Best ultralight Biplane!!!!

HomeBuiltAirplanes.com

Help Support HomeBuiltAirplanes.com:

mstull

Well-Known Member
Joined
Jun 23, 2005
Messages
1,263
Location
West Texas
One of the hardest things about designing U/Ls is passing the stall speed limit. It is hard to make wings that big without having the plane get too heavy. Many manufacturers of kits, plans, or planes, ignore that limit, and commonly lie about the stall speed of their designs.

With smaller wings, the plane looks better, has a better roll rate, comes out lighter, and may even perform better. We get so used to manufacturers' lies, it is easy to start thinking the stall speed formulas in AC103-7 must be wrong. But they are quite accurate.

If you don't care about the stall speed limit, that's fine. A lot of people don't care, and just stay "under the radar". The FAA hasn't assigned manpower to enforce Part 103 operations anyway. And manufacturers will design and sell whatever people want to buy. But be aware that zippy little planes are not legal U/Ls in the USA.

Without flaps, it takes about 145 square feet of wing area to pass the stall speed limit on a monoplane. With flaps up to 50% of total span, 129 square feet. With flaps over 50% of span, 115 square feet. Those numbers vary a little with aircraft weight. I used 250# dry weight in these calculations.

Biplanes are inherently less efficient, and need about 20% more wing area to pass the stall speed limit, for a couple reasons. The wings' proximity to each other. And double the tip losses.
 

Dana

Super Moderator
Staff member
Joined
Apr 3, 2007
Messages
9,210
Location
CT, USA
Seems to me the weight limit is the big problem... or perhaps it's just the most obvious problem.

Biplanes are less efficient, but the AC103-7 calculations make no allowance (or rather, ignore) those effects. If the wing area / camber / flaps / weight meet the stall speed calculations in the AC, the aircraft is legal, regardless of whether it actually stalls that slow. Ditto for the max speed calculations.

The Stratos looks like a neat plane, but both the stall and the max speed fall well outside the 103 limits.

-Dana

If you don't grow up by age 35, you don't have to.
 

mstull

Well-Known Member
Joined
Jun 23, 2005
Messages
1,263
Location
West Texas
Actually, Dana, AC103-7,11.b says, and even underlines for emphasis:

b. The FAA realizes that it is possible to design an ultralight which, on paper, meets the requirements of 103.1, but in reality does not. However, the designers, manufacturers of the kits, and builders are not responsible to the FAA for meeting those requirements. Operators of ultralights should bear in mind that they are responsible for meeting 103.1 during each flight. The FAA will hold the operator of a given flight responsible if it is later determined that the ultralight did not meet the applicability for operations under Part 103. Be wary of any designs which are advertised as meeting the requirements for use as an ultralight vehicle, yet provide for performance or other design innovations which are not in concert with any element of 103.1...
 

Dana

Super Moderator
Staff member
Joined
Apr 3, 2007
Messages
9,210
Location
CT, USA
Right. But appendix 2 also says:

"The information contained in this appendix is intended to assist in a determination of an ultralight's ability to comply with Section 103.1(e)(2), a maximum power-off stall speed which does not exceed 24 knots. Computations made in accordance with the information provided may be accepted as satisfactory evidence of compliance. When using this information, no factors other than those provided here should be considered." (italics added)

-Dana

If you don't grow up by age 35, you don't have to.
 

fly_boy_bc

Well-Known Member
Joined
Aug 20, 2008
Messages
236
Location
Agssiz BC
Well, its ~172 lbs. empty weight might not be ultralight enough, nor the funny way its upper and lower wings are joined. :)
What are you talking about? The empty weight is 226 Kg. which is 498.244 lb

[FONT=Arial Cyr, Arial]Specifications[/FONT]

