Would this be counter rotating props?

[Charles Carter]

I came across a APC propeller label as a "p" as for pusher prop(reversed pitched prop) and I want to know if it I installed it on my twin and I install a regular prop on the other engine would that be of any benefit? If so would it matter if placed on inboard or outboard?  Do I flip the reversed pitched differently?

Charles Carter

[Steve Helmick]

A lot of 1:1 Scale twin engine planes had/have engines that turn LH & RH...the P-38 coming to mind. For some reason I'm not hip to, the props rotated such that the tips "came over top toward centerline", if that makes it clear. The P-38 had a simple way of making the engines rotate opposite, but I can't recall what it was right now.  

As to your model, I'd say yes...and no. If both engines are available in LH & RH, or will run both directions like a Cox reedie, sure. Otherwise, matching the prop to engine and airplane are more important. However, when one engine quits...level laps are best.  Steve

[Randy Cuberly]

I came across a APC propeller label as a "p" as for pusher prop(reversed pitched prop) and I want to know if it I installed it on my twin and I install a regular prop on the other engine would that be of any benefit? If so would it matter if placed on inboard or outboard?  Do I flip the reversed pitched differently?

Charles Carter

The simplest answer to your question is NO.  It would not be counter rotating props to simply install a reverse pitch propellor on one of the engines.  To have counter rotating props  which are to overcome torque effects and and somewhat help with precession ( although the effects of precession ar not cancelled  because precession still exists in each engine propellor the effect will be lessened because one is working in one direction and the other in the opposite direction unless they are one behind the other).  The primary purpose is simply to cancel the rolling effect of torque particularly during accelleration. 

Counter rotating props would need to be opposite in pitch to each other to still have the thrust of both in the same direction but the crankshafts would turn in opposite directions.  The "normal" pitch would be on the counterclockwise turning engine and the reverse pitch prop would be on the clockwise turning engine.  It wouldn't really matter which engine was in which position on a conventional twin.

With a reverse pitch prop on a counterclockwise engine the thrust would be reversed and the prop blast would be toward the front of the airplane in a conventional twin...I think that would not work very well.     

Randy Cuberly

[Trostle]

 For some reason I'm not hip to, the props rotated such that the tips "came over top toward centerline", if that makes it clear.
 

There have been several full size twin-engine aircraft where the props rotated in opposite directions.  This was a characteristic of the higher performance twins, like the P-36, the F-7F Tigercat, the Hornet/Sea Hornet and I think also the Mosquito.  The opposite turning props equalized the effects of torque. 

I will have to do a bit of research, but with these aircraft, it was found that some unfavorable characteristics were encountered depending on the rotation as the P-38 described above or the if the rotation was oriented the opposite way.  There is a reason why it was more favorable to do it one way over the other.

I think that reference to a counter rotating propeller system is primarily when two propellers are co-axial to each other.  There are many examples of this in full scale aviation.  The RC pattern people have used counter rotating props on there models using various systems to do so.  Randy Smith had a counter rotating propeller system using a single engine on a stunt ship some time ago.  A counter rotating propeller on a stunt ship would have the advantage of essentially eliminating torque problems as well as essentially eliminating almost all problems caused by gyroscopic yaw.

Keith

[pmackenzie]

FWIW, co -axial systems with props going in opposite directions are contra-rotating.

They are very good at reducing torque and P factor, and also removing excess funds from your wallet 

Pat MacKenzie

[Bill Johnson]

As stated, the engines (or at least the prop shaft) have to turn opposite directions on the two engines to have counter-rating props. Two coaxial props (2 props on the same shaft) are called something different, contra-rotating if my memory serves.

Normal configuration is to have, as viewed from the pilot's seat, the left prop turn clockwise and the right prop turn counter-clockwise. The reason is that an engine out will cause torque and P factor to cause the plane to yaw away from the dead engine. You never want to turn in to a dead engine. That leads to dead pilots.

The P-38 was different in that the twin boom configuration had some issues with normal counter rotation. I can't recall what but there was some reason they went opposite normal practice on it.

