Gas to electric conversion chart? - RC Groups
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Mar 10, 2005, 11:43 PM
Registered User
hawknips's Avatar

Gas to electric conversion chart?

Hi all

I am looking for a gas to electric conversion chart. In other words I am looking for something that shows me if a model was designed for a .051 to .10 gas motor what kind of electric motor should you use. What bushed or brush-less motor would be comparable to what ever size gas motor the plane was built for. Anyone out there know where I can find a chart such as this? Thanks in advance.

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Mar 11, 2005, 12:24 AM
Molybdenum Member
I know a 1.60 with some prop is roughly equivalent to C50 14xl 6.7:1 22x12 10s3p. The electric version is a little heavier but has lots more thrust.
Mar 11, 2005, 02:52 AM
Pontificating Member
tone's Avatar
heheheh belive this, it ain't that simple.

For instance, you can get almost exactly the same performance as Scott's setup (a great one by the way) with other hackers at other ratios. Plus that setup is way more powerful than you asked about.
Then you also have direct drive motors like AXI and the like..

The only way to really beat the learning curve, is to pick a specific model you want to fly, and look around here for sucsessful combos, then copy.
Otherwise get used to using P-calc and motocalc for 'guesstimates'.
but in general, for most planes of 1/2A size i would think a Himax 2025-4200 would work. You can change ratios and props for more speed or more power and it will handle a model up to about 20oz with pleasant results. if you just want to putt around, it could do a 30oz model. But then so will a lot of different motors, the Hacker B-20 series, AstroFlight 020, Axi 2212, Razor 2500, Mega 16/15/x are just some i can think of easily..

Anyway, pick a plane, then the power/ratio/battery.
If you already have a motor or battery, then look for planes it(they) will work on here on the zone. Either way this place is a great source of information, but there really isn't a conversion chart like you want.
Mar 11, 2005, 03:02 AM
Registered User
I have delveloped such a conversion work sheet a couple of years ago that seems to work. It relies on airplane advertized specs and average wet power package weight. The basics are follows.
Kit selected: Skyshark SBD
Wing area: 557 Sq ", 3.868 Sq '
Max weight: 8 lbs
Wet Pwr pkg weight, 45 to 61 Cu: 1.99 lbs
Build weight: 6.01 lbs
E motor selected: Astro 25 brushless geared w/12x6 APC E prop, 15 GP 3300's
E power pkg weight in lbs: 2.718 lbs
Max weight: 6.o1 + 2.718 lbs = 8.728 lbs
Wing loading: 36.1 oz per sq ' or 2.256 lbs per sq '
Power loading: 206.82 Watts per sq '
Watts per lb: 91.65 W per lb
E power pkg weight in percent of total weight: 31 percent

This put me in the ball park for conversions and gave me a better insight to what guys are talking about. Hope this helps. My work sheet is different from this as it provides step by step notations. Vj
Mar 11, 2005, 03:14 AM
Registered User
I want to add that I attempted to comply with the general concept of watts per lb and wing loading criteria that is considered to effective. Vj
Mar 11, 2005, 03:30 AM
Registered User
hawknips's Avatar
Thanks for the useful information. I can see I have allot to learn and I see this is not an easy question. So let me start by telling you all what I have here.

I bought the House of Balsa Bonanza kit. Kit number K-13

Here are the specs
Wing area: 216 sq. in.
Wing span: 36 in.
Length: 28.5 in.
Weight: 20 to 28 oz.
Engine: TD .051 to.10
Wing loading: 14.6 - 18.6 oz./sq. ft.

It says it is 20 to 28oz. but I plan on adding re-tracks as well. I am really in to the scale flight thing. I just started the build and will need to get the motor soon.

I have found a few threads here but most of them are from 2002 to 2003 and I know motors and batteries have come along way sense then. So any other suggestions would be a great help. Thanks again I love You guys are always so helpful.

Mar 11, 2005, 03:47 AM
Registered User
Another thing I forgot. E motor specs are very important.
Example: Astroflight 25 brushless geared, 15 nicads, 12x6 APC prop.
50 A, 800W, 9900 RPM. Thats where I got the Watts to work with.
I think this concept will work for you if you follow the generally excepted watts per lb and wing loading information for the type of flying you want to do ( as in the stick'ys ) in the forums. Otherwise, follow someone else's success for a given conversion. Vj
Mar 11, 2005, 03:55 AM
Deletedfor proving Nauga wrong
asking e to glow conversion is hell... I can't even get a straight answer to what brushless motor equals a brushed motor...

