Counter rotating motors

[frank fearn]

I will be putting together a Ziroli P38 and see numerous builders installing and flying with counter-rotating engines, this is new territory for me.

No doubt some of you more experienced "twin" pilots have done this but does it improve flight characteristics and is it really worth it? I intend to use either da 50s or dle 55s and had intended building as per plan, i,e normal rotation on both but since researching it's seems as though most are reversing one.

Any advice form experience is more than welcome....

Frank

[Phil Clark]

Speak to Steve Rickett......he's built two (both Laser 360V powered).......both retained normal rotation and performed well.

Phil

[Phil Robertshaw]

Hi Frank,

I have a JU 88 with two DA 50s. On take off, adding power the plane veered quite severely left.
I have now got the starboard engine counter rotating and it now tracks straight.
It is very simple to counter rotate the DA 50 by purchasing a new pickup sensor and replacing the existing sensor. About £30. job done.

Hope this helps,

Regards. Phil

[Clive Hall]

The P-38 was designed to have counter-rotating airscrews, the starboard one rotating anticlockwise as seen by the pilot. The RAF ordered their first aircraft with right hand rotation on both shafts. Now here’s a quote from FIGHTERS Volume Four, by William Green, Pages 115-116:—

“For some unexplained reason, the British Air Purchasing Commission had requested these [rotation] modifications despite predictions by Lockheed that performance would be much inferior to the standard A.A.F. model. Two models were tested at Boscombe Down in April-June 1942, but performance was so disappointing that machines shipped to the United Kingdom were returned, and the remainder of the order cancelled.”

I think that makes the case for counter rotation on twins.

[Clive Hall]

More research into the P-38 shows an anomaly. The counter rotation as already described is the usual set-up; it is used on the DeHavilland Hornet. However photographs show the prototype P-38 with this same arrangement, but production models had the opposite. The propeller pitch is easy to read in many photos. It seems that there were some unusual airflows around the twin booms that do not happen on more conventional layouts, causing buffeting, and the solution was found by reversing the more conventional counter rotation. Probably well worth incorporating in a model.

[frank fearn]

Many thanks to you both for the response. I would prefer to follow the prototype although I have seen numerous good subjects with standard twin rotation on both.... mind blowing stuff...

https://www.youtube.com/watch?v=qM2BCIGM10I


Phil, did you leave the thrust line as it was prior to adding your starboard counter rotating motor? If its just a case of £30 or so to counter rotate, its a no brainer.

Best regards,
Frank