Firefly Slide Show

This is Jack B Hart's Legal(?) Ultralight Firefly Page

Notice to Visitors,

This page is getting out of hand. I started this page, in part, to help others who are building Kolb FireFly ultra lights, as a log of all the things that I have done to my FireFly, and as pay back to all of those who have helped me. When I started this I had no idea that it would become so long, but as time goes on, one keeps coming up with ideas on how to possibly make an incredible little plane just a little bit better and even more safe and fun to fly. I have added a section on flying techniques for people who wish to transition to a FireFly.

The changing of engines is an attempt to increase cruise range. The choice of the Victor 1 may not be the current best choice, but at the time I made the decision it appeared to me to be the best. I suspect the Victor 1 will not be the last engine on the FireFly. The Victor 1 was imported from a Canadian company, Speedwing, {2/28/15 - currently Simonini USA carries the engines and parts} is manufactured by Simonini in Italy. If you do not understand the importing process, you may want to read up a little about US Customs.

So if you are interested in reading and seeing what one old guy has gone through to fly, I welcome you to the rest of this web site. If you like some of the ideas, you are welcome to try them, but remember that with aircraft it is often better to proceed with small incremental change. That way any change that is made will probably make only a small difference in the way an aircraft flies, and this keeps the pleasure to a maximum and the surprise to a minimum. One of the objectives is to live to make another change and to fly again on another day.

Jack B. Hart FF004
Jackson, MO

Update - December 6, 2009

Soon after mounting the Victor 1+, I realized that both the Rotax 447 and the Victor 1+ produced more HP than required to comfortably fly the FireFly at 55 mphi. I started looking for a smaller and lighter engine. I picked the MZ 34. It is 70cc smaller in displacement than the Victor 1+ and does not use a tuned exhaust system. It is air cooled rather that liquid cooled, and so, it is a much lighter engine. When I purchased the engine, it was rated at 27 HP.

By bulkhead mounting the MZ 34 up side down, one can greatly reduce above the wing engine profile drag, and there is no need for a propeller extension, radiator and coolant, and a separate fuel pump. While retaining the electrical starting system and discarding the mechanical starting system, initial calculations indicated that 42 pounds could be removed from the FireFly empty weight. Also, at cruise speed (55 mphi) the engine will be operating much closer to the torque curve peak. This and a lower AOA at cruise (minus 42 pounds), should enable a cruise fuel flow rate close to 1.5 gph.

To enable MZ 34 air fuel mixture management, the Tillotson carburetor was modified so that the high and low speed jet control needles can be adjusted from the cockpit. Also, the atmospheric vent from below the control diaphragm was fitted with a tubing nipple, and the carburetor throat was drilled and positive and negative dynamic pressure port nipples were installed. These ports will be used to see if the Tillotson air fuel mixture can be effectively controlled by varying the pressure on the control diaphragm much the same way as the pressure was varied over the Bing float bowl on the Victor 1+. If so, one can save another half to one pound by not using the mechanical system on the high and low speed jet needles.

As Winter is just about here, development efforts will be slow. As things are completed I will post the results on this site.

Jack B. Hart FF004
Winchester, IN


Factory FF004 - Rotax 447 FF004 - Simonini FF004 - MZ 34
Wing Span 22 ft. <-same <-same <-same
Wing Chord 5.54 ft. 5.04 ft. 5.10 ft. <-same
Wing Area 122 sq. ft. 111 sq. ft. 112 sq. ft. <-same
Length 19' 6"(same folded) <-same <-same <-same
Height 69 in. (same folded) 70 in. 70 in. 63 in.
Folded Width       cannot fold
 At Wheels 57 in. 58 in. <-same <-same
 At Propeller 60 in. 60 in. 65 in. 10 in.
 Empty less than 254 lbs. 248 lbs.* 252 lbs.** 210 lbs.***
 Gross 500 lbs. <-same <-same <-same
Fuel Capacity 5 gal. <-same <-same <-same
Load Factors        
 Limit +4g, -2g      
 Ultimate +6g, -3g      
 Wing ->103-7 3.72 pd/sq ft 3.98 pd/sq ft <-same 3.57 pd/sq ft
 Never Exceed 80 mph <-same <-same <-same
  FAR 103.7 63 mph     57 mph
  103.7 Drag   12.1 <-same 11.0
  Actual 75 mph 74 mph(gps) 6400 rpm~` climb prop over 70 mph over 60 mph@
 Cruise 65 mph (70% power)      
 Minimum (no  mushing)   37 mph (gps)` 35 mph (gps)~`    
  FAR 103.7 27 mph     26.1 mph
  Clean 33 mph 34 mph(gps) +~`/ 31 mph    
  Flaperons 30 mph      
 Ground Effect  Flight   25 mphi~    
Engine Rotax 447 Rotax 447 436cc Simonini Victor 1+ 382cc Comp. Rad. Eng. Inc. MZ34 313cc
 Power 40 hp @ 6400 rpm 40 hp @ 6400 rpm 48 hp @ 6000 rpm 38 hp @ 5200 rpm 27 hp @ 6250 rpm
 Power Loading 11.4 pd/hp 11.2 pd/hp   15.2 pd/hp
 Gearbox or  Belt Ratio 2.58:1 2.58:1 2.76:1 2.34:1
Propeller IVO 60 in. IVO 60" 2 blades Powerfin, B, 65" 2 blades
9.5 degrees
IVO 54" 2 blades
Takeoff Distance 150 ft. or less <-same <-same <-same
Rate of Climb 1000 fpm 6400 rpm max
800-1000 fpm^~
6,000 rpm max
700-800 fpm~
Pilot Weight   200 lbs 200 lbs 200 lbs
Cruise Angle of Attack   climb prop
4 Degrees (6400 rpm)~
7 Degrees (5600 rpm)~
*Includes brakes on four inch wheels, nine inch chord ailerons, 
strobe lights, vortex generators, oil in B gear box, and cockpit 
adjustable trim for pitch and roll.

+Actual/Computed for 170 pound pilot.

~Vortex generators installed

^Summer - Winter with climb prop

`Altitude - 2000 ft. & average of up and down wind runs

**Includes brakes on four inch wheels, nine inch chord ailerons, 
vortex generators, 2.7 lbs of coolant, electric start, battery, 
cockpit adjustable radiator shutter and trim for pitch and 
roll, seat cushion, and fairings on wing struts, rear of fuselage, 
aileron torque tubes and push/pull tubes.

***Includes brakes on four inch wheels, nine inch chord ailerons, 
vortex generators,electric start, battery, cockpit adjustable air/fuel 
mixture control and trim for pitch and roll, seat cushion, and fairings 
on wing struts, aileron torque tubes and push/pull tubes. No propeller