The official aviation quiz topic!

744rules · Post by **744rules** » 18 Jan 2006, 22:59

do you mean the vortex generators ?

The are installed to reduce the drag and thus improving the aerodynamics

Avro · Post by **Avro** » 19 Jan 2006, 08:51

744rules wrote:do you mean the vortex generators ?

The are installed to reduce the drag and thus improving the aerodynamics

Yes I'm talking about the vortex generators.

But no they are not there to reduce the drag.

Chris

SN_Bigbirdy · Post by **SN_Bigbirdy** » 19 Jan 2006, 16:08

Vortex generators are added to the front of a swept-wing in order to maintain steady airflow over the control surfaces at the rear of the wing. They are typically rectangular or triangular, about a centimetre or two in size (so that the boundary layer would separate just behind the wing), and run in lines chordwise at about the thickest part of the wing, increasing the effective thickness. They can be seen on the wings and vertical tails of many

(((Hell yeah, copy-past rulez

8) )))

Simon

Avro · Post by **Avro** » 19 Jan 2006, 16:52

SN_Bigbirdy wrote:

(((Hell yeah, copy-past rulez 8) )))

Copy and paste rules indeed BUT only if you copy the correct source. You should know that one can find a lot of wrong info on the internet . Even if it's written as if it's correct.

To keep things short your answer is not totally correct.

Your source says the following:

Vortex generators are added to the front of a swept-wing in order to maintain steady airflow over the control surfaces at the rear of the wing.

This is not correct.

First of all it doesn't need to be a swept wing... but ok nearly all planes have swept wings nowadays.

The second part I've put in bold is not true !! The vortex generators which are placed in front of the aileron (or other control surfaces) are there to prevent flow separation ON THE MAIN AIRFOIL that is to say the wing. When you deflect your aileron this one will create a increase in lift on your main wing. The aileron itself will not contribute greatly to the total lift of that section. That's why the control surfaces are small since they generate a lot of lift on the component which lies in front of them due to the induced upwash.

Herewith you can see that it's not always good to do copy paste

Check with more than one source next time

BTW the explanation I gave above is only valid for he vortex generators in front of control surfaces. The other vortex generators on the wing you see have different functions. But let's not get into more details.

I hope you learned a lesson of doing blindly some copy paste today

But you may ask a question now SN_Bigbirdy

Chris

SN_Bigbirdy · Post by **SN_Bigbirdy** » 19 Jan 2006, 17:02

Since 744rules knew that we were talking about vortex generators I pass my round to him. Not enough time to find a proper question...

Meanwhile: I'm going to deal with the important copy-past law and the consequences of that

Simon

744rules · Post by **744rules** » 19 Jan 2006, 17:15

Don't know if this one has come up yet but,

Etihad allows NO animals in the cabin except ..............

Avro · Post by **Avro** » 20 Jan 2006, 16:33

744rules wrote: Etihad allows NO animals in the cabin except ..............

Eagle's ??

744rules · Post by **744rules** » 20 Jan 2006, 17:00

no, but close

realplaneshaveprops · Post by **realplaneshaveprops** » 21 Jan 2006, 10:14

Source:
http://www.etihadairways.com/Presentati ... AEF484DE78

Can I travel with my pet on Etihad Airways?

A. Etihad Airways accepts the carriage of pets as checked baggage provided all the necessary health documents and export/import licences have been obtained. The following pets are accepted for travel provided the shipment meets all the necessary requirements.

Birds
Cats
Dogs (excluding any ‘snub-nosed’ types)
Falcons*

* Falcons may be allowed inside the aircraft cabin. Please check with your local Etihad office for terms and conditions.

Koen

744rules · Post by **744rules** » 21 Jan 2006, 11:06

Falcons was the answer.

Koen, up to you

realplaneshaveprops · Post by **realplaneshaveprops** » 23 Jan 2006, 12:10

How does an Eductor Cooling system works?

The ERJ135/145 and 737NG use that system for cooling the APU system.

