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Oil temperature


S3flyer

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Its that time of year when spring is in the air and Rotax oil temperature questions are in bloom :)

 

The following is an email exchange with Roger Lee (who pointed out it would be a good idea to share in the forum so we all can learn):

 

What is the downside of changing the needle from 3 to 4 (fuel consumption, mixture issues at altitude, etc)?  I seem to recall you saying that you dropped quite a few degrees across the board when you set yours to 4.

 

Also, should I really care?  I’ve only touched the bottom of yellow (in climb with OAT at 100+) once in my 3+ years of flying (based in Dallas).  It does seem that my oil temp rides higher than some fellow Rotax flyers but one number doesn’t tell the story.  At OAT of 68F yesterday at level cruise and 3000’ MSL:

·         RPM: 5040

·         Oil Temp: 229

·         Oil PSI: 50

·         EGT: 1260

·         CHT 195

 

Everything is clearly in range so maybe I should just not worry about it?

 

From Roger:

 

I would leave my carb needle clip where it is unless you start seeing higher temps. What's a little odd about your readings is the EGT is a tad low, but the oil is a tad high. I would have expected the EGT's around 1337-1400 at 5040 rpm and the oil temp around 210-220 at the CHT & EGT temp your were getting, but they are in normal range so unless something really goes up I wouldn't worry.

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I forgot one of my spring cleaning items that helps in engine cooling....

 

The Sting S3 has a "Cabin Heater Muff" that connects to the backside of the radiator and effectively covers up 1/3 of the surface area. This is ducted to the cabin so to reduce the possibility of CO2 entering the cabin. This is also something I routinely remove when warm weather returns. Worth a few degrees of engine cooling. Does take away 3/4 of the cabin heating but that's not an issue where I fly from April to October.

 

post-27-018540200 1301861544_thumb.jpg

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  • 2 weeks later...

S3flyer:

 

I am jealous of your oil temps. I flew an early sting in 2005, and it got much hotter than yours, and real fast after takeoff. That's one reason I did not buy it. They must have fixed something. In my CT the other week on a hot day I was cruising at 240 F oil temp (7500', 5200 rpm, hot outside at 25C). WF

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  • 2 months later...

Roger,

 

I am the member of a flight club that has a 2006 CTsw. A recent flight gave me these numbers. A couple of caveats. 1. I have no idea where the carb needle is positioned and i do not believe that anyone has touched the pitch of the prop.

 

OAT 80deg/f

Alt 5500 ft

115 kts

220deg CHT

240deg OIL

55 psi oil pressure.

5200 rpm.

 

2nd Flight

OAT 80deg/f

Alt 4500 ft

115 kts

230 CHT

260 Oil Temp

35 psi oil pressure

5200rpm

 

This was after being established at altitude. Getting to altitude took a while to keep the instruments (Oil Temp and CHT) staying on the red line. Once at cruise it was rock solid at the numbers above. It seems strange to have oil temp at the top of the yellow arc as a matter of course.

 

Does anyone have any ideas to get the oil temp to the top of the green in cruise?

The 4800 on takeoff and 5200 wot at altitude in cruise also is a question.

 

 

Couple of notes.

 

5500rpm is not achievable in level flight.

4800rpm is max available during takeoff.

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From what you tell me it is absolutely the prop pitch set too course. Too little engine rpm causes temps to soar and takes away from the best all around performance. Have the school come to our web site here. The best engine / prop rpm combo is 5500-5575 rpm WOT flat and level at your normal altitude. Rotax absolutely says do not set up a prop pitch so course as to only achieve 5200 WOT which over loads the engine. If 5200 is the WOT then take out 1.75 degrees to flatten the pitch.

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Roger,

Thanks for the quick reply. I am planning on taking this from cha to Osh and the temp issue just increases pucker factor. I will try and get the guys to re pitch the prop in the next few days and will re-post with the results so people can have a reference. What could be the ramifications if we don't re-pitch?

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The ramifications are:

It will be a constant PITA and will cause some premature wear over the long haul and as a school they put more hours on quicker so the long haul will be short. It may cause more under the cowl heat so more premature wire insulation and hose fatigue. More fuel used and poorer performance. Last but not least it could cause a major system failure because of the over load on the engine parts. Rotax warned FD about this years ago and now and for the last few years FD CT's come from the factory with and engine WOT rpm of 5500.

