Prop Selection

[skippydiesel]

8 minutes ago, facthunter said:

Yes the article is quite reasonable. ............................................................ wheras a properly "tailored" fixed pitch for a particular  speed. CAN  IF this is done for your cruise  speed it will out perform any CS at that speed as well as being lighter and cheaper and more reliable..  Nev

Hi Nev - I have no doubt that you are correct however the question is: where to find such an air screw ??? and how will effect my TO/Climb out ???

 

Seems to me that the CS prop is mans attempt to achieve the best compromise in propeller application for most situations.

 

If you just want great TO/Climb performance there is a prop for your aircraft.

 

If you just want best cruise (speed/economy) again there is likely to be a prop out there somewhere.

 

BUT how do you archive some reasonable semblance of both in the one installation?? without going to a CS

[skippydiesel]

 

This quote from the last paragraph of the Foxbat article pretty much says it all:

 

"My conclusion – while a CS/IFA prop may have big advantages on a more slippery, faster cruising aircraft, the benefits for the Foxbat are more debatable. If you want to be able to run on the limit for the complete flight envelope (and your pocket can handle it), maybe a CS/IFA prop is worth it. Me? I like the simplicity of the Foxbat and the take-off performance is more than enough for all but the most extreme conditions. So I’m happy with one of the standard props."

 

So is my ATEC Zephyr in the "more slippery, faster cruising aircraft" category or is it more akin to the Foxbat ????

[facthunter]

Depends on where you operate from. Yes a lot of people play around with trying to match props with nothing but frustration. often ending up with the original prop supplied by the maker back on. . I believe under 120 knots cruise I'd stay with fixed pitch and get a good cruise prop and put up with the relatively small degradation of climb performance... or even increase climb speed  if not over trees just after take off which is bad news anyhow. Nev

[skippydiesel]

9 minutes ago, facthunter said:

Depends on where you operate from. ....................................................................................f not over trees just after take off which is bad news anyhow. Nev

 I think you must know where I fly from - got it all;

 

 

Almost all TO to the east Landings to the west. In 11 years have TO to west twice and Landed to east once. Personal max tail wind component 10 knots.

 

A lot of tall trees at eastern end

Trees power lines , stock yards at western end

About 100 m, sort of level area, at western/stock yard end thereafter sloping steeply to east befor crossing ephemeral spring at bottom of slope. Spring can reduce available landing distance by 1/3.

 

[kasper]

33 minutes ago, skippydiesel said:

So is my ATEC Zephyr in the "more slippery, faster cruising aircraft" category or is it more akin to the Foxbat ????

Hard to tell if you will be in the fast/slippery or moderate and draggy camps with the Zephyr.

 

I'll offer two ways to look at and compare to other airframes to decide which camp you are in:

1. hp/kn of cruise.  The more HP you use the less you are slippery and the more benefit you may get from CS prop

2. difference in Kn for stall and cruise - the bigger the gap the more slippery is your airframe and again possibly benefits of CS prop

 

1. is a more absolute number as it disregards the flap effect and allows very simple calc and compare between airframes ... if you trust the available 'advertised' cruise @ power settings published for aircraft ... CAFE performance data is far better and sorry to say it but even there fixed pitch on light aircraft tend to do as well if not better than CS props.

 

2. allows you to take into account the low end performance which is more of an issue on short takeoff performance.

 

Either way you take your choices and live with the outcomes.

 

This bit is thread drift - For me - I have played around over the past 30 years with fixed, ground adjustable and a couple fo CS systems on ultralights.  My strong preference is after the years to have a ground adjustable prop unless a fixed pitch wooden is already known for the airframe.  With ground adjustable I can fine tune to target climb/cruise balance as I want to get to a final point where I just leave the damn thing alone and go fly with a monitor and manage engine performance by known RPM/Throttle/fuel burn settings.

 

Cheers.

[skippydiesel]

Kasper - Thanks for that.

 

My actual performance figures (speed in indicated knots) pilot (me) & full fuel is:

 

Static  5200 rpm

Elevation 1100 ft ASL

Ground role sub 100 m on grass

Rotation 40 knots

Climb out 1500 + ft /min @ 60-80 knots - 5200-5500 rpm

Cruise climb  5400, above 2500 ft, 100 knots,500 + ft/min

Cruise 100-110 knots 5000-5200 rpm  - sub 13 - sub 14 L/hr.

