VansAirForceForums  
Home > VansAirForceForums

-POSTING RULES
-Advertise in here!
- Today's Posts | Insert Pics

Keep VAF Going
Donate methods

Point your
camera app here
to donate fast.

  #21  
Old 01-25-2021, 11:58 AM
scsmith scsmith is offline
 
Join Date: Jan 2008
Location: Ashland, OR
Posts: 2,804
Default A few points to add

Just a few points on aspects people have mentioned:

Power is constant with altitude but thrust is not. As TAS increases for the same IAS, the thrust drops off. P=T*V Still, the performance drop-off is much less than IC.

Cooling big electric motors is a challenge. Cooling the motor controller is also a challenge. Cooling the battery is important too. There is less waste heat overall, but it is inconveniently located and the components can not tolerate high temps so you have to move the heat with less delta-T

The fact that batteries are charged from ground-based power generation offers something like 40% reduction in CO2. Much better energy conversion efficiency. This is why electric cars make sense.

Fuel cells can be very light. That’s not the problem. Remember Apollo used fuel cells to go to the moon, an application where weight is really at a premium. The issue is that they are very bulky. At NASA-Glenn they have both one-pass and regenerative fuel cells running with similar power. A 100 hp one-pass fuel cell is about the size of a VW Beetle. And it is not the fuel cell itself. It is a Miriad of pumps, valves, heat exchangers and plumbing.

I can’t prove this but my suspicion is that as battery energy density increases, the potential hazards increase too. Li-ion are already pretty dangerous. After working on an electric V-TOL for a couple of years At Zee.Aero I decided against an electric self-launch sailplane. The folks I worked with were top in the field and we had a couple of spectacular accidents. Boeing and Tesla have both had big mishaps and you can bet they really know what they are doing.
It is not a realm for amateurs. It is really easy to turn a $20,000 battery into hazmat.

In 1999 I led a NASA team to design a small electric airplane to fly on Mars. At that time the best batteries were Silver-Zinc at about 130 W-hr/Kg. They had Li-ion cells in the lab at 400 and that was going to be “right around the corner”. So here we are 22 years later and we are at 260. From my work at Zee this is just about the best you can do with Lithium. There will be gradual advance but nothing like what we need. It would take a new chemistry.
Just like fusion power, it will always be “right around the corner”.

One thing people often forget about is the 30-minute VFR reserve. The Zee test vehicle had 25 minute endurance so when we went to license it the FAA said we had -5 minute endurance. The loophole we used was to license it as a motor glider. The FAA was absolutely unyielding on the reserve. And for good reason. You can’t know your state of charge to any higher confidence than you can know your fuel remaining in a dinosaur powered airplane.
__________________
Steve Smith
Aeronautical Engineer
RV-8 N825RV
IO-360 A1A
WW 200RV
"The Magic Carpet" Flying since Sept. 2009
Hobbs 635
LS6-15/18W sailplane SOLD
bought my old LS6-A back!!
VAF donation Dec 2020
Reply With Quote
  #22  
Old 01-25-2021, 12:23 PM
scsmith scsmith is offline
 
Join Date: Jan 2008
Location: Ashland, OR
Posts: 2,804
Default Motors

It is tough to get the power out of electric motors at the RPM we need. Out-runner motors run slower but still want to turn faster than we would like.

Gear boxes are heavy.

And cooling. Don’t forget cooling.
__________________
Steve Smith
Aeronautical Engineer
RV-8 N825RV
IO-360 A1A
WW 200RV
"The Magic Carpet" Flying since Sept. 2009
Hobbs 635
LS6-15/18W sailplane SOLD
bought my old LS6-A back!!
VAF donation Dec 2020
Reply With Quote
  #23  
Old 01-25-2021, 01:14 PM
blaplante blaplante is offline
 
Join Date: Jan 2010
Location: Southern California
Posts: 181
Default

Quote:
Originally Posted by scsmith View Post
It is tough to get the power out of electric motors at the RPM we need. Out-runner motors run slower but still want to turn faster than we would like.

Gear boxes are heavy.

And cooling. Don’t forget cooling.
Gearboxes are heavy, but could be lighter when they don't need to be built to withstand the pulsing torque of a 4 cylinder aircraft engine.
__________________
RV6A in phase 2 as of April 2016
Donation made Oct 2020

Last edited by blaplante : 01-25-2021 at 01:25 PM. Reason: grammar
Reply With Quote
  #24  
Old 01-25-2021, 01:35 PM
skylor's Avatar
skylor skylor is offline
 
Join Date: Aug 2009
Location: Southern California
Posts: 959
Default

Quote:
Originally Posted by blaplante View Post
Gearboxes are heavy, but could be lighter when they don't need to be built to withstand the pulsing torque of a 4 cylinder aircraft engine.
That's probably true, but electric motors don't have a perfectly smooth torque delivery either and still have drivetrain harmonics. They are probably smoother than our 4 or 6 cylinder piston engines though.

