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Old 12-19-2014, 04:38 PM   #1
ditchit
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Default Recommendation for motor/ESC for 84.5 in TopFlite P51 Mustang

Recommendations appreciated. This model has been built specifically to accommodate an electric setup with a mount and battery compartment. The previous owner was going to use a Turnigy Rotomax 1.4 but I'm kinda doubtful that would pull it around with authority.

http://www.top-flite.com/airplanes/topa0400.html

Stock Number: TOPA0400
Wingspan: 84.5 in (2140 mm)
Wing Area: 1245 in (80.3 dm)
Weight (w/radio): 17.5-19 lb (7940-8620 g)
Wing Loading: 32-35 oz/ft (98-107 g/dm)
Fuselage Length: 73.5 in (1865 mm)
Requires: 2.1-2.8 cu in glow engine or 2.5-4.2 cu in gasoline engine, 6-7 channel radio w/10 servos


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Old 12-19-2014, 06:08 PM   #2
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Originally Posted by ditchit View Post
Recommendations appreciated. This model has been built specifically to accommodate an electric setup with a mount and battery compartment. The previous owner was going to use a Turnigy Rotomax 1.4 but I'm kinda doubtful that would pull it around with authority.

http://www.top-flite.com/airplanes/topa0400.html

Stock Number: TOPA0400
Wingspan: 84.5 in (2140 mm)
Wing Area: 1245 in (80.3 dm)
Weight (w/radio): 17.5-19 lb (7940-8620 g)
Wing Loading: 32-35 oz/ft (98-107 g/dm)
Fuselage Length: 73.5 in (1865 mm)
Requires: 2.1-2.8 cu in glow engine or 2.5-4.2 cu in gasoline engine, 6-7 channel radio w/10 servos
Ah Yes, giant scale electrics.

FYI, it won't be cheap, but it isn't hard to match the power output of a 30 cc gasoline engine. Just be sure to buy quality equipment. IMHO, it's not a good idea to go cheap in giant scale electrics, just to many $$$$ involved.

For good acrobatic performance, you'll need around 140 to perhaps 160 Watts per pound of airplane, ready to fly. With a 19 pound model, that comes out to around 3000 Watts. This is in the area of the Hacker A60-14L motor. This motor is rated at 2600 Watts continuous power output. FYI, the DLE 30cc gasoline engine will put out about 2300 Watts or so.

If this is your first giant scale model, one thing of note, be danged certain you have a positive disconnect for the battery power to your model. And, if your transmitter has a throttle kill function, use it. Once you see a 3000 watt motor running at full power, you understand why.

I've got two Hacker A60 motors, one is their A60-16M, the other is the A60-5S. Both are powerhouses. The 16M motor turns a 19X12 APC-E prop at 6700 RPM on the ground, and pulls my 18 pound giant Big Stick model straight up out of sight.

You also need dual power supplies to your receiver. I use the Castle Creations BEC, along with a two cell 2300 Mah A123 (or LiFe) battery for a backup. The references below show how this was done. Castle Creations also makes quality, reliable ESC's, but they are not cheap. My two giant scale models us the CC 80 Amp HV (High Voltage) ESCs. Receiver power is a CC 12S uBEC.
http://www.castlecreations.com/produ...x-edge-hv.html

I'm a Hacker motor nut, but AeroModel is closing down shop for the Hacker distribution in the USA.

Espritmodel still has Hackers in stock though.
http://www.espritmodel.com/hacker-a6...es-motors.aspx

Another motor mfg is Motorolfly, although I do not have ANY experience with them.

Here are some references on what I've got experience with.