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Roger,

Again thanks. Its a Flying Club that i belong to not a school. I am going to push the guys to get the prop pitched to 5500 WOT using the SB from Rotax as a prod. Thanks for your information.

Chris

By the way have you looked at the pictures i posted of the right and left ailerons? The alignment is different on the left vs the right. Just one more thing that cant find reference to in any manual

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Once again, Roger is spot on!!! Your prop is making the engine labor.

 

I don't know why FD has their props this coarse. But we have to set the RPM to their specs.

 

On most all other airframes the WOT is 5800 and after climb out you are able to pull back and cruise at 5500. This set up makes the best sense and this is where the engine wants to be.

 

Your oil temp at 4500 RPM is out of the normal tolerance but not out of max (max 285F). That's also why your oil psi is down around the min (min 29 psi) range. It is losing its viscosity.

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I just read the SB on RPM:

Step Procedure

 

1 Engine speed over 5500 rpm is restricted to 5 min maximum (As detailed in the Operators Manual 912/914 Series).

 

2 Take off RPM at WOT (wide open throttle) should not be below 5200 rpm to avoid over loading the engine.

 

3 Continuous use of engine speed below 5200 rpm with WOT should be avoided.

 

Wouldn't this setting be too course? I'd think 5200rpm on take off would equate to way over 5500rpm WOT at typical cruising altitudes. Your climb would be impressive but cruise might be a disappointment. Right?

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Hi Dave,

 

You are correct. 5200 in a take off climb equates to almost 5800 WOT in cruise. Everyone needs to remember that these engines and specs are written for planes around the world and many have constant speed props and don't have our restrictions that we do here. So you have to balance out what is right for your particular brand of plane. There are some general rules, but some are not hard and fast. You all should set your props to achieve at least 5500-5550 WOT in flat and level cruise at your normal cruise altitude. This will give you the beast all around performance for our setup as we know it. Every other rpm in below that will take care of itself. There are a few specifics cases like Charlie tango that lives at an airstrip elevation of 7500' and has to cruise out at 10K-12K to get out of his valley, but that's not most of us. The other important item to remember is that if you set your prop to 5500-5800 then you have a 5 min. run time and if you break a carb cable or something similar in nature where a carb goes wide open and you only option is to go wide open with the other carb to keep flying then being at the 5500-5550 mark will let you fly to where ever you want to go, but if your WOT is 5700-5800 then you only have a 5 min. flight left.

 

If you get 5800 rpm WOT in cruise then you will have a great climb prop, but a lousy cruise Prop, poor fuel economy and temps may be up because we went too far the other way. Temps can go high if you get too flat or too course and of course take off weight and takeoff style figures into the equation. More rpm will equate to more HP for us, but more HP is more work and more work can raise temps. To course a pitch raises temps for another reason, it overloads the engine and it works too hard.

 

Like many things in life:

 

Balance is the key to a happy long living engine.

Same thing your wife says about you. smile.gif

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To quote my 4 year old son.... " no its not... huh uh... no its not... LOL :lol:

 

Yeah, you got me on that one Roger. But maybe I was only testing you!

 

I hadn't had my caffine fix yet... yeah that's it. :D

 

Seriosly, thanks for calling it out. Actually could have caused someone to over heat.

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On a recent flight made a longish descent with the power back and ended up at pattern altitude with the oil at ~110*. Had to add power to make the runway. How much damage did I do?

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None,

 

It doesn't matter if the temps dip low on any of the engine parameters it is only a short lived time and not your normal 90% flight time.

The engine temps are set up for your regular use time frame and not the few % on the high and low side because you usually don't fly like that all the time. I have had low temp alarms go off during the winter months on a long glide, it isn't a big deal.

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None,

 

It doesn't matter if the temps dip low on any of the engine parameters it is only a short lived time and not your normal 90% flight time.

The engine temps are set up for your regular use time frame and not the few % on the high and low side because you usually don't fly like that all the time. I have had low temp alarms go off during the winter months on a long glide, it isn't a big deal.

 

AHHHHH, sweet winter temps............ How I long for my Florida winter temps.