Skylor
Reply With Quote
  #25  
Old 01-25-2021, 01:37 PM
skylor's Avatar
skylor skylor is offline
 
Join Date: Aug 2009
Location: Southern California
Posts: 959
Default

Quote:
Originally Posted by scsmith View Post
Just a few points on aspects people have mentioned:

The fact that batteries are charged from ground-based power generation offers something like 40% reduction in CO2. Much better energy conversion efficiency. This is why electric cars make sense.
Here's a pretty good article on this subject:

https://www.forbes.com/sites/enrique...h=217de0b27f26

Skylor
Reply With Quote
  #26  
Old 01-25-2021, 04:13 PM
David Z David Z is online now
 
Join Date: Aug 2010
Location: Thunder Bay Ontario
Posts: 562
Default

The electricity in my area is largely hydro-electric, nuclear with limited solar and bio-fuel (basically scraps from the forestry industry). All relatively "green" ways to produce energy.

Charge the plane and car batteries over night when everybody is asleep with the stoves, lights, saunas, air compressors and everything else is off. The water is flowing through the hydro-electric turbines regardless of load.
__________________
RV8
Empennage Passed Pre-close Inspection
Wings mostly done
Fuselage started
83126
Dash 8 day job is financing the RV8
Donation till September 2021
Reply With Quote
  #27  
Old 01-25-2021, 04:56 PM
David Paule David Paule is offline
 
Join Date: Dec 2009
Location: Boulder, CO
Posts: 4,724
Default

That's fine where you are, but where I am, the solar panels are sleeping.

Dave
Reply With Quote
  #28  
Old 01-25-2021, 09:48 PM
Captain Avgas Captain Avgas is offline
 
Join Date: Oct 2005
Location: Melbourne, Australia
Posts: 1,929
Default

Quote:
Originally Posted by scsmith View Post

In 1999 I led a NASA team to design a small electric airplane to fly on Mars. At that time the best batteries were Silver-Zinc at about 130 W-hr/Kg. They had Li-ion cells in the lab at 400 and that was going to be “right around the corner”. So here we are 22 years later and we are at 260. From my work at Zee this is just about the best you can do with Lithium. There will be gradual advance but nothing like what we need. It would take a new chemistry.

Just like fusion power, it will always be “right around the corner”.
.
A very interesting post Steve. Like you, I doubt that there is any dramatic battery technology breakthrough right around the corner.

I am inclined to now believe that advances in battery technologies will be slow and incremental and that it will be a very long time before GA is broadly flying electric. There are mega dollars now being spent annually on global battery research but the nut is proving hard to crack and slow gains seem more likely than major breakthroughs.

Many people believe that the problem is simply a matter of energy density but there are many other crucial factors in producing a successful battery technology including, but not restricted to the following:

1. Suitability for low cost mass production.
2. Battery life.
3. Speed of recharge.
4. Intrinsic safety.
5. Secure availability of key elements/compounds in a political sense.

There are numerous new battery technologies in the pipeline that offer higher energy density than the current generation Li-ion. But they just don’t tick all the other boxes.
__________________
You’re only as good as your last landing
Bob Barrow
RV7A

Last edited by Captain Avgas : 01-26-2021 at 03:44 AM.
Reply With Quote
  #29  
Old 01-26-2021, 08:03 AM
Snowflake's Avatar
Snowflake Snowflake is offline
 
Join Date: Oct 2009
Location: Sidney, BC, Canada
Posts: 4,113
Default

Quote:
Originally Posted by blaplante View Post
An airplane profile (for most of us) is long duration of max cont. power.
Long duration of continuous power, yes, but not maximum. Who cruises at full throttle? If you do, there's at least one other way to be more efficient in the air...
__________________
Rob Prior
1996 RV-6 "Tweety" C-FRBP (formerly N196RV)
Reply With Quote
  #30  
Old 01-26-2021, 08:05 AM
Snowflake's Avatar
Snowflake Snowflake is offline
 
Join Date: Oct 2009
Location: Sidney, BC, Canada
Posts: 4,113
Default

Quote:
Originally Posted by scsmith View Post
Cooling big electric motors is a challenge. Cooling the motor controller is also a challenge. Cooling the battery is important too. There is less waste heat overall, but it is inconveniently located and the components can not tolerate high temps so you have to move the heat with less delta-T
At RV-speeds we have a lot of cooling air handy. Well designed, a cooling plenum could even offset the cooling drag... Like on the P-51.
__________________
Rob Prior
1996 RV-6 "Tweety" C-FRBP (formerly N196RV)
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -6. The time now is 05:25 AM.


The VAFForums come to you courtesy Delta Romeo, LLC. By viewing and participating in them you agree to build your plane using standardized methods and practices and to fly it safely and in accordance with the laws governing the country you are located in.