Raptor Aircraft

[Timbeck2]

Damn skippy you were blessed. You are obviously a steely eyed, skilled and handsome pilot if you've mastered the mighty Cherokee.

 

[Velocity173]

While I can't speak to the finances, Velocity is cranking out the twin kits as fast as they can make them.

Yeah I hear the twin is doing well. When I did my checkout there in 2011, they were hardly selling any singles. The brokerage and maint were keeping them afloat. Chief pilot was also in charge of the website. He’s left to go fly King Airs and the website is rarely updated these days. Good people though and I wish them the best with the V-Twin.

 

[OkieAviator]

While I can't speak to the finances, Velocity is cranking out the twin kits as fast as they can make them.

Which either isn't very fast or they all signed a secret pact to not post build logs, pictures or anything else out there about the V-twin.

I watched a number of the Raptor videos including this last one. Fairly depressing....

 

[Brad Smith]

I cannot feel sad for a company that promises performance numbers that would be difficult for Rutan to deliver and seem to have no clue on how to deliver on those promises. FUBAR

 

[FormerHangie]

I cannot feel sad for a company that promises performance numbers that would be difficult for Rutan to deliver and seem to have no clue on how to deliver on those promises. FUBAR

I had a feeling that this project was going to end up in disappointment, either in that the aircraft never got to the point where viable kits were available, or that it never came anywhere close to the promised performance. What always surprises me is the number of pilots that will accept extraordinary performance claims from designers with no track record. The current available aircraft are already pretty well optimized, there aren't any big gains to be had. If you want to go faster, either add power or make the aircraft smaller. If you want more room and want to maintain the same speed, you need more power, which uses more fuel.

Also, the specific fuel consumption of a diesel engine in pounds per hour is about 15% less than is a similarly powerful gasoline engine, so its effect on useful load isn't great, especially considering that diesels tend to be heavier. Since jet fuel is more dense than is gasoline, and also sells for less, there's a significant savings in fuel cost, but that may very well be more than offset by the cost of the engine.

 

[Datadriver]

Which either isn't very fast or they all signed a secret pact to not post build logs, pictures or anything else out there about the V-twin.

Not everyone screams look at me look at me, selfie, selfie, selfie, build log, etc. I am sometimes guilty of that.

 

[Crashnburn]

While I can't speak to the finances, Velocity is cranking out the twin kits as fast as they can make them.

Good to know, even though I'm only interested in the single engine airframes

 

[OkieAviator]

Not everyone screams look at me look at me, selfie, selfie, selfie, build log, etc. I am sometimes guilty of that.

Interesting perspective. However, it's more about supporting a community of builders and relaying lessons learned, build choices, problems and challenges encountered during the project. Trying to build a plane for the first time in a proverbial bubble would be extremely challenging.

 

[tspear]

Good to know, even though I'm only interested in the single engine airframes

I last talked to Velocity last spring. Back then, they had about a six month backlog if you wanted a kit. Regardless of model; if you wanted to build in the factory the backlog was closer to a year. So they still sell the XL, SUV models; however the sales numbers for the Twins are much better. The XL and the Twin in many ways fly in a similar manor; however from the Twin is much quieter, less vibration, uses two much cheaper engines....
Basically, the Twin is a much better plane in my opinion.

Tim

 

[German guy]

[...]
Basically, the Twin is a much better plane in my opinion.

It‘s also the only twin on the experimental market. I bet that many of the potential XL customers look at the RV10 as well and eventually settle on the latter.

 

[Tantalum]

That is an odd setback.. how often does your ECU in the car fail? Also, isn't there a limp mode, it's not like the thing would totally die

Granted, redundancy in AC is critical, but don't test pilots wear parachutes, and doesn't the aircraft have it's own chute as well? Seems odd. Also seems odd that they can't just get a second ECU on the thing with a simple arduino-type processor that could automatically fault to the redundant one if needed... or heck, just put a switch in the cockpit telling the engine which ECU to use.. I believe in the Diamond diesel FADEC you can cockpit select between ECU

Very peculiar..

What always surprises me is the number of pilots that will accept extraordinary performance claims from designers with no track record.

Not just pilots, but more so the general public and non pilot people, and those with money that you you want to attract as investors. Not uncommon for bold claims... and you're happy if you can deliver half of what you promised. Musk announced that his electric pick up is going to be "better" than an F-150... talk about bold claims! Most recently we have Celera promise us some serious pipedream figures...