[Paul Smith]

The Westland Wyvern and Hughes XP-11 had counter-rotating props that failed and caused many Wyverns to crash and almost killed Howard Hughes.

The seem to work OK on the Russian Bear bomber.  I guess maybe the Russians know why they bothered with counter-rotating props on a four engine plane, but they're not talking.  Maybe they just had so much power they needed more props.

[Bob Hunt]

I think everyone here is confusing "counter rotating" with "contra rotating." I have counter rotating props on my electric twin; the tops of the props turn towards the canopy. Just like the P-38. The Wyvern, the XF-11 (not XP-11...), and the Russian Bear bombers have contra rotating props. In those cases there are two props being turned opposite to each other with either a gear box or a shaft inside a shaft arrangement. 

I can tell you this much from my experiences with the counter rotating props; all of the nefarious effects of P factor and spiral airflow seem to be eliminated with this set up. Closest thing to jet flight that I've experienced in a stunt model! 

Later - Bob Hunt

[Paul Wood]

Not trying to hijack the thread, but the P-38 props rotated with the tips moving away from the cockpit. Testing showed this provided a more stable gun platform. The down side was the loss of an engine at low altitude because this rotation caused the aircraft to become uncontrollable at full power settings. Engine failure during takeoff procedure was counter to logic and covered extensively in the pilot's manual. The up side was pilots found that using differential power settings during combat made the airplane very maneuverable in turns, an area that it was weak in prior to this discovery.

Paul

[Bill Johnson]

I think everyone here is confusing "counter rotating" with "contra rotating."

Not everyone. 

[Paul Smith]

I think the more popular usage of props on twins turning the way they do is mostly based on throwing gravel and other trash away from the fuselage and an not into it.  Basic reality, not high zoot theory.

[Trostle]

I think everyone here is confusing "counter rotating" with "contra rotating." I have counter rotating props on my electric twin; the tops of the props turn towards the canopy. Just like the P-38. The Wyvern, the XF-11 (not XP-11...), and the Russian Bear bombers have contra rotating props. In those cases there are two props being turned opposite to each other with either a gear box or a shaft inside a shaft arrangement. 

Later - Bob Hunt

Not trying to make a mountain out of an ant hill, regarding the definition of counter-rotating propos versus contra rotating props, but-----

I think the current and accepted nomenclature for a two propeller assembly turning on co-axial shafts is that such are called contra-rotating propos.  The propellers on twin engine aircraft with propellers turning in opposite directions are generally referred to as counter-rotating props.

Now, let's go back to the mid 40's at the end of the war when some "co-axial" propellers appeared on some aircraft.  One notable example is the single Martin Baker MB-5 powered by the Rolls-Royce Griffon engine.  In a four-page article on Martin Baker aircraft published in the November 30, 1945 issue of The Aeroplane magazine. in the section describing the MB-5, there is one paragraph that in part states:  "This aeroplane ... was notable for its rapid take-off and rocket-like climb ... attributable to the adoption of a counter-rotating airscrew..."  then, in the October 31, 1947 issue of that magazine, in a short descriptive section on the MB-5 aircraft,  the power plant is described as the "Rolls-Royce Griffon  ... engine driving two three-blade constant-speed, counter-rotating de Havilland airscrews..."  There are, however, a large number of other magazine articles that do describe the propellers on the MB-5 as contra-rotating including a previously "Restricted" 1946 Technical Report from Boscombe Down Aircraft and Armament Experimental Establishment.  (That report is only 69 years ago, but hey, this is important stuff!) 

Also, regarding the Hughes XF-11, the design was called the XF-11 for most of the period that the two aircraft existed.  The first was destroyed in a crash on its first flight in 1946.  The second  Hughes XF-11 underwent a change to its designation in 1948 to XR-11.  It is interesting to note that at this transition, the Republic four-engine XF-12 (designed for the same mission as the Hughes XF-11) was also re-designated as the XR-12.  That Republic XF-12 "Rainbow" was powered by four Pratt & Whitney 28-cylinder R-4360 engines (the same engines as the Hughes twin XF-11)  and is claimed to be the "worlds fastest four-engine piston-powered aircraft. 

