Another E glider concept

The Main factors for power from a propeller are diameter, pitch and rpm, not the number of blades.

An increase from 2 to 3 blades gives at best about 10-15% more drag if the remaining is constant. However the efficiency of the propeller drops by 5-10% and this is a major drawback in electrical propulsion system for gliders.

Per Carlin wrote on 8/17/2020 12:58 PM:
The Main factors for power from a propeller are diameter, pitch and rpm, not the number of blades.

An increase from 2 to 3 blades gives at best about 10-15% more drag if the remaining is constant. However the efficiency of the propeller drops by 5-10% and this is a major drawback in electrical propulsion system for gliders.

I think something is missing in your explanation: for example, 3, 4 and 5 blades
are common on airplanes, and wind turbines routinely use 3 blades. My
understanding is tip speed is the ultimate limit on the power a propeller can
absorb, so adding a 3rd should 50% more power capability.

Take a look at this bad boy - Five blades!

https://hartzellprop.com/are-more-pr...blades-better/

The Hartzell site also discusses reasons for choosing more blades

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorg...ad-the-guide-1

When the propeller spins backwards in the demo reel, confidence that the engineers will make an airworthy aircraft is instantly flushed down the toilet.

On Monday, August 17, 2020 at 1:39:31 PM UTC-7, Eric Greenwell wrote:
Per Carlin wrote on 8/17/2020 12:58 PM:
The Main factors for power from a propeller are diameter, pitch and rpm, not the number of blades.

An increase from 2 to 3 blades gives at best about 10-15% more drag if the remaining is constant. However the efficiency of the propeller drops by 5-10% and this is a major drawback in electrical propulsion system for gliders.

I think something is missing in your explanation: for example, 3, 4 and 5 blades
are common on airplanes, and wind turbines routinely use 3 blades. My
understanding is tip speed is the ultimate limit on the power a propeller can
absorb, so adding a 3rd should 50% more power capability.

Take a look at this bad boy - Five blades!

https://hartzellprop.com/are-more-pr...blades-better/

The Hartzell site also discusses reasons for choosing more blades

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorg...ad-the-guide-1

On Monday, August 17, 2020 at 8:01:08 PM UTC-4, Cumungus wrote:
When the propeller spins backwards in the demo reel, confidence that the
engineers will make an airworthy aircraft is instantly flushed down the toilet.

That feature is for backing into your parking space.

On Tuesday, August 18, 2020 at 3:01:45 AM UTC+2, Dave Nadler wrote:
On Monday, August 17, 2020 at 8:01:08 PM UTC-4, Cumungus wrote:
When the propeller spins backwards in the demo reel, confidence that the
engineers will make an airworthy aircraft is instantly flushed down the toilet.

That feature is for backing into your parking space.

Or for landing downwind on golf courses..

Chris Wedgwood wrote on 8/19/2020 7:33 AM:
On Tuesday, August 18, 2020 at 3:01:45 AM UTC+2, Dave Nadler wrote:
On Monday, August 17, 2020 at 8:01:08 PM UTC-4, Cumungus wrote:
When the propeller spins backwards in the demo reel, confidence that the
engineers will make an airworthy aircraft is instantly flushed down the toilet.

That feature is for backing into your parking space.

Or for landing downwind on golf courses..

That's an interesting idea, sort of the modern tail parachute like I had on my
H301. It was enormously powerful, but not controllable, just deployed or not. An
electrically powered propeller could be used to provide adjustable drag from zero
to "a lot". The design issue is keeping the propeller from folding backwards when
you want it to produce drag.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorg...ad-the-guide-1

If you are looking for controllable drag you simply need a center pull cord at the apex of the drag chute.
Cord pulled = little drag
Cord slack = full drag

Seems simple enough to design in solenoid activated pins to prevent the
blades from folding during reverse.Â* ...But the reverse thrust just
might put the blade tips into the ground...

On 8/19/2020 9:31 AM, Eric Greenwell wrote:
Chris Wedgwood wrote on 8/19/2020 7:33 AM:
On Tuesday, August 18, 2020 at 3:01:45 AM UTC+2, Dave Nadler wrote:
On Monday, August 17, 2020 at 8:01:08 PM UTC-4, Cumungus wrote:
When the propeller spins backwards in the demo reel, confidence
that the
engineers will make an airworthy aircraft is instantly flushed down
the toilet.

That feature is for backing into your parking space.

Or for landing downwind on golf courses..

That's an interesting idea, sort of the modern tail parachute like I
had on my H301. It was enormously powerful, but not controllable, just
deployed or not. An electrically powered propeller could be used to
provide adjustable drag from zero to "a lot". The design issue is
keeping the propeller from folding backwards when you want it to
produce drag.


--
Dan, 5J