Aircraft Design Factor?
Roger N
design factor of 4 to 6 (equipment designed to withstand 4 -6X the normal
load). This is easy for industrial equipment since heavy doesn't seem to be
a bad thing. Since excess weight is a bad thing in aircraft design, I was
wondering what (typically) design factor is used?
IOW, if a plane is rated to handle +6G's, is it designed so that the
materials are at their yeild point at 6G's? Or is it designed so that 6G's
only put a fraction of the yeild forces on the materials?
Just wondering how this is done in the world where weight is much more
critical.
Thanks!
DJFawcett26
>materials are at their yeild point at 6G's? Or is it designed so that 6G's
>only put a fraction of the yeild forces on the materials?
>
Typically, we design 1.5 safety factor for ultimate in metal airframes, and a 2
safety factor for ultimate in composite airframes.
Daniel
> I have designed equipment for industrial automation purposes and often use a
> design factor of 4 to 6 (equipment designed to withstand 4 -6X the normal
> load). This is easy for industrial equipment since heavy doesn't seem to be
> a bad thing. Since excess weight is a bad thing in aircraft design, I was
> wondering what (typically) design factor is used?
>
> IOW, if a plane is rated to handle +6G's, is it designed so that the
> materials are at their yeild point at 6G's? Or is it designed so that 6G's
> only put a fraction of the yeild forces on the materials?
Semantics. Design vs ultimate. If "a plane is rated to handle
+6G's", that's its "design load". Using a 1.5X factor, the
engineer/designer will work from an "ultimate" of 9 G's. Conversely,
if the ultimate is 6 G's, then the design load is 4 G's.
Daniel
RobertR237
<re...@nospam.midwest.net> writes:
The normal, as far as I have been able to find, is a factor of 1.5 for standard
aircraft of wood or metal construction and 2.0 for aircraft of composite
construction. The 2.0 for composite was established early on when the
consistant quality of the composite construction was not as good as currently
available but it still holds true. This is one of the primary reasons that all
composite aircraft have not been able to achieve significant weight savings
over other construction methods. (Note. Its not the only reason since all
carbon fiber would achieve the weight savings but then cost become a
significant factor.)
Bob Reed
www.kisbuild.r-a-reed-assoc.com (KIS Builders Site)
KIS Cruiser in progress...Slow but steady progress....
"Ladies and Gentlemen, take my advice,
pull down your pants and Slide on the Ice!"
(M.A.S.H. Sidney Freedman)
Corrie
What about wood construction? Seems like a design rated for -2 G
would be able to handle inverted flight, but just barely. No outside
loops.
DJFawcett26
>2
>> safety factor for ultimate in composite airframes.
>
>What about wood construction? Seems like a design rated for -2 G
>would be able to handle inverted flight, but just barely. No outside
>loops.
I am not saying two 2gs. What I am saying is the g limit design is 4.4 gs for
example, a metal airplane would be designed to 6.6 gs ultimate, and a composite
airplane would be designed to 8.8 gs ultimate.
RobertR237
(Corrie) writes:
>
>> Typically, we design 1.5 safety factor for ultimate in metal airframes, and
>a 2
>> safety factor for ultimate in composite airframes.
>
>
>What about wood construction? Seems like a design rated for -2 G
>would be able to handle inverted flight, but just barely. No outside
>loops.
>
>
Wood designs used the 1.5 factor same as metal. A -2G rating would thus imply
that the design was for -3G's of load. In that case I would agree that you
should not be goind those outside loops.
Corrie
Dani...@unitedstates.com (Daniel) wrote in message news:<b07467f0.03060...@posting.google.com>...
Roger N
Thanks for the replies. I think this aircraft design kind of stuff is very
interesting. A design factor of 1.5 doesn't give you a lot of room for
error but I guess there is always sandbag testing to make sure it will
handle the loads.
On new aircraft designs, are scale models made to verify the design will
fly, or does the pilot just get in and hope it will be flyable?
