Help with Tigermoth C of G

[michael brigg]

hi I'm going to try and fly my first bi plane 36 inch tiger moth given to me ( with no history) I'm struggling to find the correct C OF G , I've flown lots of planes previous with no problems ,I've tried to work it out but its to confusing  can anybody help me i definitely don't want to take off tail heavy 

e took a picture of where I think it should be sorry its upside down

[RottenRow]

That is the OK Models Tiger Moth. They were available with either red or yellow fuselages, and silver wings. I have the red version. Probably 15 years old.

 

The C of G balance point should be at the point where the rear cabane struts meet the upper wing. Ie the rear of where the fuel tank should be (which they never added to this model for some reason..). Balance it ready to fly (with the battery in position), slightly nose down.

 

I think I have the printed instruction leaflet for this somewhere, if I can locate it I can scan it for you.

 

They fly quite well (not in the current winds though) but need rudder for turning, so don't rely just on the ailerons. I use a 3s 1800mAh LiPo in mine.

 

Brian.

[michael brigg]

hi thanks Brian I'm waiting for a calm day before flying, i never thought about rudder do you think it would it be a good idea to maybe mix rudder and ailerons a little before maiden flight ?

[Guest]

Spot on Brian

[Jon H]

8 hours ago, michael brigg said:

hi thanks Brian I'm waiting for a calm day before flying, i never thought about rudder do you think it would it be a good idea to maybe mix rudder and ailerons a little before maiden flight ?

 

No do it by hand. You have two sticks and two hands, and if you need to program a mix program the computer in your head and not the one in the radio. I say this as you will need to use rudder and aileron in opposition at times to keep the thing on an even keel and the radio will not allow this. Rudder coordination is a useful skill will be especially handy in any sort of a cross wind with any model. 

 

The rudder is sadly neglected by most model flyers and its something that always baffles me as i use my rudder almost as much as my ailerons and elevator. 

 

When it comes to c/g i was going to post something to the effect of 'balance it slightly nose down as the back edge of the top wing centre section' as that would be close enough. I then smirked to see the post above with the c/g in more or less that exact location. 

[RottenRow]

Hi Michael,

 

You could use an aileron to rudder mix, but you won’t really know how much to mix. Also, with models such as the Tiger Moth, the amount of mix required varies with both airspeed and direction of turn. It also varies during the turn, requiring a lot of rudder to start the turn but then a reduction once actually in the turn.

 

If I were you I would fly it without mix and operate both ailerons and rudder ‘manually’. You will soon see what is required to give nice smooth (co-ordinated) turns without the nose either pointing up or down.

 

As this model has two aileron servos, if you can, put them on separate channels (ie don’t use a Y-lead) and set them up for aileron differential. That is with the up-going aileron moving more than the down-going one. For a Tiger Moth, at least twice as much ‘up’ as ‘down’. This helps with the turns; the full-size TM has this.

 

Jon just beat me to this with his reply.

 

Brian.

[Geoff S]

The CoG of a Tiggie is just above the front of the front cackpit (where the compass would be on a scale/full-size).  If you have aileron differential (twice as much 'up' as 'down') then it'll fly one-handed (at least my 58" ws DB Tiggie does) but a little rudder makes the turns better.  I usually start off with a switchable rudder/elevator mix but I find I prefer to rely on applying rudder by hand and never use the mix.

[Martin Harris - Moderator]

I’m another advocate of learning to use your left thumb (mode 2) but I will admit to using mixes on gliders as they are often in an awkward position to monitor coordination due to height and view angle. 
 

The need for rudder in a coordinated turn manifests itself as the tail dropping - use sufficient rudder in the direction of the turn to bring the tail up to the level (or climb/descent) attitude.  

[michael brigg]

4 hours ago, Jon - Laser Engines said:

 

No do it by hand. You have two sticks and two hands, and if you need to program a mix program the computer in your head and not the one in the radio. I say this as you will need to use rudder and aileron in opposition at times to keep the thing on an even keel and the radio will not allow this. Rudder coordination is a useful skill will be especially handy in any sort of a cross wind with any model. 

 

The rudder is sadly neglected by most model flyers and its something that always baffles me as i use my rudder almost as much as my ailerons and elevator. 