Keith

[Bill Johnson]

Not trying to make a mountain out of an ant hill, regarding the definition of counter-rotating propos versus contra rotating props, but-----
Keith

Not at all, Keith. This is aviation history and good stuff! 

[Trostle]

Now, for more comments on conter-rotating props as on some twin-engine aircraft.  The subjects here will be the Lockheed P-38 and the deHavilland Hornet/Sea Hornet.

The single Lockheed XP-38 prototype had  Allison V-1710-11/15 engines "driving inward-rotating propellers."  The next pre-production batch of 13 YP-38's Allison V-1710-27/29 engines "driving outward-rotating propellers".  The several references I have on the P-38 do not explain the change in the directions of the propellers' rotation.  Photographs of operational P-38's in these references all appear to show outward rotating propellers.

Now with the Hornet/Sea Hornet:    The Hornet is more or less a scaled down and streamlined Mosquito using the same Rolls-Royce Merlin engines.  Reference material I have  indicates that the mosquito did not have counter-rotating propos.  The first prototype Hornet was flown without counter-rotating props.  It was later fitted with propellers that revolved in a "downward direction towards the fuselage."  I have one reference on the hornet that goes on to explain - "Airscrews rising inboard were tried first since they were preferable for fore and aft stability, but they blanketed the rudder at low speeds and rendered it ineffective for correcting swing on the ground.  Airscrews rising outwards were therefore fitted which initially showed unacceptable stability but the problem was solved by careful use of weights and correct size of tailplane."  Photographs in the several references I have on the Hornet and Sea Hornet aircraft show all of the operational aircraft with propellers that revolve in a "downward direction towards the fuselage."  Seems to be the opposite of the P-38.  Go figure.

So, which would be best in theory and in practice for our CL twin engine(motor) stunt models?  Bob hunt is having some success with his twin motor creation where he explains "the tops of the props turn towards the canopy".  What happens if the rotations are reversed?

Keith

[Paul Smith]

A CL stunter that needs optimum performance both upside right and upside down and both inside and outside loops is a lot different from a real plane flys mostly in the positive G mode.

Engine-out performance on a CL model is a non-issue.  If an engine quits you just lose.

[Elwyn Aud]

 The P-38 had a simple way of making the engines rotate opposite, but I can't recall what it was right now.  

If I remember correctly, the Allison V-1710 could have its rotation reversed by turning the crankshaft around.

[dale gleason]

P-38s originally had engines that turned both props the same direction, counter-clockwise (the American way)when viewed from the front.  Later, with a "left-hand" crank and other required mods, the P-38 had one prop turning counter-clockwise, the other clockwise (the British way). This configuration made for an easier handling airplane on takeoff...it went straight.  The P-38 with both props turning the same direction was a handful or footful, while the counter rotating version was easy to takeoff and land.

Whatever reference I recall this from, also said the crankshafts had to be marked so as to avoid confusion during maintenance.

dg

[Fred Underwood]

How soon for someone to use this in F2B  

http://www.rcuniverse.com/forum/electric-pattern-aircraft-385/9833118-contra-rotating-propeller-drive-f3a-2m-pattern-planes-17.html

[Larry Fernandez]

The P-38 had a simple way of making the engines rotate opposite, but I can't recall what it was right now.  

If I remember correctly, the Allison V-1710 could have its rotation reversed by turning the crankshaft around.

Actually the crank would remain the same, its the cam that would be ground for opposite rotation.
Not sure how the supercharger would be coupled, as it would be spinning in the opposite direction also.
Chevrolet offered a cam for the big block in the mid seventies that was reversed ground but I never understood why it would be beneficial
in a car or boat set up.

Larry, Buttfucco Stunt Team

[jim gilmore]

There have been several full size twin-engine aircraft where the props rotated in opposite directions.  This was a characteristic of the higher performance twins, like the P-36, the F-7F Tigercat, the Hornet/Sea Hornet and I think also the Mosquito.  The opposite turning props equalized the effects of torque. 



