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Discussion Starter · #41 ·
Thanks for the good info. I have already moved the motor forward. The mount is exacty 1/2” from the front of the nose and puts the back of the prop 1-3/4” in front of the nose vs. about 1/2” where I previously had it mounted. I’ll look into moving the tail servos if I’m not happy with the way it flys.
I’d move the engine out as far as you need to along with the esc and lipo to get the cg before I added weight but I wouldn’t have the mount any closer to the tip of the nose than 1/2”. That’s just my personal thought. I’d rather use stand offs/spacers to get the motor pushed out a little rather than move the mount way out on the end of the nose.
But moving the motor out that far has a negative effect in that it basically adds to the nose moment (the length from center of lift to the prop). A longer nose moment will detract from pitch authority as well as rudder authority when tumbling and pinwheels and such. But so would a chunk of lead hung way out on the nose.
The good news is you shouldn’t need to move it out too far on a mojo. They CG pretty good even electric. Mine always did, anyway.
If it was built heavy in tbe tail or the servos are on the heavy side I’d say it’s worth it to move the tail servos up one bay rather than add weight or push the motor forward too far. It’s almost a requirement on a primo.

As far as lipo brands go, I’ve had the most luck and consistency over the years with the regular blue label hobbyking lipos. Recently I’ve tried some Admiral brand pack from motionrc and I’ve been impressed so far. But time will tell how they hold up.
I’d move the engine out as far as you need to along with the esc and lipo to get the cg before I added weight but I wouldn’t have the mount any closer to the tip of the nose than 1/2”. That’s just my personal thought. I’d rather use stand offs/spacers to get the motor pushed out a little rather than move the mount way out on the end of the nose.
But moving the motor out that far has a negative effect in that it basically adds to the nose moment (the length from center of lift to the prop). A longer nose moment will detract from pitch authority as well as rudder authority when tumbling and pinwheels and such. But so would a chunk of lead hung way out on the nose.
The good news is you shouldn’t need to move it out too far on a mojo. They CG pretty good even electric. Mine always did, anyway.
If it was built heavy in tbe tail or the servos are on the heavy side I’d say it’s worth it to move the tail servos up one bay rather than add weight or push the motor forward too far. It’s almost a requirement on a primo.

As far as lipo brands go, I’ve had the most luck and consistency over the years with the regular blue label hobbyking lipos. Recently I’ve tried some Admiral brand pack from motionrc and I’ve been impressed so far. But time will tell how they hold up.
To your wood or plastic propeller question on E props, I'm using plastic or composite for 13 inch or under. For E props larger than that, I highly recommend staying with the wood props, as the plastic ones get flexy and can cavitate. I like Xoar, Sail or even the Hobby King E wood ones are working good for me.
I’ll have to find some 14-6 E props, I only have Xoar gas props in that size. I’ll start out with a 14-5 cheap E-prop and see how it pulls. Here is a pic of the motor moves out to balance the cg, kind of fugly. We shall see!
 

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I like everything about nitro except buying the fuel and occasionally having a fussy or picky engine.
I hated everything about electric. I like to fly for 10min+. I hate 4min flight times. I was never satisfied with the power. With nitro you can fly WOT for 8min and the engine doesn’t give a crap. Tank after tank. Can’t do that with E.
the lack of noise, or rather a completely different noise I don’t like either. Wulfie always made fun of me for putting piped two strokes on everything I could but there’s no sound or throttle response E can compete with like a CCP.
I hate buying and keeping up with a dozen packs and yes it takes that many to give me the flight time I want per session and then I have to recharge all those and keep up with their voltage and all that. It’s not hard but it’s a pain.
some people like to say E has more power. Sure, it can on top but by my viewpoint E HAS to have more power because you can’t fly around at 3/4-full throttle. Your plane has to do most of what it does at half throttle. Sure it’s the same for nitro but when you’re really in a groove and getting nasty with it you spend a lot of time at or near WOT. E is for low and slow with the occasional ADHD twitch.

