RV-12 Rotax compared to Sport Cruiser

Hanger directly across from me houses a Sport Cruiser with a 912. While comparing the engine installation with my RV12 I noticed the carbs had a two-into-one metal collector aircleaner where the RV has the dual K&N air cleaners. Of course the radiator and other components are placed irregular to the RV - curious to know what the difference will be.
I was told by the owner that he didn't think the RV could get the horse power with the air cleaner difference.
By the way - I was also told the Sport Cruiser is a much slicker airframe and therefore should be faster. Porcupine rivets and all!
Shut my mouth - and I did.

Dick Jacobs
~~~~~~~~~~~~~~~~~~~~~~~
RV12 (N912RJ - reserved)
ready to hang the slower than the Sport Cruiser 912 engine

Hey Dick

Since some of us can verify that our 12's go as fast as allowed for an LSA, if they go faster, then they have a problem to deal with.

John Bender

I've flown two different Sport Cruisers and am not impressed with the control harmony...or lack thereof. It is heavy in roll and very pitch sensitive.

As far as speed, it's about the same as the red RV-12 demonstrator that I had a ride in.

Real difference: The RV flies like an RV!....Great!

Mitch Garner

RV-4 flying
RV-12 under construction

sportkid said:

Hanger directly across from me houses a Sport Cruiser with a 912. While comparing the engine installation with my RV12 I noticed the carbs had a two-into-one metal collector aircleaner where the RV has the dual K&N air cleaners. Of course the radiator and other components are placed irregular to the RV - curious to know what the difference will be.
I was told by the owner that he didn't think the RV could get the horse power with the air cleaner difference.

Click to expand...

That would be the rotax intake airbox which is required to truly get 100hp out of the 912ULS. It's good for about 10hp, without it the 912ULS is an about 90hp engine.

One thing commonly missed when removing the airbox and going with just regular aircleaners is the carb vents. The little tubes are typically simply routed down the sides of the carbs and let run at normal outside pressure since there's no place to put them anymore (they normally run into the airbox).

They actually need to run into the aircleaners, as the vents need to be at the same atmospheric pressure as the venturis (I use brass barb fittings from the hardware store and drill a hole in the back of my aircleaners for this).

The carbs run rich otherwise - not too noticeable at low altitudes, but become significantly richer at higher altitudes (i.e. 5000' MSL and above). Not good....

Don't ask me why I know this.

LS

lucien said:

One thing commonly missed when removing the airbox and going with just regular aircleaners is the carb vents. The little tubes are typically simply routed down the sides of the carbs and let run at normal outside pressure since there's no place to put them anymore (they normally run into the airbox).

They actually need to run into the aircleaners, as the vents need to be at the same atmospheric pressure as the venturis (I use brass barb fittings from the hardware store and drill a hole in the back of my aircleaners for this).

The carbs run rich otherwise - not too noticeable at low altitudes, but become significantly richer at higher altitudes (i.e. 5000' MSL and above). Not good....

Don't ask me why I know this.

LS

Click to expand...

I can't help but ask....

They do not require the use of the induction air box, it is an option. I am aware that it is required to get the full rated horsepower but I have never seen any documentation saying that without it you loose 10% power output. Do you know somewhere i can find that data?
The filters are ship standard with a new 912.
I have never seen any documentation from Rotax saying to route the vent tubes into the filters. They just say the tube should be near the inlet to the filter.

Hey Guys



I flew with a Sport Cruiser and he had to run 5000 RPM to match my speed when I was running 4700. The Sport Cruiser has the same engine and prop set up. It also appeared he had his pitch set about the same as mine . His empty weight is 802 . mine 727.
He also had wheel pants and I did not.

The guy with the Sport is a long time friend and he was a little suprised with our test.

Got to admit the Sport is a good looking airplanne.But it will cost you 45K more than the 12 and its usefull load is 75 lbs less than the 12,

Brad Stiefvater
Salem SD

rvbuilder2002 said:

I can't help but ask....

They do not require the use of the induction air box, it is an option. I am aware that it is required to get the full rated horsepower but I have never seen any documentation saying that without it you loose 10% power output. Do you know somewhere i can find that data?
The filters are ship standard with a new 912.
