737 800 Pilots.

[speed_alive_rotate]

I would like to just ask, or in some questions just clarify a few tech questions regarding the 737 800. I am a rookie and am not type rated so please be patient if some of my questions are a little confused or dare I say a little silly!!

1. ELT location on the 737 800?. I believe it can be turned on from the cockpit by either setting it to manual ON or by arming it to automatic which it will be transmitting if a certain G load is exceeded. And it can obviously work and still transmit in water , but does it have a certain depth cut off?

2. Absolute Ceiling Altitude.
I can see the max service ceiling which is the certified Altitude is 41,000 ft , however the aircraft is capable of climbing higher , and so would I be correct in saying there is a Certified max Absolute ceiling , which would only obviously be tested by flight tests? I do understand the difference between Absolute ceiling and service ceiling but no matter how many sources I check I cant seem to find an absolute ceiling figure.

3. more of a general swept wing question. I understand all the positives of getting a swept wing to stall at the root first and to prevent a wing TIP STALL , however another general question keeps coming up and I am getting a little confused.It is as follows:
Why so important to prevent a stall at the root of a swept back wing??

I would greatly appreciate any feedback possible and would love to get some concrete answers. I don't like to take the easy option and just come on this forum to get quick answers but I have been searching for the above answers for few hours now and because there is such conflicting information on the internet I thought I could get some factual and reliable information here.

Again many thanks to all who can help.
Kind Regards , and safe flying
SAR

[Dit]

1. Ours are in the back galley and thus there is no switch in the flight deck. It will turn itself on with a large enough G Force or by coming into contact with water, or it can be manually turned on by the Cabin Crew.

2. You're not going to find this information as it will not be published anywhere and will be known only internally at Boeing.

3. You want the Centre of lift to move forward upon stalling and not aft, to make the aircraft naturally pitch down to aid exiting the stall.

[NSEU]

1. Ours are in the back galley and thus there is no switch in the flight deck. It will turn itself on with a large enough G Force or by coming into contact with water, or it can be manually turned on by the Cabin Crew.

What has ELT location to do with manual override? If they can put a wire from the cockpit to the ELT on one airline's 737NGs, they can do it on yours.

And it can obviously work and still transmit in water , but does it have a certain depth cut off?

I think it's generally agreed that it will not work underwater at all at the frequencies it transmits, especially in sea water which is particularly conductive (electrical conductivity is a bad thing for a radio waves).

Citing this reference... http://users.tpg.com.au/users/ldbutl...munication.pdf

There is an attenuation formula...Decibel loss per meter) = 0.0173 x the square root of (frequency x conductivity). It is more than 10db per meter in sea water at VHF frequencies. At ELT UHF frequencies, it is over 50db/meter. This is assuming the transmitter and antenna cabling is absolutely watertight.

[gretzky99]

3. You want the Centre of lift to move forward upon stalling and not aft, to make the aircraft naturally pitch down to aid exiting the stall.

Wouldn't moving the centre of lift rear, not forward, lower the nose?

[Derfred]

Wouldn't moving the centre of lift rear, not forward, lower the nose?

Yes. You want the root to stall first, thus moving the centre of lift aft and providing a nose down pitch moment which will tend to unstall the aircraft.

[NSEU]

Why so important to prevent a stall at the root of a swept back wing??

Would stalling the root first give you some roll control towards the end of the wing?

(EDIT: See Ekhard's answer below)

[speed_alive_rotate]

Thank you all so much for your replies , is it Boeing standard that the ELT is located in the aft galley?
Regarding the absolute ceiling that is great , I thought I was going crazy as I could not find that information anywhere!!
Still a little unsure on the swept wing question
once again appreciate all inputs and thoughts

[NSEU]

is it Boeing standard that the ELT is located in the aft galley?

As a rule, the transmitter unit will be as close to the antenna as possible (just slightly forward). The longer the cable run, the more you have to worry about the antenna cabling being broken in a high G accident. The aft galley would be a most unusual location, because the vertical stabiliser is over the galley. The ELT antenna has to be well forward of the stabiliser.

