Design > Stunt design
Propeller precession
Trostle:
Is your "propeller precession" quest something different than solving gyroscopic precession issues? If so, disregard all that folows.
The idea to use counter rotating propellers for CL stunt is not new.
Some time ago, Randy Smith set up a system where the rear propeller free wheeled and only the front propeller was powered. I do not know that there were any negative aspects to the system. I recall that torque problems were at least reduced if not eliminated and that gyroscopic precession problems were at least reduced, if not eliminated. I am not aware if any further work was done by him or anyone else using this approach. I do not know if any improvements were experienced that offset the additional weight/complexity of the system compared to just a single tractor propeller approach. Hopefully, Randy can shed some light on this.
Their is a single electric motor system driving a gear box for counter-rotating propellers used on CLPA models that has been available from Poland. For me, I saw this the first time in Poland at the World CL Championships in 2016. There did not appear to be any problem with the performance of this system. At the time, copies of the system were available and they still might be. It is/was a very neat integrated motor/gearbox system easily packaged in the nose of a model for CLPA.
The RC crowd has various systems available from integrated gear boxes driven by a single electric motor to systems that use two electric motors using co-axial shafts directly driving the counter rotating propellers without gear boxes. Most of these systems on the RC market are for the larger pattern ships and do not appear to be practical for our CLPA models. Certainly, these approaches are doable if the equipment can be sized to adapt to our CLPA environment.
Twin electrics for CL stunt are not new. Bob Hunt has a great flying twin where he uses contra rotating propellers and reports no problem with gyroscopic precession. With the advent of electrics, there are other twins out there doing very nicely with contra rotating propellers.
Another way to reduce gyroscopic precession is to use the Rabe Rudder approach. I do not know if this approach to use the rudder will completely negate gyroscopic precession, but it certainly can be used to minimize it to the point that it is not a detectable problem. In fact, it can be used to improve line tension in most inside and outside maneuvers through careful selection/trimming of the rudder position with any given elevator setting.
It should be remembered that for models used in the AMA CL Precision Aerobatic events, all control functions on the model "shall be through the flying lines" except for the use of the 2.4 GHZ spread spectrum radio signals to operate a retracting landing gear and/or a one-time irreversible engine or motor stop function. (Of course, the passive exhaustion of fuel to end the flight is inherent to the operation of these models.) Having some sort of electronic system to sense and then provide correction for gyroscopic precession would not be allowed under the current rules.
(Let's not get hung up here on the definition of counter-rotating props and contra-rotating props.)
So, what are your ideas?
Keith
Mark wood:
--- Quote from: Brett Buck on October 05, 2020, 05:30:27 PM --- Alternately, you posted something at 8 in the morning and were expecting learned responses by 3 the same afternoon, and then claimed the "delay" as people being "closed-minded" - when you haven't even bothered to show your "solution". It's would easy to see that and conclude you are spoiling for an argument.
It would be a lot better if you posted your idea with enough detail to evaluate it, then wait for a day or two, before you start calling people out.
Brett
--- End quote ---
Good point Brett. Sorry if came off that way. I'm not after an argument I'm interested in a dialog. I've been working on an idea for a long time and sometimes it's better to open up a discussion first. Often times outsiders are not received well within a community and ideas brought in from outside are shut down because the new guys doesn't speak the local language. This is natural as the not invented here is typical of all communities. My question was what if and what would it take to demonstrate it as in what would be a good test? My inclination is to get to a flight test but I haven't an airplane which truly exhibits issues clearly precession related enough to do a good A - B test. I'm on a bigger path than just this particular incidental observation and a divergence involving sophisticated test equipment isn't in my plans. Also several people here have done a lot of experimenting which I am very much interested and opening a dialog first is a good way in my mind to get folks talking. Trust me, if I managed to have an original idea, it would be a miracle. Now plagiarizing and making things work or applying them to something different... I can do that.
Sorry again if I came off wrong, wasn't meant that way.
Brett Buck:
--- Quote from: Mark wood on October 05, 2020, 06:42:56 PM ---Good point Brett. Sorry if came off that way. I'm not after an argument I'm interested in a dialog. I've been working on an idea for a long time and sometimes it's better to open up a discussion first. Often times outsiders are not received well within a community and ideas brought in from outside are shut down because the new guys doesn't speak the local language. This is natural as the not invented here is typical of all communities. My question was what if and what would it take to demonstrate it as in what would be a good test? My inclination is to get to a flight test but I haven't an airplane which truly exhibits issues clearly precession related enough to do a good A - B test. I'm on a bigger path than just this particular incidental observation and a divergence involving sophisticated test equipment isn't in my plans. Also several people here have done a lot of experimenting which I am very much interested and opening a dialog first is a good way in my mind to get folks talking. Trust me, if I managed to have an original idea, it would be a miracle. Now plagiarizing and making things work or applying them to something different... I can do that.
--- End quote ---
Certainly, a big part of being an engineer is knowing where to rip off good ideas.
How much have you studied the (extraordinarily extensive) literature on how precession affects stunt planes? Do you have specific questions beyond that? Or is it a more general discussion of the effects?
Brett
Ken Culbertson:
--- Quote from: Brett Buck on October 05, 2020, 05:30:27 PM ---It would be a lot better if you posted your idea with enough detail to evaluate it, then wait for a day or two, before you start calling people out.
Brett
--- End quote ---
y1
Mark wood:
I haven't done any calculation of precession of stunt planes. I also don't know what you guys have done in the treatment of the propeller in that regard. I'm going to assume that it has been treated as rigid rotating body such as a gyroscope. While that is a good first order approximation it is only roughly valid under certain constraints such as blades which are rigidly attached to the hub or rather as rigid as blades can be. My background is in rotary wing aerodynamics, helicopters. Flying rotor systems.
Quote:
Certainly, a big part of being an engineer is knowing where to rip off good ideas.
Seems like it isn't me looking for a fight. I was actually simply trying to start a conversation, however it seems I started a fight. And I apologized. The new guy has been put in his place.
Have a nice day.
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