info on MH -32 etc. airfoils
Frank
series (MH32,33,42 etc.)
all comments or comparisions to selig airfoils welcome. I already have seen
the website but would like to hear now some opinions.
Thanks
Frank
fjn...@hoflink.com
Robert Steinhaus
number application such as we encounter in model sailplanes. They are
among the best currently available. MH45 is a very efficient and
excellent flying wing airfoil. At standard sailplane chords it has
unusually low drag when operating at low coefficients of lift (Cl=.2)
(as often encountered when flying slope gliders or F3B speed task) and
has an operating range all the way up to Cl=1.25 (which is valuable when
thermal soaring at minimum sink rate). All and all MH45 is a really
excellent airfoil for flying wings with a very low coefficient of
moment. MH32 is a very versatile thermal soaring/multitask airfoil. Some
polars do not do it justice (there seems to have been some problems with
the leading edge of the wind tunnel model of the MH32 used in the Selig
Low Speed airfoil tests reported in Soartech 8 and elsewhere). The
airfoil is consciously designed to take advantage of camber changing
through lifting and lowering the flaps/ailerons a few degrees. With a
couple of degrees of reflex (raising the flaps and ailerons ~ 2 degrees)
MH32 becomes quite fast. For F3B mulltitask I still prefer the balance
of RG15 in 120" span aircaft. RG15 has a relatively sharp stall
characteristic and may not be the greatest choice for smaller sport
gliders (60" and lower span). On a large F3B/F3F glider RG15 really
comes into its own and has tremendous speed, turning, and speed
retention in turns.
Dr. Hepperle is one of the world's finest model airfoil designers. I
tend to give his MH series of airfoils strong consideration when
preparing to design a new model.
Andrew Hollom
You didn't mention what you wanted the section for, i.e. what you want it to
be good at. If you want something for F3B that has a drag bucket, then try
the AH21. You can get the coordinates from Michael Selig's excellent UIUC
site.
I have to say that I'm a little biased, because I designed it (for the
Haley's). However, it was very successful, finishing in the top three in the
World F3B championships one year (I forget which). It would have done better
if we'd worked out how to fix the transition point properly, but we only
managed this after the event.
I haven't designed any foils for some time, but I am working on something
quite different (an optimisation method) that may help to design aerofoils
in a parametric manner (i.e. you give the optimiser hints as to what you
want it to be good at, such as lift/drag, CLmax, penalties for seperation
bubbles, etc.). This should be working, and hopefully spitting aerofoils out
by the dozen, later this year. Any results will be forward to Michael Selig
for publication.
If you decide to use my section, or just want to know more, then get in
touch with me and I'll help you all I can.
Andrew.
Frank <fjn...@hoflink.com> wrote in message
news:sfd8oth...@corp.supernews.com...
James Fritz
and camber are similar to the S6063 which is becoming a very popular airfoil
in handlaunch. Do you know if anyone has tried it out?
Thanks,
James Fritz
Fort Collins, CO
Andrew Hollom wrote in message <8d83og$di3$1...@newsg2.svr.pol.co.uk>...
>Hello,
>
>You didn't mention what you wanted the section for, i.e. what you want it
to
>be good at. If you want something for F3B that has a drag bucket, then try
>the AH21. You can get the coordinates from Michael Selig's excellent UIUC
>site.
>
>
>Andrew.
Andrew Hollom
The section was designed for F3B with the Reynolds number ranging from
75,000 to 400,000 (if you're continental, the commas are not decimal points,
i.e. 75E+3 to 400E+3). These are low Reynolds numbers, but I suspect they
are relatively quite high for a hand launch glider, for which I have very
little knowledge. I've looked at the S6063 section, and it does not look
like a laminar section and it is not aft loaded at all. Conversely, the AH21
is a laminar section and is quite heavily aft loaded (and consequently has a
high pitching moment, which with hindsight I should have paid more attention
to). I would say that S6063 is not very similar to AH21.
For very low Reynolds numbers, I guess that a highly laminar section loses
its desirability because laminar flow is more likely to occur as a result of
the low Reynolds number (at least at low CL's)and also because laminar
sections tend to have a sharper nose (smaller nose radius). This is due to
the need to get a velocity distribution that will naturally promote laminar
flow and results in a relatively low CLmax. I haven't done any formal work
on anything other than F3B, though when I get my new design method up and
running, there will be no reason why I should not expand my research (which
I plan to do).
For a hand launch, I would recommend opting for a section that is known to
be good. However, I would like more people to use the AH21 for F3B and pylon
racing (where the Reynolds numbers are high) so I can get some feedback for
comparison against what the Eppler and Somers program predicts (you see, I
don't blindly believe computers!).
Andrew.
James Fritz <a...@holly.colostate.eduNOSPAM> wrote in message
news:38f7...@news.ColoState.EDU...
Robert Steinhaus
this airfoil and it does appear from computer modeling (Eppler Code) to
have outstanding characteristics for a racing gliders. Could you comment
on the turning characteristics of models built with this airfoil (AH21
9% version)? Did the models using AH21 exhibit good speed retention in
the turns (the polars would tend to indicate outstanding performance in
the straights when operating in the drag bucket at low Cls)? How about
soaring during duration task?
If feel sure that many members of the news group would appreciate
learning about the results from your inductive parametric airfoil design
program once you have a chance to finish it. Thank you for sharing
information regarding your fine airfoil.
Andrew Hollom wrote:
>
> Hello,
>
> You didn't mention what you wanted the section for, i.e. what you want it to
> be good at. If you want something for F3B that has a drag bucket, then try
> the AH21. You can get the coordinates from Michael Selig's excellent UIUC
> site.
