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Member postings for Jon - Laser Engines

Here is a list of all the postings Jon - Laser Engines has made in our forums. Click on a thread name to jump to the thread.

Thread: Single servo ailerons
16/08/2019 13:36:43
Posted by Simon Chaddock on 16/08/2019 12:03:15:

I bet the OP is beginning to wish he had never asked. wink 2

lol too true.

I hated probability at school so getting into the nitty gritty is of no interest to me at all.

The point i was trying to raise earlier is that to claim dual servos on ailerons is for redundancy is a flawed argument if you dont double up everything else (someone else said this too).

No matter what you do there are still single point failures in the system and the biggest of those is the pilot. With that in mind, and considering the reliability of well maintained equipment vs the reliability of the average pilot the entire redundancy argument is almost a moot point.

16/08/2019 08:24:33
Posted by Bob Cotsford on 15/08/2019 18:35:53:
Posted by Martin Harris on 15/08/2019 18:13:28:
Posted by Jon - Laser Engines on 15/08/2019 17:01:14:

Unless the servo fails at anything other than zero deflection, then its game over :D

...which is a pretty good reason for having a second servo!

Didn't help my WotsWot when it failed at less than 50' after take-off, maybe a better flyer could have saved it but I couldn't!

That was the point i was trying to make. Its not a criticism of you Bob, but even with a spare aileron servo in place the model still crashed. Depending on the situation it might have been recoverable, in which case the accident falls into the 99% pilot error category, but even if it was the shock of something actually going wrong means that even very good pilots may freeze and/or make bad choices when presented with an expected problem.

Also, just to really go for it what would have happened if the model only used the one good servo? more servos means more points of failure and lower reliability.

I am playing devils advocate here a little. Per surface servos on ailerons are common and so much easier than a 2 foot torque rod out to the ailerons at the end of a 40 inch wing panel. This is especially true when there is a flap in the way and the whole installation would be far more secure. There is a theoretical safety margin should one servo fail, but failure is more likely due to increased complexity.

To get back to the op however, using twin servos will not help him one little bit.

15/08/2019 17:01:14

Just on the redundancy thing it should be quite possible to land an acrowot without ailerons..in fact its possible to land most models rudder/elevator only but it does take a little care, and it might not be the easiest but it can be done. Its something i actually practice from time to time (in calm conditions i admit) but everything i own, including my 80 inch warbirds, can be landed without ailerons if i really have to so im pretty sure an acrowot will manage.

Unless the servo fails at anything other than zero deflection, then its game over :D

Also, you can add all the servos, rx's and batteries you like to the model but you still have a number of single point failures. You have one tranny, with one battery, and one lump of meat manipulating the sticks.

As pilot error accounts for most of the crashes we suffer i would say that going crazy trying to guard against equipment failure is a bit daft. Especially when a substantial number of equipment failures boil down to inadequate maintenance and care.

At the end of the day, probably 99% of models are killed by their owners and the time and energy put into inventing double redundant whatever is probably better spent on regular inspection and maintenance.

15/08/2019 08:51:23
Posted by RC Plane Flyer on 15/08/2019 07:26:47:

I am going to reset the settings back to plan recommendations 3/16 to 1/4 on see how we go. as said earlier some how I was at 5/16 with no expo to soften the sticks

Just throw out the plan and do it yourself in the air. Just keep knocking 10% off the deflection until you get to a comfortable rate of roll at full deflection. I would probably then add 10% back and then see what expo, if any i needed to add.

Things like engine tuning, c/g, control rates, propeller selection and so on are all things that you just have to work out for yourself. There is no written guide or set of fixed values that will be right for everyone all of the time. You just have to experiment

15/08/2019 08:47:22
Posted by Bob Cotsford on 14/08/2019 19:37:44:

I find that I'm using expo more often in recent years, arthritic thumbs cant sense small pressures as well as they used to so I find small control movements harder to judge than I remember

Cant fault people using expo in this sort of situation. I know some have hands that shake a bit too and again, cant do much more than fly around the issue.

14/08/2019 16:50:47

Not saying there arent use cases Martin, just that you use it after you have the basics right and not as a bandage to cover a poor base setup. To be honest this applies to more or less all tx programming. If the mechanical side is pants, sort that out first, then get the rates right, then polish with expo if you need it. I suspect that if models are set up this way most wont need it. I have only used it on 1 channel on two models in my current fleet of 12 airworthy. 

Without expo you get gradually reducing amounts of movement with stick deflection and this can be very helpful on elevator especially.

Your comment about aileron effectiveness is also fair enough and i have 10% negative expo (making the centre more sensitive) on my hurricane as its ailerons have a nasty mush/dead zone in the middle.

 

 

Edited By Jon - Laser Engines on 14/08/2019 16:53:25

14/08/2019 16:00:41

Cant disagree with the 3 previous posts.

Thread: 4 stroking a Merco...
14/08/2019 11:58:59

the problems are significant, thats why half my range and our petrol are still nowhere to be seen

Thread: Prop failure
14/08/2019 11:58:07

I have made numerous sandpaper washers and they work really well. I used 240 and 400 grit so far, both worked fine.

I have had the spinner cone come loose on the model once or twice before and there is very distinct ringing sound when that happens. That sound was not present this time and there were no fret marks on the prop or spinner mating surfaces.

Thread: Single servo ailerons
14/08/2019 11:52:19
Posted by Brian Cooper on 14/08/2019 10:59:40:

Using just one servo on the ailerons, especially on a model like the Acrowot, is very "old school".

