Tg 747-300 From Norway, joined Nov 1999, 1318 posts, RR: 0 Posted (6 years 10 months 2 days 11 hours ago) and read 12600 times:
Hi,
Just been reading about aircraft stability, and the reasons for using dorsal and ventral fins. They are installed to increase directional stability at high sideslip angles.
That makes me wondering. What desides if you instal only a dorsal, only ventral or both.
AFIK most commercial airliners uses the dorsal fin only, while some smaller jets like the Lear-jet etc. also uses the ventral fin.
Is the ventral fin installed when the regular fin and dorsal fin is not enough to produce the required stability? Is there airplanes with ventral fins but without dorsal fins?
Also, the 731,732 does not have a dorsal fin, but all other 737's do. Why is that. Did the original 737 have some other stabilizing means that couldn't be carried over to the classics and NG's?
To me it looks like the 737-300 has some kind of a dorsal fin while the -200 don't. or is it just that the -300 has a biger or more noticable dorsal fin with a more "square" look. ?
3DPlanes From United States of America, joined Apr 2006, 167 posts, RR: 0 Reply 3, posted (6 years 10 months 2 days 9 hours ago) and read 12579 times:
Not to be pedantic, but I'm curious what differentiates between a dorsal fin and a vertical stabilizer? Is it the rudder? If a dorsal fin had a rudder, would it be called a vstab instead?
A ventral fin is easy to see and define. But what makes a dorsal fin a fin? If a plane (like the A-4) always had a "leading edge extension" on the vstab, was it called a dorsal fin? Or does the name only apply to add-ons after the fact, like on the 737?
Quoting Starlionblue (Reply 1): On the A-4, they added ventral fins after a few pilots took a swim.
Did you mean A-4? As in Skyhawk? I never seen an A-4 that had a ventral fin. The only USN planes with ventral fins that I can think of (off the top of my head) would be the F-8 and the F-14.
AeroWeanie From United States of America, joined Dec 2004, 1600 posts, RR: 52 Reply 4, posted (6 years 10 months 2 days 8 hours ago) and read 12579 times:
Dorsal fins are typically added to prevent "rudder lock". Rudder lock is a decrease in the rudder hinge moment that can happen at large yaw angles. This was first brought to light by the crash of a Boeing 307 on a demo flight on March 18, 1939. The aircraft had one engine shut down to demonstrate engine-out characteristics. Full rudder was applied to counter the yawing moment. The rudder locked over at full deflection and couldn't be centered. This caused the airplane to go into spin and crash.
Ventral fins are added for added directional stability and/or to reduce the drag of an upswept rear fuselage. Dual ventral fins were added to these Hawkers to counteract the destabilizing effect of the forward canoe:
Raisbeck offers a dual aft body strake kit for the Beech King Air. This both improves directional stability and reduces drag. It is required on King Airs that carry the CATPASS pod, due to its destabilizing effect (second picture):
DH106 From United Kingdom, joined Jun 2005, 621 posts, RR: 1 Reply 5, posted (6 years 10 months 2 days 7 hours ago) and read 12554 times:
Ventral fins are also sometimes added to improve spin recovery characteristics where the tailplane may 'mask' the fin and rudder with upwards moving air from the tailplane, reducing the efficiency of the fin/rudder. The ventral position is below the tailplane and thus in this scenario is in 'clean' air.
...I watched c-beams glitter in the dark near the Tanhauser Gate....
Starlionblue From Hong Kong, joined Feb 2004, 15870 posts, RR: 66 Reply 6, posted (6 years 10 months 2 days 1 hour ago) and read 12523 times:
Quoting Tg 747-300 (Reply 2): To me it looks like the 737-300 has some kind of a dorsal fin while the -200 don't. or is it just that the -300 has a biger or more noticable dorsal fin with a more "square" look. ?
The thing you show in the pic is a fin, AKA vertical stabilizer. The little extension at the front of the 733 fin simply extends the shape.
Quoting Tg 747-300 (Reply 2):
Quoting Starlionblue (Reply 1):
On the A-4, they added ventral fins after a few pilots took a swim.
Did you mean A-4? As in Skyhawk? I never seen an A-4 that had a ventral fin. The only USN planes with ventral fins that I can think of (off the top of my head) would be the F-8 and the F-14.
Brainfart. I meant the F-8 Crusader.
