rotax 2stroke max rpm debate

[flyerme]

There is a lot of threads on topic of what the maximum rpm should be on a Rotax 2 stroke so I decided to find out the truth behind all the beliefs.I first checked the rotax manual,then rang Wal at bert flood ,then a few other dealers (qld and uk)

 

eventually I was able to email bombardier Rotax HQ Austria. was interesting on what they specified.

 

All Rotax 2 strokes share the same RPM

 

.MAX 6800 rpm REDLINE REDLINE REDLINE BEFORE ENGINE DESINTIGRATION.

 

Max Rpm should NOT exceed 6500 rpm. running no more than 5 mins max(IN STREIGHT AND LEVEL FLIGHT ONLY)

 

static full power should be around 6000 -6200 rpm max

 

take off climb should be 6200-6400 rpm max

 

and streight and level flight at full power should be 6500 Rpm 5 mins MAX

 

maximum rpm refers to full power in streight and level flight NOT TAKE OFF CLIMB!!

 

I however climb out at 6500 rpm but I may be rethinking this now.

 

 

[Patrick Normoyle]

I thought Wal had left Bert flood a few years ago, any how, your information is exactly what I use, max RPM 6400 for no more than 5 min and cruise at 6000 RPM, this is all in my Fisher Mk1 with a Blue top Rotax 582.

 

 

[horsefeathers]

Here is a cut and paste directly from the Rotax Owners manual for the 447, 503, and 582 - it seems the only difference in engine speed is with the older 40 Kw 582.

 

But, in a nutshell, 6800 rpm max for 5 minutes, 6500 rpm cruise speed

 

 

 

[flyerme]

from my rotax 582 blue top manual..different ? hence the need to contact an authority..

[horsefeathers]

uhhh, dont mean to be ULTRA picky, but a 582 doesn't have any Oil Pressure..... That looks like a page from a four stroke engine manual, perhaps a 912

 

 

[Patrick Normoyle]

Might be the oil injection ?

 

 

[horsefeathers]

Might be the oil injection ?

Oil injection on the 582 is gravity fed, and the temp of the injection oil is not monitored.

 

 

[flyerme]

uhhh, dont mean to be ULTRA picky, but a 582 doesn't have any Oil Pressure..... That looks like a page from a four stroke engine manual, perhaps a 912

I asked about that and is mentioned in another thread ,apperently it refers to the oil injection pressure for lubing the water pump/or for the 2 stroke oil injection? I forget now but minor details?its definatly a rotax 582 blue top manual.there was other descepencies in the manual I had cleared up from rotax. My good friend has an older 582 and his manual is practicly identical?wonder if they just mass produce and change a few minor details? pretty crap when Rotax themselves state one thing and their manuals another? speaking to Wal at Bert flood he recomended what the manual states (6500 max 5 mins on take off) he also mentioned (where i became lost) torque range/line? at certain revs ,power band ,etc..I cruise at 5200 revs .seems good on fuel and cruises nice at 65 knts. but I may not be running at optimum performance,5400-5800 revs cruise setting?

So as you can see theirs a lot of different info out there,I have sent a message yet again to Rotax Austraia inquiring on why they messaged one thing whilst there manual states another? I have given them engine and model numbers gear box and ratio.now to wait for a reply.

 

 

[horsefeathers]

Sorry, just dont buy it. My 582 manual has NO mention of oil pressure, and the latest manual you can download doesn't mention it. Can you post the front cover of this manual (make sure the part number is clearly visible) to clear up any inconsistency?

 

 

[horsefeathers]

[ATTACH=full]20699[/ATTACH] from my rotax 582 blue top manual..different ? hence the need to contact an authority..

Ahhh, just noticed, that picture I believe is from a specific aircraft manual - Rotax engine manuals dont specify tyre pressures. So, I would NOT take the advice in that as gospel. Thats not to say that the particular aircraft should not use those engine speeds, but read the actual Rotax manual for factory engine specs.

 

 

[skyfox1]

l take off a full power 6800 climb out then cruise 5200.to 5800 have always done it, 6800 is max rpm for rotax 503 they are in the rotax specs.

 

 

[flyerme]

Im well aware of what the latest manual states as I was ripped off buying it on cd when you get it for free off the net.idjet i am sometimes.. I have posted a pic of my Aircraft manual LW gr 582 blue top section " engine 582 blue top power plant limatations" to show the difference.This is why I became confused after purchacing the latest manual.? I have spoken with a number of rotax dealers and get different OPINIONS ? received an email this morning from a bombardier rotax with the info posted.Hence a great need for discussion as I dont want to be over or under propped?I have gone with 6500 rpm on take off and drop to 6000 after 3-4 mins but still cruise at 5200 (save fuel) but would hate to think im doing harm? ISo im up for all good input because I want my engine set right.

 

Edit - should mention with old fixed prop was only getting 5900rpm on take off. been like that for 400+ hrs before I came along

 

 

[horsefeathers]

Skyfox1 numbers match the manual, but you are not going to do any damage limiting your Max revs to 6500, so the numbers you fly sound OK as well.

