Out of trim

[Jon H]

A recent experience reminded me of something that i have seen a great many times and it got me thinking.

Firstly, this is not a criticism of anyone and i am not trying to blow my own trumpet, its just something that came to mind and is perhaps something to consider as it could come in handy.

So, to set the scene we have the maiden flight of a new model. As im sure you have all guessed from the title of the thread it was out of trim once it left the ground. The model also had slightly over sensitive rates and the two things combined with an understandably nervous pilot gave a nice bucking bronco effect to the first half circuit. Ultimately this led to a spin which would have been terminal were it not for my intervention. I was able to regain control, get the model trimmed out and we then moved forward with getting it all set up. its all nicely sorted now.

Being out of trim with slightly excessive rates or wayward c/g is not uncommon in a new model and i am sure we have all seen models follow a similar flight path to the one i described, perhaps without the happy ending.

In these cases one of the contributory factors seems to be the apparent inability of the pilot to fly the model in its out of trim condition and this brings me to the point of this thread.

What i was wondering is how many of us have really been taught trimming, and how many are comfortable with, and/or practice flying a model that is badly out of trim? I ask as the only reason i was able to rescue the situation described above is that i was comfortable to fly the model in its out of trim condition and was able to adapt to it quickly enough to maintain a normal level circuit long enough to get the trim tidied up. This was probably 2 laps of the patch in an slowly improving out of trim state. I always teach my students trimming and 'force' them to fly circuits with the model out of trim so they have some experience of how to handle it as they will have to maiden a new model eventually. I always tell them that an out trim model is no excuse for not flying a proper circuit. In essence, fly the aeroplane, worry about the trim later.

Again the objective here is not to judge anyone or criticise their flying skills, I am just curious to hear the views on this subject as i definitely think trimming is a flying skill like any other and should probably be something we practice more often.

[Bruce Collinson]

I think you're right, when I was being taught and buddied 2 years ago, my tutor turned up one day with a progress schedule (not I recall directly A Cert but headed that way) and one of the tasks was to trim a model. The model was put out of trim in flight then passed to me via the buddy box switch.

It was a salutary lesson but a very useful one, of which I was vividly reminded when flying a Wot 4 after repairs to fus and wings, which was quite out of trim.

I don't recall this task being in the A test. Perhaps it should be.

BTC

[J D 8]

I agree with Jon,having seen normal'y competent pilots struggle with a new out of trim model that if you just held in a bit of down/left/or right stick would fly fine. Last summer one fellow was struggling with a model that was swooping and then climbing all over the place, a call to cut the power down some had it under control.

With older mechanical trims you could slap them over quick to get into trim.With digital trims it is not as easy but a lot less chance of accidentally knocking the trims out of position during transport. Did that a few times,made things interesting. I know I should have checked but it was good training.

[Trevor]

Sadly I have to agree. We have lots of otherwise safe pilots who can’t trim out a model and, as a club instructor, I must take some responsibility for that. When I was learning (on the slopes, before buddy boxes) and reached the point where my instructor was getting bored, he simply reached across and pushed the trim levers into the corner, saying ‘get out of that!’. Somehow, I’ve never summoned up the nerve to do that to my ‘graduate students’!

Trevor

[Don Fry]

I have to admit, to this day I dislike a lifting off a machine that wants to roll, and descend. To the point that, when I set up the elevator neutral, I am careful to err on the up side if in doubt. It's the coordination of holding it, and trying to shift trims that does my head in. I have been known to not bother, land it, trim in the right direction, and then have another go.

But bottom line, roll and dive, to me, is stressful.

[Jon H]

Thanks for the input guys

Don, 100% i agree that models out of trim, especially in more than one axis, can be an extremely intimidating thing to deal with and the stress of the situation 15-20 seconds into a maiden flight can be too much and brain overload is the result. Its just human nature and i cant fault anyone for that.

This is why i think we should all practice flying models in this condition.

