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thepiper92 12-15-2013 02:44 AM

Setting Trim
 
I have a small issue with my Mini Switch. I am using a HK 9xr radio. I set up the trim perfectly in my home, and the rudder and elevator are spot on. When I get outside to the field, or area of snow now, the trims are off on the elevator and rudder when I turn the transmitter and plane on. The rudder veers to the right and the elevator trims up. I don't know what it is, the ailerons work fine. There isn't an extreme right on the rudder or up on the elevator, but enough that I need to adjust the trim on the transmitter, despite the trim being perfect at home with the trim on the transmitter set to zero. It's really quite annoying, because I can set up the plane great and then it is a hassle to fly and it takes away from initial enjoyment.

xmech2k 12-15-2013 03:18 AM

Um, so when you get to the field with your plane and turn it on the control positions physically have moved, or do you mean when you fly it, it doesn't go straight?

It's a rare plane that is so perfectly built straight, and perfectly balanced, and has the perfect thrust angle, that will fly straight with all the control surfaces perfectly straight. Even then, it would require different trim at different speeds.

thepiper92 12-15-2013 03:23 AM

Quote:

Originally Posted by xmech2k (Post 934435)
Um, so when you get to the field with your plane and turn it on the control positions physically have moved, or do you mean when you fly it, it doesn't go straight?

It's a rare plane that is so perfectly built straight, and perfectly balanced, and has the perfect thrust angle, that will fly straight with all the control surfaces perfectly straight. Even then, it would require different trim at different speeds.

The controls physically change in neutral vs. neutral in the house

hayofstacks 12-15-2013 04:04 AM

your control surfaces must be moving, your servos aren't centering, or your losing bind.

xmech2k 12-15-2013 05:23 AM

Quote:

Originally Posted by thepiper92 (Post 934436)
The controls physically change in neutral vs. neutral in the house

I'm at a loss then.

thepiper92 12-15-2013 05:27 AM

Quote:

Originally Posted by hayofstacks (Post 934437)
your control surfaces must be moving, your servos aren't centering, or your losing bind.

It doesn't seem to fit these potential issues. I set it up at home well trimmed, test the travel, make sure it's all tightened. Every time I go to the flying spot, the rudder goes right the same amount every time. It control perfectly other than the need to adjust trim. When I finish flying its where I left it. Could wifi from home interfer with the signal?

hayofstacks 12-15-2013 06:39 AM

no, it shouldn't.

it is one of the things I said, I doubt your loosing bind, but if you have a cheap knock off receiver, who knows?

the servo is either not centering or damaged, or your rod is slipping on the easy connector or wire in my opinion. I highly doubt your radio isn't saving the trim settings.

hayofstacks 12-15-2013 06:41 AM

why does it bug you if you have it trimmed in properly at the flying site?

thepiper92 12-15-2013 06:51 AM

Quote:

Originally Posted by hayofstacks (Post 934441)
no, it shouldn't.

it is one of the things I said, I doubt your loosing bind, but if you have a cheap knock off receiver, who knows?

the servo is either not centering or damaged, or your rod is slipping on the easy connector or wire in my opinion. I highly doubt your radio isn't saving the trim settings.

Well it's a Turnigy 9xr radio with the 9ch receiver. There is nothing wrong with the teeth of either servo, and they seem to center well. I think my wireless internet could be the issue, as I can recall having poor internet when I was trying to setup mixes while look at a youtube video of how to do so. Then again, the router seems to have issues now and then without a 2.4ghz radio on. I hope it is the internet, because I actually glued the control rod to the control rod lightly to make sure it wouldn't slip. It's not enough to have a permanent hold, but will prevent any potential slippage. The servo changes the same way every time, a few degrees right on the rudder and a few degrees up on the elevator, enough to make it uncomfortable to fly, especially the elevator. Oddly, ailerons are always centered.

xmech2k 12-15-2013 07:56 AM

Ok. I thought of one more thing. Stupid question time. Are the tx and plane powered up when you set the trim at home?

JetPlaneFlyer 12-15-2013 09:03 AM

One thing that it's not is your wireless internet, that couldn't explain it. A faulty microwave oven has been known to take out 2.4GHz signal but you would loose all control, not just have the trims move if that were the case.

As the others have said, the explanation that makes most sense is that you have mechanical issue such as a servo that doesn't centre consistently, or play/stiffness in the linkages or hinges.

Another alternative with a programmable Tx like you have, is that you you've inadvertently set up some sort of mix that offsets the controls. I've seen this one before. Try setting up the plane on a blank memory in the Tx to eliminate that possibility.

hillbille 12-15-2013 09:17 AM

Are you using a fully charged battery to set the trims at home - or - a used battery from the field that has not yet been recharged?

When the Rx was first bound to the Tx - was it bound using a fully charged battery - or - a battery that was less than full charge?

