Propeller pitch adjusting tool

[bushcaddy105]

Here's how I set the blades on my 3-blade Bolly. The idea isn't mine - it was given to me way back when I built the BC. The prop hub has an AN 4 bolt projecting forward from its centre to centralize the spinner up near the spinner nose. This bolt was accurately centred in a lathe. The hole in the tool fits over this bolt, a foolproof way of ensuring the same measuring radius for each blade. The square tube sits flat on the front of the prop hub. making each blade adjustment relative to the hub face. It doesn't matter what attitude plane is at. The carpenter's profile gauge is then pushed on to the reference blade to set the cambered  profile of the blade front face., and then used to adjust the other 2 blades to match. I have no interest in actual pitch angles, only that they are identical for the 3 blades. Performance in the air tells me which way to adjust, although this has been rarely needed once optimum was achieved early on.

 

This too, is not crude, just purpose made!

[bushcaddy105]

Apologies for the weird layout on the previous post. I kept shrinking the pics to get all the info on screen, but couldn't find a way to delete the extras. Any ideas how nto delete an image before posting?

 

Thanks.

[onetrack]

To delete an image prior to posting, you simply place your mouse cursor at the bottom right of the uploaded image in the message box, and hit the "back" button.

Edited November 15, 2020 by onetrack

[bushcaddy105]

Thanks, onetrack

[IBob]

Wow. There certainly is more than one way to defur a feline...........)

[skippydiesel]

I have a Rotax 912 question;

 

There is a lot of talk about setting the prop pitch, so that WOT is within the cruise/continual power max of 5500 RPM.

 

This is often expressed as a safety measure ie  just in case a carbi cable slips/brakes (or some other disaster, removed engine speed control & it goes to WOT  - you can still get home without "redlining" your engine.

 

This puzzles me:

 

If you set the prop pitch to WOT 5500rpm (or lower) ; I presume your engine will not get max RPM for TO, thus extending ground role and climb out will be very shallow (terrain clearance??) to allow the engine to get to or above, the Rotax recommended, 5200 RPM.

 

• Do people who fixate on the WOT technique "labour" (operate below 5200 RPM) their engines in TO & Climb??

 

• How often do Rotax 912's go to an uncontrollable WOT ?

 

• Is this a real world problem? or just a potential that rarely, if ever, happens?? (bit like a wing falling off).

 

I can see that an inflight adjustable, set to WOT at full course, would work okay, because you can then set it to fine & get above 5500 RPM on TO & climb out. I cant see how this is a good thing in a ground adjustable.

 

I set my engine by the Rotax recommended 5200 RPM STATIC (tied to a yard rail). This means that my Short Field TO role starts at 5200 & climbs rapidly getting me air born on grass in a little under 100 M. Climb out sees the RPM continue to rise with airspeed and quickly enter the red zone above 5500 RPM. By this time we are well over 1500 ft per minute.  I maintain this, until safe altitude (I have lots of hostile trees) then  throttle back to cruise climb between 5200-5500 RPM until intended altitude reached.

[IBob]

Skippydiesel, JG has some interesting reflections on all this as part of his recent writeup on the Eprop, which may be found on his Stolspeed site. (This is entirely apart from his review of the Eprop, just happens to be at the end of that review.)

Recommended reading, I would say, though it seems some folk prefer their own theories to his practical explanations.

Or, as they used to say, you can lead a horse to water, but you can't make it drink............)

[skippydiesel]

Thanks IBob - JG3's analysis was well worth rereading.

 

I think the questions I have posed above, may prompt few to ask themselves:  is my aircraft accelerating (TO) & climbing out at or above 5200 RPM - if not why not?

[Downunder]

I think 5500 wot/flat/level is too low. It leaves no spare power margins.

If set "light" on a cold day at sea level, on a hot day at altitude it will be less and a take off "heavy" on a hot and high strip is where you want power.

If set to 5500 there is also no alowance for altitude degradation.

 

I set to 5650 wot/flat/level, get 5320 at a good climb and this alows for high density altitude operation, mtow operation and a margin to increase throttle at altitude....

 

I'll add that in an emergency go-around situation the extra power would be welcomed as well....

