rv9-a

Buzz
I think you are right about the specs on Rimfire being a little optimistic I have seen that statement in several places. I am using a 3300 mAh 6S lipo in my setup and I think it may be too small. When they need to be replaced I will go larger. What is the capacity on your batteries?

rv9-a

blvdbuzzard

For my 60 sized motors I am using (4) 2650 3s batteries for a total of 5300 6s and for Christmas I had a 5500 6s under the tree. 3300 seems small to me. It would be lite weight but not much in the way of flight time.


Buzz.

crazzyflyer

My Feedback: (12)

I have A Goldberg Chipmunk set up electric. I did build the model with the top of the fuse and canopy removable for battery installation. Works great. Recommend modifing for same. Set your plane up with at least a 60 bl out runner on at least 6 cell LiPo with 30-40c for best performance. Seven cell is better but not neccessary. Tried on a 46 bl but under powered here in Colorado.
On my blog at www.crazzyflyer.blogspot.com I give an example of how to cut and modify for a hatch under the heading (electric conversiouns P-51 Mustang.) This might help.

Best of luck,

Romi

rv9-a

Buzz,

It looks like I am going to try either a 16/8 or 16/10 for a prop 17/8 will also work but don't know about ground clearance .

The parameters I used were :

Imperial units
4000' elevation
e-flight P 60 motor
80 amp speed control
3300 mAh 6S1P 25/35C
Good cooling (anything less brought warnings for high case temp)
APC 16/8

This got me 141.61 ounces of thrust, 39.44 amps, 7272 rpm and 8.53 min. I can live with that as I now have my timer set for 7 mins. on glow fuel.
If I try to increase the battery capacity say to 5000 mAh and have anything less than good cooling selected I get the high case temp. warning. I would guess this is because the motor is running longer??

Thats a cool program well worth a donation.

thanks rv9-a

blvdbuzzard

I think are a little over cautious about cooling. When I was setting up my 60 conversion, it said it would get hot. It comes down at room temperature.

Let us know how it goes.


Buzz.

rv9-a

Chipmunk is finished! I was able to use the battery to set the CG, the forward edge of the battery is just behind the firewall. That puts the CG in the middle of the suggested range. If I need to move the CG aft I can slide the battery towards the tail as much as 2". The battery compartment is completely removable. It didn't start out that way but I realized it would be a lot easier to hook up the motor leads and install the ESC if the box and battery were not in the way.
To change out the battery at the field you remove the wing, swap out the battery and put the wing back on. That shouldn't take more than 5 mins.

rv9-a

blvdbuzzard

That looks real clean and simple.

Let us know how the maiden flight goes.

Buzz.

rv9-a

It's all over but the shouting. The electric Chipmunk was flown for the first time today. It flew perfectly without any trim inputs needed. The tail wheel was not trailing straight and would cause a sharp left turn on take off, this will be fixed before any more flights.

The only problem I had was while the plane was sitting on the bench with the arming plug pulled and the receiver battery turned off the servos were twitching and one actually went full left and held there. Only when the receiver and transmitter was turned back on did the servos go to neutral and quit twitching. Where were they getting power from?? All this happened after a through range check was done, but before the first flight.

I was using with a 16/8 APC, on the bench it was pulling 57 amps at 1320 watts. A 16/10 was 65.2 amps at 1510 watts. I am going to try a 16/7 and see if I can get closer to 1200 watts the manufacture recommends.

It would be better if the wing didn't have to be removed to change batteries but the whole process takes maybe 5 mins.


rv9-a

And the best part was no slime to wipe off

blvdbuzzard

If the Rx battery was off and the ESC was not armed, it should not get any power. Yet it was getting it from some where. Did you pull the red wire from the ESC? I know it was not armed, but? Is the switch going bad? In the off position but not really off?


Glad the maiden went well. Remember that in the air, it will draw a little less then it will on the bench and you are not running full throttle the whole flight.



Buzz.

rv9-a

Yes I had pulled the red wire from the housing and insulated it. The switch was brand new. I tried to duplicate the situation back at home but the servos were rock steady. Next day at the field the same thing happened again, but with a twist. This time when the switch was off it was really off. Move it to on (transmitter off) you get twitching, turn trans. on twitching stops. So now I have two problems: I have interference at the field on my channel and I have a possible bad switch.

