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Old Jun 23, 2011, 09:49 PM
Dale
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Jeff,

Sounds like a great project, start a thread, I'll subscribe!

Dale
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Old Jun 23, 2011, 09:58 PM
Dale
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Jeff,

Here is a nice prop program in a zip file, I find it works quite well for initial studies.

Dale
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Old Jun 23, 2011, 11:24 PM
Gene
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Joined Mar 2011
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C of G

Dale,
Excellent reasoning on the electrons vs hydrocarbon fuel source, hope the FAA buys it.

Thats the best way of checking the CG I ever saw.

Is your covering Duralar or Tedlar?
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Old Jun 24, 2011, 09:49 AM
Dale
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Gene,

I think it is unfair to think of electric fuel as electrons and combustible liquid fuel as hydrocarbons. The scale of measurement and complexity is so different between the two. So much more than electrons are needed to contain electric energy. You actually need a cathode, an anode, connecting media and have electrons appropriately positioned before there is even any potential for containing electric energy. I think a fair delineation for electric fuel is the size of the container that can hold the material that actually contains the electrical energy. What other delineation could make sense, after all that is how they define the boundaries of hydrocarbon fuels?

That is still the original 25 year old Tedlar covering.

Dale
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Old Jun 24, 2011, 09:54 AM
jrb
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Hanging helps check balance: Cub & Toledo.

Sling finds CG: P-38.
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Old Jun 24, 2011, 11:31 AM
Dale
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Joined Jul 2004
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Great plum bob idea on the P38! Bridle makes it stable, hangs at correct AOA for CG purposes and levels the wings while plum bob shows the CG. May be a bit tricky to get plum bob to hang 'in line' with the single support line above the bridle.

LOL, I have the same Cub!
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Old Jun 24, 2011, 11:42 AM
jrb
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FYI: http://home.mindspring.com/~the-plum...%20Machine.htm .
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Old Jun 24, 2011, 01:22 PM
Registered User
United States, CA, Shingle Springs
Joined Jul 2007
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Quote:
Originally Posted by KiloOne View Post
Jeff,

Here is a nice prop program in a zip file, I find it works quite well for initial studies.

Dale
Thanks Dale. Can you tell me what kind of file this is? It has a .ex extension that none of my windows programs seem to recognize.

Jeff
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Old Jun 24, 2011, 01:34 PM
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Nevermind, I got it. Just had to add the last "e" on the file extension. Thanks for sharing this.

Jeff
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Old Jun 30, 2011, 08:47 PM
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Perth, Australia
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Originally Posted by jlorenco View Post
This is good stuff - thanks Dale. So, it sounds like the reason we have to limit discharge in RC applications is due to the very high amp draw from the batteries, and they can actually be discharged much lower at low discharge rates.

Jeff
I'll pitch in here with my electric car experience. The applicationis quite differnent to a plane, but I think a lot are in common with each other for large power application Lithium packs. Note my pack is LiFePO4

Rule of thumb we use for battery longevity is keep them as charged as possible, and only go to 80% Depth of Discharge (DOD). The actual voltage range we use is 3.65 to 3.2 V. While 3.65 this sounds limited, the battery is at around 95% charge capacity. I am expecting that my pack should be good for up to 10 years of use in the car (then will replace with the pack of the day at $2 probably!)

I think a car has a harder duty cycle than your plane - it is used daily (so lots of battery cycles), and is subject to varying loads (ie hard acceleration then cruising, repeat at next ligths), as opposed to hard acceleration for take-off then a fairly constant load once your cruising.

I use a battery monitoring system (BMS) that looks at every cell and has the following functionality:
  1. If any cell goes above 4.2 V it cuts out the charger.
  2. If a cell goes above 3.65 V it opens a resistor cct that bleeds off current (and hence balances the pack)
  3. If any cell goes below 2.5 V, it sounds a warning
The BMS makes sure that you do a balanced charge every time, and that if any cell is weak they you are advised if it is getting over-discharged. To me this is essential, to both prevent cell damage and ensure you don't get a power supply failure under load.

The cells I am using are 160 Ahr 3C rated - so in theory good for 480 A. Like all batteries, the harder you pull on them the greater the voltage sag - so under hard acceleration at 75% discharge, they sag to well below 3V.

Not sure if this is of use, but thought I would throw it in anyway.

Oh as an aside - we looked at a BMS that cut the power at around 80% DOD so you couldn't kill the pack. Traffic regulator here said that isn't acceptable - if the vehicle has power you must be able to tap into it in case of emergency (eg stuck on railway lines). Silly really, so we just have it that the system limits how hard you can pull if the battery is low.
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Old Jul 08, 2011, 09:38 AM
Dale
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Joined Jul 2004
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JM1 first results

Received the first JM1 late Wednesday.

Kv as I measured it was 83 rpm/V.

Testing is being done with a Culver 36x20 prop.

I placed the motor temp sensor directly on the stator windings at the rear of the motor. The stator is wound very tightly and no air flows between the stator coils. The windings are fixed with normal winding varnish.

I have not run any full power tests yet. The highest power test so far was yesterday (90 degree OAT) at 7200 watts battery output. The motor temp did stabilize after about 7 minutes at 220 degF.

Joby runs their motors with a temp sensor in the same location but I have not yet received their recommended max temp for this sensor location.

I was happy to see that the sensor temp immediately declined when the motor was turned off which confirms that the sensor is in a good spot.

When the winding temp was 220 degF I was still able to hold my hand on the cooling fins (just barely) when the motor was just turned off.

I believe that this test was encouraging. I expect to run some WOT tests today.

Attached are the graphs of the 7200 watt test.

Dale
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Old Jul 08, 2011, 11:05 AM
Gene
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Still going to Oshkosh

Dale,
Are you still going to Osh? I would like to meet with you there.

Gene
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Old Jul 08, 2011, 01:39 PM
DS JUNKY
DA VALLEY, CA
Joined Jun 2004
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220F is probably about as high you want to go for longevity but given it was 90 degree outside air temp that is not bad at all. 7200 watts is already more than your planned cruise consumption right?
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Old Jul 08, 2011, 10:42 PM
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Kilo,
I helped a friend redo the Tedlar covering on a Lazair about 10 years ago. Really neat design.

I have a question that is outside the electrification discussion, what is your Vmc on that plane? The rudder doesn't look very big. Just curious.

One nice thing about the geared 2 strokes is that if you lose an engine, it won't windmill. As you know a stopped prop creates a lot less drag than a windmilling prop. I know it figures into the whole cost/complexity/weight consideration, but if there were a way to stop a "dead" engine simply, it might be worth doing. I'm guessing a dead electric engine would windmill like crazy.

Don
(ex-RV4 Driver)
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Old Jul 09, 2011, 10:36 AM
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Australia, QLD, Worongary
Joined Apr 2011
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Quote:
Originally Posted by donmei View Post
I'm guessing a dead electric engine would windmill like crazy.
Hey if you wire it up right, it'll be a generator and so give more power to the live engine.
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