Edited November 15, 2020 by Downunder

[Kyle Communications]

5800 is max rpm at max power for 5 mins. 5500 is MAX CONTINUOUS power. The only time you really need access easily to 5800 is with a constant speed prop and that is only ever on takeoff and initial climb. It does not make any sense to set a FIXED PITCH ground adjustable prop to go to 5800. If you do set the prop for that rpm with a fixeed pitch you then take off the top of your available thrust that last 300 rpm you will never use in reality unless you have a ECU controlling the prop...thats my opinion

 

CS is probably the best you will ever get but that is for a CS prop NOT a fixed pitch one...A fixed pitch prop is a compromise as CS is not

 

[skippydiesel]

Kyle - Have just refreshed my memory of JG3's excellence prop comparison document - short term memory may no longer be what it was but I thought he said Eprop WOT setting for all aircraft  5500 RPM EXCEPT for Savanah which is 5800 RPM - I guess this means that the prop should be set to the airframe characteristics (& possibly the mission requirements) while keeping Rotax (if fitted) in mind.

[IBob]

Hi Mark, I am trying to follow your reasoning here.

If I have you right, you are saying that a fixed pitch prop set to 5800 WOT (straight and level) will never see 5800 on takeoff or climbeout, and you won't put it over 5500 for cruise, so you are never using that max power that is available for 5mins.

 

If I have you right (?) I'm not clear where your argument goes from there:

If we increase the pitch, available revs will drop further.

If we decrease the pitch (to get that 5800 on takeoff and climb) then our cruise speed will be reduced.

 

As you say, a CS prop would help resolve this, but we (mostly) don't have CS props. So we are looking for a compromise. And my impression from what I read and hear is that the compromise lies somewhere around the numbers already mentioned: 5800RPM WOT, straight and level.

 

If you would not set a ground adjustable prop to 5800 WOT, what would you set it to?

[Kyle Communications]

No Bob your not getting what I am saying.

I am saying with fixed pitch prop if you set it for WOT in flight...which you wont achieve on climb because the load on the engine is different to WOT in level flight

 

So ok we now take off and the prop is set now for LESS pitch to get to 5800 on climb. When you then drop back in level flight to 5500 rpm which is MAX continuous power for cruise..which you can do according to Rotax then you have less pitch on so your cruise speed will be less. So holding that thought if you set the prop for 5500 WOT which is max continuous power you will have more pitch on than if you would if you set it for 5800 then throttled the engine back to 5500 rpm so you will be slower. Of course setting a fixed pitch prop like I have said will most likely consume more fuel

 

If I have a CSU then its totally different. You can set the prop pit to whatever power range you want to use. You dont have that luxury with a fixed pitch prop

[Blueadventures]

I set mine for 5,500 rpm WOT S&L and this is because the carbs are set up with the spring pulling to max rpm.  The throttle cable is used to pull back to idle and rpm setting in between during flight.

 

This is so that if the throttle controls fails I can happily fly along until the fuel runs out with no over rpm issues.  When it comes to landing I would stop the engine and do a dead stick landing.

 

If I had set at 5,800 rpm and the throttle control failed I would need to stop engine within 5 minutes or damage may / would likely occur.

[Kyle Communications]

I agree with that idea thats why I set my Bolly to exactly that and that is what most aircraft owners I know set their props to as well...but that is because its a fixed pitch...if you had that issue with a CSU you could load the engine to give you 5500 but you cant do that with a fixed pitch prop

[skippydiesel]

So Kyle - If I understand (????) your Eprop  is set to  5500 RPM WOT AND still allows you to TO/climb at or above, 5200 RPM - Am I correct so far?

 

If the above is true, what then is your best climb rate & at what speed??

 

Blue adventure would seem to be setting his WOT @ 5500 RPM because he fears a run-away engine - seems an unlikely scenario to me but perhaps there are statistics to back this concern.

 

You, on the other hand , seem to feel that to allow your engine to develop 5800 RPM on TO/Climb will significantly & negatively impact on its high speed cruise

 

Have I interpreted correctly ?

[Kyle Communications]

I can only tell you how I set my Booly up on my savannah and the reasons why. I have not set the Eprop up on my aircraft as it sold the week before the Eprop arrived...BUT that Eprop was setup as per the instructions from Eprop at 5500 WOT and I cant find any mention of 5800 in any of the paperwork. 

The Savannah aircraft and all the other aircraft the prop has gone on have been setup pretty much exactly the same as I had mine setup. All of the new users have experienced increased climb rate and cruise speed...All I can tell you is that they all have increased cruise at the same RPM by at least 4 kts and up to 8 to 10 kts. also for example Dannys Savannah now easily climbs at 1500 ft/min at 60 kts...I can only go by the pictures I have seen and what they tell me

You may say as before its all an illusion and objective...the numbers dont lie

 

Danny set his prop for 5500 rpm WOT and he gets 5400 on climb

 

All I can say is I have 13 very happy customers and another 3 props on their way now

 

Yes you interperated what I said correctly about setting a fixed pitch prop to 5800 WOT 

 

A picture is attached of danny in his Savannah with the Eprop setup just how I said

5500 WOT he is cruising at 5200 and doing 92kts in level flight...if you know anything about savannahs...this is not the usual results 

 

 

 

 

[Flow]

I am thinking shining the laser against the far wall, which any recommendations on good light fine point lasers?