Have seen 120 knots, strait & level, at 500 ft (beach run)

Stall  - sorry dont have a no flap figure but in landing configuration sub 30 knots

Final approach 55-45 knots

Planning  - conservative  14 L/hr

 

Factory claim 125 knots for max cruise. If anything they tend to be a little conservative. There is complexity/differences in the standards as applied to the European compared with Australian operating environment 

 

So what think you - slippery? or draggy? or somewhere in between??

[spacesailor]

I am told the, scimitar prop will  " bend " giving a little pitch reduction on take-off,

Max revs on take-off and A corser pitch on cruise revs.

spacesailor

[skippydiesel]

1 hour ago, spacesailor said:

I am told the, scimitar prop will  " bend " giving a little pitch reduction on take-off,

Max revs on take-off and A corser pitch on cruise revs.

spacesailor

Hi Spacesailor - I have read commentary on this sort of propeller befor - seems a little like magic to me - I get the idea but does it  work effectively in application ? If it does do the blades fatigue over time ? If so what is their operational life expectancy ?

[Downunder]

4 hours ago, skippydiesel said:

So is my ATEC Zephyr in the "more slippery, faster cruising aircraft" category or is it more akin to the Foxbat ????

Your aircraft is the fast slippery one, far more able to use the benefits of an inflight adjustable prop.

The Foxbat hits an aerodynamic brick wall at about 90 kts or so.

The effort to get much more speed is beyond an adjustable prop and the power supplied.

I think you would need a very specific reason to fit one to a Foxbat/stol aircraft with the limited overall benefits given.

[skippydiesel]

All good stuff!

 

I thought I might get some comments on the Airmaster recommendations versus my choice - anyone?

[Blueadventures]

Skippy are you wanting a CS prop so you can use its braking effect on landing and pull on take-off then set for best WOT or cruise. That way you get the best slow down, climb and straight and level performance possible.  With your prop damage is a contributing factor the low drag of the aircraft and over shoot on landing or a collapse of nose wheel event?  From the air field you describe I can see benefits of CS prop at the above four phases of flight.

 

[skippydiesel]

Hi Blue - I am very happy with the performance of the Fiti  2 blade ground adjust in: 

• Ground Role - sub 100 m on grass
• Climb out - 1500 ft +/min @ 60 knots

The prop is very effective even, at idle (no brake applied) it will move the aircraft quit rapidly on relatively smooth  level ground. If I reduce my idle further the engine will stall.

• Approach to landing. The prop is still delivering  some thrust in the landing phase - not so good but manageable. Combined with a tail wind, the unwanted thrust can make things a bit too interesting at times.

I would like my new prop to deliver at least equal ground role & climb out to the Fiti . Then give me a better cruise speed that I can chose to maximise economy or speed, as the whim takes me. Then in the landing phase, reduced thrust at idle, with the option of a full power go round should it be required.

 

[Kyle Communications]

As a matter of interest Eprop are developing a CS. I asked them a few things and wont be available until mid next year

They are currently testing their versions now but no pricing yet

Here is some info I got back from them

 

"Our range of variable pitch propellers is currently being tested. Deliveries not before mid-2021, and no prices for the moment, because we have not finished the production machines, so we can't calculate the cost prices.
The performance is amazing and the weight... 3,4 kg for the 3-blade, 4 kg complete with spinner all inclusive."

 

4kg complete is amazing thats more than 2 kg less than a Bolly std prop with the extension for a savannah

 

 

[skippydiesel]

1 hour ago, Kyle Communications said:

A.........................................................

 

"Our range of variable pitch propellers is currently being tested. Deliveries not before mid-2021, and no prices for the moment, because we have not finished the production machines, so we can't calculate the cost prices.
The performance is amazing and the weight... 3,4 kg for the 3-blade, 4 kg complete with spinner all inclusive."

 

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

 

 

That's great Kyle - would they like an Australian test aircraft/pilot?

 

Weight is amazing. This is addressing one of the main drawbacks to CS  props - the changes to W&B and reduction in "pay load". Does this weight include all the actuating mechanism/system ??

 

The Airmaster recommended (for my engine but I dont think the aircraft) prop is 11.2 kg over the nose. This is 7.6 kg more than the existing prop. Given the location, I would suggest that this is a significant change for a 297 kg aircraft. My Airmaster choice is a little lighter at 9.1 kg - a step in the right direction.

 

With your insights to propeller performance I would have thought you might have been interested in the Airmaster recommendations versus my selection ??????

 

I have an enquiry in with MT - Propeller. Hope to get some answers in the next day or so.

[Kyle Communications]

I looked at all that data and agin there are some quite different results depending on blade size and type. Again you need to select the best for your particular wants and even with the CS unit there is still quite a difference between missions.

