On 8/25/21 11:49 PM, Stéphane Vander Veken wrote:
> While you are comparing different types of fires caused by engines/fuel/batteries etc., don't forget you can also have a fire caused by your wheelbrake:
> https://www.bea.aero/en/investigation-reports/notified-events/detail/accident-to-the-schempp-hirth-arcus-m-registered-d-kkoy-on-30-07-2019-at-sisteron-theze-aerodrome/
> ;-)
>

Indeed. And it's not limited to Schempp-Hirth, even Schleicher gliders
have shown the problem. See section 19:

https://members.gliding.co.uk/wp-content/uploads/sites/3/2017/10/TNS-1-2017.pdf

You would think with all the experts at Schleicher, they could add a
little of that special paint and put a stop to this! Does anybody
actually believe Jonkers would allow this to happen???

On 8/26/2021 5:20 AM, kinsell wrote:
> On 8/25/21 11:49 PM, Stéphane Vander Veken wrote:
>> While you are comparing different types of fires caused by engines/fuel/batteries etc.,
>> don't forget you can also have a fire caused by your wheelbrake:
>> https://www.bea.aero/en/investigation-reports/notified-events/detail/accident-to-the-schempp-hirth-arcus-m-registered-d-kkoy-on-30-07-2019-at-sisteron-theze-aerodrome/
>>
>> ;-)
>>
>
> Indeed.  And it's not limited to Schempp-Hirth, even Schleicher gliders have shown the
> problem.  See section 19:
>
> https://members.gliding.co.uk/wp-content/uploads/sites/3/2017/10/TNS-1-2017.pdf
>
> You would think with all the experts at Schleicher, they could add a little of that
> special paint and put a stop to this!  Does anybody actually believe Jonkers would allow
> this to happen???

I don't see a reference to Schleicher, and the picture shows a Grob. The document was
interesting reading - seems even dead mice might be a problem.

--
Eric Greenwell - USA
- "A Guide to Self-launching Sailplane Operation"
https://sites.google.com/site/motorgliders/publications/download-the-guide-1

On Thursday, August 26, 2021 at 6:23:32 AM UTC-7, Eric Greenwell wrote:
> On 8/26/2021 5:20 AM, kinsell wrote:
> > On 8/25/21 11:49 PM, Stéphane Vander Veken wrote:
> >> While you are comparing different types of fires caused by engines/fuel/batteries etc.,
> >> don't forget you can also have a fire caused by your wheelbrake:
> >> https://www.bea.aero/en/investigation-reports/notified-events/detail/accident-to-the-schempp-hirth-arcus-m-registered-d-kkoy-on-30-07-2019-at-sisteron-theze-aerodrome/
> >>
> >> ;-)
> >>
> >
> > Indeed. And it's not limited to Schempp-Hirth, even Schleicher gliders have shown the
> > problem. See section 19:
> >
> > https://members.gliding.co.uk/wp-content/uploads/sites/3/2017/10/TNS-1-2017.pdf
> >
> > You would think with all the experts at Schleicher, they could add a little of that
> > special paint and put a stop to this! Does anybody actually believe Jonkers would allow
> > this to happen???
> I don't see a reference to Schleicher, and the picture shows a Grob. The document was
> interesting reading - seems even dead mice might be a problem.
> --
> Eric Greenwell - USA
> - "A Guide to Self-launching Sailplane Operation"
> https://sites.google.com/site/motorgliders/publications/download-the-guide-1

I waited several days for Jon to provide the NTSB accident reports. I have to assume that none were filed, meaning that "extensive structural damage" did not occur. Indeed, I saw Ed Salkeld's glider at Williams Soaring - there was new glass work done to the fuselage top area immediately behind the cockpit, but it definitely wasn't "extensive structural damage." I have heard rumors of major damage done to Jack Glendening, but it is all second-hand..