 

If you look at the Rotax engine performance chart,you'll get an idea of the best rpm vs fuel consumption,but of course,this may vary due to your airframe. But its a good starting point to get the most out of your fuel tank

 

 

[flyerme]

Skyfox1 numbers match the manual, but you are not going to do any damage limiting your Max revs to 6500, so the numbers you fly sound OK as well.If you look at the Rotax engine performance chart,you'll get an idea of the best rpm vs fuel consumption,but of course,this may vary due to your airframe. But its a good starting point to get the most out of your fuel tank

cool thanks but what about my cruise setting? from what Im finding is I should be up sround 5800rpm for cruise but would this use more fuel?

I like cruising around at 5200 rpm,65 knys only uses 12 ltrs an hour and feels smoother at that setting? but was told im not in the powerband range? does that really matter?

 

side note =reason for thread I just fitted a new bolly 2 blade ground adjustable and want it set up right.thankyou:smile:

 

 

[flyerme]

does prop and aircraft matter?

 

gsc props recommend no more than 6200rpm on take off with there props on a blue top 582 ?

 

 

[Guest nunans]

cool thanks but what about my cruise setting? from what Im finding is I should be up sround 5800rpm for cruise but would this use more fuel?I like cruising around at 5200 rpm,65 knys only uses 12 ltrs an hour and feels smoother at that setting? but was told im not in the powerband range? does that really matter?

side note =reason for thread I just fitted a new bolly 2 blade ground adjustable and want it set up right.thankyou:smile:

I was in a similar boat trying to get the pitch right after I sorted the exhaust on my two stroke (the pitch was way too fine after it had been set for static rpm when the engine wasn't producing power).

 

I just set for 6400-6500 WOT in level flight, it ended up giving me 6100 static and about 6250 on takeoff.

 

The fuel burn depends on the throttle opening more than the rpm so it comes down to prop load in the end.

 

 

[horsefeathers]

does prop and aircraft matter?gsc props recommend no more than 6200rpm on take off with there props on a blue top 582 ?

You need to obviously take the prop manufacturers recommendation into account here - you dont want it self destructing just because your engine CAN spin it faster.

 

As to takeoff revs - take a quick look at the page below from the rotax manual for the 582 (Fig 1 and 2)

 

Max torque is approx 6000 - 6100, max power 6200-6300, so that's probably (once again purely from the engine perspective), the best climb speed for your engine. Going faster will not give you any extra power OR torque. You lose 10% torque by increasing revs from 6100 to to 6800. So why go to 6800 RPM on takeoff??? I can't answer that - anyone else care to offer a why on this?

 

Re cruise speed Vs fuel consumption (fig 2 and 3)

 

6000 RPM seems like the sweet spot, as it gives almost minimum fuel consumption, max torque, and almost max power. Cruise at 5300 RPM, and you'll use the same fuel, but generate less power.

 

Once again, these are pure engine figures. By cruising at 6000 RPM, you may suffer increased drag, thus slowing your aircraft down. Its a 'suck it and see' exercise for you aircraft and prop combo.

 

But at least you can see where the engine itself performs best.

 

 

 

[Zibi]

Correct me if I'm wrong, and it's been a while since I've done any serious physics calculations, but:

 

- a fixed pitch prop will always generate more thrust when it's spinning at 6800 RPM than at 6200 RPM

 

- assuming a fixed prop again, the engine will use less fuel at 5000 RPM than at 6000 RPM, after all you need to open the throttle wider.

 

At the same time the engine will give you max torque or power at lower RPM, so if you can adjust your prop, so that at full throttle it spins at 6200 RPM, you'll have the best take off performance.

 

At the same time you want it to spin at 6000 RPM in cruise, and that's going to be a different pitch setting on the prop than the one for best take off.

 

So with a fixed pitch prop, you'll have to find a sweet spot that gives you a reasonable take off performance, low cruise fuel use at designated speed, etc.

 

With an inflight adjustable prop, you can tweak it as you fly, and that's the main benefit of a adjustable prop.

 

Oh, in that all you'll also have to take into account prop limitations and prop performance at different speeds (like tips going supersonic or something).

 

 

[Rotax Service Centre]

There is a lot of threads on topic of what the maximum rpm should be on a Rotax 2 stroke so I decided to find out the truth behind all the beliefs.I first checked the rotax manual,then rang Wal at bert flood ,then a few other dealers (qld and uk)eventually I was able to email bombardier Rotax HQ Austria. was interesting on what they specified.

All Rotax 2 strokes share the same RPM

 

.MAX 6800 rpm REDLINE REDLINE REDLINE BEFORE ENGINE DESINTIGRATION.

 

Max Rpm should NOT exceed 6500 rpm. running no more than 5 mins max(IN STREIGHT AND LEVEL FLIGHT ONLY)

 

static full power should be around 6000 -6200 rpm max

 

take off climb should be 6200-6400 rpm max

 

and streight and level flight at full power should be 6500 Rpm 5 mins MAX

 

maximum rpm refers to full power in streight and level flight NOT TAKE OFF CLIMB!!

 

I however climb out at 6500 rpm but I may be rethinking this now.

