What is involved regulation wise adding an electric motor to a glider?

On 2/2/21 6:09 PM, David Scott wrote:
On Tuesday, February 2, 2021 at 1:26:10 PM UTC-8, David Scott wrote:
I DON'T mean to stir up trouble on this forum with this question, especially being new, but have been wondering about this for some time. I am wondering how feasible it would be to do this with either a homebuilt or experimental glider here in the US?

I figure this has been asked but didn't find any threads on it.

Thank you for your responses. To be clear I don't have a sailplane but would like to get into the sport and the answers to this question would possibly affect what glider I would get. I am smart enough to get all my ducks in a row before doing anything, and this is the first I have talked about it. From an engineering standpoint, it doesn't look too difficult, navigating the regulations is where I expect the most trouble.


Putting together a motorglider is a strange path towards getting
involved with the sport. Might be better to take lessons, get the
rating, and have some time under your belt before taking on a project
like this.

In my local club, I see people going solo and maybe getting their
rating, and immediately thinking about buying a glider. This is with a
reasonable selection of under utilized club ships sitting around. I
encourage them to wait a couple years first.

If you're all set on owning an electric motorglider, there's a
reasonable selection of Silent 2 Electro's on W&W. Do yourself and the
owners a big favor and pick up one of those.

-Dave

On Friday, February 5, 2021 at 9:52:57 AM UTC-8, kinsell wrote:
On 2/2/21 6:09 PM, David Scott wrote:
On Tuesday, February 2, 2021 at 1:26:10 PM UTC-8, David Scott wrote:
I DON'T mean to stir up trouble on this forum with this question, especially being new, but have been wondering about this for some time. I am wondering how feasible it would be to do this with either a homebuilt or experimental glider here in the US?

I figure this has been asked but didn't find any threads on it.

Thank you for your responses. To be clear I don't have a sailplane but would like to get into the sport and the answers to this question would possibly affect what glider I would get. I am smart enough to get all my ducks in a row before doing anything, and this is the first I have talked about it. From an engineering standpoint, it doesn't look too difficult, navigating the regulations is where I expect the most trouble.


Putting together a motorglider is a strange path towards getting
involved with the sport. Might be better to take lessons, get the
rating, and have some time under your belt before taking on a project
like this.

In my local club, I see people going solo and maybe getting their
rating, and immediately thinking about buying a glider. This is with a
reasonable selection of under utilized club ships sitting around. I
encourage them to wait a couple years first.

If you're all set on owning an electric motorglider, there's a
reasonable selection of Silent 2 Electro's on W&W. Do yourself and the
owners a big favor and pick up one of those.

-Dave

In response to the first paragraph, I am more curious as to what my options would be IF my local club dissolves and tows are no longer available. I absolutely will get flying before doing anything else! The single place club gliders are 2 1-26s and a LET L-33, @$40hr. It sounds like none let you reach much of the areas soaring because of their low performance from club YouTube videos. Since my whole interest would be cross country, or the wave window south of Mt Hood, I will need to get access to a better glider than the club offers.

The Grasshopper has some very interesting aspects. It is the first articulated pylon I have seen, a design I have thought about quite a lot to get it tucked into the fuselage with the smallest opening possible. Designing it to be as compact as possible to fit as many gliders would be an obvious design criteria.

I do not want to reinvent the wheel, just make as few modifications as necessary for a different application. With this in mind electric paramotors are quite interesting. 110-120 lbs of thrust with 4ah batteries would be a good starting point, perhaps. I am not saying the cheapest versions are acceptable but the higher volume will bring the prices down. It looks like $5-$6k would buy the parts needed for a glider, plus the pylon assembly. A complete paramotor weighs around 65lbs so I figure this is close to what it would add to a glider, if done right. The biggest problem to an electric propulsion system is the batteries, and those are going to get vast improvements in the near future.


This is all just food for thought. To add more food I have a few questions. Let us use a 500lb 15 meter glider as the reference.

Any idea on how much thrust is need to sustain altitude?
How much thrust is needed to climb at 200 fpm? 300 fpm?