Tom

On 8/22/21 9:41 AM, jfitch wrote:
> On Saturday, August 21, 2021 at 7:01:23 PM UTC-7, 2G wrote:
>> Yes, it does. According to LZ Designs there are 270 FES gliders flying right now. The number of know fires is, at least, 3, and probably double that number. This puts the odds of having a "fire" (really a thermal runaway) at 1 in 100 (minimum), or more likely 1 in 50. This is about the same as the Space Shuttle.
>> Tom
>
> I know of 3 fires in the AS Wankel powerplant in US gliders alone, with fewer numbers in the fleet. Since you are flying that powerplant you are risking your life every flight.
>
> In the Netherlands crash of the Pipistrel they in fact established that the batteries "played no roll in the cause of the accident."
>

That's what they said. They also said a windmilling prop causes no drag
if it isn't generating electricity. Makes you wonder if the Dutch put
their A team on the investigation.

That aircraft had major electrical problems, and was not airworthy by
any reasonable definition. It should have stayed parked far away from
any structures, or other aircraft. Similar to a Chevy Bolt.

On 8/30/2021 7:52 AM, kinsell wrote:
> On 8/22/21 9:41 AM, jfitch wrote:
>> On Saturday, August 21, 2021 at 7:01:23 PM UTC-7, 2G wrote:
>>> Yes, it does. According to LZ Designs there are 270 FES gliders flying right now. The
>>> number of know fires is, at least, 3, and probably double that number. This puts the
>>> odds of having a "fire" (really a thermal runaway) at 1 in 100 (minimum), or more
>>> likely 1 in 50. This is about the same as the Space Shuttle.
>>> Tom
>>
>> I know of 3 fires in the AS Wankel powerplant in US gliders alone, with fewer numbers in
>> the fleet. Since you are flying that powerplant you are risking your life every flight.
>>
>> In the Netherlands crash of the Pipistrel they in fact established that the batteries
>> "played no roll in the cause of the accident."
>>
>
> That's what they said.  They also said a windmilling prop causes no drag if it isn't
> generating electricity.  Makes you wonder if the Dutch put their A team on the investigation.
>
> That aircraft had major electrical problems, and was not airworthy by any reasonable
> definition.  It should have stayed parked far away from any structures, or other
> aircraft.  Similar to a Chevy Bolt.

If the electric motor isn't operating (unpowered), it will spin easily, and it will take
only a small amount of power to spin the propeller; hence, relatively low drag on the
order of a feathered propeller.

--
Eric Greenwell - USA
- "A Guide to Self-launching Sailplane Operation"
https://sites.google.com/site/motorgliders/publications/download-the-guide-1

> >>
> >> In the Netherlands crash of the Pipistrel they in fact established that the batteries
> >> "played no roll in the cause of the accident."
> > That's what they said. They also said a windmilling prop causes no drag if it isn't
> > generating electricity. Makes you wonder if the Dutch put their A team on the investigation.

Mr. Kinsell; Before slamming the Dutch (who apparently write/read English better than some), their report did not say that a windmilling prop produced no drag, it stated that "the propeller does not produce extra aerodynamic drag; the aeroplane will sink with its natural sink rate". They were comparing it to the energy-generating propeller, which that craft did not have and which would have increased drag.

Dee

On Monday, August 30, 2021 at 1:20:47 PM UTC-7, phlyi...@gmail.com wrote:
> > >>
> > >> In the Netherlands crash of the Pipistrel they in fact established that the batteries
> > >> "played no roll in the cause of the accident."
> > > That's what they said. They also said a windmilling prop causes no drag if it isn't
> > > generating electricity. Makes you wonder if the Dutch put their A team on the investigation.
> Mr. Kinsell; Before slamming the Dutch (who apparently write/read English better than some), their report did not say that a windmilling prop produced no drag, it stated that "the propeller does not produce extra aerodynamic drag; the aeroplane will sink with its natural sink rate". They were comparing it to the energy-generating propeller, which that craft did not have and which would have increased drag.
>
> Dee

That report also said that the electrical propulsion system played no role in the accident. This demonstrably false. The report also said that the rear battery's SOC (state of charge) was ZERO, which was erroneous since it was based on the cell with the lowest voltage (there could be just ONE cell with low voltage and the system will report zero SOC). This guy was dealing with multiple electrical problems that same day and was having to deal with what, he thought, was a completely depleted battery. This, obviously, distracted him from the primary task at hand, flying the airplane.