I could go on for days and reminisce about the pros of nitro vs e. I believe I have here a time or four. E works for some. It just doesn’t suit my style. Just like a fatty extra just doesn’t suit my needs and expectations. I need an edge or slick to wad up into a burr to make me giggle.
Here you go, plug. A nitro CCP beat down on the best slap ever designed. This old slab by this point had its wing ripped off twice. Once in a mid air and the next doing WOT wing tip KE touch n goes at nash. The tail was loose as a goose and so was the covering from nitro soak. It was over 5lbs at this point. The old thundertiger 46 was almost worn slick out. It wouldn’t start without a healthy prime and a starter but by hell once it did it ripped. Until it and I meet again in Valhalla 🤘🏻

Wood Fire Gas Flame Grass
 

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Gregory, that motor is out to the max imho. Pull that ESC right up behind it and put the lipo on the opposite side.
And E props are a must. I like xoar and falcon. Falcon respond better imho. I’ve become a falcon fan on gas too. Just my 2cents.
 

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Discussion Starter · #44 ·
Gregory, that motor is out to the max imho. Pull that CG right up behind it and put the lipo on the opposite side.
And E props are a must. I like xoar and falcon. Falcon respond better imho. I’ve become a falcon fan on gas too. Just my 2cents.
Thanks for the suggestions. I’ll give it a try next week, If I don’t like the way it pulls, I’ll look at new more compact servos and/or possible moving them back a bay. Since i glued the wings on, I hope there is enough wire to solder the new servos from the tail side. Tough finding Falcon or that matter 14-6 E-props. I’ll check with a local hobby shop and see if they have any. Maiden will be with the 14-5 that’s on it in the picture. Charging a Lipo now to see who many amps that prop pulls, and then I start to button it all up.
 

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Discussion Starter · #45 ·
I’ve read Swanny recommend 2+ degrees of right on mounting the motor which is about what I have. (used washers to shim it). Do you guys have any down or do you mount is parallel with the fuse tube?
 

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I’ve always ran a degree or two of down and right thrust but a few here have made compelling arguments that none is needed on a slab at all.
 

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Discussion Starter · #47 ·
I’ve always ran a degree or two of down and right thrust but a few here have made compelling arguments that none is needed on a slab at all.
Good deal, I have about 2 degrees of both. I checked out the motor/14-5 prop. I’m getting 850w @ 60-65A so the ESC should be good for a 14-6. 850w isn’t quite Bro power, but will be good enough to get the Mojo trimmed out and flying. 😀.
 

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Discussion Starter · #48 ·
Came in at 4 lbs. 7ozs. Not a light weight. With battery in place I’m at 4.5-5” on cg. I’ll try it like that, I don’t want to add anymore weight to the nose.
 

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I can now balance the cg at 4.5” and move it back once I get used to how it flys. I think it’s a little tail heavy due to the full size servos in it and my e-setup weighs less then the glow setup that was on it. I may fill in the jaws behind the motor with balsa so I have more area to Velcro the battery on.
I’d move the engine out as far as you need to along with the esc and lipo to get the cg before I added weight but I wouldn’t have the mount any closer to the tip of the nose than 1/2”. That’s just my personal thought. I’d rather use stand offs/spacers to get the motor pushed out a little rather than move the mount way out on the end of the nose.
But moving the motor out that far has a negative effect in that it basically adds to the nose moment (the length from center of lift to the prop). A longer nose moment will detract from pitch authority as well as rudder authority when tumbling and pinwheels and such.
Go with mini servos in the tail, or move them up a bay towards front. I found out the hard way exactly what Jake is talking about. Prowler picked up Bob's GBR R3 50" at IowaBro 2 years ago. Bob had a Hacker 4S set up on it; I smoked that shortly, trying bigger props. Swapped in a Value Hobby G32 I had, using 2 2700 4S in parallel. Even with that battery set up, it seemed tailheavy, so I moved G32 forward. Flew better for CG(didn't wanna outside loop when I rolled inverted), but it sucked for tumbles, poptops, and harrier. Zamfir, who cut the kits, and had a great-flying GBR 50 of his own, looked at mine and said my motor was too far out forward. Took his advice, bought a new BadAss motor ( BadAss 3520-560Kv Brushless Motor ) and switched to 6S. I started with 2 3S 2200 in series; too light/too short flights-still tailheavy. I've now settled on either 2 2700 3S or 2 3300 3S in series, and the plane is an ANIMAL now for poptops, crankshafts, and the like. It'll wrap up like crazy! Moving the motor back really changed that nose moment to the better :)
 

