Need advice on ultralight idea

HomeBuiltAirplanes.com

Help Support HomeBuiltAirplanes.com:

TFF

Well-Known Member
Joined
Apr 28, 2010
Messages
12,812
Location
Memphis, TN
Pretty much the reason for UL weight is if you crash out of the air, you only make a small crater in someone’s property. More weight, bigger hole. More weight means insurance and being able to defend yourself if sued.

Doubling the area of the T2 wing needs a big think. That is a major restructuring. Although many elements can be the same, you can’t just stretch it and be ok. T2 wing has to be metal covered. If you go fabric, the whole wing guts are different, just like Rockiedog said. The Hummel UL I have seen fly is probably faster than UL limits, but it does make weight. It has to be using .016 skins but the spar is almost a foot deep to be strong enough. .016 skins look like aluminum foil.
 

GeneG

Well-Known Member
Joined
Jul 5, 2019
Messages
74
Location
Arkansas
Pretty much the reason for UL weight is if you crash out of the air, you only make a small crater in someone’s property. More weight, bigger hole. More weight means insurance and being able to defend yourself if sued.

Doubling the area of the T2 wing needs a big think. That is a major restructuring. Although many elements can be the same, you can’t just stretch it and be ok. T2 wing has to be metal covered. If you go fabric, the whole wing guts are different, just like Rockiedog said. The Hummel UL I have seen fly is probably faster than UL limits, but it does make weight. It has to be using .016 skins but the spar is almost a foot deep to be strong enough. .016 skins look like aluminum foil.
Most likely the spar is that deep because it's 18% rather than for the ultimate strength.
 

pictsidhe

Well-Known Member
Joined
Jul 15, 2014
Messages
7,421
Location
North Carolina
Delta versus wye changes the effective number of turns. Your motor will be capabale of the same power and torque whichever way it is wound. The voltage and current can only be traded against each other. If you buy a 100V wye wound motor and want it to run from 57V, swapping the connections to delta will do that. It won't make it more powerful, nor more torquey.


My primary choice is a true induction motor that is water cooled. The magnetism is therefore induced into the rotor.

The second choice is a permenent magnet motor. The use of delta verses y windings changes the angular attraction of the rotor and the therefore affects the rotor speed vs torque available given the input current.

Span is good except I am facing a weight limit that I wish was more generous.

Thanks.
 

pictsidhe

Well-Known Member
Joined
Jul 15, 2014
Messages
7,421
Location
North Carolina
If you try to hire an engineer to double the wing area of the teenie while reducing weight to 254lbs he's going to do one of a few things:
Suck through his teeth for longer than most tradesmen can manage.
Laugh,
Rub his hands with glee, this will COST you!
 

GeneG

Well-Known Member
Joined
Jul 5, 2019
Messages
74
Location
Arkansas
Delta versus wye changes the effective number of turns. Your motor will be capabale of the same power and torque whichever way it is wound. The voltage and current can only be traded against each other. If you buy a 100V wye wound motor and want it to run from 57V, swapping the connections to delta will do that. It won't make it more powerful, nor more torquey.
I agree that you don't get something for nothing. Putting more copper into the stator should allow greater overall current through it enabling an increase in available power. The trade off is increased torque for motor weight vs more heating in the windings plus higher energy use. The end goal is to produce as much power for the weight as possible? Wiring for delta and running the motor at the same voltage as you would in wye configuration should certainly produce more overall power per weight no? That is why I am interested in the water cooled version of this motor. The higher applied power is for limited climb out or emergency and not continuous duty.
If I am wrong, Please correct me.
Thanks again.
 

pictsidhe

Well-Known Member
Joined
Jul 15, 2014
Messages
7,421
Location
North Carolina
I agree that you don't get something for nothing. Putting more copper into the stator should allow greater overall current through it enabling an increase in available power. The trade off is increased torque for motor weight vs more heating in the windings plus higher energy use. The end goal is to produce as much power for the weight as possible? Wiring for delta and running the motor at the same voltage as you would in wye configuration should certainly produce more overall power per weight no? That is why I am interested in the water cooled version of this motor. The higher applied power is for limited climb out or emergency and not continuous duty.
If I am wrong, Please correct me.
Thanks again.
Motor manufacturers are well aware of the benefits of stuffing as much copper as they can in motors. If you open a motor up to rewind it, you'll have your work cut out matching the standard amount of copper.
If you rewire a wye motor delta then run it at the same voltage, you have effectively reduced the number of turns and increased the kV. it will now spin 73% faster, giving 73% more power for the same resistive power loss, while sucking 73% more current. It will have the same torque. Hysteresis losses in the magnetic circuits will increase a lot due to the higher frequency. Maybe it will be fine, maybe it will come apart or cook itself. If you want to push a motor 73% past it's rated power, it's extremely unlikely to like it for very long. If your lucky, you'll just lose a lot of efficiency. Compare the weight savings of the motor to the extra batteries it will need for your flight.
I'd recommend leaving power ratings to the manufacturer. if you order direct, you can choose the kV to suit your battery pack. The maximum torque and rpm capabilities are dependent on the physical size of the motor, not how it is wound.
Yes, water cooled motors can be pushed a bit harder for their size, but now you need a radiator, so look at the total weight. Great for boats, though.
Believe it or not, the guys who design these motors do tend to know what they're doing.
 