So, the report is dead wrong: the Pipistrel's electrical problems clearly played a role in the accident.

On Monday, August 30, 2021 at 6:38:01 PM UTC-7, 2G wrote:

> So, the report is dead wrong: the Pipistrel's electrical problems clearly played a role in the accident.
Just as much as the pilot's decision to get out of bed that morning.

The propulsion system did get him into that air that day, without which there would have been no accident. The report is talking about proximate cause. You are not.

On Tuesday, August 31, 2021 at 8:27:18 AM UTC-7, jfitch wrote:
> On Monday, August 30, 2021 at 6:38:01 PM UTC-7, 2G wrote:
>
> > So, the report is dead wrong: the Pipistrel's electrical problems clearly played a role in the accident.
> Just as much as the pilot's decision to get out of bed that morning.
>
> The propulsion system did get him into that air that day, without which there would have been no accident. The report is talking about proximate cause. You are not.

I, of course, was talking about CONTRIBUTING factors. It is pretty obvious that something was distracting him from the primary task of flying the plane, and a "dead" battery would do it. It is also obvious that he got into the air - there would have been no crash w/o it - so I don't see the point you're trying to make.

Tom

On Tuesday, August 31, 2021 at 3:04:59 PM UTC-4, 2G wrote:
> On Tuesday, August 31, 2021 at 8:27:18 AM UTC-7, jfitch wrote:
> > On Monday, August 30, 2021 at 6:38:01 PM UTC-7, 2G wrote:
> >
> > > So, the report is dead wrong: the Pipistrel's electrical problems clearly played a role in the accident.
> > Just as much as the pilot's decision to get out of bed that morning.
> >
> > The propulsion system did get him into that air that day, without which there would have been no accident. The report is talking about proximate cause. You are not.
> I, of course, was talking about CONTRIBUTING factors. It is pretty obvious that something was distracting him from the primary task of flying the plane, and a "dead" battery would do it. It is also obvious that he got into the air - there would have been no crash w/o it - so I don't see the point you're trying to make.
>
> Tom

Hey Kingfish, settle down and have a drink! You need to quit arguing with your motor glide friends. Old Bob The Purist.

On Monday, August 30, 2021 at 12:51:18 PM UTC-4, Eric Greenwell wrote:
> On 8/30/2021 7:52 AM, kinsell wrote:
> > On 8/22/21 9:41 AM, jfitch wrote:
> >> On Saturday, August 21, 2021 at 7:01:23 PM UTC-7, 2G wrote:
> >>> Yes, it does. According to LZ Designs there are 270 FES gliders flying right now. The
> >>> number of know fires is, at least, 3, and probably double that number. This puts the
> >>> odds of having a "fire" (really a thermal runaway) at 1 in 100 (minimum), or more
> >>> likely 1 in 50. This is about the same as the Space Shuttle.
> >>> Tom
> >>
> >> I know of 3 fires in the AS Wankel powerplant in US gliders alone, with fewer numbers in
> >> the fleet. Since you are flying that powerplant you are risking your life every flight.
> >>
> >> In the Netherlands crash of the Pipistrel they in fact established that the batteries
> >> "played no roll in the cause of the accident."
> >>
> >
> > That's what they said. They also said a windmilling prop causes no drag if it isn't
> > generating electricity. Makes you wonder if the Dutch put their A team on the investigation.
> >
> > That aircraft had major electrical problems, and was not airworthy by any reasonable
> > definition. It should have stayed parked far away from any structures, or other
> > aircraft. Similar to a Chevy Bolt.
> If the electric motor isn't operating (unpowered), it will spin easily, and it will take
> only a small amount of power to spin the propeller; hence, relatively low drag on the
> order of a feathered propeller.
> --
> Eric Greenwell - USA
> - "A Guide to Self-launching Sailplane Operation"
> https://sites.google.com/site/motorgliders/publications/download-the-guide-1

Not true in my experience. The windmilling prop on my 24EL reduces the glide angle from about 44 to about 20. Stopping the prop with the brake yields something in the middle.
UH

