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Author Topic: Pusher Propeller  (Read 1192 times)

Offline Haoyang Wang

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Pusher Propeller
« on: February 01, 2019, 02:28:45 AM »
As I understand it, a pusher propeller helps maintaining line tension when the plane circles counter clockwise, while a tracker propeller does the same when the plane circles clockwise (i.e., inverted). Now, as stunt and combat planes have to fly in both ways, does it really matter which way the lines are tighter than the other?  ???

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Haoyang

Offline Ken Culbertson

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Re: Pusher Propeller
« Reply #1 on: February 01, 2019, 07:47:15 AM »
As I understand it, a pusher propeller helps maintaining line tension when the plane circles counter clockwise, while a tracker propeller does the same when the plane circles clockwise (i.e., inverted). Now, as stunt and combat planes have to fly in both ways, does it really matter which way the lines are tighter than the other?  ???

Thanks,
Haoyang
Having recently made the transition I can say that it does help me.  It only seems to hurt in the 6 laps of inverted.  All of the maneuvers except the outside loops are entered from upright level flight after a full lap.  Having better tension in that lap makes the entry easier, especially in wind and at 45/42.   I also find that my ships have less of a tendency to "pop" off the ground during takeoff but that may be more the slower power up than the direction of the prop.  I have not studied or even discussed this with the more knowledgeable of physics among us but I do think that the gyroscopic effect of the electric motor has a more favorable impact than does an IC's piston.

Combat is different.  You spend as much time upright and inverted as the match dictates.  I can see it helping in the launch.  I have had quite a few combat ships "pop" in on me when released improperly but that is only for a split second and anticipated so not much of a problem.  I can't speak for the current crop of ships since my combat (at least fast) days are over.

Ken
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Offline Igor Burger

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Re: Pusher Propeller
« Reply #2 on: February 01, 2019, 08:08:11 AM »
As I understand it, a pusher propeller helps maintaining line tension when the plane circles counter clockwise, while a tracker propeller does the same when the plane circles clockwise (i.e., inverted). Now, as stunt and combat planes have to fly in both ways, does it really matter which way the lines are tighter than the other?  ???

Thanks,
Haoyang

Well, it is too simplified understanding.

Yes, prop has torque which makes rolling moment, but it is task of trimming to remove it. We have flaps or trimming tab to put the wing to level and thus it does not make any difference.

The real effect is precession. The difference is mostly visible in second corner of hourglass where pusher prop yaws model out of the circle and thus makes lines tighter. But yes, you are right that there are also places where it does not help, because just opposite happens in second corner of triangle. Fortunately it is also trimmable (to some extent) with Rabe rudder.

But there is still one difference and that is precession in straight flight, precession of pusher prop makes pitching moment down -  means the same direction like drag of landing gears and thrust line of motor over the wing line (as used on classic models). That must be counterbalanced by permanent elevator deflection what can make different force down or up wind. That can cause hunting. Therefore and with usage of mentioned trimming, normal prop is easier to trim and pusher prop does not bring any advantage. I know several fliers who tried pushers and went back when they found that model with pusher was more difficult (but usually not at all) to trim to its best potential.

Offline Ken Culbertson

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Re: Pusher Propeller
« Reply #3 on: February 01, 2019, 10:17:16 AM »
Well, it is too simplified understanding.

Yes, prop has torque which makes rolling moment, but it is task of trimming to remove it. We have flaps or trimming tab to put the wing to level and thus it does not make any difference.

The real effect is precession. The difference is mostly visible in second corner of hourglass where pusher prop yaws model out of the circle and thus makes lines tighter. But yes, you are right that there are also places where it does not help, because just opposite happens in second corner of triangle. Fortunately it is also trimmable (to some extent) with Rabe rudder.

But there is still one difference and that is precession in straight flight, precession of pusher prop makes pitching moment down -  means the same direction like drag of landing gears and thrust line of motor over the wing line (as used on classic models). That must be counterbalanced by permanent elevator deflection what can make different force down or up wind. That can cause hunting. Therefore and with usage of mentioned trimming, normal prop is easier to trim and pusher prop does not bring any advantage. I know several fliers who tried pushers and went back when they found that model with pusher was more difficult (but usually not at all) to trim to its best potential.