And even specifying the desired prop.. desired thrust.. desired pitch speed (which matches the thrust in a thrust calculator) desired RPM.. desired voltage to the motor... no one will say.... "Yep.. this motor will do it."

A "speed 500" is pretty close to the power of a .049 when run on 6 to 8 cells and given the appropriate propeller for the aircraft. And thats the only glow-electric conversion that I KNOW comes out on power output. You generally lose performance with the speed 500 direct drive compared to a .049 if you use NiCds because of the weight. If you gear drive with a larger prop.. you can get close to the .049 powered performance even with the ADDITIONAL weight penalty.

Thats from experience putting a speed 500 into a 2 meter sailplane... which I had originally used a .049 in (and I eventually ripped the electric drive out... and stuck on a .10... THEN it flew the way I wanted. till the wings folded.)
Mar 11, 2005, 03:56 AM
Registered User
Threshold's Avatar
The real problem seems to be what does someone mean when they say this is the right motor for this aeroplane. If its a trainer you might want a 0.5 to 1 power to weight ratio, if its a 3D plane you might want a 2:1 power to weight ratio. What we need is a simple chart

weight thrust in oz prop amp draw rec battery battery weight

you could do without the battery info too. That could be your choice depending on how long you wanted to fly verses wing loading.

All this comparing it to an IC motor which probably is the wrong size anyway is not helpfull. I buy my electric motors from a guy who makes them himself, and he gives exactly that info above so you can work out what your power to weight ratio will be for a given weight of aircraft.
Mar 11, 2005, 04:02 AM
Registered User
vintage1's Avatar
Originally Posted by hawknips
Hi all

I am looking for a gas to electric conversion chart. In other words I am looking for something that shows me if a model was designed for a .051 to .10 gas motor what kind of electric motor should you use. What bushed or brush-less motor would be comparable to what ever size gas motor the plane was built for. Anyone out there know where I can find a chart such as this? Thanks in advance.

If that is all you want to do. get a long can 480 and a 3s LIPO pack (2100mAh or greater), and a 5-6" prop. 18-20K RPM on a 5.5"" prop?

Appx 20 oz of thrust (6x3) and about 55mph pitch speed, unloading to give about 60mph top speed on a slippery auframe.

It will be close enough.

Better motor would be permax 450T on 6x4, or mega 16/15/4 bryshless. All on same pack

Of course, you don't NEED all that power and RPM for most .10 models, but that is a simple effective 1:1 swapout.

Note 1 power to weight is not a ratio
Note 2 a 550 motor is overkill to replace a .10. - Nearer .15 to .20
Last edited by vintage1; Mar 11, 2005 at 04:09 AM.
Mar 11, 2005, 04:05 AM
Deletedfor proving Nauga wrong
no one who has flown glow (and not sailplanes or e-power before) wants 0.5:1 even on a trainer... if its not 0.75:1 or better.. then it seems like an underpowered hunk of junk... even if it is a trainer or a motor-glider.

I know how to handle a motor-glider on 0.3:1.. and do just fine... but I really don't enjoy that type flying much any more. (constantly looking for thermals because tis about the only way to climb)
Mar 11, 2005, 04:13 AM
Registered User
vintage1's Avatar
Oh. Looking at that kit, a gear box might be no bad thing on those motors I mentioned.

Something like 2.33:1 and an 8x6 prop. Otherwise keep it all the same. Its a heavy miodel for the size. I would normally use a geared 400 for that size of model and shoot for 17-20oz or less, but a 480 will be spot on on 3s LIPO.