[IBob]

Flow, when I was looking around, someone suggested the laser 'bullets' used for sighting rifles: basically, a laser built into a shell case so you can put it in the gun. The sports stores have them, I don't know about cost.

[IBob]

Right, we seem once more to be talking in circles re prop pitch.

I would like to suggest removing the Eprop from the conversation for now: it's not what this conversation was about.

So, this is my reading of what we have:

 

I think we all agree that a fixed pitch prop is a compromise: if set for best takeoff and climb it will be slow in cruise and vice versa.

So, the question for most pilots becomes how to find a good compromise between best takeoff/climb and best cruise.

And the suggestion from the Rotax camp is to set the prop pitch for 5800RPM WOT straight and level.

With that pitch setting, Rotax say we can have 5800RPM for a max of 5minutes.

And with that pitch setting, Rotax say the max continuous power thereafter is 5500RPM.

 

If we instead pitch the prop to 5500RPM WOT straight and level, the max continuous power setting is now approximately 5200RPM.

So if you have your prop pitched to this, and fly at 5200RPM you are flying at the max continuous power setting of your engine.

 

 

 

 

 

 

 

 

[Kyle Communications]

I understand what your saying Bob...but thats not how most set their engines up regardless of what type of fixed pitched prop you have.  Everyone I know sets their prop to 5500 WOT and most cruise at 5000 or 5200 so this fits into what you are saying. Which again provides the most thrust you can get at cruise rpm. I think rotax says that 75% power for cruise is 5000 rpm. If you set for 5800 WOT one would expect that that would be max fuel flow as well and when you throttle back the fuel flow will be less. Power is related to fuel flow. If you set WOT for 5500 one would think that that would also be drawing max fuel flow. then when you drop the rpm back for cruise your fuel flow comes back. 

 

I am certainly no motor mechanic or engine designer. All I know is the way I set my engine up is the way I have always got the best out of my engine and aircraft performance regardless of what prop is on the front. The engine parameters for temps and pressures have all been perfect as per the manual no matter how long the engine was running continuously for that flight. My fuel flow at 5000 rpm was 15.3lt/hr. So for a fixed pitch prop this to me seems the best performance I could get. As I said earlier I do not know of anyone certainly in my group that I frequent set their prop at WOT for 5800. 

[skippydiesel]

11 minutes ago, IBob said:

Right, we seem once more to be talking in circles re prop pitch.

I would like to suggest removing the Eprop from the conversation for now: it's not what this conversation was about.

So, this is my reading of what we have:

 

I think we all agree that a fixed pitch prop is a compromise: if set for best takeoff and climb it will be slow in cruise and vice versa.

So, the question for most pilots becomes how to find a good compromise between best takeoff/climb and best cruise.

And the suggestion from the Rotax camp is to set the prop pitch for 5800RPM WOT straight and level.

With that pitch setting, Rotax say we can have 5800RPM for a max of 5minutes.

And with that pitch setting, Rotax say the max continuous power thereafter is 5500RPM.

 

If we instead pitch the prop to 5500RPM WOT straight and level, the max continuous power setting is now approximately 5200RPM.

So if you have your prop pitched to this, and fly at 5200RPM you are flying at the max continuous power setting of your engine.

 

 

 

 

 

 

 

 

IBob - The only reason the Eprop came up is that there seems to be a suggestion (no outright statement) that it can be set for 5500 RPM WOT and still achieve a 5200 RPM climb out. The climb out RPM will of course be influenced by climb attitude and speed. Hence my interest in these figures. This is not just for Eprop but for anyone setting their prop pitch based on WOT.

 

I think I understand why people are fixated on WOT - if I am correct, this is not the way I would ever set my ground adjustable prop pitch.

 

I, like you, will follow the Rotax advice for a ground adjustable prop - Minimum static RPM 5200. WOT then becomes a factor of in flight management by the pilot, hopefully keeping in mind the Rotax time limitation of 5 minutes at Max RPM 5800.

 

This allows the engine to develop full power/RPM during the TO/Climb Out, a critical time for any aircraft, while giving the pilot the option to cruise at Max Continuous RPM of 5500 OR BELOW or select Max 8500 RPM in an aborted landing

 

By allowing the engine to operate in its best performance range (5200-5800RPM) the aircraft can be asked for best rate or angle of climb (ie a Short Field TO)- it seems likely, to me, that a prop set for 5500 RPM WOT not facilitate this.

