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Convair 880 Cruise Mach, VMO/MMO Question  
User currently offlineBlackbird From , joined Dec 1969, posts, RR:
Posted (7 years 5 months 1 hour ago) and read 10647 times:

Okay, I've been getting so much conflicting data regarding the Convair 880.

I checked the FAA, it says it's VMO is 373 kts and 393 above 21,500 feet about, MMO is .884.

However a website which is owned by a bunch of guys who actually want to keep a CV-880 from getting scrapped, and may be some of the most knowledgeable people on the aircraft alive (other than some pilots who are still alive), and my friend asked their historian and they said they often shot approaches at 400 kts before slowing down, additionally stating the gears (main-gear speedbrake) could be extended at such a high-speed. The Jon Proctor book about the CV-880 also said something similar about flying the downwind approach on the barber pole, and passing the outer marker (the start of Final Approach) at 250 kts and being able to make a normal landing. The Historian of the CV-880 site confirmed the same thing according to my friend who e-mailed him.

Some have said it's MMO was 0.91, and could sustain normal cruise speeds up to 0.87, which makes sense since it was said to be faster than other jet of the era. The Mach 0.884 figure however does not seem to make much sense, because the 707-120 had the same exact mmo, contrary to 411A (who claims to have been a pilot of a 707-320) statements, I checked the FAA website which confirmed the early figures I had for the 707, a MMO of .884 for the -120/-220, 0.887 for the -320, and 0.90 for the -120B/-320B/720B.

I am getting all sorts of conflicting data and all I'm looking for is precisely accurate information.

Andrea Kent

55 replies: All unread, showing first 25:
 
User currently offline411A From United States of America, joined Nov 2001, 1826 posts, RR: 8
Reply 1, posted (7 years 4 months 4 weeks 1 day 20 hours ago) and read 10612 times:

The Type Certificate Data Sheet tells all, I'm afraid, inspite of what others might think...spotters books or otherwise.

User currently offlineBlackbird From , joined Dec 1969, posts, RR:
Reply 2, posted (7 years 4 months 4 weeks 1 day 16 hours ago) and read 10584 times:

BTW, what is the .Mmo of the L-1011?

User currently offlineBoeingfixer From Canada, joined Jul 2005, 531 posts, RR: 0
Reply 3, posted (7 years 4 months 4 weeks 1 day 14 hours ago) and read 10578 times:

Quoting Blackbird (Reply 2):
BTW, what is the .Mmo of the L-1011?

According to the Type Certificate Data Sheet (TCDS), the Mmo for all L-1011 models is M=0.90.

Cheers,

John



Cheers, John YYC
User currently offlineG4LASRamper From United States of America, joined Dec 2006, 170 posts, RR: 0
Reply 4, posted (7 years 4 months 4 weeks 1 day 14 hours ago) and read 10573 times:

A friend of mine who flew as an F/O on the 880 for TWA said figuring the bug speed for the aircraft was easy. Whether by design or coincidence, all one had to do was take the landing weight and divide it by 1000, i.e. 150,000 lb landing weight meant a bug speed of 150 knots. Probably didn't get down to that speed until somewhere inside the outer though...  Smile


"A pig that doesn't fly is just a pig." - Porco Rosso
User currently offlineJetlagged From United Kingdom, joined Jan 2005, 2556 posts, RR: 24
Reply 5, posted (7 years 4 months 4 weeks 1 day 11 hours ago) and read 10549 times:

Even though the MMO for the CV-880 and the 707 might be very similar doesn't mean the max cruise speed are also the same. The advertised 600 mph (TAS) cruise speed (880 ft/sec) refers to altitudes around the 21-23,000 ft mark (M=0.86). At 35,000 ft the TAS would be lower for the same Mach No.

The FAA numbers look to be genuine enough. Memory plays tricks and on rare occasions pilots have been known to exaggerate.  Smile

High speed descents weren't unique to the CV-880, but led to accidents, hence the 250 below 10,000 ft limit.



The glass isn't half empty, or half full, it's twice as big as it needs to be.
User currently offlineBlackbird From , joined Dec 1969, posts, RR:
Reply 6, posted (7 years 4 months 4 weeks 19 hours ago) and read 10499 times:

.Mmo appears to be around Mach 0.884, just like the 707-120, but I'm wondering, did the CV-880 have a bad mach tuck problem like the 707 if it went past that point? Because the DC-8's .Mmo was 0.88, although I've been told it can physically fly at 0.95 (whether with or without the 4%-chord increase) even though it's fuel-burn rate would be absolutely obscene.

