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UL Power/RV-12 Weight and Balance

Just reviewed the Jabiru 2200 Weights. We are almost exactly the same
at each station (Arm) and total weight.


Alschief said:
Just weighed our RV12 with the UL260Is engine. It is as close as I can gety it to a final weight at this time.
The weights were 158 lbs Front, 267 Lbs. L Wheel 272 lbs R Wheel
697 lbs. Total.
We are validating the engine mounting location.
I need the Arm's used by another builder to confirm my arm values for the above locations.

https://picasaweb.google.com/111690756223683866568/January18201202#
Click to expand...
 
Very well done.

We saw two UL Power engines at Sebring and they are a fine example of beautiful workmanship....machined cylinder fins, rather than cast and overall, a well detailed engine.

If the innards hold up as well as it looks, it should be a great motor...and no gearbox.

Best,
 
pierre smith said:
We saw two UL Power engines at Sebring and they are a fine example of beautiful workmanship....machined cylinder fins, rather than cast and overall, a well detailed engine.

If the innards hold up as well as it looks, it should be a great motor...and no gearbox.

Best,
Click to expand...

I saw the same engines you did and I agree. Not only does ULPower has beautiful workmanship, but I also love the simplicity of the engine, air cooled, EFI, direct drive. Can't get any better than that. :D
 
pierre smith said:
We saw two UL Power engines at Sebring and they are a fine example of beautiful workmanship....machined cylinder fins, rather than cast and overall, a well detailed engine.

If the innards hold up as well as it looks, it should be a great motor...and no gearbox.

Best,
Click to expand...

I know that no gear box seems like a big benefit... less weight, less parts to fail, etc, but there is a very specific reason that an engine like the Rotax 912 has a gear box.... Maximized Performance.

Any engine that has to turn a prop. faster than about 2800 RPM to get good power output, is not living up to its full performance potential.
The smaller prop. diam. that is required to keep the tip speeds in check when turning the prop at higher RPM's is less efficient than turning a longer blade (higher aspect ratio) propeller at lower speed (this is one of the major factors that has prevented the VW conversions from ever reaching their true potential).
 
Here I go again

I say that because I voiced similar concerns in the Jabiru engine thread a while back. A response back was ?don't worry, we do this for a living and we know what we are doing and we won't do something that won't work.? OK, I am fine with that, nothing more said.

Now here I am again about to say what some don't want to hear. I am taking deep breaths contemplating submitting this post.

My main points:
Rudi has it right (in a different thread) when he says the 12 is a sweet spot regarding payload and performance within the LSA envelope. Van's says the design works because it is an integrated package and everything is sized and specifically designed as light as possible. I sure hear that, having built one and massaged every part in the plane.

Weight & Balance
When moded out with most of the alternate engine choices the sweet spot appears to go away, my opinion. An additional 20 pounds on the nose-wheel may result in forward CG issues with typical passenger loads when the fuel is burned off. Remember the pilot and passenger sit forward of the spars and the CG in this design. What is going to happen to the happy control harmony?

Structural integrity
Look at the firewall. The structure and motor mount hard points sure appear to be specifically designed for the Rotax circular engine mount. The Rotax is an 87 cubic inch power plant. It makes it's horsepower through RPMs not a lot of torque. An engine with twice the displacement is going to have heavier reciprocating parts and potentially more vibration issues. Look at the top motor mount hard points (picture below). They are unlike all of the other heavier built RVs which have the top and bottom motor mount brackets widely spaced with the top brackets tied directly into the longerons. Those firewalls are designed for a variety of engines.

Here is a picture of one of the RV-12 top motor mount brackets.
632289448_3da4Y-L.jpg

These brackets are just pop riveted onto the instrument shelf. Now I am not an aeronautical or structural engineer but the design looks minimal and optimized for the Rotax power-plant to me. To cantilever a heavier and more powerful engine off these mounts an additional 12? or so forward of the Rotax position seems cavalier to say the least.

I agree the UL engines (and others) are a work of mechanical art. They are simple, traditional but modern and not too expensive. They would be great perhaps on a redesigned and more robust firewall with careful consideration of weight & balance, or an RV-9.

The argument for choice in engines with the ability to chose price, air or water cooling, manufacturer, USA or import, etc. is a strong one. The question: Is the 12 compatible? Doubts exist in my mind.

