Have "pusher" props now become the standard for "E" powered competitors?

[Ted Fancher]

While I'm at it I'm also interested in the current state of thought re the left hand rotation/pusher prop preference for the Electric competitors.  Is using them pretty much the standard now?  Haven't heard much of late and was curious.  Thanks.

Merry Christmas to all in Sparky's world.

Ted

[Fred Underwood]

Ted,

Another Igor link with a good suggestion as to competitive E props and rotation direction.

http://87.197.134.200/props/props.htm

Fred

[Frank Imbriaco]

Ted :
Some, like I, believe in the benefits of EP props. Others like tractor. After many hundreds of flights on 3 electric ships( Hunt designed RD-1, Caprice, and Ryan's Eagle) and a knock-around  Top Flight Nobler, I'm convinced that in turbulence, the pusher prop has saved me time and again.
 When the lines go slack, the ship flies back out.
 Frank

[Howard Rush]

Is using them pretty much the standard now?

No

[bob whitney]

   my E-Scorpio would get lite at the upper right corner of the hourglass with a RH prop went to a LH prop and stays out great.cant tell any diff any place else.

[Lauri Malila]

I used them for some years in my IC but have since gone back to normal. Model flies happier with tractor. L

[RandySmith]

While I'm at it I'm also interested in the current state of thought re the left hand rotation/pusher prop preference for the Electric competitors.  Is using them pretty much the standard now?  Haven't heard much of late and was curious.  Thanks.

Merry Christmas to all in Sparky's world.

Ted

NO

[Larry Wong]

After using L/H props for couple years, I've decided that the PULL was to hard and had to fight it sometimes but it also saved me in wind changes! I'm back to R/H tractor props there were some changes in trimming , the VG's helped that on hour glass..

[frank williams]

Hi Ted
Some good thoughts here by Peter German .... and a design specifically for pusher props.
https://stunthanger.com/smf/stunt-design/specific-fuselage-design-for-cw-rotating-props/
Frank

[Randy Powell]

I started with one. I have since gone back to tractor.

[Tim Wescott]

They were way popular for a few years.  Then people realized that they made some things better and other things worse, and the choice of a pusher became yet another thing that's peculiar to a certain airframe.

I haven't done this myself, but from reading the experiences of others I can say that if all else is equal, swapping out a prop for it's mirror image will require a comprehensive re-trim.  Particularly if you forget to reverse the motor rotation.

[Ted Fancher]

"snip"
Particularly if you forget to reverse the motor rotation.

Ya think!

Do you do "Technical Aeronautical Stand Up Comedy" on your days off, Tim?

Ted

[Randy Cuberly]

Ya think!

Do you do "Technical Aeronautical Stand Up Comedy" on your days off, Tim?

Ted

I suspect maybe even on his "Days On".   

Randy Cuberly

[Paul Walker]

I tried to comment earlier, but it got lost in cyberspacce..

I believe people  who use the APC's  do so because of cost.

The hollow Igor props are the only way to go. Once you experience the lack of precession due to this prop you will never go back.

Sorry, you IC guys can't experiennce these 16 g props. You have no idea how good they are.

[Randy Cuberly]

I tried to comment earlier, but it got lost in cyberspacce..

I believe people  who use the APC's  do so because of cost.

The hollow Igor props are the only way to go. Once you experience the lack of precession due to this prop you will never go back.

Sorry, you IC guys can't experiennce these 16 g props. You have no idea how good they are.

Well, Surgey Belko from Ukraine did make some carbon covered 3 blade foam props for his Belko Engines.  I have several of them (for my two Belko Engines) but they are in sizes that are most useful for those engines and are all relatively high pitch.  They are very light and work quite well on those engines.  I certainly experienced the lack of precession with these props on my 53 oz GeoXL.  I have some photos of them but have lost my reduction program for the moment (probably didn't pay the bill).

Not sure if He makes them anymore!  I tried several years ago to get him interested in making some other sizes, when he visited Tucson, but I think He simply had too many irons in the fire at that time.  Wish someone would pick up that process and do it!

The picture below shows one of the props.  It's an 11.8-6.25 and weighs about 17 grams.  Very stiff also!

Randy Cuberly

[Ted Fancher]

I tried to comment earlier, but it got lost in cyberspacce..

I believe people  who use the APC's  do so because of cost.

The hollow Igor props are the only way to go. Once you experience the lack of precession due to this prop you will never go back.

