View Full Version : Need help Converting Trainer(Midwest Aero-Star .40) to electric.

10-12-2005, 07:44 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(yes, yes):rolleyes: 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!


10-13-2005, 01:08 PM
OK I will make a suggestion:

AXI 4120-18, PQ 4400 5S or TP equivalent; Phoenix 45, Electron 6 or equivalent receiver; Hitec HS 81MG servos all around. I think a 14x7APCE will give around 48Amps max with about 500 + Watts. This is off the top of my head without running the numbers, but I had a similar set-up on my SIG LT-40 ARF and it flew with authority. I did overhaul and lighten the airframe AND since you are building from a kit this gives you the oportunity to make whatever modifications you desire. Also, choose a light weight covering. I like using the Ultracote " Lite" or regular transparents mixed with opagues. You will need a firewall motor mount. I would suggest the Espri Models aluminum mount for the AXI 4120. You will have to choose the mount post lengths. I don't know the plane, but I suspect you will need to get the battery up behind the firewall for CG. I would probably make a hatch on the top of the fuseladge above where the fuel tank goes and install a battery tray below. Your gonna need some building skills!

I think with this set-up you might be able to keep the weight at around 5lbs and get some nice performance with flight times easily around 8-10 minutes

Oops! One last thing. I would STRONGLY recommend you convert the plane to a tail dragger configuration. You loose the weight of that nose gear and get better prop clearance.


Mike Wizynajtys
10-13-2005, 01:30 PM
I'd recomend a similar setup to Norms with the following changes. I'd get the AXI 2826-12 and use a 4S battery pack. I'd do it that way to save weight and money. In my opinion, 5S packs are expensive and too heavy for a trainer.

The setup I recomended should fly well on an APC 13x8 Electric prop. You can also play with the APC 14x8.5 and maybe even a 13x10 pitch prop if you want more speed.....not usually with a trainer, but sometimes people want that.

OH, I use Thunder Power 4S3P packs myself, I don't know what the weight or current handling of a PQ 4400 4S is. It might be a good, affordable alternative.


10-13-2005, 01:57 PM
Hey Mike,

You might get by with the 2826-12 on 4S but with the wingloading of this plane I think you will not have anything to spare in terms of power. I would rather go up a notch and not push the motor and I don't think your weight savings would be significant compared to the loose of power. But that's just my opinion of course.

Mike Wizynajtys
10-13-2005, 02:23 PM
Well, Motocalc tells me that the 4S based system with an APC 14x8.5 will provide 51 mph and a power to weight ratio of 0.8:1. That ought to be plenty for a trainer. I fly a 4S3P power system in my 5 lb E-Sport 10 with great success. In that plane I have a Plettenberg Orbit 20-18. It's comparable to the AXI 2826-12.

I had an AXI 4120-14 when they first came out. It's a nice motor, but I found it to be on the heavy side for it's performance. Now that the 2826 is available I no longer consider the 4120-14. A fella could go for the hotter wind 2826-10, but you'd have to watch your current draw and maybe setp down on prop size.

To each his own. I'd rather have a light weight trainer, but a fast one can sometimes be good too.


10-13-2005, 02:57 PM
Well, one last comment.

I don't know the Midwest trainer, but most of the trainers are clunky plywood beasts that are almost always tail heavy without some added weight up front. I would bet that with the 2826 in the nose on 4S the airplane will be tail heavy even with the batteries pushed up as far as you can get them, and I would rather have the weight in that old antique 4120-18 and batteries than in lead. I think the 4120-18 on 5S will balance the plane nicely but this is all speculative on my part. I also think the 5S system will fly nice and cool with little stress on the motor or battery. Motocalc only gives you performance numbers and doesn't take into account other real world factors when setting up a plane, and I will say again that with a 4400 5S or TP pack the weight difference between the two systems will not be a significant factor. Of course this is all off the top of my head , and as you say, to each his own.

Actually, I bet your set-up would be perfect for the Sig LT25, but again this is only a guess!


Mike Wizynajtys
10-13-2005, 03:19 PM
The 4120-18 is a different animal. I could have swore you were recomending the 4120-14. Did you edit your recomendation? The 4120-14 is so close in performance to the 2826-12 that they are interchangable IMHO. Well, all except for the weight.

With the ability to slide the battery pack forward into the fuel tank compartment I would think the balance issue could be handled, but maybe not. A 5S power system will definitely be adequate and I suppose if he intends to fly more aerobatic planes in the 6 lb range than it might be a better choice. If however he is going to be looking at the 4.5 to 5 lb range the smaller power system will be just fine. At least it would be for me.


