First off apologies for the blurred pics. Damn camera kept focusing on parts of the floor instead of the model, and I couldn't figure out how to stop it.

Hi all, this is like my 3rd time posting here, been prowling a few days now. I've started this project and I think I'm far enough along that I should start to share and possibly pick some brains concerning power plant and batteries.

The project I am doing is converting an original GP PT 40 from glow to electric. I have a plane that my dad made back in the late 80's or early 90's, can't recall which. I've had the bird for about 10 years but in storage and did not take the best of care when handling. I was gentle enough not to break much, and kept it on top of stuff and stood upright (nose down) without wings attached, wings stood on one end and when moved I'd make sure it was placed on the other end. The engine I removed when I first got the plane, I knew it would be in storage for awhile so I disassembled it thinking I'll get a rebuild kit and go. I still have the complete engine in pieces. I've never really been a fan of glow craft. Well a bit about my history flying.

I've been building and flying since the 90's when my father got me into it. He had the trainer but he never really soloed it. I've witnessed a few of the pro's at our local field test fly it, so I know it has been airworthy. My dad could build one hell of a plane. I've built at least 2 models on my own prior and assisted my father building a Gentle Lady. We flew that thing forever. I got my only electric kit one year for my birthday, it was a Carl Goldberg Mirage 550. Building and flying that plane is the extent of my electric usage and knowledge. I did learn enough that I preferred it over glow any day.

Anyway after about 20 years, my brother has sort of gotten me interested in the sport again. I decided instead of purchasing a new plane to do this conversion and at the same time preserve something that has great memories for me. So I dug out the trainer.

When I first got it in my head to do this I knew what I was getting into so I refrained from looking up specs and such. I figured I should focus first on determining the usability and integrity of the airframe before looking at anything else. A bad airframe would have ended the project there.

I got to storage and faced this.



There was visible damage other than the monokote holes.



It has been sitting for well over 20 years, so I knew there would be hinge replacement in my future. I was well right to decide to do them as well. Most the nylon crumbled. The former that holds the wing seating mounts are all solid though. I decided it would be worth it, though it has seen better days. The last time my father flew it, well let's leave it at she landed hard. I will say a lake was involved.

Next step was to remove the existing monokote to check the structural integrity.
Removal went well. It was my first monokote removal other than for the odd spot repair. I've never attempted a full strip and recover.




Again once all monokote was off I found a bit more damage, which I expected.
One rib was split about an inch or so long with the grain in the middle of one rib. I ended up gluing 4 small strips of balsa 2 on either side to fix that. One rib had the thin cover strip pealing away, and one had a small piece broken off the same type striping on different rib. The pics don't translate these well so I'll not post them. I did find a few bad spots on the wings. Both are old damage and were most likely repaired by my father, though I don't recall either of them.




The fuse had some damage as well. In fact it looks like the tale has been cut off, most likely from a cartwheel landing.




The repair is solid as well as the rest of the fuselage. I've pretty much finished my rough sand and have gotten more than 95% of the old sticky stuff from the old monokote. I'm going to do a few repairs after rough sanding then I'll get to final sanding and I'll update the pictures.

If anyone would be willing to suggest a place to start concerning power plant, I'm open to suggestion. I've taken a look around and have seen the various descriptions and tools available to help me select the proper engine. I am just having a hard time getting my head around them.

Some specs:
(These are near as I can find, this bird has been out of production awhile, closest GP has is the PT 40 MKII)
Wingspan: 60 in (1520 mm)
Wing Area: 675 inē (44 dmē)
Length: 49 in (1245 mm)
Weight: 5 - 5.5 lbs (2270 - 2500 g)

What I would like is moderate performance. Based on the 65 - 100 - 150 rule I'd like somewhere in the 100 range for this model per pound. I'd like to keep the batteries as lipo in a 4s pack I'm fuzzy on the mA stuffs. I'd like flight time around 10 - 15 mins mixed. Any help is greatly appreciated even if it's to a explanation of what all the numbers mean.

Looking forward to getting back to the skies. I'd love to hear comments about the project so feel free, even if it's to tell me I'm insane.

A key question is what size prop can you swing, and what prop would you like to swing?

If you can swing a big prop you can go with a lower KV motor, 12 inches and you'll probably want 700-800 KV (at a guess).

I have a 770 KV on my 5lbs trainer, similar specs, I think I can just fit a 13, but have stuck to 12 so far, 12x10 currently.

I has a nice crisp sound to it on the static test.

On 12x6 it was pulling about 55A on 4s (static test), haven't checked the 12x10.

http://www.rcgroups.com/forums/showthread.php?t=1481669

Dave

I've been looking at using a 12. It should give me the middle range performance I'm looking for. I'm looking to do loops and a roll or two. No snap rolls, cuban 8's or immelmanns.

I'm sitting high enough now to only sling a 10". I've already considered ways to get me the height. Went to my LHS today and got a great idea to make a custom rod style gear. It would allow me to get the height I'd need to move to a 12 and feel comfortable I can do both, strip or field landings and takeoffs. I considered larger tires, and I think that would be ideal if I were on a paved strip only.

Also at the LHS the guy suggested a Rimfire motor, sadly I did not get the model. It was $75.00 marked down from $100. Said I could most likely get away with running a 4c setup, he said 2c 2p actually. What would be the power benefit off a parallel set vs a 4 pack?