Sorry, you IC guys can't experiennce these 16 g props. You have no idea how good they are.

Thanks, Paul.  No accounting for such neanderthals apparently.  Are Igor's props push me or pull you?  Either way? I haven't seen one yet.

Ted

[Steve Helmick]

Ya think!

Do you do "Technical Aeronautical Stand Up Comedy" on your days off, Tim?

Ted

I've seen it done/attempted, so it's not all that funny! The thing about 'lectrics is that all sorts of new ways to have stuff go wrong are possible. Being really good with glow engines after decades of use doesn't seem to help all that much. Thoroughness and good planning appears to work. Still not interested. I can't think of anybody around here using LH props on the front of their stunters.    Steve

[Randy Cuberly]

I've seen it done/attempted, so it's not all that funny! The thing about 'lectrics is that all sorts of new ways to have stuff go wrong are possible. Being really good with glow engines after decades of use doesn't seem to help all that much. Thoroughness and good planning appears to work. Still not interested. I can't think of anybody around here using LH props on the front of their stunters.    Steve

I tried one on my PA but just couldn't figure out how to make the airplane go forward without putting the engine in the rear!   Worked out to Be way too tail heavy     

Also not interested in 'lectrons!
Randy Cuberly

[Steve Helmick]

I'm not really opposed to 'lectrons...just not interested in using them for airborne purposes. In fact, I love my Makita 18v. cordless drill, love using those battery packs on my Sullivan starter, and I just ordered a 110v. chainsaw for use around the homestead. Had to dig out and use my Dad's Mac 10-10 last Monday, and found that pulling that starting cord was no fun at all. Never really noticed why it started when it (rarely) did, but it was zero fun. Last time I used it was about 1980, 20'+ up a Cottonwood. Wasn't fun then, either. Consulted with several friends who have used different brands of gas saws and every one of them said gas chainsaws are a girl dog to start, and brand didn't matter. The 'lectric saw should be here next week. It'll go under the plastic tree, when that goes up. Steve

[Ted Fancher]

I tried one on my PA but just couldn't figure out how to make the airplane go forward without putting the engine in the rear!   Worked out to Be way too tail heavy     "snip"
Randy Cuberly

Hmmmm.  Reasonably clever, Mr Cuberly but way too verbose for the "stand-up tour".  Also, the arcane nature of the phrase "tail heavy" may expose the speaker to potential charges of harassment from ladies in the audience who find themselves offended based on their ill informed interpretation of the phrase since the development of twerking as an art form.

Ted

[Tim Wescott]

Do you do "Technical Aeronautical Stand Up Comedy" on your days off, Tim?

There's no reason that technical discourse cannot be leavened by humor.

And I think I've forgotten what a "day off" is.

[Randy Cuberly]

Hmmmm.  Reasonably clever, Mr Cuberly but way too verbose for the "stand-up tour".  Also, the arcane nature of the phrase "tail heavy" may expose the speaker to potential charges of harassment from ladies in the audience who find themselves offended based on their ill informed interpretation of the phrase since the development of twerking as an art form.

Ted

I just call'em like they are!  Uhhhh In my crowd PC stands for "pretty callous"...Way of life for us desert rats!

As for a "stand up tour" I prefer to lay down when I'm insulting women.  The beating hurts less with no fall at the end!     

Randy Cuberly

[Paul Walker]

Are Igor's props push me or pull you?  Either way? I haven't seen one yet.

Ted
[/quote]

If you have seen one of my planes in the last 3 years, then you have seen one!

These hollow props are "tractors" in your vernacular.

[Igor Burger]

Yes, the best pusher is tractor, everyone knows :-P

Ted, the point is that usual concept of stunter with thrust line over the wing and LG down wants go naturalry "down" the nose. RH rotating tractor prop has precession just opposite what can counterbalance it to some extent, so it is easier to trim the model (and still needs little bit down stab/elevator). Several guys I know tried pusher props, but precession adds even more nose down moment and it is simply more difficult to trim such model. Peter Germann tried to "adopt" existing standard stunter to such prop by moving thrust line to wing and use retractable gears to make symetric model. That makes it 1:1 for pusher or tractor.

However it reminds me of Tango by Luciano Compostella which had thrust line under the wing .... :- ))))))))) 

[Igor Burger]

Are Igor's props push me or pull you?  Either way? I haven't seen one yet.

