L/D

[DJFawcett26]

Hello All,

Since this is about the most resouceful group I know, I though somebody may be
able to help. I have been trying to find the supersonic L/D of the B-1A or B
and the SR-71. Does anybody have any information concerning either. I realize
that the L/D is mach dependent, but I can not fine anything at any mach number.
I am doing a comparative analysis on a supersonic configuration, and the info
would be most helpful.

Thanks in advance for any help

Best Regards,

Dave

[Orval Fairbairn]

In article >,
(DJFawcett26) wrote:

> Hello All,
>
> Since this is about the most resouceful group I know, I though somebody may
> be
> able to help. I have been trying to find the supersonic L/D of the B-1A or B
> and the SR-71. Does anybody have any information concerning either. I
> realize
> that the L/D is mach dependent, but I can not fine anything at any mach
> number.
> I am doing a comparative analysis on a supersonic configuration, and the
> info
> would be most helpful.
>
> Thanks in advance for any help
>
> Best Regards,
>
> Dave

Supersonic L/D is very complex, as angle of attack affects drag
drastically. You would almost need a complete set of aerodynamic tables
which show normal force and axial force coefficients as a function of
both Mach no. and alpha. I am sorry, but there is really no simple
answer.

[DJFawcett26]

>Supersonic L/D is very complex, as angle of attack affects drag
>drastically. You would almost need a complete set of aerodynamic tables
>which show normal force and axial force coefficients as a function of
>both Mach no. and alpha. I am sorry, but there is really no simple
>answer.

I realize there is no simple answer, I was trying to elude to that point when I
first asked the question. Of course alpha effects drag which effects L/D, and
on, and on, we go. I am not asking for a detailed engineering exercise. All I
am really asking "is there any L/D published data that may be found". This is
a very, very, very top level analysis, not a detailed engineering exercise.
You might say extremely parametric is nature. All configurations have an
optimum L/D (max) for given mach point (taking into account everything you
describe and more), and that is what one usually finds in the publications.
Everybody shows there best.

I do appreciate your response, but all I am looking for is something ( that is
somewhat reasonable) to turn into a point on a chart - LOL.

Thanks again

Dave

[Richard Isakson]

Dave,

I don't know if this will help but when you need data sometimes anything
will do.

"Supersonic and Subsonic Airplane Design", Gerald Corning, 1970, lists the
projected cruise L/D of the Boeing SST (2707-300) as 7.35 at mach 2.7 and
60,000 feet. Boeing was quite proud of the -300 until they started doing
powered wind tunnel tests. It turned out that at cruise the engine exhaust
hit the tail and would have burnt it off. Faced with pressure from Congress
and the need for yet another complete airplane redesign, Boeing killed the
program. When it comes to an American SST, "that's the rest of the story".

I'll see if I have anything else around here but you might try a search of
"Aviation Week" for that period. A long time ago I found some of my work
there before I had even finished with it.

Rich

[Stealth Pilot]

On 06 Jul 2004 02:31:43 GMT, (DJFawcett26) wrote:

>Hello All,
>
>Since this is about the most resouceful group I know, I though somebody may be
>able to help. I have been trying to find the supersonic L/D of the B-1A or B
>and the SR-71. Does anybody have any information concerning either. I realize
>that the L/D is mach dependent, but I can not fine anything at any mach number.
> I am doing a comparative analysis on a supersonic configuration, and the info
>would be most helpful.
>
>Thanks in advance for any help
>
>Best Regards,
>
>Dave

I had a quick look through my books.
only reference that may be useful is of the concorde.
scaling off the diagram gives a max L/d of 7.47 or say 7.5 at mach 2.
not the aircraft you want but a number nevertheless.

there is a graph showing l/d with mach for some "transport" aircraft.
dont know which one. figure 12.26 in the book below.

fundamentals of flight by richard shevell. 2nd edition. page 215.

Stealth Pilot
Australia.

[DJFawcett26]

Appreciate the help guys! You're right Rich, at a point, anything with do.
And Stealth Pilot, thanks very much!

[anonymous coward]

On Wed, 07 Jul 2004 00:00:24 +0800, Stealth Pilot wrote:

> On 06 Jul 2004 02:31:43 GMT, (DJFawcett26) wrote:
>
>>Hello All,
>>
>>Since this is about the most resouceful group I know, I though somebody may be
>>able to help. I have been trying to find the supersonic L/D of the B-1A or B
>>and the SR-71. Does anybody have any information concerning either. I realize
>>that the L/D is mach dependent, but I can not fine anything at any mach number.
>> I am doing a comparative analysis on a supersonic configuration, and the info
>>would be most helpful.
>>
>>Thanks in advance for any help
>>
>>Best Regards,
>>
>>Dave
>
> I had a quick look through my books.
> only reference that may be useful is of the concorde.
> scaling off the diagram gives a max L/d of 7.47 or say 7.5 at mach 2.
> not the aircraft you want but a number nevertheless.
>
> there is a graph showing l/d with mach for some "transport" aircraft.
> dont know which one. figure 12.26 in the book below.
>
> fundamentals of flight by richard shevell. 2nd edition. page 215.
>
> Stealth Pilot
> Australia.

Somewhere on the internet there is a page giving a L/D value for the
Valkyrie. Apparently it had the best L/D of any supersonic aircraft to
date, due to its novel wing design.

AC