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Low Wing Balancing CG


Tom Doyle
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I visited one of our local model shops, Steve Webb Models, yesterday with a friend who was buying his first low wing trainer, a World Models Super Sport 40, when the subject of balancing (CG) cropped up. I happened to mention that when balancing low wing models I invert them on my balancing jig because they are less sensitive due to the pendulum effect. I have done this for many years having first read about the method, presumably in RCM&E. The shop assistant immediately criticised my method of balancing and insisted that all low wing models, and especially the Super Sport 40, be balanced the right way up. In fact, he said that if the SS40 is balanced inverted, it will require lead in the nose whereas balancing it the right way up requires no lead! So, what’s going on here and which is the correct way to balance low wing models? Tom D.

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Well I'm totally with you on this Tom.  In most cases, it's just about impossible to balance a low-wing model right way up, as the mass of the cockpit and fuselage makes the centre of gravity (which in reality is in 3 dimensions of course) higher than the point of balancing and thus it is unstable.  I can't quite envisage how a CG can be substantially different when the model is balanced right way up as opposed to balancing it upside down!
 
Cheers,
 
Tim.
 
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HI Tom,

Thanks for brining my attention to this.

Thanks for your invitation to comment, although perhaps you could point me to where you sent or posted your request on RCMF as I am unable to find it?

A high wing model is easier to balance the right way up because of it’s mass and a low winger can be easier to balance upside down again due to the cockpit, fuselage etc being on top when the correct way up ( i.e. wheels down).

In fact there is no right or wrong way to balance a model providing it is balanced correctly on the C of G.

Providing the model is level or slightly nose down on an ‘empty tank’ has always been my preference for beginners.

 I must admit I have always balanced all my models the right way up and never really had a problem with C of G on many, many models. I also balance my models laterally.

I usually balance models various ways, on fingers, dowls, books, C of G machines, it depends where I am at the time and what’s available!

There’s several shop assistants at SWM and they range from a 17 year old with limited experience to the shop manger with over 20 years experience  and usually Fred ‘ribstock’ Webb (age 79) is ‘at hand’ and modeller since the age of  6 years of age.

Dave is a also a noted flyer and accomplished modeller, who was Paul Heckles ‘tweaked and trained’ in aerobatics and set ups. There are usually a number of customers and helpers around that also offer advice.

I happen to know that your friend and yourself have spoke to old Fred for over an hour regard a crashed Super Sport 40 or was it two Super Sport 40’s that had crashed?

I doubt Fred would give ‘duff’ information as he tends to have more aero modelling knowledge in his little finger than most of us! I’m sure he will have given you good advice.

I understand the a model was described as being ‘elevator’ twitchy (a Super Sport 40) and crashed because of this and that a member of SWM staff suggested it may have a rearward C of G as that is what the models compliant sounded ‘like’.

As this model had already been balanced upside down? By your friend - I have no explanation as to why it would have a read ward C of G and crash in the manner described. That is if it did have a rearward C of G and it wasn’t just stick trouble. I was not there to see this model fly and it’s almost impossible to comment without further information as to the total set up.

It should be noted that my staff did not balance the model being asked about.

Certainly the staff you spoke to - like me has always balanced models the right way up and again had no problem with any of his models, nor has in gone through ‘loads of models’ as suggested. In fact he is the only beginner I have trained that took off and landed on his first day flying with a 58 span trainer. I my opinion he is a very good flyer.

He is probably taking my lead regard C of G, while I admit it is easier to balance a low wing inverted and indeed is the preference of many modellers including David Boddington who is a very experienced modeller as I’m sure we’d all agree!
 

In this case the model

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continued...
 