Koen

Avro · Post by **Avro** » 23 Jan 2006, 20:05

As far as I know the eductor system will work by using the outflow air of the APU exhaust. This exhaust will form a low pressure area which will suck in outside air into the eductor inlet. That air goes then into the heat exchanger with the oil system before going out in the exhaust again.

Thanks to that device (using the low pressure sucking in the air) you can save weight since you don't need a cooling air vent fan.

BTW I'm wondering if it wouldn't be even possible to design only one opening which could house both the air inlet and the exhaust

If you would have an inner duct and outer duct. In the outer duct you'll have the exhaust which would pass through a swirler (like in the combustion chamber). The swirl will then induce a low pressure inside the swirl which will then suck in some air into the inner duct. This would save some space, weight. But you might loose more energy due to the swirl... I'll have to study that. Thanks for asking the question Koen, it gave me an idea... but probably not feasible..

Chris

realplaneshaveprops · Post by **realplaneshaveprops** » 24 Jan 2006, 00:06

Correct Chris, you're next

Koen

Avro · Post by **Avro** » 24 Jan 2006, 23:09

Why do we have on big planes both AC and DC circuits. Why not all in DC or all in AC ??

Chris

PS: AC = alternative current, DC= continuous current

MD-11 · Post by **MD-11** » 25 Jan 2006, 11:40

Avro wrote:PS: AC = alternative current, DC= continuous current

DC = Direct Current or gelijkstroom in Dutch.

The answer to the question is a mistery to me however.

Unless it has something to do with power for the batteries which use DC.

Avro · Post by **Avro** » 25 Jan 2006, 12:25

MD-11 wrote:
Avro wrote:PS: AC = alternative current, DC= continuous current
DC = Direct Current or gelijkstroom in Dutch.

Don't be picky

Unless it has something to do with power for the batteries which use DC.

Yep I accept that for the first part of the question. Indeed DC is the only way to use batteries.

But now, why do they also need AC in bigger planes and don't simply use DC for everyting. (Since DC can be used technicaly for every feature)

Chris

realplaneshaveprops · Post by **realplaneshaveprops** » 25 Jan 2006, 19:55

Because it's easier to generate Alternate current!
An other reason is that you can make an electrical motor smaller for the same power. The higher the frequency, the smaller the motor, but the higher the frequency, the higher the frequency losses. The 400Hz was a choice between the pro's and contra's.

Koen

Avro · Post by **Avro** » 25 Jan 2006, 20:03

jan_olieslagers wrote:Don't know if this answer is still valid today but it certainly was at one time: some basic flight instruments are based upon gyroscopes, and the gyroscopes are/were driven by three phase AC, 110V 400Hz IIRC.

Well I don't know for every gyro, but I know that avionics can be operated either in DC or AC current. That's however not the main reason for the use of AC in big aircrafts. Not I mentioned larger aircraft than small GA plane

nother answer might be that AC can be transformed to different voltages rather easily, using (indeed!) a transformer.

Well it can be transformed easily ok, but you can have both DC and AC generators, that's not much the problem either

An other reason is that you can make an electrical motor smaller for the same power. The higher the frequency, the smaller the motor, but the higher the frequency, the higher the frequency losses. The 400Hz was a choice between the pro's and contra's.

You are getting very close here Koen. It's indeed because we can use higher frequencies and higher voltages. Thanks to this one can save on cable weight by transporting high powers with smaller cables (in diameter) and thus save quite some weight.

Anyway, now that I asked the question I realize that it can be quite ambiguous and that several answers are plausible

So I don't know but I'd say you both Jan and you Koen answered the question more or less correctly. Decide among yoursleve which one can ask the next round of questions.

Chris

realplaneshaveprops · Post by **realplaneshaveprops** » 25 Jan 2006, 20:20

So I don't know but I'd say you both Jan and you Koen answered the question more or less correctly. Decide among yoursleve which one can ask the next round of questions.

Jan, go ahead!

Koen