Don't even think about Nicklel cells - you need to keep weight down. Glo models are normally produced without much regard to weight.
Mar 11, 2005, 07:38 AM
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Bruce Abbott's Avatar
This opinion brought to you by Motocalc

MotOpinion - HOB Bonanza (K13)
Sea Level, 101.3kPa, 20C

Motor: Mega ACn 16-15-5 ; 1800rpm/V; 0.8A no-load; 0.1 Ohms.
Battery: E-Tec ET-1700HP (ba); 3 cells; 1700mAh @ 3.7V; 0.035 Ohms/cell.
Speed Control: Castle Creations Phoenix 25 ; 0.0065 Ohms; High rate.
Drive System: APC 7x4 (ba); 7x4 (Pconst=1.2; Tconst=1) direct drive.
Airframe: HOB Bonanza (K13);; 25.6oz; 17.2oz/sq.ft; Cd=0.052; Cl=0.52; Clopt=0.66; Clmax=1.2.
Stats: 93 W/lb in; 73 W/lb out; 20mph stall; 26mph opt @ 55% (50:13); 30mph level @ 60% (44:39); 1146ft/min @ 29.6; -219ft/min @ -5.4.

Power System Notes:

The full-throttle motor current at the best lift-to-drag ratio airspeed (15.1A) falls between the motor's maximum efficiency current (8.14A) and its current at theoretical maximum output (41.8A), thus making effective use of the motor.

Aerodynamic Notes:

The static pitch speed (52.6mph) is within the range of approximately 2.5 to 3 times the model's stall speed (19.6mph), which is considered ideal for good performance.

With a wing loading of 17.2oz/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 (20.7oz) to weight (25.6oz) ratio is 0.807:1, which will result in very short take-off runs, no difficulty taking off from grass surfaces (assuming sufficiently large wheels), and steep climb-outs.

At the best lift-to-drag ratio airspeed, the excess-thrust (12.5oz) to weight (25.6oz) ratio is 0.486:1, which will give steep climbs and excellent acceleration. This model should be able to do consecutive loops, and has sufficient in-flight thrust for almost any aerobatic maneuver.
Mar 11, 2005, 04:33 PM
Balsa Flies Better!

All of the HOB airplanes are basically the same- the differences are cosmetic- wider fuses- tail feathers etc. The designer (Fred Reese) would not agree with your decision to put retracts in this airplane. I suggest you ask and see if anybody has been successful at flying one of these airplanes with retracts. They are not slow, and the Bonanza is really much faster than scale speed (well, they all are, but this one is the most egregious.) If you haven't got a lot of experience- I highly recommend trying the lightweight approach with this airplane- shoot for 20 oz- hack and leave out what you can. A possible lightweight candidate for a motor is an Axi 2208/26 swinging a 7" prop on 3s lipoly. I would not go less than 125 watts in this airplane, and I fly mine on around 175-200 swinging 7" props. An 8" prop won't clear, but will haul the airplane around looking somewhat unscalelike- actually might be kind of fun on 125 watts and an 8" prop come to think of it. Flew one on 75 brushed watts and a 9" prop-not really great- pushed everything hard- motor was hot, airplane wouldn't even loop without a dive. Lots of options, but I'd ditch the retracts.

Victor- have you flown that SBD yet? S calc says you're gonna be very unhappy- you don't have enough watts to fly at anything less than full throttle, and you'll have maybe 3-4 minutes of duration. It's way undergunned.

Mar 11, 2005, 05:51 PM
Pontificating Member
tone's Avatar
I do like the look of the bonanza, but the wing loading is a bit high at 28oz All Up..

Figure on the Mega noted above as a pretty good answer. the Himax i talked about will do it ok. The Axi 2208/26 which i have on my 15oz e-starter is a fine performer on 2s lipo, it would draw too much on 3s for my taste. A great little motor, but i think you'd be pushing it too hard on this plane. The Axi 2212/26 would be ok, but it sounds like a 7 inch prop is about the biggest you should use to have a scale look. So the AXI might not be a great choice here...
The mega 16/15/4 is great with the 7x4 APC prop direct drive, and a friend flys a very heavy formosa with retracts (24oz i think), with it. Very fast and powerful.

This is about the same weight of plane that Wattage sells and includes it's Cobalt 400, but i haven't heard anyone that really likes the setup. The motor is an AMP hog.

I agree with MegowCoupe. Keep it as light as possible for the best lower speed handling. I might go for the Razor 2500 if i could spin a 9 or 10 inch prop, but it sounds like that isn't an option. It is lighter by far than other 200 watt systems.

For me, the Mega 16/15/4 would be a good, reasonably economical direct drive solution. 3s 2100 or 2600 25amp battery, and a Castle Creations 25 weighs about 9oz and spins the 7x4 very well. You'll get about 200-225 watts or so..

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