The Question LSA and CSU specifically of the Jab 230 d and Airmaster CSU.

[SSCBD]

 

Airmaster Propellers CSU state that:

Performance tests have shown up to:

• 33% shorter ground roll

• 10% better climb than fixed pitch prop

• 20% improvement in cruise and economy

Also provided was an Endorsement Specifically  J430 which is the 4 seat VH version

 

Sohrab Ghasimi - Jabiru J430There were some significant improvements in performance as follows: 20-30% reduction in ground roll, Higher climb rate, Smoother running and an increase of cruise speed to of 15 - 20%.

PDF from Airmaster of above information.

http://www.gap.aero/pdf/airmaster/Airmaster_propeller-systems-332-420.pdf

 

SO THE QUESTION

Why don’t Jab offer this option? To me its a huge increase of (not being rude) a sluggish Jab 230 specifically looking at HOT 30c plus weather and short strips.

Yes it costs a lot - 8k but worth it in my opinion for a 30% ish, take off distance reduction.  

From Jab 230 quoted  seal level etc

Roll of  226m

To 50ft  354m

So in my head 30% reduction takeoff is 100m, so 250m ish to 50 ft.  

Yes I have GA and LSA CSU in other aircraft but cant find any exact reason for Jab 230D not having them as option.

If correct the cruise speed increase of 15to 20% would push the Jab right up to the VNE of 140kts but still can be managed.

ALSO

As those who know and fly CSU equipped, GA or RAA planes when you select landing mode or push the blue lever its like a brake dragging or slowing the aircraft.

This would also decrease the float and landing roll.

So anyone know of other Jabs with CSU or why the factory won’t put them on as a option.  It a option I would put on after anyway.

Edited September 25, 2020 by SSCBD

[Thruster88]

I think the performance gains are exaggerated. The picture shows the performance of a Cherokee 6 with 260hp fixed pitch v 260hp constant speed v 300hp constant speed. This aircraft is only a little faster than a jab 230 so I think a valid example. The fixed pitch Cherokee 260 is obviously optimised for cruise but the take off and climb do not suffer that much. Naturally the salesman were able to convince nearly everyone that they should get the CS or people would question their manhood. 

 

In my RV6-A winding the blue knob in really does put the brake on, great for getting down to flap extension speed.

 

[facthunter]

I'd be a bit worried about the torsional harmonics. and reliability .( Chucking blades) A 2 blade wooden prop is best in this regard. Don't forget the Schneider Trophy speed planes were all fixed pitch. Not many of our planes actually NEED a CS prop They don't go fast enough.. I've flown some planes that have a wood prop and a metal prop option and the wood prop is nicer feeling. It won't be quite as efficient or expensive and if you crash there's less damage to the engine. Nev

[old man emu]

On 25/09/2020 at 5:16 PM, facthunter said:

Not many of our planes actually NEED a CS prop They don't go fast enough..

True enough, but would you say that the engines of "our planes" don't have the wide range of horsepower output that the CSU takes advantage of?

 

Would you agree that a CSU performs a similar function to a car gearbox in making the best use of the available horsepower?

 

I hate talking about horsepower. I would rather go to the more basic level and talk about torque. Torque is simply a force acting on something from a distance (i.e. a piston pushing down on a crankshaft, using that leverage to rotate it), while horsepower is torque multiplied by RPM, or a measurement of how quickly that torque can be applied to do work.

 

Torque, also referred to as a moment of force, is a measure of rotational force and is quantified as force x distance, where distance is measured perpendicular from the axis of rotation. In imperial units, the unit of measurement is the pound-force foot (lbf. -ft.) In metric  it is Newton metres.

.

In practice, the amount of torque that a particular engine installed in its place of employment produces varies with the amount of fuel/air mixture introduced to it (how far the throttle is pushed).

 

 

Horsepower is a measure of how much Work can be done in a unit of time.

Work = force x (distance an object is moved), In calculating horsepower in a rotating system such as a piston and crankshaft, velocity of the crankshaft is used. That velocity is reported as Revolutions per minute (RPM).