My only reason for posting is safe RV-12s and happy pilots. Do I sound too much like a Van's Fan Boy? I guess I am.;)

Tony
 
Man I take my hat of the to the real experimenters out there! You are pushing the status quo.

That said very little of these experiments turn out to be better, and you have to compromise somewhere on the original design.

I said it somewhere else too, I am happy to stay with the masses the std vans 912 design, it works and it works good. Lots of people put hours on that design and we have safety in numbers. I don't want to do the re-engineering or be a constant test pilot for my own FW FWD design.

So as a general rule for safety I support Tony. Not all of us has the inclination to do better, but if you can and pull it off, WELL DONE my hat of to you!
 
Firewall redesign

I too am taking a deep breath-----I tend to agree with Rudy that the firewall was designed around the Rotax engine. My concern has always been centered around the engine mounting and related firewall components differing greatly greatlhy from the typical Continental and Lycoming installations. I just have to have faith in Van's engineering staff and their understanding of Rotax's requirements for potential destructive forces involved with thrust, torque and vibration. Rotax engines have been around for a long time and have thousands of hours installations to gather experiencial data from which hopefully has been applied to the RV12 installation. I would think that any other power plant would have unique dynamics that would dictate the design of the engine mount and the structure of the fire wall.

Due to potential liability issues, I would think that a power plant provider would want to provide testing with their engines installed on a stationary mock up of the RV12 firewall before offering the substitute engine. If the engine mounting and firewall system did not show signs of fatigue or cracking or any other failure after several thousand hrs of testing then engine provider has shown proper due-diligence.

As a design build mechanical contractor I have witnessed 100's of mechanical and electrical failures caused by unproven design on non-conventional installations.

All that being said, my hats off to those who are willing to venture into the unknown and unproven. In closing, I hope that the engine providers will be responsible and provide adequate testing on the RV12 installatin before too many of us fly off into the eternal wild blue yonder.

Gary
 
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Tony, you mention "To cantilever a heavier and more powerful engine off these mounts an additional 12? or so forward of the Rotax position seems cavalier to say the least."

While the ULPower 260iS is more powerful, it isn't heavier, though its more-compact (front to back) design makes the leverage look different.

As for the comments about needing a shorter prop to use peak hp (at UL's 3200rpm), when an outfit like, say, Sensenich matches an airframe and engine, they take that into account. A prop must match both; there's a lot more science involved than meets the eye, and certainly a lot more than mere length and pitch numbers can tell you. And you still need ground clearance for the prop tips.

As for CG shifts, that won't be a factor; once the CG of the FWF is established (based on the weight and placement of components), the effect on the "happy flight controls" will be just about nil. Remember, the installed weights of the FWF packages are very close.

Were I doing it, I'd probably add mounting to intersect the longerons, as well. With the slight weight advantage of the 260 (it's lighter, so more structure can be added), I think the small added mount weight of the added tubes and backing, etc., (maybe a pound; two, tops) would be well-placed. (So, I would not be adding structure to support a heavier engine -- 'cuz it's not heavier; I'd be doing it to have a stronger assembly.)

And remember that the torque on the airframe isn't a result of the torque of the engine; it's a reaction to the torque on the propeller and its relationship to the torque axis -- and all those arguments about longer blades and slower rotation translate into more torque on the mount from the Rotax... which makes the factory mount, with its mounting points and narrow track, more questionable from this standpoint. But I trust they have a pretty good handle on what's needed.
 
Tim Kern said:
Tony, you mention "To cantilever a heavier and more powerful engine off these mounts an additional 12? or so forward of the Rotax position seems cavalier to say the least."

While the ULPower 260iS is more powerful, it isn't heavier, though its more-compact (front to back) design makes the leverage look different.

Were I doing it, I'd probably add mounting to intersect the longerons, as well. With the slight weight advantage of the 260 (it's lighter, so more structure can be added), I think the small added mount weight of the added tubes and backing, etc., (maybe a pound; two, tops) would be well-placed. (So, I would not be adding structure to support a heavier engine -- 'cuz it's not heavier; I'd be doing it to have a stronger assembly.)
Click to expand...

Technically, the 260iS is about 10 lbs. heavier than the Rotax apples to apples, with exhaust, rads, oil cooler, oil and coolant. The power to weight ratios are almost identical.
 
Seems like it's a question of numbers. If it makes sense and you are EAB, I say go for it. I LOVE "EXPERIMENTAL".
 
rv6ejguy said:
Technically, the 260iS is about 10 lbs. heavier than the Rotax apples to apples, with exhaust, rads, oil cooler, oil and coolant. The power to weight ratios are almost identical.
Click to expand...

