700xn

[coolice]

Align have have over complicated it and have just missed all the important stuff, ease of maintenance etc. CoG on this MAJ custom Trex is bang on with a 3500 pack up front so I don’t see why they’ve had to push the engine forward, just no need.

The plastic clutch stack in the old Trex was rubbish so will be interesting to see how the gearbox on the new XN performs over time.

Hey buddy

Yeah they are a nice layout the Maj frames, with lower maintenance perhaps compared to adding additional gears. But the C/G will move slightly as the fuel tank empties from full to empty, as it's not directly under the mainshaft. So your LiPo Rx pack positioning will be made on a compromise between a full and empty tank, usually when the tanks half full so the change in flight from tail to nose heavy is minimised.
It'll be a minimal change of course, but there still. The old 700N's suffer the same.

Hence Aligns thinking here by moving the engine forward with the additional drive gears, to put the tank directly under the mainshaft. Thus as that weight changes with the fuel being burned, the models C/G stays neutral.
If width wasn't an issue a main gear diameter change over additional gears could have been used, but then that adds width that a slim heli doesn't want :-)

Ian Contessa

[George J]

I hear you completely Ian but I think you’re talking about such a tiny difference that any advantage in flight is completely lost and 98% of pilots owning the new XN will not notice any difference, I notice zero difference when flying the MAJ version apart from performance in the 2nd half of the tank for example.

[Grumpy]

CoG on this MAJ custom Trex is bang on with a 3500 pack up front so I don’t see why they’ve had to push the engine forward, just no need.

Does the MAJ frame have the rudder servo up front?

[George J]

This pic is from the previous MAJ frame but the rudder servo is in the same position.

[Grumpy]

Thank's George.
I know as per Ian's comment previously that it seems like a 75g servo wouldn't make much difference to CG position, but consider that balancing is about moment arms not only weight. The distance something moves is just as important as how much it weighs. When you look at how far the rudder servo moved backward on the new 700XN compared to the nose mounted position on previous nitros then it's impact on CG will be quite significant. Moving a 75g servo 400mm has exactly the same effect on CG as moving a 600g engine 50mm.

[George J]

Thank's George.
I know as per Ian's comment previously that it seems like a 75g servo wouldn't make much difference to CG position, but consider that balancing is about moment arms not only weight. The distance something moves is just as important as how much it weighs. When you look at how far the rudder servo moved backward on the new 700XN compared to the nose mounted position on previous nitros then it's impact on CG will be quite significant. Moving a 75g servo 400mm has exactly the same effect on CG as moving a 600g engine 50mm.

Yes absolutely, I’d personally have wanted to keep that servo up front as it makes quite a difference.

[JamieD]

Why not use a belt to cover the gap?

[Grumpy]

Why not use a belt to cover the gap?

If you used a belt drive the main rotor would spin backward! Also with a belt the 'pinion' needs more teeth (18t is usually about the minimum tooth count for a belt drive), so the main gear needs to be much bigger to keep the same ratio (check the size of the Protos Max main gear!) which would need a complete re-design of the drivetrain and frame to fit in.

Realistically if you went with a belt it would have to be a two stage (belt primary and gear secondary) drive system like the Goblins use... which again is a total redesign of the whole heli.

PS... The 'rotor spinning the wrong way' issue is why Align used two small idler gears instead of one larger one.

[DaveG]

Align are taking features of other manufacturers and incorporating them into their own helicopters and then fudging everything else to make it work.

The tank under the mainshaft, taken from the synergy N7 I believe?.? As gaui did with the NX7 also.
the forward rake of the helicopter, taken from the goblin ??

Best helicopters they have ever produced were the original 600N and 700N, cheap, cheerful and the worked! You could upgrade them if you wished but worked great out of the box, the modern craps has upgrades or 'fixes' available straight away as the kit s released as they are rushing or not putting effort into designing the heli's correctly.

[bigpops]

I think it's a bit rich to say that the forward rake is stolen or copied from another helicopter. It's simply common sense to have taller back skids than front to lift the tail out of the grass. I've had the old Trex 700 nitro skids on the back, and the F3C (stock) skids on the front of my Trex 700L for well over 2 years now to lift the tail up. You don't even have to do that. A few washers and longer skid screws will do.

[Grumpy]

Getting the fuel tank near to the CG is part of the design of any heli. It's just due to other design considerations (like having a motor in the way) some manage to achieve it better than others. On the 700XN Align had to move the motor forward to fix a CG problem and this gave them space to put the tank bang on the CG where previously they couldn't because the motor was in the way.

As already noted raked landing gear has been done for years. Mixing the F3C and standard LG legs to get a nose down stance was a trick that's been known for ages on the Trex 600 and 700 to keep the tail rotor out of the dirt, long before SAB tried it. If Align were copying from anyone it was probably from their own helicopters that had been modified by the end users.

[chrisleematt21]

Has anyone done a review on this ? I am looking at getting one.

[Grumpy]

There is a build review or two over on Helifreak though nothing in terms of longer term ownership experience. I do know that Align have already done a 'recall ' on the idler gears and they sent out a new gear housing and larger bearings for the front gear. They also now advise lubricating of the gears after every 5 flights.

[chrisleematt21]

There is a build review or two over on Helifreak though nothing in terms of longer term ownership experience. I do know that Align have already done a 'recall ' on the idler gears and they sent out a new gear housing and larger bearings for the front gear. They also now advise lubricating of the gears after every 5 flights.

I saw a bit about the idler gear on rcgroups. I will have a look on heli freak, just wondered what people thought about it.