On 8/31/2021 4:16 PM, Hank Nixon wrote:
> On Monday, August 30, 2021 at 12:51:18 PM UTC-4, Eric Greenwell wrote:
>> On 8/30/2021 7:52 AM, kinsell wrote:
....
>>>> In the Netherlands crash of the Pipistrel they in fact established that the batteries
>>>> "played no roll in the cause of the accident."
>>>>
>>>
>>> That's what they said. They also said a windmilling prop causes no drag if it isn't
>>> generating electricity. Makes you wonder if the Dutch put their A team on the investigation.
>>>
>>> That aircraft had major electrical problems, and was not airworthy by any reasonable
>>> definition. It should have stayed parked far away from any structures, or other
>>> aircraft. Similar to a Chevy Bolt.
>> If the electric motor isn't operating (unpowered), it will spin easily, and it will take
>> only a small amount of power to spin the propeller; hence, relatively low drag on the
>> order of a feathered propeller.
>> --
>> Eric Greenwell - USA
>> - "A Guide to Self-launching Sailplane Operation"
>> https://sites.google.com/site/motorgliders/publications/download-the-guide-1
>
> Not true in my experience. The windmilling prop on my 24EL reduces the glide angle from about 44 to about 20. Stopping the prop with the brake yields something in the middle.
> UH
>
Is that with an unpowered motor that can be easily turned by hand (essentially no
resistance, no "cogging")? Though, 20:1 sounds pretty good: my ASH26E is about 20:1 with
the mast up, prop stopped (and probably with the gear down - not sure about that).

--
Eric Greenwell - USA
- "A Guide to Self-launching Sailplane Operation"
https://sites.google.com/site/motorgliders/publications/download-the-guide-1

On Tuesday, August 31, 2021 at 4:16:53 PM UTC-7, Hank Nixon wrote:
> Not true in my experience. The windmilling prop on my 24EL reduces the glide angle from about 44 to about 20. Stopping the prop with the brake yields something in the middle.
> UH
The Pipistrel is an airplane, not a glider. Prop is always there, not something you can retract, therefore no difference in flight characteristics other than throttle on, throttle off - with which the pilot would have been well familiar.

The prop stopped vs prop freewheeling drag has been studied extensively in both aircraft and boats, the answer is "it depends" on a lot of factors, neither answer is right for every situation.

On Tuesday, August 31, 2021 at 6:52:15 PM UTC-5, jfitch wrote:
> On Tuesday, August 31, 2021 at 4:16:53 PM UTC-7, Hank Nixon wrote:
> > Not true in my experience. The windmilling prop on my 24EL reduces the glide angle from about 44 to about 20. Stopping the prop with the brake yields something in the middle.
> > UH
> The Pipistrel is an airplane, not a glider. Prop is always there, not something you can retract, therefore no difference in flight characteristics other than throttle on, throttle off - with which the pilot would have been well familiar.
>
> The prop stopped vs prop freewheeling drag has been studied extensively in both aircraft and boats, the answer is "it depends" on a lot of factors, neither answer is right for every situation.

Spinning prop produces greater drag. A windmilling propeller creates much more drag, by an order of magnitude at least. The obvious example is an autogyro or helicopter in autorotation, which drops like a stone if the rotor stopped. Drag is a function of blade area for a stopped rotor and a function of disc area for a windmilling one.
Aviation stack exchange

On Tuesday, August 31, 2021 at 5:04:30 PM UTC-7, phlyi...@gmail.com wrote:
> On Tuesday, August 31, 2021 at 6:52:15 PM UTC-5, jfitch wrote:
> > On Tuesday, August 31, 2021 at 4:16:53 PM UTC-7, Hank Nixon wrote:
> > > Not true in my experience. The windmilling prop on my 24EL reduces the glide angle from about 44 to about 20. Stopping the prop with the brake yields something in the middle.
> > > UH
> > The Pipistrel is an airplane, not a glider. Prop is always there, not something you can retract, therefore no difference in flight characteristics other than throttle on, throttle off - with which the pilot would have been well familiar.
> >
> > The prop stopped vs prop freewheeling drag has been studied extensively in both aircraft and boats, the answer is "it depends" on a lot of factors, neither answer is right for every situation.
> Spinning prop produces greater drag. A windmilling propeller creates much more drag, by an order of magnitude at least. The obvious example is an autogyro or helicopter in autorotation, which drops like a stone if the rotor stopped. Drag is a function of blade area for a stopped rotor and a function of disc area for a windmilling one.
> Aviation stack exchange

This is a commonly held belief that is simply not true. First off, why would a windmilling prop generate more drag than a stationary prop? The difference is that the engine is being driven thru compression cycles. But each compression is followed by decompression, which recovers most of the energy of compression (like a spring).