Keith

is the p-36 above a typo for p=38 ??

[Elwyn Aud]

Actually the crank would remain the same, its the cam that would be ground for opposite rotation.
Not sure how the supercharger would be coupled, as it would be spinning in the opposite direction also.
Chevrolet offered a cam for the big block in the mid seventies that was reversed ground but I never understood why it would be beneficial
in a car or boat set up.

Larry, Buttfucco Stunt Team

Looked up some more info as I usually know just enough to be dangerous. Here's a quote from Wikipedia-
 Another key feature of the V-1710 design was its ability to turn the output shaft clockwise or counter-clockwise by assembling the engine with the crankshaft turned end-for-end, by installing an idler gear in the drive train to the supercharger, camshafts, and accessories, installing a starter turning the proper direction, and re-arranging the ignition wiring on the right side to accommodate a changed firing order

[Bob Hunt]

 Bob hunt is having some success with his twin motor creation where he explains "the tops of the props turn towards the canopy".  What happens if the rotations are reversed?

Keith

That's a great question, Keith. Truth is, we can easily reverse the rotation of the motors by simply reversing any two wires on each motor and switching the props from one motor to the other. Why haven't we done this yet? We are having too much fun flying the twin in the initial mode (top of the props turning towards the canopy) to stop and experiment!  Really, this thing is so enjoyable and easy to fly that I doubt switching the rotation of the props would improve anything. To run a proper (no pun intended...) test program I suppose we should explore every possible configuration. On the twin thread that I started here years ago, Howard Rush posted a chart that showed all the possibilities. Some of it was tongue in cheek, but it did explain the possibilities. I promise that I will at least explore the option that has the top of the props turning away from the canopy. I'll bet, however, that I'll opt to change it back to the current rotation scheme quickly. It just feels so good and so right!

Later - Bob Hunt     

[John Cralley]

For what it is worth, the Wikipedia article on the P 38 says that the counter rotating props on the plane were originally setup to turn towards the canopy. Later they were changed to rotate away from the canopy because this made for a more stable platform for firing the guns. I've no idea why this would be the case.

[Balsa Butcher]

To add to the historical tone of this post: The original P-38 and early experimental (YP-38) versions had counter-rotating props. When the Brits learned of its performance (pre-Battle of Britian) they ordered a version for themselves. They specified a non-turbo engine with non-counter rotating props, in fact the same engine as was in the P-40's they were receiving from the US at the time. Like Pre WWII planners in the US, high altitude performance was not an issue. More important was commonality between both fighters which  seemed like a good idea at the time. 

Kelly Johnson advised against it but the Brits insisted. Prototypes were manufactured and delivered. They performed so poorly that the Brits turned them down and blamed Lockheed for designing a dog. The contract for 60 aircraft was completed but none were delivered. They were re-configured with counter rotating props and used by the US, some as fighters for home defense, most for advanced training. 

[Trostle]

To add to the historical tone of this post: The original P-38 and early experimental (YP-38) versions had counter-rotating props. When the Brits learned of its performance (pre-Battle of Britian) they ordered a version for themselves. They specified a non-turbo engine with non-counter rotating props, in fact the same engine as was in the P-40's they were receiving from the US at the time.

 Prototypes were manufactured and delivered. They performed so poorly that the Brits turned them down and blamed Lockheed for designing a dog. The contract for 60 aircraft was completed but none were delivered. They were re-configured with counter rotating props and used by the US, some as fighters for home defense, most for advanced training. 

One account I have regarding the history of the P-38's that the British ordered is that the US export policy at that time was that surperchargers could not be sold to foreign entities.  Thus, the several P-38's that were sent to the British were a disappointment.

Keith

[Trostle]

More on the counter-rotating props of twin engine aircraft:  Enter this saga the North American F-82.  From a fairly comprehensive two-volume history of North American Aircraft published in 1998, the following was written:

The XP-82 was first scheduled to fly in May 1945 but it was "discovered that the XP-82 had an unusual problem.  It wouldn't fly.  Nor would it fly the next day or the next."  A month later, with less fuel on board and "with some difficulty the airplane left the ground and completed a short flight."  The engines "of opposite rotation, had been so that the propeller blades swung upward toward the center.  This created an airflow that produced drag instead of lift and stalled the center section of the wing, approximately one-fourth of the total area.  After the engines were changed to the opposite sides, ... a perfectly normal take-off" was made.