On Sunday, February 7, 2021 at 2:46:31 PM UTC-5, David Scott wrote:
On Friday, February 5, 2021 at 9:52:57 AM UTC-8, kinsell wrote:
On 2/2/21 6:09 PM, David Scott wrote:
On Tuesday, February 2, 2021 at 1:26:10 PM UTC-8, David Scott wrote:
I DON'T mean to stir up trouble on this forum with this question, especially being new, but have been wondering about this for some time. I am wondering how feasible it would be to do this with either a homebuilt or experimental glider here in the US?

I figure this has been asked but didn't find any threads on it.

Thank you for your responses. To be clear I don't have a sailplane but would like to get into the sport and the answers to this question would possibly affect what glider I would get. I am smart enough to get all my ducks in a row before doing anything, and this is the first I have talked about it. From an engineering standpoint, it doesn't look too difficult, navigating the regulations is where I expect the most trouble.


Putting together a motorglider is a strange path towards getting
involved with the sport. Might be better to take lessons, get the
rating, and have some time under your belt before taking on a project
like this.

In my local club, I see people going solo and maybe getting their
rating, and immediately thinking about buying a glider. This is with a
reasonable selection of under utilized club ships sitting around. I
encourage them to wait a couple years first.

If you're all set on owning an electric motorglider, there's a
reasonable selection of Silent 2 Electro's on W&W. Do yourself and the
owners a big favor and pick up one of those.

-Dave
In response to the first paragraph, I am more curious as to what my options would be IF my local club dissolves and tows are no longer available. I absolutely will get flying before doing anything else! The single place club gliders are 2 1-26s and a LET L-33, @$40hr. It sounds like none let you reach much of the areas soaring because of their low performance from club YouTube videos. Since my whole interest would be cross country, or the wave window south of Mt Hood, I will need to get access to a better glider than the club offers.

The Grasshopper has some very interesting aspects. It is the first articulated pylon I have seen, a design I have thought about quite a lot to get it tucked into the fuselage with the smallest opening possible. Designing it to be as compact as possible to fit as many gliders would be an obvious design criteria.

I do not want to reinvent the wheel, just make as few modifications as necessary for a different application. With this in mind electric paramotors are quite interesting. 110-120 lbs of thrust with 4ah batteries would be a good starting point, perhaps. I am not saying the cheapest versions are acceptable but the higher volume will bring the prices down. It looks like $5-$6k would buy the parts needed for a glider, plus the pylon assembly. A complete paramotor weighs around 65lbs so I figure this is close to what it would add to a glider, if done right. The biggest problem to an electric propulsion system is the batteries, and those are going to get vast improvements in the near future.


This is all just food for thought. To add more food I have a few questions. Let us use a 500lb 15 meter glider as the reference.

Any idea on how much thrust is need to sustain altitude?
How much thrust is needed to climb at 200 fpm? 300 fpm?

Some data from first hand experience:
ASW-24E converted to electric from 2 cycle Rotax gas.
Power system including all items is right at 100 lb added to pure sailplane airframe weight.
This is a pylon mounted retractable system.
Battery is 120 volt,4.9 kwh lithium ion weighing 60 lb.
Climb rate at 160 amps is 300 ft/minute. Actual power delivered is about 16kw.
Climb rate at 230 amps is 500 ft/minute. Actual power delivered is about 23kw at this time
Your cost estimate is a bit less than1/2 what it would require for parts, not including items required to do the airframe conversion and assuming the person doing this can fabricate required items, engineer and wire the system, design and construct the prop, etc.
This assumes perfect efficiency and nothing destroyed or scrapped going through the learning process. Of those I am aware of that have done ,or are doing this, nobody has had that good fortune.
FWIW
UH

On Sunday, February 7, 2021 at 12:30:26 PM UTC-8, Hank Nixon wrote:
On Sunday, February 7, 2021 at 2:46:31 PM UTC-5, David Scott wrote:
On Friday, February 5, 2021 at 9:52:57 AM UTC-8, kinsell wrote:
On 2/2/21 6:09 PM, David Scott wrote:
On Tuesday, February 2, 2021 at 1:26:10 PM UTC-8, David Scott wrote:
I DON'T mean to stir up trouble on this forum with this question, especially being new, but have been wondering about this for some time. I am wondering how feasible it would be to do this with either a homebuilt or experimental glider here in the US?