How much of the additional difficulty in trimming might be attributed to familiarity with the counter clockwise rotation we grew up with and have used all of our lives?
The only things that I have noticed right off are that I use less rudder offset on single top only rudders and the amount of elevator bias is different.  You are right that killing inverted hunting is more difficult with clockwise but I think that is more that we know instinctively how to fix it spinning the other way and I am also not so sure that it is not also a characteristic of electrics in general.  On the ships I have converted from IC to DC all have picked up some inverted hunting that I had to trim out, even on those that I did not change the prop direction.

Maybe it is a matter of degree.  Many of us just don't have the time to trim past CG, wings level, turns the same and doesn't hunt on it's own.  That is going to be the same procedure either way.  If you have the time and compete at the level where perfect trim may be the difference in winning or not then maybe there is no advantage.

Ken
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USAF 1968-1974 TAC

Offline Ken Culbertson

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Re: Pusher Propeller
« Reply #4 on: February 05, 2019, 01:20:31 PM »
You are right that killing inverted hunting is more difficult with clockwise but I think that is more that we know instinctively how to fix it spinning the other way and I am also not so sure that it is not also a characteristic of electrics in general.
Ken
I am elaborating on this only because I am experiencing severe inverted hunting on my converted Nobler AFTER switching from counter to clockwise.  Severe enough that I have to look out for the game warden.
I thought it was my geriatric reflexes until I flew my twister and it was rock solid (clockwise prop).  It never hunted IC and all that has changed is a 1/2" forward shift in the CG and going from a 10-6W counter using IC to a 12-6 clockwise on electric.

One of three things is causing this.  #1 nose heavy,  #2 that huge prop. #3 line friction.  Nobler's (and this one is a stock ARF) don't normally hunt if trimmed.  Electric has added 4oz and the ship is now at a porkey 45 so I would like to avoid tail weight so my question is really what can I do in the prop area that would affect hunting?  As for #3, I never hear of wiping your lines with either silicone or teflon sprays.  Is there a reason?  Level inverted is the only place in the pattern you are trying to fly level and being judged with three wraps in the lines.

ken

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Online Brent Williams

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Re: Pusher Propeller
« Reply #5 on: February 05, 2019, 06:31:39 PM »
I am elaborating on this only because I am experiencing severe inverted hunting on my converted Nobler AFTER switching from counter to clockwise.  Severe enough that I have to look out for the game warden.
I thought it was my geriatric reflexes until I flew my twister and it was rock solid (clockwise prop).  It never hunted IC and all that has changed is a 1/2" forward shift in the CG and going from a 10-6W counter using IC to a 12-6 clockwise on electric.

One of three things is causing this.  #1 nose heavy,  #2 that huge prop. #3 line friction.  Nobler's (and this one is a stock ARF) don't normally hunt if trimmed.  Electric has added 4oz and the ship is now at a porkey 45 so I would like to avoid tail weight so my question is really what can I do in the prop area that would affect hunting?  As for #3, I never hear of wiping your lines with either silicone or teflon sprays.  Is there a reason?  Level inverted is the only place in the pattern you are trying to fly level and being judged with three wraps in the lines.

ken

When the ground thaws around here, I will be chasing the hunt in my Gieseke Nobler also.  It hunted a bit with glow power and it is quite pronounced with the E-power.  It is packing several additional ounces in the nose, which shall probably be relocated at least 1 -2" rearward soon.  I am running the 11x5.5 in standard rotation.
Laser-cut, "Ted Fancher Precision-Pro" Hard Point Handle Kits are available again.  PM for info.
https://stunthanger.com/smf/brent-williams'-fancher-handles-and-cl-parts/ted-fancher's-precision-pro-handle-kit-by-brent-williams-information/

Offline Ken Culbertson

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Re: Pusher Propeller
« Reply #6 on: February 05, 2019, 08:39:10 PM »
When the ground thaws around here, I will be chasing the hunt in my Gieseke Nobler also.  It hunted a bit with glow power and it is quite pronounced with the E-power.  It is packing several additional ounces in the nose, which shall probably be relocated at least 1 -2" rearward soon.  I am running the 11x5.5 in standard rotation.
Damn, I was going to try an 11-5.5 standard this weekend.  It has to be nose weight.  It wants to drop a wing in the 4th corner of the hourglass, that is new and it is a nose heavy side affect too.  I am getting by with a 4s 2200 battery.  I simply can't get any smaller there and the battery is already up against the wing LE.  When I see these conversion kits, the one thing I notice is that there is little room for a battery in the classic 8-9" classic nose.  I guess it is tail weight again.

ken
AMA 15382
If it is not broke you are not trying hard enough.
USAF 1968-1974 TAC


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