"There are no stupid questions, but there are a lot of inquisitive idiots." - from Citadel by John Ringo
Tg 747-300 From Norway, joined Nov 1999, 1318 posts, RR: 0 Reply 7, posted (6 years 10 months 2 days ago) and read 12519 times:
Quoting Starlionblue (Reply 6): The thing you show in the pic is a fin, AKA vertical stabilizer. The little extension at the front of the 733 fin simply extends the shape.
That was suprising, always been under the impression that the extension on the -300 was a dorsal fin.
Then could somebody please point out in a picture what a dorsal fin looks like?
Starlionblue From Hong Kong, joined Feb 2004, 15870 posts, RR: 66 Reply 8, posted (6 years 10 months 2 days ago) and read 12523 times:
Quoting Tg 747-300 (Reply 7): Quoting Starlionblue (Reply 6):
The thing you show in the pic is a fin, AKA vertical stabilizer. The little extension at the front of the 733 fin simply extends the shape.
That was suprising, always been under the impression that the extension on the -300 was a dorsal fin.
Then could somebody please point out in a picture what a dorsal fin looks like?
Oh dear. "Dorsal" means "on the back". So any fin on the top of the plane is a dorsal fin.
The thing you are referring to (front extension to the fin) is part of the dorsal fin (AKA vertical stabilizer) and has to do with stability. My guess is that since the 737Classics have more powerful engines than the 737Jurassics they need more lateral stability for engine out situations. Thus the enlarged fin.
"There are no stupid questions, but there are a lot of inquisitive idiots." - from Citadel by John Ringo
Tg 747-300 From Norway, joined Nov 1999, 1318 posts, RR: 0 Reply 9, posted (6 years 10 months 2 days ago) and read 12511 times:
Quoting Starlionblue (Reply 8): Oh dear. "Dorsal" means "on the back". So any fin on the top of the plane is a dorsal fin
Seems like I've learning something new all the time (which is great )
I looked up in my JAA "Principles of Flight". They describe and highlight the dorsal fin as an area similar to what i was refering to on the -300. So I guess thats where I got my ideea from. "The dorsal fin is located in front of the main fin, while the ventral is located below."
Jetlagged From United Kingdom, joined Jan 2005, 2452 posts, RR: 17 Reply 10, posted (6 years 10 months 1 day 23 hours ago) and read 12502 times:
The 737 Classic has increased side area ahead of the aerodynamic centre due to the CFM56 engines, hence the need to increase the fin area for directional stability. The 737 Classic had a slightly longer tail arm than the 737 Original, which also helps directional stability.
Directional control in the event of an engine failure comes primarily from the rudder, although the increased fin area will help too.
The 737 type of fin extension used to be known as a fin fillet in the good old days.
Sometimes ventral fins are added at the insistence of the certifying authority, as happened in the case of the 707 and the UK CAA, as I recall.
I had wondered about those Learjet fins. Nice to know the reason they are fitted.
The glass isn't half empty, or half full, it's twice as big as it needs to be.
Starlionblue From Hong Kong, joined Feb 2004, 15870 posts, RR: 66 Reply 11, posted (6 years 10 months 1 day 22 hours ago) and read 12494 times:
Quoting Tg 747-300 (Reply 9): I looked up in my JAA "Principles of Flight". They describe and highlight the dorsal fin as an area similar to what i was refering to on the -300. So I guess thats where I got my ideea from. "The dorsal fin is located in front of the main fin, while the ventral is located below."
I see the confusion. The JAA's definition of fin is pretty arbitrary, not to mention flawed, in my humble opinion. But who am I to argue?
"There are no stupid questions, but there are a lot of inquisitive idiots." - from Citadel by John Ringo
474218 From United States of America, joined Oct 2005, 6340 posts, RR: 10 Reply 12, posted (6 years 10 months 1 day 22 hours ago) and read 12491 times:
Quoting Starlionblue (Reply 8): Oh dear. "Dorsal" means "on the back". So any fin on the top of the plane is a dorsal fin.
The actual name for fin on top of and aircraft is the "VERTICAL STABILIZER". A dorsal fin can be described as a fairing that extends the vertical stabilizer further forward on the fuselage. A couple of reasons for adding a dorsal fin could be added to increase stability or reduce buffeting. The following site shows a dorsal fin added to a Piper Cherokee, just forward of the vertical stabilizer. http://www.planetools.com/NEWIACdorsalfin.htm
Starlionblue From Hong Kong, joined Feb 2004, 15870 posts, RR: 66 Reply 13, posted (6 years 10 months 1 day 21 hours ago) and read 12480 times:
Quoting 474218 (Reply 12): Quoting Starlionblue (Reply 8):
Oh dear. "Dorsal" means "on the back". So any fin on the top of the plane is a dorsal fin.