"C" and what it is
http://www.wattflyer.com/forums/showthread.php?t=65869

Model airplane Power Systems
http://www.wattflyer.com/forums/showthread.php?t=73275

Giant Scale Power System:
Battery Backup System

http://www.wattflyer.com/forums/showthread.php?t=63794

Giant Scale electric motors vs Gasoline Engines
http://www.wattflyer.com/forums/showthread.php?t=58035

Great Planes Giant Big Stick Electric Conversion
http://www.wattflyer.com/forums/showthread.php?t=65052

Giant Scale Cessna Model
http://www.wattflyer.com/forums/showthread.php?t=66414

Redwing MXSR Model
http://www.wattflyer.com/forums/showthread.php?t=72225

The only problem I've had with the A60 motors is in that Big Stick, where when flying over the field at full throttle, about 5 feet off the ground, the model got hit with a big down draft. The landing gear splayed out, the prop hit the ground, and broke off the motor shaft. The prop show it dug into the grass field four inches deep. Picked up a new motor shaft, installed it, and am still flying that model. FYI the A60 motors have a threaded 8 mm shaft on it, no prop adaptors are used. It's got around 300 flights on it now.

With proper quality equipment, these giant electrics have absolutely reliable performance. If you don't fly more than about 60-70% of the battery pack on any given flight, all will work out very well.

It's interesting at out club field. More than once, I've watched a fellow club member spend an hour or more, trying to get his gasser to go, only to find out the plug was shot, the ignition didn't work, the ignition kill unit shut down the ignition, or what ever. While I just plug in my electrics and go fly, with a smile on my face!

Let us know if you have any questions/comments.

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Old 12-19-2014, 06:23 PM   #3
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http://www3.towerhobbies.com/cgi-bin...1p?&I=TOPA0400
Tech notes:
(41-70cc)(Gas)

You'll want in the 4k to 5k watts range. I'm not up to date n the motors in that size range. I still use DLE55 for my 50cc class models.
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Old 12-19-2014, 06:45 PM   #4
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Originally Posted by fhhuber View Post
http://www3.towerhobbies.com/cgi-bin...1p?&I=TOPA0400
Tech notes:
(41-70cc)(Gas)

You'll want in the 4k to 5k watts range. I'm not up to date n the motors in that size range. I still use DLE55 for my 50cc class models.
Yikes

I should have looked at the specs in Tower Hobbies. Tower indicates weight up to 23 pounds not 17 pounds. That would require around 4000 Watts or more, which puts it out of range of the Hacker A60 series motors. The DLE 55cc gasser is good for around 3600 Watts. Most of what I've posted still applies though.

Hacker makes an A80 series motor which will easily handle a model of this size. But, IMHO, you are quickly approaching the limit of what is reasonable in cost for giant electric models.
http://www.espritmodel.com/hacker-a808-motor.aspx

Just search youtube for Hacker A80 motors.
https://www.youtube.com/watch?v=U_Hkw4II-ck

Or

http://shop.subsonicplanes.com/produ...&categoryId=39
There are also some motors out there with a "50 cc" rating on them. Also have zero experience with them.

One big issue with giant electrics, and LiPo power for the batteries, is the cost per flight of the battery pack. That pack won't be cheap, and it will have a limited number of flights before it's performance starts to drop off. I use those A123 battery packs which last a long long time. But for a Hacker A80 motor, you'd need some 45 of those 2300 Mah cells in series/parallel configuration.

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Old 12-19-2014, 09:57 PM   #5
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Cost per flight of a 5000 watt system isn't that bad... over 300 flights per pack set in the big EDF pulling 105 amps peak from 20C rated 5000 mah packs, but averaging closer to 75 amps over the flight.

At $110 for a set of 3 4S packs (newest set I have is now 2.5 yrs old with 3 years being max that they have delivered current demanded) thats about 30 cents a flight. Then the packs will get moved to a lower demand for another year of flying 4S aircraft.