If you have a model you know well, the trusty hack that you always bring out on windy days for example, why not set it out of trim, a few clicks down and few to the left or whatever. Then takeoff and go for a flight. As you know where its going to go you have half the battle won and already know the corrective action in your mind. Fly 3 or 4 laps, left and right, do a landing. Trim it so its even worse, do it again and so on. After a few flights i doubt you will have the same trepidation you feel now. Before the flight it may also be a good idea to hold the tranny, close your eyes and try to find the trims so that you dont have to take your eye off the model to find them in the heat of the moment.

All that said, the idea of abandoning the flight and landing if its too far gone is a worthy recommendation. It comes back to not forgetting to fly the model. Asking an assistant to move the trims for you in an extreme case is also not a bad idea, just dont forget to fly the model while you are giving him the instructions on what to do. If the flight is to be abandoned due to poor trim, just remember than the landing may be pretty ugly. If available, why not choose the long grass or the corn? i had a Hurricane some years back that had too much elevator travel, i knew i couldnt land it like that so i landed gear up in the crop. I had already decided to do that in case of emergency before the flight so i didnt have to actually come up with a plan while focused on the model in the air. 

Trevor, i usually give my students a pretty hard time. i give them models out of trim, i am obsessed with keeping the wings level, i make them fly in strong wind and disable their ailerons on the buddy box to teach rudder control, circuit planning, and to simulate a case of reversed ailerons where they have to get down with rudder only. They hate me for it, right up until its time for their first cross wind landing. I dont go out of my way to make it difficult, but im there to teach them to fly and not just pass their solo. Its all worth it when they finally go 'ohhh i see why you made me do that now'.

 

 

Edited By Jon - Laser Engines on 09/11/2018 17:18:41

[Stuphedd]

I learned to fly , in the days when very few instructors were availiable , so we taught ourselves ,

There were only 2 of us into radio early propo , and we rarely went home with an unscathed airframe .

One day we got a new guy in the club , he watched and then said let me have a go , he took the plane , played with a bit said there was nothing wrong with the plane and gave the TX back to me , It flew brilliantly It did what I thought it should , all he had done was trim it , he did the same for my mate , with the same result !

Now 50 years later I test fly/trim most models that fly at our club , having a trimmed aircraft lets you really enjoying the flying aspect . It took me ages to exactly trim my model for my B cert the way that let me fly relaxed !

My biggest "Bitch" about Test /Trim flying other peoples planes is how they set up the rates , or more important lack of setting them up . I like options preferably 100 and 50% , One or the other will give you an aircraft you should be able to trim , then you can fine tune the trim and the rates ( CG is another mystery to some people too )

cheers

[Don Fry]

Pete, this thread is somwhat cerebral at present.

Don't get us going on the relative merits of rates, and exponential .

[Jon H]

Posted by Don Fry on 09/11/2018 19:21:41:

Pete, this thread is somwhat cerebral at present.

Don't get us going on the relative merits of rates, and exponential .

While another aspect for sure i understand where he is coming from. If the model is so sensitive you cant fly it then its hard to trim, but equally, if its miles out of trim you cant get the rates right either. I am very critical of kit manufacturers as in the case described in my first post we started at about 75% of the recommended minimum and ended up at less than half of the recommended minimum. Even without the trim issue, using the recommended travel would have likely caused significant difficulty to anyone testing the model irrespective of the trim situation. The addition of large amounts of expo would have made things worse in this case. As you say though Don, that is another conversation entirely.

Pete, as a curiosity do you ever teach people how to fly their models when out of trim? and then show them how to trim their own models as that chap did for you?

[Ron Gray]

I’m no expert but before you even get to trimming in flight the control surfaces and mechanical connections need to have been correctly setup first. My own experience of watching others, and, tbh, my own early flights, leads me to believe that not enough attention is given to these before taking to the air.

[Geoff S]

I've found that an apparently unstable model is, in reality, merely out of trim and it's the pilot having to hold in aileron or elevator to keep the model flying straight and level. I hasten to add that I'm talking about relatively minor trim issues. I just get up reasonably high and release the sticks and see what's needed.

My main problem is lack of dexterity. I can't easily move my fingers independently, particularly my right hand - the left's not so bad but I am right handed so I've needed to learn to do things with my left. That means I need to let go of the stick to use the trim.