[FONT=Arial Cyr, Arial]Engine type[/FONT] [FONT=Arial Cyr, Arial]Rotax–503UL[/FONT] [FONT=Arial Cyr, Arial]Rotax–582UL[/FONT] [FONT=Arial Cyr, Arial]Rotax–912ULS[/FONT] [FONT=Arial Cyr, Arial]Engine power, hp[/FONT] [FONT=Arial Cyr, Arial]50[/FONT] [FONT=Arial Cyr, Arial]64,4[/FONT] [FONT=Arial Cyr, Arial]100[/FONT] [FONT=Arial Cyr, Arial]Max takeoff weight, kg[/FONT] [FONT=Arial Cyr, Arial]350[/FONT] [FONT=Arial Cyr, Arial]400[/FONT] [FONT=Arial Cyr, Arial]450[/FONT] [FONT=Arial Cyr, Arial]Empty weight, kg[/FONT] [FONT=Arial Cyr, Arial]226[/FONT] [FONT=Arial Cyr, Arial]248[/FONT] [FONT=Arial Cyr, Arial]277[/FONT] [FONT=Arial Cyr, Arial]Mass of fuel (in main tanks), kg[/FONT] [FONT=Arial Cyr, Arial]37[/FONT] [FONT=Arial Cyr, Arial]37[/FONT] [FONT=Arial Cyr, Arial]37[/FONT] [FONT=Arial Cyr, Arial]Maximal speed of horizontal flight, km/h[/FONT] [FONT=Arial Cyr, Arial]115[/FONT] [FONT=Arial Cyr, Arial]120[/FONT] [FONT=Arial Cyr, Arial]150[/FONT] [FONT=Arial Cyr, Arial]Cruising speed of flight, km/h[/FONT] [FONT=Arial Cyr, Arial]90...100[/FONT] [FONT=Arial Cyr, Arial]90...100[/FONT] [FONT=Arial Cyr, Arial]90...100[/FONT] [FONT=Arial Cyr, Arial]Take-off speed, km/h[/FONT] [FONT=Arial Cyr, Arial]60...65[/FONT] [FONT=Arial Cyr, Arial]65...70[/FONT] [FONT=Arial Cyr, Arial]65...70[/FONT] [FONT=Arial Cyr, Arial]Landing speed, km/h[/FONT] [FONT=Arial Cyr, Arial]60...65[/FONT] [FONT=Arial Cyr, Arial]65...70[/FONT] [FONT=Arial Cyr, Arial]65...70[/FONT] [FONT=Arial Cyr, Arial]Maximal rate-of-climb, m/sec[/FONT] [FONT=Arial Cyr, Arial]3.4...3.5[/FONT] [FONT=Arial Cyr, Arial]3.4...3.5[/FONT] [FONT=Arial Cyr, Arial]6.0...6.5[/FONT] [FONT=Arial Cyr, Arial]Take-off run, m[/FONT] [FONT=Arial Cyr, Arial]90[/FONT] [FONT=Arial Cyr, Arial]70[/FONT] [FONT=Arial Cyr, Arial]65[/FONT] [FONT=Arial Cyr, Arial]Landing run, m[/FONT] [FONT=Arial Cyr, Arial]85[/FONT] [FONT=Arial Cyr, Arial]95[/FONT] [FONT=Arial Cyr, Arial]95[/FONT] [FONT=Arial Cyr, Arial]Allowed speed of cross-wind at take-off, m/sec[/FONT] [FONT=Arial Cyr, Arial]6[/FONT] [FONT=Arial Cyr, Arial]6[/FONT] [FONT=Arial Cyr, Arial]6[/FONT] [FONT=Arial Cyr, Arial]Allowed speed of head wind at take-off and landing, m/sec[/FONT] [FONT=Arial Cyr, Arial]10[/FONT] [FONT=Arial Cyr, Arial]10[/FONT] [FONT=Arial Cyr, Arial]10[/FONT] [FONT=Arial Cyr, Arial]Allowed speed of tail wind at landing, m/sec[/FONT] [FONT=Arial Cyr, Arial]2[/FONT] [FONT=Arial Cyr, Arial]2[/FONT] [FONT=Arial Cyr, Arial]2[/FONT] [FONT=Arial Cyr, Arial]Service ceiling, m[/FONT] [FONT=Arial Cyr, Arial]3500[/FONT] [FONT=Arial Cyr, Arial]4000[/FONT] [FONT=Arial Cyr, Arial]4800[/FONT] [FONT=Arial Cyr, Arial]Duration of flight[/FONT] [FONT=Arial Cyr, Arial]2h. 35min.[/FONT] [FONT=Arial Cyr, Arial]2h. 35min.[/FONT] [FONT=Arial Cyr, Arial]3h. 07min.[/FONT] [FONT=Arial Cyr, Arial] Total wing area, sq. m[/FONT] [FONT=Arial Cyr, Arial]14,29[/FONT] [FONT=Arial Cyr, Arial]14,29[/FONT] [FONT=Arial Cyr, Arial]14,29[/FONT] [FONT=Arial Cyr, Arial]Upper wing span, m[/FONT] [FONT=Arial Cyr, Arial]8,11[/FONT] [FONT=Arial Cyr, Arial]8,11[/FONT] [FONT=Arial Cyr, Arial]8,11[/FONT] [FONT=Arial Cyr, Arial]Plane length, m[/FONT] [FONT=Arial Cyr, Arial]5,32[/FONT] [FONT=Arial Cyr, Arial]5,32[/FONT] [FONT=Arial Cyr, Arial]5,32[/FONT] [FONT=Arial Cyr, Arial]Parking height, m[/FONT] [FONT=Arial Cyr, Arial]2,25[/FONT] [FONT=Arial Cyr, Arial]2,25[/FONT] [FONT=Arial Cyr, Arial]2,25[/FONT]
 

bmcj

Well-Known Member
HBA Supporter
Joined
Apr 10, 2007
Messages
13,355
Location
Fresno, California
Thanks Fly Boy. I thought 172 sounded a bit too low, but I did not have the numbers to make an argument with.

Bruce :)
 

Latest posts

Top