Here is an actual study of the subject:
https://peter2000.co.uk/aviation/misc/prop.pdf
He found that a stationary prop generated MORE drag than a windmilling prop at higher pitches (which is counter-intuitive). In any case, the largest difference was a factor of two, not an order of magnitude.

BTW, a helicopter's behavior is completely irrelevant since the blades are not props but rotating wings (hence the term "rotary wing aircraft").

Tom

On Tuesday, August 31, 2021 at 3:20:59 PM UTC-7, youngbl...@gmail.com wrote:
> On Tuesday, August 31, 2021 at 3:04:59 PM UTC-4, 2G wrote:
> > On Tuesday, August 31, 2021 at 8:27:18 AM UTC-7, jfitch wrote:
> > > On Monday, August 30, 2021 at 6:38:01 PM UTC-7, 2G wrote:
> > >
> > > > So, the report is dead wrong: the Pipistrel's electrical problems clearly played a role in the accident.
> > > Just as much as the pilot's decision to get out of bed that morning.
> > >
> > > The propulsion system did get him into that air that day, without which there would have been no accident. The report is talking about proximate cause. You are not.
> > I, of course, was talking about CONTRIBUTING factors. It is pretty obvious that something was distracting him from the primary task of flying the plane, and a "dead" battery would do it. It is also obvious that he got into the air - there would have been no crash w/o it - so I don't see the point you're trying to make.
> >
> > Tom
> Hey Kingfish, settle down and have a drink! You need to quit arguing with your motor glide friends. Old Bob The Purist.

Hey Blackface Bob, I don't take advice from racists. PERIOD.

Tom

Uh> ⁸Not true in my experience. The windmilling prop on my 24EL reduces the glide angle from about 44 to about 20. Stopping the prop with the brake yields something in the middle.

2G> This is a commonly held belief that is simply not true.

Just to add to the practical vs the theoretical (btw Hank is actually flying an electrical 24)

The ultralight tow planes used at wallaby ranch have centrifugal clutches between the engines and the prop to allow the extra drag from windmilling to significantly shorten there cycle time.

On 9/1/21 3:41 AM, RR wrote:
> Uh> ⁸Not true in my experience. The windmilling prop on my 24EL reduces the glide angle from about 44 to about 20. Stopping the prop with the brake yields something in the middle.
>
> 2G> This is a commonly held belief that is simply not true.
>
>
> Just to add to the practical vs the theoretical (btw Hank is actually flying an electrical 24)
>
> The ultralight tow planes used at wallaby ranch have centrifugal clutches between the engines and the prop to allow the extra drag from windmilling to significantly shorten there cycle time.
>

The statement in the report is:

The propeller fitted on I-D057 windmills when the power lever is
set to idle and has minimal ability to extract energy from the airflow,
so effective recuperation is zero. Therefore the propeller does not
produce extra aerodynamic drag; the aeroplane will sink with its natural
sink rate.

Taken in its entirety, the statement is patently false. Just because
generating electricity does create extra drag doesn't mean extra drag
isn't created if you're not. In addition, this airplane had a history
of unexplained friction in the motor noted during preflight inspection.

The report ruled out technical defects as contributing factors to the
accident. They found ten out of 96 cells in the rear battery pack being
weak or dead, and >>assumed<< they had been discharged after the crash.
This is the same battery pack that displayed whistling sounds during
charging! Did they further investigate that? No. Did they determine
why the BMS system indicated 90% state of health with ten dead cells? No.