Go with the new li battery and the weight would be equal�� and you would have more juice for your electronic toys (I mean instruments)!
 
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rv6ejguy said:
Technically, the 260iS is about 10 lbs. heavier than the Rotax apples to apples, with exhaust, rads, oil cooler, oil and coolant. The power to weight ratios are almost identical.
Click to expand...

Technically, the installed weight of the 912uls is 160.2 and the UL260iS is 159.3. They are nearly identical in weight with UL being slightly lighter as someone else mentioned earlier. If you're building E-AB, the UL260iS has a lot lower price with a cost saving over the Rotax of nearly $10,000, plus fuel injection, FADEC control and the option of a 50A alternator and no gearbox. And all the talk about inefficient prop speeds ignores that the no one runs the UL at redline of 3300rpm, but rather cruising in the 2600-2700rpm range, which when mated to the right prop, makes for a very fuel efficient, speedy, quiet, smooth engine setup with a little more horsepower and a lot more torque.
 
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RV 12 Version

Ron

It would be very interesting if vans offered a version of the RV12 with a UL engine and wing tanks.

Vans has the ability to do this best.

I think they would sell more than the current version.

Joe Dallas






QUOTE=rongawer;1028016]Technically, the installed weight of the 912uls is 160.2 and the UL260iS is 159.3. They are nearly identical in weight with UL being slightly lighter as someone else mentioned earlier. If you're building E-AB, the UL260iS has a lot lower price with a cost saving over the Rotax of nearly $10,000, plus fuel injection, FADEC control and the option of a 50A alternator and no gearbox. And all the talk about inefficient prop speeds ignores that the no one runs the UL at redline of 3300rpm, but rather cruising in the 2600-2700rpm range, which when mated to the right prop, makes for a very fuel efficient, speedy, quiet, smooth engine setup with a little more horsepower and a lot more torque.[/QUOTE]
 
joedallas said:
It would be very interesting if vans offered a version of the RV12 with a UL engine and wing tanks.
Vans has the ability to do this best.
I think they would sell more than the current version.
Click to expand...

If that came about, I would sell my CT and buy an RV-12 (S-LSA).
 
912 weight

Weight rotax


Engine with carburetors
124.7lbs / 56.6Kg

Exhaust System
8.8lbs / 4.0Kg

Air Box
2.9lbs / 1.3Kg

Air Filter
0.7lbs / 0.3Kg

Liquid Radiator
2.2lbs / 1.0Kg

Oil Radiator
1.1lbs / 0.5Kg

Regulator-Rectifier
0.2lbs / 0.1Kg

Installed Weight
140.6lbs / 63.8Kg

Weight/power ratio
1.41lbs/HP / 0.87Kg/KW

ul
Installed weight
72.3 kg [159.3 lbs] (including all accessories, oil and exhaust
 
Nice start

Nice Start

Now add the break down showing True HP, wet weight, hoses, fuel system, CG arm of engine, vibration, cost of engine, cost of rebuild of each engine, cost of gear box service.

and also a photo of the final look of the install.

Some like Rotax and some of us Just Don't.

That is why it would nice if we had a choice.

Joe Dallas


crashley said:
Weight rotax


Engine with carburetors
124.7lbs / 56.6Kg

Exhaust System
8.8lbs / 4.0Kg

Air Box
2.9lbs / 1.3Kg

Air Filter
0.7lbs / 0.3Kg

Liquid Radiator
2.2lbs / 1.0Kg

Oil Radiator
1.1lbs / 0.5Kg

Regulator-Rectifier
0.2lbs / 0.1Kg

Installed Weight
140.6lbs / 63.8Kg

Weight/power ratio
1.41lbs/HP / 0.87Kg/KW

ul
Installed weight
72.3 kg [159.3 lbs] (including all accessories, oil and exhaust
Click to expand...
 
I must admit the ULs look great and specifications and price are promising as well.
We are pretty close to the factory and quite few in use around here.
Unfortunately they seem to have a poor reputation and I have seen builders replace them by Rotax and an LSA munufacturer change their production line from UL to Rotax. Both for good reasons.

I have got two 912's and quite happy with them.
I think the gearbox and resulting efficient large prop ar a bonus.
There are issues with every engine but 40000 airworthy ones do mean something compared to the handful UL ones.
 
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