Why am I asking these questions - because it sounds to me as though your plane is coming on at the field in a fail safe mode - or - your original bind settings were BEFORE trimming the aircraft - and - your plane is reverting to those settings now at every new power up. If this is the case then setting the trims as you want - and then RE-BIND the RX should solve the problem.

Worth checking into either way.

Hillbille

JetPlaneFlyer 12-15-2013 09:33 AM

if it was in fail safe mode then the controls would not respond, the motor would not run, and the plane would not fly... So it would be pretty obvious.

Battery charge state does not effect trim position.

If i recall correctly the 9x system does not automatically set fail safe at bind position like Spektrum does. You have to set fail safe separately on the 9x.

solentlife 12-15-2013 11:24 AM

Quote:

Originally Posted by hillbille (Post 934451)
Are you using a fully charged battery to set the trims at home - or - a used battery from the field that has not yet been recharged?

When the Rx was first bound to the Tx - was it bound using a fully charged battery - or - a battery that was less than full charge?

Why am I asking these questions - because it sounds to me as though your plane is coming on at the field in a fail safe mode - or - your original bind settings were BEFORE trimming the aircraft - and - your plane is reverting to those settings now at every new power up. If this is the case then setting the trims as you want - and then RE-BIND the RX should solve the problem.

Worth checking into either way.

Hillbille

It's a 9x radio - not a Spekie ...

Nigel

solentlife 12-15-2013 11:33 AM

Quote:

Originally Posted by thepiper92 (Post 934432)
I have a small issue with my Mini Switch. I am using a HK 9xr radio. I set up the trim perfectly in my home, and the rudder and elevator are spot on. When I get outside to the field, or area of snow now, the trims are off on the elevator and rudder when I turn the transmitter and plane on. The rudder veers to the right and the elevator trims up. I don't know what it is, the ailerons work fine. There isn't an extreme right on the rudder or up on the elevator, but enough that I need to adjust the trim on the transmitter, despite the trim being perfect at home with the trim on the transmitter set to zero. It's really quite annoying, because I can set up the plane great and then it is a hassle to fly and it takes away from initial enjoyment.

I know this sounds stupid question ...

But when you set trims at home do you have both Tx and Model powered properly ... and you are using the trim buttons by each stick ?

Bear with me : You are basically powering up all ... eyeballing the model and adjusting trims on the TX watching the rudder / elevators etc. alter and align ?

Once you have that ... I would note down the position of each indicator on the 9x screen ... you have bars down each side and along bottom of the screen that show where the Trims are set to.

Ideally - you should adjust all surfaces mechanically to neutral aligned and have those indicators centred ... giving you maximum +/- trim range.

Once you fly and find the real trim settings that have straight level cruise flight ... back home you should then adjust control rods to set surfaces to that with Tx trims back to centre ... or the lazy way is to use the Subtrim in the menu to do it ...

Nigel

dgjessing 12-15-2013 02:22 PM

I wonder if it could have something to do with the airframe warping a bit in the cold outside?

JetPlaneFlyer 12-15-2013 02:42 PM

Quote:

Originally Posted by dgjessing (Post 934465)
I wonder if it could have something to do with the airframe warping a bit in the cold outside?

Good call!

Why didnt i think of that, given the time of year and the OP's location I'm sure that's the reason. It's actually quite common if you are flying on the cold that the trims go out. Reason is that there is a huge difference in the rate of thermal expansion between the foam (or wood) that the plane is made from and the steel or carbon fibre that the pushrods are typically made from. This is especially noticeable if the pushrods run the full length of the fuselage, short pushrods are much less effected.

Foam has a very high rate of expansion, steel much less and carbon almost nothing. Going from a warm room to a cold field will make the foam of the fuselage contract, causing the pushrod to get longer (relatively) and deflect the surface.

The solution is simple, only set the trims when you are outside in the cold, dont adjust them in a warm house. If you wanted to be 'clever' and engineer a fix then you could change the pushrods to plastic which would more closely match the expansion of the foam.

solentlife 12-15-2013 03:57 PM

Cold deforming the airframe ?

Given the OP wording - I don't think we are talking about one click if any that differential thermal expansion would cause.

Like many here I fly in warm and cold weather ... never noted such changes ... and certainly not to the apparent extent OP suggests.

Nigel

hayofstacks 12-15-2013 04:32 PM

x2. I've had the same trim settings on the same models year round. were talking 110 to -15.

I don't get what the big deal is if the plane saves its trims at the flying site. I've never had a plane trimmed perfectly before the first flight.

JetPlaneFlyer 12-15-2013 04:36 PM

Nigel, it's far more than one click. it can make a very noticeable difference. Back in the day it was noticeable if you used the 'Sullivan Snake' nylon pushrods in balsa models as the pushrod had higher expansion. These days with foam models the problem is reversed and the fuselage has the higher rate of expansion. Normally you dont notice it because you dont go from extremes of hot and cold.

