Jump to content

Recommended Posts

Who can I call in regards to ign problems with a 912uls  ie large rev drop on mag under 3000rpm but all ok on higher revs 

what to look for??

thanks

Link to post
Share on other sites
24 minutes ago, Rodr said:

Who can I call in regards to ign problems with a 912uls  ie large rev drop on mag under 3000rpm but all ok on higher revs 

what to look for??

thanks

Rotax Owners Forum. LAME. ? Bert Flood. Whoever sold it to you. 

Link to post
Share on other sites
11 hours ago, Rodr said:

Who can I call in regards to ign problems with a 912uls  ie large rev drop on mag under 3000rpm but all ok on higher revs 

what to look for??

thanks

That's completely normal. Mag checks should always be done at 3000rpm or higher.

  • Agree 1
Link to post
Share on other sites
21 hours ago, Rodr said:

Who can I call in regards to ign problems with a 912uls  ie large rev drop on mag under 3000rpm but all ok on higher revs 

what to look for??

thanks

As per JG3 - I do my Rotax 912 RPM checks at or above 4000 rpm

Link to post
Share on other sites
7 minutes ago, skippydiesel said:

As per JG3 - I do my Rotax 912 RPM checks at or above 4000 rpm

Agree with 3000rpm as my ignition check setting ... can't do 4000 as that's enough to take off and on wet grass all braked wheels will skid at that much power 😀

Link to post
Share on other sites
34 minutes ago, kasper said:

Agree with 3000rpm as my ignition check setting ... can't do 4000 as that's enough to take off and on wet grass all braked wheels will skid at that much power 😀

Well expect to have inconsistent/less significant, ignition rpm drops

Link to post
Share on other sites
2 hours ago, Flightrite said:

There’s so many of these donks out there these days that this sort of knowledge should be common?

My guess at an explanation: lots of direct drive operators out there, jump into a Rotax motivated craft and cant get their head around doing a ignition/carb heat check at 4000 RPM

Link to post
Share on other sites

So someone buys/operates a new type of powerplant (to them) and they have no idea about basic engine checks? That’s poor airmanship right from the get go! Too many poorly trained and ill equipped drivers out there as it is! 
There's so much info avail today on every plane/engine that not knowing the basics is just lazy!

Link to post
Share on other sites

Well my need to check at 3,000 is aircraft specific ... but is not uncommon for 912 trikes.

 

1. the same wing I have a rotax 912 on - Raven wing on an EclipsR trike - flies two people on a Rotax 447 with only 40 HP - Raven wing on a RavenX trike 

2. the 912 is putting out 46hp at 3,000rpm so its brake system is working pretty well to hold just that ignition check rpm

3. the 912 at 4,000rpm is putting out over 55hp ... there is not enough rubber on the ground to hold it 

... not surprising given the cruise power setting for the 912 on the trike is only 4,300rpm.

  • Like 1
Link to post
Share on other sites

These days there is a lot of "INFO" out there and the bulk of it is misleading and supposition.. Just stick to the makers recommendation(s). This includes the total package, plane and engine.. Be nice to know exactly what you are checking also so the check has more validity... Nev

Link to post
Share on other sites
2 hours ago, tillmanr said:

Search for rotax-owner.com for lots of useful information.

Or register your ownership with Rotax, and get regular news, updates, and notifications etc from them.

Link to post
Share on other sites
5 hours ago, kasper said:

 

... not surprising given the cruise power setting for the 912 on the trike is only 4,300rpm.

That RPM setting for continues cruise would concern me - Rotax 9's should be run at about 5200 + rpm

Link to post
Share on other sites
1 hour ago, skippydiesel said:

That RPM setting for continues cruise would concern me - Rotax 9's should be run at about 5200 + rpm

I would BUT for the fact it’s a trike and it’s been propped to that power setting. 4300 by the book burns 11lph when the power is fully absorbed.  The aircraft burns 11lph when cruising at 4300.  The prop is correctly set for the rpm.  
 

thw result is that it’s burning the correct mix and it’s ok.  The 912 in this airframe goes for hundreds of hours and never misses a beat.   The only failure I’ve had on the engine was a failure of 1 ignition unit - and that was found with ign check at 3000 😛

 

if your engine is burning the correct fuel for the rpm your prop is set to the correct cruise.  
 

on the raven you simply can’t run 5200+ because the airframe is coming out of the top side of the drag bucket above 4300 … all it does is make you exhausted holding the bar or make you climb at many hundreds of fpm.  Cruise climb at 4600 gives over 500fpm at mtow … I’m not going to run it any where near 5200

Link to post
Share on other sites

I confess to having no experience/idea of trike's and their particular characteristics BUT I do have an idea of what the Rotax manuals say on the matter and your figures would appear to be outside the recommendations.