I have never seen any documentation from Rotax saying to route the vent tubes into the filters. They just say the tube should be near the inlet to the filter.

Click to expand...

These requirements are spelled out in the installation manual.

The airbox performance is alluded to in chapter 16. i.e. it says that "performance data as specified..... can only be warranted by employment of the genuine Rotax airbox". That just means 100hp is only guaranteed when using the box. It just happens to be about a 10hp drop without it.

The requirements for the vent lines are in a caution in 15.1.1:
"
The float chamber venting lines (3) lines have to be routed into a ram-air and vacuum free zone or into the airbox, according to the requirements and release of BRP-Powertrain. See section 16. These lines must not be routed into the slipstream or down the firewall."

And the most important:
"Pressure differences between intake pressure and pressure in the carburetor chambers may lead to engine malfunction due to incorrect fuel supply."

Fig 59 shows how the vents should be routed, to nipples on the airbox.

The wording is a little vague but it generally means the carb vents have to be at the same atmospheric pressure as the venturis - that means in the same atmosphere inside the filters, not just near them on the outside. It's not a huge deal at sea level and lower altitudes, which is why this is not very well known and most of the time doesn't lead to way too rich running.

But trust me, I can personally attest to the need to have the vent lines inside the filters. if you do any flying at higher altitudes you'll really notice the EGT's dropping and the plugs will get pretty cokey in short order. I live at 7000' MSL and usually fly around 10,000'. When I fixed mine, the EGT's rose almost 100F and were back in the 1300-1400 range where they needed to be. Before that the lines were simply fitted through the side of the float bowls through the bowl retention spring like you usually see on a lot of installations (no idea how the RV-12 handles the vents?). The plugs always came out dark brown and sometimes black....

LS

lucien said:

These requirements are spelled out in the installation manual.

The airbox performance is alluded to in chapter 16. i.e. it says that "performance data as specified..... can only be warranted by employment of the genuine Rotax airbox". That just means 100hp is only guaranteed when using the box. It just happens to be about a 10hp drop without it.

The requirements for the vent lines are in a caution in 15.1.1:
"
The float chamber venting lines (3) lines have to be routed into a ram-air and vacuum free zone or into the airbox, according to the requirements and release of BRP-Powertrain. See section 16. These lines must not be routed into the slipstream or down the firewall.
Pressure differences between intake pressure and pressure in the carburetor chambers may lead to engine malfunction due to incorrect fuel supply."
Fig 59 shows how the vents should be routed, to nipples on the airbox.

The wording is a little vague but it generally means the carb vents have to be at the same atmospheric pressure as the venturis. It's not a huge deal at sea level and lower altitudes, which is why this is not very well known.

But if you do any flying at higher altitudes you'll really notice the EGT's dropping and the plugs will get pretty cokey in short order.

I live at 7000' MSL and usually fly around 10,000'. When I fixed mine, the EGT's rose almost 100F and were back in the 1300-1400 range where they needed to be. Before that the lines were simply fitted through the side of the float bowls through the bowl retention spring like you usually see on a lot of installations (no idea how the RV-12 handles the vents?). The plugs always came out dark brown and sometimes black....

LS

Click to expand...

Very interesting info.

Where would one route the lines if you are using the K&N air filters? From what you are saying -12s operating at higher alts would benifit by running them into the filters? You you mean drilling a hole in the rubber part of the filter?

Geico266 said:

Very interesting info.

Where would one route the lines if you are using the K&N air filters? From what you are saying -12s operating at higher alts would benifit by running them into the filters? You you mean drilling a hole in the rubber part of the filter?

Click to expand...

Exactly. If anyone's interested, I'll take a picture of the mod I've done to mine.

I bought a couple of barbed fittings down at Lowes - i.e. male-to-male with a disk in the center. Then drilled suitably sized holes in the rubber in the back of the filters (the round/flat K&N's). Push the barbs in until the disk sits flat on the back of the filter, put the vent line on and that's it.

I'd do it even at sea level as this is really the correct handling of the lines. I was suitably shocked the first time I pulled my plugs for inspection. Almost black and I was of course worried about what was going on inside the combustion chambers. After the fix, they come out nice and antique-white like they're supposed to....

Fortunately, the fix is very cheap and easy to do and restores the carburettors to working correctly....