10-13-2005, 03:29 PM
Thanks guy!

I followed some threads around and it seems that if I have 100watts per pounds I should be ok.

With the setup of Viflyer, I check some combos on Hobby Lobby and the one with the AXI 4120/18 with a Jeti 70 amp brushless controller (http://www.hobby-lobby.com/brushless-combo-axi.htm#412018) and a PQ44004 4 CELL 14.8V 4400MAH LIPO PACK (http://www.hobby-lobby.com/polyquest.htm) looks good to me.
AXI say that with a 14x9.5 prop it will give 511watts at 37.9amps, so with the pack I chose wich can give average 53 amps continuous at 14.4 volts I should have a good fly time ?!?

I'm i wrong?

* Sleepyness in the morning can kill Zzzzzzz .........


Mike Wizynajtys
10-13-2005, 03:55 PM
100 watts per lb is good for medium aerobatics. I think it's more than is needed for a trainer, but that's me....not you.

With 5S you'll have a 18.5V system. Probably 16-17V under load.

I don't know of a 14x9.5 prop. APC makes a 14x8.5 electric and a 14x10 electric. I think if you go with the 4120-18 you'll want to swing a 15"

Seeing that this plane is a trainer and you probably won't fly it at full power much. You should have very good duration. You might even get two flights out of one charge. You'll have to experiment a little to figure that out. If you were going to use Thunder Power 5S3P 6000mah packs then I'm certain would get two flights per charge without much trouble.

I serial wire 2 TP 4S3P 6000 packs together for 8S3P on my Ultra Stick 60. I can get two 10 minute flights out of one charge without trouble. In fact, I have a fair amount left in the pack when I'm done, but I haven't wanted to push it to 3 flights. I'd rather charge than loose the plane or damage the cells.


10-13-2005, 04:27 PM
Hey Mike!

Is the 4120-18 setup over kill for my trainer.

You recommend to convert to a tail dragger, that is fine with me, and I suppose I should lighten my fuse so I will have less weight...

I have already made an access point on the nose of the plane, because access to the tank was difficult, so I should have place for the battery pack there and easy access too it, I suppose I have to protect very well the LiPo pack, so it's not dammage in rough landings?

Another question could I re-use the setup in anoher plane later? A low wing trainer or something like that?

What kinda charger should I get for LiPo since you seems to have a lot of experience with electrics, and since I want to stick to electrics in the futur.


*** sleepines in the morning goes away with stress ....:eek:


Mike Wizynajtys
10-13-2005, 05:41 PM
I didn't recomend you switch from trike to tail dragger. I think Norm did. What's this plane for? In other words, are you going to be training with it, or do you already know how to fly a plane like this and you are just building it for sport flying?

The reason I ask is that I don't recomend beginners swap out their trike gear untill they have gained a fair amount of experience. I like to make the training experience as stress free as possible. You can add the tail dragger skill down the road after you gain experience. Now that could mean you need to get some longer LG so that the prop has clearence. These things all come into play and you are the final word on what is best for you. Well, you and your instructor, assumming you have one.

Is the 4120-18 overkill? Not really.....it depends. If you're looking for a power system that will grow with you then it might be the best choice. It depends on where you want to end up. If flying a 6-7 lb sport aerobatic plane is where you want to go after this plane then the system Norm recomended should be pretty good. This is a little more costly now, but it will end up being cheaper in the long run.

One thing to remember. Those batteries need to have good cooling. So, as you construct the plane keep that in mind and look for places to add air intake holes and exit holes. The exit holes will need to be roughly twice the size of the intake holes.

What kind of Lipo charger should you get? There are lots of them out there. I have and like my Orbit Micro Loader quite a lot. It's a little expensive, but it handles a lot of different charging jobs, including my Lipos and my radio NiCd batteries and even a small lead acid battery I carry around when I'm flying indoors. If all you want is a Lipo charger the AstroFlight 109 is fantastic. It's affordable, easy to use, fast and handles packs from tiny up to 10S. BTW, I have a pair of AF 109s because of their speed and low cost.

Do you have any friends locally that fly electric power? If so, I'd ask them what they use and if they are happy. Many times someone locally stocks and supports some very good products that aren't always mentioned here on these discussion boards. It's worth looking into.

I hope all this helps. It's kind of a lot to digest all at once.