Airfoil choice

[Antonia]

Good evening All,
After a bit of constructive advice please. I have a third scale composite wing project coming together in my head for a fuselage that came my way. The fuselage has a fillet that is for a modified Pflug Dirk DS airfoil that I can't find any co-ordinates for, but with a maximum of 2mm up and 2mm down flap movement for the full speed range would suggest a very critical airfoil to my mind, so...

I've been playing around with a few airfoils that would fit into the fillet with minimal blending at the root, my list is-

MH32 thickened at the root to 12.4% at 258mm chord then thinning down to the standard 8.7% at the first trapezoidal break and continuing at that standard thickness to the tip at 92mm chord through several trapezoidal changes, the half wing area span is 3.688 metres.

Second is a HQW-2.5/12 at the root thinning down to 11% at first trapezoidal break, then thinning down to 10% at the second trapezoidal 1.6 metres out, again the with the same thickness to the 92mm tip chord.

I did think with the HQ section to go to a HQW-3/10 from the last trapezoidal to the tip which is 334mm long, for the slower thermaling turning end of the speed envelope.

The third and last was to copy the sections detailed in Dr. Helmut Quabeck website for the HKM AS33 - http://www.hq-modellflug.de/as_33-hkm.htm which is a similar wing platform to my project but 400mm less span.

Your thoughts please, thanks Antonia

[john greenfield]

Hi Antonia. Happy Christmas to you and Mel.

Before we can comment on aerofoil choice we need a bit more info as to how you intend to fly the model. do you want a floaty thermal machine or a high speed rocket ship?

AEB

[Barry_Cole]

Hi Antonia. Happy Christmas to you and Mel.

Before we can comment on aerofoil choice we need a bit more info as to how you intend to fly the model. do you want a floaty thermal machine or a high speed rocket ship?

AEB

Knowing Antonia she will want both.....

BC

[Antonia]

Thanks Barry

John, not a high speed rocket ship for sure, think GPS able to cross sink at a reasonable speed if needed, the main spar is calculated to 55 m/s - (123 mph) as a max speed, at a weight of 160N (16.3 Kg) with a bit in reserve. To be able to bleed the speed back to climb well in thermals without being too prone to tip stalls, somewhat like my Hmodel ASH 25, I think it uses the HQW 2.5 airfoil, but I could be wrong.

[LarsWikstrom]

Hi Antonia, My knowledge of profiles is low; however, I like the characteristics of Ritz2; the profile of the classic Alpina.
Ritz2 is great for thermals and flying slow while also performing very well at speed when you use ballast as the sink rate then is almost the same. How it react to flaps, I outside my knowledge.
Lars

[john greenfield]

Hi Antonia

My choice would be to go with the HQW-2.5 series.

AEB

[Antonia]

Thank you for your thoughts Lars and John.
John, what are your thoughts on changing the airfoil to HQW3/10 for the last trapezoidal? I’ve attached a close up image to show platform at the end of the wing to give a better idea of wing tip.

[LarsWikstrom]

What is the effect of moving it closer to the leading edge of I may ask?

[john greenfield]

Antonia

To be honest at the very small chords you have at the wingtip the difference in the aerofoil performance is so minimal that changing section will not really have any effect and may make the build harder..

AEB

[roo Hawkins]

Hi I used a hq 2.5 on my 7 meter ash can not remember what thickness but can have a look at my templates if you need to know . I used a thiner hq on the last part of the wing with no washout.