam and option b) simply said "Dihedral". Had it said "Geometric Dihedral" then it would have been worth considering.

I understood that "dihedral" describes anything that contributes to lateral stability (i.e. sweepback, geometric dihedral, the fin etc...). I ignored this option straight away as it was not descriptive enough. Was this a little rash?

BTW, I answered "vortices" for the same reasons as CAT 3C but I'm not at all confident about any of the exams I took on Monday so I could be wrong! :rolleyes: :(

[carbonfibre]

Alex

I totally agree with you they should be clear and concise, but rarely has that been the case since JAR.

Theres the correct way and the JAA way, if i remember correctly isnt this supposed to be in the aerodynamics / principles of flight paper? and not the systems?

Argggghh all i can say is thank F--k i got mine outta the way

Ah well if someone finds out can they post it on here

Would be interesting

Good luck anyway guys hope it pans out:D

[Keith.Williams.]

NineEighteen,

I cannot agree with your definition of dihedral.

The term (lateral) dihedral is commonly abreviated to "dihedral". It refers to the situation in which the wings or tailplane are angled upwards from root to tip. Its principal purpose is to increase lateral stability.

The term "longitudinal dihedral" refers to the relationship between the angles of incidence of the wing and tailplane (or canard). This is one of the factors that contribute to longitudinal stability.

The term "dihedral effect" is commonly used to refer to the way in which wing sweep back increases lateral stability, making the aircraft behave as if it had a greater degree of dihedral.

The question referred to in this string has already been challenged by EPTA and CABAIR (CCAT). If other schools have also challenged it, then it is likley that it will be scrapped and the points awarded to all students who took the exam.

All of the FTOs will be informed of the results of all such challenges about two or three weeks after the exam.

[BritishGuy]

Keith, just a quick question then......SO lets say that if someone gets their results in a week and gets 74%, and a few wks down the line they scrap the quesiton and award the results to the folk having just sat the exam, is it true to say that in this case the guy that got 74% will now get a letter saying that he/she actually got 75% now as a result of scrapping a question?? Has this ever happened??

[RowleyUK]

very bad question indeed!!

Went for dihedral myself basing my theories on the same as Keith!

Ahhhh well looks another resit!!

I have all the possible answers written down for this question at home and i will post the question as it was word for word in the exam!! includin the 4 options!

[Keith.Williams.]

Britishguy,

There are essentially two ways in which questions can be challenged. The first is by the students making a comment on the scrap paper provided in the exam. The second is by the FTOs who have until the end of business on the Friday of the exam week, to register any problems reported to them by their students.

The reason for this tight timescale is to enable the examiners to consider, and decide upon all challenges before starting to mark the papers. So whatever mark you receive in your exam results takes account of all challenges lodged.

If a challenge is accepted as being valid, the question to which it refers is temporarily removed from the question bank and the marks are awarded to all students who took the exam. The subject question is then examined by the appropriate JAA committee at a later date. Defective questions are either scrapped or modified, before being reused.

The best way to deal with problem questions is to lodge a challenge at the end of the exam, then report the problem to your CGI. He can probably make a more reasoned argument which has a better chance of being accepted by the examiners.

[RowleyUK]

Any news on an appeal with this one???

[Alex Whittingham]

It will take a week or two.

[moku]

Well I put B for this one also.

Yet another I can add to the list that is quickly dragging me to that 74% :D

[Keith.Williams.]

Although the formal statements will take a while longer, I have heard that the challenge was accepted. So if you get a result of 74% you actually did rather worse. If you get 75% you are very very lucky! Having defective questions in your exam can sometimes be quite helpful, provided you get the message back to your FTO before the end of the exam week.

[NineEighteen]

Thanks very much Keith. Your help is greatly appreciated, I really wish my FTO was as dependable as PPRuNe. :ok:

[BritishGuy]

Right, as the appeal was accepted, did they (the CAA) at least indicate what the actual answer was?? It would be intersting to know.

Just forgot to add-I'll second NineEighteen on that statement. Thanks for clarifying the odd question I've asked you Keith.

[RowleyUK]

Keith,


Will we ALL be awarded an additional 2% for this question regardless as to which answers we put?? or will it only be awarded to the people who appealed and made notes on their exam paper??

I put dihedral but nobody seems to belive this would cause the torsion despite your previous post!

[Alex Whittingham]

According to the examiner, all the candidates will be credited with the marks for this question. He acknowledges the question is inherently unsafe and it will be referred back to the Subject Experts at the JAA.

[Keith.Williams.]

Rowley,

As stated by Alex, all students taking the exam will get the marks for this question.

Although I said that dihedral would tend to cause wing twist I do not believe that this is the option the examiners were looking for.

To assess any possible twisting effects we should imagine that we have made vertical chordwise cuts through the wing roots and fixed the wings back on using a single horizontal pin. Now imagine the effects of the drag at the tips of dihedral wings. The tips are higher than the horizontal pin, so the drag will tend to cause the wings to rotate leading upwards. The lift at the tips of swept back wings will have a similar effect, but tending to rotate the wings leading edge down. This is why swept back wings are less prone to divergence. As the lift bends them upwards it also twists the tips leading edge down, thereby reducing the lift at the tips. This reduces the bending effect, so the wings do not diverge.

But the degree of twisting is proportional to the amount by which the tips are above and behind the roots. Lots of aircraft have 20 degress or more of sweepback, but dihedral angle is usually only a few degrees. this coupled with the fact that lift is much greater than drag, means that the torsional effects of sweep back are much greater than those of dihedral.

[RowleyUK]

Thanks for that Keith!

Thanks to both of you for pushing the question to these people!

[RowleyUK]

Have just been told by my school.........they are aware of an appeal against this question but they are unsure as to wether it has been accepted!!:confused: :confused:

Are you two receiving inside info (alex,Kieth);) ;) I pray to God that you are right with this...........cos right now i could do with every mark i can get my hands on!!!

[Alex Whittingham]

No inside info, the examiner sent an e-mail to all the CGIs. Get your school to check their e-mail more often.

[RowleyUK]

Wilco............

Unforunately im a victim of a school that shows little interest once i have walked out of the door!!.............hence my questions to you on pprune!

[moku]

Well all that worry over nothing..... Passed with78%:O

[NineEighteen]

If you get 75% you are very very lucky! :p

[Keith.Williams.]

NineEighteen,

Can I take that this means you rather like the appeals system?

For all students taking the JAR exams, it is worth remembering (among all that other stuff filling your heads) that spotting defective questions and reporting them to your CGI can score extra points for everyone.

It isn't really what the examiners wanted to achieve, but it is a perfectly reasonable consequence of their failure to provide consistently good questions.

[avrodamo]

I passed with 84% so im well chuffed...got all the others too....beers and Discovery Wings for me now !!!!

[NineEighteen]

Keith,

That's understating it somewhat...this appeal obviously saved my bacon. I'm sad to say that my FTO failed to make the point you outline below. If I spot any dodgy ones in the future I'll be sure to have my instructors query it.

Thanks to all involved in getting this question withdrawn! I clearly need the help! :rolleyes: If the truth be known, I believe my state of mind in exams is costing me more than my knowledge but that's another thread I guess...

Thanks again! :ok:

[RowleyUK]

Me passed with 88%!!!!!!!:p :p


Thats all 14 in the bag!!

Ohhhhhhhhhhhh Yeassssssssssssssssssssssss!!!!!!!!!