>
Andrew Hollom
I assume you are referring to the turns in the speed task, which are the
most demanding. I went to a few competitions and some of the earlier
practice sessions with the new aerofoil, and it didn't seem deficient
(though it was very noisy without transition!). I would guess that it would
be desirable for the speed task to couple the flaps with the elevator to
shift the drag bucket up during a turn. While I'm on the subject of flap
usage, AH21 was designed to use up flap for the speed task (to bring the
drag bucket down to zero lift), zero flap for the distance task, and down
flap for the duration. I cannot remember the settings, but I could find out.
The soaring ability was okay, but the duration task was by far the easiest
(probably a Clark Y would have been good enough!). However, I think they are
changing (or have changed) the duration task to make it longer and therefore
more of a challenge.
I mentioned that it was initially very noisy. This we think was due to
laminar separation bubbles and dissappeared with the application of
transition strips to both the upper and lower surfaces. However, this was
not the best solution, and my father and Denis Oglesby devised a pneumatic
transition system. This comprised of a series of holes connecting the lower
surface to the upper surface, the holes being a large diameter on the L/S
and very small on the U/S. Doing this allowed transition to occur when there
was an appreciable pressure difference, but when there was not (in the speed
task) the transition was weaker. This significantly reduced the drag for the
speed task while maintaning performance in the other two tasks.
Unfortunately, this was done just after their very nearly successful world
championships (around 1990, my memory is failing me), and we reckon they
would have won if it had been done earlier (it was that beneficial).
One last point, the aerofoil was designed with a thickness of 9%, but was
easily at its best when scaled down to 7%. It was the 7% variant that nearly
won the worlds, the original 9% version would definately not have done as
well.
Oops, one more last point, AH21 is aft loaded and has a high pitching
moment. This incurs a high trim drag which isn't a good thing. An idea I've
had is to augment the pitch stability with a small solid state rate gyro.
This should allow the CG to be moved aft, reducing the trim drag (perhaps it
could even be allowed to become unstable?). I have experience of these
devices, because I used to work at BAe Airbus, and I wrote a flight control
system for a flying wind tunnel model. This model used three rate gyros (in
roll, pitch and yaw) and they worked very well indeed. Model helicopters use
them most, though there was someone who once used them in a model racing car
(automatic opposite lock!), but it was banned.
Hope this helps,
Andrew.
Robert Steinhaus <hone...@hotmail.com> wrote in message
news:38FA12...@hotmail.com...
Robert Steinhaus
(dare I say down right exciting). F3B is a very competitive and rather
highly refined glider competition area. Airfoil selection has been so
thoroughly worked on by competitors I largely have despaired that there
be any real alternate choices other than the familiar (RG15, MH32,
etc.). AH21 (7%) would seem to have very outstanding performance at both
low Cls [in the drag bucket] and at high Cls [good max Cl while
operating at high angles of attack]. If AH21 (7%) has any serious
deficiencies it is mostly in the mid range Cls where as you mention
coordinated flap/elevator mixing may shift the drag bucket up
sufficiently to be very efficient in the speed turns. Do you have any
estimates for zero lift angle and coefficient of moment for the two
versions (7% and 9%) of your AH21 airfoil? Since the airfoil was
designed to incorporate simultaneous raising and lowering ailerons and
flaps together (camber changing) do you have any suggestion on flap and
aileron percentage chords when using the airfoil this way to extend its
performance range?
The search for a new and improved F3B airfoil is a little like the
search for the holy grail. Coming up with something better than the
traditional airfoils used in F3B is very very hard. While I can not say
yet that AH21 is dominatingly superior to the traditional F3B airfoil
selections (some wind tunnel confirmation and flight testing is needed
first) AH21 looks terribly interesting on the computer simulations and
you should be congratulated on your fine work.
Jacques Blain
CM = -0.077
Zero lift angle = -2.75
These results are usually a good starting. Mr. Hollom probably has better
ones.
Andrew Hollom
Wow! Very good estimates. Robert also mailed me directly and I replied to
this and neglected the group (oops), so here is my reply of yesterday...
Robert,
I'm glad to be a glimmer of light! I fully intend to have a range of new
sections for various applications, with the first ones hopefully being
published by the end of the year.
The figures you requested are:-
Thickness Alpha0 Cm0
9% -3.47 -0.0974
7% -2.75 -0.08
The pitching moment values are viscously corrected (for Re=400000, the
inviscid value for 9% being -0.0991, I'm not sure for the 7% as I only had
the graphs and no tabulated output to hand(and so the Alpha0 and Cm0 may be
a little inaccurate)) and for an incidence of zero (relative to the chord
line). Naturally, the pitching moment varies slightly with alpha and
Reynolds number (it reduces slightly with Re due to separation).
I will need to wade through my paperwork and perhaps do some analysis on the
flap angles we used and the flap chord (I think it was either 22.5 or 25%
though). However, I cannot guarantee when I could do this work, sorry but
I'm pretty busy. The new optimisation method will determine the optimal flap
chords and deflections as an inherent part of the 'automatic' design
process.
I hope this is useful, and please keep in contact with me about what you are
doing (you see, I might need a guinea pig or two for testing the new
section(s), which I feel sure will be better than AH21). While I'm on the
subject of perhaps using you as a 'guinea pig', could you tell me a little
about yourself (in an aeronautical sense)?
Thanks,
Andrew.
Jacques Blain <jbl...@tecnar-automation.com> wrote in message
news:FUgL4.2906$vq5.1...@weber.videotron.net...