Switch to Electric?

Not with Lithioum cells.

I just had a peek at an example cell - E-tech 1200. Now that is 1.2AH at

3.6V roughly - will tolerate 5A, and peak at 10A (just) so that is 36W (peak) of cell and weighs in at .85oz.

Compare with a Nicad sub C where you get maybe 50W of power at 2 oz, but will flatten it in about 3 minutes trying, and you can see that the LiPos are ahead on power density by a factor of two, and on energy density by about FIVE.

So about 60 of those in series/parallel will get you the battery power - thats 51oz of pack, or a shade over 3lb. In fact you wouldn't use those - the Thunder Power Lipos are bigger but I don't have definite data on em.

I'd guess another lb or so for the motor, giving a total of about 4.5lb of power pack to equal a 3bhp motor, AND most importantly, gearable too, so that the prop efficiency can be totally matched for either speed or thrust, depending.

I'd guess that would be a close match for a 180 size engine.

Throttle it back to half power and its good for 15 minutes.

AND it won't wear out, make a racket,deasdstick without warning, has (almost) infinite throttle control and won't generate slime, or consume expensive fuel. Bearings eventually go, but not that fast. No side load. Just thrust by and large (although some gearboxes will put a side load on).

If it wasn't for the cost, there would be no technical reason - just a few emotional ones - to ever buy an IC engine again.

Ahnd if these thiungs DO get the volume (and LIPOS have come out of laptop computers and cellphones, PIC controllers and power FETS are commodity items from the switched mode power supply industry, and the motors are just miniature three phasers, or mass volume produced itemns that go in power tools and electric windows etc..) then the prices WILL come down. There is far less machining on a brushless motor and far less assembly than on a big 4 stroke, the controllers are just a board stuffed with electronics, and lithiumn batteries are ultimately not expensive on materials - just a huge amount of R & D to get over costwise.

Nope, the days of 'slap in a cheap .40' are numbered. It will be 'slap in this integrated motor/controller and plug in this pack, and stick an

11x6 on it and go fly'

I remember when model shops stocked flat rubber motors.

In 20 years IC engines will be as rare as wakefield motors :-)

Reply to
The Natural Philosopher
Loading thread data ...

That's rubbish. I can get 20 minutes out of a $15 motor and $30 pack.

Ok it weighs in at 7 0z, and flies at 18mph, but taking your words strictly...:-)

Reply to
The Natural Philosopher

Power density is about the same I reckon, on Lipolys, given the fact that if you take the total model design into account, you don't need such heavy structures to support a 19th century repicrocating engine up front :-)

Or a tank,or fuel weight, or throttle servo, or muffler, or onboard glo driver...or seperate reciever power pack....

Before Lipo, I did some calcs, and worked out that at best, a Nicad or Nimh power plant all up was capable of 200W or a little more, per lb of weight.

With Liply, its nearer 400W/lb, which menas 2lb per bhp roughly.

I dunno what a stock 60 with tank,. servo, plumbing,. muffler and mount weighs in at, but I'd say it was very similar. SURE the 60 is rated at more than a bhp, but its all at the wring RPM, and you can't gear it. In practice the electric will turn the same prop at the same RPM...

Reply to
The Natural Philosopher

That's not the point tho. You have to look at the total package - the engine and fuel and ancillaries and airframe wight to mount it on, before its a fair comparison.

Heaven forbid :-)

I think its not doable without some thermal or sloping off waves assistance :-) But albatrosses do it on just a few fish on the way, so its not too far fetched :-)

However I'd say that and 11lb plane would need at least 100W to stay in the air: and at say 40mph, would take 100 hours to do the crossing, that is 10Kw/h capacity....which with Lipo technology is well over 100lb of cells :(

Well probably a lot less since big cells would be the order of teh day...but certainly well over 5lb.

OTOH, I'd be surprised if a 2.5cc diesel could do say 100 hours on 5lb of fuel as well.

Agreed.

Depends on definitions of truly cheap. I got two brushless motors, and controllers and a Lipoly pack for $300 last month. Not teh worlds best or most efficient, but still very good. Small motors and controllers are sub $130 and the packs cost - well maybe $50-$100 for a small setup.

As long as you don't mind your flying being done with a 25oz plane, rather than a 5lb one, and top speeds only around the 50mph, rather than

120mph mark, its all within reach of this very average modeller.
Reply to
The Natural Philosopher

Show me an electric that can fly 500 miles and stay aloft 24 hours (FAI restrictions!)

Reply to
Paul McIntosh

But we are talking NOW.

Reply to
Paul McIntosh

Take the rest of the words strictly. The amount of power available in your tiny electric is miniscule compared to a slimer.

Reply to
Paul McIntosh

Even still, the Glow is still superior in weight/power density. It also enjoys a great advantage in initial cost. Even considering paying for fuel, it takes a fairly long time to amortize the cost of competitive electrics.