So what does the RV-12 do with the vents? I havn't seen any pictures but I hope they don't leave the vent lines "hanging in the breeze". They probably have their own mod for the filters?...

LS

lucien said:

Exactly. If anyone's interested, I'll take a picture of the mod I've done to mine.

I bought a couple of barbed fittings down at Lowes - i.e. male-to-male with a disk in the center. Then drilled suitably sized holes in the rubber in the back of the filters (the round/flat K&N's). Push the barbs in until the disk sits flat on the back of the filter, put the vent line on and that's it.

I'd do it even at sea level as this is really the correct handling of the lines. I was suitably shocked the first time I pulled my plugs for inspection. Almost black and I was of course worried about what was going on inside the combustion chambers. After the fix, they come out nice and antique-white like they're supposed to....

Fortunately, the fix is very cheap and easy to do and restores the carburettors to working correctly....

So what does the RV-12 do with the vents? I havn't seen any pictures but I hope they don't leave the vent lines "hanging in the breeze". They probably have their own mod for the filters?...

LS

Click to expand...

I'm sure there are high alt RV-12 flyiers that would like to see the pics. This mod would not effect lower alts right? Might be a good thing to do anyway.


Currently, the tubes are just as you describe, hanging on the outside under the bowl clips. Stock.

Geico266 said:

I'm sure there are high alt RV-12 flyiers that would like to see the pics.


Currently, the tubes are just as you describe, hanging on the outside under the bowl clips. Stock.

Click to expand...

Oh dear... Interesting. If it were me, I'd talk to Vans about it and see what their take is. That definitely contravenes the installation manual......
PS: or maybe they get around it by splitting hairs on "....routed into a ram-air and vacuum free zone OR into the airbox.....". But the possibility of a pressure differential between the venturi area and outside the filter is real due to the drag of the air filters. And it definitely causes the carburettors to run rich (plus the mod is too cheap and easy to do ).

I'll bring my camera out to the hangar today and take a pic of the mod. I use the same K&N's that it looks like Vans uses too.

PPS: this a requirement of the carburettor installations and for proper operation of them so, no, there'd of course be no adverse affects at lower altitudes. The mixture would be correct at all times. I suspect the pressure differential that does arise at sea level is less than what arises at higher alts, maybe that's why it's less noticeable. Or maybe the carbs just accidentally run lean enough down there for it not to show considerably on the EGT's and plugs?

LS

lucien said:

These requirements are spelled out in the installation manual.

The airbox performance is alluded to in chapter 16. i.e. it says that "performance data as specified..... can only be warranted by employment of the genuine Rotax airbox". That just means 100hp is only guaranteed when using the box. It just happens to be about a 10hp drop without it.

The requirements for the vent lines are in a caution in 15.1.1:
"
The float chamber venting lines (3) lines have to be routed into a ram-air and vacuum free zone or into the airbox, according to the requirements and release of BRP-Powertrain. See section 16. These lines must not be routed into the slipstream or down the firewall."

And the most important:
"Pressure differences between intake pressure and pressure in the carburetor chambers may lead to engine malfunction due to incorrect fuel supply."

Fig 59 shows how the vents should be routed, to nipples on the airbox.

The wording is a little vague but it generally means the carb vents have to be at the same atmospheric pressure as the venturis - that means in the same atmosphere inside the filters, not just near them on the outside. It's not a huge deal at sea level and lower altitudes, which is why this is not very well known and most of the time doesn't lead to way too rich running.
LS

Click to expand...

I am still interested in where the documentation is that indicates a 10% HP loss if the Rotax induction air box is not used ( I was involved in testing of installations both with and without that did not indicate it was nearly that much)?
As for vagueness of what to do with the vent lines...I don't think it is vague at all. It specifically says "they have to be routed into a ram-air and vacuum free zone or into the airbox". It does not say attached to nipples on the air box or air filters.

lucien said:

Oh dear... Interesting. If it were me, I'd talk to Vans about it and see what their take is. That definitely contravenes the installation manual......
PS: or maybe they get around it by splitting hairs on "....routed into a ram-air and vacuum free zone OR into the airbox.....". But the possibility of a pressure differential between the venturi area and outside the filter is real due to the drag of the air filters. And it definitely causes the carburettors to run rich (plus the mod is too cheap and easy to do ).

