patrickrio
Well-Known Member
- Joined
- Aug 15, 2020
- Messages
- 365
The dramatic drop in carbon fiber and vacuum infusion costs are exiting catalysts already leading to some exciting new work here by all of you… but when combined with home availability of cheap computers and software that can do advanced structural analysis and computational fluid dynamics on a home budget, as well as cheap DIY 3D printing and DIY CNC tech; Rapid prototyping AND EVEN DESTRUCTION TESTING of complex carbon fiber airplane parts is now possible for us working stiffs.
For USA legal part 103 UltraLight aircraft (sorry, vehicles…), it is now possible to design AND TEST a reasonably priced carbon fiber airplane that is just as fun to fly as past ultralights, but also has cross country abilities due to slow fuel burn at sustained maximum ultralight speed of 55 Knots CAS.
There are two FAA ultralight special rulings that are going to be very important for these designs I think: #1 was, I believe, a FAA ruling in response to Windward SparrowHawk. The FAA ruled that unpowered gliders that weigh under 70KG/155lbs do not have to meet the stall requirements of 24 Knots nor a flight speed of 55 Knots. It was argued that there really was no level flight speed for an non motorized glider (true…) and that 24 Knots stall actually reduced the safety of gliders. The FAA apparently agreed and removed the stall speed rule as well as confirmed that there was no upper speed limit of any kind on an unpowered ultralight glider that meets weight limits. #2 is the FAA ruling that motorized 103 ultralights that have electronic limiting of level flight speed via reduction of engine or motor power are legal AS LONG AS this setting cannot be increased from within the cockpit during flight. Descent speed can exceed 55 Knots, but having the motor assist with the descent speed was not addressed; It might be legal to make high speed descents with a lot of power assist, but might also be pushing luck. High speed gliding descents are clearly allowed.
The minimum reading of the rules mean that a highly efficient powered ultralight aircraft could climb to altitude at speeds approaching 55 Knots CAS, Fly level at 55 knots CAS with electronic speed limiting of engine power which can be quite a bit faster than 55 knots actual speed at higher altitudes, and then descend at faster than 55 knots CAS if capable of high speed glides. The low stall speed requirement would mean that the best performing aircraft would need to be built very light to reduce stall speed (probably lighter than the 115kg/254lbs part 103 limit…), and might need more complicated flaps. OR in a best case, a motorglider built extremely light might be able to request a FAA ruling to change stall speed for the whole motorglider class like Sparrowhawk did for unpowered gliders.
The design I am currently contemplating would be custom sized for each pilot or pilot range. The wings would be continuously varying airfoil shapes optimized to the reynolds number at each location in span, as is currently done in many gliders including sparrowhawk. The outer wing airfoils would thus be the same for all pilot weights, with the wing root section lengthening or shortening with pilot weight. You would just add indexed sections to the mold with the appropriate for span location airfoils for heavier pilots. The changeable inner sections would also have the inner flap hinge and flaps would also lengthen with increasing pilot weight as a result. Female wing molds would be CNC cut for accuracy and low labor costs.
The pilot “pod” would also change size with different pilot sizes. Female molds for shell and possibly inner frame, seat would be milled. Also safety foam/honeycomb crush zones would be cnc milled as necessary for fitting curves perfectly.
Tail feathers would also have female molds CNC milled. Flat carbon fiber panels could be laser cut for wing ribs, and bulkheads and such. Pultrusion tubes and slats would be incorporated.
The key to this customization is construction of a cheap router CNC for foam molds (or maybe MDF??) I have built several 3D printers and a laser cutter, so I think building a wing and pod sized, accurate foam CNC on the cheap is very doable. Maybe as cheap as 500 dollars. It might also be useful to build a CNC flat table hot wire foam cutter to reduce the foam to be cut by CNC Bit Cutter.