DJFawcett26
>fly, or does the pilot just get in and hope it will be flyable?
Personally, I think scale models only prove you can fly a scale model of a
given design. Heck, I can make a scale lawn mower, dog house, and car fly!
No, the pilot should not just get in and try to fly. To insure some degree of
safety, that is what all the analytical, CFD, and Wind Tunnel testing is for.
But still, Mother Nature sometimes doesn't agree with man made equations, and
computer programs. Sometimes the wind tunnel even gets a big thumbs down by
Mother Nature - LOL
Barnyard BOb --
"Roger N" <re...@nospam.midwest.net> wrote:
>
>Thanks for the replies. I think this aircraft design kind of stuff is very
>interesting. A design factor of 1.5 doesn't give you a lot of room for
>error but I guess there is always sandbag testing to make sure it will
>handle the loads.
++++++++++++++++++++++++++++++++++++++++++++
A design factor of 1.5 is faaaar from shabby, Roger..
Remember, the craft is gotta' be light enuff to F-L-Y.
FWIW --
If one cowboyz a 6 G 'loomnum winged aero-bucket...
it will take 9 G's or more to get you a boot hill tombstone.
Whatz wrong with that?
You want... 12G's or ?????
Barnyard BOb - 50 years of flight
RJ Cook
would use minimum design load factors of +6 and -3, then multiply those
factors by a structural material safety factor of 1.5 for ultimate design
loads of +9 and -4.5. This is the current standard.
RJ
"Roger N" <re...@nospam.midwest.net> wrote in message
news:nefDa.30080$rO.27...@newsread1.prod.itd.earthlink.net...
RobertR237
<re...@nospam.midwest.net> writes:
>
>
>Thanks for the replies. I think this aircraft design kind of stuff is very
>interesting. A design factor of 1.5 doesn't give you a lot of room for
>error but I guess there is always sandbag testing to make sure it will
>handle the loads.
>
Whoa there, the 1.5 is a multiplier not the rating. An aircraft is designed
based on the intended configuration and usage. An aircraft designed for
standard category use will not have the same requirements as one designed for
aerobatics. The configuration and usage will determine the basic requirements
of the aircraft. If the design is to be used for mild aerobatics the design
requirements might call for a +6 g's and -4 g's capability. The design
(safety) factor of 1.5 is then applied and the resulting structure is designed
for +8 g's and -6 g's. On the other hand if you want a design for extreeme
aerobatics you might design it for +8 g's and -6 g's which would then be
factored to +12 g's and -9 g's. The design factor is always above and beyond
the design requirement.
>On new aircraft designs, are scale models made to verify the design will
>fly, or does the pilot just get in and hope it will be flyable?
>
Scale models have not generally proven very useful in verification of anything
outside of wind tunnels. The best verfication is adhearing to known and
accepted design standards. Even then, it is not always a guarantee. For the
most part, the first flight of any new design is a TEST flight. The scrap
yards are littered with great ideas that just didn't pan out. Its unfortunate
that a few have taken their designers, builders, or test pilots with them.
Dave Hyde
> On new aircraft designs, are scale models made to verify the design will
> fly, or does the pilot just get in and hope it will be flyable?
Depends on the design(*). There has been flight testing done on
scale mnodels of the F-18E, F-15, X-31, Starship, and a bunch
that never really saw the light of day. Unless you can afford
to *heavily* instrument a subscale model there isn't a whole
lot to be gained from (unmanned) testing. You might be able to
verify that the configuration is somewhat viable, but scale factors
throw much of the results off unless (and in some cases even if)
you've got the data and the skills to make appropriate corrections.
Then there's the whole engine scaling problem, to say nothing of
using an unpiloted vehicle to evaluate flying qualities.
IOW, the best scale model to thoroughly evaluate a homebuilt
concept is 100% :-)
(*) A more direct answer is, "Yes, occasionally scale models
are made and flown, but often with little useful gained."
Dave 'supersize it(tm)' Hyde
na...@brick.net