Hi to all concerned with this debate..Rotax make and design the engine to a specification to deliver the required power output,max and cruise and to obtain the specified TBO without any failures.This output is Dyno performance and they are not really concerned with what aircraft you have or your frugal attempts to reduce fuel consumption or cruise speeds.There is to many varied designs of aircraft,draggy ones and slippery ones.Rotax publish recommendations to cover the best for their engines and its up to the manufacturer or operator to use this or apply their own and except the consquences.

Whilst Rotax manufacture the engine the ultimate responcibility of performance etc is the aircraft manufacturer.Whilst the max limit is 6800 RPM for 5 min the 582 is robust enough to over prop and under prop and still do the job,depending on the propeller you have fitted..

 

We set the Austflight drifter 582 strut brace with 4 blade Brolga prop with 17degree pitch blocks to obtain 6420RPM static which related to about 6550 climb out and 6800/6900 full throttle straight and level and advised owners after reaching a safe height on take off to then reduce Rpm back to around 6200..

 

Rotax fuel the engine to assist cooling of the combustion chamber during full power and yes it uses a lot of fuel,but it is the safety valve,if you dont use full power on take off and resist pulling back on the throttle to early,this is when the dredded piston siezure occurs.Your life is worth more than a little less of fuel.. I have seen a lot of engine prop combinations over the years and this 582 engine can handle a lot of punishment but it is still a 2 stroke engine and as such is subject to design/operator limitations.Since unleaded fuel and better oils come on the market we have very little problems with the 582 and my customers regulary obtain 600 hrs between overhauls with no decarboning and only carby maintenance,regular servicing etc,no opening of the engine..

 

 

[Guest wildman5354]

1st, the Power Graph/Chart for engines is at FULL THROTTLE at ALL RPMs. you get a power curve for your engine, go to a specific rpm, find the hp for that rpm on the curve, that is the hp AT FULL THROTTLE!!! same for the TORQUE and FUEL CONSUMPTION!!! if you want to know these values at REDUCED THROTTLE OPENINGS you need to know RPM, MANIFOLD PRESSURE and AMBIENT AIR TEMPERATURE and a PERFORMANCE CHART from the engine manufacturer. if you set the prop pitch to hold the rpm to 6200 @ FULL THROTTLE then you look on the power chart that hp IS correct. if you then throttle back to 5800 rpm and look at the chart you ARE NOT making that hp indicated for that rpm. again, the Power Graph/Chart for engines is at FULL THROTTLE at ALL RPMs.

 

2nd, the statement "Correct me if I'm wrong, and it's been a while since I've done any serious physics calculations, but:- a fixed pitch prop will always generate more thrust when it's spinning at 6800 RPM than at 6200 RPM" is generally true (for a fixed pitch prop) as long as the tip speed is below the speed of sound. as the tip speed approaches mach .9+ thrust will drop significantly.

 

3rd, all rotax 2-stroke engines are DE-TUNED derivatives of snowmobile engines. the 582 for example is a 583 detuned from ~100hp to ~65hp. this has 2 effects - much, much more longevity and much better fuel efficiency. but, they are still built for the stresses the snowmobile engines are designed to operate with. the 583 revs to 8000rpm+ and does not "MAX 6800 rpm REDLINE REDLINE REDLINE BEFORE ENGINE DESINTIGRATION" as mentioned above. the limits on the "AIRCRAFT" engines are for longevity reasons. 2-stroke engine life decreases exponentially as power/rpm are increased, everything else being the same. so if you propped your 582 to rev to 6800rpm at full throttle level flight and flew at full throttle for cruise the engine wouldn't last as long as if you propped it to 6500rpm full throttle level flight and flew at full throttle for cruise.

 

 

[taiowa]

Great info on this thread. Let me add a tiny bit more. This from my Rotax guru in Marin County.

 

During a discussion about why i'm not getting decent EGT at 5600 rpm with my present prop (Culver 60x28 on a Rotax 277), he explained why my EGT will go up if I prop the engine to reach 6200 rpm.

 

I'll paraphrase as closely as I can: "it seems counter intuitive, but a 2-stroke Rotax will run richer, thus achieve a lower EGT if it's over propped. Here's why: the cylinder displacement defines the volume of air drawn per stroke. For a slide carb, this means that when your slide position is higher than it should be because the engine is trying to accelerate. The amount of air drawn per stroke will be the same, but because the needle is up higher than it otherwise would be, more fuel will be delivered with that air, thus the engine runs rich. Now, if you prop correctly, that same rpm will occur at a lower slide setting, and the engine will be running leaner. Further, at wide open throttle, rpm will be better matched, and you will be in the power band with maximum HP and appropriate EGT - 1100 being about ideal."

 

Wildman's statement #1 above may be correct for 4-stroke gas or diesel engine taking dynamic data on a dyno while accelerating to rpm, or loaded to drop rpm, at WOT. That's not how a 2-stroke would be tested...it just wouldn't make sense because the engine wouldn't run right.

 

Statement #3 is very helpful, and explains why my 503 would run away from its propeller - it was propped as an aircraft engine, but was a snowmobile engine capable of more power. Very interesting. Amusing, even.