Tail fins Whats the point????

[joshua jones]

Since recently taking up Heli flying (well attempting it) i have been wondering what the purpose of tail fins are. As my best guess would be, Vertical to protect the tail blades smashing into the deck and the horizontal maybee to provide tail stability durring fast forward flight  or when in down wash durring the hover.

 

However at least one of my theories must be flawed as the carbon replacements availiable are full of "lightening holes" and especially in the Horizontal plane i can see no benifit in it been there at all.

 

If one of you would be so kind as to shed some light on this please.......

[Stefan Hafner]

I'm not a heli flyer but in terms if aerodynamics i think it is a way of adding damping as there will be a very limited force resisting motion on a Heli without fins. Adding fins will increse the drag and make the controlls less sensitive.  This would also explain the holes in the Carbon replacements as these, as i undestand it, are used mainly on 3D style machines.

[joshua jones]

Stefan,

 

Thanks for that its always obvious when its explained is it  i didn't consider that but it does make sense, ans so my idea of adding some holes there to try and combat the tail heavy condition of the stock Belt CP should really wait untill my piloting skills improve.

 

Josh

[Owen Hailey]

Hi Josh

I always take them of, as I do not see how thay can make any diffrence on normal flying, and I am a grate fan of Night flyer On youtube, and this man knows his suff as he is one of the main heli pioners of model heli desine, and has clearly had a lot to do with heli desine, and he always takes them of, and tells you lots of information about how to get the best out of your flying, both heli and plain's, so take a look at his vids and you wil be amazed at how much he will teach you.

Happy Hovering Owen.  

[wlfk]

On a full-size helicopter, the fins are a more efficient way of countering torque at high flight speeds than the tail rotor. They keep the helicopter flying efficiently, nose pointed forwards... Some helicopters and autogyros are known to be pitch-unstable when flying without damping, and I guess the horizontal stabiliser is likely to help on this score.

 

And as suggested, they also help keep the tailblades away from the ground when landing. I have flown without, and I think this feature is useful.

 

Most model helicopters fly better forwards than backwards, so I reckon the fins must be doing something significant. Having said that, most helicopters have the bulk of the canopy in front of the nose, so I reckon that if it wasn't for the tail rotor acting as a disc, they would actually have a natural inclination to fly backwards.

 

Really, it's a question of balance. Some Bell helicopters don't have enough tail authority to hover in gusty sidewinds, and this has led to accidents. You probably want the helicopter to be more stable flying forwards.  than backwards, but you don't want it so stable forwards, that you can't override this. How you find that balance will depend on the helicopter and in particular the canopy it uses.

 

I also suspect some of the value in going 'finless' is that much of the tail rotor's output is often blown against the side of the fins. Presumably a finless helicopter tail is likely to be more efficient when not in FFF - i.e. 3d. Look at eurocopter Fenestron designs for one way round this.

[Geoff Goodwin]

I believe Stefan has the nearest correct answer. They are generally there to provide stability in forward flight.

 

Since in 3D this is not desirable, sure take them off. I would be suprised if the heavily perforated ones you see do anything to aid stability. Tail fins are in fact a liability in rearward flight and another good reason for the 3D guys to take them off or put a load of holes in them!  The vertical fin often has a dual function in that it provides a skid to stop the tail rotor striking the ground.

 

Once you start taking the flight envelope to extremes, all manner of issues need to be considered to effect the desired level of stability or instability. So you start to get refinements you see on full size, especially those for use in combat where instability tends to equate to quicker response.

 

So back to Joshua's question, I think he already had a grasp of what they really do and wlfk is also right about achieving a balance in the performance that suits the purpose. Really in general terms no right or wrong to them, your choice in the end is to get the performance that suits your particular need.

 

Since 3D is not my cup of tea however impresssive it looks I will retain solid fins and enjoy more relaxed helicopter flying complete with Gyro of course

[Former Member]

[This posting has been removed]

[Geoff Goodwin]

Eric
Interesting comment about them "more to give a visual clue".  I have never flown without them and wondered about that aspect. To be honest, I seriously doubt that is the main function and wondered how you came to form that view?

 

I have always found the visual aspect of Helicopters difficult to say the least. I can never recall any real help from trying to spot the fins when once in while I do something silly. My usual response to any orientation issues is to do something positive and watch carefully for the anticipated response. If it isn't what I expected then I do a very rapid re-evaluation of what the model's orientation is! - Actually not confined to Helis, but will openly admit to having occasional visual problems with a Heli where is is very rare with fixed wing.

 

I have been passed the "box" a number of time by fellows who have flown models (not helis) to a dot and have no clue how to get them back! - Not lost one yet, but one took nearly ten minutes to cruise back once, it was slow flying and downwind - Sorry I digress!

[winchweight]

Tail fin = keeps the aircraft straight in forward flight, helping to overcome the torque effect by offloading the tail rotor and therefore requiring less power.

