Giving Electric a good look with a SIG 4 Star 20 EG - RC Groups
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Jan 02, 2018, 11:12 AM
Village Wizard
Gene Chernosky's Avatar
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Giving Electric a good look with a SIG 4 Star 20 EG


I've been doing this hobby for 50+ years, roots in glow-fuel. Recently, I bought a SIG 4 Star 20 EG kit, and I'd like to go electric on it. I don't want a fast plane, rather one with plenty of thrust for maneuvering. Flights of 10-15 minutes are good.

So, set me up with a motor, prop, speed control and battery recommendation...and don't try to break the bank, please.

And, while I'm asking questions, what would be some good servos to put in that plane? I've got 4 new Hitec HS-81's to play with.

Thanks for your time!
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Jan 02, 2018, 12:19 PM
Registered User
manuel v's Avatar
Motor to 90 watts/lb.
79-100g weight.
Kv 1145
Propeller APC 10x5., 9x6
3s2200ma
ESC 25-30A.
8 minutes flight.


Motor to 110 watts/lb. (Not is necessary)
95-125g weight.
Kv 1200
Propeller APC 10x5., 9x6
3s2200ma.
ESC 30-40A
Jan 02, 2018, 01:12 PM
Registered User
Ken Myers's Avatar
Quote:
Originally Posted by Gene Chernosky
Flights of 10-15 minutes are good.
You won't get 10-15 minutes with the type of flying you describe. 7 or 8 minutes would be the norm for a sport model.

At my field, the glow guys average about 7 or 8 minutes a flight, but your milage may vary.
Jan 02, 2018, 02:33 PM
Village Wizard
Gene Chernosky's Avatar
Hmm, a .46 2 stroker on 10% nitro fuel will get 15 minute plus flights with a 10 oz tank.

Possibly I should stay with a .30 4 stroke for the front and a 4 oz tank...EASY 15+ minutes flights with that.
Jan 02, 2018, 03:15 PM
I'd rather be Flying
davecee's Avatar
....
Last edited by davecee; Jan 03, 2018 at 08:29 PM.
Jan 03, 2018, 12:29 PM
Village Wizard
Gene Chernosky's Avatar
Looking closely at a Park 480 1320kv, 40A ESC w/ UBEC 4A, 3s1p 30c 2200mAH, APC 9x4.7SF, Hitec HS-81 servos.

Will build plane as light as possible, probably take a bay off of each wing tip, knocking it down to 43" W/S.

If all it get are 5-10 minute flights...oh well...electrics do have limitations...and charge times vs. just fill up the tank again.
Jan 03, 2018, 01:04 PM
Registered User
Ken Myers's Avatar
SF (slow fly) props are not a good choice for sport planes.
You might want to consider an APC 9x6E thin electric to start with and see what amps your power meter indicates at full throttle. Also the 4.7" pitch is really too low for a sport plane. Most electric sport planes fly in the 50 mph to 65mph range at full tilt.
Jan 03, 2018, 01:33 PM
Registered User
yorkiepap's Avatar
Quote:
Originally Posted by Gene Chernosky
Looking closely at a Park 480 1320kv, 40A ESC w/ UBEC 4A, 3s1p 30c 2200mAH, APC 9x4.7SF, Hitec HS-81 servos.

Will build plane as light as possible, probably take a bay off of each wing tip, knocking it down to 43" W/S.

If all it get are 5-10 minute flights...oh well...electrics do have limitations...and charge times vs. just fill up the tank again.
Hey Gene,
I looked at the Tower listing, & the 2nd review(4 mos ago), by oflyn, showed his setup for easy 15min flights you may want to look at. Hard to say how true his review is. See what you think.....

Denny

https://www.towerhobbies.com/cgi-bin...&I=LXEZHM&P=ML
Jan 03, 2018, 01:38 PM
Village Wizard
Gene Chernosky's Avatar
This motor pulls 25.2 amps with a 9x5 on 11.1v, per the webpage. Max amps was 28.

Hmm, a 4.7 pitch on a 1320kv motor running on 11.1 volts, in a perfect world, would generate 65.21mph...so I am in the 50-65 window easily.
Jan 03, 2018, 02:05 PM
Village Wizard
Gene Chernosky's Avatar
I read the review. For one thing, he was using a higher capacity of battery. Higher capacity means more weight, and cost...delicate balance. Possibly that is why I got answers of less than 10 minutes flight time...light flies better!
Jan 03, 2018, 02:36 PM
homo ludens modellisticus
Ron van Sommeren's Avatar
Quote:
Originally Posted by Gene Chernosky
... roots in glow-fuel. ... and I'd like to go electric on it. ...
Some well-structured reading and handy e-tools for rainy/windy days.
Will save you, and us a lot of questions. Notably the 'what went wrong?' kind of questions
Will also prevent you from burning up several controllers and/or motors and/or battery:
E-flight primer and tools

And please, do your RC equipment, wallet, ego, battery, controller, motor, house/garage/car a big favour ... get a watt-meter. It will more than pay for itself, will save you at least one fried motor and one fried controller. Will also help you finding the best setup.

Vriendelijke groeten Ron
Jan 03, 2018, 03:35 PM
Registered User
Ken Myers's Avatar
The RPM limit for an APC 9x4.7SF slow fly prop is 7222 RPM. The limit is set by APC Prop.
https://www.apcprop.com/technical-in...on/rpm-limits/

Please don't use APC slow fly props on sport planes. They are very inefficient at high rpm and suck amps, which shortens flight time.
Jan 03, 2018, 03:44 PM
An itch?. Scratch build.
eflightray's Avatar
Gene, you are quoting figures as though they are accurate and valid. Many figures quoted by electric motor manufacturers are calculated, not necessarily accurate for every motor they supply. (Do you believe a car manufacturers brochure MPG figures ?).

Likewise, using prop pitch, motor kv and voltage, will not guarantee a models speed, there are losses, and drag to consider.

If trying to keep the wing loading down by building light, why reduce the wing area by deleting two wing panels ?

Electric is different to IC power, there isn't a direct relationship when it come to the flying. But a lot of people now enjoy it, many will fly both electric and IC power and accept there is a difference.

Try electric power. If you don't like it, nothing lost, just experience gained.

Ray.
Jan 03, 2018, 04:12 PM
Village Wizard
Gene Chernosky's Avatar
Quote:
Originally Posted by Ken Myers
The RPM limit for an APC 9x4.7SF slow fly prop is 7222 RPM. The limit is set by APC Prop.
https://www.apcprop.com/technical-in...on/rpm-limits/

Please don't use APC slow fly props on sport planes. They are very inefficient at high rpm and suck amps, which shortens flight time.
I had never paid any attention to that page as 'wet power' props typically can handle what you throw at them. Duly noted, APC 9x6E selected...the initial recommendation from the other source specified a 9x6 as well.

Everything else is in order...2200 mAH x 30 is 60 amps...will only be drawing 25-28...ESC is a 40 amp...still good.
Jan 03, 2018, 04:36 PM
I'd rather be Flying
davecee's Avatar
....
Last edited by davecee; Jan 03, 2018 at 08:29 PM.


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