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Came in at 4 lbs. 7ozs. Not a light weight.
With your quoted 850W, you're at about 190W/lb. Not bad, certainly will pull out of hover nicely, but won't be a rocket. You'll be wanting more like 250-300W/lb for Bro Powah :)
 

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Discussion Starter · #51 ·
With your quoted 850W, you're at about 190W/lb. Not bad, certainly will pull out of hover nicely, but won't be a rocket. You'll be wanting more like 250-300W/lb for Bro Powah :)
Thanks, you all have a lot more experience with the Mojo/power setups and I appreciate everyone’s input. If it’s a dog, I’ll re-visit moving or replacing the rear servos and moving the motor back. I don’t think the G32 can handle 250-300 watts/lb. With a 14-6, I may get close to 950-1000w which would be around 200+watts/lb.
 

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Discussion Starter · #53 ·
Question for you guys. I maidened the Mojo yesterday. Interesting is all I can say. On takeoff, it was pitching down pretty severely when I released the elevator. It took about 12-15 clicks of up trim to level it out at 1/2 throttle. Tail was sagging a bit and it was a tad tail heavy. When I went inverted it pitched down a lot due to the elevator trim. I have zero’d all the end points and adjusted the ailerons to follow the tube. I put some right and down pitch to the motor when I mounted it. Could the down pitch cause this, or being tail heavy? CG is about 5” using 4s-3300 Lipos.
 

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That's odd. You say tail heavy, but it pitches down. Usually if it is tail heavy, the plane will pitch up.
Usually with a profile, like your Mojo, you don't want any motor down thrust or right thrust. I'd take that out and make it as straight on as possible - that is how I set up all my birds.
It definitely sounds like your down thrust is causing that.
 

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The very first thing to check is to make sure your ailerons are parallel to the tube and the horizontal stab. They should not be drooping or raised compared to the tube or stab.

If you trim the elevator for hands off level upright flight, then it dives during hands off level inverted flight, then the plane is nose heavy.

If you add too much down thrust, it will require some extra up elevator trim to keep the plane from diving. More throttle might require even more up elevator trim. However a Mojo 40 shouldn't really need any down thrust.

This extra elevator trim will not really matter for the CG test in the second paragraph as long as the same throttle position is used to trim the elevator for both upright and inverted hands off level flight.
 

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Discussion Starter · #56 ·
That's odd. You say tail heavy, but it pitches down. Usually if it is tail heavy, the plane will pitch up.
Usually with a profile, like your Mojo, you don't want any motor down thrust or right thrust. I'd take that out and make it as straight on as possible - that is how I set up all my birds.
It definitely sounds like your down thrust is causing that.
I know it’s odd, but if you think about it after trimming the elevator is about 1/4” above above level. It’s definitely tail heavy so it should pitch up when inverted, but when inverted, the trimmed out elevator for upright level flight is now the opposite. It’s lifting the tail pushing the nose down (like giving it up elevator when inverted). Make sense?. We are going out of town for a couple weeks, when I return I’ll re-drill the mount for zero down motor pitch and remove the washer for the right pitch.
 

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Discussion Starter · #57 ·
The very first thing to check is to make sure your ailerons are parallel to the tube and the horizontal stab. They should not be drooping or raised compared to the tube or stab.