I'll bring my camera out to the hangar today and take a pic of the mod. I use the same K&N's that it looks like Vans uses too.

PPS: this a requirement of the carburettor installations and for proper operation of them so, no, there'd of course be no adverse affects at lower altitudes. The mixture would be correct at all times. I suspect the pressure differential that does arise at sea level is less than what arises at higher alts, maybe that's why it's less noticeable. Or maybe the carbs just accidentally run lean enough down there for it not to show considerably on the EGT's and plugs?

LS

Click to expand...

I don't think the current RV-12 engine installation is contravenes to the current installation manual. Remember it says "they have to be routed into a ram-air and vacuum free zone or into the air box". There needs to be evidence that it is not routed to a ram air and vacuum free zone to justify the need for the mod. that you propose.
I have flown an RV-12 round trip from Portland to Oshkosh (about 1750 statute miles each way) at 11,000-12,000 ft altitude range for a good majority of the route, and saw no indication of excessive richness in either the EGT's or the condition of the plugs after the trip.
I am interested in the information you have posted, but one problem I have with the information is the generalization that all airplanes with a Rotax 912 that are not using the (very expensive) Rotax induction air box, should have this modification. I believe it is a modification because it is not documented in the install manual. I am not meaning to be critical...making generalizations is a mistake made all the time...even between the different RV models.
My point is...just because your airplane needed a mod. such as this, doesn't mean an RV-12 does.
I would be interested in seeing photos of what filters you are using (from your previous description it sounded like you were using the round flat style K&N filter. The RV-12 (and what is shipped as standard equipment with a new 912 engine) uses the conical K&N filter that is manufactured by K&N exclusively for Rotax.
I would also be interested in having more information about what airplane this described problem existed on (photos of the engine installation would be great). There is a wide range of airplanes (and their associated engine installations), that use the 912 Rotax. The Kitfox for example...a totally different cowling and associated cooling airflow style. I imagine there is a lot of difference as far as air pressure balance and flow going on within the cowling than on an RV-12 or a lot of other airplanes.

Your info has developed a curiosity and I plan to investigate it further, but I think it is incorrect to generalize that an RV-12 should have this mod done. It may be totally appropriate to log on to a discussion group catering to teh model airplane you fly and suggest that they all do it (at least they would have somewhat similar engine/cowling installations) but I would still need to see evidence that it is not possibly a problem that exists because of something specific to your airplane...

...I have been in this business for a long time...one thing I have learned...Every time I think I can deduce what would be right, I find out how much I don't know.

rvbuilder2002 said:

I am still interested in where the documentation is that indicates a 10% HP loss if the Rotax induction air box is not used ( I was involved in testing of installations both with and without that did not indicate it was nearly that much)?

Click to expand...

I don't want to start a fight about this, so I'm going to make this short and probably my last post on the subject.

As for the power output, see my previous comments on this, I think they're clear.

As for vagueness of what to do with the vent lines...I don't think it is vague at all. It specifically says "they have to be routed into a ram-air and vacuum free zone or into the airbox". It does not say attached to nipples on the air box or air filters.

Click to expand...

No. The installation manual is quite explicit about this, you need to look at it. See also Fig. 59 on page 93 of the current manual - you'll see the vent lines are routed to nipples on the intake airbox. That part, at least, is as clear as you can get. Also read the material in chapter 15 and 16.

I don't think the current RV-12 engine installation is contravenes to the current installation manual. Remember it says "they have to be routed into a ram-air and vacuum free zone or into the air box". There needs to be evidence that it is not routed to a ram air and vacuum free zone to justify the need for the mod. that you propose.

Click to expand...

Again the manual is very clear about the _requirements_. In particular, the requirement that there be no pressure difference between the intake pressure and the carb chamber pressure (which is one of the functions of the vent line). This is in 15.1. You're quite right that it's up to whoever does the installation to insure that this requirement is met. I'm also not saying the RV12 doesn't meet that requirement - I shouldn't have suggested that it did, you're right. It might or it might not and I don't know. But I do know what Rotax requires as far as venting the carburettors (and incidentally how that is to be done on my particular installation) because it's written right there in the documentation and it's sitting right in front of me. I'm just saying if the vents are just routed to the sides of the carbs, there _may_ be a problem and you should investigate it. That's all.