Regarding the plane's cruise mach number-- so Mach 0.86 is the likely capability: with a 393 IAS (the old speed gauge had a problem due to some kind of compression effect). The CV-880 was capable at flying up to 41,000 feet though. While I know some pilots exaggerate about some things, It just seems as if 400 kts seems to pop up a lot-- and that brings on another quesiton: Even though it is stated to be able to max out at 373 kias at sea-level, if it can do 393 kias at altitude (even if due to a compression effect), could it do 393 kias at lower altitude as well (after all wouldn't the 393 kt ram air at low altitude be the same as the 373 kt ram air at altitude with the compression effect making the speed gauge read 393 kts?)?

Was the plane able to exceed the listed performance specs? Or something like that?

Just curious,
Andrea Kent


User currently offlineJetlagged From United Kingdom, joined Jan 2005, 2556 posts, RR: 24
Reply 7, posted (7 years 4 months 4 weeks 8 hours ago) and read 10453 times:

It isn't unusual for VMO at sea level to be a little less than VMO at altitude. The dynamic pressure will be much the same for the same CAS, so at sea level at 373 knots it is somewhat less than at altitude at 393 knots.

I don't know what other criteria are used in determining VMO and MMO, or why VMO typically decreases with altitude.

MMO and VMO are operational limits, not to be confused with VMD/MMD and VNE/MNE, which may well be higher.

According to the FAA type certificate, the CV-880 Model 22 had a VNE of 398 knots. For the CV-880 Model 22M it is 399 knots. VNE appears to be unaffected by altitude. MNE = 0.884 (same as MMO) for both versions.

So an 880 could descend at 398 or 399 knots depending on version, without exceeding VNE, though it would be in excess of VMO.



The glass isn't half empty, or half full, it's twice as big as it needs to be.
User currently offlineBlackbird From , joined Dec 1969, posts, RR:
Reply 8, posted (7 years 4 months 4 weeks 7 hours ago) and read 10448 times:

Modern aircraft seem to take this compression effect into account more so than the older designs. Man, it's weird... it just seems as if the IAS readings seem to go up... do they ever go down at higher altitudes at all on these older speed-gauge?

You know, I was always under the impression that the CV-880M was drastically more underpowered than the CV-880. Actually their thrust to weight ratios are almost the same.

With that said, why didn't Delta and TWA convert their CV-880's? It would have given a lower takeoff and landing speed, more versatility in the seating layout.

Andrea Kent


User currently offline411A From United States of America, joined Nov 2001, 1826 posts, RR: 8
Reply 9, posted (7 years 4 months 4 weeks 6 hours ago) and read 10438 times:

What many younger folks are unaware of is the fact that these rather old jet airliner designs did not have especially accurate (by todays standards) air data computers.
Nearly all had the KIFIS system, Kollsman Intergrated Flight Instrument System, which provided, among other things, altitude, indicated airspeed, indicated mach number, vertical speed and indicated ram air temperature.
As such, and due mainly to compressability effects at higher IAS/mach numbers, the indications provided to the pilots was, to say the least, certainly not up to todays standards.
Therefore, it is not unusual to see rather wide variations with regard to indicated airspeeds/mach numbers versus aircraft altitude.
Even the faster piston engined airliners (DC-7, 1649 Constellations) had decreasing limiting operating airspeeds as altitudes increased for much the same reasons as stated above.


User currently offlineBlackbird From , joined Dec 1969, posts, RR:
Reply 10, posted (7 years 4 months 4 weeks 4 hours ago) and read 10422 times:

From what I've been reading, the Kollman-Drum showed a rise in speed up to the twenty thousand range, then began falling off at higher altitudes. The new air-speed indicators really do seem far more accurate when you compare the old and the new.

While not entirely related to the Convair 880, or 707-320... does anybody here know the 727's VNE (I know it's vmo is 390/350 depending on mode and depending on mode M = 0.88/0.90 .Mmo) is? Because I just read something really interesting on an old page at PPRUNE: ((in addition to being an excellent source of fiber...) A forum which stands for Professional Pilot's RUmor NEtwork -- The topic was in regards 727-100's .Vmo

LINK: http://www.pprune.org/forums/archive/index.php/t-99506.html

Despite the fact that the listed .Vmo for the 727-100 is 390 kts, and even stated by forum members, a member named "Turbine Blade" wrote something which appears to suggest the 727-100 is capable of performing beyond 390 kts:

Quote:
Hello...i have seen the 727 (aaaa what a wonderful machine !!) doing 420kts Indicated at 2000ft !! At the time aloud banging noise started at the nose area.I was new at the 27 so i was told that this sound comes from the nose gear doors banging at high speeds due to aerodynamic loads created by the fuselage !
:cool:

Is it's .Vne that high? Is the plane capable of performing beyond it's listed specs?

