View Full Version : Converting Critical Mass to Electric

09-30-2005, 05:35 AM
I just purchased, should be here buy next Friday.

I'm going with an AXI 4130/20 and LIPO's. I'm really excited about this plane. It's a KMP. I think with the wieght and size I should be OK. I will add mechanical retracts. It's a glass fuse and cowl, balsa built up wings.

Any input on battery configuration would be appreciated and prop size. I will post pictures when it arrives and the progress on the build.:D


09-30-2005, 11:45 AM
on a 4130/20 you need roughly 8S...4130/16 would have been enough on 6S and a 15*10E; that's what I have on my H9 8lbs warbirds.
Bttw, HL recommends even a lighter setup: 4120/14 on 5S...

09-30-2005, 12:46 PM
I am flying a Hanger9 Corsair with an AUW of 8.18 lbs using 6s driving an Axi 4130/16. Flies GREAT!


09-30-2005, 01:04 PM
I have 2 4130/20's so I'm trying to use them in something. Do you think it would be better to get the 4130/16 for this plane. Do you have pictures of your battery setup? Thanks guys for responding so quickly. Gotta love this site.


09-30-2005, 01:46 PM
4130/20 will need more cells, hence more weight. I find the critical mass already heavy in wing loading (compared to H9 warbirds). I definitely think you could swap towards a 4130/16..
batteries are velcroed on a plywood layer glued till the firewall (see pic, front is on the left).
I use some straps (yellow on pic)to hold them fine (the plywood is close to the top of the fuse, not the bottom.

09-30-2005, 04:41 PM
Hi Marty

Post #3, I forgot to mention that I am pulling 50 Amps at 100% throttle and have 63 Amps available.


10-01-2005, 02:36 AM
Thank you guy's. Geoff Are your 2 packs in series or parrallel? I already have 4-3s packs that are 2100mah each that I was going to use. How many minutes are you getting on a flight?

Greg Covey
10-01-2005, 03:04 PM
You can view Hobby Lobby's setup for the KMP Critical Mass at the link below. http://www.hobby-lobby.com/criticalmass.htm I would not stray too far from their recommended setup and flying weight of 7.5lbs. It appears that there is not much ground clearance left after using a 12" prop so keep the RPMs high.

10-01-2005, 04:35 PM
..good point on the prop clearance...I was also a bit concerned when I saw the plane...

10-03-2005, 07:52 AM
Hi Marty

Packs are 2 x 3.2 amp 3S in series giving me 6 cells @ 22,2 volts with a 10C discharge of 64 Amps.

Flew again Saturday and rises from the ground @ 60% throttle and general flying @ 40-50% throttle.


10-04-2005, 02:38 PM
I feel dum, Hobby- lobby has it all there for you. I can't believe the prop price. In another plane I do have the 4120/14 AXI so I will swap it out. Battery packs and the prop are the only items I need to complete it.

Thanks Greg for giving the site.

Mad Skill
10-05-2005, 03:51 AM
I have had this plane about two months and im just about finished building it. I hope to maiden next saturday. I went with hobby lobbys set up with the 5S3P 6000 and the Axi 4120/14. I hope this flies good, its a great looking plane.

10-05-2005, 07:00 AM
can you tell us the total weight?
what type of retract did you install?

10-05-2005, 12:04 PM
Mad Skill, awesome let us know how it flies with that setup. Can you show some pictures? I'm curious to see if it's enough power to scream.


Mad Skill
10-05-2005, 10:24 PM
I went with the retract set that is on hobby lobbys site. Superlite Retract Set, .60 Size. I havent been able to weigh any thing yet. Im still in the building process. I cant wait to get it in the air.

Mad Skill
10-06-2005, 04:06 AM
Picture from hobby lobbys web site.

10-11-2005, 01:19 PM
I recieved the plane on Friday. First looks: nice looking plane. The 2 wheel pockets for retracts are the same direction so an easy fix was cut the curved area and turn it around. The finish on the fuselage is really nice. The film they use for the wings is so so. Theres a lot of cleaning to do to the wing. It's like glue or something. The rods they supply I don't care for, so replaced them with better ones. Also there wasn't a spinner but this seems to be the norm for KMP. I had an extra that I'll use.