I figure this has been asked but didn't find any threads on it.

Thank you for your responses. To be clear I don't have a sailplane but would like to get into the sport and the answers to this question would possibly affect what glider I would get. I am smart enough to get all my ducks in a row before doing anything, and this is the first I have talked about it. From an engineering standpoint, it doesn't look too difficult, navigating the regulations is where I expect the most trouble.


Putting together a motorglider is a strange path towards getting
involved with the sport. Might be better to take lessons, get the
rating, and have some time under your belt before taking on a project
like this.

In my local club, I see people going solo and maybe getting their
rating, and immediately thinking about buying a glider. This is with a
reasonable selection of under utilized club ships sitting around. I
encourage them to wait a couple years first.

If you're all set on owning an electric motorglider, there's a
reasonable selection of Silent 2 Electro's on W&W. Do yourself and the
owners a big favor and pick up one of those.

-Dave
In response to the first paragraph, I am more curious as to what my options would be IF my local club dissolves and tows are no longer available. I absolutely will get flying before doing anything else! The single place club gliders are 2 1-26s and a LET L-33, @$40hr. It sounds like none let you reach much of the areas soaring because of their low performance from club YouTube videos. Since my whole interest would be cross country, or the wave window south of Mt Hood, I will need to get access to a better glider than the club offers.

The Grasshopper has some very interesting aspects. It is the first articulated pylon I have seen, a design I have thought about quite a lot to get it tucked into the fuselage with the smallest opening possible. Designing it to be as compact as possible to fit as many gliders would be an obvious design criteria.

I do not want to reinvent the wheel, just make as few modifications as necessary for a different application. With this in mind electric paramotors are quite interesting. 110-120 lbs of thrust with 4ah batteries would be a good starting point, perhaps. I am not saying the cheapest versions are acceptable but the higher volume will bring the prices down. It looks like $5-$6k would buy the parts needed for a glider, plus the pylon assembly. A complete paramotor weighs around 65lbs so I figure this is close to what it would add to a glider, if done right. The biggest problem to an electric propulsion system is the batteries, and those are going to get vast improvements in the near future.


This is all just food for thought. To add more food I have a few questions. Let us use a 500lb 15 meter glider as the reference.

Any idea on how much thrust is need to sustain altitude?
How much thrust is needed to climb at 200 fpm? 300 fpm?

Some data from first hand experience:
ASW-24E converted to electric from 2 cycle Rotax gas.
Power system including all items is right at 100 lb added to pure sailplane airframe weight.
This is a pylon mounted retractable system.
Battery is 120 volt,4.9 kwh lithium ion weighing 60 lb.
Climb rate at 160 amps is 300 ft/minute. Actual power delivered is about 16kw.
Climb rate at 230 amps is 500 ft/minute. Actual power delivered is about 23kw at this time
Your cost estimate is a bit less than1/2 what it would require for parts, not including items required to do the airframe conversion and assuming the person doing this can fabricate required items, engineer and wire the system, design and construct the prop, etc.
This assumes perfect efficiency and nothing destroyed or scrapped going through the learning process. Of those I am aware of that have done ,or are doing this, nobody has had that good fortune.
FWIW
UH
That is good for a start but without knowing the efficiency it doesn't tell much. The devil is in the details, of which there are a lot.

What propeller do you use? Any photos of it extended?

Can the glider chosen for this modification support an extra 100 lb in
the fuselage? If the batteries are carried in the wings, what's the
remaining weight of the non-lifting parts? Can the wings sustain the
extra bending load?