And did I read that statement about the landing gears right? - Did he have the gears out at 420 kts?  Wow! Or were the doors (while flush with the fuselage) just banging around even with the gears retracted up?


Andrea Kent


User currently offlinePGNCS From United States of America, joined Apr 2007, 2825 posts, RR: 45
Reply 11, posted (7 years 4 months 4 weeks 4 hours ago) and read 10417 times:

Quoting Jetlagged (Reply 5):
Memory plays tricks and on rare occasions pilots have been known to exaggerate.

Say it isn't so!  Wink


User currently offlineBlackbird From , joined Dec 1969, posts, RR:
Reply 12, posted (7 years 4 months 4 weeks 1 hour ago) and read 10397 times:

LoL @ PGNCS,

Andrea Kent
Pi is approximately equal to 3.1415926535897932384626...


User currently offlinePGNCS From United States of America, joined Apr 2007, 2825 posts, RR: 45
Reply 13, posted (7 years 4 months 4 weeks ago) and read 10393 times:

Quoting Blackbird (Reply 12):
LoL @ PGNCS,

Andrea Kent
Pi is approximately equal to 3.1415926535897932384626...

Come on, now...can't you get a little more precise than that? Big grin


User currently offlineBlackbird From , joined Dec 1969, posts, RR:
Reply 14, posted (7 years 4 months 3 weeks 6 days 21 hours ago) and read 10371 times:

PGNCS,

I just put that in to get around the minimum text requirement -- if you don't post enough (like one line of text), it won't let you post...

Andrea Kent


User currently offline411A From United States of America, joined Nov 2001, 1826 posts, RR: 8
Reply 15, posted (7 years 4 months 3 weeks 6 days 20 hours ago) and read 10365 times:

I'm suspect, Blackbird, that you have your V speed nomenclature just slightly mixed up.

Turbojet/turbofan powered swept wing airliners, with a few exceptions, don't have a Vne.

They have a Vmo and Mmo.

B727, for example has the following listed speeds....

Vmo 390 Mmo .90

---or---

Vmo 350 Mmo .88

Depending on the specific model.

IF some looney pilot (other than test pilots) was flying the airplane at 420 KIAS, and the FAA found out, his/her license would likely be suspended/revoked.

To fly the airplane beyond the stated limiting airspeeds (in the AFM) invalidates the certification requirements/standards of the particular model, and in addition, is very foolish.


User currently offlineBlackbird From , joined Dec 1969, posts, RR:
Reply 16, posted (7 years 4 months 3 weeks 6 days 19 hours ago) and read 10355 times:

411A,

I'm just trying to duplicate accurate flight sim conditions and perform the flight profiles done before the 250 kt speed restriction.

Back to the gear door thing... was the gear extended at 420? Or was the wind just making the doors (flush and covering the gear well) bang around. The wording was kind of confusing to me.

Andrea Kent

[Edited 2007-04-28 03:50:21]

User currently offlineJetlagged From United Kingdom, joined Jan 2005, 2556 posts, RR: 24
Reply 17, posted (7 years 4 months 3 weeks 5 days 19 hours ago) and read 10303 times:

Quoting 411A (Reply 15):
I'm suspect, Blackbird, that you have your V speed nomenclature just slightly mixed up.

Turbojet/turbofan powered swept wing airliners, with a few exceptions, don't have a Vne.

They have a Vmo and Mmo.

Why wouldn't turbojet/turbofan powered swept wing airliners, as a class of aircraft, have a Vne specified? Vmo/Mmo may well be the operating limit but that doesn't mean to say that other limits don't apply in certain circumstances.

According to the FAA type certificate of the CV-880, it has Vne defined as well as Vmo. IIRC the CV-880 had swept wings and was an airliner with turbine engines.



The glass isn't half empty, or half full, it's twice as big as it needs to be.
User currently offline411A From United States of America, joined Nov 2001, 1826 posts, RR: 8
Reply 18, posted (7 years 4 months 3 weeks 5 days 19 hours ago) and read 10300 times:

There is no Vne with newer designs, Jetlagged, because the certification standards were changed later on...so no Vne.
Only Vmo, which by definition, is the maximum operating airspeed limit, just as Mmo is the maximum allowed mach number.
Go faster, get the overspeed warning.
Simple as that.

It goes further.
Lets say you convert a multi-piston engined airplane to turbopropeller power.
Vne goes away.
It is replaced by Vmo, which by the way, is lower than the former Vne.

