Definitions of M speeds. Mdi/Mde?

[ftp]

Hi,

I was talking aerodynamics with someone today (yes it was an interview) and am looking for an answer on something that stumped me. We were on the subject of high speed airfoils and had just finished talking about Mdr and Mcrit. I was then asked if I could define Mdi (or it may have been Mde). I've never heard of these before. Any ideas?

Does anyone have a list of obscure M or V speeds?

I took a few minutes to search, but couldn't find it myself. Thanks in advance everyone.

ftp

[BelArgUSA]

Speeds

By convention, V is a speed (expressed in knots generally in aviation).
V = veloce, vitesse, velocidad, in latin and latin languages...
And same convention, M is an expression of speed, but in Mach number.
Speeds such as Vmo - max operating speed, then Mmo, max operating Mach number.
Example for 747-200 = Vmo is 383 KIAS or Mmo is Mach .92...
xxx

Happy contrails

[ChristiaanJ]

ftp,
You already have me stumped with Mdr !

Mcrit is formally defined as the Mach number where the airflow somewhere locally reaches the speed of sound.

The "dr" sounds like "drag rise", which would make Mdr the Mach number at which the additional drag due to Mach effects becomes measurable (1%? 5%?), which is usually somewhere above Mcrit. Also known as the "drag divergence" Mach number.

So I would be curious about Mdi (or Mde?) too !

CJ

[BelArgUSA]

Other speed/Mach names...

to ftp and Christiaan -
xxx
I have seen many Vspeeds and Mspeed definitions and limits.
Some are "official" accepted names... some are not.
I got trained in the USA... and I came across books from UK with other names or definitions.
As pilot, after all, we only need to study/remember a few, that are our aircraft limits.
The others you forget. Heaven's sake, for me was 40+ years ago...!
Alzheimer is taking place...
xxx
A fact of interest, about V speeds and M number limits...
Some airplanes have V speeds and Mach limits, some do not.
Examples -
xxx
Boeing 747 landing gear placard indicates -
VLO/MLO Extension = 270 KIAS or Mach .82
VLO/MLO Retraction = 230 KIAS or Mach .82
VLE/MLE Extended = 320 KIAS or Mach .82.
xxx
But for 747, flaps there are only Vspeed limitations, no Mach number.
The VFE Flaps 1 in the 747 is 275 KIAS - nowhere a MFE limitation.
This because Boeing 747 max altitude for flaps use is 20,000 feet.
xxx
Compare to the DC8-63/73...
The DC8 has a VFE Flaps 12 of 230 KIAS and MFE Mach .46...
Because Douglas does not have 20,000 feet max altitude flaps extension limit.
You could extend flaps at high altitude, with a Douglas DC8...
xxx

Happy contrails
xxx

[ChristiaanJ]

I think ftp is asking an aerodynamics question, and BelArgUSA is looking at the aircraft operation side....

We all use abbreviatons and acronyms that are only valid in our own narrow field.

As an Dutch aeronautical engineering student, I was taught one set of abbreviations/symbols/notations for stability derivatives, angular rates, etc. etc., probably mostly of European/German origin. The moment I started reading American tech literature such as NACA/NASA Tech Notes, I had to get accustomed to a whole new set of notations. Then I went to work in France, and lo and behold, they had their own set of notations, with very little similarity to the ones I knew.... We live and learn.

So.... I think ftp would have been justified in asking what was meant with Mdi during his interview.

Maybe it was just "drag increase" Mach number? I.e., the same as Mdr or Mdd?

Oh, and... BelArgUSA...it would be interesting to know for an ancient like me exactly how Mmo, and the typical cruise Mach number, are related to Mcrit and M(drag rise). In the particular AFM on my shelf, Mmo is 2.04....

CJ

[ftp]

Thanks ChristiaanJ

Yeah, I'm just trying to find out if someone has a definition of what Mdi (or it may have been Mde) is that was being referenced. The rest of my first post was explaining the context of the situation when it came up. I was talking to a senior airbus guy who I believe was of British background.

I'm just looking for the definitions (or a reference of different M speeds) for my own interest.

Thanks

[sycamore]

Don`t know if this helps,but it`s from a test-flying qualities hand-book-Stinton; Vd/Md=design diving speed and Mach no.;Vdf/Mdf- demonstrated flight diving speed and Mach no.

[ChristiaanJ]

sycamore,
I'll leave ftp to answer, but I think we're hunting for a theoretical aerodynamics abbreviation... as ftp said, they were discussing airfoils...
Md and Mdf are obviously flight test abbreviations, and probably familiar to certification test pilots as well.

Without an "abbreviations" list at the head of an article or document.... we're all lost.

p, q and r mean anything to any of you guys, by any chance?

ftp,
Sycamore may have a good idea. Maybe you should post this on the PPRuNe Flight Test forum as well? It may ring somebody else's bell over there.

CJ

[nick2007]

I found a reference to Mdes (subscript des for descent) in an ESDU article.
Though this doesn't really fit the context of your interview discussion...