SlowCo
1 MW
Very nice. Hope it will get you up safely in the air soon. How will the prop be positioned correctly to be able to retract it back into the hull?
Self-launching sailplane conversion
- Thread starter AC5ME
- Start date
The electronic braking provides about 15lbs of force measured tangent to the rotor, I'm hoping this will be sufficient to prevent windmilling but I don't know until I do some flight testing. I have a mirror in the cockpit to verify the prop is vertical, I hope I can rotate the motor slowly enough to stop it there reliably.
SlowCo
1 MW
I hope you'll make a video of the first flight and post it here. Very interested.
And if you haven't seen this thread already it is worth reading: https://endless-sphere.com/forums/viewtopic.php?f=30&t=113852&start=125
And if you haven't seen this thread already it is worth reading: https://endless-sphere.com/forums/viewtopic.php?f=30&t=113852&start=125
red
10 mW
- Joined
- Mar 28, 2009
- Messages
- 34
AC5ME,
Sorry, I can't help with the actual conversion, but you seem to be on-track. I send best wishes. I have some input that you may want to consider.
For the flight testing, I am hoping that you can tow up in the usual sailplane manner, and then conduct your performance testing while airborne, with no need to test the self-launching aspect on a do-or-die basis at first.
Assuming you are familiar with "Ground Effect," I would suggest a very long runway for testing, maybe even with enough length to launch and land without turning, if necessary. Build up some excess airspeed in Ground Effect, before commencing the initial climb.
In case your prop-stopper does not work as expected, you may want the ability to lower the motor and prop almost down to the fuselage, and have it held there. This trick may allow the prop-stopper to operate as it should, if it did not do the job with the power pole upright. A mechanical prop-stopper (made from flexible plastic) may do the job for you, if needed, but use that option only if all else fails. Once the prop is stopped, you can lower the motor and prop completely.
Seems like you will be making heavy demands on the batteries, on a continuing basis. I would want a sailplane parachute on my back as a matter of routine, but that's just me.
Interesting project. Best wishes. Please keep us posted.
Sorry, I can't help with the actual conversion, but you seem to be on-track. I send best wishes. I have some input that you may want to consider.
For the flight testing, I am hoping that you can tow up in the usual sailplane manner, and then conduct your performance testing while airborne, with no need to test the self-launching aspect on a do-or-die basis at first.
Assuming you are familiar with "Ground Effect," I would suggest a very long runway for testing, maybe even with enough length to launch and land without turning, if necessary. Build up some excess airspeed in Ground Effect, before commencing the initial climb.
In case your prop-stopper does not work as expected, you may want the ability to lower the motor and prop almost down to the fuselage, and have it held there. This trick may allow the prop-stopper to operate as it should, if it did not do the job with the power pole upright. A mechanical prop-stopper (made from flexible plastic) may do the job for you, if needed, but use that option only if all else fails. Once the prop is stopped, you can lower the motor and prop completely.
Seems like you will be making heavy demands on the batteries, on a continuing basis. I would want a sailplane parachute on my back as a matter of routine, but that's just me.
Interesting project. Best wishes. Please keep us posted.
topspeed
10 W
- Joined
- Sep 6, 2020
- Messages
- 91
I am working on a 2 KW possible cruise consumption system as we "speak". last 16 years I have sketched economical versions and now past 2 months on one of those suited for very economical cruise.That is two seater...I recall Electra One boasted 3 kw for cruise..that is a single seater.
PC-Aero Elektra One - Wikipedia
en.wikipedia.org
It has retractable main gear.
If someone made a plane using 2 kw for cruise that would be very affordable and lite weight.
I could tag some key words....lifting fuselage, large propeller, pusher, good aspect ratio.
Ecyclist
1 kW
You have to be able to stop the propeller vertically and put it inside the fuselage automatically and as quickly as you can. Don't even try to take off without being able to do that. You will kill yourself. It's a cool project and I'm very impressed, but I'm telling you, you have to do it right. You better make sure that stowing away works every time. This thing, the moment is not powered up, will produce a lot of drag. You might even not be able to use a parachute 1. You might not get high enough. 2. You might hit prop while getting out. Please, please, please be careful.
owen3371
1 µW
Excellent!I'm doing the sane with my alisport silent self launch,emrax-188 with emsiso controller and 2.1kw battery pack(x2)
owen3371
1 µW
topspeed
10 W
- Joined
- Sep 6, 2020
- Messages
- 91
AleGaggioli
1 µW
Hi!
I'm working on the same motor and inverter for a different purposem but I'm having some problems, It would be great if you could send me your dcf file that you used to program the emsiso
Thank you!
s-petersen
100 mW
Very cool, but if using Li-on batteries, I would find a way to release and drop the batteries in case of fire.