Ted


If you have seen one of my planes in the last 3 years, then you have seen one!

These hollow props are "tractors" in your vernacular.

They must be really good, world champ flies them  :- ))))))))))

No, the main idea of light props was that we had problem with accelearting and especially decceleratin with active timers, ESCs usually do not have brake and recuperation while going to lower RPM, so those light props are quicker in changing RPM and it is visible in wind. But lower precession is definitelly nice thing.

[Brett Buck]

Ted, the point is that usual concept of stunter with thrust line over the wing and LG down wants go naturalry "down" the nose. RH rotating tractor prop has precession just opposite what can counterbalance it to some extent, so it is easier to trim the model (and still needs little bit down stab/elevator). Several guys I know tried pusher props, but precession adds even more nose down moment and it is simply more difficult to trim such model.

      Thanks, that's what I would have predicted, but not having any electric models, I couldn't confirm it.

 

No, the main idea of light props was that we had problem with accelearting and especially decceleratin with active timers, ESCs usually do not have brake and recuperation while going to lower RPM, so those light props are quicker in changing RPM and it is visible in wind.

      I have two different loops simulated that would handle conventional prop inertia OK, but it requires a dedicated/integrated ESC and feedback, and, it's limited by the current available. At any point in time, it has a commanded RPM, and a servo loop with  very high bandwidth to drive it either way.   I also don't know how to implement some parts, but I assume I can figure that out when the need arises.   

    But one of the things that really made an impression when I flew Paul's (with a Cox/Resinger prop, not yours) a few years ago was how well it responded up and down. That was probably the most surprising thing about it, it was like a perfect 4-2 break that wouldn't change at semi-random from day to day. I see far more people having problems with setting the gain (usually vastly too high for the conditions to the point of instability) than limitations with the ESC response.

     Brett

[Igor Burger]

I see far more people having problems with setting the gain (usually vastly too high for the conditions to the point of instability) than limitations with the ESC response.

Exactly! The problem is that Emotor does not have infinity power, so if timer asks for more than current battery voltage and motor KV can do, the system command is "overdone" and motor goes for full throttle. And it is still overdone also when timer tells motor to slow down, but that command is still over that physical maximum, plus motor is already unloaded so it even runs faster and faster also if timer says slower and slower. Result is that it works in reality just opposite and flyer has feeling that it respods too late. That is why I recommend to go up with gain very slowly.

[Brett Buck]

Exactly! The problem is that Emotor does not have infinity power, so if timer asks for more than current battery voltage and motor KV can do, the system command is "overdone" and motor goes for full throttle. And it is still overdone also when timer tells motor to slow down, but that command is still over that physical maximum, plus motor is already unloaded so it even runs faster and faster also if timer says slower and slower.

      Right, classic "windup" in the integral signal due to encountering a non-linearity (in this case, the saturation of the throttle). That's why the system to fix it would require that the (slow) feedback control and the (fast) servo loop needs to be in a single integrated system rather than a controller and separate ESC, you could put the limiter in the slow loop to keep it from exceeding the max, and add a bunch of lead or a feedforward. That's why I had earlier, erroneously, assumed that you used the Y axis acceleration/load factor to gain lead in the system, because every time I did it, that's seemed to helo dramatically.

    As noted above, I can't implement my system with my current knowledge, and I have other irons in the fire and haven't gotten back to it yet. The drive stage looks suspiciously like a MOSFET stereo audio amplifier I made for someone back in the 80's.

      Brett

p.s. I also look at using the bellcrank angle instead of the load factor, that was a lot messier because that, too, required a bunch of lead and a lot of processing compared to the load.

[Ted Fancher]

Are Igor's props push me or pull you?  Either way? I haven't seen one yet.

Ted


If you have seen one of my planes in the last 3 years, then you have seen one!

These hollow props are "tractors" in your vernacular.

Thanks, Paul.

"Tractor/Pusher" are not my "preferred" terminology in an informed setting but they are ones that pretty much everybody can decipher without doing the mental imaging thing; i.e. is right/left hand rotation correct when viewed from the front or the back of the plane, etc.  I haven't a hang-up about talking "plain" if it makes things more manageable for the entire audience (especially when talking "plane").

Pretty much the only time I've seen your airplanes in recent years was at the critiquing session in Woodland prior to the WCs in Oz.  I was always across the circle from the launch and pick-up operations and the airplane configuration was never germane to our purpose that day.  Were you using right or left hand rotation props then?  As I recall you more or less initiated and advocated their use due to superior performance in vertical maneuvers. 

