Happy-flier
Topic Author
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Is The CV990 Still A Viable High-speed Design?

Tue Sep 11, 2007 5:39 am

I had a thought the other day about the rather unique airframe, but mainly wings (and shock bodies) of the Convair 990 and, given that this design is over 45 years old today and with advances in technology - especially materials - wanted to ask: If a 990 airframe were re-engined with fuel-efficient high-bypass engines, would be able to provide efficient high-speed cruise compared to jets of comparable size and weight flying today? I figure that the airframe might be a bit heavier than aircraft sharing its overall dimensions, if only because they weren't using composites back then . . . but what if an exact replica of a CV990 were built largely from composites - could those same kind of wings, shock bodies and all, offer any performance benefit today?
May the wind be always at your back . . . except during takeoff & landing.
 
boeing767mech
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RE: Is The CV990 Still A Viable High-speed Design?

Tue Sep 11, 2007 8:03 am

Interesting question. If you hung a set of JT8D-219's off the wing it probably still cruise at high speeds no problem, But if you hund a set of say CFM56's(which Convair was looking into dong on the 880) or a set of V2500's now you have to redesign the pylons and wing attach points. Also now having a bigger engine you have to take into consideration of will the airflow the same over the wings and will the shock bodies still do there work as designed and placed on the wing.

I wish had won the 330 mil for the lottery I would have bought CV990 SN2,24,and 29 and flown one until I ran out of money.

David
Never under-estimate the predictably of stupidty
 
Starglider
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RE: Is The CV990 Still A Viable High-speed Design?

Tue Sep 11, 2007 8:04 am

Quoting Happy-flier (Thread starter):
what if an exact replica of a CV990 were built largely from composites - could those same kind of wings, shock bodies and all, offer any performance benefit today?

Theoretically, yes. Practically, probably not as an exact replica because four high bypass engines would be overdone. An aircraft of this size with current high-bypass engines would most likely be a twin. If a twin, the wing would have to be modified because of altered wing bending moments due to the omission of the outboard engines and relocation (slightly more outboard) of the inboard engines.



Starglider
 
411A
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RE: Is The CV990 Still A Viable High-speed Design?

Tue Sep 11, 2007 12:01 pm

Close examination of the CV990 TCDS reveals rather severe speed penalties regarding the presence of fuel/no fuel in the anti-shock bodies.
The design was severely compromised because of this, and any type of re-engining would not address this issue to any significant degree.
The wing design used, altho of a rather high speed design, had severe drag problems without the very necessary anti-shock (or, as they were called at the time) 'speed' bodies.
In addition, the hydraulic system does not meet current standards for 14CFR25.
Nor, does the electrical system.
 
Dougloid
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RE: Is The CV990 Still A Viable High-speed Design?

Tue Sep 11, 2007 1:22 pm

Big version: Width: 738 Height: 516 File size: 63kb
If you believe in coincidence, you haven't looked close enough-Joe Leaphorn
 
DH106
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RE: Is The CV990 Still A Viable High-speed Design?

Tue Sep 11, 2007 2:53 pm

Quoting Boeing767mech (Reply 1):
I wish had won the 330 mil for the lottery I would have bought CV990 SN2,24,and 29 and flown one until I ran out of money

Absolutely  Smile
Glad you left SN 30 for me  Wink
...I watched c-beams glitter in the dark near the Tanhauser Gate....
 
411A
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RE: Is The CV990 Still A Viable High-speed Design?

Tue Sep 11, 2007 4:13 pm

Quoting Boeing767mech (Reply 1):
I wish had won the 330 mil for the lottery I would have bought CV990 SN2,24,and 29 and flown one until I ran out of money.

Although the Coronado was a delight to fly, at least according to a couple of Spantax Captains I spoke with years ago...the flying would have to be done outside of the USA, Europe, and many other places now, simply because it exceeds the noise specifications for a TOW in excess of 75,000 pounds.

By the way, both the 880 and 990 used the same sort of arrangement that the B707 did for control surface assist....balance panels.
A very clever design...the only shortcoming being the absolute necessity of being sure that the balance panel cavities were clear of ice and snow in the wintertime.
 
DH106
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RE: Is The CV990 Still A Viable High-speed Design?

Tue Sep 11, 2007 6:11 pm

Quoting 411A (Reply 6):
simply because it exceeds the noise specifications for a TOW in excess of 75,000 pounds.

Is that regulation for commercial operations only, or for ANY category of aircraft operation including private ?