The instructions in one 737NG AMM for servicing the transmitter unit mention the removal of sculptured ceiling panels in the cabin. The location is given as station 770, which is about 6 windows from the aft door. The antenna is at station 797 (27 inches aft of the transmitter). Another airline's 737NG AMM shows the transmitter unit at station 794 and the antenna at station 795.6.

[172_driver]

In my previous airline I believe we only had portable ELTs, at least one in the aft galley. Current airline we've got an ELT switch in the flight deck. Couldn't tell you exactly where it's located.

[eckhard]

Why so important to prevent a stall at the root of a swept back wing??

I think this may be confusing the generally accepted idea that it is important to prevent a stall at the tip of a swept back wing.

If the tip stalls before the root, lift will be lost from the aft portion of the wing. This will produce a pitch up which will tend to exacerbate the stall.

On the other hand, if the root can be made to stall first, lift will be lost from the front portion of the wing. This will produce a pitch down which will tend to prevent further stalling.

[speed_alive_rotate]

@eckhard
Thank you so much for your message. That is exactly why I am getting confused. I know and 100% agree with your point on wanting the root to stall rather than the tip on a swept back wing.
The exact question:
Why so important to prevent stall at the root of a swept back wing?
Maybe it is sort of a trick question and you would have to argue in the case of wanting it to stall at he root rather than the tip first including all your mentioned points.

Many thanks , would love to hear your thoughts
SAR

[Chesty Morgan]

Plus, of course, wings tend not to stall at the same time as each other so a tip stall will lead to a bigger wing drop as well as a nose up pitch moment.

[Piltdown Man]

The absolute ceiling question is not really with knowing. This is because at many weights and temperatures you might not even get to your service ceiling. Also I understand that various operators have engines with different thrust ratings, so unless all the variables are known, this value can not be determined.

PM

[NSEU]

Originally Posted by speed alive rotate

@ eckhard: Why so important to prevent stall at the root of a swept back wing?

Are you asking if there are any advantages at all in preventing stall at the root? (other than preventing stall)

It sounds like you've found a badly worded exam question which has raised some debate.

[speed_alive_rotate]

I agree with you NSEU , I believe the question is badly written as discussed above it is the root which we do want to stall first .
Many thanks all for your contribution ,
SAR

[speed_alive_rotate]

Thanks again for all those who contributed to my last few questions. As you may have guessed I have a few more questions I would love your help with- I'm trying hard to prepare for any possible interview and am really putting the hours study in so would be most grateful for any help.
Just regarding the 737 800 CFM 56-7B engines:

Is there a critical engine???- I would say no as jet engines do not suffer the characteristics of a critical engine as Prop driven aircraft .
So which way do the fans rotate???
Do they both rotate anti clockwise as seen from the front??
I understand the expense of counter rotating engines would be rediculous!!
Would love if anybody could help clear this up for me.

Many Thanks,
SAR

[too_much]

738 will go up to 51,000 ft if the climb is extremely slow and weights are at a
Minimum. Tried it in the sim once.

[speed_alive_rotate]

Have you any insight into my recent question @Toomuch
Would love to hear any words of wisdom , and many thanks for your contribution to my previous post.

Regards,
SAR

[ImbracableCrunk]

I would really hesitate to use sim data for much. Most sims don't have very good data for that type of maneuver. For example, my company has 4 Level D 737 sims and only one of them has the data for fully developed stall recovery. I would imagine most sims wouldn't bother having accurate data for very high altitude maneuvering. The stuff costs money so why bother?

[Jhieminga]

Originally Posted by speed_alive_rotate

Is there a critical engine???- I would say no as jet engines do not suffer the characteristics of a critical engine as Prop driven aircraft .
So which way do the fans rotate???
Do they both rotate anti clockwise as seen from the front??
I understand the expense of counter rotating engines would be rediculous!!

The CFM-56 engines all rotate clockwise (as seen in the direction of flight, so your assumption is correct).
In the regulations, the critical engine is described as the "engine whose failure would most adversely affect the performance or handling abilities of an aircraft". Theoretically you could get some slightly different effects between two gas turbines but for all intents and purposes both engines are equally critical on a 737. You need a bootfull of rudder no matter which one fails.