Dan
5J

On 2/7/21 1:30 PM, Hank Nixon wrote:
On Sunday, February 7, 2021 at 2:46:31 PM UTC-5, David Scott wrote:
On Friday, February 5, 2021 at 9:52:57 AM UTC-8, kinsell wrote:
On 2/2/21 6:09 PM, David Scott wrote:
On Tuesday, February 2, 2021 at 1:26:10 PM UTC-8, David Scott wrote:
I DON'T mean to stir up trouble on this forum with this question, especially being new, but have been wondering about this for some time. I am wondering how feasible it would be to do this with either a homebuilt or experimental glider here in the US?

I figure this has been asked but didn't find any threads on it.

Thank you for your responses. To be clear I don't have a sailplane but would like to get into the sport and the answers to this question would possibly affect what glider I would get. I am smart enough to get all my ducks in a row before doing anything, and this is the first I have talked about it. From an engineering standpoint, it doesn't look too difficult, navigating the regulations is where I expect the most trouble.


Putting together a motorglider is a strange path towards getting
involved with the sport. Might be better to take lessons, get the
rating, and have some time under your belt before taking on a project
like this.

In my local club, I see people going solo and maybe getting their
rating, and immediately thinking about buying a glider. This is with a
reasonable selection of under utilized club ships sitting around. I
encourage them to wait a couple years first.

If you're all set on owning an electric motorglider, there's a
reasonable selection of Silent 2 Electro's on W&W. Do yourself and the
owners a big favor and pick up one of those.

-Dave
In response to the first paragraph, I am more curious as to what my options would be IF my local club dissolves and tows are no longer available. I absolutely will get flying before doing anything else! The single place club gliders are 2 1-26s and a LET L-33, @$40hr. It sounds like none let you reach much of the areas soaring because of their low performance from club YouTube videos. Since my whole interest would be cross country, or the wave window south of Mt Hood, I will need to get access to a better glider than the club offers.

The Grasshopper has some very interesting aspects. It is the first articulated pylon I have seen, a design I have thought about quite a lot to get it tucked into the fuselage with the smallest opening possible. Designing it to be as compact as possible to fit as many gliders would be an obvious design criteria.

I do not want to reinvent the wheel, just make as few modifications as necessary for a different application. With this in mind electric paramotors are quite interesting. 110-120 lbs of thrust with 4ah batteries would be a good starting point, perhaps. I am not saying the cheapest versions are acceptable but the higher volume will bring the prices down. It looks like $5-$6k would buy the parts needed for a glider, plus the pylon assembly. A complete paramotor weighs around 65lbs so I figure this is close to what it would add to a glider, if done right. The biggest problem to an electric propulsion system is the batteries, and those are going to get vast improvements in the near future.


This is all just food for thought. To add more food I have a few questions. Let us use a 500lb 15 meter glider as the reference.

Any idea on how much thrust is need to sustain altitude?
How much thrust is needed to climb at 200 fpm? 300 fpm?

Some data from first hand experience:
ASW-24E converted to electric from 2 cycle Rotax gas.
Power system including all items is right at 100 lb added to pure sailplane airframe weight.
This is a pylon mounted retractable system.
Battery is 120 volt,4.9 kwh lithium ion weighing 60 lb.
Climb rate at 160 amps is 300 ft/minute. Actual power delivered is about 16kw.
Climb rate at 230 amps is 500 ft/minute. Actual power delivered is about 23kw at this time
Your cost estimate is a bit less than1/2 what it would require for parts, not including items required to do the airframe conversion and assuming the person doing this can fabricate required items, engineer and wire the system, design and construct the prop, etc.
This assumes perfect efficiency and nothing destroyed or scrapped going through the learning process. Of those I am aware of that have done ,or are doing this, nobody has had that good fortune.
FWIW
UH

On 2/7/21 12:46 PM, David Scott wrote:

The biggest problem to an electric propulsion system is the batteries, and those are going to get vast improvements in the near future.

That's a big red flag. I hope you're not doing this project assuming
the batteries are going to be a lot better. Lithium batteries have been
commercially available for about 20 years, and the annual compounded
rate of improvement in energy density is not that impressive. It's been
claimed that batteries are somehow subject to Moore's Law, which is an
extremely incorrect assumption.

