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What Is The 'Fin' Underneath The ERJ-145XR?  
User currently offlineWeb From United States of America, joined Jun 2005, 427 posts, RR: 0
Posted (8 years 4 months 2 days ago) and read 9701 times:

I've noticed the ERJ-145XR has a 'fin' underneath the wingbox, while the -145ER & LR don't. What is it and what purpose does it serve?


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23 replies: All unread, jump to last
 
User currently offlineEssentialPowr From United States of America, joined Sep 2000, 1820 posts, RR: 2
Reply 1, posted (8 years 4 months 1 day 23 hours ago) and read 9694 times:

In the event of a wheels up landing, it's designed to prevent the ventral tank from contacting the ground.

User currently offline3MilesToWRO From Poland, joined Mar 2006, 280 posts, RR: 0
Reply 2, posted (8 years 4 months 1 day 21 hours ago) and read 9655 times:

You mean it's supposed to carry whole airplane belly-landed? I dare to doubt. If there is a tank in this place, much better protection would be a strong but flat shield.
I'd rather think this part is some antenna. (antenna, or aerial? You know, the part for radio waves)


User currently offlineEssentialPowr From United States of America, joined Sep 2000, 1820 posts, RR: 2
Reply 3, posted (8 years 4 months 1 day 20 hours ago) and read 9650 times:

As I said, it's a skid to protect the tank.

-The XRs do have a ventral tank in this location

-A "strong, flat shield" as you put it, would transfer damage and friction heat to the ventral tank much more severely, and faster, than a belly skid.


User currently offlineJamesbuk From United Kingdom, joined May 2005, 3968 posts, RR: 4
Reply 4, posted (8 years 4 months 1 day 20 hours ago) and read 9644 times:

Quoting 3MilesToWRO (Reply 2):
3MilesToWRO

Dude this company would've spent millions developing this one bit, doing months of research and development also testing and this is the best possible place and shape for this part!!

Rgds --James--

P.s. Sorry if i seemed to come across arrogant i just couldnt think of another way to phrase it!!!

[Edited 2006-04-22 23:51:48]


You cant have your cake and eat it... What the hells the point in having it then!!!
User currently offline3MilesToWRO From Poland, joined Mar 2006, 280 posts, RR: 0
Reply 5, posted (8 years 4 months 1 day 20 hours ago) and read 9640 times:

Quoting EssentialPowr (Reply 3):
A "strong, flat shield" as you put it, would transfer damage and friction heat to the ventral tank much more severely, and faster, than a belly skid.

Well, if this is attached to some kind of "safety cage" under this tank, it can work as such a bumper. Otherwise this skid would crumble into the tank under the weight of a plane - this vision was why I doubted  Smile


User currently offlineCitationJet From United States of America, joined Mar 2003, 2432 posts, RR: 3
Reply 6, posted (8 years 4 months 1 day 20 hours ago) and read 9635 times:

Quoting 3MilesToWRO (Reply 5):
Otherwise this skid would crumble into the tank under the weight of a plane

Cessna calls these skid rails. They are designed to protect the fuel tank in the event of a wheels up landing. They are not designed to crush or crumble, but rather to wear away as it scrapes along the concrete runway.
You can see the skid rails on the following Citation 525 and 750 aircraft:


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User currently offlineJamesbuk From United Kingdom, joined May 2005, 3968 posts, RR: 4
Reply 7, posted (8 years 4 months 1 day 20 hours ago) and read 9633 times:

Quoting 3MilesToWRO (Reply 5):
Well, if this is attached to some kind of "safety cage" under this tank, it can work as such a bumper.

That would be to large and be very unaerodynamic, The one currently made on the aircraft are probably strengthened massively to cope with the loads of a landing so not to crumble into the fuel tank.

Rgds --James--



You cant have your cake and eat it... What the hells the point in having it then!!!
User currently offlineEssentialPowr From United States of America, joined Sep 2000, 1820 posts, RR: 2
Reply 8, posted (8 years 4 months 1 day 14 hours ago) and read 9569 times:

Well, if this is attached to some kind of "safety cage" under this tank, it can work as such a bumper. Otherwise this skid would crumble into the tank under the weight of a plane - this vision was why I doubted [/quote]

Engineers are a pretty savy bunch, right?

Quoting EssentialPowr (Reply 3):
As I said, it's a skid to protect the tank.

Maybe we need to define what a skid is? Guess so...


User currently offlineCorey07850 From United States of America, joined Feb 2004, 2527 posts, RR: 5
Reply 9, posted (8 years 4 months 1 day 14 hours ago) and read 9558 times:

It looks like there's also a small vent tube or antenna attached to it as well... Can anyone confirm whether or not it has a dual purpose?

User currently offlineTroubleshooter From Germany, joined Feb 2005, 423 posts, RR: 5
Reply 10, posted (8 years 4 months 1 day 11 hours ago) and read 9532 times:

Quoting Corey07850 (Reply 9):
It looks like there's also a small vent tube or antenna attached to it as well... Can anyone confirm whether or not it has a dual purpose?

The small "tube" is the fuel line shroud drain. It is installed on all ERJs. The same goes for the skid. The only difference is that they had to redesign it for the XR version. All ERJs have this device between the main landing gears to protect the fuselage (and the fuel tanks) in the case of a gear-up landing.

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This job sucks!!! I love this job!!!
User currently offlineEMBQA From United States of America, joined Oct 2003, 9364 posts, RR: 11
Reply 11, posted (8 years 4 months 1 day 9 hours ago) and read 9513 times:

Quoting Troubleshooter (Reply 10):
All ERJs have this device between the main landing gears to protect the fuselage (and the fuel tanks) in the case of a gear-up landing.

