Weight and balance with a Jab 3300?

It looks as though a 3300 would add about 40 lbs to the aircraft. I have a private ticket and am not limited to Light Sport. The ease of wing removal and re-install, plus ease of construction, makes the aircraft very attractive to me. The 3300 would improve climb and a bit of speed in the cruise. The Vne is listed at 149mph (from what I have been able to find out). The correct prop should give a pretty good climb rate while staying safely under the Vne.

I guess the big question is "can a safe range for weight and balance be achieved"? Any opinions?

I guess the big question is "can a safe range for weight and balance be achieved"? Any opinions?

The simple answer is yes you can fix the weight and balance issue created by the heaver engine with lead in the tail, it is safe. You would be giving up more payload, you indicated about 40 pounds for the engine then perhaps 5 to balance the aircraft and if you are making a nice cross country aircraft you will want the auto pilot, wheel pants, lights and interior. This will take your empty weight up to about 820 pounds and will leave you with only 500 pounds of payload then less the 20 gallons of fuel at 120 pounds and you are down to 380 pounds of cabin load and if going cross country you would need the 50 pounds of baggage so you would have 330 pounds left for the seats. This works for a guy that is the FAA standard 170 pounds and his trophy wife but may be of concern to some of us that are a good bit larger and who like to fly with our male friends who are not 120 pounds.

The RV-12 is the result of many small and some large compromises just like all aircraft and the use of the light weight Rotax engine and the cab forward design works very well but it does not like a change to a heaver engine very much, good luck with you plan to improve the RV-12 and keep us informed as to the progress as it will be most interesting.

Best regards,
Vern

Have you considered looking a a wobbly prop option on the Rotax instead? Indeed, what about a 914 with a VP?

Get the right plane for the mission!

Since you are not limited to Light Sport why not just build 9A or 7A?

Jetguy said:

Since you are not limited to Light Sport why not just build 9A or 7A?

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The 12 is a bit quicker and easier to build. The build process (pulled rivets for the most part, etc) allows me to do it with out assistance most of the time. Being able to store off airport (no hangar fees) is definately a plus.

Just a few reasons I can think off just off hand. I would love to build a 7, but given the higher cost per hour to operate and unavoidable hangar fees etc., it is not in the cards for me.

Not so simple??

Since you are going to redesign the front of the airplane and the firewall (yes?) anyway, would it possible to shorten the front of the fuselage a bit and then mount the engine closer to the wing leading edge? Lead weight in the tail really compounds the aeronautical problems and is not a good solution. I'd like to see how you do all of that. Best of luck and skill.

It's probably being planned

The folks at US Jabiru completed a FWF kit for the Rans S-19, and I was under the impression that they will be doing the RV-12 next.

Check with them... http://www.usjabiru.com/

I've got no dog in the fight, but I do like the idea of the simple, air cooled, higher HP Jabiru for LSA use.

Good Luck! dj

Update: Just found this thread: http://www.vansairforce.com/community/showthread.php?t=66354

It appears they are doing a FWF for the smaller Jab. Probably a bit disappointing for those interested in a 3300 powered RV-12. It will be interesting to see performance numbers on this one. But this is experimental aviation!

I hadn't caught in the other thread that they were using an 85 hp Jabiru (2200). Considering the Rans S-19 is using the 3300, that's a bit disappointing. I thought the weight was about the same between the Jabiru 3300 and the Rotax (but not sure where I got that idea!).

Bob

My question is, "Why do you want the 3300 over the 912?"

The 912 is a great engine and the extra HP will only really help with climb, not so much with cruise, and the climb rate (900 FPM at GW) is pretty darn good. (Better than a C-172, PA28, etc.)

Put a 914 turbo in your EAB.

Jabiru -12

The completed, flying weight of the Rotax is about the same as that of the flying Jabiru 3300. The Rans S-19 we built weighs the same as the factory-built S-LSAs, it's faster and it climbs better. You can read an unbiased opinion here: http://www.bydanjohnson.com/Sidebar.cfm?Article_ID=1355

We are building the RV-12 with the 2200 first to see how it performs against the Rotax-powered E-LSAs. Then we may move on to the 3300. The main issue is not weight and balance at all, but the geometry of the firewall. The RV-12 is a lighter airplane than the S-19 and we think it will perform well with an even further reduction in weight as equipped with the 85-hp 2200. I posted a link to our photo build log in the RV-12 Project Status thread.

Thanks!
Katie
Jabiru USA

N941WR said:

My question is, "Why do you want the 3300 over the 912?"

The 912 is a great engine and the extra HP will only really help with climb, not so much with cruise, and the climb rate (900 FPM at GW) is pretty darn good. (Better than a C-172, PA28, etc.)