 

Horsepower is the product of torque and rotational speed of the crankshaft

HP = Torque x RPM

Since the units of Torque and RPM don't match, a conversion factor is required so that the answer is reported in Watts or ft lbf/min

 

So, for Imperial units HP = (Torque x RPM)/5252

 

The only time that we like to avail ourselves of all the HP an engine can produce is during takeoff, but I wonder if relying blindly using full throttle at takeoff, then reducing power a short time after rotation is a major cause of EFATO. (Meat for another thread)

[skippydiesel]

I agree with all of the proceeding comments BUT I have this powerful urge to "improve" on near perfection. 

 

Yes yes I know and understand all the logical arguments for staying with my very nice  2 blade ground adjustable BUT if I had the spare dosh I would certainly look into an electric CSP.

 

So with all that dealt with, what would be your comments on the following:

 

• Why do most CSP supplier/manufactures push 3 bladed props for Roptax 912 ULS applications ? Most but not all have  a lighter/simpler two blade unit(s) hidden away somewhere but you have to look for it.
• Why do hydraulic CSP, for Rotax 912 ULS, fairly consistently have lighter installed weight quoted?
• Why does the actuating motor/system have to be in the propeller hub ,when it could conceivably be mounted above the crankcase and deliver its pitch movements through the hollow Rotax 912 propeller shaft?
• Your recommendation(s) on the  "best bang for the buck" supplier?

 

[SSCBD]

May I suggest you are missing my point,  of the performance increase in takeoff distance / roll including reduced - not floating on landing. It is the Aussie Summers with density altitude and tight strips that makes this system attractive with a fully loaded Jab 230 - if the performance  increase reported is correct, which I would expect from other LSA aircraft i have flown with CSU. But I have zero information on the Jab 230 and the gen4 3300 engine real time increase. Any Jab owners can put any light on why? 

   

[facthunter]

The car analogy is not very appropriate.OME. as, Cars have to idle, accelerate and run at widely varying speeds. A planes cruising speed is in quite a narrow range. At higher cruise levels you will be at full throttle, but certainly not at full power. due density height considerations..

  The torque of the engine depends on what torque the prop can absorb as well as the engine's characteristics enabling it to produce the torque. IF planes capable of 350knots can run a fixed pitch prop something at up to 130 knots won't have much difficulty "Matching" the prop to the task. You will lose a bit on take off but it's not of a great order. There's also COST, weight and reliability. Prop blades want to go to fine if the mechanism fails (centrifugal turning moment). If they go fine the RPM required to stay above stall may not work. (Prop overspeed) It also makes the prop more likely to fail as well as the engine. The useable range of rpm's with pistons does give a cruise range and is used also with constant speed props to get max range but works with fixed pitch as well..

 There IS an advantage but is it always worth it with cheap simple and safe planes when downsides are taken into account?  

  Skippy, the hollow driveshaft offers an ideal way to control a CS or inflight variable  prop but any linkage  must be kept play free or it will be imprecise and wander. At least it's simple and relatively reliable. However the prop must be kept in control or the engine can't be used. The usual way is pitchlocks but that's not practical on cheap  stuff. Nev

[facthunter]

3 minutes ago, facthunter said:

The car analogy is not very appropriate.OME. as, Cars have to idle, accelerate and run at widely varying speeds. A planes cruising speed is in quite a narrow range. At higher cruise levels you will be at full throttle, but certainly not at full power. due density height considerations..

  The torque of the engine depends on what torque the prop can absorb as well as the engine's characteristics enabling it to produce the torque. IF planes capable of 350knots can run a fixed pitch prop something at up to 130 knots won't have much difficulty "Matching" the prop to the task. You will lose a bit on take off but it's not of a great order. There's also COST, weight and reliability. Prop blades want to go to fine if the mechanism fails (centrifugal turning moment). If they go fine the RPM required to stay above stall may not work. (Prop overspeed) It also makes the prop more likely to fail as well as the engine. The useable range of rpm's with pistons does give a cruise range and is used also with constant speed props to get max range but works with fixed pitch as well..