If you trim the elevator for hands off level upright flight, then it dives during hands off level inverted flight, then the plane is nose heavy.

If you add too much down thrust, it will require some extra up elevator trim to keep the plane from diving. More throttle might require even more up elevator trim. However a Mojo 40 shouldn't really need any down thrust.

This extra elevator trim will not really matter for the CG test in the second paragraph as long as the same throttle position is used to trim the elevator for both upright and inverted hands off level flight.
I’ve triple checked the cg, it’s tail heavy and probably needs about 8 ozs. of nose weight to get the cg it at 4-1/4”. Since I have up elevator trim for level upright flight, when inverted wouldn’t it make the nose pitch down?

Ailerons are even with the horizontal fuse tube on the inside. If I put a straight edge on the centerline of the outside wing, the outside aileron looks to be up about 1/2 the thickness. Their may be a bit of warp in them, I’ll check that next.


I’ll remove the right thrust and re-drill the mount foe zero down motor thrust when I get back in a couple weeks. I think this may be a big part of the problem.

Thanks for all the suggestions, I’ve not run into anything like this before in my 15 years of rc flying, but then again profiles are a bit different. I converted a Sabre 47 years ago from glow to electric and only had to add a little nose weight.
 

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I kinda went through the same thing with my mojo 25. Ended up using a bigger motor and moved it as far forward as could. Now,flys great ,inverted or not about the same. You be right,if the tail is trimmed up,its not going to fly right inverted. The als trim just a bit off will muck with you,i now pin a strip of wood to wing tip centered on rib,then adj al to wood pointer,then do other side. If in dought on bal,add weight to nose temporarily and fly. Adding weight is bad,its the last thing to do. By the time your done,you will have learned a bunch,i sure did. Some guys fly tail heavy,it makes the plane very twitchy,but helps hovers,you have to stay on the sticks all the time,i dont care for it.
 

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Discussion Starter · #59 ·
I kinda went through the same thing with my mojo 25. Ended up using a bigger motor and moved it as far forward as could. Now,flys great ,inverted or not about the same. You be right,if the tail is trimmed up,its not going to fly right inverted. The als trim just a bit off will muck with you,i now pin a strip of wood to wing tip centered on rib,then adj al to wood pointer,then do other side. If in dought on bal,add weight to nose temporarily and fly. Adding weight is bad,its the last thing to do. By the time your done,you will have learned a bunch,i sure did. Some guys fly tail heavy,it makes the plane very twitchy,but helps hovers,you have to stay on the sticks all the time,i dont care for it.
Thanks, I’m going to re-check the ailerons, I may have a slight warp in at least one of them. I’ll add weight just to fly it and see if it’s ok, if I have to add weight to the nose I’ll go to a bigger motor and/or a larger capacity Lipo like a 4000mAh. At least that way, I would get usable weight. I’ll also look at how hard it would be to move the servos back a bay or go to smaller size servos. Problem is the servo wires are run through the tube and would be a pain to redo. I’m going to remount the motor with zero down and zero right thrust. I think that may be a big part of the problem, and moving the motor out in front of the fuse might be adding to the problems.
 

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Your on the right track. I have moved motors foward 1.5 inches,still fly good. If i were real good flyer it might matter,but for me its fine. Weight is everything to 3d planes. Since i still build heavy,i try not to,but tend to anyways i now move servos forward,dont take much tailweight to bal if needed. Or,if needed build the front mount longer,not as bad as adding weight. I fought my 25 mojo built by someone else much tailheavy,rebuilt nose longer ,it now flys fine. Trim,that is every thing is right makes a good plane that flys nice. A cj plane has much forgiveness built in,3d planes dont forgive shit. Even my 202 got a bit of twist in its body,i can see it roll out every time because of it. Two years ago i did not know, Now i understand how important a light,straight plane is,and good servos. Thats what 3d does,it makes us aware of shortcomings and to try to be better,not just flying round and round a heavy badly setup turd. I was a cj,now i know better. Just me,having fun at myself.
 
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