Sig/Herr Breezy Day Cub - Motor Selection Advice

[FL-Hawkeye]

Started my build and I need to select a motor. The design is from 2001 and I understand that motor technology has advanced a bit.

TooJung2Die in an earlier post of mine suggested a motor in the 250 range. Herr suggested a "280 Speed Electric" which I assume is in the 250 range.

I'm thinking a Park 250 brushless outrunner motor will work. Link below.

The motor in the Herr drawing extends .84 from the front of the fire wall. See attached image. The specs on the Park 250 state that the "case length" is .9 inches (23mm).

The firewall has a 1" hole for the original motor mounting (see pic). Depending on how the new motor mounts, I may cut a new plywood firewall if the hole causes mounting problems. For clarity, I'm not running the motor through the hole like the Herr drawing shows.

https://www.horizonhobby.com/produc...IO5ElxF5NvNPPbHF4dAZvOgVjOL3347oaAgNmEALw_wcB

Questions are:

1. Is the Park 250 a good choice?
2. Are there better choices? Maybe a FlightTest motor? I could not make sense of the FlightTest specs to see if one was a good candidate.
3. Am I missing anything?

Thanks in advance for your advice. More questions coming....

Mark

 

[Hai-Lee]

Having built a few older electric designs in the past I would recommend a motor that is close in weight even if it means more thrust.

You can easily decrease the prop diameter or pitch to return the thrust level to the same as the original design.

With a more powerful motor you can increase the thrust later if you want a brisker performance.

If you do not match the motor weight and possibly the battery weight as well you may find that you are adding copious quantities of lead just to get the bird to balance and as the added weight is not at the very nose of the bird the overall weight increases and the plane's performance can suffer.

Just a few things to consider!

Have fun!

 

[FL-Hawkeye]

Hai-Lee,

Good suggestion. But, Herr did not include any specifics on the motor other than "280 Speed Electric".

I think Sig is missing out on sales by not suggesting what components to use in their models and including them in their catalogs...

Mark

 

[TooJung2Die]

I'm thinking a Park 250 brushless outrunner motor will work. Link below.

I think that will be plenty of motor for an airplane this size. Are you thinking it'll be under 8 oz? I have a 250 size (whatever that means) in the Contest Commercial, 36" wingspan, 150 gram AUW. It'll climb near vertical with a tiny 2s battery on board. It's almost too much motor.
You could use this motor too: Suppo Park 250

 

[rockyboy]

I think that will be plenty of motor for an airplane this size. Are you thinking it'll be under 8 oz? I have a 250 size (whatever that means) in the Contest Commercial, 36" wingspan, 150 gram AUW. It'll climb near vertical with a tiny 2s battery on board. It's almost too much motor.
You could use this motor too: Suppo Park 250

Those motors should be just fine for it, but consider what HaiLee said and try to push your battery location as far forward as you can since the modern brushless will weigh less than the older brushed version. If you can adjust weight forward (servos or batteries etc) you can come in under the expected weight and balance out with an even better flying model.

 

[TooJung2Die]

You can experiment with locating the electronics before you cover the airplane. Mount the motor and tape on the wing and tail feathers. Then see where the battery and other electronics need to go to get the CG right. Try to get it slightly nose heavy because the covering will add more weight to the tail. Ideally you won't need any ballast when finished.

 

[Born2bwire]

Maxx Product Inc. still carries a line of brushed can motors. If you're really uncertain about the brushless you can still get a conventional Speed 300 motor.

https://www.maxxprod.com/mpi/mpi-10.html

 

[Robert007]

I’m building a Herr Air Boss that also calls for a Speed 280 motor. It’s 8-11 ounces 225-320gm.
A current radicalrc.com GWS Speed 280 specs: 4x2.5 prop, 8.4 volts, 2.5Amps, 100g Thrust, 21watts Input.
An E-Flite 180BL 2200Kv specs: Draws 2.9Amps on a Hyperion 2 cell LiPo 50c, 24.4 Watts input on my test bench. (Don’t know the thrust).
An E-Flite 250 BL has at least twice the power.
Electric RBC recommendations: Less than 50W/lb - will fly a very lightweight / low wing loading slow flyer.
Speed 280 gives 42 watts/lb at 8 oz
E-Flite 180BL gives 48.8 watts/lb at 8 oz
Now, it seems to me that a modern motor should have more power out than a twenty year old technology, therefore the 180BL should give similar or better performance than the Speed 280. (At least that’s what I intend as a first trial on my Air Boss).
What think you all?