The actual name for fin on top of and aircraft is the "VERTICAL STABILIZER". A dorsal fin can be described as a fairing that extends the vertical stabilizer further forward on the fuselage. A couple of reasons for adding a dorsal fin could be added to increase stability or reduce buffeting. The following site shows a dorsal fin added to a Piper Cherokee, just forward of the vertical stabilizer. http://www.planetools.com/NEWIACdors...n.htm
It's all semantics. Plenty of sources call the vertical stabilizer "fin".
But I would agree that many manufacturers will call it "dorsal fin". That's fine, as long as everyone is clear on what we are talking about. Which obviously is not the case.
"There are no stupid questions, but there are a lot of inquisitive idiots." - from Citadel by John Ringo
Jetlagged From United Kingdom, joined Jan 2005, 2452 posts, RR: 17 Reply 15, posted (6 years 10 months 1 day 21 hours ago) and read 12474 times:
Quoting 474218 (Reply 12): The actual name for fin on top of and aircraft is the "VERTICAL STABILIZER"
Only if you are an American. In the UK, for example, it's traditionally known simply as the fin. All other types of fin need some qualifying adjective, like ventral.
We also still have things called tailplanes too. None of this horizontal stabiliser nonsense.
Not sure when this style of redundant verbage started, but I'd guess NASA had something to do with it. EVA for a "space-walk" is bad enough, until you remember it stands for "extra-vehicular activity".
Anyway, if you want to use these long words for precision, it should really be a directional stabiliser, not a vertical stabiliser.
The glass isn't half empty, or half full, it's twice as big as it needs to be.
Miamiair From , joined Dec 1969, posts, RR: Reply 16, posted (6 years 10 months 1 day 21 hours ago) and read 12470 times:
Quoting Tg 747-300 (Reply 2): To me it looks like the 737-300 has some kind of a dorsal fin while the -200 don't. or is it just that the -300 has a biger or more noticable dorsal fin with a more "square" look. ?
It may be semantics, but you are correct. The extension to the 737-300/-400/-500 vertical stabilizer is a dorsal fin.
The 707-100 did have a ventral fin; was not required on the -300.
Starlionblue From Hong Kong, joined Feb 2004, 15870 posts, RR: 66 Reply 17, posted (6 years 10 months 1 day 21 hours ago) and read 12467 times:
Quoting Jetlagged (Reply 15): Anyway, if you want to use these long words for precision, it should really be a directional stabiliser, not a vertical stabiliser.
Isn't the horizontal one also directional?
"There are no stupid questions, but there are a lot of inquisitive idiots." - from Citadel by John Ringo
DH106 From United Kingdom, joined Jun 2005, 621 posts, RR: 1 Reply 18, posted (6 years 10 months 1 day 20 hours ago) and read 12462 times:
Quoting Miamiair (Reply 16): The 707-100 did have a ventral fin; was not required on the -300.
All -400 series (Conway powered) have a the larger sized ventral fin, and -100/720 aircraft have a smaller fin. I think some -300s do have the smaller fin also. Perhaps it was fitted if the certifying authority of the country of the original buyer required it.
...I watched c-beams glitter in the dark near the Tanhauser Gate....
DH106 From United Kingdom, joined Jun 2005, 621 posts, RR: 1 Reply 19, posted (6 years 10 months 1 day 14 hours ago) and read 12423 times:
Quoting DH106 (Reply 18): All -400 series (Conway powered) have a the larger sized ventral fin, and -100/720 aircraft have a smaller fin. I think some -300s do have the smaller fin also. Perhaps it was fitted if the certifying authority of the country of the original buyer required it.
Having said the above, all the series '-300s' I can find pictures of on A.Net with a ventral fin seem to be -400 series masquerading as -300's
Serial nos: 17607,17608,17626,17682,17930,18084 - they're all labelled as -3xx series, but clearly have the -400 type trailing nose gear door, what look like Conway engines and the said ventral fin. What say our experts?
...I watched c-beams glitter in the dark near the Tanhauser Gate....
Texfly101 From United States of America, joined Jan 2006, 351 posts, RR: 0 Reply 23, posted (6 years 10 months 15 hours ago) and read 12325 times:
Probably one of the most interesting of the dorsal and ventral control surface investigations, particularly at high angles of attack and high mach, where the effects become very apparent as to directional control and stability, is the 1950's NASA X-15 research project. The aircraft had a removable ventral fin that was investigated for on and off, and measured control stability transients in its regime of flight. For anyone who is interested, Jay Miller's book, "The X-Planes" (Aerofax) is a good read regarding this as is Jenkins "Hypersonic! The Story of the North American X-15".
