Gyro in a twin?

[Marcus]

My Dad and I have have built a Galaxy Models Twin Scorpion, and I was wondering if it needs a gyro in it. Any thoughts? And if so, what gyro should we use?

[Tim Mackey]

The use of Gyros in model fixed wing aircraft is both rare, and pretty much useless.

A twin is NOT a good model if you  / Dad are inexperienced.

[Simon Chaddock]

The question I ask is what were you expecting the gyro to do for you? Most (if not all) RC model aircraft are aerodynamically stable in normal flight so you don't need (or want) any artificial stability.

Following on from Timbo's comment I note that Galaxy themselves say the standard Scorpion is a good introduction to low wing flying (not a novice's model) and the twin version is another level beyond that.

 

[David Ashby - Moderator]

I've seen them fly and they fly well Marcus (without gyro) but make sure your engines are reliable

[David Perry]

Simon C,

the use of a gyro in a twin is to cater for the engine-out "plane yaws, rolls and crashes" scenario.

 

They are used, and to good effect, but its rare.  Most sports twins (as distinct from true scale heavies) are stable even OEI, so the gyro is not needed.

HOWEVER, if Sir wants a gyro, Sir can have a gyro.  A cheap helicopter gyro in the rudder channel is the way to go. 

 

The best option though is reliable engines in a good design.  I cant remember my last engine flame out. A far cry from twenty years ago!

 

D

[Mason Fenlon]

  As father of the aforementioned Marcus, it was me that asked him to put the question on this forum because I have previously appreciated the advice that has been on offer and I couldn't see a logical answer as to why or why not have a gyro on a twin.  I note Timbo's points - but when do you cease to be inexperienced?  The Twin Scorpion is the 4th Model that we have built from kit form and is the 9th aircraft in our current 'Hangar' (not counting the 2 strange creatures that I have built from scratch).  Marcus is a very competent flyer (in my view - and I do it for real) and has been the test pilot on the maiden flights of 7 of the 9 aircraft we possess and even test pilot on the 2 machines that I designed- a twin electric and an IC  pusher delta .  The Scorpion is a stepping stone - my ultimate ambition is to build a Brian Taylor Mosquito (for me) and we needed something inexpensive on which to train on the art of setting up and flying twins (and including engines and the kit it is <£100 and a worthwhile risk-reduction exercise).

 As for the nub of the question - my thought was simply that of would a gyro be of benefit to feed in corrective yaw input in the event of a single engine failure?  In this case, would I be making what is a difficult in the real world, let alone on models, somewhat easy to handle (they do it with flight stability on fast jets).  Ultimately, David's point is most telling -- the key must be to avoid being on a single engine approach!  In this case, I have selected a pair of OS Engines as, in my limited experience to date, they are reliable.  I am looking at getting a tachometer to try and match them in the set up phase and wish to learn from this exercise.

 I have the luxury of being able to indulge in a hobby (with my son) that I could never do as a kid, and I am relishing the challenges.  I fly like a dolt; Marcus does extremely well and even if we have the odd prang (we've only killed one Depron model in nearly 200 flights) I enjoy the re-build (which is why I start with kits - easy to rebuild what you understand and built in the first place!)  I shall keep encouraging him to take the steps forward that will enable him to enjoy this hobby to its full limits.

[David Ashby - Moderator]

OS engines are excellent Mason and the Scorpion I saw wasn't too bad with a dead engine as (from memory) they're both pretty close to the fus'. I guess i.c. twins are pretty rare but if you fancy an i.c. Mosquito then the Scorpion will make a good machine on which to practice. 

 

Let us know how it goes Good luck. 

[David Perry]

And whilst the Scorpion might be totally benign on one, the Mozzie almost certainly wont be -  because that wing plan and the engine spacing will make it a doddle to "tip stall" (almost always a result of yaw or side slip being present at the point of stall). The addition of a gyro wont stop the tip stalling, but it might well buy you some time just after the one engine has failed at high power settings, or if you dont notice it has failed and then whack the throttle open.

 

Note to Marcus' dad: this hobby is about doing things YOUR way. If you want to see what a gyro does for you, buy one and fit it. Good gyros these days can be switched on and off from the tranny anyway. As they say at the Nike factory...just do it!

 

As Capt Ashby says, good luck and let us know.

D

 

d

[flytilbroke]

Hi Marcus and Mason, Welcome aboard.

 This does sound like you are having fun. Pease keep us up to date with your experience of twin flight. I would certainly be interested in reading your opinion of a Gyro, given that you decide to use one of course.

 

Have Fun.

[Frank Skilbeck]

Just make sure you don't get a heading hold gyro, as when you turn on ailerons it will apply opposite rudder.