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I think that many, including myself, like the simplicity(?) of air cooling without the radiator and all the other related hardware. Not that a Rotax is a bad engine. But given a choice of a bit more HP and no radiator hardware... it becomes attractive.

Arguably the RV-12 is one of the easiest builds in the kit industry based on a well designed, parts/component complete and very well documented kit. That is what attracts pilots like myself that have a full PPL. (That and I see LSA in my future medically )

Jetguy's point is well taken... especially if Dirtbos is looking for an easy build. Going outside of Van's specs and plans will add some complexity to the build. Might as well build a -9.?

Phyrcooler said:

..................Going outside of Van's specs and plans will add some complexity to the build. Might as well build a -9.?

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I posted my reasoning for going with a 12 previously in this thread. "Easier" to me means being able to build the plane alone, more than anything. I have fabricated all of my life. Scratch built long travel 400 to 500 hp sand cars as an example. A 12 would be a "piece of cake". If Jabiru USA is able to work out the installation, it will be my choice. They have the "skill" and know how. I would be able to perform the modifications without a problem.

I have flown the Rotax 912 in the Sport Cruiser and others. It's OK but I don't like the engine. It is my understanding that the 912 performs its best at sea level and "runs out of throttle" at higher altitudes. The 3300 does not. It may produce a better true airspeed at altitude. It will be interesting to see the performance numbers if Jabiru USA does do the conversion. I doubt it will "set the world on fire", but it should be a bit better.

As suggested in an earlier post, I also like the simplicity. Both in the installation and maintenance.

Dirtbos said:

It looks as though a 3300 would add about 40 lbs to the aircraft. I have a private ticket and am not limited to Light Sport. The ease of wing removal and re-install, plus ease of construction, makes the aircraft very attractive to me. The 3300 would improve climb and a bit of speed in the cruise. The Vne is listed at 149mph (from what I have been able to find out). The correct prop should give a pretty good climb rate while staying safely under the Vne.

I guess the big question is "can a safe range for weight and balance be achieved"? Any opinions?

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After some research regarding your question (actually it was done before you posted the question) I've concluded it will be difficult to hang any engine on the RV-12 other that the 912. The reason being the airplane was literally designed around the Rotax engine.

I would prefer a 0200 or 0235 for the simplicity, reliability and track record of these engines. But in conversing with one of the guys at Van's, it became clear such an installation would require much modification and it certainly won't guarantee a better airplane.

So why do it?

It makes more sense to select an airplane that will accommodate the engine you want to use rather than get it to work in the 12.

If I did a 12, I would go with the 912. There are thousands of the them in service and they work. It is the engine of choice for LSA applications.

I've also learned that Don Rivera has decided to market his fuel injection system for the engine if the twin carbs seem a bit too quirky. I saw the proto type when at his shop last year. I don't know how sensitive the engine will be to manual leaning but that can be worked out.

Direct drive is preferable in my book, but I do not know anything about the Jab 3300. I do believe Zenith has one installed in the factory 750 but I don't know how it is working out.

Good luck.

All non-supercharged engines "run out of throttle" at higher altitudes, including the 3300. Proper mixture control does help, but doesn't remove the basic fact of less air up there.

You can adjust the prop on an RV-12 for better cruise speed and less climb or better climb or more cruise speed, regardless of the engine. But that's the trade-off, unless you install a governor and variable-pitch prop.

And unless you can remove and reinstall the wings by yourself in less than half an hour, you won't bother. It'll be too much trouble to haul the plane to the airport, set-up, preflight, fly, refuel, disassemble, haul it home and put it away. There's no way you'll go for a midweek lunch flight, for example. But any of the RV aircraft, including the -12, can be tied down outside. Consider a canopy cover and lock.

Dave

The 2200 is lighter than the 912 but produces 15 less hp, the 3300 is about 35 pounds heavier than the 912 but produces 20 more hp so you have a tradeoff there. All naturally aspirated engines lose power in direct proportion to air density changes at WOT.

Both engines have their warts and both work pretty well when installed and operated properly so you have choices based on personal preference. That's a good thing.

Both engines benefit from fuel injection but users have to weigh the cost against hp and fuel flow benefits.

Dirtbos, I notice David's comment...

"After some research regarding your question... I've concluded it will be difficult to hang any engine on the RV-12 other that the 912. The reason being the airplane was literally designed around the Rotax engine."

...is exactly what Van stated in one of the post-introduction videos that are available at the Vans website. You may feel the task is well within your capabilities, mechanically speaking, but given the talent pool at Vans I'd explore the idea with Ken Kreuger and/or even Van, if possible, to further vet the notion.