So, the F-82 ended up with its counter rotating props turning the same way that the operational P-38 did, which was opposite of the deHavilland Hornet/Sea Hornet.  Go figure.

Keith

[Chris Cox]

For what it is worth, twin engine aircraft generally have what is considered to be a "critical engine".  This would typically be the left side engine.  The reason is because, when angle attack is factored in, the engine with the down going blade, produces more thrust than the blade travelling upwards.  Therefore, with a standard RH rotation engine, the down going blade (right side) produces more thrust than the up going blade (left side).  During single engine operations, to have a failed "right" engine is more favourable (neither engine is ideal, of course) than the right engine failing. The reason being, is that, should the left side engine fail, more thrust is being produced further from the aircraft centre-line by the right engine, thus requiring additional rudder to counteract. The aircraft will run out of available rudder sooner than had the right engine failed where the greater thrust would be found closer to the aircraft centre-line.  As a result, the "minimum control speed" will be based on the higher of the two speeds.

To make things even more confusing, the slipstream effect of the left engine is more effective in providing added yaw control than the right engine, therefore making the left engine even more critical should power be lost.

So, from a real aircraft perspective and the ability for a pilot to control and aircraft with an engine out, it would be best to have a RH rotation engine on the left side and a LH rotation engine on the right.  To do the reverse, such as has been suggested regarding the P-38 above, may indeed help the pilot aim the guns better, it would also mean a much higher minimum control speed should either engine fail.  In other words, engine failures in P-38's are not a good idea.

Cheers

[Chris Cox]

I should review before posting.  Slight error in one of my sentences (too many left's and right's).

Should have said, "During single engine operations, to have a failed "right" engine is more favourable (neither engine is ideal, of course) than having a "left" engine failing.

Regarding Keith's question of how Bob's airplane would fly if he reversed the rotation direction of both engines, there would indeed be a trim change due to the now reversed slipstream effect coming off the two props.  Not sure how big a change, or if it would even be felt, but technically, it would exist.

[Clancy Arnold]

Friends
I will try to clear up some misconceptions presented here.
First my sources.  I served as Lefty Gardner's crew chief at the Indianapolis Air Show in 1982.  At that time P-38 N25Y was owned and flown by Lefty Gardner.  Today N25Y is the Red Bull P-38.   I have a copy Of Martin Caidin's book "Fork-tailed Devil the P-38" which I have read many times.

The first P-38 built, the "XP-38" had inward turning Props.  That is at the top of the circle the tips were moving towards the Canopy.  All later versions of the P-38 had outward turning props.  The change was made, along with a bigger fillet between the wing and cockpit, to reduce turbulence.  See the picture below, the guy in the light colored shirt by the right main gear is me.
The only "P-38s" built to have both props turning the same direction were built on a contract for the RAF and were designated P-322's.  
Two things the picture shows are the Supercharger Air intake on top of the engine Nacelle and the missing Turbocharger air intake near the wing trailing edge.
The P-38 did not use shaft driven Superchargers, it used Exhaust driven Turbochargers.  That is except Lefty's N25Y which has shaft driven Superchargers.  The picture below was taken while Lefty and I worked to stop an oil leak on the right Supercharger.  An oil line fitting had not been lock-wired and had loosened up. I tightened and then lock-wired the fitting.  You want Pucker Factor!  On the next flight Lefty shut down and feathered the LEFT engine and did a slow roll down the flight line on the engine I had just worked on.  Check the March 1986 issue of Model Aviation starting on page 75 to see My P-38.
Clancy

[Balsa Butcher]

Thanks for that Clancy, The Reno air races haven't been the same since the Lefty and the "White Lightening" retired. The source of the Brit P-38 story is Warren Bodie's well researched book which claims to be the definitive book on P-38 history. It has a lot of info that is not found in other accounts.