Just to add in other examples of ventral fins, look at the F-16, F-104, and B707. usually, any airplane that has rudder blanking at high AOA will have a ventral fin for added stability. Add in fuselage area or stores area ahead of the COP and you usually need added longitudinal control surfaces behind the COP. A lot of times, this area is designed in the beginning as every designer knows how airplanes get bigger with time.
Starlionblue From Hong Kong, joined Feb 2004, 15870 posts, RR: 66 Reply 24, posted (6 years 10 months 13 hours ago) and read 12303 times:
Quoting Texfly101 (Reply 23): usually, any airplane that has rudder blanking at high AOA will have a ventral fin for added stability.
Chuck Yeager would have had an easier time if rudder blanking had been better known in 1974.
"There are no stupid questions, but there are a lot of inquisitive idiots." - from Citadel by John Ringo
25 Lehpron: The words 'dorsal' and 'ventral' come from aquatic animals, dorsal fins on top and ventrals below. Sharks, fish, whales, etc all have them. No, when
26 Texfly101: I think you might be referring to his flight in 1963 in the NF-104. That flight was in a specially configured, rocket assisted F-104 that was set up
27 Starlionblue: Of course I meant 1947. Oops. Texfly101, I am referring to the X-1. They had to trim the tailplane since the elevator was completely blanked at high
28 Jetlagged: Strictly speaking it should be the longitudinal stabiliser. As in longitudinal and directional stability. I still prefer tailplane. Only because your
29 BoeingOnFinal: Described above, ventral fins are added to reduse drag of a non sweep fuselage. What is the difference between a sweep (swept?) and non sweep fuselage
30 HAWK21M: What Makes you think I was talking BOEING. regds MEL
31 IFIXCF6: You people would have fun with "cockpit" vs. "flightdeck" I'm reminded of a book of engineering that a friend found at a garage sale. It was written i
33 Jetlagged: Me too, but that's an odd ball as French terms like aileron and longeron must have been pretty well established by 1922. "Vessel" sounds quaint, but
34 Areopagus: The first prototype XP-56 Black Bullet, depending on what you make of the dorsal spine. http://www.wpafb.af.mil/museum/research/p56.htm Exactly so. I
35 OldAeroGuy: The 707 series ventral fins were there as ground over-rotation protectors to prevent the type of takeoff rotation stall that caused a Comet accident.
36 Jetlagged: That may be true, but you can be sure that the ventral fin area was part of the directional stability calculations.[Edited 2006-08-02 21:35:08]
37 OldAeroGuy: You have to determine what the directional stability is based on the airplane configuration, but the ventral fin was not required for the 707's to ha
38 DH106: So - are you saying that the fin was required for British certification? If so - why don't the -300's on the British register have them?
39 OldAeroGuy: No, a safe airplane has no national boundaries. Minimum unstick speed is a requirement for all Cert agencies.
40 DH106: Granted, and nice cliché - but why then wasn't the fin fitted to ALL 707's?
41 HAWK21M: Whats the Seating Capacity of the A380 to warrant that name. regds MEL
42 Jetlagged: It's called "the bridge" on a ship regardless of the ship's size, so long as the structure spans the ship (hence the name of course). If not it's usua
43 Lehpron: Which is why we see many russian airliners for domestic flights within the USA.
44 Starlionblue: Good one. Still, it is more a perception and operational cost issue than a safety issue.
45 Ptrjong: Quoting sir Winston Churchill: The short words are the best, and the old words best of all. Peter
46 Chimborazo: Yep. In the "Building the Biggest" doc on the A-380 the uber-camp guy (who is prettly funny) in charge of the the big thing sticking out of the top o
47 Viscount724: In case others haven't noticed, Reply 46 reactivated a 6-year-old thread. Just a suggestion, but when a years-old thread is reactivated, it would be h
48 Jetlagged: The weird and wonderful A.net search function. It doesn't sort the posts it finds by date so you can easily dig up a very old thread and reply to it
49 LH707330: The -300 and the -400 are pretty much identical except for the engines. The trailing door was changed sometime in 1963/4 IIRC for all models. Most of
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In the UK, for example, it's traditionally known simply as the fin. All other types of fin need some qualifying adjective, like ventral.
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