“Micro” ultralight sailplane

The Micro is a concept for an all composite ultralight sailplane. At this stage it is truly a “blue sky” exercise, since I have neither the expertise or resources to complete such an ambitious project. It was inspired by existing ultralight sailplanes such as the LightHawk, and SparrowHawk.

This class of aircraft is designed to take advantage of the FAA’s Part 103 rules, which allow unlicensed operation and are exempt from normal FAA type certification requirements. Among other limitations, the empty weight must not exceed 70.4kg or 155lbs.

Having flown gliders briefly as a student pilot in the late 80s, I became acutely aware of the high cost of the hobby. Since then, I have hoped for a low cost alternative to the beautiful, but high priced European sailplanes. In addition to lower cost, ultralights offer the potential to work “microlift” or lift that is too weak to be exploited by traditional “heavy” gliders. This has been shown to be possible with aircraft such as the Carbon Dragon, SparrowHawk and others. Given that we have very few “booming” days up here in N. Calif., the low wing loading of the ultralights have even more appeal.

The structure would be carbon fiber prepreg and Nomex honeycomb cores, done in female molds. Though not shown, full span flaperons, like the LightHawk would be used, as well as spoilers. I believe retractable gear is possible without exceeding the weight target. Though apparently abandoned by the other production UL gliders, I like the idea of “bomb bay” doors for foot launch capability, though it’s hard to imagine self launching off a hill trying to support a 150lb glider while sprinting at top speed! A 15mph breeze would lighten the load by half though. Estimated specs follow.

Wing span

15m

49.2 ft

Wing area

9.29 sq m

100 sq ft

Airfoil

DAR_EX

 

Aspect ratio

24.2

 

Fuselage length

 6.1 m

 20 ft

Empty weight

68.1 kg

150 lbs

Single wing weight

16.34 kg

36 lbs

Max. takeoff weight

163.44 kg

360 lbs

Min. takeoff weight

113.5 kg

250 lbs

Maximum Payload

95.3 kg

210 lbs

Wing loading at MTOW

17.6 kg m^2

3.6 lbs/sq ft

Max. speed (VNE)

144.8 km/hr

90 mph

Maneuvering airspeed

88.5 km/hr

55 mph

L/D at maneuvering speed

25.4

 

Stall speed: 127kg, 280lb

41.8 km/hr

26 mph

Stall speed, MTOW

46.7 km/hr

29 mph

Best glide ratio

34.5 @ 56.3 km/hr

34.5 @ 35 mph

Min. sinking rate 127kg, 280lb gross

.37 m/sec @ 46.7 km/hr

73 fpm @ 29 mph

Design max. loading:

-7g/-7g

 

All disclaimers apply, the above are only WAGs at best, and wanton violations of the laws of physics at worst.

Wing Analysis Plus was used to design and tweak the airfoil. The foil has got a decent l/d, but a wicked and rather early stall. I can improve the stall behavior somewhat, but at the expense of the l/d needed to achieve reasonable performance at these low Reynolds numbers. I have gained a great deal of respect for the pros who do this for a living, particularly guys like Dr. Mark Drela, who tweaked  the LightHawk foils, and has worked on many pioneering projects such as the endurance record breaking MIT Daedalus human powered aircraft.

 

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2003 Dave Design