It is far better to use two servos, and then dial-in expo and rates to suit. . . There seems to be a mental barrier about using more than 30% expo. . It is permitted to use more if required. . Just keep dialling it in until the correct "feel" is accomplished.

Also, by using two servos, they can be individually "tuned" to get the best out of the aeroplane.

B.C.

Its not a mental barrier, using excessive expo makes many models extremely unpleasant to fly. 30% is already excessive and i have never needed to use more than 10% on any model i have ever owned. Granted, most are sport and scale, but an acrowot is hardly a twitchy monster.

I would always fly with no expo and get the rates right first. Then, if you feel you must add some expo. If you do it the other way around you end up like a friend did with 60% expo on the elevator of his spitfire which made the model impossible to land. Knocking the rates down by about 30% and removing all the expo made it an absolute doddle to land.

Just dialling in expo is completely the wrong thing to do.

Thread: 4 stroking a Merco...
14/08/2019 11:33:05
Posted by Foxfan on 14/08/2019 10:41:45:

Yes, that's a shame, Jon. Especially where the smaller engines are concerned. We don't all want vast airframes in the shed, requiring huge, expensive engines.

 

The problem for us was cost. A 45 or 50 costs the same to make as our 70. as the 70 is the same physical size as the 45, 50 and 62 used to be it just didnt work. When we brought out the 50 it killed the 45 dead. The 62 did the same to the 50 a few years later, and finally 70 killed the 62. Moving forward to 2012 the 155 killed the 150 stone dead even though it was a little more expensive. As for support of discontinued engines we had to call time on it in 2016. nearly 25 years of support after discontinuation was deemed to be more than satisfactory and the vast majority of the engines were worn out by this point anyway and beyond economical repair.

while i understand that not everyone wants a massive model the only way we could offer a 50 size engine would be to charge the price of the 70 for it and shift the whole range up in price to make the stack work. I suspect this would not be a popular move!

For your merco efforts if you like i can supply some cams and a pinion drive to save you the gear cutting problem. I can either supply new ones at their normal prices or i could rescue some from a deceased engine and let you have them for a considerable discount. if you let me know the width of the crankcase i will try and work out if our cams stand a chance of fitting.

Edited By Jon - Laser Engines on 14/08/2019 11:33:50

14/08/2019 10:10:58

If you buy a laser 45, 50, 61, 62, 75, 90, 120v, 150v or 180v thats fine but dont pay much for it and dont expect any support if you have to fix it. They were all discontinued the best part of 30 years ago and we no longer support them in any way for spares or service. I cant even supply a new exhaust or carb so be warned, you are on your own if it needs repairs.

Thread: Prop failure
14/08/2019 08:54:36

Sorry John but what did you expect? Your post was nothing more than a deliberate jab at me and i really dont appreciate it.

Thread: 4 stroking a Merco...
14/08/2019 08:40:40

The example above seems to have a number of magnum parts on it. The carb, intake, head and cam follower bush all look like magnum parts to me.

Thread: Laser cut kit, how many of you sand off the brown laser scorching before gluing?
13/08/2019 16:57:07

i just cyano it together and move on

Thread: Single servo ailerons
13/08/2019 16:48:23
Posted by alex nicol on 13/08/2019 16:45:16:

Apologies if this a bit obvious

Before anything is adjusted, have you measured the aileron deflection and compared it to the recommended deflections?

Also have you checked the balance point

Alex

Alex makes a valid point about referencing the recommended throws but dont feel you have to abide by them. If you want more or less then by all means go for it. I totally ignored the recommended settings for my acrowot xl as i considered them to be excessive in the extreme.

13/08/2019 15:17:13

I would ask yourself the following:

Do i need to use full stick deflection on ailerons at any point during the flight?

If the answer is no, then lower the rates first. Keep reducing the rates until you get to a stage where full deflection gives you a nice rate of roll (as in you pull up to do a roll, slap the stick over and it feels nice/controllable etc) and then look at expo if you feel you need it. I really suspect you wont need it.

The more of the stick deflection you use the softer the response will feel. If you find after all this that you are at about 20% rates, measure the deflection and fit a smaller output wheel on the servo. Reset the rates back up to get yourself back to the deflection you measured before. This will also make the model feel smoother as some servos do not have fantastic resolution and move in fairly large steps (relatively speaking) and this is noticeable when you have such small movement of the servo as the error is being magnified by the geometry of your control linkage.

I also agree that you dont need differential on an acrowot.

Thread: ASP prop driver stuck!
13/08/2019 14:56:24
Posted by Engine Doctor on 13/08/2019 11:54:35:

yes Agree with John; although a 15 min job to us who have done it many times may be a daunting task to the un-initiated .

Yea i know, hence the wink

Still, the principals are the same as a 2 stroke its just that there are more wiggly bits inside. As long as you remember where they all came from and which way they were facing at the time then its pretty straight forward

But yes, the suspense is killing us all

13/08/2019 11:01:04

Aluminium has a nasty habit of picking up and friction welding itself. I wouldnt recommend trying to run it as is.

And more work? a strip and rebuild on one of those is a 15 minute job

12/08/2019 19:04:31
Posted by Martin Harris on 12/08/2019 14:03:21:

Wouldn't that put a heavy load on the front bearing and crankcase casting though? I would favour holding the driver to press the crankshaft through it, which wouldn't require any further stripping.

Edited By Martin Harris on 12/08/2019 14:03:45

As the engine wont work as is anyway breaking a bearing wont make it any more useless than it is already. Gentle pressure wont harm it but some common sense would have to be applied. That said, it takes a quite astonishing amount of force to get some cranks out. Goodness knows how they get so tight.

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