 There IS an advantage but is it always worth it with cheap simple and safe planes when downsides are taken into account?  

  Skippy, the hollow driveshaft offers an ideal way to control a CS or inflight variable  prop but any linkage  must be kept play free or it will be imprecise and wander. At least it's simple and relatively reliable. However the prop must be kept in control or the engine can't be used. The usual way is pitchlocks but that's not practical on cheap  stuff. As a minimum you need to have the fine pitch stop set to provide a safe speed (margin above stall ) which enables you to stay flying for a while if things go wrong .Nev

 

[jackc]

Sorry, but it’s another thing to go wrong,  if you are looking to eek out every last bit of performance from your plane because you are not happy with its current performance, get another plane 🙂

You can only make a pig fly so fast!!!

[skippydiesel]

1 hour ago, jackc said:

Sorry, but it’s another thing to go wrong,  if you are looking to eek out every last bit of performance from your plane because you are not happy with its current performance, get another plane 🙂

You can only make a pig fly so fast!!!

Very strongly put. Unfortunately, wrong (no offence intended). Consider the following:

Short very marginal strip (this is my situation). 

With a ground adjustable or fixed pitch, you have no option but to select for or pitch your prop for climb advantage or even best climb performance. All TO’s/landings will be short field. Do you agree so far?

This “climb” prop will have a negative impact on cruise performance and therefore fuel consumption/trip - most would find this to be an undesirable ramification of selecting a fine pitched prop. Agreed?

So along comes the solution - a way of having the best of both situations - the ability to select for fine pitch for best short filed/climb performance and then select a courser pitch for best cruise and economy - an inflight adjustable propeller (the most common of which seems to be the Constant Speed).

I have a mate who, like you, pores scorn on having any sort of inflight adjustable prop but then he operates off a long strip, with very good flat approach/departure conditions (no trees, rising ground, power lines, buildings, etc). He has his ground adjustable set for optimum cruise and doesn’t even notice the negative impact this has on his take off roll & climb performance. This works well for him but would have me in the trees.

Another situation, that suites a CS reversing prop, is amphibians – I have no experience but am told that its very handy to have a way of slowing and even backing your aircraft.

Lastly – a lot of motor gliders have feathering props to minimise drag.

The way I see it is there are three penalties that the procurer of an inflight adjustable must accept:

1.      Greater purchase & maintenance cost

2.      Higher weight, usually well forward, so likely to impact on W&B

3.      Increased complexity and potential for failure

Offsetting the above is the potential for greater control over aircraft performance.

[Thruster88]

59 minutes ago, skippydiesel said:

Very strongly put. Unfortunately, wrong (no offence intended). Consider the following:

Short very marginal strip (this is my situation). 

With a ground adjustable or fixed pitch, you have no option but to select for or pitch your prop for climb advantage or even best climb performance. All TO’s/landings will be short field. Do you agree so far?

This “climb” prop will have a negative impact on cruise performance and therefore fuel consumption/trip - most would find this to be an undesirable ramification of selecting a fine pitched prop. Agreed?

So along comes the solution - a way of having the best of both situations - the ability to select for fine pitch for best short filed/climb performance and then select a courser pitch for best cruise and economy - an inflight adjustable propeller (the most common of which seems to be the Constant Speed).

I have a mate who, like you, pores scorn on having any sort of inflight adjustable prop but then he operates off a long strip, with very good flat approach/departure conditions (no trees, rising ground, power lines, buildings, etc). He has his ground adjustable set for optimum cruise and doesn’t even notice the negative impact this has on his take off roll & climb performance. This works well for him but would have me in the trees.

Another situation, that suites a CS reversing prop, is amphibians – I have no experience but am told that its very handy to have a way of slowing and even backing your aircraft.

Lastly – a lot of motor gliders have feathering props to minimise drag.

The way I see it is there are three penalties that the procurer of an inflight adjustable must accept:

1.      Greater purchase & maintenance cost

2.      Higher weight, usually well forward, so likely to impact on W&B

3.      Increased complexity and potential for failure

Offsetting the above is the potential for greater control over aircraft performance.

