duke
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How Similar Are The 707 And The 720?

Sun Aug 06, 2006 2:28 am

The Boeing 720, which was produced from 1959 to 1967 (more or less) in 154 examples, was going to be called the 707-020 (or -000), but the name was changed, it is said because United Airlines didn't like it. It was almost the same length as the 707-100 short body (Qantas' -138), but had modifications to the wings, lower fuel capacity, and apparently other changes in gross weight. That is about all I know about what was different (later, the 720s wing changes, or some of them, I don't know exactly, were incorporated into the 707-100B).

What I am really interested in is, if you compare all the physical changes that were made to the 707-100 to produce the 707-300 with all the changes to the 707 to produce the 720, which would be physically more similar, the 707-100 and the 720 or the 707-100 and the 707-300? I don't mean externally only, I mean inside parts and materials as well. I get the feeling that, at the extreme, a 707-138B and a 720B would be very, very similar physically. Or am I wrong?
 
TheCheese
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RE: How Similar Are The 707 And The 720?

Sun Aug 06, 2006 4:01 am

The 707-100 series is more like the 720 than it is the 707-300/400 series.

The 720 is basically a 707-100 with a "wing glove" added to the leading edge of the section of the wing inboard of the engines closest to the fuselage (to increase low-speed performance) and smaller overwing fuel tanks for decreased range, and I believe a shorter fuselage than all but the Qantas 707-100s (Qantas got the shortest-bodied 707s, to maximize their range on trans-Pacific routes).

Later 707s (the 300s and RR powered 400s) had a much longer fuselage, and a completely redesigned wing.

720 was designed to compete with the Convair 880, which United was strongly considering over the other short/midrange 1st generation jets. In fact, United and Convair had agreed to 18 of 19 selling points in their sales contract, when Boeing offered United the 720.

Much to Convair's consternation, United went with the Boeing product.
 
CV990
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RE: How Similar Are The 707 And The 720?

Sun Aug 06, 2006 6:22 am

Hi!

The 707-100 and 200 versions had exactely the same lenght, the only difference was the fact that the 200 version used the 300 P&W engines! The 720 was smaller than the 707-100/200 and was LONGER then the 707-138!!! So resuming we have:

707-100/200 - 144 feet and 6 inches
720 - 136 feet and 2 inches
707-138 - 134 feet and 6 inches

Regards
CV990, the Maserati of the skies!
 
fanofjets
Posts: 1977
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RE: How Similar Are The 707 And The 720?

Sun Aug 06, 2006 2:27 pm

I also heard that the 720 used lighter-weight structural components than those found on the 707 family. There were more differences between the aircraft than met the eye.

On the outside, the easiest way of distinguishing between the two types is that most (there were a few exceptions) Boeing 720s had one overwing emergency exit on each side, whereas the 707 family passenger jets had two.
The aeroplane has unveiled for us the true face of the earth. -Antoine de Saint-Exupery
 
citationjet
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RE: How Similar Are The 707 And The 720?

Mon Aug 07, 2006 12:37 am

Boeing Flown: 701,702,703;717;720;721,722;731,732,733,734,735,737,738,739;741,742,743,744,747SP;752,753;762,763;772,773.
 
justplanesmart
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RE: How Similar Are The 707 And The 720?

Tue Aug 08, 2006 9:38 pm

"So many planes; so little time..."
 
isitsafenow
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RE: How Similar Are The 707 And The 720?

Tue Aug 08, 2006 9:45 pm

To tell the dif at a quick view, the 720 had one exit window over the wing vs. two with the 707. The Eastern 720 was the lone exception. Eastern had their 720's delivered with two exit windows over the wing because Eastern planned to use the 720 as an all coach airplane. It never did and went with two classes like most of their other aircraft.
NW did use their 720B's in one class after utilizing two classes after delivery.
The all coach was 116 pax....I know, I was there.
safe
If two people agree on EVERYTHING, then one isn't necessary.
 
CF-CPI
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RE: How Similar Are The 707 And The 720?

Tue Aug 08, 2006 11:15 pm

Quoting Isitsafenow (Reply 6):
NW did use their 720B's in one class after utilizing two classes after delivery.
The all coach was 116 pax....I know, I was there.

I understand it was 5 across throughout the aircraft, which would make it a 1-class economy plus of sorts. They used 'warm and welcoming reds and golds'.
Does anyone have a pic?
 
411A
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RE: How Similar Are The 707 And The 720?

Wed Aug 09, 2006 10:43 am

As far as aircraft systems are concerned, the differences are....

Electrical....none.
Hydraulics....none.
Pneumatics...none.
Except some 707's have high pressure air bottle(s) for engine starting where no ground pneumatics are available.

Pressurisation.
Most all 720's have only 2 turbocompressors, whereas most all 707's have three.
A few 707's have four.

Air Conditioning.
2 packs on both.
However, most 707's have air cycle machines (2), however some have freon systems, both old and newer versions.
Freon systems have no alternate bleed air selection for pressurisation.