 

Horizontal stab = keeps the airframe in a more level attitude in forward flight. Some fullsize (Bell 412) have a sprung stab which increases angle of attack with increased speed to pull the tail back down.

[Tim Mackey]

I know you edited that  word Shaun

[Geoff Goodwin]

Joshua,

 

"so my idea of adding some holes there to try and combat the tail heavy condition of the stock Belt CP should really wait untill my piloting skills improve."

 

I hope you have balanced your helicopter to get the CG in the right place. If its tail heavy before take off it will most likely try to hover that way too!

 

I have never tried a Belt CP so I don't know if the condition is common even when all balanced up, but that's what happens on every other helicopter I have flown. 

[Owen Hailey]

Hi all

I dont no whether its just me, but all my single rota heli's seam to have a slitly tail drop on the clime out, but the c of g is just fine, as when the power is backed of the heli then levels out and flys fine, and if you try to make the nose the slitest bit hever it is totaly imposible to get a good controled hover, so I tend to ignor the tail heavy look and all is well.

Happy hovering Owen.

[joshua jones]

Wow,

 

Ok thanks  guys that certainly give me somethings to think over, and for now they shall stay where they are. The Belt as asked above does have the common problem of been tail heavy AND personally in my opinion overly so its something that most Belt owners will agree about. I understand about balance and cg and really this was the main part of my enquiry you see its quite bad really to the point i use 2100mah and 2500 mah lipos as far forward as possible in place of the stock 1800mah ones and even like this it needs execsive trim to maintain a stable hover which with my limited knowledge cant be right. Surely the whole point of a good set up ie level swash plate even links is to give a nice even performance accross the ranges of possible stick positions in flight. If it then needs excessive trim just to hover stabley which it does this cant be good and i would of thought a model that needs very little triming to achive this would be a much better condition to achive?

 

Thanks to all who have contributed.

Josh

[wlfk]

Helicopter CoG doesn't need to be spot-on in the beginning. I don't know how far out yours is, but there is some latitude.

It becomes more important when you try to fly inverted. If your helicopter is nose-heavy the right way up, you add back-trim to hover nicely. If you're flying upside down and your helicopter is nose-heavy, you need to add forward trim!

[Geoff Goodwin]

wlfk

Whilst you are not wrong, I think relying on trim to correct any CG irregularity is not good practice. Getting the CG spot on is always a good way to start especially if you are new. Of course getting the rest of the set up "right" is equally important

 

The less "fight" the novice has to contend with, the better chance to succeed. For people who have progressed it becomes more a question of choice and how comfortable you are with the need to quickly trim out. Personally I'm old school and try to set all my models up so they fly true with zero trim or as near to it as possible!

 

With small models it seems more critical as well.

 

Don't get me wrong, as you get experienced you get to know what latitude to allow, but without seeing the model yourself, the best way is surely to advise on getting it right.

 

Josh is dead right that with the linkages / swash set up right you should not expect excessive trim. If the balance is good to it makes me think design could be an issue. After all some models fly better than others. In this instance and if Josh is new to the game it would be sensible to get the model checked over by some-one with more experience.

 

Edit: If trying to hover outside in a breeze you will need forward trim and possibly quite a lot, as the model is in fact flying forward as fast as the wind is blowing to hold position over the ground.

[joshua jones]

Geoff,

 

   Thanks for your thoughts there and i have to agree 100% i have allways set up my fixed wing models to fly straight and true without the need to excessively trim them and so it was a logical step for me assume the same practice with the Heli's to.

 

Pleased to report that my progress has been very good over the last week and i can comfortably hover out an entire battery so im rightfully very happy at the minute. The CG problems i was having are also much much better> The Belt CP is well known for its tail heavy condition you see and as i mounted all component gear inc radio in the advised locations it showed this tail heavy condition quite alot. Thankfully i havent and wouldnt ever use Esky radio gear which led to thinking that there recomendations for loacting these items within the model were probably also suspect, so the other day i completely stripped it and rebuilt it from the ground up ( i took it apart to the point that it resembled the exploded diagram, every single piece was stripped) taking extra care in the rebuild been very accurate. Moved all the radio gear under or just infront of the main shaft and also hollowed out the virticle tail fin it now resembles the carbon versions but plastic.

The model now flys very nicely and im pleased with my efforts.

 

One thing i did not know and all beginners are probably the same, is the trimming should in my opinion not done how many peolpe advise ie as the models scoots and slides around the floor with its training gear on. And SHOULD be done in the hover at LEAST 18inches high preferably a ittle more. Any trim introduced on the ground then needs retrimming once in the air and is really pretty pointless to do. Instead  if anyone reading this whos at this stage you should learn to hold the model still during taKe off using the tx sticks (after al thats what there for!!!) conter acting the torque etc

 

anyway i would thank all who have added to my questions and im off to practice some more......................................

 

Josh