Fuel Choice

[mort-uk]

Hi

New to the forums, but I've been reading for a while.

I acquired a Nexus 30 with all the gear some months ago from somone who had lost interest/patience.
For the last few months I've been reading books, rebuilding the heli, teaching myself how to set it up, flying simulators etc. Technically I'm quite confident now, however I'm being frustrated by a stubborn engine which is preventing me from moving on to the flying stage.

I suspect its the fuel, reasons for this being I cant think of any other possible reason why the engine will not start.

The engine is a MDS 38. When I got it I read the instructions, dissasembled as much as sensible, cleaned and reassembled. Fitted to a bench for testing, screwed in a new plug, connected to fuel and fired her up. It started first time. I checked setting of main and mid needles and when I was happy I fitted it to the heli.

Now I cant get it started again. I see fuel drawn up the pipe, I have a glow (double checking plug and glow stick outside of engine), the starter is spinning the cone no problems ( in the right direction). But it wont fire.

After giving it a real good going over this afternoon I'm down to suspecting the fuel. I'm using fuel that came with the kit I originally got, its Model Technics Duraglo 10 (9% synthetic, 6% castor, 10% nitro, 75% methanol) I dont know how old it is.

My question is, would 'bad' fuel cause this problem? Or am I missing something?

A quick google reveals that Model Technics is a bit cheap and cheerful and that old fuel can cause problems.

I'd appreciate any advice.

[G-DAVE]

Hi Mort
I think you have come to the correct conclusion yourself.
Your not sure how old the fuel you are using is - Fuel does go off with time - I don't like any fuels with castor in it, it can gum engines up and when it gets on the engine / mechanics after it leaves the exhaust it will gum up every thing it lands on .
get some new stuff - choose from Magnum - Coolpower - or Wildcat.
The engine in your heli is not the brightest thing on the market - the main problem being the Carb. which makes them difficult to get running correctly.
However that is a budget thing and with new fuel you should be able to at least get it running.
If money is not a problem get a O.S. 30 size engine it will fit straight into your heli and give you hours of reliable starting/running.
Dave D

[Raptorite]

Hi Mort-uk,

I use model technics fuel myself, in my case Contest 10 for all bar the 90 which runs on Racing 30.

Nitro based fuel does have a tendancy to degrade after a period of time, if the fuel you have is anything over 6 months old, I would be tempted to change it, or at least mix it 50/50 with new fuel.

As you by the sounds of it have never managed to get the motor running after it was installed in the heli, I would first look at things like the plumbing, filters, header tank if you have one etc. There is no reason why it wont run in the heli if it did on the bench with presumably the same fuel.

Make sure the fuel lines are all clear and connected the right way round, pay particular attention to both the clunk line (fuel line inside the tank) and pressure line from the exhaust, also make sure the pressure line and feed to the carb are connected the right way round to the main tank. The pressure line should be connected to the top somewhere and the feed to the carb should be connected to the nipple in the centre of the bung.

If you have checked all of that and still have no joy, try taking the fuel line off the carb and try turning it over on the starter, you should see a nice consistent stream of fuel coming out of the fuel line, if not, there must be a blockage or failure somewhere.

It is also worth pointing out that if the model has been left with any fuel in the tank for long periods of time, the nitro in the fuel will eat away at the silicone fuel lines ultimately causing it to weaken and fail, so if that is the case it is best to replace all the fuel lines.

I hope this helps.

Cheers,

Pete.

[mort-uk]

Thanks for your replies.

Last night I took out the tank and checked the fuel lines/clunk etc. Ready for when I get new fuel today. With it all back together I disconnected the pressure line from the exhaust and blew in and watched the fuel flow through and out of the disconnected carb tube, I couldnt detect any leaks and it all seems to be working fine.

I cant really do much more until I get new fuel today, but I have all afternoon to crack this problem

I have done a lot of searching for info on the MDS 38 and its quite difficult to find a good word said about it, so I may just go for the OS32 if this engine causes much more frustration.

[mort-uk]

Well, I bought some fresh Duraglo 16 and its now starting first time everytime

The shop I went to didnt stock Coolpower so I just opted for some more of the Model Technics, but obviously fresh and the 16 not the 10 I had been using.

I've done some fine tuning and the engine has nice smooth pick up from idle to full throttle (using head loaders, not blades). I've also not got any vibration issues, which is a bonus.

However, all is not well with the tail, even at quarter throttle the heli starts to yaw quite fast (on a concrete garage floor), I can control the yaw if I apply opposite stick, but obvisouly something isnt right.

