Thrust From United States of America, joined Sep 2003, 2631 posts, RR: 17 Posted (6 years 10 months 2 weeks 2 days 21 hours ago) and read 2526 times:
This has puzzled me for some time now. I have noticed that the early turbojet 707-100s had the ventrical tail fins that are a distinguishing feature of the 707, but 707s that were built and delivered with turbofans did not have the tail fin. My question is why? 707-100 turbojets that were retrofitted with the turbofans retained the fin, but why did Boeing choose to remove it for 707s built with turbofans?
TripleDelta From Croatia, joined Jul 2004, 968 posts, RR: 8 Reply 1, posted (6 years 10 months 2 weeks 2 days 20 hours ago) and read 2491 times:
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If you're referring to the pointy antenna ontop the fin, as far as I know that was an HF antenna, for long-range comm equipment. Probably, by the time the turbofan version entered service, newer and more precise long-range comm and nav equipment was entering service and the old HF setup was not needed anymore. That would explain why the re-engined early versions retained the antenna.
Timz From United States of America, joined Sep 1999, 6181 posts, RR: 8 Reply 2, posted (6 years 10 months 2 weeks 2 days 19 hours ago) and read 2468 times:
Yeah, we can't figure out whether you're talking about the ventral fin (below the tail) or what. The later 707-320Bs and -320Cs had no ventral fin, but as I recall all the -120/120B/320/420s had them all their lives. Along with the early -320Bs.
N747PA From United States of America, joined Mar 2005, 50 posts, RR: 0 Reply 3, posted (6 years 10 months 2 weeks 2 days 18 hours ago) and read 2452 times:
Here's some good info on ventral fins in this guide (Reply #1)
Thrust From United States of America, joined Sep 2003, 2631 posts, RR: 17 Reply 4, posted (6 years 10 months 2 weeks 2 days 5 hours ago) and read 2380 times:
The HF antenna is what I refer to, people. I hope that clears it up.
HAWK21M From India, joined Jan 2001, 29818 posts, RR: 61 Reply 5, posted (6 years 10 months 2 weeks 2 days 5 hours ago) and read 2376 times:
Even on the B737s the Earlier "Wire" HF Antenna was later incorporated into the Vertical Stablizer LE.
I wonder why the B707 type was not used on the B737.
Any Reason.
regds
MEL
411A From United States of America, joined Nov 2001, 1826 posts, RR: 10 Reply 6, posted (6 years 10 months 2 weeks 1 day 21 hours ago) and read 2332 times:
And, someone mentioned the various sizes of ventral fins.
When the 707 basic airframe was stretched to the -300 length, there was a definite problem in three areas...rudder power scheduling, spiral stability, and yaw damper effectiveness.
The British Air Registration Board (now the UK CAA), and specifically, the head of the certification branch, D.P Davies told Boeing that, if these concerns were not delt with in a reasonable fashion, the aircraft would NOT be allowed on the British civil register, and as such, BOAC would not be able to operate the type.
All ARB concerns were addressed, and the improvements were incorporated in all 707 models.
NB. DP Davies went on to write a book (Handling the Big Jets) which sets out the many problems encountered in early generation swept wing civil jet
transport aircraft.
If you can find a copy (now out of print) it makes very interesting reading.
One simple answer about the lack of HF antenna. Those 720-022 were medium range aircrafts, and United used them on domestic routes only, so they didn't need the long range navigation equipment, as VOR were the most used navigation system over land in the US (correct me if I'm wrong here).
Note that this is not the case with some others 720s operators :
About the tail fin, it was indeed present on every 720s, and on 707s Model 120 to 320, some very early 320B and every Conways 420s. Powered rudders were added in the 320B and Cs series, with a bigger tail, eliminating the need of the fin to prevent 'Dutch Roll'.
You can see here 4 types of tails the 707 had in her life span.
The first one, introduced with the Model 120 in 1958. Note how much shorter it is.
The third one was introduced with the tail fin modification. This is a Conway Model 420, but the tail was similar on retrofitted -120s and -320s. Note how much taller the tail is.
And the most common one, found on almost every 320Bs and all 320Cs. With that tail, and some other refinements in controls and lateral stability, Boeing could get rid of the tail fin.
As you can see too, the fins were not the same size for all variants too. Short-body 707s and 720s had a shorter fin installed, Intercontinental Model 320s and 420s had the bigger one. I'm sure there is more variations than this, but the basics are here.
Hope it can clear up a bit the confusion about all those setups .
"For radar identification throw your jumpseat rider out the window."
411A From United States of America, joined Nov 2001, 1826 posts, RR: 10 Reply 9, posted (6 years 10 months 1 week 5 days 9 hours ago) and read 2175 times:
A slight bit of mis-information, MrFord, about early 707's.
Not only did the -320 series have a hydraulic powered rudder, (most) shorter -100 series did as well.
In fact, one of the early accidents with the 707 was an AA aircraft departing IDL, and experienced a rudder hardover, followed by a dive into Flushing Bay.
Further, there were only two variations of ventral fin used, the smaller 13 inch, and the larger 39 inch.
And yes, you are quite correct about the UAL 720's....used for US domestic service, with no long range (HF) comm or nav equipment.
When the British ARB objected to the handling charactistics of the -320's proposed for BOAC, all previous models had the rudder power scheduling modified by service bulletin, which made these earlier aircraft a bit easier (and safer) to fly.
I personally flew both the -100 series and the -300 series.
Heavy on the controls, as the ailerons/elevators only had balance panel (servo tab) assist.
C133 From United States of America, joined Jan 2005, 221 posts, RR: 0 Reply 10, posted (6 years 10 months 1 week 5 days 3 hours ago) and read 2148 times:
Not sure if the short tail airplanes had powered rudders, but it seems logical. Then, the taller versions originally had parallel yaw damper systems which caused some problems and had to be off for take-off and landing. These were replaced with dependable series type yaw dampers in the late sixties, still the industry standard today, I believe.
American's 720s were all built without the HF comm antenna, but all 123s had it. None had HF radios installed and were purely domestic airplanes. ('Domestic' including Mexico and Canada.)
[Edited 2005-04-08 17:33:33]
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C133 From United States of America, joined Jan 2005, 221 posts, RR: 0 Reply 11, posted (6 years 10 months 1 week 5 days 2 hours ago) and read 2145 times:
Timz From United States of America, joined Sep 1999, 6181 posts, RR: 8 Reply 12, posted (6 years 10 months 1 week 4 days 22 hours ago) and read 2126 times:
I just recently read (maybe here) about AA or somebody trading fins with another airline that needed the HF antenna. Maybe Cearley mentions it-- I'll check.
C133 From United States of America, joined Jan 2005, 221 posts, RR: 0 Reply 13, posted (6 years 10 months 1 week 4 days 19 hours ago) and read 2120 times:
Here's proof it could be changed from the factory configuration. Same airplane, 21 years difference in age:
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