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Roberts Engineering
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795 Kuykendall Road, Albertville, AL 35951
Telephone 256-891-1613
See the ROOTES BLOWER animation link below
Three inch TURBINAIR TRUFOIL fan with twelve NACA6713 airfoil blades mounted on thrust test fixture.
A new method of staging the blank was used to rough and finish a turbofan with a NACA 6713 airfoil. The new method cuts the blade with the proper airfoil from tip to root with the proper twist based on the desired pitch of the turbofan. The new turbofan is still 3 Inches in diameter. Its pitch is 6 Inches. This size has to do with the size of the radio controlled boat in which I intend to mount the turbofan. Diameters and pitches are limited only by the machine in which the turbofan blades are cut. The number of blades is reduced from eighteen to twelve.
The 3 inch fan was tested on a rig especially made to obtain thrust measurements. At 16300 rpm the turbo fan produces 9 oz of thrust. This compares to Great Planes' turbo fan of 8.5 oz at 29000 rpm. This fan produces 12 oz at 19000 rpm.
The NACA6713 airfoil compares to the LA203 as having high lift capability. The Eppler 471 has a much thinner section. If the Clark Y has a lift factor of one then the LA203 has a lift factor of seven. The 6713 falls into the same lift category as the LA203.
The next step is to mount the fan in a nacelle to see if there is any improvement in thrust.
Fan module ready to assemble into Nacelle
The aluminum fan rides on ball bearings mounted inside the stationary blade unit. The drive shaft is extended from the stationary side as seen on the left in the photo. The inlet spinner has a NACA6713 airfoil profile. The exit side matches the Nacelle choke profile. The Nacelle is now made and is shown in the photo below with the strut and fan mounted..
Turbofan mounted in nacelle as viewed from the drive end.
10x4.7 TRUFOIL TURBINAIR propeller.
I have an Electrifly BLT R/C training plane that has an APC 10x4.7 plastic propeller. Using the same machining technology that I used on the turbofan I made the propeller as shown in the photo. The APC propeller produces 4oz of static thrust at 3000rpm. The Roberts propeller produces 6oz at the same rpm. The propeller is cut from ash wood and is coated with cyanoacrylate for strength. I tested the propeller at 6000rpm and got a thrust of 24oz. The blade airfoil is a NACA 6713 and has the proper helix based on the 4.7 pitch from tip to root. The trailing edge is slightly shaped for style. The propeller is mounted in pusher mode and rotates CW as seen. The root form has been increased in thickness for additional strength.
20x6 TRUFOIL TURBINAIR Propeller
The 20dia x 6in pitch TRUFOIL propeller is made with a NACA6713 airfoil from tip to root with the proper helix angle at all diameters. The root form at the hub has been thickened for strength. Made from ash wood and coated with cyanoacrylate. This propeller has been tested against a commercial 22 in dia x 8 in pitch. 22 x 8 at 6200 rpm produced 16 lb of thrust. 20 x 6 Trufoil propeller produced 16 lb of thrust at 5700 rpm.
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| Revised 07/13/08 |
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