[Russ Popel]

Thanks Chris ,I had just about finished a dissertation on critical engine etc. all that work for nothing. The only information I can offer on this thread is that the F7F engines both turn right hand as viewed from cockpit which is the normal reference point.

[Howard Rush]

I served as Lefty Gardner's crew chief at the Indianapolis Air Show in 1982.

Not Dave Gardner, who is, I think, right handed.  

The King said, "You're right, I'm left, she's gone."

Hope this helps.  

[Keith Miller]

Charles - see what you started?   

[Charles Carter]

Thanks gentlemen for your responses.  I find it very fascinating.  Bob Hunt loves his setup  and Windy Urtnowski said counter rotating props was a better setup on his twins and he highly recommended it.  Who does make or modify cranks for a OS Max 25 LA to turn in the opposite direction of stock?

Charles Carter   

[Randy Cuberly]

Thanks gentlemen for your responses.  I find it very fascinating.  Bob Hunt loves his setup  and Windy Urtnowski said counter rotating props was a better setup on his twins and he highly recommended it.  Who does make or modify cranks for a OS Max 25 LA to turn in the opposite direction of stock?

Charles Carter   

Fox made some for Fox 35's.  I don't think I've ever seen any for OS engines, but could be wrong!

The photo shows two L&J Fox 35's set up for a twin.  The one on the left has a reverse (Left Hand) crank in it.  They are otherwise identical.

Randy Cuberly

[Chris McMillin]

Hi Clancy,
All Allison V-1710 engines have superchargers on the rear case. They all provide supercharging through their geared drives to blower impellers that provide supercharging. In addition to this, as you know, the P-38 in stock form had turbochargers on top of the nacelle. These provided additional boost as the airplane climbed above the Allisons critical altitude of supercharging which was betwenn 15,000 and 25,000 feet depending on blower gearing but we'll just say around 20,000 feet the GE turbo boosted air to the Allison's internal blower and made it so it had high horsepower until way up high into the 40,000 foot altitude range.
 This is much like the B-17 which had "moderately" supercharged R-1820 Wrights, the B-24 which also had "moderately" supercharged R-1830 Pratts, and the P-47 Thunderbolt which had GE turbo just like the bombers and the P-38, and it had a single speed blower version of the famous R-2800 Pratt. These airplanes used the turbos to gain boost at altitudes that the engine driven blowers could not. However the engines did not have their internal blowers removed, they simply work in unison with the turbo.
 Most P-38's by the 70's had their turbos removed after their service or aerial mapping careers because of maintenance problems (usually they would have a turbo wheel fire from lack of lubrication seal on the large diameter wheels, and the fire thing is never good) and parts and manufacture of the GE turbos had ceased long ago, as well these things happened on new airplanes in service and shortly after for instance the turbo fire that forced Jim Ruble to abandon Glen McCarthy's highly modified Bendix racer P-38H which was flying at high altitude and high boost over Arizona in the 1947 race. It was a nearly new airplane with brand new engines and turbos when prepped for the race by the rich businessman's crew. These type failures lead to the incorporation of using different intake and exhaust systems customized for each airplane, though many approximate Lefty's airplane. His airplane was modified in the 40's under the ownership of JD Reed in Houston for pylon racing and had a couple of interesting configurations through it's career. When the turbos were removed an optimized gear ratio for best operation was chosen for the supercharger gear, but since the airplanes weren't used as Warbirds at high altitude anymore, it was usually not critical except for racing. 

Chris, great explaination of the aid counter rotating props give us in handling single engine ops in twins. Speaking of VMC, it really wasn't a known term in the WWII days and when I flew a couple of airshow seasons in the B-25 back in the 80's the airplane was operated in such a way that we broke ground between 90 and 100, and cleaned up in a shallow climb while trying to attain "Takeoff Safety Speed" of 145, which was a defacto VMC! The old manuals from WWII and even deep into the 50's are quaint to sometimes comical in their content compared to manuals and terms today. IIRC you have some experience in old airplanes so I would think you've run into this too.

