MH30 with flaps for thermalling

[soholingo]

I know that this MH30 airfoil is made for speed. But I was wondering if it could be a semi effecitve airfoilf for thermaling? Especially if I have flaps to use for cambering...

How much camber should I add to assist in thermaling


jay

[stephen.s1]

Start with 3-4°. If you can control it with a slider, all the better. You can vary it whilst airborne in different conditions.

Cheers

[Jack Hyde]

I ran some polars for MH32 with flaps neutral, up(reflex) and drooped (increased camber) . Increased droop gives less drag at high cl but a lot more drag at low cl.

[soholingo]

why mh32? I know thats a good all purpose wing. MH30 was built for speed so I am interestested in how it would thermal.

[Jack Hyde]

I talked about MH32 because I had results already run for that foil. The MH32 has become
very popular on RC sailplanes, offerring better penetration than the SD7037 that was popular
earlier.
Why did you select the MH30? It is thinner and less cambered than the MH32, so it produces
a lower max lift coefficient but less drag at low cl's, hence good for high speed, needs
more speed to get required lift.
I used Profili to compare cl and cd for the 2 with and without 5 deg of flap droop.

MH32 at max cl/cd cl= 0.9 cd= .017 at cl=0.5 cd=.015
MH32,5deg flap at max cl/cd cl= 1.0 cd= .016 at cl=0.5 cd=.021

MH30 at max cl/cd cl= 0.7 cd= .013 at cl=0.5 cd=.014
MH30,5deg flap at max cl/cd cl= 0.9 cd= .015 at cl=0.5 cd=.019

For both airfoils cd with flaps becomes greater than without flaps for cl less than 0.8.

I will let you sort out the significance of the numbers. I would use the MH32 because it
has been successfully used on many very good TD sailplanes. I don't know of any plane with
the MH30. With the right wing loading it might be a winner.

[soholingo]

thanks for the response... I have profili and I have NO idea how you generated those numbers or what they mean. I will have to do some more research. But I have the MH30 because I wanted to go fast, it would be nice if the mh30 would thermal pretty well too... I was hoping for someone with experience with a flapped mh30 wing. BUT if I can learn how to interpret the number that may be good enough...

thanks again...

Jay

[Jack Hyde]

The short version is :
lift is proportional to cl x vel^2 lift is good
drag is prop to cd x vel^2 drag is bad
lift / drag = glide path = cl/cd = L/D
sink rate = vel x L/D
To thermal you need to get into upgoing air and fly at a sink rate that is less than the up velocity of the air. Need to fly slow with a high L/D. High speed foils produce relatively low cl so require higher velocity to get enough lift to match the weight of the plane.

I tried 5 times to attach the cl vs cd curves. I have them on a jpeg file but it gets rejected as not being a .jpeg file when I try to post it. What is wrong?

[soholingo]

Jack you are the man!!!! I appreciate the hand holding.. I now have something else to learn... profili...

what are polars, and how are they used?

j

[Jack Hyde]

I got the polar plots to post on a different site. See:
http://www.rcuniverse.com/forum/Polar_plots_for_MH30_foil/m_1367892/tm.htm