You know whats funny? I have so many fuel tanks sitting around. I think I'll take all of them to an auction just to get rid of them.

Joined the wing sections together and installed Futaba servos.

Mad Skill
10-11-2005, 02:39 PM
mmmdowning, thats great you receiveid yours.
I am almost finished with mine. I tried to CG it last night and found it to be a little tail heavy. I got all three batteries behind the fire wall and still to tail heavy. I think if I use a flight battery instead of the bec I might be able to get some weight in the nose.

10-11-2005, 04:52 PM
Mad Skill
I've learned from others that using a BEC, if battery dies ,etc... you loose control of your servos. So I like running with an extra battery. The battery pack that I'm looking at is all in one pack. 18.5 6000 mah. Makes it a little long. If you went with the 3 battery packs in parrallel can you put one of the 3 in the nose? I would try putting the reciever batery in the nose. I will probably attach mine under the motor mount.

Did you catch some of the mistakes in the directions?
Some of the order of progress are switched around and the length for the aileron rods are measured at 300mm. Way way to long.

Keep posting, I'm curious to see how it goes. Are you using the CF prop from Hobby Lobby?

Mad Skill
10-12-2005, 12:44 AM
I am using the CF prop from hobby lobby, it really looks good and i think that i will have good peformance with it. I didnt notice any big mistakes in the directions.
I could probably fit one of the batteries in the nose but then I would have to take the cowl on and off to get to the battery.

Mad Skill
10-12-2005, 05:06 AM
I got it to balance with one of the batteries on the motor mount and the other two behind the fire wall. I also had to use a flight battery instead of the bec.

10-12-2005, 05:06 PM
Hi guys!

I want to setup my Aero-Star .40 as an electric trainer.

I have 2 foamies :D that I fly regularly, and I a want bigger, but I DON'T want a gas plane:p , It's to messy.

So, I have started to build this plane a year ago from a kit, but It's a slow process and in the middle of it I bought RTF foamies. I would like to convert to electric my Midwest.

The specs are theses:
Wingspan: 62"
Wing Area: 675 sq.in
Wing Loading: 17 to 19 oz/sq ft
Weight: 5 to 5.5 lbs
Length: 52.5"
Airfoil: Flat-Bottom, High-Wing

So it's simple what do I need(motor, ESC and battery packs) ?

Thanks to all for the futur answers!


Mad Skill
10-13-2005, 03:25 PM
I finished it up last night. 1098 whatts at WOT. 8.5 pounds flying weight. I hope to madien this sunday afternoon.

Mad Skill
10-19-2005, 03:49 AM
mmmdowning, how are you doing with your critical mass?

10-19-2005, 04:04 AM
I just got home an hour ago from court. I've gotten as far as wings are glued, stab is done. I ordered 2 props 12x11 apc, and a servo for the retracts. I thought I had one, but not. They came in today. I'm hoping to complete the plane on Friday, I am off on Fridays so I can devote time to the hobby. The motor is mounted, The ailerons are done, and the canopy is glued on with a pilot. I will take pictures and post on friday. My work week in court has been very busy. I'm not on trial but am a witness.

Mad Skill have you been able to fly? This past week end on saturday we had Chip Hyde stop by and meet the club and fly. Man I wish I was that good. A really nice guy. Then on Sunday way way to windy.

Let us know how it goes?

Mad Skill
10-19-2005, 12:43 PM
I tried to madien on sunday and it was way to windy here also. I had a problem with the flight battery going down and I will have to get a new one.

10-24-2005, 12:26 PM
Had to order the smaller retracts. The ones I had were to big. I should recieve them this week. Did you notice Hobby_Lobby took the data off their site?

Mad Skill
10-24-2005, 01:09 PM
Yea i noticed that, I guess they are going to stop selling it.