To be honest I have not been interested really in a CS unit because of what i stated before. The cost performance ratio is way out of balance. The extra weight you carry affects carrying capacity and weight and balance dramatically and then you get beaten around the head for the costs.

I dont think the Eprop version will be very cheap either so the cost will be similar when you are up at that level of money but the difference in weight and balance is very dramatic.

The blade design of the Eprop is very different and from what I have seen much better in performance than any other prop when setup the same so I would think their CS unit would be even quite a lot better than whats available now

On that airmaster chart I would take either the SNR68C or the WR70W as you want a fast climb but cruise will be affected but again not knowing what your airfield is like or the existing performance is it is hard to decide. But the big lesson to take away from those results is again a CS is still a compromise

 

[skippydiesel]

Kyle - you sound a little coy - a bit of this and that and some sugar to wash it all down. I expected more punch!

 

In LSA class aircraft, I think the cost of any inflight adjustable/CS is indefensible. What I mean is, those that purchase one are not so concerned with the cost effective rational. They want the effect and the cost is just a pain to bear.  Its not rational, so lets put that point to one side.

 

The additional weight of most CS props is a concern but again manageable. It would be better not to have a significant weight change - hence my interest in minimising this factor AND my interest in the Eprop development in this area

 

The question for me is - can I find a prop that will equal, my very satisfactory (see my erlier descriptions), existing ground role/climb out AND give me a higher/more economical cruise speed. My existing prop can be adjusted to do both BUT not during flight.

 

 

[Kyle Communications]

hahahaha you should know my answer to your last part of your post....put on a Eprop and it will be better than your Fitti  😁

 

 

 

[Kyle Communications]

As far as punch in my comments...I just can not justify the cost of a CS prop as I said so its never really been a big thing in my front of mind. Of course there are plenty of people around that have the bucks and good luck to them but my bank balance is stretched far enough

 

[skippydiesel]

4 minutes ago, Kyle Communications said:

hahahaha you should know my answer to your last part of your post....put on a Eprop and it will be better than your Fitti  😁

 

 

 

Juts wanted to give you an opening

[skippydiesel]

2 minutes ago, Kyle Communications said:

As far as punch in my comments...I just can not justify the cost of a CS prop as I said so its never really been a big thing in my front of mind. Of course there are plenty of people around that have the bucks and good luck to them but my bank balance is stretched far enough

 

As I said, I agree - but again that's not what my reserch/goal is about.

 

Ultimately I will consider cost, who wouldn't. At this stage its about trying to select the best prop for the objectives as stated. Then if there are one or more offerings, that seem to be about equal, (no clear winner) I will use cost to make the decision.

[Kyle Communications]

Actually its interesting all this talk on props be it fixed or CS type and performance mission

When I was in the USA flying the RANS S-21 to see if I would like it they use a Whirlwind 75 inch STOL prop as their standard prop. It is well known that its a great STOL prop but not that good for cruise. I was looking for a alternative and thats when I came upon the Eprop from someone in another country. They have tried almost every brand of prop..but not the Whirlwind though. Here the WW is about 3.5k at least maybe even more now.

The WW is a very popular propeller as it is a locally made USA product and from what I have read does work very well. Tim Howes has one on his Storch and he said he noticed a big difference in performance

 

Obviously if there isnt much difference between your choices in performance then price is a big factor unless you have way too much money to burn.

There is of course no better prop than a CS.

As a matter of interest would you consider a manual IFA rather than a electrically driven CSU?....Personally I would like the manual type as less to go wrong especially knowing one guy who has replaced the DC motor in his Airmaster a couple of times and also a lot of others have had issues the same even with the other brands. A IFA is still complex mechanically essentially but it takes out another possibile failure factor

 

[skippydiesel]

From a purely philosophical position I am all for KISS.

 

As usual I have what I would call mitigating factors that degrade the simple approach. So when it comes to propellers, I am reluctant to move away from my ground adjustable that has served me so well, to something as complex as a CS prop, so may be a (manual) in flight adjustable may be a good compromise. I certainly would not rule it out - suggested suppliers ?

[Kyle Communications]

I saw one in Europe some time ago not sure who it was from the only other was that Bolly one I posted the video of. That IFA was used on that aussie guys video of the turbine he had on a test stand a few years ago. I think from memory that was a bolly one. I will see if I can find out

 

[Kyle Communications]

 

[FlyBoy1960]

The Bolly in-flight adjustable is being tested/developed at our airfield. There have been a couple of blades that have let go and the other day (about three weeks ago) the propeller went into beta mode at about 200 AGL after rotation requiring the aircraft to crash land into a pond. I am not sure if they are going to keep going with the project