Ye I've been thinking the same thing:
You want to be able to drop the batteries in an emergency.
IMHO a burning battery landing on someone's head is better than a burning aircraft, with pilot!
You are aware of the old 'blades fold back due to aero drag' type propellors?
The centrifugal force of spinning them and then thrust 'open' them as soon as they start rotating.
The fold away mechanism is then a simple hinged parallelogram arrangement.
Now everything stays more aero during folding/unfolding and there is no prop drag as it is only ever open after it starts spinning.
With a T tail you can implement a highly efficient pusher prop right at the back and skip the whole folding mechanism.
Weight distribution needs to be designed for however.
The accident at Uvalde shows why this is important.
Incident Jonker JS-MD 3 RES OK-3314, Thursday 29 August 2024
During the task at FAI World Gliding Championship held at Garner Field (UVA/KUVA), Uvalde,Texas, the Czech female pilot of a JS-MD 3 RES had to outland into the shallow lake near Comanche...
asn.flightsafety.org
They had final glide made but decided to deploy the engine for good measure. The controller immediately overheated and the failure mode was the prop freewheeled creating a lot of drag, resulting in a water landing.
There was an interesting talk about these issues. The certification standards for these motors (ICE or electric) is pretty lax as it was considered that a failure just results in them being a glider. Turns out there are ways that this can put you into a worse spot than not having it.
It must have taking a fair amount of mental acrobatics to discount and ignore the beauty and simplicity of the self folding/unfolding propeller post prior to yours..?
I assume a lot of design and build is already done for the 'old' style self launcher?
What about a Ducted Fan then? (Where you don't need blade-span)
Here's a 30kw (45 max) example, specifically for glider self launching:
Commercially available:
It must have taking a fair amount of mental acrobatics to discount and ignore the beauty and simplicity of the self folding/unfolding propeller post prior to yours..?
I didn't reply to your comment because it was not relevant to what I was talking about.
A folding prop won't fold if it is still spinning, and a prop being driven by airflow creates a lot of drag. The accident at Uvalde occurred due to an overheated controller that was unable to stop the prop from spinning. If it had been a folding prop the end result would have been the same.
As for EDF's they are incredibly inefficient at the low airspeeds that gliders climb at.
I'm not familiar with said accident, but it seems to me that disconnecting the battery from the motor will stop any motor from spinning.
Are you saying that, with a folding propeller; centrifugal force alone will keep it unfolded, where airflow will keep it spinning?
That does not seem at all likely, or to be the case in any of the working folding propellers in current use.
This design would be more efficient behind a T tail IMHO. Or 2 parallel hinged arms could be implemented to fold this arrangement away into the fuselage.
Yes; EDFs are inefficient. Especially when made cheaply with a large blade tip too shroud clearance/gap. (tip vortices)
But their practicality and easy retraction may well make them worth considering.
I NB that 'in place' tip machining and frangible materials don't yet seem to be 'on the radar' of EDF makers.
Some thought put to turning motor heat into thrust using the Meredith Effect, stators as heatsinks and duct shape might also help.
Your assumptions are incorrect.
The airflow through a prop will keep is spinning at high speed until the aircraft is slowed drastically. In my aircraft I have to be below 70 knots for the prop to stop and that is with a big ICE engine dragging it down. An electric motor has very little drag in comparison.
In manned gliders with retractable engines the prop is positioned for retraction by operating a compression release. In electric ones they motor brake fills that role.
In addition to manned aircraft I have a bunch of large scale R/C electric gliders with folding props. The props will not stop unless you apply some kind of motor brake. If they don't stop spinning they will not fold.
I stand corrected! Thx helno.
I really thought wind resistance would overcome centrifugal force!
Ye; if you have to apply a brake anyway to make it fold, why bother to fold it in the 1st place if you can just brake is where you want it.
I do see that some spring force (or elastic bands in RC) get them folded without needing a brake though.
I wish I could find a damn video of a prop folding and unfolding FFS!
Without checking, I would guess that air pressure in low-speed (glider type) flight is insufficient to force a prop to fold against the unpowered spinning forces, unless there is a spring mechanism strong enough to overcome these forces below some speed at which the prop would never be used while unpowered.
Maybe in much faster airstreams (such as turboprop or jet craft experience?) the pressure would be sufficient, but I'm not sure. I don't have enough experience with aerodynamics / mechanics to know; just my "intuitive feel" for these things based on my limited knowledge...but intuition is not a replacement for experimental test results or knowledge from previous such.