So thats tonights job

[Stuart]

what transmitter and gyro are you using, I suspect it will be the Revo mixing that you will need to set, provided your not using a heading hold gyro.

Once we know the Tx and Gyro we can fix it for you.

[mort-uk]

I'm using a Sanwa RD6000 Tx and CSM ICG 180 gyro.

I had a very quick look at revo whilst it was running and it didnt appear to make much difference. Although my knowledge in this area is a tad vague to say the least

The Gyro 'orientation' is correct as without the engine running if I move the tail it makes the correct tail rotor pitch direction changes.

Like I say I'll be going through the whole tail rotor/gyro setup tonight, so any pointers would be handy, although sadly I cant run up the engine in the evening due to close proximity of grumpy neighbours.

[G-DAVE]

You don't say which way it's yawing - It's normal for a heli to yaw prior to reaching the lift off point - because the the tail trim wil be set for hovering not quarter throttle .

Dave

[mort-uk]

The tail is moving right (looking from rear) as the throttle is increased.

I went through it last night and all revo for mid and high was at 0% so I guess it wasn't countering the torque effect. I've added in a rough setting for now and tested without the engine running. I'll do a run up tonight.

[antsis]

Mort

I used the CSM180 on my hawk sport and didn't need the revo mix. If the tail is yawing right, it means that the gyro is not countering the torque. Check the gain setting on the gyro. 50% is a good starting point. If the gain is too high, the tail will start to wag.

Ant

[G-DAVE]

[quote="mort-uk"]The tail is moving right (looking from rear) as the throttle is increased.

It's better to refer to yaw in terms of the helicopter not the tail - what you mean is the heli yaw's Left!!!!
Dave D

[Raptorite]

Hi Mort,

Having now established that there is a possible mix up in the direction of the tail, it might be possible that the bench tests you did with the model is actually operating in the reverse sense. This sounds highly likely to me as the heli is yawing left, this is probably because the gyro isnt doing its job. As the main rotors spin clockwise, or in other words right, the torque of which will want to yaw the model to the left, thus the gyro is supposed to counter the torque by adding enough right rudder (tail) to counter act the torque.

If in this instance the gyro is reversed, it will try to counter the torque by adding left rudder instead of right, which will only serve to exacerbate the left yawing.

As the CSM 180 does not have an adjustable reverse switch it relies on the orientation of the gyro case to determine its direction. In order to reverse it therefore, you will need to take the gyro off the model turn it over and re-attach it with a new double sided foam pad.

Give it a try and let us know how you get on.

Cheers,

Pete.

[mort-uk]

Hi again

Thanks for all your input.
Well I double checked the gyro orientation, and it was definately ok.

I did a couple of more tests on the floor and decided that the trim was mechanically way out so altered that.

This weekend I felt confident enough to get it out in the open and get it light on the skids and take it from there.

So training gear on etc. I went for it. Throttle/pitch settings seemed fine and I could quite happily get it to hover about a foot off the ground (as much as I dare), however, the tail was still drifting and I was spending all my time and concentration trying to correct the yaw. I trimmed to full right and the heli would just about hold straight, so I landed and mechanically added that trim so trim was centered on the tx.

I went up again and this time I was yawing the other way :roll:

Anyway I went through about 2 tanks and by this time it started getting gusty so packed up after doing a couple of other checks.

Anyway, I'm still unhappy about whats going on in the tail department, to the point I'm starting to suspect my gyro isn't working correctly, however to establish that I really need to understand what to expect from a gyro and properly setup helicopter.
Incidentally I should add that the gyro gain was on max. On the bench if I turn the heli I can see the gyro making the correct moves to correct the action, but in flight this doesnt appear to be having much affect.

Any advice on setting up gyros, tips, or a general tail trimming routine and what I should expect when I hover when the system is working correctly would help.

I'm off to my local club in the next week or so anyway, I think I've done about as much 'ground' work as I can on my own, so time to get to know the experts

[antsis]

On the CSM HH gyros such as the 400 and 560, CSM recommend approx 8 degrees of right rudder at the neutral position. If your gain is almost at max, the tail should be wagging like a happy dog.

Are you sure the rudder servo is ok? I've been caught with a servo that seemed to worked fine on the ground, but had no strength when under load.

Ant

[mort-uk]

I've read elsewhere that somone else had a problem with this gyro and was forever chasing the tail. So as I was thinking about it anyway I'm going to buy a heading hold gyro and take it from there, its probably better in the long run anyway.