Before the first flight I did a very extensive range check. With the plane tied down and the motor running at various speeds I could get to about 175' before I lost the signal. This was with the antenna completely collapsed.

I went ahead and flew and had another great flight, several touch and go's and a few maneuvers and landed at 7 min. I checked the battery and I had about 25% left. Swapped out the battery and went for a second flight pretty much duplicating the first. I came in for a landing and was turning from base to final and the plane went ape, I had no control and now no plane [&o] I didn't check the battery at the field but when I put it on the charger for a storage charge it went into the discharge mode so it was above 23.1 volts.

I am thinking switch, if it can be on when it says off maybe it can go off when it is supposed to be on.

My first inclination was to say to hell with this hobby but maybe there will be just one more Chipmunk. I really did like not having to wipe the slime off when done flying

blvdbuzzard

That is too bad about your Chipmunk. Were you able to salvage anything?


Just because you turn on the Rx and the servos twitch, does not mean you have interference. The Rx is LOOKING for a signal so it will receive anything it can. Now, if you have the Tx on and it does that, then you have a real problem.

I have this one ready to go with a 90fs engine. It is built pretty well and the covering is right up there.

http://www.gravesrc.com/AIRBORNE_MOD.../abma004rf.htm


Buzz.

rv9-a

I was able to salvage everything except the plane. It broke in two just behind the wing. I have hooked every thing up and bench ran the motor, no run out and it runs as smooth as it did before.

That is a nice looking Chipmunk. Is there any more info about it posted it? I looked but didn't come up with anything.

rv9-a

blvdbuzzard

Search for world models Chipmunk. it is pretty much an ARF version of the Goldberg one. I have built (2) Goldberg Chippies and this one is liter weight. It comes with flaps all ready set up.

http://www.theworldmodels.com/para/p...airplaneid=126

http://www.rcuniverse.com/magazine/a...article_id=814

Buzz.

rv9-a

Thanks for the links to your Chipmunk. It looks like a very good plane. I was going to order one until I went to Tower's website today.
They have free shipping plus $ 25.00 off for a $ 199.00 order or more. That's a combined offer which they seldom do. So I have
another CG Chipmunk, three rolls of covering and a new switch on the way.


rv9-a

blvdbuzzard

You can never live without a Chipmunk once you have the bug .

The ARF went together pretty well. I was really impressed with the fit and finish. Yet I would like to build another CG Chipmunk.


Buzz.

rv9-a

Well the second electric Chipmunk is just about ready to cover. I decided I would build it as designed as far as a removable hatch is concerned. As stated before it takes about 5 mins. to change out the battery, no big deal. I am adding some holes for ventilation that can be opened up if needed.

I was a little disappointed in in some of the wood in this kit, especially in the fuse. The bottom of the fuse was laser cut and the sides and top appeared to be cut on a CNC router with a 3/16" bit. This leaves quit a radius that needs to be squared or things will not snap together as stated in the manual. Couple that with some questionable wood and you have problems. If you look closely at the attached pictures you can see the rounded cuts in the three knock outs on the right fuse side. All the other tabs have been squared up.

rv9-a

The Goldberg Chipmunk uses plastic for the wing tips and the fuselage bottom. Personally I don't like them and replace them with balsa. Attached are some pics showing how I did the fuse bottom. The last picture shows where I can open up some holes for ventilation if needed.

blvdbuzzard

Looking good. When I built mine, I too replaced the wing center plastic cover with balsa and the tips. The plastic wing tips would not fit the wing. They were about 1/8 to wide.


Buzz.

rv9-a

I never did like those plastic parts, they can be a real bear cat in the fit and finish dept. This cowling is going to be a challenge they were not very careful how the excess was removed when it came out of the mold. My last cowling had too much cut off so the hole in front was oval shaped, the left one in the picture. Great Planes replaced it with a new one. If I can't get this one to work I will go to a fiberglass one.

rv9-a

blvdbuzzard

I think it was Fiberglas specialties had the fiberglass set for the Chipmonk. I will need to order a set for my Cub when I get around to it.

I wonder how bad they get warped in the heat as they are traveling around the country in the brown trucks?

Sometimes you spend more time on the plastic parts then the rest of the airframe.


Buzz.

rv9-a

I was ready to go with Fiberglass Specialty but I was able to get the included parts to work. They came out better than expected.
I finished the covering today and will start trimming out. If I can get some good weather for painting I should be ready to go in about
a week.