I would not write them off yet.
An IO540 is a very good engine. And speed is hardly affected by weight, at speeds well above Vbg (typical piston GA cruise point on the curve).
58 USG is not good however. They ought to increase it. I am sure they can. Most wings are not fully used.
I think the MOGAS requirement is misguided because in their market only 100LL is relevant.
Also I know for a fact that anything up to and including 9.5:1 is fine for 91UL – this has been proved in the US Experimental market. Lycoming are unfortunately running a complex business-political agenda and they could just as easily not certify the IO390 because they want to withdraw support for it (due to low sales) but they don’t want to say so openly.
Customers who want efficiency with a small cabin will go to Mooney
I think that involves a number of dodgy assumptions 
And speed is hardly affected by weight…
Speed not, but payload, fuel consumption and range are. And I think, for most buyers the latter three far outweigh speed.
An IO540 is a very good engine.
In 1955 I might have agreed. With this old standard engine that a lot of airframes share, there is just nothing left about the Panthera that would be innovative. They stand no chance against the competition. For less money than a new Panthera you will get a Cirrus SR22T G5 which has oxygen, TKS, 5 seats, more payload, etc. Unless they switch to a Diesel engine, they can just as well give up and save money. What the market really doesn’t need is a new airframe that isn’t significantly better than the existing.
An IO540 is a very good engine
It is. But the fact that the Panthera was trying to define a market segment with the engine previously planned, it is a disaster for this project.
What this does look like is unfortunately a not uncommon marketing disaster which leaves the development team between a rock and a hard place.
- The Panthera was expected to run 200 kts.
- The Panthera was expected to work on Mogas.
- The range of the Panthera was based on the consumption of the IO390.
all of this was marketed as an airplane which will fly 200 kts and 1000 NM range.
The obvious reason for the switch to a big bore engine is that they could not make it run 200 kt with the IO390. So they decided to sacrifice the efficiency and the Mogas compatibility to a larger engine in order to reach the marketing promises at least where speed is concerned. Whether this will happen is open, but what is brutally clear is that with this engine they are in one bed with just about all the other airplanes in that segment but with significantly reduced range (if the fuel quantity stays the same). so the Panthera has no advantage over either the Mooney Acclaim, the SR22 (ok, it is faster but has much shorter legs) or the Corvalis. Instead it might run 200 kt but for maybe 2 hours plus reserve (with 58 USG) so it’s range will be near 400 NM instead of 1000…..
So the question would be: What DID it actually run and how was the performance in general with the IO390 and wouldn’t it have been better to admit their bragging and publish real figures (maybe 160-180 kts, which still outruns the SR20 or even the Mooney 201) and a range of 800 NM due to the speed loss? What would be the better airplane?
IMHO with this step, all the advantages this plane had are gone.
Pipistrel’s remark that “We are targeting the same cruise speed of 200 knots true” does indicate that the IO-390 would not have met that target. In that case the problem is aerodynamics. And then the range also suffers, no matter which engine.
Adding 90 lbs at the forward end could be a CoG challenge, even if the weight increase can be handled without major structural changes. The battery could be moved to the tail, but that would mean long heavy cables. On the other hand, for all I know there could have been a rear-CoG problem in the IO-390 design, and the IO-540 could be a solution.
The IO-540 will be a little more expensive to maintain. It will probably burn more fuel than advertised, although that will be due to aerodynamics rather than because of the IO-540, which I believe has the same sfc as the 4-cylinder. Larger internal friction is partially made up for by delivering the same HP at a lower RPM. (That is my experience based on comparing O-540 in PA-28-236 with 4-cyl Lyc’s in PA-28.)
The Panthera was in a difficult market from the beginning, and probably had too small fuel tanks from the beginning too. Poor manufacturer’s support, handling quirks, new operational restrictions, a couple of bad accidents or many other things could destroy the project, but I don’t really see the engine switch change that much. Added payload is an advantage. If the rest of the promises hold up, I think it is still an attractive and interesting aircraft.
That’s my view also i.e. we cannot be sure the IO540 will be a disaster.
The engine is not much less efficient. Sure it has greater losses but those are significant (relative to an IO390 or even IO360) only at unrealistically low power settings – as can be seen here by extending the curves to the “south west” till they intercept the zero power output, and doing the same for the other engines.
The engine fund will be higher too, but at c. €15/hr it is barely significant today against the fuel price. And the increment in the engine fund over an IO390 is likely to be utterly negligible. Even more utterly negligible if the “industry” shafts that engine on OH costs, due to the very low numbers in existence. Look at the huge OH costs of (especially some rare variants of) TIO-540 engines as an example – really not justified by the actual work that needs to be done, unless you are throwing away an inconel exhaust system and the turbo(s). I don’t have the numbers to hand but TB21 owners – TIO-540-AB1AD – have seen astronomical OH quotes – $120k in one case I recall. That engine variant is used only in one other aircraft which is an unmanned drone. But any engine shop can OH an IO540-xxxx. It would not surprise me if Pipistrel, who being almost wholly Rotax players, and not experienced in the big engine marketplace, had belatedly realised that the IO390 would be a liability because nobody (literally nobody?) uses it.
I do think they need bigger tanks. At least as a factory option. Is the wing already completely full? Very few GA wings are full. Most are limited seemingly arbitrarily, sometimes maybe for structural reasons.
The back mounted battery is OK. The TB20 has the same. The positive cable is about 6mm diameter – my guess would be 1kg. The negative is the airframe
More payload is always great. Most GA types really struggle with being legally loaded.
It is probably true the test flights showed their perf claims would not be reached, but that is pretty normal for GA. I recall 210kt TAS claimed for the original DA42. How far off is that, for that variant?
OTOH just because something is normal doesn’t mean it is good, because a bug chunk of the market would have been the much better efficiency. They are bound to deliver much of that still (the cockpit design is an impressive exercise in internal space versus volume of air to be displaced in flight) however.
Jetfuel/Diesel is not going to happen. (balance issue)
yes, the 540 is heavier than the 390, but the stall speed of the Panthera is significantly lower than originally calculated, so the extra weight of the engine is welcomed with an even higher useful load than originally quoted for the 390 installation. The official numbers will come out in a few months. Prepare to be pleasantly surprised.
390 engine is still available for “experimental” customers.
Certified Version will only have the 540.
an even higher useful load than originally quoted for the 390 installation
Well, it better be higher, because the new engine will need more fuel and that has to be carried.
As a first measure, Pipistrel should finally stop their bullshit marketing and understand that those people who really buy aircraft can’t be fooled that easily. Bullshit marketing actually has bad effects as people will get very wary of companies doing that. Remember the DA42 disaster? ISTR that they were all also quoting that magic 200-knot number ten years ago…
And unless Pipistrel increase the fuel capacity, they will lose the final bit of credibility within the business…
Why not jetfuel?
The sma is not heavier then an io540. It is roughly 440lbs. it would be a so much better choice..
And for a given range, a lot less fuel on board to start with..
Justbecause, you sound like you are associated with the company, correct?