Chris...

[Chris McMillin]

I came across a APC propeller label as a "p" as for pusher prop(reversed pitched prop) and I want to know if it I installed it on my twin and I install a regular prop on the other engine would that be of any benefit? If so would it matter if placed on inboard or outboard?  Do I flip the reversed pitched differently?

Charles Carter

Charles,
edit(Finally found that you have had an answer, very good and we all would love to see pics of your stuff)edit
It would if you had an engine to turn the pusher prop the correct direction. You'd need a crank timed for reverse rotation. If it was an electric motor model, simply change the rotation by swapping the wires on one motor.
It's supposed to help with trim on R/C models, and should be a benefit to some degree on C/L models.
Chris...

[Charles Carter]

Who can rework a stock crank and change the timing for reverse rotation?  The engine is a OS Max 25LA.


Charles Carter

[Howard Rush]

The benefit probably won't be much.  Gordan Delaney can give you the lowdown on how to make a twin fly really, really well.

[phil c]

Who can rework a stock crank and change the timing for reverse rotation?  The engine is a OS Max 25LA.


Charles Carter

I don't think you can rework a crank without welding on new material and remachining the intake port for reverse timing.  Not the best way to build a crankshaft.
You would probably have to just make a new shaft, not a trivial job with the heat treating and grinding required.
It would be something simple for OS to do, but they never have.

[Randy Cuberly]

The benefit probably won't be much.  Gordan Delaney can give you the lowdown on how to make a twin fly really, really well.

I agree with Howard.
After flying Gordon's twin Pathfinder with FP15's on it I decided it and Gordon were magic and there had to be some sort of witchcraft involved.  Truly a great flying airplane!  Both engines turned CCW but there are some different thrustline angles from one to the other.

Randy Cuberly

[Igor Burger]

How soon for someone to use this in F2B  

http://www.rcuniverse.com/forum/electric-pattern-aircraft-385/9833118-contra-rotating-propeller-drive-f3a-2m-pattern-planes-17.html

very soon ... even in negative numbers :- )))

[Randy Cuberly]

very soon ... even in negative numbers :- )))

Very interesting Igor!  Is that set up on co-axial shafts or gears or both?

Randy Cuberly

[Igor Burger]

it is geared inrunner

[Igor Burger]

................................

[Fred Underwood]

The internals of a gear driven though for RC

http://www.ralphschweizer.com/download/Contra%20User%20Installation%20Guide%20VIII%201-28-2012.pdf

[Randy Cuberly]

it is geared inrunner

So it appears to be geared co-axial shafts.  Who made the gear drive and do you know the approximate efficiency of the gear drive?
I'm wondering about energy usage for smaller battery systems like typically used for Control Line.

Just engineering curiosity for the most part.

Randy Cuberly

[Igor Burger]

yes it is coaxial shaft, but not planetary reductor like that R/C type from Fred's picures ... the unit is so far too heavy over 300g, but I hope they will learn how to make it lighter, I flew that model, but it was too heavy for my style of flying so I was not able to see advantages ... and BTW it is terribly noisy :- )))

... efficieny does not look to be a problem, battery was enough for those 2 props, so here I do not see problem. Model had my active timer and it stronly accelerated uphill, so it had certainly more thrust then combo before rework and battery was still enough. We have overloaded motors, so geared inrunner at higher rpm could be advantage and cotraprop can also reduce prop loses, so I think it will easily cover loses in gearbox.

[Fred Underwood]

Old Contra video, Randy Smith airplane



There is an old thread in Stunthanger

http://stunthanger.com/smf/index.php?action=printpage;topic=27784.0

[Randy Cuberly]

Old Contra video, Randy Smith airplane



There is an old thread in Stunthanger

http://stunthanger.com/smf/index.php?action=printpage;topic=27784.0

Yes but I think Randy Smith's system had only one shaft driven prop and the other was reverse pitch and free wheeling behind the front one.  In other words driven by prop wash from the front one.  Not a very efficient set up.  Lots of Drag.

Randy Cuberly