...I have been in this business for a long time...one thing I have learned...Every time I think I can deduce what would be right, I find out how much I don't know.

Click to expand...

Then you should also know that if you _don't_ follow the recommendations and/or requirements of your engine's manufacturer, you're strictly on your own with that engine and are essentially in test pilot territory. It would be even worse when their documentation is explicit about the installation requirements for that engine, as is the case here, and you purposely ignore them. Again, not saying that's definitely the case here. I _am_ saying I'd be suspicious if I saw the lines routed out "in the breeze" and would definitely investigate whether the installation was done correctly.

I'm one of these wierd guys who likes to follow manufacturer recommendations - I like to fly rather than tinker or try to improve upon methods and techniques that have already been worked out for me by the manufacturer. But, YMMV.

Good luck with your efforts, and let us know what you find out.

LS

Float Chamber Carb Vents

Reading this post has inspired some thoughts on the subject. First, I think that LS may be on the right track in stating that these vent lines need to be in a static air environment, same as ambient pressure. That is difficult to find in a tube that is traveling at 120Kts. Plumbing these lines into the card intake area would seem to me to put them in a low pressure area, hence the leaner burn. Not sure where you would find an ambient pressure area that would provide the best source, but I sure can see the need, if you intend to have this altitude compensating carb perform it's magic. So, does anyone know what magic that the Rotax intake airbox uses to provide the needed source?? Maybe we don't need to buy this expensive unit, but, as experimenters, make our own. We just need to understand the theory. Just my thoughts

Tom

todehnal said:

Reading this post has inspired some thoughts on the subject. First, I think that LS may be on the right track in stating that these vent lines need to be in a static air environment, same as ambient pressure. That is difficult to find in a tube that is traveling at 120Kts. Plumbing these lines into the card intake area would seem to me to put them in a low pressure area, hence the leaner burn. Not sure where you would find an ambient pressure area that would provide the best source, but I sure can see the need, if you intend to have this altitude compensating carb perform it's magic. So, does anyone know what magic that the Rotax intake airbox uses to provide the needed source?? Maybe we don't need to buy this expensive unit, but, as experimenters, make our own. We just need to understand the theory. Just my thoughts

Tom

Click to expand...

well, what you need is the carburettor chamber pressure to be the same as the intake pressure. That is, the lines need to be at the same pressure as the atmosphere at the venturi openings. This is what is spelled out in the installation manual.

This is taken care of with the Rotax airbox by the provision of fittings that open into the box for fitment of the carb vent lines.

But when you use air filters alone and leave the lines out in the ambient atmosphere outside the filters, the possibility arises of a pressure differential between the lines and the intake area behind the filters, due to the drag of the filters. It's not much with the K&N's but it's there.

The best way to guarantee equal pressure on the lines and the intake is to run the lines into the filters. I.e. replicate the method of the airbox.

That's really all that needs to be done, unless some other way of guaranteeing this pressure equalization is developed. But usually, simply leaving the lines unconnected (and thus isolated from the intake atmosphere) leads to the malfunction of the mixture control in the carbs.

I think rvbuilder is researching the vans installation now, to see if provisions were made for this. I'm skeptical, tho, since disconnected vent lines usually means this hasn't been attended to. As to how severe the problem is without fixing it, it could range from not very to very very as in my case....

LS

Not sure this is relevant or of interest to anyone, but when I was in Spartanburg, SC for a week end of FUEL INJECTION 101, there was a 912 or 914 on the floor with an intake Don Rivera had created for a customer to accommodate the AFP system.

Seems like a single fuel injection system would be a lot less complicated than 2 carburetors and all that goes along it, although such a change would mandate going back to square one with an LSA machine being marketed as the RV-12.

I believe Rotax knows about the AFP work but they remain married to carburetors.

rvbuilder2002 said:

I am interested in the information you have posted, but one problem I have with the information is the generalization that all airplanes with a Rotax 912 that are not using the (very expensive) Rotax induction air box, should have this modification. I believe it is a modification because it is not documented in the install manual. I am not meaning to be critical...making generalizations is a mistake made all the time...even between the different RV models.
My point is...just because your airplane needed a mod. such as this, doesn't mean an RV-12 does.

Click to expand...