How does John Travolta manage with his 707 - is it exempt from noise regulations because it is operated privately, or does it need exemptions to that rule to fly?
...I watched c-beams glitter in the dark near the Tanhauser Gate....
 
TheSonntag
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RE: Is The CV990 Still A Viable High-speed Design?

Tue Sep 11, 2007 6:34 pm

Quoting DH106 (Reply 7):
Is that regulation for commercial operations only, or for ANY category of aircraft operation including private ?

How does John Travolta manage with his 707 - is it exempt from noise regulations because it is operated privately, or does it need exemptions to that rule to fly?

Privately Owned Old Jets - Noise Limits? (by TheSonntag Sep 8 2007 in Tech Ops)

No real answer was given so far, though  Wink

I somewhat doubt that High bypass turbofans are able to work at the desired speed. Remember, the faster you go, the less efficient they get.
 
411A
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RE: Is The CV990 Still A Viable High-speed Design?

Tue Sep 11, 2007 8:18 pm

Quoting DH106 (Reply 7):
Is that regulation for commercial operations only, or for ANY category of aircraft operation including private ?

How does John Travolta manage with his 707 - is it exempt from noise regulations because it is operated privately, or does it need exemptions to that rule to fly?

As I indicated in another recent thread, the noise limitation as regards 75,000 pounds applies to all aircraft, commercial or private, except for military and government flights.

Also indicated in the same thread, is reference to JT's B707.
It IS equipped with stage three hushkits, built and installed (as I recall) by Burbank Aeromautical.

Sorry for the bad news for those of you that admire these older airplanes (and, there certainly was a lot to admire)...but them's the facts.
 
TheSonntag
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RE: Is The CV990 Still A Viable High-speed Design?

Tue Sep 11, 2007 9:22 pm

The only exemption existing is that for supersonic aircraft. Isn't the rule still in place that SSTs have to be operated so that noise emissions are as low as possible (=deafening)?
 
DH106
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RE: Is The CV990 Still A Viable High-speed Design?

Tue Sep 11, 2007 9:33 pm

So with regard to these regulations - how would you operate, for example, an old fighter jet type aircraft ?
There are several I believe on the UK register (Jet Provosts etc.).
...I watched c-beams glitter in the dark near the Tanhauser Gate....
 
SEPilot
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RE: Is The CV990 Still A Viable High-speed Design?

Tue Sep 11, 2007 10:33 pm

Quoting DH106 (Reply 11):
So with regard to these regulations - how would you operate, for example, an old fighter jet type aircraft ?

Do they exceed 75,000 pounds?
The problem with making things foolproof is that fools are so doggone ingenious...Dan Keebler
 
DH106
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RE: Is The CV990 Still A Viable High-speed Design?

Tue Sep 11, 2007 11:56 pm

Quoting SEPilot (Reply 12):
Do they exceed 75,000 pounds?

No - guess not. So you can make as much racket as you like with a aircraft sub-75K pounds?
...I watched c-beams glitter in the dark near the Tanhauser Gate....
 
Happy-flier
Topic Author
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RE: Is The CV990 Still A Viable High-speed Design?

Thu Sep 13, 2007 3:23 am

It might only help marginally with noise reduction, but I figure that they could probably make a 990 work with JT8D-209s, possibly de-rated - weren't the original GE's in the 16,000 lb thrust range? I'm sure they burned a lot of fuel to make that measley 16,000 lbs of thrust though! And the smoke ... man.
May the wind be always at your back . . . except during takeoff & landing.
 
Starglider
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RE: Is The CV990 Still A Viable High-speed Design?

Thu Sep 13, 2007 3:53 am

Quoting Happy-flier (Reply 14):
And the smoke ... man.

Yeah, i recall the 990 back in the 70s and early 80s. Those GE CJ805-23 engines had a very particular sound to them when near idle power. Mostly Spantax and Swissair operated them here. On a clear day you could easily spot them coming and going. You saw the black smoke from far away before you could see the aircraft itself approach. On quiet days, four streams of black smoke still hung over the approach path while the aircraft was already parking at the gate.

Starglider
 
timz
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RE: Is The CV990 Still A Viable High-speed Design?

Fri Sep 14, 2007 3:54 am

Quoting DH106 (Reply 13):
So you can make as much racket as you like with a aircraft sub-75K pounds?

Suspect not-- but the sound measurements are taken on the ground at specified distances from the runway, and sub-75K aircraft are probably high enough when they go over the sensors that they don't exceed the Stage III limits.

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