Still think you're underestimating the scope of the project. For
example, the Glasflugel folks are working on a self-launch retrofit for
Libelle's. Been at it for five years, been flying for three years, and
they're still not ready to announce pricing or availability. See story
at 7:50 he

https://www.youtube.com/watch?v=DZNr2BIOXBw

Someone converted a Cessna Caravan to electric and put on a big demo
flight for the press. It suffered a partial inverter failure during
that flight, now has been converted back to turbo jet and is up for
sale. The good folks at GP Gliders are five years late in delivering
product, when they finally got one out the door last year, the motor
lasted 10 minutes before something burned out. You'd think electric
systems would be so reliable, but there's tons of things that can go wrong.

The Antares was one of the first on the market, never really lived up to
its promised performance. On a hot day, the motor can overheat after a
thousand foot climb, batteries didn't deliver the capacity or lifetime
they were supposed to. Mr. Nadler may someday enlighten us with a few
more of its weak points.

Dave

On Tuesday, February 2, 2021 at 4:26:10 PM UTC-5, David Scott wrote:
I DON'T mean to stir up trouble on this forum with this question, especially being new, but have been wondering about this for some time. I am wondering how feasible it would be to do this with either a homebuilt or experimental glider here in the US?

I figure this has been asked but didn't find any threads on it.

Having done this I can provide you with the following guidance .
It can be done in the experimental category
It is a major change and will invalidate the AW certificate.
Getting a replacement certificate will requi
1) Review of the engineering and execution of the modification by a DAR. I doubt any FSDO would issue without some other entity taking responsibility.
2) Current condition inspection after modification
3) Revised flight and maintenance manual pages and proposed operating limitations affected by the change .
4) Inspection by an airworthiness inspector from the affected FSDO or MIDO.
5) Issuance of a new AW certificate and operating limitations including limitations for phase 1 flight testing.
6) After completion of phase 1, and pilot certification of normal characteristics, it should be able to be flown in accordance with the "usual" operating limitations that are issued for the category.
As to the issue of feasibility, it is very much affected by the knowledge and experience of the person doing the modification nand resources available to that individual .
To my knowledge this has been done once so far in the US .
If you want an electric sailplane- buy one.
FWIW
UH

On 2/3/2021 10:50 AM, Hank Nixon wrote:
If you want an electric sailplane- buy one.

Take two aspirin, and call me in the morning.

On Tuesday, February 2, 2021 at 1:26:10 PM UTC-8, David Scott wrote:

Others have pointed out that this is easier for an Experimental glider. It is easiest for an experimental, amateur-built glider. For E-AB, depending on the operating limitations, you might have to notify the FAA and repeat Phase I testing. But nobody wants to see your engineering validation, and only the person signing off the annual condition inspection needs to review your workmanship. The FAA or DAR only wants to see that the paperwork is correct and that placards and operating limitations are correctly spelled out. A good DAR will look the airplane over to make sure it doesn't look particularly dangerous, but they aren't required to.

We have FES going into one of our glider kits right now, and are preparing for the installation of electric self-launch systems in future models.

--Bob K.

On Wednesday, February 3, 2021 at 11:35:51 AM UTC-8, Bob Kuykendall wrote:
On Tuesday, February 2, 2021 at 1:26:10 PM UTC-8, David Scott wrote:

Others have pointed out that this is easier for an Experimental glider. It is easiest for an experimental, amateur-built glider. For E-AB, depending on the operating limitations, you might have to notify the FAA and repeat Phase I testing. But nobody wants to see your engineering validation, and only the person signing off the annual condition inspection needs to review your workmanship. The FAA or DAR only wants to see that the paperwork is correct and that placards and operating limitations are correctly spelled out.. A good DAR will look the airplane over to make sure it doesn't look particularly dangerous, but they aren't required to.

We have FES going into one of our glider kits right now, and are preparing for the installation of electric self-launch systems in future models.

--Bob K.
Since I am new here what kit do you produce? Are you preparing for FES or retractable pylon?
Any idea how much thrust an FES produces? My search came up empty.