For initial design direction, I think a very good place to start is SparrowHawk. Specifications we want to look at are as follows:
Wingspan 36ft/11m
Wing Area 70sq ft/6.5m^2
Empty weight 155lb/70kg
Gross Weight 415lb/188kg Max
Max pilot weight 260lb/118kg
Stall Speed 32kn/37mph/59kmh
Never Exceed Speed 123kn/142mph/228kmh
G limits at 415lb +5.5/-4
Maximum Glide 36:1 at 50kn/58mph/93kmh
Min Sink 119ft/min||0.5m/s at 38kn/44mph/70kmh
So the first thing is that the stall speed is 6knots too high for motorized ultralights. Not important if you can get a favorable FAA ruling. Otherwise, you need to lose gross weight, increase flap size or complexity for more stall lift, or increase wing size from 70sq ft. note though that the L/D of the wing must be very efficient compared to most wing designs, as it is lifting 415lb with only 70sq ft of area. I think this is because of a well designed, continuously variable airfoil. The advantage of carbon design….
How much horsepower would SparrowHawk need to climb at 500ft/min? Min sink is about 120ft/min… So converting 620ft/min to ft/sec = 10.3333 ft/sec for 415 lb equals 4288.3333/550=7.8 Horsepower needed for a 500ft/min climb at sea level at 32knots ground speed. Amazing. Clearly our design will have increased drag due to changes necessary to add a propeller, and also add tri gear/conventional gear. It also needs to add weight for engine/gas or motor/batteries. Sparrowhawk is also capable of some pretty speedy descents. Amazing that this is an ultralight like a breezy or something. Completely different speed class. Also note, 500ft/min at this low speed is a CRAZY climb angle.
Since lightness improves the ability to meet the stall speed requirements, how light can we go? We would want a light motor that sips fuel so we might be able to reduce fuel weight too… and maybe we would do our initial testing on a plane sized for a light pilot to reduce initial design costs and complexity. Let’s do the initial design for a 150lb pilot then. The lightest motor in the 10-15 HP class required that I have found is the Raket 120 Aero single cylinder:
Raket 120 Aero ES-RD Ratio 1:3
With Battery, Exhaust, and propeller it weighs about 11kg/24lbs for about 14 HP. 5 gallons of gas would weigh about 35lbs. Min weight of 150lb Pilot, Engine and gas is about 210 lbs. Maybe less if we get fuel consumption down and can carry less gas.
How light is the limit? The E-12n is the lightest motorized ultralight design I have seen… Data on it at nestofdragons.net….supposedly 45kg/100lbs empty and 140kg/310lbs gross weight with 1.5 gallons of fuel and a 200lb pilot. Airframe without an engine and propeller is about 34kg/75lbs which is crazy light. With our pilot of 150lbs and 1.5 gallons gas, this plane would weigh 260 lbs. Wonder if this is even possible…. I wonder if there is some exaggeration here?
E-12 - Nest of Dragons
But we probably want a 4 stroke engine, so what is the lightest option there? I also like Fuel Injection for reliability and efficiency. Here is a new, lightweight EFI single piston:
ECH440 | Command PRO EFI | KOHLER
Supposedly it can be stripped to about 35 lbs. Then add a propeller for about 40lbs at 14 hp. But it is only a single piston, and the B&S small block v twins are really too much horsepower for the application but if necessary they can be stripped to 45lbs. There are supposed to be several other brands about to release single cylinder EFI engines too, so we might get some lower weights from one of the manufacturers.
The only EFI twins that seem to be almost the right size are the new 20hp EFI outboards from Tohatsu, Mercury and Suzuki. They are inline twin cylinder engines. Engine block is shared with 9.9hp and 15hp sizes. Should be able to strip the power heads on those to around 35lbs but you need to add a small radiator and water pump because they are water cooled. Also need a redrive of some sort.
Suzuki Marine - Product Lines - Outboard Motors - Products - DF20A_EFI - 2012 - DF20A_EFI
MFS20 | Portable | TOHATSU North America
FourStroke 2.5-25hp | Mercury Marine
To be honest, I am not seeing 10-15hp 4 stroke EFI twins that are in the right weight range. Maybe the new industrial EFI singles coming out will work.
In any case, I think that the rapid prototype phase will be cheaper and safer to do by creating full scale and weight electric drones, with about 20-25 min flight time on the batteries. The motors could be attached to simple belt redrives. Would need about a 7-10KW motor and enough inexpensive lipo batteries sufficient for 20-25 minutes. Also need a few powerful r/c servos and transmitter/receiver. And also a FAA R/D exemption for drones over 55lbs….Not sure how hard those are to get since the rule is newish, but doing a full license, n number registration and paying for ADS-B for registered drones above 55lbs would really not be cost effective. The alternative is putting someones life on the line during rapid prototyping which is not a good idea. There must be a way to do this without too much expense.