In the example (post 2) the take off to 50 feet was only reduced from 415metres fixed pitch to 378meters with the constant speed prop. This is a full hydraulic prop which will keep the engine at maximum horsepower,  2700rpm at all times during the takeoff and climb,  it doesn't get any better. There is improvement but is it really that significant? 

 

Another down side for the constant speed prop is it will mask engine power loss. With a fixed pitch any loss of power (sunken carb float anyone🤔) will result in reduced RPM, with constant speed RPM will stay the same until power loss is significant 

[RFguy]

I am used to watching the torque gauge in a helicopter.(as a pax) 

 

Does any setup with these fancy props allow for such metering ?

 

sunken float ha ha.

[skippydiesel]

1 hour ago, Thruster88 said:

In the example (post 2) the take off to 50 feet was only reduced from 415metres fixed pitch to 378meters with the constant speed prop. This is a full hydraulic prop which will keep the engine at maximum horsepower,  2700rpm at all times during the takeoff and climb,  it doesn't get any better. There is improvement but is it really that significant? 

 

Another down side for the constant speed prop is it will mask engine power loss. With a fixed pitch any loss of power (sunken carb float anyone🤔) will result in reduced RPM, with constant speed RPM will stay the same until power loss is significant 

 

Hi Thruster - In my situation (all TO/Landings are short field)  I would gain only very little, from a CSP on take off role and climb out BUT would hope to se significant improvement in cruise. 

 

To me there is no question that there would be improvements in engine/prop  performance delivery - the Q is would it be cost effective ? I think the cost, about $8-12 K, is unlikely to be recouped in performance gains  (RAA class aircraft)  but then why are we flying at all?

 

In regard to your sunken carby float scenario - dont know. I suspect that even with a CSP there would be a power/rpm reduction especially at max rpm TO power. I have my CSP endorsement. from way back in my GA days but have no recollection of such a power loss being discussed or for that matter how any such power loss would be "masked" by a CSP.

[walrus]

Thruster and RFguy, yes. You have to monitor fuel flow as well as manifold pressure to ensure your CS prop is not masking power loss. You are taught that amongst other things in a CS endoresement.

 

A  CS prop saves you from the niggling crap you can see on American threads: “what did you set your prop to? Yadda, Yadda. A CS prop is almost always, by definition, at the optimum pitch for the manifold pressure you have selected.

 

Someone told me “you can buy a lot of fuel for the price of a CS Prop”. True, but I can’t stuff money in my fuel tanks. I bought one for range considerations. Coincidentally, the weight saving from a lithium battery balances out the extra prop weight.

 

Confession: I love doing Caribou style steep approaches. A CS prop set full fine is a great airbrake.

[Thruster88]

8 hours ago, skippydiesel said:

 

Hi Thruster - In my situation (all TO/Landings are short field)  I would gain only very little, from a CSP on take off role and climb out BUT would hope to se significant improvement in cruise. 

 

To me there is no question that there would be improvements in engine/prop  performance delivery - the Q is would it be cost effective ? I think the cost, about $8-12 K, is unlikely to be recouped in performance gains  (RAA class aircraft)  but then why are we flying at all?

 

In regard to your sunken carby float scenario - dont know. I suspect that even with a CSP there would be a power/rpm reduction especially at max rpm TO power. I have my CSP endorsement. from way back in my GA days but have no recollection of such a power loss being discussed or for that matter how any such power loss would be "masked" by a CSP.

I am not sure how the electrically adjusted propellers handle the takeoff situation, do they adjust to and stay at pre determined position or do they make adjustment as airspeed increases to keep a constant RPM. If it is the former then yes any loss of power will result in reduced RPM just like a fixed pitch. If they adjust automatically then power loss can be masked. If I simulate a power loss in the RV at low cruise power by excessive leaning there is no change in rpm or manifold pressure, the engine just runs a little rough and there is a loss of airspeed. As the power falls the prop just goes fine. The flow meter into the carburetor will show a reduction but it jumps around a lot and is of limited use. Fuel flow gauges on GA types with injected engines are just pressure gauges, a partially blocked injector (had one in the shop this year) will still show normal fuel flow.

