Counter-Rotating Props

[Ron Van Putte]

On Jan 27, 2005, at 12:21 PM, Keith Hoard wrote:

> I guess if you guys were REALLY serious about pattern models, you’d 
> design counter-rotating props for the engines. . .

Speaking about counter-rotating props:  Have any of you seen the Hirobo 
Mini Lama RC Electric Helicopter?  I'm talking about the non-tethered 
version.  I was over in Pensacola a couple of evenings ago at a local 
high school gymnasium that Tony Stillman has arranged for the electric 
airplane pilot to fly in for a two hours on a weekday evening.  Tony 
delivered one of these helicopters to Steve Rojecki.  I watched as they 
removed the helicopter and transmitter from the shipping box, installed 
the LiPo battery (included) in the helicopter, snapped in a transmitter 
battery pack and turned the system on.  Steve proceeded to take it off 
and fly it around.  I was impressed.  I was even more impressed when 
Steve announced, "Who said flying a helicopter is hard?  This is easy!" 
  It turns out that he'd NEVER flown a helicopter before!

Ron Van Putte

> From: discussion-request at nsrca.org 
> [mailto:discussion-request at nsrca.org] On Behalf Of Rcmaster199 at aol.com
> Sent: Thursday, January 27, 2005 12:17 PM
> To: discussion at nsrca.org
> Subject: Re: Throt/ Rud
>
>  
>
> Bob, this is exactly how I feel. Why not learn to use the sticks?
>
>   
>
> On the money with P-Factor (not to be confused with K-factor) and GP 
> also. Slipstream is the key and it could be significantly straightened 
> by doing something similar to what Nat has done with the Xpress series 
> of models. Strakes surrounding  the CG help reduce the effects. This 
> is a design feature tha belongs on all pattern models. IMHO
>
>  
>
> MattK
>
>  
>
>  In a message dated 1/27/2005 8:18:27 AM Eastern Standard Time, 
> bob at toprudder.com writes:
>
> Ed,
>
>  
>
> I am a very firm believer (no one will convince me otherwise) of 
> exactly what you describe. Slipstream effect is the whole reason we 
> put right thrust in our engines. It has NOTHING to do with torque, 
> P-factor, or gyroscopic precession.
>
>  
>
> The issue of transitioning from vertical to horizontal (either to 
> inverted or upright) is a gyroscopic precession issue. The best way to 
> counter that is to use lighter weight props turning at lower rpm -- 
> less spinning mass and less gyroscopic effect.
>
>  
>
> P-factor only exists at high angle of attacks, which does not happen 
> in a vertical climb.
>
>   
>
> Torque tries to roll the plane, and some schools of thought are that, 
> to counter the torque-induced roll, the left wing has to lift more 
> than the right, causing more induced drag on the left. While this may 
> be true for a lot of planes while taking off, this does not apply to 
> pattern planes in a vertical climb since both wing panels would be 
> fighting the torque equally.
>
>  
>
> Gyroscopic precession only occurs when the airplane is moving around 
> its pitch axis, as when pulling or pushing a corner. It is most 
> noticeable when the airplane is slow, since there is less aerodynamic 
> stabilizing force available from the rudder/fin.  IMHO, no 
> throttle-rudder mix is going to correct this. It might be possible to 
> mix elevator to rudder, and enable/disable the mix based on throttle 
> position.
>
>  
>
> When I flew a Cap21 in pattern, I had to use left rudder when pulling 
> an inside corner at the top of square loops. I had to use a TON of 
> right rudder when pushing a corner, and this was with about 5 degrees 
> of right thrust.
>
>  
>
> IMHO, learn to do it with your thumbs. Practice enough and it will 
> become automatic. Just my 2CW.
>
>  
>
> Bob R.
>
>
>
> Edward Skorepa <edsko at xmission.com> wrote:
>
> I'm confused too. I know, I know I shouldn't argue with someone like 
> chip but I believe the main reason we're putting right thrust is an 
> asymmetric vertical fin. On most conventional airplanes the area above 
> thrust line is much greater then area below. So, the spiraling slip 
> stream  will hit the top portion of the vertical fin from the left 
> pushing tail to the right thus right thrust. When inverted, the 
> spiraling slip stream will hit vertical fin from the right because fin 
> is now on the opposite side and  pushes tail to the left. To 
> straighten the flight path, we need now the left thrust which is 
> already there. During inverted push ups, why do we need to use left 
> rudder? The spiraling slip stream misses completely vertical fin and 
> the right (left when inverted) thrust is causing airplane to yaw left. 
> If you have a big gasser, turn on smoke, do inverted push up and watch 
> where the smoke goes. However, Chip's approach of fixing the inverted 
> push ups problem is quite interesting and I'll try it on my new bird 
> I'm working on right now.
>
> ed
>
>  
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