In digging for RV-12 info here and elsewhere, the feedback I've received is that there are two generic reasons to prefer a 3300 or 200 over the Rotax: the engine's considerably more complex (complexity not usually being a good thing in GA aircraft), and the USA distribution/support system leaves something to be desired. Having said that, these two engines appear to have their own issues in the 'real world' as well (adequate heat dissipation & failure to make it to TBO for the 3300; weight & cost for the 200). Most 912 owners seem generally satisfied with the engine and manage to cope acceptably with the Rotax issues, so in your shoes that would take me back to gaining a clearer understanding, from a design standpoint, about the liabilities of moving away from the 912.

Good luck on the digging.

Jack

Dirtbos said:

I have flown the Rotax 912 in the Sport Cruiser and others. It's OK but I don't like the engine. It is my understanding that the 912 performs its best at sea level and "runs out of throttle" at higher altitudes. The 3300 does not. It may produce a better true airspeed at altitude. It will be interesting to see the performance numbers if Jabiru USA does do the conversion. I doubt it will "set the world on fire", but it should be a bit better.

As suggested in an earlier post, I also like the simplicity. Both in the installation and maintenance.

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For what it's worth, the 912ULS on my Tornado gives no abnormal trouble at high altitudes. I can still get about 600fpm climb at 10,000' MSL and the EGT's still run in the 1300F range. The Jab will have the same altitude-related power losses since it's also a naturally aspirated engine.

Another disadvantage of the Jab is the high RPM operation, especially with the 2200 - you have to run a pretty small diameter prop to accommodate the higher RPM power output. The effect on climb performance vs. the 912 (with an approx. 2200 rpm prop speed) is going to be obvious (tho it should perform well at speed).

Finally, I havn't found my 912 to be a high maintenance engine. The worst problems I've had on mine have all been routine maintenance issues, the most expensive being the carb rebuild I had to do at 400 hours. You'll have to periodically change the coolant and the rubber hoses - every 5 years if you really want to go by the book, but my hoses are still in good condition at 5 years (so I'm going "on condition").

There's also a lot of mythology about the gearbox which is pretty much just that - horror stories only. The 912ULS gearbox is very strong and has lots of built-in self protection (overload clutch and dog hub system). Vans uses the Sensenitch prop on it also which (I'm pretty sure) meets the MOI requirements of the box. As long your prop isn't a gigantic monster that weighs a ton, the gearbox gives no trouble. So the RV12 installation shouldn't give any trouble.

My 912 has been basically a change-the-oil-and-go-fly engine for the last couple years I've owned it.

So personally, I'm not convinced the Jab would necessarily be a preferable alternative to the 912 on the RV12 airframe. On other planes, yeah, but I don't see any advantage on the 12....

LS

Jack Tyler said:

..................so in your shoes that would take me back to gaining a clearer understanding, from a design standpoint, about the liabilities of moving away from the 912.

Good luck on the digging.

Jack

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All I am going to do at this point is wait and see. Jabiru USA apparently has had good success with the S-19. If they are able to build a successful RV-12/3300 combination and fly it successfully, it will be a viable option for me and others. They are in the business of selling engines and aircraft. If they are able to put the combination together, it will be to their benefit (RE: engine sales). In my opinion, it will also be to the benefit of many potential builders. If it "can?t be done" as many of those who have posted here have indicated, they will not proceed. Time will tell.

It would seem to me that the only issues would be weight and balance and rudder pedal space (due to firewall modification). As stated above, the overall installed weight of the two engines are very close. So it would probably boil down to the 3300 engine location in regards to the firewall. We?ll see.

lucien said:

Another disadvantage of the Jab is the high RPM operation, especially with the 2200 - you have to run a pretty small diameter prop to accommodate the higher RPM power output.

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Not sure I understand this statement. Both Jabiru engines, 2200 and 3300, are rated at 3300 rpm.

Mel said:

Not sure I understand this statement. Both Jabiru engines, 2200 and 3300, are rated at 3300 rpm.

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Right - that translates to max power at 3300 _prop_ rpm, with, of course, decreasing power outputs available as you go down from that. I believe the 3300 has a little flatter power curve below 3300, but my recollection is a little foggy. So I stand corrected if there's not a difference between them?

OTOH, the 912 ULS with the 2.43:1 ratio, develops max power somewhere around 2200 prop RPM (at the gearbox of course). Quite a bit lower RPM which allows a larger prop diameter to take advantage of the power available at that RPM.

Quite a bit more usable RPM range for a plane like the RV12. On other airframes, it's not such a big disadvantage, but on the 12 it probably would be....

LS