By the way, I've no problem whatsoever re the beneficence of lighter rotating masses particularly when the motive force for the propeller's mass is also a contributor.  On the other hand, having flown a lot of real airplanes with propellers I remain more a devotee of P-factor management at least on the IC stunters with which I used to play!  I still scratch my head over the lack of interest in the phenomenon when we're talking about tethered, high thrust to weight ratio toys maneuvering primarily in the pitch axis while requiring consistent tension on the lines by which control input is applied. 

On the other hand I've no doubt that precession becomes more of an issue the more mass you've got spinning at high rates.  The proper approach to the two issues should, no doubt, be appropriately different.

Ted

[Igor Burger]

The timer is feed forward system, not feed back, I do not know if it can be called windup, I think windup is problem of feed back system with integrating component, but it is basically the same, power is lower than system needs (or asks for). However the ESC itself is feed back PID system. ESC has some anti windup routines inside. But since it is internal component, it cannot solve problem of outer regulator causing that problem.

I was thinking how to prevent it in timer without infromation from ESC or direct measuring of prop RPM (as I do not have feedback). But it is easy to solve by simple adjusting gain (sensitivity) so I gave up. I spent 4 years tuning until I got it work as it is now and I do not want to accelerate some technology racing or fix what is not broken, so I do not plan to do anything around. I decided I will leave it as it is and as it was last 8 years :- P

If I have to compare it to IC engine, it basically does exactly the same thing, even there are some analogies in settings, for example sensitivity is something like choke area (and sensitivity to fuel pressure differnces nose up nose down), piped engine has some upper and lower RPM where it runs defined by pipe geometry and baffles, timer allows to set them as parameters, but there is one difference favoring Epower - the regulator does not overheat, so while some not so well set engines can change their regulation properties when they get hot, electrinic regulator does not do that, so at least that is advantage over IC so it can easily compete with much stronger IC engines. 

[Tim Wescott]

As noted above, I can't implement my system with my current knowledge, and I have other irons in the fire and haven't gotten back to it yet. The drive stage looks suspiciously like a MOSFET stereo audio amplifier I made for someone back in the 80's.

If I were going to go down that road I'd start with an existing open-source ESC design based on a 32-bit ARM and just change the programming.  There are good candidates out there -- the one I looked at ("VESC" I think -- it was designed for skate boards at any rate) pretty much looked like what I would design.  Since I usually respond to any circuit or software that I didn't design with "oh, this must be crap" I suspect it's a winner.

If you DO make a braking ESC pay close attention to where the current from the motor goes during braking -- it's hard to schedule things to get the power to burn up in the motor and still have a smooth transition between acceleration and braking, it's hard to schedule things to get it to burn up in an off-board resistor (although it can be done), and randomly dumping large amounts of current into a LiIon battery pack is a Really Bad Idea.

[Igor Burger]

having flown a lot of real airplanes with propellers I remain more a devotee of P-factor management at least on the IC stunters with which I used to play!  I still scratch my head over the lack of interest in the phenomenon when we're talking about tethered, high thrust to weight ratio toys maneuvering primarily in the pitch axis while requiring consistent tension on the lines by which control input is applied. 

Depends what P-factor, there are 2 - one comes from wing AoA in tight turns, which is limited by keeping prop at 0 AoA also during tigh turn. Knowing the AoA during turns, their diameter etc, the model and its fuselage can be designed to have it at 0 AoA. ... done on Max Bee.

The other is effect of side wind which has also 2 components - one is yaw angle at prop wich makes it pitching up just like precession. So since it adds to precession it can be ballanced just like we balance precession - thrust line, LG drag and tail AoA ... that also answers why we need all those balancing forces stronger than comes from precession only and why those light props still need positive AoA on tail, negative angle on motor etc. Second component is simply side wind, here I do not know easy solution. Once I tried tilted stab (at angle to the wing) but it is not good solution because it makes opposite yaw force than necessary for compensating precession in turs. So the best solution for now I use (and probably everyone without knowing) proper handle neutral which can compensate it to some extent.