 

Fuel burn is but one measure  - most engines have optimum engine  speeds, particularly those that are expected to deliver high continuous power (aircraft, pump, generator, tractor, marine  applications). The engine speed is not just about power but also things like, lubricant reticulation, coolant speed/flow, removal of heat, torque delivery, reserve torque, etc etc.

 

You mentioned "hundreds of hours" - why not thousands?

 

Sounds to me that your aircraft is well overpowered resulting in sub optimal power settings to maintain easy control

Link to post
Share on other sites

I can’t say thousands as I’m only a weekend flyer.  The engines in all the raven 912 eclipsR trikes have performed perfectly for the past 20 years and there is no history of issues.  Only know that because I worked at the factory building them for years and flying them as an owner.  
 

we set that engine / prop combo up and it works. 
 

As for overpower I’ll agree.  But you tell me what 50hp 4 stroke engine was available 20 years ago that would sell to the market?   There wasn’t and the market was anti-2 stroke so there was and remains no option except the 912. 

Link to post
Share on other sites

A friend of mine has one of those trike thingies with a 80 HP Rotax donk (which I think is the common HP)? & he runs it it at a much higher power setting using around 15 lph, (that’s what he plans) at 60 kts, seems happy at higher revs, prop /wing combo must have a lot to do with it.

on a side note bend in one once many years ago, felt really strange, not for me😉

Link to post
Share on other sites
10 hours ago, skippydiesel said:

I do have an idea of what the Rotax manuals say on the matter and your figures would appear to be outside the recommendations.

Can you provide a reference to the recommendations in the manual? I can't find anything.

 

I have heard for many years that the 912 should be run at over 5000 rpm but I have never seen anything official from Rotax. It seems as likely as not to just be folklore.

 

Exactly what problems are people anticipating running < 5000 rpm (assuming unleaded fuel)? Is there any real decrease in engine life?

Link to post
Share on other sites

Engines don't "LIKE" anything. They are inanimate pieces of machinery. They either work ok or they don't and usage experience will bear that out. Most engines have rpm's that are not good from a harmonic point of view If you know what they are avoiding them is best. Jabiru say avoid over propping for their engines. The ferry settings for Merlins and big radials Mostly GEARED are at very slow engine RPM's. Slow RPMS reduce friction and it obeys the "square " rule. Double revs is 4 times the friction.  Max power is  above MAX torque also. There may be MP limits apply at lower RPMs. Flying at full throttle height is efficient on a supercharged engine. Nev

  • Agree 1
Link to post
Share on other sites
5 hours ago, facthunter said:

Engines don't "LIKE" anything. They are inanimate pieces of machinery. They either work ok or they don't and usage experience will bear that out. Most engines have rpm's that are not good from a harmonic point of view If you know what they are avoiding them is best. Jabiru say avoid over propping for their engines. The ferry settings for Merlins and big radials Mostly GEARED are at very slow engine RPM's. Slow RPMS reduce friction and it obeys the "square " rule. Double revs is 4 times the friction.  Max power is  above MAX torque also. There may be MP limits apply at lower RPMs. Flying at full throttle height is efficient on a supercharged engine. Nev

Your point ???

Link to post
Share on other sites

I may not have the tech training/experience of Nev but I do know that no engine likes to "luge" under load. I am using the unscientific word like to summarise all the negative impacts/behaviours of an engine operating in a RPM  band below its optimum when under load.. 

 

There is unlikely to be any ill effects from operating a Rotax 9 being operated below its optimum RPM range, when lightly loaded however I would class this as more like a  "loitering" condition rather than cruise

 

 

Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...