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#11
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FES climb rate question.
As is the new LAK 17c FES https://www.youtube.com/watch?v=rxe6DIfPKb4
More prop clearance, 16s batteries and higher max RPM for 2.5 m/s climb rate. The angle of attack of the wing is smaller, back to what it was on the 17a (vs the 17b that was based on the fuselage of the LAK 19) These gliders are sustainers only. Looks like the Silent 2 is rated for self-launch. As is the miniLak FES, also a 13.5M glider. It works well for them because they are lighter than the 18M gliders. -- Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me) |
#12
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FES climb rate question.
On Monday, October 12, 2020 at 3:18:05 PM UTC-5, Mana wrote:
As is the new LAK 17c FES https://www.youtube.com/watch?v=rxe6DIfPKb4 More prop clearance, Looks like keeping the tail down is interesting at 1:30 in the video. What does the POH ask you to do with the stick? If you use it to hold down the tail and hit a bump, then how high can the tail bounce before entering lawn mower mode? Technically self launch, but with grass or tiger country, the tow line didn't look all that long and having the batteries full seems wise. |
#13
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FES climb rate question.
Take-off performance looks impressive. I was surprised by the amount of noise - sounded not unlike a petrol engined aircraft as it passed the camera, although presumably it is actually much less loud.
Any idea what the endurance is of that aircraft? As the owner of a petrol self-launcher, I like to know that I have enough endurance for a launch to 2,100 feet (700 m), a relight if necessary, and a reasonable self-retrieve later if necessary. I will stick to petrol until batteries can cope with at least that. |
#14
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FES climb rate question.
On Friday, October 16, 2020 at 7:11:13 AM UTC-7, waremark wrote:
Take-off performance looks impressive. I was surprised by the amount of noise - sounded not unlike a petrol engined aircraft as it passed the camera, although presumably it is actually much less loud. Any idea what the endurance is of that aircraft? As the owner of a petrol self-launcher, I like to know that I have enough endurance for a launch to 2,100 feet (700 m), a relight if necessary, and a reasonable self-retrieve later if necessary. I will stick to petrol until batteries can cope with at least that. I would like to know if it can even launch to 2,100 ft without the motor/controller overheating. Tom |
#15
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FES climb rate question.
On Friday, October 16, 2020 at 8:11:13 AM UTC-6, waremark wrote:
Take-off performance looks impressive. I was surprised by the amount of noise - sounded not unlike a petrol engined aircraft as it passed the camera, although presumably it is actually much less loud. Any idea what the endurance is of that aircraft? As the owner of a petrol self-launcher, I like to know that I have enough endurance for a launch to 2,100 feet (700 m), a relight if necessary, and a reasonable self-retrieve later if necessary. I will stick to petrol until batteries can cope with at least that. Much of the noise you hear from any propeller-driven aircraft comes from the tips of the propeller breaking the sound barrier. That won't change between an electric vs petrol engine. The longer the propeller, the faster the tips move. |
#16
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FES climb rate question.
On Friday, October 16, 2020 at 4:53:50 PM UTC-7, John Foster wrote:
On Friday, October 16, 2020 at 8:11:13 AM UTC-6, waremark wrote: Take-off performance looks impressive. I was surprised by the amount of noise - sounded not unlike a petrol engined aircraft as it passed the camera, although presumably it is actually much less loud. Any idea what the endurance is of that aircraft? As the owner of a petrol self-launcher, I like to know that I have enough endurance for a launch to 2,100 feet (700 m), a relight if necessary, and a reasonable self-retrieve later if necessary. I will stick to petrol until batteries can cope with at least that. Much of the noise you hear from any propeller-driven aircraft comes from the tips of the propeller breaking the sound barrier. That won't change between an electric vs petrol engine. The longer the propeller, the faster the tips move. My ASH31Mi has a 1.55m diameter propeller that has a max rpm of 2500. If you do the math, this works out to 454 mph, well below the speed of sound. Few GA aircraft have props that go supersonic, and you can really tell those few that can. Tom |
#17
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FES climb rate question.
Much of the noise you hear from any propeller-driven aircraft comes from the tips of the propeller breaking the sound barrier. That won't change between an electric vs petrol engine. The longer the propeller, the faster the tips move.
You're right that a fair amount of noise comes from the prop, and in particular that petrol vs electric won't change this. However, I do not agree that it's because of breaking the sound barrier. Good prop design will keep the max tip speed below 0.6-0.7 Mach at max RPM and flight speed. It would be extremely hard to spin a well-specced prop fast enough that you'd see tips breaking the sound barrier. In an airplane which doesn't have a prop specifically designed to work transsonic (which AFAIK is pretty much any airplane outside of a handful of research ones), the prop loses so much efficiency as the tips approach Mach that you either actually slow down or dramatically increase the required engine power. |
#18
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FES climb rate question.
John Foster wrote on 10/16/2020 4:53 PM:
On Friday, October 16, 2020 at 8:11:13 AM UTC-6, waremark wrote: Take-off performance looks impressive. I was surprised by the amount of noise - sounded not unlike a petrol engined aircraft as it passed the camera, although presumably it is actually much less loud. Any idea what the endurance is of that aircraft? As the owner of a petrol self-launcher, I like to know that I have enough endurance for a launch to 2,100 feet (700 m), a relight if necessary, and a reasonable self-retrieve later if necessary. I will stick to petrol until batteries can cope with at least that. Much of the noise you hear from any propeller-driven aircraft comes from the tips of the propeller breaking the sound barrier. That won't change between an electric vs petrol engine. The longer the propeller, the faster the tips move. The longer the propeller, the slower it turns. -- 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 |
#19
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FES climb rate question.
On Saturday, 17 October 2020 at 00:53:50 UTC+1, wrote:
Much of the noise you hear from any propeller-driven aircraft comes from the tips of the propeller breaking the sound barrier. That won't change between an electric vs petrol engine. The longer the propeller, the faster the tips move. It does happen, but rarer than you think. The Harvard is an example that comes to mind. For me, the only one. Maybe design has moved on a bit since then |
#20
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FES climb rate question.
On Fri, 16 Oct 2020 16:53:48 -0700, John Foster wrote:
Much of the noise you hear from any propeller-driven aircraft comes from the tips of the propeller breaking the sound barrier. That won't change between an electric vs petrol engine. True, provided that the prop diameter, number of prop blades and RPM are the same. The longer the propeller, the faster the tips move. True only if the RPM stays the same. The quietest propeller-driven aircraft I've heard is the Antares 20 - it uses a large (2m diameter), slow turning two blade propeller. From 50m to the side all you can hear as it accelerates past you on take-off is a quiet fluttering/puttering noise. At the other end of the scale, for shear prop-generated racket you can't beat a CRESCO top-dressing aircraft - but you'll need to visit NZ during the top-dressing season to hear that, unless your local jump club has a CESCO PAC-750, which is probably just as loud. -- Martin | martin at Gregorie | gregorie dot org |
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