I also have a confession. My Ballerina was out of aileron trim. It wasn't too bad but I couldn't seem to correct it and it seemed to be getting worse. Eventually it got so bad I had to land which was less than perfect. When I checked I realised I'd been moving the trim the wrong way. No wonder it kept getting worse. I felt like a total idiot - probably because I was! I'd never done it before and now I make a mental note that if it's going (say) right put in left trim.

On a maiden I try to check everything in the workshop, especially CoG and (of course) control directions. I hate messing about at the field doing things better done in a calm environment with a bench and all the tools I may need. I usually put a little up-trim on the elevator as I'd rather be trimming down when the model is climbing than up when the model is headin g towards the ground.

btw I was never taught to trim.

Geoff

[Former Member]

[This posting has been removed]

[Martin Harris - Moderator]

A development which may well spread to other radios if they don't already have it is "autotrimming" - the Jeti implementation allows you to assign a switch (I use a non-locking one but those with similar difficulties to Geoff's could use a standard one) to the function which when operated, moves the trims towards any offset until convergence is reached. All you need to do is fly straight and level while it's active and when you find that the sticks are in the middle - you're trimmed! Coarse movements will hurry the process up if the trim is a long way off and become intuitive once you're used to it.

I love it - and when I'm trimming models for other people it only serves to remind me how much!

[John Stainforth]

Martin,

Autotrimming sounds like a brilliant invention. So good, I think other manufacturers are bound to follow suit. I don't think this innovation is in any Spectrum sets yet, but I could be wrong.

[Mark Howard 1]

I use auto-trim on the Horus too for the first rough trim on a maiden, it makes the process much easier.

I also find that swapping the trim switches makes life so much easier too. With swapped trims the left hand stick switches control the right hand stick trims and vice versa. If you are flying mode 2 the elevator trim is done using the throttle trim switch and the aileron trim is done with the rudder switch. You can set the throttle and then fly on aileron/elevator only whilst the left hand is trimming the right stick. It's easy to do on Frsky Tx's and I think the Jeti's too but not sure about other transmitters. It's a major help on transmitters where the trim switches are small and not so easy to find by feel alone (like the Jeti).

[Don Fry]

I once tried swapping the trim switches. But in the heat of the moment, putting in a bucket of down elevator trim, the motor stopped. Went back to normal.

Habits die hard. My car is left hand drive. My old one was right. And quite a few times got in to the wrong side.

[Chris Walby]

Martin/Mark, I think you are missing Jon's point, you guys have years of experience and find it a minor challenge to maiden an out of trim model.

Martin (thanks for the help) maiden and trimmed my Electric Hurricane, flew it scale and landed it without issue. I have flow it a number of times (and will continue to persist) with what I can only describe a very challenging model to fly for me!

I agree with Jon and can remember sweating on "dead stick" being called with my electric foamie (prior A) and then all the way through (with electric) and beyond my B with possibly 2 actual semi dead sticks. It was not until a visit to Buckminister's intro pylon day where every landing all day was a dead stick that reminded to practice a bit more.

Its a product of the times we are in where controls are sophisticated enough to stabilise flight and most ARFT's have benign flight envelopes. This leaves a gap where pilots don't necessarily pick up the skills to cope with unusual (poorly trimmed) situations.

This is not meant to be a criticism of anyone, merely an personal observation from a new boy

Chris....off to the simulator and un-trim a foamie... for some much needed practice

[cymaz]

A club member, who has been tutoring me on basic aerobatics, reminds me regularly that trimming is never finished. I’ve taken notice to what he said over the years. We spent about a month changing various aspects of my plane and changing the controls mechanics long before doing any practice routines. Adjusting linkages, sealing gaps, moving control horn heights, rates , etc

Now, I’m not saying everyone must go and do F3a schedules, only that if you study this it will help. All models fly using the same principles of physics. So a well trimmed F3a model flies well.....a well trimmed winter hack will do the same.

[Martin Dance 1]

'Autotrimming sounds like a brilliant invention. So good, I think other manufacturers are bound to follow suit.'

Auto trim was available on the Ace R/C Micropro 8000 Tx in the 1980's! Based on an encoder first published in RCM (US mag) in the early '80's. I thought it was a clever idea back then and was surprised no mainstream manufacturer picked up on it.