Reply to
Paul McIntosh

In article , The Natural Philosopher wrote: | Paul McIntosh wrote: | | > But we are talking NOW. | | Yes, we are. Equivalent power to weight between an average 4 stroke and | electric is there. Right now.

Are you sure?

Suppose you want to do something crazy, like, oh, I dunno, fly your plane across the Atlantic ... suppose a 1 lb engine and 5.5 lbs of fuel can do this for you -- could you do the same with 0.3 lbs of motor and 6.2 lbs of batteries?

Also, four strokes are known to produce less power power per weight than two strokes ... so you're skewing the comparison a bit. That's like only saying that electrics suck compared to glow planes, and using only brushed can motors for your comparison.

The only reason that you can get close to `equal power with equal weight' from electrics is that the (expensive, brushless) motors+ESC are a good deal smaller than the equivilent glow engine+servo, so you can use the extra weight for batteries. Which is fine if you just want a short flight ...

But it's coming :)

| It just cots a lot in teh bigger power levels.

And even in the smaller power levels. To come up with an electric power system comparable to a 0.061 with a 4 oz fuel tank and the same weight will cost you quite a bit.

Reply to
Doug McLaren

You can get three HP in less than 3lbs? For how long?

Reply to
Paul McIntosh

Electrics are coming along, but are not hear the capacity of glow. To get equivalent performance costs a LOT more money. Just duration in any reasonabley sized plane makes electrics out of the question.

Reply to
Paul McIntosh

OK, put a 4oz tank on a Norvel .049 and then give the same task to an electric. The Norvel will run full throttle (20,000 RPMs or better) for probably 20 minutes on that much fuel. I remember the old Baby Bees with their 1/2 oz tank going about 5 minutes or more. There are precious few speed 400 electrics that even run that fast with the same prop.

Reply to
Paul McIntosh

Gotta differ with you on this one. I flew 1/2A for years. I now have a Speed-280 model of equal size and performance to, say, the HOB P-51 (which will take an 0.61). On an 800 NiMh pack, I get consistent

15-minute flights. Total cost: motor is $1.55, pack is $18. (Price of an 0.61 is something like $60 nowadays, ain't it?).

Moe

Reply to
Moe Blues

Now you're talking energy to weight ratio not power to weight ratio. The two are not the same thing.

Reply to
Grant Edwards

Don't forget to add $50 or more for a charger!

Reply to
Paul McIntosh

Current draw for a Speed 280 with a 5X4 prop is under 5 amps. 10 amps is overkill, 20 is just wasting weight.

Try Jameco. Speed 280 motors are $1.75 purchased one at a time. Buy ten and they're $1.55 each. I'm not using a gearbox--direct drive.

This has to be one of those "eye of the beholder" things. The in-flight performance of my plane is identical to my 1/2A models of the same size, at least to my eye. The only difference is the lack of fuel.

Without wandering too far from the original topic, there's one other place were electrics thoroughly trounce glow or gas--LMR applications. The ability to turn the motor off, then switch it back on when desired is something neither glow nor gas has equalled (yet).

Moe

Reply to
Moe Blues

There is NO Speed 280 $1.75 can motor that will turn a 5X4 prop any where near the same speed as a typical 1/2A! Put that prop on a Norvel and it will be running over 20K. By your own numbers, the can motor is drawing less than 5 amps so it can't be putting out more than .05HP (5A X 8V = 40W, assuing 100% efficiency).

Give up. The more you try to justify it, the deeper the hole gets!

Reply to
Paul McIntosh

Uh-huh. You're absolutely right. Electric flight is nothing more than a passing fad. Like fire or the invention of the wheel, it will never catch on.

I guess if aircraft performance isn't the criteria, but screaming-high prop rpm is, then the glow engines really are the way to go. Some of us prefer to look at actual flight performance, though.

Moe

Reply to
Moe Blues

You'll be the envy of your club. When I joined my club, I had never even owned a gas plane. Everyone told me that I would have to get gas if I wanted to be serious about flying. In their estimation, electrics were merely toys. A few of the guys had Zagi's, but that was it.

Well I bought an UltraStick 40 ARF and put a Jeti 45/3 in it with 18

3000 nimh batteries. The thing flew great in all whether. I eventually put a 2:1 gear box on it and could hover and perform any manuever that the gas guys could.

Suddenly, I was getting some respect at the club and everyone was asking questions about electric power. Now there are several members that have switched to electric.

I can only imagine what the plane would have flown like back then, if I had owned LiPoly cells at the time.

Go get yourself and UltraStick. Its a great first plane for learning more advanced flight and will fly perfect with electric power.

-- dtanderson

If it ain't broke, I probably didn't fly it.

----------------------------------------------------------------------------------- Posted from the RCGroups.com Discussion Forums. Visit us at

formatting link

Reply to
dtanderson

Screaming prop RPM is an indication of power. Your electric don't have it!

Funny how people losing discussions always start with the sarcastic remarks....

Reply to
Paul McIntosh

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.