Gyro in a twin?

[Martin Harris - Moderator]

Chessiegolf,

 

From your mail you seem to have some twin experience and I must admit that the majority of mine has been on a model that laughed in the face of asymmetry!  In fact, on its maiden flight (and my first twin experience) it lost an engine while I was trimming it and once I'd worked out that the non-revolving prop was the reason for its odd flying characteristics, found it easy enough to land for a relight.

 

Have you actually tried a gyro in roll on a twin?  I'd be interested to know if it behaved as you have outlined - certainly, my gut feeling is against it in principle but if it has been proved to work well (particularky in an engine out at rotation scenario) then I'd be delighted to be educated.

 

I do recall watching an electric Hornet suffering an electric motor failure during a high speed pass, but my impression was that although it rolled it was a flick roll - which might not have responded to aileron depending on the model.  On a couple of occasions, I've experienced inadvertent flick rolls on small combat models (no rudders) due to streamer cuts on wingtips which wouldn't respond to opposite aileron at all.

[John Rickett 102]

Martin,

I have now built three twins and four multis, one of the twins and one of the multis had a gyro on the rudder and I don't think I could discern any difference between those and the non gyro equipped models when an engine died - they would all roll, the rate seemingly proportional to the amount of throttle opening. The recovery method has always been to bring the power right back until alierons could hold off the roll, re-trim the rudder and then land as soon as possible. I have not flown a model with a gyro on ailerons but the one I'm building now will have that set-up so it will be interesting to see how it fares

Hopefully I will be able to report that it works fine - but then I don't intend to suffer any more engine failures!   

[Martin Harris - Moderator]

Chessiegolf,

 

That's certainly established your credentials!

 

I'll be very interested in your findings.  Of course, all models behave differently but whatever yours does will act as an indication - what is it youre building?

 

Have you done any experiments with thrust lines adjusted to provide some help?

 

Modern full size practice is to hold a little bank into the live engine and apparently they don't teach you not to turn into the dead engine any more - but I suppose modern designs have had a lot of development into better engine out characteristics.

[Mason Fenlon]

Well, she is up and flying (we have had 3 successful flights - and Marcus thinks she handles beautifully).  We are still going through the trmming process to make sure everyting is squared away and reliable, but it is interesting to note (cos I asked him to check) she has fantastic rudder authority (being a twin tail) and that may (hopefully not) come in handy...

 

From an 'audio' perspective, it sounds as though the engines are at 'odds' with each other.  Is this a common thing for IC twins - does anyone have any experience of such things?  I am thinking harmonics etc (from a purely audio perspective) - cos she screams along in a lovely straight line!

Edited By Mason Fenlon on 31/05/2009 23:10:42

[Martin Harris - Moderator]

Sounds like what you're hearing is the beat (a "wahwahwah" sound) when the two engines are almost, but not quite, synchronised. When absolutely synchronised there is no beat.  If you visualise 2 sine waves slightly out of phase superimposed on each other, the curves will coincide every so often and drift apart and back together in between.

 

I know that some people spend an awful lot of time getting the revs the same on twins using rev counters and think that the real sign of them being synched is getting the beat sound and struggle to achieve both!

 

In my opinion it's far more important to have each engine running reliably and the technique I use is to tune each engine individually to normal peak revs (on the rich side, nose up) and assuming they are within a hundred rpm or so, richen the higher revving engine slightly until the beat disappears. If the engines are very imbalanced, throttle back the faster one on the ATV or linkage but ask yourself why there's so much difference before committing to flight. Once happy with the engines I would normally only fine tune by ear.

Edited By Martin Harris on 31/05/2009 23:54:30

[Mason Fenlon]

Martin

 

Thanks for that.  We will fly her a few more times and then see how everything beds in (although the engines are not brand new) then we shall see under what conditions the beat/harmonic is occurring and adjust as necessary.

[lipofirefighter]

Glad to here your scorpion flys well

I have after 11 years just got my scorpion on to the c of g balance and find that even with  the battery well forward and 2 os 25s i still need a 10oz weight in the nose and wondered if you had expirenced the same problem

[Mason Fenlon]

Lipofirefighter

 

We put the Scorpion on the C-of-G machine before it ever got to its first flight and, yes, it was significantly tail heavy.  There is a lot of wood aft of the balance point and even with a pair of OS 35s I had to install a significant amount of weight in the nose (and the structure up their is not really geared for it - just a cowling).  Unfortunately I forget just how much it weighed - I shall find out.

 

Having had two weeks at home recently (and covered Marcus's B-17 which should be ready for its maiden at the end of this month) I decided to have a look at the Scorpion set-up again.  I have opted to use a different set of engine mounts and this will move the engines forward by about 2cm.  Hopefully this amont of mass moved forward (all already ahead of the c-of-g) will reduce the nose weight (which is all dead weight!).

 

Haven't finished it yet because it needs new throttle linkages making; will let you know in due course.

[lipofirefighter]

Many thanks for your conformation, add the weight and she will be ready for a test fly

My next twin project is to finish cambria sky van which I have had for in excess of 20 years I hope too put 2 rcv 60s in it.

Many thanks again 

Edited By lipofirefighter on 03/05/2010 10:59:11

[lipofirefighter]

dont no what happened there it should read cambria sky van

[A.A. Barry]

GUys, can you couple it to the engines and then when one dies the other will cut out as well?????

A.A.Barry

[A.A. Barry]

OK, all you gyro nuts what is this one good for??????????? G410t "Piezo Gyro", got it Ebay 3yrs ago, never used it

 A.A.Barry

[Peter 'Ivanna Crashalot' Savage]

that'll be for a helicopter

[Biggles' Elder Brother - Moderator]

Hi Peter,

 

seem to have missed you for a while. Have we just been following different threads or have you been off doing other things?

 

BEB 

[Peter 'Ivanna Crashalot' Savage]

erm, well i've been camping for the weekend