JetPlaneFlyer 12-15-2013 04:44 PM

The math:

Coef of thermal exp of polystyrene fuslelage = 0.00008 per degree C
Coef of thermal exp of carbon fibre pushrod = almost zero
length of pushrod = (say) 400mm
Temp difference = (say) 30C

0.00008 x 400mm x 30C = 1mm

So that means the pushrod effectively gets longer (relative to the fuselage) by 1mm which would cause a very noticable trim change.

references for expansion rates: http://www.engineeringtoolbox.com/li...ents-d_95.html

Bear in mind that my day job is a mechanical design engineer, so I get paid to do this sort of stuff. I'd bet a pile of cash that this is the OP's problem.

solentlife 12-15-2013 05:28 PM

Quote:

Originally Posted by JetPlaneFlyer (Post 934479)
Nigel, it's far more than one click. it can make a very noticeable difference. Back in the day it was noticeable if you used the 'Sullivan Snake' nylon pushrods in balsa models as the pushrod had higher expansion. These days with foam models the problem is reversed and the fuselage has the higher rate of expansion. Normally you dont notice it because you dont go from extremes of hot and cold.

I live in a northern clime ... 60 North ... and winters are cold ... summers are warm ... temp. difference about 60 C ...

I fly all year round ... EVERY flight incurs a click somewhere on a trim ... but never more than a very small amount .....

No model stays perfectly trimmed day after day ...

The impression of the OP's words is more than just a slight offset ... 1mm TE is not enough ... not according the impression of his post.... and assuming a 30C drop.

I'm not saying it's wrong - I'm saying it doesn't seem enough.

Nigel

thepiper92 12-15-2013 05:35 PM

Quote:

Originally Posted by JetPlaneFlyer (Post 934480)
The math:

Coef of thermal exp of polystyrene fuslelage = 0.00008 per degree C
Coef of thermal exp of carbon fibre pushrod = almost zero
length of pushrod = (say) 400mm
Temp difference = (say) 30C

0.00008 x 400mm x 30C = 1mm

So that means the pushrod effectively gets longer (relative to the fuselage) by 1mm which would cause a very noticable trim change.

references for expansion rates: http://www.engineeringtoolbox.com/li...ents-d_95.html

Bear in mind that my day job is a mechanical design engineer, so I get paid to do this sort of stuff. I'd bet a pile of cash that this is the OP's problem.

This makes a lot of sense, but this trim change occurred when it was warmer weather too. I was flying in -23 C weather yesterday, but was flying in 10 C as well, before the planes motor shaft snapped and was out of service for a time. Reading up, is wireless internet not 2.4ghz, and with a Turnigy radio, it likely wouldn't be the best a frequency hopping to avoid interference.

Solentlife, at home I was leaving the transmitter trim at zero, all controls right in the middle, and physically adjust the pushrod and control horns to make center it all out. I can then power the rudder and elevator and it would always center. I could also leave the plane and come back to it a couple days later and find the trims still the same, but the moment I carry the plane to the site, turn the transmitter on, then plug the battery in, the trim for the rudder and elevator are always off, where the bottom of the foam of the elevator is lined up with the top of the foam of the h stab, and the left side of the foam on the rudder is lined up with the right side of the foam of the v stab. Essentially, both have moved the thickness of the foam, around 3mm, and it is like that consistently, it's not that one time it will be a 15 degree difference, and another is 5. It's always the same, even though at home the centering will be spot on, and is consistently spot on until I leave the home.

Also, oddly enough, I once had a cheaper Turnigy 6x, and that is the reason I destroyed my first plane cloud fly by axn, or whatever the name is. I would set it up and throw the plane, and it would bank right, so much that it couldn't be corrected. I thought it was me, as I couldn't fly, but it couldn't have been. After getting the 9xr, it has much less of an issue, but the issue still exists slightly, thankfully it leaves the plane controllable still.

JetPlaneFlyer 12-15-2013 05:39 PM

Nigel, that's not 1mm at the TE, it's Imm at the pushrod, so that would be 3 or 4mm at the TE.

Also I under-estimated the temperature difference. Typical daytime temp in Winnipeg is around -20C this time of year, so that would be a 40C swing between indoors and out. Unless you set your trim in the house then go outside (like the OP is doing) it's not an issue. You surely cant argue with basic properties of materials. The expansion rates I quoted may vary a bit from one type of foam to the next but the principal is unquestionable.

Thepiper92, honestly, this is the only logical explanation, Interference cannot cause something like this. The simple answer is set your trims in the field and fly. Dont go messing with them when you get home. You shouldnt be too concerned if the elevator and rudder are 'dead straight' or not, the important thing is the plane flies straight, so once you have it trimmed to fly straight dont mess with it.

solentlife 12-15-2013 05:51 PM

Quote:

Originally Posted by JetPlaneFlyer (Post 934490)
Nigel, that's not 1mm at the TE, it's Imm at the pushrod, so that would be 3 or 4mm at the TE.

I typed TE as short for Thermal Expansion ...not Trailing Edge.

We can soon sort this part ... watch my questions in next post.

Nigel


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