Yaw damper.
Earlier airplanes have parellel system yaw dampers, later airplanes have the series type.
Some have been converted from parallel to series, at customer request.

Flight controls.
Same.

Fuel.
720's have no provision for center tank fuel, nor reserve outboard tanks.

Quite a mixed bag, depending on original customer specification and mod status later on.
 
duke
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RE: How Similar Are The 707 And The 720?

Wed Aug 09, 2006 5:16 pm

Good info guys, so what were the "lower weight structural components"?
 
justplanesmart
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Joined: Thu Mar 15, 2001 3:25 pm

RE: How Similar Are The 707 And The 720?

Wed Aug 09, 2006 9:26 pm

Quoting Isitsafenow (Reply 6):
To tell the dif at a quick view, the 720 had one exit window over the wing vs. two with the 707. The Eastern 720 was the lone exception.

I used to think that was the case, and in terms of production configurations it was. However, several 720-051B aircraft were modified to have two overwing exits after Northwest sold them. These photos show the same airframe with Olympic Airlines both before and after the additional exits were installed:


View Large View Medium
Click here for bigger photo!

Photo © Howard Chaloner
View Large View Medium
Click here for bigger photo!

Photo © Marcel Walther

"So many planes; so little time..."
 
DH106
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RE: How Similar Are The 707 And The 720?

Wed Aug 09, 2006 9:47 pm

One question I've always wondered about and not answered by a quick scan of the above links was why the change in nose gear door design when the -300 was produced from the earlier -100/-200 series, and yet the -400 which was essentially a RR Conway powered -300 but reverted to the earlier single trailing door rather than the -300's small door each side.
Anyone any insight?
...I watched c-beams glitter in the dark near the Tanhauser Gate....
 
N231YE
Posts: 2620
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RE: How Similar Are The 707 And The 720?

Thu Aug 10, 2006 9:01 am

One thing not mentioned; the 727 was the replacement for the 720. Like the 720, the 727 was used for shorter range-high performance applications. But unlike the 720, the 727 was designed to cut deep into "propeller territory;" the smaller airports that could not receive jetliners such as the 707, DC-8, or the 720 of this matter.

The 727 was originally going to have 4 engines, like United wanted, but Eastern, wanted a more economical 2 engine setup, so Boeing compromised with 3 engines on the 727.
 
iRISH251
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RE: How Similar Are The 707 And The 720?

Fri Aug 11, 2006 9:39 pm

DH106

The spade-type nosegear door also featured on some early 707-320B/320C but was superseded by the later version with two side-opening doors which remained open with the gear extended. This design was also used on later production "short" 707s but not on any 720s, as far as I know. The -420 series, despite the high model number, was produced fairly early in the 707's life and that's why it featured the early door design.
 
DH106
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RE: How Similar Are The 707 And The 720?

Sat Aug 12, 2006 12:13 am

Quoting Irish251 (Reply 13):
The spade-type nosegear door also featured on some early 707-320B/320C but was superseded by the later version with two side-opening doors which remained open with the gear extended. This design was also used on later production "short" 707s but not on any 720s, as far as I know. The -420 series, despite the high model number, was produced fairly early in the 707's life and that's why it featured the early door design.

Good info - thanks.

I've never seen a -300 with the spade type door, but having said that I made a point on another thread recently about -300s/-400s versions - in that some 707s nominally being referred to as -300s seem in fact to be -400s in disguise Big grin !!
What I mean by this is that even though they are referred to as -300s, they have the spade type nose gear door, a large under-tail ventral fin and engines that look like Conways with all FOUR engines having a compressor above them (not 3 as the -300s have). All features of the -400 series.

Checkout these for examples:
http://www.airliners.net/open.file/1093104/L/
http://www.airliners.net/open.file/1093097/L/
http://www.airliners.net/open.file/1071985/L/
http://www.airliners.net/open.file/1052918/L/
...I watched c-beams glitter in the dark near the Tanhauser Gate....
 
duke
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RE: How Similar Are The 707 And The 720?

Sat Aug 12, 2006 1:27 am

Since the discussion has moved onto these external details, I will contribute what I know about one 707 technical detail. It's something that's practically unique to the plane among commercial airliners, the horizontal monopole antenna sticking out from the tail tip. It seems to have been a standard feature on all 707/720 and KC-135s (and the 367-80 prototype which originally didn't have it, was fitted with it early on) with the following notable exceptions:

-The 720 was originally delivered without it, as it was considered not to be needed on domestic routes. Then some airlines asked for it and became standard. I think the 29 United Airlines 720s and American's first batch of 10 720s (all the turbojet ones, later converted to B standard with turbofans) were the ones, and the only ones, so delivered. Interestingly, however, American later sold some of these 720s and switched their tails with the tails of 707s (all -100s?) because the airlines buying them wanted the antenna. So, some American 707s ended up without the monopole.

-TWA's first turbojet 707-100s had the monopole. But all the airline's turbofan -100Bs were delivered without it EXCEPT ONE. Why this was so is still a mystery to me.
 
