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-   -   Twin rudders as air brake (https://www.rcuniverse.com/forum/rc-jets-120/11586754-twin-rudders-air-brake.html)

flyinfool1 09-13-2013 08:03 AM

Twin rudders as air brake
 
I am building a YA Stingray.

I plan to use the rudders as additional air brakes set up on a slider.

What are the pros and cons of turning both rudders in vs turning both rudders out?

How much deflection is a good amount to start with?

kelly vallee 09-13-2013 08:23 AM

I have been using the rubbers as air brake for years on my jet. With no problems, I turn them in.

mr_matt 09-13-2013 08:54 AM

On my stingray, I have the rudders canted inward. Very effective. Not sure of the throw but it is all I can get. I use it in dead calm conditions with the main speed brake. No trim change to speak of either, not sure if you canted them outwards if it would be different

I don't use it with any sort of headwind, not needed.

I set up my last Bobcat with rudders canted outward (a_lot_of throw with 8411s on the rudders) and when I deployed them the Bobcat just stopped! Totally unnecessary on the Bobcat!

jason 09-13-2013 09:50 AM


Originally Posted by kelly vallee (Post 11614929)
I have been using the rubbers as air brake for years on my jet. With no problems, I turn them in.

Never heard of them used for that before :p

FalconWings 09-13-2013 10:36 AM


Originally Posted by jason (Post 11615002)
Never heard of them used for that before :p

Im assuming with no lube? Would ribbed ones work too?

:-)

BaldEagel 09-13-2013 12:56 PM

The P20 Duckty has, as a matter of course used the rudders as air brakes canted outwards, no other option, little bit nervous at using them inwards as that is towards the jet efflux and the rudders are a bit close, works extremely well, maximum deflection seems to make no difference to the flight characteristics of the airframe, nor the rudder effectiveness in yaw.

Mike

flyinfool1 09-14-2013 12:07 PM

My thought was that if you want the rudders to still have yaw control while being deployed as an air brake, that canted out would cause an increase in drag in the inboard side of the turn and a reduction in drag on the outside of the turn. This is MY theory, I just have no clue if it will make a difference.
It seems that most turn them in with good results while some turn them out with good results. In all of my searching I have not found a case where one way is superior to another.

I guess I'll see which way is easier to program when I get that far. Maybe I'll set up both on a switch to try it out.

BaldEagel 09-14-2013 03:00 PM

I don't think anyone is suggesting that one way is better than the other, just the point that if your rudders are close to the turbine efflux canting out would make more sense.

Mike

flyinfool1 09-17-2013 08:45 AM

If the rudders were in danger of getting scorched by the efflux, would they not get scorched in normal use as rudders on the side that turns in when you gave a rudder input?

BaldEagel 09-17-2013 02:31 PM

I think the air flow with both turned in may be restricted rather than with one turned in and one turned out.

Mike

mr_matt 09-17-2013 03:53 PM

Guys I have done this exact thing (inward canting rudders) on a Stingray (the plane in the original question) and there are no problems with heat or anything else, it has maybe 1000 flights on it.

BaldEagel 09-18-2013 01:16 AM

I can see on the Stingray this would work as the fins are well outboard compared with the Duckty, for me I think the discussion turned a bit academic rather than about a particular airframe, sorry for diverting the thread subject.

Mike

jetster81 09-18-2013 02:15 AM


Originally Posted by mr_matt (Post 11618170)
Guys I have done this exact thing (inward canting rudders) on a Stingray (the plane in the original question) and there are no problems with heat or anything else, it has maybe 1000 flights on it.

Can you tell me if you have max throws and is there any pitch change when applying?

Woketman 09-18-2013 08:41 AM

I used to do this 16 years ago on my first Kangaroo. I canted them outwards initially because I was concerned with heat. But Matt is right, even inwards they would be fine. But it also seemed, aerodynamically, to me to be better outwards. Think about it: outwards, when kicked into a yaw by a gust, the rudder on the right (for a nose left gust) sees more drag and therefore tends to increase yaw stability.

mr_matt 09-18-2013 09:12 AM


Originally Posted by jetster81 (Post 11618375)
Can you tell me if you have max throws and is there any pitch change when applying?


Hello,

I really don't know. I know I still have maybe 5-10 degrees of throw left going in board. In my experience you rarely use that much rudder on landing for it to matter.

I use only because I had extra channel available. I think it is much more important to make sure the speedbrake is rigged with the proper geometry needed to get it to open. I have helped 2 other guys and neither of them had a speedbrake that would reliably open. I have a 9411 on it and it opens fine. With a proper speedbrake that is about all you will need 95% of the time.

And I have no pitch change. As I said before I canted outward on a Bobcat and it worked fine.

BaldEagel 09-18-2013 09:13 AM

OK if its time for oneupmanship. LOL

When Robert Newman first designed the Panic over 25 years ago, he split the single rudder and had two servo's operating it so he could use the split surface as an air brake in the flat inverted spins he used to do down onto the deck, yes he had an undercarriage on the top wing.

Mike

jetster81 09-18-2013 10:48 AM


Originally Posted by BaldEagel (Post 11618595)
OK if its time for oneupmanship. LOL

When Robert Newman first designed the Panic over 25 years ago, he split the single rudder and had two servo's operating it so he could use the split surface as an air brake in the flat inverted spins he used to do down onto the deck, yes he had an undercarriage on the top wing.

Mike


You are right I remember that one well, and several other oddball variations also.

flyinfool1 09-18-2013 12:45 PM


Originally Posted by BaldEagel (Post 11618363)
I can see on the Stingray this would work as the fins are well outboard compared with the Duckty, for me I think the discussion turned a bit academic rather than about a particular airframe, sorry for diverting the thread subject.

Mike

Don't be sorry for diverting the thread, I had intended it to more of an academic question than of the specific airframe. I was wanting to know if there is an aerodynamic reason to favor in vs out. This would apply to many airframes on the market.

chrispol 10-02-2013 03:52 PM

I do the same on my hotspot, slows it down quite a bit and bring the nose up

Dr Honda 10-02-2013 04:33 PM


Originally Posted by chrispol (Post 11629540)
I do the same on my hotspot, slows it down quite a bit and bring the nose up


I was just thinking of this too.


So... you are going out then? Since the rudders lean in, that would make the nose lift a little.

If that's correct... how much do you deflect?

Woketman 10-02-2013 05:15 PM

Even if the verticals did not lean in, the fact that the rudders are above the aero center yields a nose up moment (pitch) too!

chrispol 10-03-2013 04:08 AM

I bring both rudder in towards each other, as far as they go, the way i set mine up i retain rudder functionality also

basically i set my flap switch to control it all, 0=normal 1=airbrake 2=rudders in + airbrake

flyinfool1 10-03-2013 11:51 AM


Originally Posted by chrispol (Post 11629817)
I bring both rudder in towards each other, as far as they go, the way i set mine up i retain rudder functionality also

basically i set my flap switch to control it all, 0=normal 1=airbrake 2=rudders in + airbrake

I like that idea, That is how I will set up my Stingray.

Woketman 10-03-2013 12:50 PM

I think that having them go outwards is a bit better, yaw stability-wise.

Wayne22 10-04-2013 08:22 PM

In the old Super Reaper, we had them programmed to go outwards....noticeable slow down, and no pitch change.......


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