The big EDF is a power hog... the P-51 you could fly at lower throttle more of the time and get longer flights on the same packs.
Pic in avatar: BVM EVF 5612 on 12S.. 14.5 lbs plane RTF, 22 lb static max thrust. 105 amp peak at 48 V under load.... 5040 watts
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Old 12-19-2014, 10:44 PM   #6
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At $110 for a set of 3 4S packs

Out of curiosity, what brand of LiPo's

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Old 12-20-2014, 12:30 AM   #7
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SkyLiPo 20C 4S 5000 .... 2.5 years ago
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Old 12-20-2014, 12:51 AM   #8
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ditchit,

IMHO this one goes over the crossover point of electric vs. gas. I'd go gas and call it a day

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Old 12-20-2014, 01:56 AM   #9
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http://www.nitroplanes.com/77p-sl500...-20c-4444.html Price is up a bit... now about $160 and out of stock.for a set of 3.

http://www.hobbyking.com/hobbyking/s...Lipo_Pack.html
Need 3...
Might want to go to 6 at 4S X 4000 mah and do a series-parallel for longer flight duration. For that I would build a custom harness.

Adequate to fly:
http://www.hobbyking.com/hobbyking/s...hless_ESC.html
Costs more with the data logging but it helps monitor the system. This can pull enough current to fry an Astro Flite Wattmeter.
Might be marginal depending on prop choice...

Better:
http://www.hobbyking.com/hobbyking/s...arehouse_.html

http://www.hobbyking.com/hobbyking/s...arehouse_.html
From comments:
25/02/2013
I have the 50cc rotomax and castle hv160 on 12s and i am only pulling 111 amps with a vess 24a. A 160 is over kill imo.


I'll let you look for the 4 blade prop... 2 blade would drag on the pavement.
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Old 12-20-2014, 03:15 AM   #10
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Originally Posted by dahawk View Post
ditchit,

IMHO this one goes over the crossover point of electric vs. gas. I'd go gas and call it a day

- Hawk
We've had three or four of those 50 cc sized gassers go in at our club in the past two years. Suspicion is vibration got to something important. I personally measured vibration levels of over 25 G's on a club members aileron servo of a giant scale 50 cc gasser model several years ago.

Electrics don't do that.

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Old 12-20-2014, 03:17 AM   #11
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Properly set up gassers don't do that either...
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Old 12-20-2014, 03:59 AM   #12
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The only point I was trying to make was that at this weight, ~20#'s , electric can become impractical. Especially, with the size and cost of the lipo neeed to power it in comparison to fuel. Sure, can it done in electric? Of course it can but I would be asking myself: " Why ?" I look at my Buddie's GP Super Sportster with his DLE setup and think to myself: " This plane would be silly in an electric version"

I only fly electric but my biggest plane is 63" WS and weighs about 7# w/ 5S lipo.

To each his own, I guess.
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Old 12-20-2014, 04:04 AM   #13
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Originally Posted by dahawk View Post
The only point I was trying to make was that at this weight, ~20#'s , electric can become impractical. Especially, with the size and cost of the lipo neeed to power it in comparison to fuel. Sure, can it done in electric? Of course it can but I would be asking myself: " Why ?" I look at my Buddie's GP Super Sportster with his DLE setup and think to myself: " This plane would be silly in an electric version"

I only fly electric but my biggest plane is 63" WS and weighs about 7# w/ 5S lipo.

To each his own, I guess.
Yeah

IHMO my giant scale 3000 watt models are pushing it a Bit. Not the least of it is the requirements for a high power 12 VDC 60 Amp power lead acid type of battery for those that don't have AC power available at their field. I'm charging the A123 packs at 30 Amps. That is pulling 55 Amps out of my 12 Volt DC power supply. Below is what it takes to put out 55 Amps at 12 Volts DC when AC power is not available.

Harbor Freight Gasoline/Alternator Setup
http://www.wattflyer.com/forums/showthread.php?t=66066,

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Old 12-20-2014, 06:51 AM   #14
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Originally Posted by fhhuber View Post
Properly set up gassers don't do that either...
Yup

My "G" meter showed that if you can see vibration or movement on any servo location, that's likely more than 10 G's vibration level.

I go back (way the hell back ) to the days when all receivers and servos used "Stand up" components for the electronics. Vibration wound up breaking off the leads of some of those parts. My models were averaging about 30 flights between servo failures. Even wrote an article back in the mid 1960's that was published in the defunct RCM magazine on how to keep vibration out of your radio.