In this case the model had already been balanced by the customer and had crashed? I’m not totally sure of the details as I was not there and I did not witness the conversations.
I haven’t spoke to Fred ‘Ribstock’ Webb yet, but I’ll ask what was said when I see him.
You may have seen his 40 year old plus 4 engine Viscount in the mag’s recently. Amazing after all these years it gets ‘mag’ interest!
I think in this case something might have been lost in the communication as the assistant was referring to a modeller that balanced a Super Sport 40 upside down and did it incorrectly as it needed more lead that he used. I am fairly sure the assistant was only advising that he balances his the right way up and has not had a problem. I have to say – neither have I in 35 years including my first low wing model that I designed my self when I was 13 years old I say this while acknowledging that inverted low wing balancing is the preferred method of many and is easier.
Am I right in understanding this model had been balanced upside down and yet showed tendencies of a rearward C of G? In which case? Had it been balanced correctly is the question to be asked, which the sales assistant did ask and tried to discover in discussion with your friend – advising that he balanced the right way up and I spoke to him this morning and he’s confident that if he had set up the model and flown it would still be a ‘complete model’.
In my experience knowing his models and his flying, I’m sure he is correct. I think this was the point he was making, perhaps not as direct as I have just made it.
I trust this advises my opnion, I consider the matter closed unless there is any new input.
The offer of checking his model still stands as it does for anyone buying a model at our shop.
While the problems described could easily be a C of G problems they could also be one of hundred other things. Without checking a model impossible to say what the problem was.
Models I have found twitchy test flying for or saving a model mid flight for others.
1. C of G rearward
2. Incorrect incidences
3. Tail Plane loose
4. Not enough bands on the wings
5. Radio Interference
6. Dodgy batteries
7. Loose engine
8. Incorrect thrust line
9. Parts falling of various
10. Loose covering
11. Loose servo tray
12. Snakes not secure
13. Arial loose in Tx
14. Modeller flying the wrong model
15. Loose tailplane
16. Too much control movement
17. Loose sticks on TX
18. Out of balance prop
19. Leaking fuel tank
20. and lastly inability to fly or inexperience.
Just 20 reasons…and there’s more!
Phew that was longer than intended.
Please point out where you have posted on RCMF, so I can see that post. I am unable to find it.
Thanks for bringing this too my attention (by email – Ann – phoned me today)
As Fred ‘ribstock’ web will have mentioned, I’m at home with health problems for some years now, but the shop is going ‘great guns’ as usual – I am proud and ‘grateful’ to have such good staff.

Best Regards
 
Steve Webb
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P.s, sorry I wrote that on my lap top and then pasted it. I hope it pasted o.k....didnt realise I'd done a book...sorry..
 
I also meant to say it was terrible news regard Mike Bradley's death, I will miss Mike, he was one of my favourite chaps. I know I should have favourites , but he was a kindred spirit aware of the trials of the self employed
 
One o the nicest chaps in modelling. A club modeller, but one who did enjoy the hobby.
 
Thanks for telling Ribstock Webb, who told me. We sent modelling mags, and things when we heard Mike was getting worse. I understand although he couldnt thank us himself as he was too poorly, he passed his thanks on through your friend or a member of the club. It was great to hear from him.
 
Regards
 
 
Steve

Edited By Steven Webb on 28/03/2009 12:50:58

Edited By Steven Webb on 28/03/2009 13:02:45

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Hi Eric, I know who you are now. The motorbike .... ah ah...
 
I saw the post and then spent a while writing an 'article' on my lap top. I wasnt near the internet. I didnt realise how much I'd written. I hope it didnt sound like I was getting at anyone. I just let it flow....
 
I suppose I could have answered with, either way is o.k as long as the model is balanced, but upside down is easier on a low wing.
 
Funny enough I was talking to Dave BODDO Boddington of Mills replica and god like aeromodelling status yesterday and he said he's a upside down balancer.
 
I then realised I always did my low wings  the right way up( wheels down I mean), but....I always turned the model upside down to dot he lateral balance...just my method I guess.
 
Thanks Eric
 
I'll pass on regards to 'Ribstock'
 
Steve
 
 
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Hey Eric, see you soon.
 
Uou dont happen to know how I put an avitatar up on my posts. I notice you have a little pic and so do others, but how?
 
See Ya
 
Steve
 
Ps 'ps, you listed - loose tailplane twice, items 3 and 15.'
 
Yeah It happens a lot I guess...

Edited By Steven Webb (Steve Webb Models) on 31/03/2009 08:58:06

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Steven - go into your profile page and click the black and white silhouette that appears by your name. Then upload a suitable small JPEG image from your PC and once David or I approves it, BINGO!

Edited By Timbo - Moderator on 31/03/2009 10:12:57

Edited By Timbo - Moderator on 31/03/2009 10:13:27

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Phew! Having had time to reflect on Steve’s reply for a few days and, as Steve has since pointed out, spoken to lace>Adrianlace> at SWM, I’d like to make a few final comments.

