Two others have now come forward with their data, another Subaru and a Mazda.
I saw the Mazda.... I haven't yet seen a substantiated equal weight Subaru.
The fact is there are lots of people now flying RV's with Lycomings after swapping out a failed or unsupported sub. engine install. They know exactly what the weight difference is. The info is out there for anyone that actually wants to find it.
Here is W&B of two very similar airframes to compare. Both were weighted on the same certified scales.
It is sad that a lot of information regarding successful engine conversions is supposed to be taken at face value, but when anything is detected as even slightly negative, a way is found to discount it. Anti alternative engine people are always criticized for being closed minded, but it appears to go both ways.
If weight differences in many instances of engine swaps are mentioned, it is discounted because engine swaps "always result in other changes happening at the same time" that makes the information useless.
How do you know that?
I know of numerous instances where it was not the case. Changes to airplanes (other than removing some alternative engines) rarely make them lighter, but even if that were the case, that would mean that the weight reduction change by switching to a Lyc would have been even more than 105 lbs, because the new changes likely added some weight.
Or in other cases were very similarly equipped airplanes have weight differences of 100 lbs or more, it is discounted because evidence is not being provided the proves the airframes are otherwise exactly the same.
If your goal is to know that the weight difference is 85 lbs vs 100 lbs, this is important. But a difference of 85 lbs is still not trivial and will have to be dealt with, which makes this info still useful to people working through the decision on what powerplant to use.
I am involved in experiments with RV's on just about a daily basis so I am not ignorant on the importance of the fine details. But I also know that when we are talking about big differences that influence performance, that info can be very useful as well, even if we don't know an exact # down to the pound or Kt.
Regardless of what may be thought, I am not anti alternative engines. These forums are full of older posts I have made regarding the subject, so I wont bother repeating any of it (and causing this thread to drift off the cliff any further after this).
What I am a big proponent of is full disclosure of the real world experience that experimenters have... all of the good and the bad.
That comes from years (decades actually) of dealing with RV builders via tech support and seeing the aftermath that results from them not going deep enough with there research.
If a subi engine installation can be done that results in an airplane with a power to weight ratio that is equal to that of a Lycoming, then the far right side of the experimental movement has failed a lot of people because there is tons of evidence to show that if it is being done successfully, only a small percentage that try are able to find the holy grail they seek.
If it is something easily within reach there must be a serious break down within the experimental culture.....
What I did actually say was that the U.S. representatives of Rotax (the ones that work directly with OEM customers) actually advise OEM customers that it will require more cooling system capabilities. And I also said that I myself didn't understand the scientific reasons for it, but that doesn't mean it is not real. If you are not willing to accept that, it is your prerogative. What would be my motive for making that up? Unless you assume that it implies an improperly engineered engine installation. If that were the case then all the OEM customers are making the same mistakes (including the designer and manufacturer of the engine).Scott, you asked me to take the Rotax 912iS increased cooling requirements at face value a couple months back where your comments made no logical sense and you said you couldn't provide details to back up your statements.
I can see from your many posts you feel everyone should have a Lycoming in their RV. That's fine. Your opinion is crystal clear. We got it.
As we've seen countless times, some folks will take pretty well any opportunity to diss alternative engines, for any reason. .
I am having visions about using an F1 Rocket as a starting point and stuffing an LT 4 (650 HP supercharged ZO-6 engine) partway into a deeply concave firewall to keep the C of G manageable. The pilot would move to the back seat and the front seat would be gone. P51 style rad and scoop below. Bruce B would be taking another run at the altitude record if you put full length -4 wings on it.
It should be lighter than a 540 Rocket with 2 guys.
I would really like to know more about the RV7 that this thread began with what a cool setup sort of like those 3/4 Mustangs at Reno .Sort of like putting the Exp in Exp aircraft .I bet you could get around 300hp direct drive LS2 at less than 3000rpm .Sure would be a great thread with no bickering from the usual experts.
Bob
I am also not concerned about the auto engine itself, more about the added components (e. g. gearbox) and the engineering and testing associated with it. If it's done right, I don't see why a auto engine conversion couldn't be just as reliable as a 'real' aircraft engine. The engineering and testing part however seems to be an almost impossible hurdle to overcome for small companies.
No, it is not impossible. To be blunt, engineering and test doesn't get done because most of the folks doing them are ignorant in the dictionary sense (i.e. simply lack the required knowledge), and/or just blow it off.
I've been interested in alternative engines since the mid-90's. I knew a lot about engines, so how hard could it be? Bought a "tested" drive from a vendor, which turned out to be a mess in multiple areas.
Fast forward. After OSH 98 we measured and modeled the old drive, did a torsional analysis, tweaked the model inputs for a better result, designed a drive to match the new model, built that drive, and conducted live torsional telemetry for comparison to the computer model...tied to a truck in front of my hangar, with an obsolete FM transmitter, a cast off o-scope, and a Fluke multimeter. Crappy equipment, but we got great data, so much so that we designed a viscous torsional damper for the drive, then built and tested it, further reducing measured shaft and belt loads. When I flew it to S&F in the spring of 2000 I knew exactly what was going on up front. The Wheatstone bridge was still glued to the propshaft, protected by a strip of duct tape...which almost nobody asked about.
I was lucky; "we" included my friend and mentor Steve Crow, a very, very smart guy, so I had a huge push up the learning curve. Thanks Steve.
Point is, first, it required knowledge, deep knowledge, in an area totally unfamiliar to the average well-qualified builder. I simply didn't know what I didn't know, and what was on the message boards back then was mostly BS (still is). Second, it required a lot of work. But third, tools were available, it didn't require cubic dollars, and 90's was the Dark Ages compared to the tools available today. Remember, this was just two guys, with one at long distance.
Look around. Alt engines have already entered the mainstream. For example, Continental now says there are about 5000 Mercedes-based diesels out there. They're certified, the CD-135 and CD-155. Yep, the early ones were a mess...but you don't hear much about them now. The factory is all in, with committed engineers doing the work, getting the data, making the improvements. That's what it takes. Check back in another 10 years.
If a guy wants to "experiment" with TLAR design, then do the break, fix, break, fix routine until he has a useful system, well, fine. It's not a lot better than the 1000 Monkeys Method, but given enough time and effort it can work. Hopefully the guy is having fun with the challenge, but I assure you, the engineering and measurement method is just as much fun, and a whole lot more successful.
I have a real jones with vendors who use the Monkeys Method with customers, while convincing them they are "experimenting". Kurt covered that very well. If the customers really know what they're getting into, fine, but most don't.
Not to kick the dead, but I once walked down the road at S&F while having a conversation with Bud Warren, who informed me that "All that torsional stuff is just bulls####. I don't even think it exists." Kinda made my head spin, but it didn't seem like there was any point in trying to convince him. That's EAB.
Talking RV7A N577AZ shown in #10 in this thread? CoolGood Day all,
Im the new owner of the black lawn dart with the ls1 in it. Feel free to ask any questions.
I love this thing
Bring it to KWVI anytime! Would love to see it!
According to Flight Aware, it's flown about a dozen times in the last 9 or 10 days.The LS-1 plane has been parked outside @ X50 in Florida for at least a couple of months. I have not seen it fly.
Good Day all,
Im the new owner of the black lawn dart with the ls1 in it. Feel free to ask any questions.
I love this thing
GMC, he responded to me on YouTube.. Empty weight of 1412, fueled up at 1664, gross weight of 2400 (yikes) pounds!
The LS-1 plane has been parked outside @ X50 in Florida for at least a couple of months. I have not seen it fly.