JH25 aerofoil section

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Doc J

New member
Oct 7, 2018
2
0
#1
Hi Guys,
this is the basis of the sections that I have been using for the Schwing, Schwing Corsa, Stormbird, Redshift and the new Firebird.

Designed to be a high response profile that works well with the control surfaces, its a double convex section.

As you can see it looks a bit weird compared to "Conventional" sections, but it works well and will take a nice lot of ballast.

Unlike the "super secret" sections we se so often, this one is open house and available to anyone who wants to use it or play with it.

Cheers,

Doc.

JH.25 polars.png
JH25 general..png
 
Nov 5, 2018
7
0
#2
Dear James,

I need some extra tuition on aerodynamics. I took the chart from Cm (pitching moment) and Alpha (α). The colors should be the same as you released on the 8Th of october. There seen the different Re number spectrum (0.1 to 0.3) we use on modelplanes/unmannedvehicles and quiet not in the range of positive mach numbers. So fast so good.

While disturbing the pitch axis (on the pic within the red circle) at Alpha -2° the detected different behaviours (the spread that starts at 4°α turns into upside-down). Based on different reynold numbers it indicates that different control inputs are required to achieve stabilization.
I am interessted in the drop of near and
JH.25 polars extend.png
below Alpha -5°. Your chart pictures nicely the situation above 13 degrees on the positive side. Is it possible to know more what happens more on the left side of this chart. I certainly do not know why the airfoil changes behaviour (on this chart five times) as indicated by the brown graph and the violet one (or the dark red at Re 0.300). What should a pilot know about this phenomenon or is it just a normal state of flying this objects?

Many thanks for your help. I have no proven education on this type of Things. I if I termed something wrong than please correct.

Cheers
Chris
 
Dec 13, 2017
305
19
Taiwan
#3
HI Chris,
yes the chart does start to do some nice dances around the negative portion of the envelope - but in fact most aerofoils do this.

I think that at higher negative angles the bottom boundary layer is detached or beginning to detach, and that will have some strange effects on the entire lift profile around the transitions - as we see on the graph.

I have never really looked at this in great detail as I have not noticed any bad effects in the flight envelope.

Happily we rarely fly at high negative alpha angles for any length of time.

Cheers,

James