BTW.. (so much for that being my last post on this ) a couple other items I left out of my previous reply.

Rotax of course permits "modifications" all the time by allowing the airframe manufacturer leeway to meet a requirement in a way suitable to that aircraft. They do that by not specifying exactly how it is to be done, but only that it has to be done by some means or other. That's the intent of the note in 15.1 regarding venting the carburettors to an atmosphere of equal pressure to the intake. They don't care how you do it, only that a) here's the result you must obtain and b) you still have to do it.

"generalizations" in the sense of specifying a general requirement are not a mistake. General requirements that, say, cooling hoses be routed from the outlets on the engine to the radiator but leaving how they're to be routed, the exact brand and type of hose, etc., up to the airframe manufacturer are just the kind of thing you should expect from an engine manufacturer's documentation, particularly with Rotax's documentation.

Likewise the general requirement by Rotax concerning venting the carburettors. Yes, this requirement extends to any installation of a 912 series engine. Without the airbox it doesn't appear that they care how you do it, but they still caution you in big letters to do it all the same.

I would also be interested in having more information about what airplane this described problem existed on (photos of the engine installation would be great). There is a wide range of airplanes (and their associated engine installations), that use the 912 Rotax. The Kitfox for example...a totally different cowling and associated cooling airflow style. I imagine there is a lot of difference as far as air pressure balance and flow going on within the cowling than on an RV-12 or a lot of other airplanes.

Click to expand...

My airplane is a Titan Tornado (II SS). But the carb venting requirement is the same on all aircraft using the 912 as I said - the results to be obtained are clear regardless of how. Hopefully I'll make it to the airport today and can take pics for anyone that may still be interested .

LS

More Carb Vent Line Issues

I think we are all interested in seeig pictures. Also, do you think that it would be beneficial to have the two carb vents tied together, as it would seem that an airbox would provide??

My other thought is that, if it's simply a matter of establishing ventura pressure to the vent line, why in the world wouldn't that be handled on the carb itself? It seems like that would offer a simple solution, anyway.

Looking forward to your pictures!!

Tom

I just sold my Sportcruiser 2 months ago. It is definately alot faster than the 12. The Sportcruiser cannot maintain 120 kts, more like 115 TAS.

The Sportcruiser looks and is finished far better than the 12 too. The 'heavy' aileron takes getting used to but I think its more a case of super sensitive pitch than heavy aileron.

SportCruiser is still the Best LSA out there, in my opinion.

Chunky

Have you flown an RV-12?

lucien said:

BTW.. (so much for that being my last post on this ) a couple other items I left out of my previous reply.

Rotax of course permits "modifications" all the time by allowing the airframe manufacturer leeway to meet a requirement in a way suitable to that aircraft. They do that by not specifying exactly how it is to be done, but only that it has to be done by some means or other. That's the intent of the note in 15.1 regarding venting the carburettors to an atmosphere of equal pressure to the intake. They don't care how you do it, only that a) here's the result you must obtain and b) you still have to do it.

Click to expand...

My comment about modifications was in the context that they deliver the engine with the conical K&N filters (It sounds like you are using the round flat filters which is another installation difference compared to the RV-12). The engine does not come with the Rotax air box. It is an expensive option. If they specifically intended users to route the vent line into the filters that they supply with the engine, if not using teh optional air box, I would think that the very detailed install manual would direct the installer to do that. What it does say is "they have to be routed into a ram-air and vacuum free zone or into the air box" I am not meaning to say that routing into the filters is a bad idea (if your installation requires it). In your case it sounds like it was necessary. Where I disagree with you is that in a previous post you made it sound like if you do not use the optional air box then you should route the vent lines into air filters. The Rotax documentation does not say this.

lucien said:

"generalizations" in the sense of specifying a general requirement are not a mistake. General requirements that, say, cooling hoses be routed from the outlets on the engine to the radiator but leaving how they're to be routed, the exact brand and type of hose, etc., up to the airframe manufacturer are just the kind of thing you should expect from an engine manufacturer's documentation, particularly with Rotax's documentation.

Click to expand...

