Can a SkyPup break the FAR103 constrained distance without refueling/landing record by flying an electric motor?

Homebuilt Aircraft & Kit Plane Forum

Help Support Homebuilt Aircraft & Kit Plane Forum:

Vigilant1

Well-Known Member
Lifetime Supporter
Joined
Jan 24, 2011
Messages
6,225
Location
US
We can also calculate when an airplane with the efficiency of Archaeopteryx has a 4 hour autonomy. Since it is basically capable of flying at max FAR103 speed this represents the limits of usefulness for an out and back flight distance of 2 hours each way without recharge and about 110 miles distance without using altitude and winds at differing altitudes to affect the trip.

It is probably right about 10kwh of battery. The minimal 12.00 Hamburger machine. (10 dollar hamburger with 2 dollars of electricity at 20 cents a kwh)
Better re-price that burger. If we spend about $12k to get that 10kwh battery (Pipistrel's price) and we get 500 cycles out of it (midrange of Pipistrel's 300-700 cycle estimate), the battery depletion cost for each trip is $24. Maybe you'll get more cycles at this low C rate, we can only hope.

Or, just burn 1 gal of gasoline ($3) for the same amount of mechanical energy at the prop.
 

trimtab

Well-Known Member
Joined
Apr 30, 2014
Messages
189
Location
rocky mountains, rocky, usa
The max gross weight is not regulated by Part 103. Just the empty weight. The 5gal fuel regulation is meaningless, and would have to suffer some sort of jaw dropping arbitrary "interpretation" the FAA is so fond of these days. So what you are left with is some sort of light airframe, including the batteries in the empty weight per the regs that were written in another epoch.

Nonetheless, a 6kW electric could sustain a 12:1 aircraft with a 70% efficient fixed pitch prop at 35 mph IAS with a flight weight of 550 lbs up to around 9k density altitude. The thrust of course is about 50lbs at sea level, goes down with altitude, naturally. The prop diameter required for the thrust required is quite large if one wants to limit the power to 6kw. So limiting the diameter to about 50" requires about 21-22 hp at 35-40mph.

Power assisted hang gliders fly at around 8:1 to 10:1. Gross weight was in the 270 lb range. Flight speeds under power were around 27mph. Using the same math, this would require around 3kW to sustain, which seems low. Nonetheless, I flew at a weight of 360 lbs with a 9kW@sea level engine at 8k' DA several times, and the math was spot on to predict a climb rate of 180-200 fpm at 8k' launch at ~24 mph IAS.

So the math is there at least.
 

Vigilant1

Well-Known Member
Lifetime Supporter
Joined
Jan 24, 2011
Messages
6,225
Location
US
The max gross weight is not regulated by Part 103. Just the empty weight. The 5gal fuel regulation is meaningless, and would have to suffer some sort of jaw dropping arbitrary "interpretation" the FAA is so fond of these days. So what you are left with is some sort of light airframe, including the batteries in the empty weight per the regs that were written in another epoch.

Nonetheless, a 6kW electric could sustain a 12:1 aircraft with a 70% efficient fixed pitch prop at 35 mph IAS with a flight weight of 550 lbs up to around 9k density altitude. The thrust of course is about 50lbs at sea level, goes down with altitude, naturally. The prop diameter required for the thrust required is quite large if one wants to limit the power to 6kw. So limiting the diameter to about 50" requires about 21-22 hp at 35-40mph.

Power assisted hang gliders fly at around 8:1 to 10:1. Gross weight was in the 270 lb range. Flight speeds under power were around 27mph. Using the same math, this would require around 3kW to sustain, which seems low. Nonetheless, I flew at a weight of 360 lbs with a 9kW@sea level engine at 8k' DA several times, and the math was spot on to predict a climb rate of 180-200 fpm at 8k' launch at ~24 mph IAS.

So the math is there at least.
The math is there for instantaneous flight.
Given that optimistic power requirement (6000kw = 8 HP), what does our range work out to? Each hour of flight requires approx 73 lbs of batteries (Pipistrel kwh/lb) if we burn them down to 0% DoD (they won't last long if we do that).
 

patrickrio

Well-Known Member
Joined
Aug 15, 2020
Messages
278
Can it (400 miles) be done on pure electric under part 103?
454 pound part 103 @ 28:1 L/D (probably possible with a custom airframe) = 17 lbs of thrust (using my 4/1 rule of thumb) = ~3000 W. This is well within the model motor range so...........

Based on a quick run through some online model calculators:
30 Inch prop* yields about 70% efficiency at 60 MPH - selected as the best design L/D because it is just under the part 103 limit. Thus we need a 4.2Kw motor.
4.2 Kw @ 95% system efficiency = 4.4 Kw of battery.
4.4Kw x 6.6 hours = 29.5 KwHr for the task. This doesn't include any climb energy or assistance from thermals.
SWAG ... cut the power needed in half = 15ish KwHr of battery? IF that is actually enough then the battery pack, using the 8#/KwHr example ends up in the 120 pound range.