Now with surface mounted components in our receivers and servos, those problems are much reduced. But still not zero.

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Old 12-20-2014, 10:48 AM   #15
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Much appreciate all the input guys. I did big electrics few years back up to a 40% Extra 300 with a Plettenburg Predator but then moved onto jets. I'm committed to electric on this one. Sure I could put a DLE in it but it wouldn't sound right. This bird is going to be a large scale demo model for MrRcSound system at shows here in the UK.

Looks to me like the RotoMax 50cc on 12S will do the job and be economical although the can is 22mm too long for the existing mount which only allows for 80mm.

YouTube Video
ERROR: If you can see this, then YouTube is down or you don't have Flash installed.
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Old 12-21-2014, 07:17 AM   #16
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Originally Posted by ditchit View Post
Much appreciate all the input guys. I did big electrics few years back up to a 40% Extra 300 with a Plettenburg Predator but then moved onto jets. I'm committed to electric on this one. Sure I could put a DLE in it but it wouldn't sound right. This bird is going to be a large scale demo model for MrRcSound system at shows here in the UK.

Looks to me like the RotoMax 50cc on 12S will do the job and be economical although the can is 22mm too long for the existing mount which only allows for 80mm.
I just ran the numbers through motocalc.com. Battery is a 6000 Mah 12S LiPo with a weight of 60 Ounces. Total weight is assumed to be 370 ounces or 23 pounds. Motocalc predicts 167 Watts per pound of airplane, so your electric conversion will not embarrass anyone, assuming the 21X12 prop measures the proper Amps, and Watts.

Motocalc predicts that this combo with a 21X12 prop will pull 95 Amps, 4000 Watts, and 6700 RPM at full power. Motor efficiency is 91% which is very good. Rate of climb is 3000 feet per minute at a climb out of 61 degrees. You can hang a 22X12 prop on it, but motocalc predicts the motor will run hot, so use a bit of caution and keep tabs on your motor and how hot it's getting. If you can hold your fingers on it for 15 seconds without branding yourself after landing, your motor is OK.

Just be sure to check your Amps, Volts and Watts to make danged certain your motor and power system is running within specifications of your motor/esc/battery pack.

The stall speed is 31 Mph, so keep that in mind during take off and landings.

Here is the motocalc analysis report:

MotOpinion - P51 Giant Scale
Sea Level, 29.92inHg, 59F

Motor: HK Rotomax 50cc; 172rpm/V; 1.6A no-load; 0.021 Ohms.
Battery: Hacker TopFuel EcoX 5800mAh (20C); 12 cells; 5800mAh @ 3.7V; 0.002 Ohms/cell.

Speed Control: Castle Creations Special; 0.001 Ohms; High rate.
Drive System: HK 50 cc Electric; 21x12 (Pconst=1.31; Tconst=0.95) direct drive.

Airframe: TF P51 Giant Scale; 1245sq.in; 376.9oz RTF; 43.6oz/sq.ft; Cd=0.055; Cl=0.47; Clopt=0.71; Clmax=1.24.
Stats: 167 W/lb in; 152 W/lb out; 30mph stall; 40mph opt @ 62% (43:24, 86F); 49mph level @ 75% (30:14, 93F); 3121ft/min @ 61.7; -362ft/min @ -5.9.

Power System Notes:

The full-throttle motor current at the best lift-to-drag ratio airspeed (83.9A) falls approximately between the motor's maximum efficiency current (56.8A) and its current at theoretical maximum output (1008A), thus making effective use of the motor.
The voltage (42.1V) exceeds 12V. Be sure the speed control is rated for at least the number of cells specified above.

Aerodynamic Notes:

The static pitch speed (76mph) is within the range of approximately 2.5 to 3 times the model's stall speed (30mph), which is considered ideal for good performance.

With a wing loading of 43.6oz/sq.ft, a model of this size will have flying characteristics suited to an experienced pilot. The plane will fly fast, and be readily able to handle fairly strong winds.