I did find a video suppsedly for a bell folding prop wind tunnel test, but it doesn't appear to have any helpful info on test conditions, what it actually is under test, etc. However, it seems to show the folding mechanism is a forced-actuation, not passive, as I'd expect for something seemingly designed for a more typical powered-flight aircraft (vs glider).
Semi-related side thought: the fluid pressure in water is probably enough to force a boat prop to fold even while spinning unpowered in the water flow. It might even be enough to require a mechanism to keep the prop open against the water flow.
Water is much denser than air--for instance you can be knocked down by inches-deep water around your ankles if it's flowing fast enough, and it doesnt' have to be very fast--no more than a few MPH. It would take quite a gust of air at a similar very low depth to do more than irritate you.
Maybe in much faster airstreams (such as turboprop or jet craft experience?) the pressure would be sufficient, but I'm not sure. I don't have enough experience with aerodynamics / mechanics to know; just my "intuitive feel" for these things based on my limited knowledge...but intuition is not a replacement for experimental test results or knowledge from previous such.
I did find a video suppsedly for a bell folding prop wind tunnel test, but it doesn't appear to have any helpful info on test conditions, what it actually is under test, etc. However, it seems to show the folding mechanism is a forced-actuation, not passive, as I'd expect for something seemingly designed for a more typical powered-flight aircraft (vs glider).
Semi-related side thought: the fluid pressure in water is probably enough to force a boat prop to fold even while spinning unpowered in the water flow. It might even be enough to require a mechanism to keep the prop open against the water flow.
Water is much denser than air--for instance you can be knocked down by inches-deep water around your ankles if it's flowing fast enough, and it doesnt' have to be very fast--no more than a few MPH. It would take quite a gust of air at a similar very low depth to do more than irritate you.
Maybe in much faster airstreams (such as turboprop or jet craft experience?) the pressure would be sufficient, but I'm not sure. I don't have enough experience with aerodynamics / mechanics to know; just my "intuitive feel" for these things based on my limited knowledge...but intuition is not a replacement for experimental test results or knowledge from previous such.
You have it backwards. The faster you are moving the faster the prop will be driven by the airflow.
On multiengine aircraft an failure can be very confusing as the dead engine is still turning. Until the prop is feathered it will create a lot of drag.
This video shows what happens. They close the mixture (fuel) on one engine and then restart it simply by reopening the mixture. The second simulated shutdown they do they feather the prop to stop the engine and reduce drag.
Anyways this is enough of an off topic discussion. I'd love to hear how the testing went on this aircraft.
Without checking, I would guess that air pressure in low-speed (glider type) flight is insufficient to force a prop to fold against the unpowered spinning forces, unless there is a spring mechanism strong enough to overcome these forces below some speed at which the prop would never be used while unpowered.
Maybe in much faster airstreams (such as turboprop or jet craft experience?) the pressure would be sufficient, but I'm not sure. I don't have enough experience with aerodynamics / mechanics to know; just my "intuitive feel" for these things based on my limited knowledge...but intuition is not a replacement for experimental test results or knowledge from previous such.
I did find a video suppsedly for a bell folding prop wind tunnel test, but it doesn't appear to have any helpful info on test conditions, what it actually is under test, etc. However, it seems to show the folding mechanism is a forced-actuation, not passive, as I'd expect for something seemingly designed for a more typical powered-flight aircraft (vs glider).
Semi-related side thought: the fluid pressure in water is probably enough to force a boat prop to fold even while spinning unpowered in the water flow. It might even be enough to require a mechanism to keep the prop open against the water flow.
Water is much denser than air--for instance you can be knocked down by inches-deep water around your ankles if it's flowing fast enough, and it doesnt' have to be very fast--no more than a few MPH. It would take quite a gust of air at a similar very low depth to do more than irritate you.
A modern high-performance glider/sailplane may have a VNE (velocity never exceed) as high as 155knots (180mph, 290km/h). This is its maximum allowed speed. It could go faster but it’s not structurally designed and tested to do so.
During a cross country flight, the glider may be climbing in thermals, rising air currents, while flying slowly at perhaps 50mph. But when ‘cruising’ between thermals might be flying at speeds between 70mph (112km/h) and 100mph (161km/h) or more.
So not so slow. And Solar Powered with not a panel/cell in sight!!
(Thermals)Shot for the video, but that whole feathering and folding process there is powered etc.
If it doesn't auto fold its expensive and adds weight and complexity.
Water or air; it would seem that centrifugal only just wins out against 'folding drag' if some spring force or elastic gets them folded when you cut power to a motor.
BUT:
IIRC You can short the phase wires together with a relay switch to get braking when power is cut..? Plug Braking?
Or switch in a resistor for the load.
???