I wasn't meaning of generalizations in that context. I meant the generalization you implied by saying that because you had to do this modification to your Titan Tornado to get the engine to run properly at higher altitudes, that anyone flying with a Rotax 912 and not using the optional Rotax air box should do this modification also. I am not saying that it didn't solve your problem. I am saying that just because the problem existed on a Titan Tornado doesn't mean it will exist on an RV-12 (or any number of other airplanes using the Rotax 912).

Chunky said:

I just sold my Sportcruiser 2 months ago. It is definately alot faster than the 12. The Sportcruiser cannot maintain 120 kts, more like 115 TAS.

The Sportcruiser looks and is finished far better than the 12 too. The 'heavy' aileron takes getting used to but I think its more a case of super sensitive pitch than heavy aileron.

SportCruiser is still the Best LSA out there, in my opinion.

Click to expand...

I have flown the RV-12 on a 3500 mile round trip flight averaging 117 kts TAS. This is without the not yet available optional wheel pants...(so I am wondering where the "Alot Faster than an RV-12" comes from )

As for heavy ailerons I have never flown a Sport Cruiser so I don't know but I have found a preference for airplanes with nicely balance control harmony (which the RV-12 happens to have) rather than having to "get used to it".

rvbuilder2002 said:

My comment about modifications was in the context that they deliver the engine with the conical K&N filters (It sounds like you are using the round flat filters which is another installation difference compared to the RV-12). The engine does not come with the Rotax air box. It is an expensive option. If they specifically intended users to route the vent line into the filters that they supply with the engine, if not using teh optional air box, I would think that the very detailed install manual would direct the installer to do that.

Click to expand...

Unfortunately, the translations of the Rotax manuals are pretty Byzantine in a lot of places (I wonder where they got their translator ). I've been slogging through these things from Rotax for over 10 years now, but it's still sometimes like being a lawyer trying to figure out exactly what they're trying to convey in many cases.

What it does say is "they have to be routed into a ram-air and vacuum free zone or into the air box" I am not meaning to say that routing into the filters is a bad idea (if your installation requires it). In your case it sounds like it was necessary. Where I disagree with you is that in a previous post you made it sound like if you do not use the optional air box then you should route the vent lines into air filters. The Rotax documentation does not say this.

Click to expand...

True, but the smoking gun is the statement in 15.1.1 about pressure differences. That's the _result_ your installation has to achieve. Also, the way it's done with the airbox is strongly suggestive of what you need to do with the vents in case the box _isn't_ used and you use some other form of intake including just filters by themselves. And like I said, they make it clear (to my reading anyway) what the intended result is supposed to be.

Splitting hairs on the meaning of "...ram-air and vacuum free zone or into the airbox..." you do at your own risk (keep in mind the quality of their translations in so doing ).

I wasn't meaning of generalizations in that context. I meant the generalization you implied by saying that because you had to do this modification to your Titan Tornado to get the engine to run properly at higher altitudes, that anyone flying with a Rotax 912 and not using the optional Rotax air box should do this modification also. I am not saying that it didn't solve your problem. I am saying that just because the problem existed on a Titan Tornado doesn't mean it will exist on an RV-12 (or any number of other airplanes using the Rotax 912).

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Ah, ok, noted. However, I will still say the requirement on venting the carburettors applies to any 912 engine in any airframe. Yes, how you may meet the requirement may differ from one airframe to the next, but that "Pressure differences between intake pressure and pressure in the carburetor chambers may lead to engine malfunction due to incorrect fuel supply" holds true in every installation of this engine.

So any installation has to solve for that problem, regardless.

Like I said, I'm extremely suspicious of disconnected lines simply running along the sides of the carbs having met this requirement. Unless no air filters are being used and the venturis are completely unobstructed into the cowling I can't see how the lines and the carburettor mouths can possibly be guaranteed to be at the same atmospheric pressure at all times. Not without some really fancy engineering anyway.....

LS

todehnal said:

I think we are all interested in seeig pictures. Also, do you think that it would be beneficial to have the two carb vents tied together, as it would seem that an airbox would provide??

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Not unless the intake system was shared between the carbs like it is on the Rotax airbox. The lines would have to be routed seperately into each intake otherwise.
The 914 has a shared line system depicted in the parts manual, tho the 914 is a different animal altogether....

My other thought is that, if it's simply a matter of establishing ventura pressure to the vent line, why in the world wouldn't that be handled on the carb itself? It seems like that would offer a simple solution, anyway.