Given the small amount of recorded data available from the accident,
it's remarkable they ruled out technical faults as possible contributing
factors. We really don't know what the pilot was dealing with leading
up to the accident. Do we really know the fire in the forward battery
didn't start prior to impact? Lithium battery fires give off hydrogen
floride gas, an extremely nasty substance to be inhaling.

-Dave

My Pipistrel Sinus was a 15-meter glider, though not a good one.  The
propeller was fully feathering.

Dan
5J

On 8/31/21 5:52 PM, jfitch wrote:
> On Tuesday, August 31, 2021 at 4:16:53 PM UTC-7, Hank Nixon wrote:
>> Not true in my experience. The windmilling prop on my 24EL reduces the glide angle from about 44 to about 20. Stopping the prop with the brake yields something in the middle.
>> UH
> The Pipistrel is an airplane, not a glider. Prop is always there, not something you can retract, therefore no difference in flight characteristics other than throttle on, throttle off - with which the pilot would have been well familiar.
>
> The prop stopped vs prop freewheeling drag has been studied extensively in both aircraft and boats, the answer is "it depends" on a lot of factors, neither answer is right for every situation.

On Tuesday, August 31, 2021 at 5:04:30 PM UTC-7, phlyi...@gmail.com wrote:
> On Tuesday, August 31, 2021 at 6:52:15 PM UTC-5, jfitch wrote:
> > On Tuesday, August 31, 2021 at 4:16:53 PM UTC-7, Hank Nixon wrote:
> > > Not true in my experience. The windmilling prop on my 24EL reduces the glide angle from about 44 to about 20. Stopping the prop with the brake yields something in the middle.
> > > UH
> > The Pipistrel is an airplane, not a glider. Prop is always there, not something you can retract, therefore no difference in flight characteristics other than throttle on, throttle off - with which the pilot would have been well familiar.
> >
> > The prop stopped vs prop freewheeling drag has been studied extensively in both aircraft and boats, the answer is "it depends" on a lot of factors, neither answer is right for every situation.
> Spinning prop produces greater drag. A windmilling propeller creates much more drag, by an order of magnitude at least. The obvious example is an autogyro or helicopter in autorotation, which drops like a stone if the rotor stopped. Drag is a function of blade area for a stopped rotor and a function of disc area for a windmilling one.
> Aviation stack exchange
There is an incomplete theory which predicts that. There are *many* empirical tests which refute it, tunnel and airborne. Sometimes less, sometimes more, depends on the prop design, pitch, surrounding field flow, retarding torque on shaft etc. Either the theory must change to fit the facts, or we must adopt "alternative facts".

On 9/1/2021 5:41 AM, RR wrote:
> UH> Not true in my experience. The windmilling prop on my 24EL reduces the glide angle from about 44 to about 20. Stopping the prop with the brake yields something in the middle.
>
> 2G> This is a commonly held belief that is simply not true.
>
>
> Just to add to the practical vs the theoretical (btw Hank is actually flying an electrical 24)
>
> The ultralight tow planes used at wallaby ranch have centrifugal clutches between the engines and the prop to allow the extra drag from windmilling to significantly shorten there cycle time.
>

Where do people get the idea that if the prop is free to spin it adds
"NO" drag? A locked (but not feathered) prop clearly creates a fair bit
of drag. Letting it spin only allows it a certain motion, the blades
are still approximately perpendicular to the airflow. It interacts with
more, not less, air. It's more similar to a disc that covers the whole
swept area.

A freely spinning *glider* must be creating a LOT of drag - witness its
descent rate in a stable (non-accelerating) spin!

On Wednesday, September 1, 2021 at 9:46:57 AM UTC-7, Moshe Braner wrote:
> On 9/1/2021 5:41 AM, RR wrote:
> > UH> Not true in my experience. The windmilling prop on my 24EL reduces the glide angle from about 44 to about 20. Stopping the prop with the brake yields something in the middle.
> >
> > 2G> This is a commonly held belief that is simply not true.
> >
> >
> > Just to add to the practical vs the theoretical (btw Hank is actually flying an electrical 24)
> >
> > The ultralight tow planes used at wallaby ranch have centrifugal clutches between the engines and the prop to allow the extra drag from windmilling to significantly shorten there cycle time.
> >
> Where do people get the idea that if the prop is free to spin it adds
> "NO" drag? A locked (but not feathered) prop clearly creates a fair bit
> of drag. Letting it spin only allows it a certain motion, the blades
> are still approximately perpendicular to the airflow. It interacts with
> more, not less, air. It's more similar to a disc that covers the whole
> swept area.
>
> A freely spinning *glider* must be creating a LOT of drag - witness its
> descent rate in a stable (non-accelerating) spin!