The static thrust (522.3oz) to weight (376.9oz) ratio is 1.39:1, which will result in extremely short take-off runs, no difficulty taking off from grass surfaces (assuming sufficiently large wheels), and vertical climb-outs. This model will probably be able to perform a hover or torque roll.

At the best lift-to-drag ratio airspeed, the excess-thrust (315.3oz) to weight (376.9oz) ratio is 0.84:1, which will give very steep climbs and incredible acceleration. This model can easily do consecutive loops, and has sufficient in-flight thrust for any aerobatic maneuver.

General Notes:

This analysis is based on calculations that take motor heating effects into account.

These calculations are based on mathematical models that may not account for all limitations of the components used. Always consult the power system component manufacturers to ensure that no limits (current, rpm, etc.) are being exceeded.



Be sure to post videos when you've got it done!

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Old 12-21-2014, 09:43 AM   #17
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Thanks Kyle. That's awesome. Can motocalc work out the optimum 3 and 4 blade prop? Not sure which I'll go for yet. 4 blade prop and spinner isn't cheap.
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Old 12-21-2014, 02:26 PM   #18
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Selections for 3 and 4 blade props are severely limited. Its unlikely that you'll find one this large optimized for e-power off the shelf.

Revising a pair of 2 blade wood props to make a 4 is possible. (and used to be the common way to get big 4-blade props for scale models) For E-power you can save a bit of weight vs the glow/gas method by using aircraft ply plates epoxied to the hub faces instead of the metal plates bolted on as required for gasoline.
Note that you might actually want the weight...

To get a very scale appearing prop start out with one that is 1 to 2 in extra dia and carve it down in size and reshape blades at the rear. Leave the leading edge alone (except reshaping the tip which is close to squared off for the Mustang) if you want it to be usable for flight.
To optimize for E-power you'd underchamber the blades. (carve out the back side... leave the face alone) This can get tricky as you would be needing to remove material evenly on all 4 blades.

(Wal Mart of all places....)
http://www.walmart.com/ip/39751096?w...962889&veh=sem


Finding the right dia for 4 blade is not as simple in this large a prop as for smaller sizes.

Starting at 10X6 prop expecting to turn appx 10k rpm you trade 1 inch dia or pitch for each added blade. (to keep load on the motor the same)

20 inch dia even though turning lower rpm I would expect to trade 1 inch dia AND 1 inch pitch (or 2 inches dia) for each added blade. (to keep load on the motor the same)
EG if the 21 X 12 is the start point I might try a 18X11 4-blade.

These are a basic guide in the search for the best prop....

As you can see the gas version 4-blade is bolted together. There is a potential to replace just one blade, Though damaging just one would be extremely rare.
You can get one of the production line 4-blade props and then replace blades by cutting normal 2-blade props.
Not much cheaper to buy 2 of the 2-blade props than buying a complete new 4-blade though.

**************

Mounting note: If its practical to just pull a bolt for each blade and oversize drill those holes to fit the motor hub, do it that way. If not then drill aiming for the joints between blades. (remember... these are not glued... just the plates and bolts hold it together)
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Old 12-27-2014, 03:05 PM   #19
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Thanks for the prop advice. I suspect I'll be going for a 4 blade prop from Biela with a Truturn P51 spinner. I'll be flying at a few UK Shows next season so its important to me it looks scale...and nothing will look better than those 4 yellow prop tips on a low fast pass...

Sound system tested out. Sounds awesome.

YouTube Video
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Old 12-27-2014, 10:52 PM   #20
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Default Scratch Built Propellers

FYI, for those interested in custom building your own propellers for flying in scale models, be aware of the very significant centrifugal forces involved. On my giant scale Big Stick with its 19x12 APC-E prop, that centrifugal force is on the order of 850 pounds!

It would be a very good idea to do the first prop testing with your motor bolted to a properly secured piece of 2X4 Lumber before trying it in your model. If that prop should ever shed a blade, there won't be much left of the front of your model.

Take a look:
http://www.wattflyer.com/forums/showthread.php?t=70174

DennyV
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