Correct. All ERJ's have a belly skid plate. The standard ERJ's is much smaller and maybe 8" tall. The 145XR is about 16" tall. This, as said above is designed to support the fuselage and protect the belly tank in the event of a gear up landing. What you are seeing is also not the actual skid plate, but the areodynamic fairing for it. The actual skid plate is a very heavy 'I' beam construction. Trust me..it's stout and dosn't move. I've smacked my head into it a few times doing lower belly inspections.



"It's not the size of the dog in the fight, but the size of the fight in the dog"
User currently offlineTroubleshooter From Germany, joined Feb 2005, 423 posts, RR: 5
Reply 12, posted (8 years 3 months 4 weeks 1 day 16 hours ago) and read 9316 times:

Here´s a quote from my maintenance training notes describing the purpose and the design features of the keel ski. Unfortunately I can not upload a picture.

Quote:
KEEL SKI
The keel ski is a structure installed on the outer side of the landing
gear compartment bottom, at the airplane center line.
It is a protection for the wing structure against retracted landing gear
landings.
It has a longitudinal keel machined from AL 7050-T7451 plate. A
titanium plate on the lower part of the ski permits the necessary
strength in the ground contact areas.



This job sucks!!! I love this job!!!
User currently offlineMD-90 From United States of America, joined Jan 2000, 8506 posts, RR: 12
Reply 13, posted (8 years 3 months 4 weeks 12 hours ago) and read 9183 times:

There are also similiar fins that help control stall behavior.

Niki Lauda's Lear 60 is a good example, and so is the Piaggio P.180:


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User currently offlineWingscrubber From UK - England, joined Sep 2001, 848 posts, RR: 0
Reply 14, posted (8 years 3 months 4 weeks 9 hours ago) and read 9163 times:

Quoting MD-90 (Reply 13):
There are also similiar fins that help control stall behavior.

These are completely different; the belly skids serve no aerodynamic purpose, these examples you give as you state are for in-flight stability.



Resident TechOps Troll
User currently offlineHAWK21M From India, joined Jan 2001, 31667 posts, RR: 56
Reply 15, posted (8 years 3 months 3 weeks 4 days 3 hours ago) and read 9043 times:

Quoting MD-90 (Reply 13):
There are also similiar fins that help control stall behavior.

You are referring to Ventral fins.Those would be more aft.
This looks like a Keel beam skid.
regds
MEL



Think of the brighter side!
User currently offlineWeb From United States of America, joined Jun 2005, 427 posts, RR: 0
Reply 16, posted (8 years 3 months 3 weeks 2 days 20 hours ago) and read 8990 times:

Thanks all for your insight. Now for another ERJ question: What are the yellow 'rakes' on the wings for?

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User currently offlineEMBQA From United States of America, joined Oct 2003, 9364 posts, RR: 11
Reply 17, posted (8 years 3 months 3 weeks 2 days 19 hours ago) and read 8985 times:

[quote=Web,reply=16]What are the yellow 'rakes' on the wings for?

For smacking your head into and causing intense pain and bad words to come out of your mouth..

They help direct the airflow over the aileron.



"It's not the size of the dog in the fight, but the size of the fight in the dog"
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17015 posts, RR: 67
Reply 18, posted (8 years 3 months 3 weeks 2 days 18 hours ago) and read 8969 times:

Quoting Web (Reply 16):
What are the yellow 'rakes' on the wings for?

They are called vortilons and direct airflow as EMBQA says. The color is purely there to warn rampers. Apparently they're pretty sharp.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineMD-90 From United States of America, joined Jan 2000, 8506 posts, RR: 12
Reply 19, posted (8 years 3 months 3 weeks 1 day 9 hours ago) and read 8822 times:

They help maintain airflow during a stall.

Some planes absolutely have to have them, like the Berkut:

http://www.berkut13.com/inflt01.jpg


User currently offlineKBGRbillT From United States of America, joined Sep 2004, 155 posts, RR: 0
Reply 20, posted (8 years 3 months 2 weeks 2 days 19 hours ago) and read 8580 times:

Quoting HAWK21M (Reply 15):
You are referring to Ventral fins.Those would be more aft.

Also known as strakes.


User currently offlineMD-90 From United States of America, joined Jan 2000, 8506 posts, RR: 12
Reply 21, posted (4 years 3 months 3 weeks 2 days 21 hours ago) and read 6373 times:

Since we're resurrecting old threads this week...wow that was quite embarrassing to completely misunderstand the question.

User currently offlineA342 From Germany, joined Jul 2005, 4681 posts, RR: 3
Reply 22, posted (4 years 3 months 3 weeks 2 days 17 hours ago) and read 6281 times:

I would have guessed that those fins under the tail help to maintain directional stability in case of an engine-out situation during takeoff (remember, the XR has substantially more powerful engines than the standard version).


Exceptions confirm the rule.
User currently offlineflybaurLAX From United States of America, joined Oct 2008, 638 posts, RR: 0
Reply 23, posted (4 years 3 months 3 weeks 2 days 9 hours ago) and read 6074 times:

Quoting A342 (Reply 22):
I would have guessed that those fins under the tail help to maintain directional stability in case of an engine-out situation during takeoff (remember, the XR has substantially more powerful engines than the standard version).

I would think that it's too small to affect the stability in an engine out situation. It's also placed relatively close to the engines, and being so small I just can't see that really being of any help.



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