 

In summary I am saying just be careful with constant speed props.  Ignition, carburetor faults or burned valves that would show up as reduced RPM in a fixed pitch can be masked by a constant speed automatically adjusting to a finer pitch.

[walrus]

They adjust to keep constant rpm. Fuel flow and MAP ‘should” confirm you are making rated power, but I guess an engine analyser with individual EGT’s would be needed to absolutely confirm there isn’t a burned valve or clogged injector somewhere.....

[facthunter]

Constant speed props DO mask torque loss. A torquemeter is  a very complex thing and hard to organise, IF your prop can go so fine as to create negative thrust you will not be able to maintain flight if that happens accidently. There's a whole new world of issues you bring into the equation with variable pitch props. There is a distinct safety aspect to a lot of them as well as cost and weight.. I love them when they are there on a plane that justifies it..Like particularly turbines where obviously the engine will not take fixed pitch in the starting cycle. . without some problems. Nev

[SSCBD]

1 hour ago, facthunter said:

Constant speed props DO mask torque loss. A torquemeter is  a very complex thing and hard to organise, IF your prop can go so fine as to create negative thrust you will not be able to maintain flight if that happens accidently. There's a whole new world of issues you bring into the equation with variable pitch props. There is a distinct safety aspect to a lot of them as well as cost and weight.. I love them when they are there on a plane that justifies it..Like particularly turbines where obviously the engine will not take fixed pitch in the starting cycle. . without some problems. Nev

FT A lot of CSU's are being fitted to RAA  LSA aircraft these days specifically with Rotax engines. My Question is why I cant see any on GEN4 engines. 

And as I stated - the performance increase Quoted by  - Airmaster Propellers CSU state that:

 

Performance tests have shown up to:

• 33% shorter ground roll

• 10% better climb than fixed pitch prop

• 20% improvement in cruise and economy

Also provided was an Endorsement Specifically  J430 which is the 4 seat VH version

 

Sohrab Ghasimi - Jabiru J430There were some significant improvements in performance as follows: 20-30% reduction in ground roll, Higher climb rate, Smoother running and an increase of cruise speed to of 15 - 20%.

PDF from Airmaster of above information.

http://www.gap.aero/pdf/airmaster/Airmaster_propeller-systems-332-420.pdf

 

 

SO if you operate in say far nth QLD and tight strips in a Jab 230 for example - and you had the money WHY NOT Have the extra performance. 

 

 

 

 

[facthunter]

I wouldn't put a CS prop on a Jab myself. I doubt the makers recommend it as well.  I would also have to verify those claims. Better than what? A wood prop is generally about 8-10% less efficient than a metal of exotic carbon etc prop because of it's better dimensioning.

  If a planes performance is marginal ANY improvement will  seem exaggerated.. A matched for  cruise, prop will be as good as a CS or maybe even better as the WHOLE length of the blade will be designed for that speed... The pivoting part of the adjustable blades are slimmed down and not conducive to long life. A blade off usually means you aren't going anywhere but down and the motor may be hanging at a bad angle or missing.. Nev

[Jaba-who]

Getting back to your original question. “Why don’t Jabiru offer them as an option”. 

 

Simple -

Jabiru already support several propellers models/ brands because they have trialled them and feel confident that they will not induce increased loads on the Engines components  ( in particular the fly wheel and the associated bolts.)  

 

To trial other brands takes time and money and may have very little or no financial return for them. They offer a product that works well  for most people out of the box. 
There are so many other brands of propellor available and so many more that will become available in the future that it would be an endless costly exercise to try to test and endorse them all. 

If an owner wants to change the already reasonable propellor for something Jabiru have not trialled, and have no control over, then quite reasonably Jabiru says you do it at your own risk.  

Exact same reason why if you bought a new car that works fine and you decide you want to change engine components for parts made by another manufacturer. You would never expect the car manufacturer to offer and endorse someone else’s brands engine components. 
 