 

I

[Darren Jelley]

Hi Marcus and Mason

Try the GWS pg-03 gyro. It is designed for aircraft and can be used on the rudder or ailerons.  I have used one very successfully on the galaxy mosquito fitted with 2 x sc15 and would have lost the plane a couple of times with flame out at low speed/high throttle if it wasn't there.  Turn it up to abt 75% to start then as you get more confident you can back it off gradually.  The Main thing with flying the twin is learn to use the rudder (if you don't already)

 

Good luck with it

 

Darren

[Martin Harris - Moderator]

It's also good practice to avoid turning into a dead engine.  Although modern full size practice doesn't seem to give much account to this due to better rudder authority and airframe design, if you're flying near the stall (climbing to get some altitude for a circuit, for example) turning into the dead engine can result in a tip stall.

 

I remember watching a large WW2 model twin climbing out under good control at a show but it rolled over and spun in after attempting a climbing turn to fly a circuit into the dead engine.

 

Normal practice in full size also includes, typically, a 5 degree bank towards the live engine which gives an appreciable decrease in the minimum control airspeed - but I doubt that many of us would be able to maintain a small bank angle like that from the ground.

 

The track record of IC model Mosquitoes isn't too good so why not give yourself a little help with a gyro on rudder.  It may also help to add a little left thrust on the left engine to reduce asymmetry in the event of a starboard engine failure.  The Mossie doesn't have its fin in the direct propwash so needs all the help it can get on one engine with its highly tapered wings.

 

If you've any doubt it's probably best to cut the throttle and treat it as a complete deadstick - there's an old saying that the purpose of the remaining engine is to fly the aircraft to the site of the crash!

 

 

[Mason Fenlon]

Thanks for the tips and direction.  The Mossie is a long way off yet - the plans have arrived (Christmas present from Marcus to Me) but we will not start to build until we have completed the B-17 that Marcus has on the go (so probably not before Winter 09/10).  Hence the desire to get some practice in on the Scorpion Twin (which will be running two OS35s).

 

We have still to get the Galaxy Scorpion airborne - waiting for a suitably calm day in Yorkshire before we wend it skywards.   We will keep you informed.

[Darren Jelley]

 

I don't know what radio setup you are using but a simple way to set up the throttles is to make sure everything is balanced i.e. equal length throws etc. Engines tuned. Then (because I just use a standard 7 ch set ) I use a "V-tail mixer". Throttle channel to elevators and ch 6 to ailerons. one output to each throttle servo. This means both throttles operate together on throttle stick, and ch6 can be used to fine tune or (if you want to) bring one engine down to practice flame outs in a controlled manner.  If you use a computerised set this can be done in the tx program.

 

Good luck with the maiden.  Once you hear those two engines in sync you will be hooked!

 

Darren 

[Mason Fenlon]

At the moment. the Scorpion is on a Futaba FF9 and so I guess I could slave channel 7/8/9 to the throttle and achieve the same effect - I must admit that they are currently mechanically trimmed to match (but that doesn't necessarily eliminate any differences in Servo performance) and are on a y-lead (primarily because I'm using a 7-channel receiver and I've hooked up Ch 7 to the Nose wheel steering; however, I have a 'gash' model that I designed that has an 8-channel Rx so this could easily be overcome).  I am hoping to get the engines up and runing again (its been a while) this weekend and then use a tacho to measure their relative performance across the power band.  Ultimately, although it sounds strange to deliberately go assymmetric, there is merit in being able to practice SE flight in a 'controlled' manner (and at a time of one's own choosing).  First, of course, we (well mostly Marcus!) need to log a few hours to get happy with the model.

 

Thanks for the tip.

 

PS The mossie will (eventually) be on 2.4GHz and on a Spektrum DX7.

[Peter 'Ivanna Crashalot' Savage]

I would have thought if one engine cuts the smart thing to do would be to cut the other engine then glide it into a safe area, it would be; almost definately smashing the model by leaving the engine running or cutting the engine and hoping it glides well with the possibility of minimal damage.

I would think this made more sense and i would not think that a rudder would have enough deflection to counteract an engine failure, but if the engines are reliable enough it will probably barely ever happen

[Martin Harris - Moderator]

It very much depends on the model.  A heavy Mossie would be a handful with an engine out and a deadstick might well be appropriate but if faced with a risky situation, e.g. over trees, poor landing surface etc. with careful handling it might be more appropriate to get to a safer position on one engine. If you know your model and it has a reasonable layout it shouldn't be a case of almost definitely smashing it as long as you appreciate the need to maintain a good airspeed. However, if in doubt, your advice is very valid.