I recently acquired a MP8K Tx, converted it to 2.4gHz and can confirm auto trim works.

[Trevor]

Autotrim is indeed a boon, especially for maiden flights. However, just as subtrim on transmitters led to increased ignorance on the need to set up the mechanical linkages properly, I fear that widely available autotrim will only add to the 'trim ignorance' problem we are discussing.

As for the idea of deliberately putting your model out of trim for practice, I find that test flying other people's is enough to keep my hand in!

[Cuban8]

I'm really surprised that so many of us don't make use of incidence meters to confirm the accuracy of a model before its maiden flight. Certainly, checking for squareness between wing/fuselage/tailplane is vital and can easily be assertained with a simple measuring tape - but what about the angular relationship between the wing/fuselage/tailplane i.e the angle presented to the airflow?

True, if you build accurately and the designer has got it right, then the model should, 'fly straight off the board'. How accurate is accurate? How accurate can you build anyway? Most importantly, how can you put your mind at rest and be happy that the model is not concealing a hidden fault despite passing an 'eyeball' test? Your wing isn't half washout and half wash-in?

For me the answer is to spend time checking rigging angles against the plan with an incidence meter. It only takes a slight discrepancy in the position of a wing dowel, or a few extra strokes of the sanding block on a wing seat to build in an unnoticable error of several degrees from ideal and give you a very busy work load on the trims. Perhaps even to the extent of not having enough adjustment available to get the model under control.

An incidence meter is easy to build from simple materials and coupled to an inexpensive digital inclinometer from Ebay is a powerful tool in your armoury. The one I made to supplement my Robart example cost under fifteen quid, and can be designed to fit almost any size of wing.

 

 

 

 

Edited By Cuban8 on 10/11/2018 10:01:19

[Peter Christy]

If you think an out-of-trim aeroplane is tricky, wait till you have to deal with an out-of-trim helicopter!!!

--

Pete

[Jon H]

Posted by Peter Christy on 10/11/2018 09:56:16:

If you think an out-of-trim aeroplane is tricky, wait till you have to deal with an out-of-trim helicopter!!!

--

Pete

aint that the truth!

To all the comments suggesting that more attention needs to be paid to the setup of the model i again completely agree. In the case i mention the root cause was a small error in the setup meaning the elevator wasnt totally level. This was then compounded by other factors like the excessive rates from the instructions.

Even with those sorts of things ruled out and the model set up correctly its not a guarantee everything will be fine. My Sea Fury is a prime example as it was very out of trim due to an incidence error in the design of the model. This has been well documented on RCU as everyone that owns one needs stacks of down trim to keep it on an even keel. Once trimmed like that its perfect, but the model is wrong.

This brings me back to should we practice flying out of trim? Personally i dont practice as such, but as most of my models are a mix of scale biplanes and WWII fighters its virtually impossible to trim them as the requirements change so much with air speed so i get my practice every flight i make. My P39 suffers trim changes in pitch and yaw as airspeed changes with left rudder needed at slow speed and right rudder at high speed, exactly like the full size. Add a bit of gyro effect from the long nose/heavy spinner, large roll/yaw and yaw/roll interactions and its quite an enjoyable challenge

[cymaz]

Posted by Jon - Laser Engines on 10/11/2018 10:46:28:

Posted by Peter Christy on 10/11/2018 09:56:16:

If you think an out-of-trim aeroplane is tricky, wait till you have to deal with an out-of-trim helicopter!!!

--

Pete

aint that the truth!

This brings me back to should we practice flying out of trim? Personally i dont practice as such, but as most of my models are a mix of scale biplanes and WWII fighters its virtually impossible to trim them as the requirements change so much with air speed so i get my practice every flight i make. My P39 Add a bit of gyro effect from the long nose/heavy spinner, large roll/yaw and yaw/roll interactions and its quite an enjoyable challenge

Good thoughts Jon...what some might say an enjoyable challenge others may liken it to wrestling a tiger by the tail.

[Trevor]

Of course the a lot of this trimming hassle would go away if we just took the springs off the sticks