> >

First let me stress that it was never my intention to call into question advice given by members of staff at SWM. On the contrary, I have the highest regard for SWM’s reputation and the superb service they provide to the modelling fraternity.

> >

The original purpose of my post was to seek reassurance that my way of balancing a low wing model i.e. inverted, is a technically acceptable method. I think we now all agree that either way, right way up or inverted works. Being an engineer, my preference is always to use a jig where one is available. Anyone who has used the Multiplex balancing jig will know that it is over sensitive if a low wing model is placed on it right way up. Enough said.

> >

Turning now to Steve’s initial reply, I feel I must clarify one or two points.

> >

Last Friday I visited SWM with a friend Geoff, to buy another Super Sport 40.  Geoff is relatively new to our hobby and about a week earlier, was going to move on to his first low winger, an SS40. I helped build the model with him and then, that nightmare scenario of all nightmare scenarios, I crashed it on its maiden flight! I know those of you who have been in the hobby a long time have probably been there too, but it doesn’t make my pain and guilt any easier to bear.

> >

I would like to make clear that in my opinion there was nothing wrong with the model. As an engineer, I like to think that models I assemble/build are done to a high standard and the SS40 in question was set up exactly in accordance with the manufacturer’s recommendations. All the throws were as specified and the CG was spot on. That leaves two possibilities for the probable cause of its demise. One, pilot error and I’m the first to accept that it was my fault or two, something else.

> >

When the model took off I was taken completely by surprise by its uncharacteristic behaviour. Within in feet of leaving the strip, I new I had a problem on my hands. Contrary to what Steve said, it wasn’t elevator twitchy but it was excessively sensitive on aileron and rolled inverted at the slightest stick input; it was as though it had positive expo. Needless to say the flight was very short.

> >

The model was controlled by a new 2.4 transmitter and receiver (no names this time) which was also being used for the first time. Strangely, when the transmitter was checked afterwards, various settings in the model memory had disappeared including -40% expo which I had previously set. Geoff contacted the lace>UKlace> distributor the following morning and the Tx was returned to them – apparently it should ha

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Don't know what happened to the rest of previous post but here is missing bit.
 

apparently it should have been returned some time ago under a recall notice. Geoff now has a new replacement Tx. The reason for the original recall probably had nothing to do the model crash, but it does leave a question mark, especially after reading the following post by Trevor Heley which is elsewhere in this forum. http://www.modelflying.co.uk/forums/postings.asp?th=14300 Some of the symptoms described by Trevor are ominously similar.

> >

The new SS40 will be ready shortly but initially it will be flown on 35meg before transferring it to the 2.4 equipment (good advice given by SMW). Also, another club member will give it its maiden flight - two successive crashes would leave me psychologically scarred for life.

> >

If anyone would like to know the outcome with the next SS40 flight, please let me know otherwise, I’ll consider this post closed.

> >

Tom D

> >

PS Message to Eric. I’m in Sandbach Ericand I see you’re a fellow biker. Have you been out this year yet? I’m afraid I’m a warm weather rider. Just spent today at Oulton Park waching a friend's son practice for this year's Superstock 600 racing, awesome riding!

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Thanks for the post Tom, all very interesting.

I wrote far too much in reply, I know, but its my name over the door and my address.

I know what goes in to keeping SWM the way it is and what has gone in to it.

Promise I will never leave such a big post again!

Forum comments sometimes really make me feel annoyed! I know I shouldnt be worried - half the time people dont mean what they say.

One RCMF recently there was a post asking if wed gone bust!

Our phone was off for 15 minutes. We had a Thunderstorm that made the phones go down and some idiot posted had we gone bust?

23 years with the phones working, 15 minute down.

I see similar comments posted about other businesses when web sites are down or an email isnt replied to. What people do not realise is that negative comments can do harm and damage to a business, the owner can take comments far more personally than intended, but then its our name and address over the door!

Some people reading comments like our staff need retraining, firstly must not know the shop, but secondly what if they are new and thought thats what SWM was like?

Anyway, please post back how you get on, your dealing with a well proven model that has sold in its 100s around the world, Im sorry to hear youve had problems with it. Thats very unusual, a bit like saying people have problems with Wot 4s.

LOL

Take Care, and your welcome at SWM anytime, as is anyone else!

Steve

Edited By Steven Webb (Steve Webb Models) on 01/04/2009 15:30:39

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