First a comparison to a helicopter - now one with a glider in a spin! What is next, the Titanic in free descent? Get REAL, folks.

Tom

On Wednesday, September 1, 2021 at 10:55:01 PM UTC-4, 2G wrote:
> On Wednesday, September 1, 2021 at 9:46:57 AM UTC-7, Moshe Braner wrote:
> > On 9/1/2021 5:41 AM, RR wrote:
> > > UH> Not true in my experience. The windmilling prop on my 24EL reduces the glide angle from about 44 to about 20. Stopping the prop with the brake yields something in the middle.
> > >
> > > 2G> This is a commonly held belief that is simply not true.
> > >
> > >
> > > Just to add to the practical vs the theoretical (btw Hank is actually flying an electrical 24)
> > >
> > > The ultralight tow planes used at wallaby ranch have centrifugal clutches between the engines and the prop to allow the extra drag from windmilling to significantly shorten there cycle time.
> > >
> > Where do people get the idea that if the prop is free to spin it adds
> > "NO" drag? A locked (but not feathered) prop clearly creates a fair bit
> > of drag. Letting it spin only allows it a certain motion, the blades
> > are still approximately perpendicular to the airflow. It interacts with
> > more, not less, air. It's more similar to a disc that covers the whole
> > swept area.
> >
> > A freely spinning *glider* must be creating a LOT of drag - witness its
> > descent rate in a stable (non-accelerating) spin!
> First a comparison to a helicopter - now one with a glider in a spin! What is next, the Titanic in free descent? Get REAL, folks.
>
> Tom
After the last Citabria tow of the day, I would stop the engine,(after cooling)
and do a dead stick landing a roll to the tie down; the descent rate with prop stopped
was markedly less than windmilling.
JMF

On 9/1/21 10:46 AM, Moshe Braner wrote:

> Where do people get the idea that if the prop is free to spin it adds
> "NO" drag?

If it really was free to spin, it would add significant drag. But is it
ever truly free to spin? The motors used on electric aircraft have
powerful permanent magnets in them, there's going to be some cogging
effect that reduces the rpm.

Point of curiosity, does an aircraft like the Alpha have a prop brake?
Seems like sitting on the ramp, a good wind could produce enough
rotation to be a hazard to bystanders.

On Wednesday, September 1, 2021 at 9:46:57 AM UTC-7, Moshe Braner wrote:

> Where do people get the idea that if the prop is free to spin it adds
> "NO" drag?
I don't think anyone has that idea. An unpowered prop creates drag, the question originally was, does it create extraordinary or "extra" drag on an airplane? Of course not, it is part of the design, is always present, has been present every time you flew it, is today no different than yesterday, and is by definition ordinary. There are not two modes: prop deployed and prop stowed, as there might be in a glider. That degenerated into: does a spinning prop create more drag than a stopped one. You can do all the internet speculation you want, but this has been tested, many times, for many configurations. The answer is not yes or no, it is "it depends" on the specific conditions.

The energy lost in a stopped prop is fairly easy to calculate. A spinning prop is considerably more complicated. To spin it at exactly the critical speed to create zero lift on its blades, you must overcome only the profile drag of the blades, similar to running a variable pitch on the ground set to zero pitch. At this speed it creates no drag (to a first order at least). The power required to spin it at that speed is the energy lost, as it must be extracted from the airstream which means it must be spinning slower that the critical speed, creating some drag. If the shaft has torque drag due to turning an engine, more power is required, creating more drag. The calculations become quite complex. From empirical measurements, we know that it may, or may not be more drag than the same prop stopped, depending on a number of factors unique to the installation and operating conditions.