Not legal to fly faster than Vmo/Mmo, unless the filght is for test purposes, flown in accordance with the manufacturers test procedures, or for STC development.

Just the way it is...


User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 59
Reply 19, posted (7 years 4 months 3 weeks 5 days 19 hours ago) and read 10297 times:
AIRLINERS.NET CREW
DATABASE EDITOR




Quoting 411A (Reply 18):
Lets say you convert a multi-piston engined airplane to turbopropeller power.
Vne goes away.
It is replaced by Vmo, which by the way, is lower than the former Vne.

If you converted a turboprop to piston, would the reverse be true?

Also,

What was your most memorable moment flying the 707?


2H4





Intentionally Left Blank
User currently offlineBoeingFixer From Canada, joined Jul 2005, 531 posts, RR: 0
Reply 20, posted (7 years 4 months 3 weeks 5 days 18 hours ago) and read 10294 times:

Vne and Vno are two terms that are not used under current parts 121 and 135 of the FAR's. Vne is the airspeed limit in still air and does not provide any gust protection limits. Vno is the airspeed limit at which a 30 ft/sec vertical gust should not damage the aircraft. Vno was set at 90% of Vd for flutter protection. Vne, Vmo and Mmo can be seen together on some older TCDS's. You will find that the Vne is higher than the Vmo on those older TCDS's but all modern aircraft certified under part 121/135 will only have Vmo/Mmo.

Cheers,

John



Cheers, John YYC
User currently offline411A From United States of America, joined Nov 2001, 1826 posts, RR: 8
Reply 21, posted (7 years 4 months 3 weeks 5 days 15 hours ago) and read 10275 times:

Quoting 2H4 (Reply 19):
If you converted a turboprop to piston, would the reverse be true?

Also,

What was your most memorable moment flying the 707?

Turbine to piston?
More than likely not, the Vmo would stay the same.
We may find out now that the Orinda engine has come back from the dead, under new owners.

707 memorable moments.
1. Dense FD smoke over DaNang VietNam enroute HKG-BKK
Not nice.
2. Clear air turbulence departing Madras one early evening.
Being tossed around like a cork in the ocean, and looking out the LH side window at the left wing...and hoping the Boeing folks bolted it on, really tight...and wondering how the engines stayed attached.
3. Instructing brand new First Officers (with 270 total hours) how to be proficient.


User currently offline2H4 From United States of America, joined Oct 2004, 8955 posts, RR: 59
Reply 22, posted (7 years 4 months 3 weeks 5 days 15 hours ago) and read 10273 times:
AIRLINERS.NET CREW
DATABASE EDITOR




Quoting 411A (Reply 21):
We may find out now that the Orinda engine has come back from the dead, under new owners.

You read my mind.  Smile

Quoting 411A (Reply 21):
707 memorable moments.

Good ones.


2H4





Intentionally Left Blank
User currently offlineDH106 From United Kingdom, joined Jun 2005, 626 posts, RR: 1
Reply 23, posted (7 years 4 months 3 weeks 5 days 12 hours ago) and read 10262 times:

Seen no mention here of the Convair 990 which had an even higher Vmo/Mmo than the 880.
It had a much thinner wing section and those distinctive 'canoe flairings' to try minimise the transonic shock waves over the wing. Nowadays, modern supercritical sections achieve the same goal.



...I watched c-beams glitter in the dark near the Tanhauser Gate....
User currently offlineStarglider From Netherlands, joined Sep 2006, 678 posts, RR: 44
Reply 24, posted (7 years 4 months 3 weeks 5 days 7 hours ago) and read 10242 times:

Quoting DH106 (Reply 23):
Seen no mention here of the Convair 990 which had an even higher Vmo/Mmo than the 880.



The 990 had several Vmo/Mmo limitations depending on certain conditions.

(CV-990) Model 30, 30A: -5, -6 and -8 with empty Outboard Anti-Shock Bodies:
Vmo : 377 kt at sea level to 417 kt at 21,500 ft.
Mmo : 0.912 M above 21,500 ft.

(CV-990) Model 30, 30A: -5 with fuel in Outboard Anti-Shock bodies:
Vmo : 357 kt at sea level up to 21,400 ft.
Mmo : 0.784 M above 21,400 ft.

(CV-990) Model 30, 30A: -6 and -8 with fuel in Outboard Anti-Shock bodies (-5 post S.B. 990-28-12):
Vmo : 321 kt at sea level up to 21,600 ft.
Mmo : 0.718 M above 21,600 ft.