 

The other end of the scale is something like the Extra Slim Twin in my avatar - 999 times out of a thousand it will perform brilliantly on one engine - the slab sided fuselages and fins in the slipstream mean it can continue to perform on one engine with a virtually full repertoire of manouevres.

 

What about the 1 in a thousand?  Try losing the inside engine in a flat spin at 30 feet!

[Peter 'Ivanna Crashalot' Savage]

There is one solution... go to electric!!!

[Martin Harris - Moderator]

Great idea - but I do recall watching an electric Hornet spin in when a motor seized, so you'd still need to be aware of the possibility of a failure.  Recently, I saw an electric prop shed a blade for no apparent reason.  As most electrics these days are brushless, you could get an ESC fault, a LVC cut-off (especially on a twin battery set-up, a prop being shed, a wiring fault etc. etc. so you still need to bear a motor failure in mind.

[Peter 'Ivanna Crashalot' Savage]

although the chances of an engine stalling is still a lot higher than anything going wrong with an electric motor

[Martin Harris - Moderator]

Agreed, but my point was that your "solution" is not a guarantee of drama-free flight - good airmanship is to anticipate the ever possible eventuality of an asymmetric power situation.

 

As my current build is an electric Mosquito I'm certainly not against the idea...

[John Rickett 102]

 If the purpose is to try to maintain straight and level flight, a gyro operating on ailerons will probably be more effective than on the rudder(s). My experience is that with one engine dying (on high power) the model will roll very quickly. A gyro may still not be the complete answer because if the rolling force is greater with one engine out than the ailerons can counteract, the model is going to roll anyway. The solution is to chop or at least reduce the power of the running engine(s) and try to maintain flying speed. This of course can be at odds with the instincts when trying to make it back to the patch!
The most problematical time is when at low speed and high power - takeoff or low circuits for instance, but at least you may be able to quickly recognise which engine has cut and take corrective actions. What seem to contribute to the desmise of a lot of twins and multis is being some distance away when the engine cuts and not being able to ascertain if the unexpected roll is to the left or right. Still the best course of action is to reduce the power, its better to descend into the groung upright and flat than in a spiral dive!

As regards engine settings - set-up each motor as if it were in a single engined model ie, make sure each engine is running happily just as you would with a single, it doesn't matter if there are a few hundred revs difference at full throttle, but a sudden difference of 7000 revs is another story! Do not be tempted to tune one engine to match the other, this action is bound to lead to one of them not running at optimum. A slight difference in revs may want to pull the aircraft off line during the start of the take off run but if the engines are opened slowly the effect will be minimal and once rudder authority is gained the power can be advanced to full and a straight takeoff achieved.

Twins and multis are great fun, you just need to be self disciplined in ensuring the engine, plumbing, fuel, plugs etc are spot on.

All of this gets away from the original question as to the effectiveness of a gyro in twins but perhaps shows that a gyro can't remedy another cause. A gyro will help to stabilise twitchiness about an axis but the heart of the problem is in making sure the engines are preforming satisfactorily in the first place.

Hope this helps                

[Martin Harris - Moderator]

Good post which gives a lot of very important advice.  The one thing I'm not sure about, though, is using the gyro to pick up a wing.

 

I think that the typical crash scenario is that an engine dies, a yaw is induced giving some roll couple.  The ailerons are used to counteract this and hopefully the pilot is capable of inputting some rudder, but more often than not the ailerons are overused.  A climb to safety height is commenced, airspeed drops off and an incipient stall is exacerbated by the wash in effect of the aileron, leading to a wing drop.  Instinct (or learned response) kicks in and more aileron is input to raise the dropping wing, while the rudder input is forgotten and the model spins.

 

Wouldn't the gyro simply attempt the same thing?

[Peter 'Ivanna Crashalot' Savage]

how about converting it to one massive engine! cure your problems straight away!

[John Rickett 102]

Martin,

There are two points here - the model being close to the stall at the point of engine failure and the model being well above the stall and suffering the same mishap. If near the stall then attempting to pick up with aileron may provoke the stall anyway, so you are correct that there may be nothing to gain. 

However lets hope that most people are not generally mushing along asking for trouble but rather an engine cuts and the model immediately rolls. In those first couple of seconds while you're trying to figure out what has happened, and more importantly which way its rolled, because it can often be confusing, stabilising the wings may save the day. Yes the model is going to slow down and it will yaw to some degree (depending upon fin/rudder authority, speed and asymetric thrust) which will only increase the speed decay, but in my experience the roll rate is more dramatic and disorientating than the yaw, so attempting to reduce that roll rate until the brain and fingers are working in harmony again could make the difference between getiing down in one piece and rekitting!