 

I also wonder what effect, if any, this has on aircraft performance in high density altitude situations.

 

This may all be just "tickety- boo" if you have a nice long runway, with shallow departure angles BUT the day you depart from a more challenging field may be a bit "stressful"

 

 

[skippydiesel]

2 minutes ago, Kyle Communications said:

I understand what your saying Bob...but thats not how most set their engines up regardless of what type of fixed pitched prop you have.  Everyone I know sets their prop to 5500 WOT and most cruise at 5000 or 5200 so this fits into what you are saying. Which again provides the most thrust you can get at cruise rpm. I think rotax says that 75% power for cruise is 5000 rpm. If you set for 5800 WOT one would expect that that would be max fuel flow as well and when you throttle back the fuel flow will be less. Power is related to fuel flow. If you set WOT for 5500 one would think that that would also be drawing max fuel flow. then when you drop the rpm back for cruise your fuel flow comes back. 

 

I am certainly no motor mechanic or engine designer. All I know is the way I set my engine up is the way I have always got the best out of my engine and aircraft performance regardless of what prop is on the front. The engine parameters for temps and pressures have all been perfect as per the manual no matter how long the engine was running continuously for that flight. My fuel flow at 5000 rpm was 15.3lt/hr. So for a fixed pitch prop this to me seems the best performance I could get. As I said earlier I do not know of anyone certainly in my group that I frequent set their prop at WOT for 5800. 

Kyle - Like you, I am just an amateur mechanic, struggling with what might be the best settings for my Rotax - so please do not take this personally.

 

I think it has become evident that airframe performance is a significant factor in this debate ie draggy airframes may have different demands on engine/prop performance, compared with the less draggy. This in tern will influence pitch settings being selected. Someone out there will know the answear to this.

 

I do not set for WOT - I set for static RPM.

 

WOT is controlled by me, in climb out,  by selecting the aircraft attitude and then when cruise is entered, by my hand on the throttle. This seems to work for me & my home field and as far as I understand, is within Rotax guidelines .

 

As for fuel flow as a measure of power being developed - this has been discussed befor and if memory serves me right  - my approach leads to a lower fuel consumption, at any given RPM, because my engine is not developing its maximum power at that RPM - so I routinely see 12 L/hour (or lower) at 5000 RPM .

 

In support of this view is the fuel flow/RPM figures that CS prop users seem to be reporting - quite low RPM's with high (compared to mine) fuel fuel flows.

 

Any concerns of having a "run away" engine RPM, have been mitigated by using very good quality cables, regularly checked for binding/free play at service, that also have additional safety stops in place, should the carburettor cable/lever clamp slip.

 

In the very unlikely event of an uncommanded  WOT in flight, I would again control the RPM using attitude - this would mean a climb to higher altitude - a good thing! as it would give me time and more glide options when I turn the engine off and glide to a safe landing (conceivable this could be repeated several times to extend range) ie I dont see using pitch to bring WOT down to 5500 as either necessary or desirable in my situation.

[Kyle Communications]

Not taking anything personally..you have your opinion and I have mine. I am no expert at all and dont profess to be but using real world examples and my own facts and figures. How I set mine up works for me and many others it seems. Airframes also make a difference..slippery or draggy.

 

The Bolly setup as I said when the savannah tied on the ground produced 5200 rpm on the ground as it was set for 5500 maybe a little higher WOT in flight. WOT rpm in flight produced 97kts and 5000 rpm in flight produced 85kts. Dannys savannah was 1 or 2 kts better at 5000 rpm on his savannah but he had a slightly smaller diameter Bolly prop. If he cruised at 5000 rpm I had to sit at 5200 rpm to remain parallel with him. With the Eprop set the same (which is the same as per the Eprop instructions) on his savannah he now cruises at 90kts at 5000 rpm and 92kts at 5200 rpm as confirmed by the picture I posted.

 

Maybe it has more to do with aircraft drag and design than what we think...dont know. All I know is it all works how we set them up and the engine does not appear to be stressed and the fuel flow is quite acceptable and under what Rotax says. When setting your prop no matter what it is you will usually go with the manufacturers specifications. There was never any spec supplied with the Bolly but there is specs supplied with the Eprop. If you follow the spec as supplied by the prop manufacturer which is setup for the engine they have specified it for then that is the outcome.

 

 

 

 

 

 

[skippydiesel]

To dwell a little more on the airframe:  Just BS ing but how does this sound ? - For a given horsepower & prop pitch setting , it seems likely that an airframe that is  "slipperier" will allow the prop to achieve a higher RPM  and aircraft air speed what say you?

 

If this is correct - comparing pitch, RPM, air speed and fuel flow only has meaning for very similar airframes.