454 gross weight (AC 103-7 standard plane) - 120 battery - 96# jockey that can fly an ultralight = 238 pounds for plane and power system (minus battery weight).

MY conclusion:
It looks like it should be possible - but not easy.

* Picked based on "feel" from previous calculations in this speed/power range. Lots of variables here with electric motors and reduction units.
Standard plane would be 254 plus 170lb pilot = 424lbs standard weight for electric per 103-7(no gasoline, battery weight doesn't count as fuel per rulings)

Lightest existing airframes with a suitable L/D above 25/1 I have found are: Haig Minibat (probably too dangerous and none available), Haig American Eaglet (more available, less dangerous but still dangerous), Archytaeopteryx (lightest safe airframe I have found at 119lbs without all power parts) Swift (also light and safe), Gekon (heavier by 30lbs but very high L/D speed), Bosch 1Comet (looks like it might end up with best L/D at highest speed with the lowest weight of bunch). All of these have better L/D at higher speed than the Mitchell Wing with lower airframe weight but are all very expensive. The more modern ones should all fly better and be safer.

The limit of weight appears to be right around 119lbs for 135 lbs available for motor and battery. So your max battery weight of 120lbs is probably a realistic max battery weight in an FAR103 ultralight under the most ideal circumstances... that's the limit.

There are battery packs available for purchase currently that achieve 330Wh/kg or 150Wh/lb when sized to 120lbs with all necessary electronics included. So that means 16kWh for 120lbs. The OpenPPG battery packs above can fit 14.5kWh in 120lbs, also currently available. Supposedly there are all up packs that will reach 400Wh/kg (nearly 20kWh in a 120lb battery pack) with all electronics available for purchase by the end of the year, but we will see.....

A responsible pilot of planes with these batteries would fly most of the time with a 60% charge which increases battery life MANY times over continual full charges. so 60% charges would hold 9.6kWh, 8.7kWh and 12kWh for the above described 120lb battery packs. pricing is going to be $3000-$4500 for these packs, at current prices.

The weight of 170 for the pilot is a good weight to use, because if the aircraft meets the standard weight with that standard pilot and the other 103-7 requirements are met, a pilot that weighs MORE and thus requires a slightly higher landing speed can still fly and call it an ultralight. probably better not to say exactly what the stall speed is with the heavier pilot though... wink wink.
 

Hot Wings

Grumpy Cynic
HBA Supporter
Log Member
Joined
Nov 14, 2009
Messages
7,724
Location
Rocky Mountains
At this point, the FAA interpretation is that batteries are part of the aircraft's empty weight... so a 120# battery leaves only 134# for airframe and engine.
Did my math wrong. 😖 You are quite right about the battery weight.

I went from the anticipated gross weight with a light pilot. It would work for LSA, but not for part 103.
 

cluttonfred

Well-Known Member
HBA Supporter
Joined
Feb 13, 2010
Messages
8,305
Location
Fort Walton Beach, Florida, USA
That sounds like a fun project. On the battery weight issue, I'd get a 30 lb portable battery pack (the weight of 5 gallons of gasoline), charge it off the plane, paint it red and write "FUEL" on the side in big letters. If that were your only battery, it would be hard to argue that you were doing anything but following the spirit of part 103. If you have more than 30 lb of batteries then the FAA interpretation seems justified.
 

Tiger Tim

Well-Known Member
Joined
Apr 26, 2013
Messages
3,763
Location
Thunder Bay
On the battery weight issue, I'd get a 30 lb portable battery pack (the weight of 5 gallons of gasoline), charge it off the plane, paint it red and write "FUEL" on the side in big letters.
You missed a step (though I’m sure for you it’s probably so obvious you wouldn’t need to think of it) and that’s to also not be a jerk about it. Just be cool and you could probably get away with this plan forever.
 

cluttonfred

Well-Known Member
HBA Supporter
Joined
Feb 13, 2010
Messages
8,305
Location
Fort Walton Beach, Florida, USA
That's a good point, but then again you'd probably need to avoid drawing attention in the first place by trying to set records. :-/

You missed a step (though I’m sure for you it’s probably so obvious you wouldn’t need to think of it) and that’s to also not be a jerk about it. Just be cool and you could probably get away with this plan forever.
 

John.Roo

Well-Known Member
Joined
Oct 8, 2013
Messages
768
Location
Letohrad / Czech Republic
At this point, the FAA interpretation is that batteries are part of the aircraft's empty weight... so a 120# battery leaves only 134# for airframe and engine.
This is a very important point.
I have been facing EW problem already and finally we agreed with our authorities, that EW will be calculated simply from MTOM minus weight of crew.
Requirement for two seater is reserve 2x 100 kg (range 70-200 kg), for one seater is 1x 110 kg (range 70-110 kg). So we are alowed to go to 400 kg EW for two seat airplane with complete electric propulsion (incl. motor, controler, BMS system and battery - charger doesn´t have to be aboard).

Makes no sense for me to make weight and balance without batteries - they are affecting CG a lot and they have same weight charged vs discharged (fuel is affecting CG position much more).