OK, so that is the first round of thinking on this. What do you think?
For USA legal part 103 UltraLight aircraft (sorry, vehicles…), it is now possible to design AND TEST a reasonably priced carbon fiber airplane that is just as fun to fly as past ultralights, but also has cross country abilities due to slow fuel burn at sustained maximum ultralight speed of 55 Knots CAS.
There are two FAA ultralight special rulings that are going to be very important for these designs I think: #1 was, I believe, a FAA ruling in response to Windward SparrowHawk. The FAA ruled that unpowered gliders that weigh under 70KG/155lbs do not have to meet the stall requirements of 24 Knots nor a flight speed of 55 Knots. It was argued that there really was no level flight speed for an non motorized glider (true…) and that 24 Knots stall actually reduced the safety of gliders. The FAA apparently agreed and removed the stall speed rule as well as confirmed that there was no upper speed limit of any kind on an unpowered ultralight glider that meets weight limits. #2 is the FAA ruling that motorized 103 ultralights that have electronic limiting of level flight speed via reduction of engine or motor power are legal AS LONG AS this setting cannot be increased from within the cockpit during flight. Descent speed can exceed 55 Knots, but having the motor assist with the descent speed was not addressed; It might be legal to make high speed descents with a lot of power assist, but might also be pushing luck. High speed gliding descents are clearly allowed.
The minimum reading of the rules mean that a highly efficient powered ultralight aircraft could climb to altitude at speeds approaching 55 Knots CAS, Fly level at 55 knots CAS with electronic speed limiting of engine power which can be quite a bit faster than 55 knots actual speed at higher altitudes, and then descend at faster than 55 knots CAS if capable of high speed glides. The low stall speed requirement would mean that the best performing aircraft would need to be built very light to reduce stall speed (probably lighter than the 115kg/254lbs part 103 limit…), and might need more complicated flaps. OR in a best case, a motorglider built extremely light might be able to request a FAA ruling to change stall speed for the whole motorglider class like Sparrowhawk did for unpowered gliders.
The design I am currently contemplating would be custom sized for each pilot or pilot range. The wings would be continuously varying airfoil shapes optimized to the reynolds number at each location in span, as is currently done in many gliders including sparrowhawk. The outer wing airfoils would thus be the same for all pilot weights, with the wing root section lengthening or shortening with pilot weight. You would just add indexed sections to the mold with the appropriate for span location airfoils for heavier pilots. The changeable inner sections would also have the inner flap hinge and flaps would also lengthen with increasing pilot weight as a result. Female wing molds would be CNC cut for accuracy and low labor costs.
The pilot “pod” would also change size with different pilot sizes. Female molds for shell and possibly inner frame, seat would be milled. Also safety foam/honeycomb crush zones would be cnc milled as necessary for fitting curves perfectly.
Tail feathers would also have female molds CNC milled. Flat carbon fiber panels could be laser cut for wing ribs, and bulkheads and such. Pultrusion tubes and slats would be incorporated.
The key to this customization is construction of a cheap router CNC for foam molds (or maybe MDF??) I have built several 3D printers and a laser cutter, so I think building a wing and pod sized, accurate foam CNC on the cheap is very doable. Maybe as cheap as 500 dollars. It might also be useful to build a CNC flat table hot wire foam cutter to reduce the foam to be cut by CNC Bit Cutter.
For initial design direction, I think a very good place to start is SparrowHawk. Specifications we want to look at are as follows:
Wingspan 36ft/11m
Wing Area 70sq ft/6.5m^2
Empty weight 155lb/70kg
Gross Weight 415lb/188kg Max
Max pilot weight 260lb/118kg
Stall Speed 32kn/37mph/59kmh
Never Exceed Speed 123kn/142mph/228kmh
G limits at 415lb +5.5/-4
Maximum Glide 36:1 at 50kn/58mph/93kmh
Min Sink 119ft/min||0.5m/s at 38kn/44mph/70kmh
So the first thing is that the stall speed is 6knots too high for motorized ultralights. Not important if you can get a favorable FAA ruling. Otherwise, you need to lose gross weight, increase flap size or complexity for more stall lift, or increase wing size from 70sq ft. note though that the L/D of the wing must be very efficient compared to most wing designs, as it is lifting 415lb with only 70sq ft of area. I think this is because of a well designed, continuously variable airfoil. The advantage of carbon design….