DH106
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RE: How Similar Are The 707 And The 720?

Sat Aug 12, 2006 2:23 am

Quoting Duke (Reply 15):
-TWA's first turbojet 707-100s had the monopole. But all the airline's turbofan -100Bs were delivered without it EXCEPT ONE. Why this was so is still a mystery to me.

Checking through the database looking into Duke's point, it's also obvious there's a mix of nose gear door types on the fan -131B's . Some have the rear single door like the earlier turbojets, some have the later twin side doors.
...I watched c-beams glitter in the dark near the Tanhauser Gate....
 
DH106
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RE: How Similar Are The 707 And The 720?

Sat Aug 12, 2006 2:35 am

Quoting DH106 (Reply 14):
What I mean by this is that even though they are referred to as -300s, they have the spade type nose gear door, a large under-tail ventral fin and engines that look like Conways with all FOUR engines having a compressor above them (not 3 as the -300s have). All features of the -400 series.

Answering my own question here - but I think the -300 I mention above are early turboJET JT3 powered -300s, not Conway -400s (but the engines are very difficult to tell apart).
...I watched c-beams glitter in the dark near the Tanhauser Gate....
 
113312
Posts: 580
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RE: How Similar Are The 707 And The 720?

Sat Aug 12, 2006 3:16 pm

Some of the above info was incorrect. All B720 aircraft, both fan and non-fan versions, had 2 turbocompressors. Most B707s, 120-320 series had 3 turbocompressors but some, notably -123, -123B, and 323B/C had 2 turbocompressors.

Many people, looking at pictures of tubojet powered 707-120, 220, 320 and 420 think that these have 4 but that simply isn't true. Although all of the pylons look the same, turbocompressors are only installed in 3!

EMC
 
411A
Posts: 1788
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RE: How Similar Are The 707 And The 720?

Sun Aug 13, 2006 10:23 am

Wrong.

The former Presidental aircraft had 4 turbo-compressors.
In addition, many of those 707's with 2 mentioned, were later converted by other operators to 3.

'Tis a fact.

Original build many times means nothing, where 707's are concerned.
MANY mods carried out later on.
 
iRISH251
Posts: 620
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RE: How Similar Are The 707 And The 720?

Mon Aug 14, 2006 6:42 am

Here are some 707s with JT-3B turbofans and the early nosewheel door arrangement.


View Large View Medium
Click here for bigger photo!

Photo © Pedro Aragão



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Photo © Bob Garrard



View Large View Medium
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Photo © Eduard Marmet

 
411A
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RE: How Similar Are The 707 And The 720?

Mon Aug 14, 2006 9:48 am

Generally speaking (there are some exceptions, but only a few, IIRC) when the later -320B advanced models were introduced, these were fitted with fillet flaps and the later style nose gear doors.
A design improvement, as were the fillet flaps and indeed the larger fan inlet bypass doors.
However, there are some -320B models with the small inlet doors, yet had fillet flaps.
Quite a mixed bag, depending on original customer option.
 
2H4
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RE: How Similar Are The 707 And The 720?

Mon Aug 14, 2006 11:06 am




Quoting 411A (Reply 21):
Quite a mixed bag, depending on original customer option.

Would you say the airliners back then were more "custom-built" to the specifications of individual airlines than modern airliners? It sure seems to be the case.




2H4


Intentionally Left Blank
 
411A
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RE: How Similar Are The 707 And The 720?

Mon Aug 14, 2006 11:53 am

No, not especially custom built, 2H4.
The original 707 was a basic design in many ways, and as engines improved, the body lengthened, weights increased, changes had to be made to the design, to accept these changes demanded by the various airlines.
In addition, the British (D.P. Davies in particular as he was head of the ARB certification office) insisted that the rudder power be increased, the artificial rudder feel improved, and various other changes for the aircraft to be accepted onto the British civil register, for BOAC.
All of these improvements were then incorporated into the basic design along the way.
Also, South Africian Airways, operating from JHB, required full span leading edge devices on their early 707's, to enable reasonable fuel weights to be uplifted, for their longer range flights from the higher altitude of JHB.
These changes as well were incorporated into the basic design of the -300 series airplane.

In short, customer requirements drove the design, and other operators benefited as a result.
 
ImperialEagle
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RE: How Similar Are The 707 And The 720?

Fri Aug 18, 2006 6:15 am

Quoting Fanofjets (Reply 3):
I also heard that the 720 used lighter-weight structural components than those found on the 707 family. There were more differences between the aircraft than met the eye

The whole structure of the 720 was of a different weight than the 707 series. Part of the reason you see hardly any left airworthy.

Quoting Isitsafenow (Reply 6):
NW did use their 720B's in one class

Correct. Called the "720B Special" with much fan fare (sales department hyperbole) towards the end of their career with NW.

720B was HOT,HOT,HOT. Flew on many of NW's. If you had the good fortune to be on board one with a light load, it was like the launch of a Space Shuttle" on take-off----awesome!
"If everything seems under control, you're just not going fast enough!"

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