But slower speed had its advantages as well, Modern Air flew the 990 trans-Atlantic, from Philadelphia to Vienna non-stop at M. 0.78, at that speed it had more than 20 percent range increase.


Starglider

[Edited 2007-04-29 16:33:56]

25 Blackbird : DH-106, I always thought the thickness (not thickness/chord ratio... just the thickness) was the same as the CV880. Andrea Kent
26 Post contains images DH106 : The 880 and 990 both had the same 120' 0" span, and to my eye seem to have the same wing planform shape (obviously minus the shock bodies on the 990)
27 Blackbird : DH-106, The CV-880 had a 35-degree sweepback angle. The CV-990 had a 39-degree sweepback... thus same thickness, longer section, lower thickness to ch
28 DH106 : Hmmmm - interesting, are you sure? Checkout the silhouettes inside the front (880) and rear (990) covers of Jon Proctor's excellent book. I make them
29 Blackbird : To the best of my knowldge, the CV-880 had a 35-degree wingsweep. Andrea Kent
30 Post contains links DH106 : Yes, it's interesting Andrea. 35 or 39. Proctor's book certainly quotes 35deg for the 880 (page 10), but no figure for the 990. All schematic drawings
31 Blackbird : I think the FAA site (there's a bunch of PDF documents you can find with make and model) which discussed the performance and capabilities of the CV-88
32 Post contains links Starglider : Andrea, It is 39 deg for the CV-990. See link below and scroll down to page 28: Table 1. - Physical Characteristics of the CV-990 Airplane. http://nt
33 Blackbird : The CV-880 is 35 right? Andrea Kent
34 DH106 : Well, tricky one. Either: all the schematic drawings I can find are wrong (about half a dozen at last count). They all measure at 39deg - same as 990
35 Post contains images DH106 : Here's an image of the Lisbon 880 - N8806E (ship #21) from Google Earth, oriented as close to 'north' as I can make it. It's a bit fuzzy and not quite
36 Blackbird : I remember the FAA document saying it was 35-degrees, although I could be wrong and it may as well be 39-degrees. One thing I remember though was the
37 Blackbird : What speed does the overspeed warning typically sound at on say the 707, 727, CV-880/CV-880M, L-1011, and CV-990? Andrea Kent
38 411A : L-1011....M.90 Unless, the aeroplane was on the British or Omani civil registers, then M.88
39 Blackbird : What indicated airspeed if, applicable at low altitiudes, did the L-1011's overspeed sound at? Andrea Kent
40 411A : L1011.....375 KIAS................
41 Blackbird : What was the 707-420's story? They to my knowledge had a lower VMO/MMO and stuff, and if I recall they took off with a 30-degree flap detent. Why the
42 BoeingFixer : It was officially known as the 707-400 series. The customer #'s were 430(Lufthansa), 436(BOAC), 437(Air India), 441(Varig), 458(El Al), 465(BE). Dire
43 DH106 : The -400's carried the larger of the two ventral fin sizes didn't they?
44 Blackbird : Was there any -420B's or -420C designs with the 320B/C wing? Andrea Kent
45 411A : Regarding the differences between the wing (IE; NACA number) of the 707-400 and 707-320 straight pipe (non-fan) series aircraft....there ain't any. Ho
46 DH106 : Don't all later model 707's have full span LE devices? I remember a thread some time back about whether they should be called slats, Kreugers or just
47 411A : If you refer to my previous post on the subject, DH106, you will note that my reference was to older -320 and 400 series straight-pipe (non-fan) aircr
48 DH106 : Okay, so only SAA aircraft of early -300 series (non-fan) had full span LE device. Later (fan) -300's all had them.
49 411A : Yes, DH106, that is correct. You should understand that many 707's, after they left the factory, were modified by their original or succeeding operato
50 2H4 : 411A....what, in your opinion, was the single most clever design aspect of the B707? 2H4
51 411A : The single most clever device with the original B707, was the certification pilot...and getting it certified in the first place. The early models were
52 Blackbird : Didn't the 707-400 series have T/C's on all four engines? Also... What was the -120/-220 and 120B flap settings? Which were used for takeoff, and whic
53 411A : 1. Yes, T/C's on all four engines, I believe. I flew RB.508 powered aircraft only a short while. 2. 10, 20, 30, 40, 50. 20/30 for takeoff, 50 for land
54 Blackbird : The -120B had the same settings as the 120/220? The 720/720B I take it was the same as the 120/120B? Andrea Kent
55 411A : Same settings, yes, so far as I remember. Nearly all my flying was done in the long body models.
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