I have been looking at a host of designs on the Aerofred.com and been wondering to construct a few. Now, when I go on make a CAD drawing, I run into a problem of Aerfoil selection.

Request advise....

1.     What is the best thickness of airfoil to be used for a stunt Control Line model. Will 16 to 18% thickness be ok or we need more.

2.     What would be the ideal airfoil section to be used.... I been using NACA 16 to NACA 18 as of now. Any changes.

3.     What is the most suited wingspan for good stable stunt flying. Currently I use the 42 inch Shoestring on a 50 ft line (using a 3.2cc Disel engine Equivalent to .19 Cu in Glow).  Should it be better to go bigger on span, or maybe a .25 to .35 Cu in engine.... In that case what would be the most suited line length.

Regards

1. If your airplane has flaps, I suggest 18 to 21% including flaps.

2. For an airfoil without flaps, I have had success with combat planes flying at Reynolds numbers around 600,000 with an NACA 0016.5 with maximum thickness linearly squished forward from 30% chord to 25% chord.  For an airfoil with flaps, good airfoils include the Impact's, about 21% thick at the mean aerodynamic chord, and the Max Bee's, about 18% at the mean aerodynamic chord.  I can send you coordinates for those airfoils.  You might try using XFOIL or JavaFoil to design your own, but I have had difficulty with those programs with the sort of flaps we use for stunt planes. 

3. Most competitive stunt planes have wingspans of about 150 cm and fly on 20 to 21 meter lines.   

Quote from: shobhit17 on March 02, 2026, 09:07:46 PMI have been looking at a host of designs on the Aerofred.com and been wondering to construct a few. Now, when I go on make a CAD drawing, I run into a problem of Aerfoil selection.

Request advise....
 Currently I use the 42 inch Shoestring on a 50 ft line (using a 3.2cc Disel engine Equivalent to .19 Cu in Glow).  Should it be better to go bigger on span, or maybe a .25 to .35 Cu in engine.... In that case what would be the most suited line length.

Regards

IMO a typical 19-size sport glow engine is a bit small for a CG Shoestring unless built very light. I had a Shoestring w/ an OS 25 LA and a CG Cosmic Wind w/ McCoy 35 Redhead. Both are the same basic size as a Shoestring and flew well. But I prefer the 25 LA (or 25 FP ABN) on a typical 40" wing stunter just because they are so user friendly. And I flew both of my models on 60' Spectra lines.

Colin

Quote from: Colin McRae on March 03, 2026, 09:36:00 AMIMO a typical 19-size sport glow engine is a bit small for a CG Shoestring unless built very light. I had a Shoestring w/ an OS 25 LA and a CG Cosmic Wind w/ McCoy 35 Redhead. Both are the same basic size as a Shoestring and flew well. But I prefer the 25 LA (or 25 FP ABN) on a typical 40" wing stunter just because they are so user friendly. And I flew both of my models on 60' Spectra lines.

Colin

Thanks a lot Colin..

Well here in my country the engines aren't relatively cheap. The best and easily available is the 3.2cc Sharma Engine which is the most popular here in India. manufactured by M/S Shamra Model and Aero Engines for the last about 45 years.  Using a smaller line of 50 inches probably gets me the required line tension.

Buy I understand a longer line gives better space to manoeuvre and do the aeros better.  Thanks for your advice... will try and get into a 25LA and a 60 ft line for my shoestring.

Could you also please advice on the suitable aerfoil to be used....

Regards
Shobhit

I was not sure where you lived. If you can get your hands on one of these engines they all have about the same power output if they are in good operating condition.

OS 25 LA
OS 25 FP (original version)
OS 25 FP (ABN)

The original OS 25 FP engine used an iron piston and steel cylinder liner. Recommended to run 25% oil fuel. The later more modern ABN version (aluminum piston w/ nickel plated brass liner) can use 20% oil. And I typically run 10% nitro fuel.

On these engines I run an APC 9-4 sport prop at around 12,000 rpm on the ground for best performance.

Best of luck

Colin

Quote from: Howard Rush on March 03, 2026, 01:31:25 AM1. If your airplane has flaps, I suggest 18 to 21% including flaps.

2. For an airfoil without flaps, I have had success with combat planes flying at Reynolds numbers around 600,000 with an NACA 0016.5 with maximum thickness linearly squished forward from 30% chord to 25% chord.  For an airfoil with flaps, good airfoils include the Impact's, about 21% thick at the mean aerodynamic chord, and the Max Bee's, about 18% at the mean aerodynamic chord.  I can send you coordinates for those airfoils.  You might try using XFOIL or JavaFoil to design your own, but I have had difficulty with those programs with the sort of flaps we use for stunt planes.  Though I am not too comfortable using new apps or programmes... but will surely give it my best try.

3. Most competitive stunt planes have wingspans of about 150 cm and fly on 20 to 21 meter lines.   

Thanks Horward..... That is going to be very useful to me as I am generally concentrating on mostly 16% aerfoils....
Will request you to send me the coordinates of your aerfoils..... Will also try to use the sites you have mentioned for the aerfoils....

Regards

Quote from: Colin McRae on March 03, 2026, 10:53:12 AMI was not sure where you lived. If you can get your hands on one of these engines they all have about the same power output if they are in good operating condition.

OS 25 LA
OS 25 FP (original version)
OS 25 FP (ABN)

The original OS 25 FP engine used an iron piston and steel cylinder liner. Recommended to run 25% oil fuel. The later more modern ABN version (aluminum piston w/ nickel plated brass liner) can use 20% oil. And I typically run 10% nitro fuel.

On these engines I run an APC 9-4 sport prop at around 12,000 rpm on the ground for best performance.

Best of luck

Colin

Thanks a lot Colin.

Well I have the indian distributer of OS engines in my city and we are good friends. Will look to get the engine you have proposed. I have been using the 9x6 prop mostly but will now use the 9x4 prop. 

Yes I live in the City of Jodhpur (Rajasthan) in India,