[Fredvon4]

These discussion always amuse and frustrate me

I am frustrated by the terms used...a forward mounted ENGINE is always a TRACTOR propulsion system and a rear mounted engine is USUALLY a pusher ...but not always

RH or LH (or CW vs CCW) I can figure out for Tractor configuration

BUT when the MFG and poster discuss Tractor or PUSHER props it can get confusing very fast....IMO a front mounted engine is NEVER using a PUSHER PROP

If I have a twin engine craft ...one rotating CW and one CCW BOTH propellers are Tractor props...just that one is made RH and one is LH
Confused....
If I have a single front mounted engine that I can set up to spin CW or CCW...the prop is still a Tractor ....PULLING and NOT PUSHING!

 I sure wish more prop makers would make identical props in both CW and CCW so I can have two of the same dimension and brand on my RH and LH TeeDee .049s...
sheesh

[Igor Burger]

If you DO make a braking ESC pay close attention to where the current from the motor goes during braking

There are braking ESCs, but they are not in our size (at least as far as I know). It needs "little" more components to be able to push it back to battery against its voltage for recuperation, so it is not trivial thing, plus some firmware, that is reason why it is used only on larger ESCs with price somwhere else than our. Good ESCs are expensive anyway, so I do not tjonh there is wiable way to do it.

Much easier way is to use prop with underchambered airfoil like we used on piped engines for the same reason (the airfoil drag gets high when blade comes to low slippage close 0 AoA or under - means in level flight or descending, while gets lower going up). Some flyers prefere them also on E motors, but they pay with battery capacity for it.

[Igor Burger]

These discussion always amuse and frustrate me

:- )))

It is historical problem, when we had only CW rotating engines, makers did "reversed" props prepared to be mounted on pusher engines flipped upside down. So they had mounted surface on top (instead of bottom) and reversed blades. They were marked as "pushers" because they were pushers. Since we have Emotors which can rotate both side it does not matter how props are done, but makers simply keep that "P" marking till now :- )))

[Frank Imbriaco]

Dean : Come out come out where ever you are...

[Brett Buck]

The timer is feed forward system, not feed back, I do not know if it can be called windup, I think windup is problem of feed back system with integrating component, but it is basically the same, power is lower than system needs (or asks for). However the ESC itself is feed back PID system. ESC has some anti windup routines inside. But since it is internal component, it cannot solve problem of outer regulator causing that problem.

   Right, that's why I wanted an integrated system, so I could control that myself, instead of a "black box".

     BTW, I am surprised to learn that the ESC itself is PID. What is the input signal supposed to represent, the torque or the RPM? I would have expected PI or PD, not both integral and derivative at the same time.

If I have to compare it to IC engine, it basically does exactly the same thing, even there are some analogies in settings, for example sensitivity is something like choke area (and sensitivity to fuel pressure differnces nose up nose down), piped engine has some upper and lower RPM where it runs defined by pipe geometry and baffles, timer allows to set them as parameters, but there is one difference favoring Epower - the regulator does not overheat, so while some not so well set engines can change their regulation properties when they get hot, electrinic regulator does not do that, so at least that is advantage over IC so it can easily compete with much stronger IC engines.

       That is more or less identical to a conversation Paul and I had at the 2015 Golden State contest - and in particular, how you can be *too* clever and have the engine brake work too strongly, if you permit the lower limit to be too low. Also that, once electric power density is good enough, the other advantages like perfect control, will make it a trump card.

    And, as was discussed before:

http://www.clstunt.com/htdocs/dc/dcboard.php?az=show_topic&forum=103&topic_id=183913&mesg_id=183913
 
     Brett

[Howard Rush]

Depends what P-factor, there are 2 - one comes from wing AoA in tight turns, which is limited by keeping prop at 0 AoA also during tigh turn. Knowing the AoA during turns, their diameter etc, the model and its fuselage can be designed to have it at 0 AoA. ... done on Max Bee.

The other is effect of side wind which has also 2 components - one is yaw angle at prop wich makes it pitching up just like precession. So since it adds to precession it can be ballanced just like we balance precession - thrust line, LG drag and tail AoA ... that also answers why we need all those balancing forces stronger than comes from precession only and why those light props still need positive AoA on tail, negative angle on motor etc. Second component is simply side wind, here I do not know easy solution. Once I tried tilted stab (at angle to the wing) but it is not good solution because it makes opposite yaw force than necessary for compensating precession in turs. So the best solution for now I use (and probably everyone without knowing) proper handle neutral which can compensate it to some extent.

Has anyone measured force and moment of a prop at an angle of attack experimentally?