Edited September 28, 2020 by Jaba-who

[Jaba-who]

5 hours ago, SSCBD said:

FT A lot of CSU's are being fitted to RAA  LSA aircraft these days specifically with Rotax engines. My Question is why I cant see any on GEN4 engines. 

And as I stated - the performance increase Quoted by  - Airmaster Propellers CSU state that:

 

Performance tests have shown up to:

• 33% shorter ground roll

• 10% better climb than fixed pitch prop

• 20% improvement in cruise and economy

Also provided was an Endorsement Specifically  J430 which is the 4 seat VH version

 

Sohrab Ghasimi - Jabiru J430There were some significant improvements in performance as follows: 20-30% reduction in ground roll, Higher climb rate, Smoother running and an increase of cruise speed to of 15 - 20%.

PDF from Airmaster of above information.

http://www.gap.aero/pdf/airmaster/Airmaster_propeller-systems-332-420.pdf

 

 

SO if you operate in say far nth QLD and tight strips in a Jab 230 for example - and you had the money WHY NOT Have the extra performance. 

 

 

 

 

Don’t need it! 
(Definitely Don’t need it at the cost of no warranty ) 

[Thruster88]

On 28/09/2020 at 10:23 AM, facthunter said:

Constant speed props DO mask torque loss. A torquemeter is  a very complex thing and hard to organise, IF your prop can go so fine as to create negative thrust you will not be able to maintain flight if that happens accidently. There's a whole new world of issues you bring into the equation with variable pitch props. There is a distinct safety aspect to a lot of them as well as cost and weight.. I love them when they are there on a plane that justifies it..Like particularly turbines where obviously the engine will not take fixed pitch in the starting cycle. . without some problems. Nev

It appears the prop went very fine in this case, ie loss of normal glide performance. Certified constant speed propellers have pitch stops. I am not expecting a meaningful follow up report from raaus.

 

21/9/2020	Jacobs Well	QLD	EDRA Aeronautica	Super Petrel LS	Rotax	912ULS	STATUS: Under investigation EXTRACT FROM REPORT SUBMISSION: After fitting a new experimental pr...
STATUS: Under investigation EXTRACT FROM REPORT SUBMISSION: After fitting a new experimental propeller and IFA system a number of ground runs and several cancelled take-off runs appeared to prove the system operational and ready for flight. Take-off and initial climb out was normal to 250 feet at 65 knots with IFA prop control set to 5400 in AUTO setting which maintains RPM thru pitch adjustment regardless of throttle setting. At 250 the engine RPM started to increase to 6000. Throttled back and the aircraft started to slow down dramatically, attempted to adjust pitch control in MANUAL setting did not improve airspeed, immediately pitched nose down to maintain glide but steeper than usual angle required to maintain flying sped best speed attained was 50 knots. Propeller control was then set to manual override in EMERGENCY setting, however it was determined that height and airspeed were decaying rapidly and opted to alight aircraft on a lake of nearby sand mine that was to the right of runway centre line. Selected wheels up and flew aircraft at 50 knots with full power the final 300 meters horizontal distance and touched down approx. on the shoreline of the lake which was thick mud but skidded into deep water. Touch down was very heavy and engine mounts flexed significantly enough for prop to strike the fuselage deck and gouge small hole. The aircraft remained afloat and was stable but engine propellor vibrated during plow taxi to water edge. Recovered aircraft to dry land. Possible failure of slipper clutch yet to be verified

[walrus]

Airmaster CSU props have backup mechanical pitch stops to prevent this type of failure. You set them as partof the installation routine.

[skippydiesel]

On 28/09/2020 at 5:08 PM, Jaba-who said:

Don’t need it! 
(Definitely Don’t need it at the cost of no warranty ) 

As I suggested - this is not a need, for most people/situations, its a want. This want is entirely consistent with wanting a RAA registerable aircraft and most other recreational activities.

[Kenlsa]

More weight, complexity and cost.
Reduced useful load.

Followed by further cost at service intervals.

Further followed by more paths for failure.

And further followed by immediate stress selecting your out landing spot.

Ken