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A flight design reseller has informed us that our prop is set correctly and that from the factory fd sets the rpm for 5500 at 0ft msl and standard temp, so the low rpm 4800 at take off 90oat and 5200 wot at both 4500 80Oat and 5200 at 6500 80 oat is perfectly normal and is not a cause for concern. The top of the green arc on the CHT during cruise and the top of the yellow arc on the oil temp also should not be a concern.

Planning Cha to Osh and keep hearing a little voice in the back of my head.

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Well they are correct up to a point. 5500 at 0' msl is the correct answer.

The problem with that is we don't fly there. FD used to swear by 5200 rpm WOT too, but they were wrong. I complained to them and so did Rotax until FD finally put the WOT setting at 5500 rpm from the factory. FD sets the throttle and prop pitch to sea level because they sell around the world and you don't know where each plane will end up. So now it is upon the owner to decide if he wants to leave it there and take the performance and temp hit or change it.

You should set that 5500 rpm WOT for your normal cruise altitude. That's where the plane spends most of its flight time and not at sea level or on the ground. Damn few of us can say we fly at sea level unless you are 10' off the deck on a beach. Many dealers and mechanics don't understand how the Rotax engine and prop setup should be and some don't even know how to do it. Even the Rotax Operators manual and its SB's say your settings are wrong. FD or any other aircraft MFG don't always have the right answer or they wouldn't need to put out SB's or make product changes.

Your rpm really is too low and the prop needs a little flatter pitch for better all around performance and better temp management. Trust me I have reset more CT props than anyone in the nation and many other aircraft Mfg props can be added to that number. Not a single person has ever gone back to that low rpm setting. I'll match the real performance numbers against anyones. It's counter productive.

 

 

I heard through the grapevine that who the dealer was and you called them. I would say that they may have set your rpm right in Florida at sea level, but you don't live or fly there so you need to correct for your own density altitude.

 

With a little luck some of the pilots here that had the lower rpm numbers and now have the 5500 WOT will chime in here.

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Roger,

I will continue to advocate for the prop change. However on a more serious note would you be concerned running 1200miles round trip, with a portion over lake Michigan at the current settings?

My plan is altitudes between 5500 and 7500 ft. Not sea level

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Hi Mocfly,

 

There is nothing wrong with your settings to fly across country and they are within the normal range.

The only thing you will loose is some performance and a little warmer temps, but that's ok. You can reset a prop anytime.

 

The key to this entire post is setting your rpm and prop for your normal cruise altitude and that is usually where you live. If you live in the mountains don't set the prop and rpm for sea level or vise versa. But when you do fly from one extreme to the other there will be some difference in engine a plane performance, but that's just the way it is with a ground adjustable prop.

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Roger,

Well I guess we really do live in a small community.

We here at kcha are at 682msl. With the terrain around us I would say that most of the time we are at 3500 msl. Add summer temps of 85-90 and our da changes to over 6500ft. I hope I can make the argument for changing the pitch. It just seems counter intuitive to have to stair step from to to 5500 ft taking 25 minutes so as not to run either on top of the yellow or over red. Then never able to run in the green on the oil temp until descending into the pattern.

There are a few other things in the public domain about how people run the engine which worry me.

One comment" just throttle back to 4000 rpm and enjoy the views" everything I have read tells me this is not the way to run this engine

Another " On take off at approximate 500 agl throttle back to 3950 to avoid goin into the red"

I can't speak to engine dynamics as well as you can, and for your replies I thank you.

The power reduction at 500ft really worries me

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I live where it is hotter and I fly much heavier and I never have to cut back, slow down, or step climb. I never run over 230F oil temp and never over 220F CHT. In cruise I run 215FR-220F oil and 210F for CHT's for the hot summer months. It 's all in the set up. Just proved it this last weekend with 4 planes. Three I set up and no issue. One running a much lower WOT rpm setting and it was 250F on the oil and had to climb really slow and reduce throttle.

 

p.s.

I have a CT owner out of Tallahassee, FL coming here tomorrow for me to reduce his pitch to get 5500-5575 WOT at 6500' msl on his way to Alaska. The difference will be minimal when he gets back to Florida because he doesn't fly at sea level, but at 4500-6500 normally. Right now he is loosing performance and wasting fuel which is one big reason for him to change since he has long legs to fly. It's a 30 min. job and if you don't like it you can always go back to the original setting, it's not carved in stone.

 

p.s.s.

It's your plane tell the mechanic where you want it set, it isn't his decision he works for you and you pay him.

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