How much horsepower would SparrowHawk need to climb at 500ft/min? Min sink is about 120ft/min… So converting 620ft/min to ft/sec = 10.3333 ft/sec for 415 lb equals 4288.3333/550=7.8 Horsepower needed for a 500ft/min climb at sea level at 32knots ground speed. Amazing. Clearly our design will have increased drag due to changes necessary to add a propeller, and also add tri gear/conventional gear. It also needs to add weight for engine/gas or motor/batteries. Sparrowhawk is also capable of some pretty speedy descents. Amazing that this is an ultralight like a breezy or something. Completely different speed class. Also note, 500ft/min at this low speed is a CRAZY climb angle.
Since lightness improves the ability to meet the stall speed requirements, how light can we go? We would want a light motor that sips fuel so we might be able to reduce fuel weight too… and maybe we would do our initial testing on a plane sized for a light pilot to reduce initial design costs and complexity. Let’s do the initial design for a 150lb pilot then. The lightest motor in the 10-15 HP class required that I have found is the Raket 120 Aero single cylinder:
Raket 120 Aero ES-RD Ratio 1:3
With Battery, Exhaust, and propeller it weighs about 11kg/24lbs for about 14 HP. 5 gallons of gas would weigh about 35lbs. Min weight of 150lb Pilot, Engine and gas is about 210 lbs. Maybe less if we get fuel consumption down and can carry less gas.
How light is the limit? The E-12n is the lightest motorized ultralight design I have seen… Data on it at nestofdragons.net….supposedly 45kg/100lbs empty and 140kg/310lbs gross weight with 1.5 gallons of fuel and a 200lb pilot. Airframe without an engine and propeller is about 34kg/75lbs which is crazy light. With our pilot of 150lbs and 1.5 gallons gas, this plane would weigh 260 lbs. Wonder if this is even possible…. I wonder if there is some exaggeration here?
E-12 - Nest of Dragons
But we probably want a 4 stroke engine, so what is the lightest option there? I also like Fuel Injection for reliability and efficiency. Here is a new, lightweight EFI single piston:
ECH440 | Command PRO EFI | KOHLER
Supposedly it can be stripped to about 35 lbs. Then add a propeller for about 40lbs at 14 hp. But it is only a single piston, and the B&S small block v twins are really too much horsepower for the application but if necessary they can be stripped to 45lbs. There are supposed to be several other brands about to release single cylinder EFI engines too, so we might get some lower weights from one of the manufacturers.
The only EFI twins that seem to be almost the right size are the new 20hp EFI outboards from Tohatsu, Mercury and Suzuki. They are inline twin cylinder engines. Engine block is shared with 9.9hp and 15hp sizes. Should be able to strip the power heads on those to around 35lbs but you need to add a small radiator and water pump because they are water cooled. Also need a redrive of some sort.
Suzuki Marine - Product Lines - Outboard Motors - Products - DF20A_EFI - 2012 - DF20A_EFI
MFS20 | Portable | TOHATSU North America
FourStroke 2.5-25hp | Mercury Marine
To be honest, I am not seeing 10-15hp 4 stroke EFI twins that are in the right weight range. Maybe the new industrial EFI singles coming out will work.
In any case, I think that the rapid prototype phase will be cheaper and safer to do by creating full scale and weight electric drones, with about 20-25 min flight time on the batteries. The motors could be attached to simple belt redrives. Would need about a 7-10KW motor and enough inexpensive lipo batteries sufficient for 20-25 minutes. Also need a few powerful r/c servos and transmitter/receiver. And also a FAA R/D exemption for drones over 55lbs….Not sure how hard those are to get since the rule is newish, but doing a full license, n number registration and paying for ADS-B for registered drones above 55lbs would really not be cost effective. The alternative is putting someones life on the line during rapid prototyping which is not a good idea. There must be a way to do this without too much expense.
OK, so that is the first round of thinking on this. What do you think?