I'm also done with most major repairs, and have refitted all hinges. Also if you notice it's missing it's cheeks. I'm considering making a cowl from scratch but am not sure to make it from balsa and some thin ply or fab it from fiberglass. At this point I'm considering this only. It's not priority till I have a motor and know how large a cowl I need, lengthwise.

I've read about that conversion. It's been part of the reason for my rework.

Why don't you take the gear you have, reverse it and move it forward then you have a tail dragger? Buy a tail wheel for $9 and done. You'll have all the height you need then and put whatever wheels you want on it.. Just my 2 cents.

Why not go with the largest lite wheels that will fit on existing axles- plus it will make touch and goes easier!

Originally Posted by gewiens

Why don't you take the gear you have, reverse it and move it forward then you have a tail dragger? Buy a tail wheel for $9 and done. You'll have all the height you need then and put whatever wheels you want on it.. Just my 2 cents.

I thought about the possibility, but wouldn't I get prop strike when the tail came off the ground?

Originally Posted by jim e

Why not go with the largest lite wheels that will fit on existing axles- plus it will make touch and goes easier!

I'm currently looking at moving all tires up an inch and a half larger. I think I could sling an 11 or 12 soleley on paved strip, as she sits now, larger wheels are an option.

I'll be posting more pics tonight and better ones at that. I've removed all the old monokote and residue, and I've completed all cosmetic repairs. You will notice that the tail section on the top fuse panel you could tell there was a height difference, I've filled that in so it won't be so drastic. Final sanding is near complete. I'll take a few pics before I re-monokote it.

Using http://www.s4a.ch/eflight/motorcalc_e.htm online calc program. A Monster Power, Easy match from HK, Power 32 from Leaders, Gforce 32, Tacon 32 you should have around 5 plus pounds of thrust on a 12X6 APC "E" prop.

https://www.leaderhobby.com/product....=9394001223655

http://www.hobbyking.com/hobbyking/s...er_770kv_.html

http://www.valuehobby.com/power-syst...g32-800kv.html

http://www.hobbypartz.com/96m604-big...520-770kv.html

http://www.hobbypartz.com/monsterpow...ess-motor.html

They use a 60 amp ESC.


They should fly the plane really well.

Buzz.

[QUOTE=dedStik;20852854]I thought about the possibility, but wouldn't I get prop strike when the tail came off the ground?

Well with bigger wheels it should be better. Or give the gear a bit of a twist to make them stand up a bit more.

Originally Posted by blvdbuzzard

Using http://www.s4a.ch/eflight/motorcalc_e.htm online calc program. A Monster Power, Easy match from HK, Power 32 from Leaders, Gforce 32, Tacon 32 you should have around 5 plus pounds of thrust on a 12X6 APC "E" prop.

https://www.leaderhobby.com/product....=9394001223655

http://www.hobbyking.com/hobbyking/s...er_770kv_.html

http://www.valuehobby.com/power-syst...g32-800kv.html

http://www.hobbypartz.com/96m604-big...520-770kv.html

http://www.hobbypartz.com/monsterpow...ess-motor.html

They use a 60 amp ESC.


They should fly the plane really well.

Buzz.

Was that with 4s or 5s?

Well I've finished most of the hard stuff, still have a bit of touch ups I'm doing to the fuse but for the most part I'm ready to monokote the wings at the very least. Need to figure out if I'm modifying the landing gear or not.





Well there's the wings all finished out and ready for monokote. I've gotten the ailerons refitted and rehinged. I've also gotten the ailerons recovered. Tomorrow I'll start the wings themselves.

That was using a 4s 5000mah battery. If you go up to a 5s, you go over the max amps for the motor.

Buzz.

My motor specs may be off (it's an OK Hobby infinite 3025-770KV) so I will first say it may be my motor, but mine won't pull 5lbs thrust on a 4S 12x6.

It's pretty good, but not 5lbs good.

It also runs out of thrust at a relatively low speed, climbout is much better with a 12x8, even better with a 12x10, but it will still spin the prop at about the same speed in a static test.
Dave

I just completed this kit a couple weeks ago. It has a Rimfire 32 and a 60amp ESC. I intended on using a 4S 3300 mah but the prop I had was too big. I had a 3S 2200 with me and it was able to fly with that. Got 5 minutes on the 3S. I have since adjusted the prop but haven't been able to get out due to weather. I didn't takeoff or land it but did fly it. The guy that did those other duties said the 32 and 4S should give me over 10 minutes and takeoff with half throttle. The kit was given to me by a friend. That was given to him by his brother. The kit was started then stored in his attic for years. The plans had to be re-scanned and I scanned the manual. It's a pdf document so if it would help I can send it to you. I got pics but I think it's on my comp at work.

Good luck with the conversion.

I found the a copy of the manual on the Great Planes site, I really could use another copy of the plans as it was so long ago, I'm not sure if I still have them, and most plans I do still have are too badly damaged.

I had looked on the GP site and didn't find the manual. Must have missed it. Anyway, the place I got the plans scanned and printed, I'll check and see if they have a way to put them on a disk. If so, I'll send a copy to you. If they don't I can have a set printed and send them to you.