This way seems to me safe. You cannot cross MTOM (well, of course you can but at least you have reasonable weight reserve for crew) and CG is affected only by actual crew weight (therefore we have to achieve safe range of CG between 70-200 kg).

I hope FAA (CAA or any local aviation authorities) will before or later accept that rules are basically written for ICE propulsion systems and with comming electric propulsion systems needs some changes.
 

Hot Wings

Grumpy Cynic
HBA Supporter
Log Member
Joined
Nov 14, 2009
Messages
7,724
Location
Rocky Mountains
I hope FAA (CAA or any local aviation authorities) will before or later accept that rules are basically written for ICE propulsion systems and with comming electric propulsion systems needs some changes.
For part 103 and LSA the reason weight and speed were originally set as parameters was to reduce the possible damage to ground 'targets' by limiting kinetic energy.
I believe (Vs know/think) this is why the FAA lawyer decided that batteries needed to be counted as structural weight in part 103s.*

I think that decision could be modified by making the observation that in the event of a crash with an ICE 103 that there would probably be half (on average) of the 30 pound fuel on board. We could then argue that electric should be granted a 15 pound allowance for the battery weight to make things equal. It isn't a lot but 6% increase in empty weight is significant when we start counting ounces.

* I think Rainbow just asked for too much.
 

Vigilant1

Well-Known Member
Lifetime Supporter
Joined
Jan 24, 2011
Messages
6,225
Location
US
... we could then argue that electric should be granted a 15 pound allowance for the battery weight to make things equal. It isn't a lot but 6% increase in empty weight is significant when we start counting ounces.
Right, it sure isn't a lot. 15 lbs of batteries has the same "airplane motive potential" as about 3 cups of gasoline.

Maybe the lawyers should make the case that the lack of flammable fuels offers an improvement in safety to people/objects on the ground equivalent to X lbs of acft empty weight. If they converted the 5 gallons of fuel into energy value, then divided that by the square of the stall speed (assumed crash speed), they get the allowable increase in acft weight for an electric plane. It would be a LOT of pounds.
Obviously, we'd be assuming every crash of an IC airplane leads to a conflagration.
On a broader note, any effort to get a rulemaking making committee together to modify Part 103 leads to the very real risk that it will be made more restrictive and we'll lose something that is really pretty good as it is.
found an equivalent KE for an aircraft weight at stall velocity squared
 

Vigilant1

Well-Known Member
Lifetime Supporter
Joined
Jan 24, 2011
Messages
6,225
Location
US
Maybe the lawyers should make the case that the lack of flammable fuels offers an improvement in safety to people/objects on the ground equivalent to X lbs of acft empty weight. If they converted the 5 gallons of fuel into energy value, then divided that by the square of the stall speed (assumed crash speed), they get the allowable increase in acft weight for an electric plane. It would be a LOT of pounds.
Obviously, we'd be assuming every crash of an IC airplane leads to a conflagration.
And the answer is:
Energy in the allowed 5 gal of gasoline ("Lower Heating Value)=585 Mjjoules
Let's say an ultralight might crash into the school bus/orphanage/convent at, worst case, 200 mph. If our plane was electric and didn't have that fuel aboard, it could weigh up to 322,000 lbs to have the same crash energy as that 5 gal of gasoline carried by the IC engine plane. (If it ignites)
 

TFF

Well-Known Member
Joined
Apr 28, 2010
Messages
14,731
Location
Memphis, TN
FAI F3A pattern planes are weighed with battery so I would think they are recording any record flights the same way.
 

John.Roo

Well-Known Member
Joined
Oct 8, 2013
Messages
768
Location
Letohrad / Czech Republic
For part 103 and LSA the reason weight and speed were originally set as parameters was to reduce the possible damage to ground 'targets' by limiting kinetic energy.
I believe (Vs know/think) this is why the FAA lawyer decided that batteries needed to be counted as structural weight in part 103s.*

I think that decision could be modified by making the observation that in the event of a crash with an ICE 103 that there would probably be half (on average) of the 30 pound fuel on board. We could then argue that electric should be granted a 15 pound allowance for the battery weight to make things equal. It isn't a lot but 6% increase in empty weight is significant when we start counting ounces.

* I think Rainbow just asked for too much.
I would say that in this case FAA should allow weight of full fuel tank.
Battery has 100% known weight. If is a part of structure (Empty Weight), than no way how to cross MTOM with "too much fuel aboard". You only have to keep enough weight reserve for pilot.
1 kWh = 5 kg (11 lb)
If they want to convince pilots to use epectricpropulsion systems with al limitations than is necessary to re-write the rules a little bit ;)

I have personal experience with Sagitta (old one seat project from CR). Sagitta has 30 kg battery. That is 6 kWh. Could be maybe 5 kWh but that is really border. It means 25-30 kg (55-66 lb). 15 kW TakeOff power = 3C discharge rate. That is OK.
Endurance... 45-50 minutes of powered flight. Maybe hour. Of course much more in thermals :) This simple small plane may could reach Parts 103 weight requirements, but definitelly not stall speed so....
 
Top