 

When it comes to c/g i was going to post something to the effect of 'balance it slightly nose down as the back edge of the top wing centre section' as that would be close enough. I then smirked to see the post above with the c/g in more or less that exact location. 

thanks again yes your right, i don't use the rudder enough I've had many a take off with my planes violently swinging from left to right because there's not enough air over the wings, going to practice more with rudder before maiden flight 

[michael brigg]

3 hours ago, Geoff S said:

The CoG of a Tiggie is just above the front of the front cackpit (where the compass would be on a scale/full-size).  If you have aileron differential (twice as much 'up' as 'down') then it'll fly one-handed (at least my 58" ws DB Tiggie does) but a little rudder makes the turns better.  I usually start off with a switchable rudder/elevator mix but I find I prefer to rely on applying rudder by hand and never use the mix.

 

31 minutes ago, michael brigg said:

thanks again yes your right, i don't use the rudder enough I've had many a take off with my planes violently swinging from left to right because there's not enough air over the wings, going to practice more with rudder before maiden flight 

 

13 hours ago, RottenRow said:

That is the OK Models Tiger Moth. They were available with either red or yellow fuselages, and silver wings. I have the red version. Probably 15 years old.

 

The C of G balance point should be at the point where the rear cabane struts meet the upper wing. Ie the rear of where the fuel tank should be (which they never added to this model for some reason..). Balance it ready to fly (with the battery in position), slightly nose down.

 

I think I have the printed instruction leaflet for this somewhere, if I can locate it I can scan it for you.

 

They fly quite well (not in the current winds though) but need rudder for turning, so don't rely just on the ailerons. I use a 3s 1800mAh LiPo in mine.

 

Brian.

thanks Brian battery needs to be in this position for balance to be correct , i think a little cutting maybe required as i don't want to add weight

[RottenRow]

Really? Mine balances with the battery in its tray, well forward and half way into the cowl.

 

Check that no-one has previously added any nose weight inside the cowl.

 

Perhaps you have a very heavy motor?

 

Brian.

[michael brigg]

yours looks identical , no nose weights the motor is 7.2 volt and has a reduction gear box , maybe that's the extra weight ? . I've also got a 3s battery on this now I'm not sure if that's no good for the 7.2 v motor it works but how long for 

[michael brigg]

just ordered a 2s pack just incase i burn out the motor i don't mind cutting a hole under the servos if that's what it takes my balance point is correct as per your instructions and picture thanks Brian

[RottenRow]

Ah that will explain things then. Mine has a small brushless motor and no gearbox, so much lighter. It is a type called a bell motor (because the rotating part looks a bit like a bell).

 

Your motor is a brushed motor (probably a 400 or 480) and was really intended for use with the old NiCd battery packs, in this case a 6 cell pack I would think. The speed controller is marked 6-10 NC (meaning it’s suitable for use with 6 to 10 NiCd cells, ie upto 12V).

 

Running that motor on a 3s LiPo might well damage it, it will draw more current than it is designed for which will reduce the brush and commutator life and possibly overheat the windings.

 

A problem with using that ESC with a LiPo battery is that it won’t have the correct low battery cut off setting, which means you could over discharge the battery which will permanently damage it. So you will need to make sure that you land in plenty of time. I couldn’t locate a copy of the ESC manual on the internet, so couldn’t find out any more about it.

 

Brian.

[RottenRow]

Hi Michael,

 

Our last postings crossed…

 

Yes a 2s battery will be kinder for the motor. Still be aware of not letting the battery discharge too much though. Definitely not below 6V, preferably higher.

 

If you like the way the model flies you might like to think about upgrading it to a brushless motor and matching ESC.

 

Brian.

[michael brigg]

thanks everything you said is correct, all my planes are fitted with low battery voltage alarms  so over discharge is normally not a problem , i think the esc is obsolete but it works fine so I'm not changing it ,thank you again for your really useful information, l might need you again ive got over 20 planes to maiden flight this year weather permitting

[michael brigg]

I've got lots of esc's and motors yes i will change them if i like how it fly's thanks 

[RottenRow]

Michael,

 

As mentioned previously, I have the instruction manual for this model. I have scanned the first and last pages, I didn't bother with the rest as they are concerned with the assembly of the model and yours is already assembled.

 

You will notice that this model was originally designed (in 2002) for an IC engine in the range .10 to .25. No mention of electric back then!

 

The back page shows the C og G which is in the position that was previously discussed. Also provided are initial control surface travels, which might be useful.

 

OK Tiger Moth.pdf

 

Brian.