GeneG

Well-Known Member
Joined
Jul 5, 2019
Messages
74
Location
Arkansas
Motor manufacturers are well aware of the benefits of stuffing as much copper as they can in motors. If you open a motor up to rewind it, you'll have your work cut out matching the standard amount of copper.
If you rewire a wye motor delta then run it at the same voltage, you have effectively reduced the number of turns and increased the kV. it will now spin 73% faster, giving 73% more power for the same resistive power loss, while sucking 73% more current. It will have the same torque. Hysteresis losses in the magnetic circuits will increase a lot due to the higher frequency. Maybe it will be fine, maybe it will come apart or cook itself. If you want to push a motor 73% past it's rated power, it's extremely unlikely to like it for very long. If your lucky, you'll just lose a lot of efficiency. Compare the weight savings of the motor to the extra batteries it will need for your flight.
I'd recommend leaving power ratings to the manufacturer. if you order direct, you can choose the kV to suit your battery pack. The maximum torque and rpm capabilities are dependent on the physical size of the motor, not how it is wound.
Yes, water cooled motors can be pushed a bit harder for their size, but now you need a radiator, so look at the total weight. Great for boats, though.
Believe it or not, the guys who design these motors do tend to know what they're doing.
Thanks for the lesson. I didn't really want to get into rewinding anyway.
 

pictsidhe

Well-Known Member
Joined
Jul 15, 2014
Messages
7,421
Location
North Carolina
Reduce it to 12%, the spar caps will need to be 50% heavier to have the same safety margin. It will aerodynamically lift just as much weight, but it will either be a lot heavier or more highly stressed.
 

GeneG

Well-Known Member
Joined
Jul 5, 2019
Messages
74
Location
Arkansas
Take a look at Advisory Circular AC103-7, I don't have a link handy but google will find it. In particular, the appendices to the AC contain tables intended to be used to determine whether an ultralight meets the legal limits... but they're also great for preliminary sizing of an ultralight intended to be legal.

As for batteries, the FAA has said that battery weight can not be considered as "fuel" but must be included in the 254# empty weight limit.
I haven't been able to locate this decision. I have only found differing views.
Can you please direct me to the faa documentation for this?
Thank you
 

jedi

Well-Known Member
Joined
Aug 8, 2009
Messages
2,084
Location
Sahuarita Arizona, Renton Washington, USA
I haven't been able to locate this decision. I have only found differing views.
Can you please direct me to the faa documentation for this?
Thank you
https://aviation.stackexchange.com/questions/5204/does-the-weight-of-the-battery-count-as-fuel-in-a-battery-powered-ultralight

Max Ultralight weight is 254 pounds including the batteries. This has put a huge damper on battery powered Ultralights but has not killed the beast. You can still get the seaplane float allowance if that would help. The additional weight and power requirements of the water operations would likely eat any advantage from the weight and the stall speed requirement still stands as a negative against the increased weight.

You could build a big control line model and run it in a circle which is what most ULs do anyway. Might make a good amusement ride. The lines make it a kite (FAR 101) and avoids the 254 UL weight limit and stall speed but impose other limitations.
 

GeneG

Well-Known Member
Joined
Jul 5, 2019
Messages
74
Location
Arkansas
https://aviation.stackexchange.com/questions/5204/does-the-weight-of-the-battery-count-as-fuel-in-a-battery-powered-ultralight

Max Ultralight weight is 254 pounds including the batteries. This has put a huge damper on battery powered Ultralights but has not killed the beast. You can still get the seaplane float allowance if that would help. The additional weight and power requirements of the water operations would likely eat any advantage from the weight and the stall speed requirement still stands as a negative against the increased weight.

You could build a big control line model and run it in a circle which is what most ULs do anyway. Might make a good amusement ride. The lines make it a kite (FAR 101) and avoids the 254 UL weight limit and stall speed but impose other limitations.

Thanks for the link. Seems still hearsav and not written in stone.
Then they wonder why aviation is dying.
 

BJC

Well-Known Member
HBA Supporter
Joined
Oct 7, 2013
Messages
11,058
Location
97FL, Florida, USA
Thanks for the link. Seems still hearsav and not written in stone.
Then they wonder why aviation is dying.
Doesn’t have to be written in stone. But you can believe that the opinion there is what the FAA will consider the law if they decide to go after a potential violator.

Part 103 is, in essence, the FAA’a way of saying, “If you build and operate an airplane that meets this criteria, we won’t bother regulating it or you.” That is a good deal. There are lots of reasons that sport aviation is declining, but not considering batteries to be consumable fuel isn’t one.


BJC
 

GeneG

Well-Known Member
Joined
Jul 5, 2019
Messages
74
Location
Arkansas
It still seems hearsay if not enshrined into official notice.
Then they wonder why aviation is dying.

Sorry, cross post.
 
2
Top