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I've asked myself that exact same question 1000 times ever since I ran across all this on my own 912 a while back.....

Looking forward to your pictures!!

Tom

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I'm currently not allowed to post pictures, so I'll only do so at the moderator's allowance.

LS

lucien said:

I'm currently not allowed to post pictures, so I'll only do so at the moderator's allowance.

LS

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Are you sure you are not allowed to post pictures? I have never heard of such a restriction and I am a moderator.

The pictures do need to be hosted elsewhere. This is the same for everyone. http://www.vansairforce.net/articles/ImagesInForums/images.htm

n5lp said:

Are you sure you are not allowed to post pictures? I have never heard of such a restriction and I am a moderator.

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Well it says I can't post attachments, which is generally the only way I could post .jpg's off my machine onto a post.

I can post links from http URL's but not attachments.

LS

Ah, wait. My bad for not RTFM. Sorry

LS

Hopefully this works. Anyway, here's a pic of the vent line-to-air filter setup I have on my 1/3 carburettor on my 912ULS. The fitting is a brass barbed connector I got at Lowes. Drill a hole, push it in (and make sure all the rubber bits are cleaned out of filter afterwards!)

LS



http://yfrog.com/2dcarbventj

Thanks for posting the pics LS. This is interesting.

Geico266 said:

Thanks for posting the pics LS. This is interesting.

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Yep, looks low tech and like something out of a low-grade sci-fi movie, but you can see the concept. The filter body is like a mini airbox/intake plenum and the vent line runs into it just like it does if it were the Rotax airbox.

A real head-scratcher (it was for me when I first had to research this), but this is indeed how the lines are supposed to be handled from everything I can gather in the manuals and talking to other folks who're experienced with 912 installations. I sure can't argue with the results as now the carbs run nice and lean all the way up to the SP alt. limit of 10,000' MSL.....

Strange but true.

LS

It seems the warmer the weather gets, the richer my plugs look. Has anyone tried venting the vent tubes into the air filters as described above in this post or had success in another way? The only change I made to the default carb set up was to lean the idle mix. It's getting into the 90's here in SC. Also, does anyone know at what rpm the idle mix no longer has an effect on the overall mixture?

Thanks, Rick.

Carb Setuo!

It seems the warmer the weather gets, the richer my plugs look. Has anyone tried venting the vent tubes into the air filters as described above in this post or had success in another way? The only change I made to the default carb set up was to lean the idle mix. It's getting into the 90's here in SC. Also, does anyone know at what rpm the idle mix no longer has an effect on the overall mixture?

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Some of the info on this thread is from a gentleman who is flying a 912 as a pusher on a ultralight. Which means that the engine is uncowled and installed in a totally different set up than the RV12. So disregard most of his advise. Don't connect you vent tube to your air filter. There are some Scenarios where fuel can come out of that tube, for instance if one of your floats in the carb bowl stops floating then as the bowl overflows it will come out that tube. So if you have it connected to your filter then you will get an even richer mixture in your carb, not good. What do you mean, "richer my plugs look"? What type of fuel are you using, 91UL or 100LL? How many hours a month are you flying? Once you start up do you keep your idle RPM at 1800RPM or Higher? Do you replace your spark plugs with new ones every annual? When was the last time you balanced your carbs? All that being said if you have a smooth idle at 1800 rpm or better and a smooth transition to full power then dont worry about the plugs. Just throw them away at annual and replace with new ones. They are only about $3.00 each. We fly in 100F here in Texas us 91UL 98% of the time with no problems. If you are running 100% 100ll then Im sure your plugs are going to look Dirty. Then put some decalin in your fuel. Good luck.

Photos

Post a photo of your installation and of the "barbed" fittings. I also fly from a high airport.

I guess I should have said "the darker my plugs look". Anyway, thanks for the reply. I think leaning my idle mixture has helped a lot. RV12Roger, look at post 28 for a pic of the barbed fitting into the air filter.

Rick

In Jan. of 2010 I was only about 2/3 thru my build so missed this interesting post. My question: Did any RV12 drivers do the mod LS promoted, and what were the results? Certainly is curious after 4 pages of posts there has been no further comment for over two years. Like the whole deal just evaporated. Or did it? Just very curious.
Dick Seiders