The current available aircraft are already pretty well optimized

This is the part where I'll disagree a bit... the current crop of GA aircraft (Cirrus, Mako, most experimentals excluded) are effectively flying on 1950s technology.. wing, overall design, powerplant, etc. I fail to believe that the powerplants operating today's GA aircraft are "well optimized" .. I mean, take a Continental 550, you have a 9, NINE FREAKING LITERS, putting out a wimpy 300 horsepower. By comparison, my Toyota FJ has a 4 liter putting out 260 hp.. that put's out almost twice the power per liter than the Conti.. and that's a very basic Toyota engine that's gotten plenty of off road abuse.. and despite hauling around a box shape still manages about 19 mpg on the highway. If you get to into the performance car realm you can squeeze 100 hp out of a liter.. so Conti's putting out 33 hp per liter and AC engines still having a shoddy (at best) reliability record I'll say we're thoroughly in the dark ages on engine tech

I mean even looking at the experimental market you have very fast and capable machines with comparatively small engines sipping gas. I genuinely believe that this is one area where restrictive regulations have actually severely handicapped the advancement of safety


**I hope we continue to see innovation and bold claims.. in 1950's the average car could not boast the kind of performance specs a car built and sold today does... keep that in mind, the lion's share of GA aircraft flying are using 1950s tech.. or older, the engine tech is really 1930s era design. It's honestly completely pathetic

 

[jsstevens]

This is the part where I'll disagree a bit... the current crop of GA aircraft (Cirrus, Mako, most experimentals excluded) are effectively flying on 1950s technology.. wing, overall design, powerplant, etc. I fail to believe that the powerplants operating today's GA aircraft are "well optimized" .. I mean, take a Continental 550, you have a 9, NINE FREAKING LITERS, putting out a wimpy 300 horsepower. By comparison, my Toyota FJ has a 4 liter putting out 260 hp.. that put's out almost twice the power per liter than the Conti.. and that's a very basic Toyota engine that's gotten plenty of off road abuse.. and despite hauling around a box shape still manages about 19 mpg on the highway. If you get to into the performance car realm you can squeeze 100 hp out of a liter.. so Conti's putting out 33 hp per liter and AC engines still having a shoddy (at best) reliability record I'll say we're thoroughly in the dark ages on engine tech

I mean even looking at the experimental market you have very fast and capable machines with comparatively small engines sipping gas. I genuinely believe that this is one area where restrictive regulations have actually severely handicapped the advancement of safety


**I hope we continue to see innovation and bold claims.. in 1950's the average car could not boast the kind of performance specs a car built and sold today does... keep that in mind, the lion's share of GA aircraft flying are using 1950s tech.. or older, the engine tech is really 1930s era design. It's honestly completely pathetic

Apples to oranges comparison. There are three main areas where comparing car power plants to air plane power plants break down 1) cars develop high power at high RPMs which don’t translate to propellers without heavy, complex and inefficient step down mechanisms, 2) cars operate over a highly variable RPM range which makes their management for power and efficiency complex while aircraft operate predominately in a narrow and high (relative to the engine) RPM range (which can be easily optimized with simple mechanical systems), 3) cars operate on average at a low percentage of rated power (10-20%?) while airplanes operate at a much higher level (75%+) for sustained periods.

John

 

[will44s]

This is the part where I'll disagree a bit... the current crop of GA aircraft (Cirrus, Mako, most experimentals excluded) are effectively flying on 1950s technology.. wing, overall design, powerplant, etc. I fail to believe that the powerplants operating today's GA aircraft are "well optimized" .. I mean, take a Continental 550, you have a 9, NINE FREAKING LITERS, putting out a wimpy 300 horsepower. By comparison, my Toyota FJ has a 4 liter putting out 260 hp.. that put's out almost twice the power per liter than the Conti.. and that's a very basic Toyota engine that's gotten plenty of off road abuse.. and despite hauling around a box shape still manages about 19 mpg on the highway. If you get to into the performance car realm you can squeeze 100 hp out of a liter.. so Conti's putting out 33 hp per liter and AC engines still having a shoddy (at best) reliability record I'll say we're thoroughly in the dark ages on engine tech

There are definitely improvements that could be had but its not all disparaging. Our engines still stack up fairly well.
First the BSFC is almost identical. Low to mid .4 range.
As for the dismal power per liter, most of it is from the 2700rpm redline. If you pull up a torque curve of your FJ engine and see were the HP peaks it explains a lot.
And the trick for high reliability with high duty cycle hasn't changed in 70 years, electric or gas. Even new designs with those goals make there engines big and spin them slow.

 

[donjohnston]

Which either isn't very fast or they all signed a secret pact to not post build logs, pictures or anything else out there about the V-twin.

Not everyone is into creating content for the general public. That you can't find a build log has no bearing on how many kits have been sold.

 

[Tantalum]

John

Thanks for biting, it's a fun area to geek out on

1) cars develop high power at high RPMs which don’t translate to propellers without heavy, complex and inefficient step down mechanisms

True, they've managed to reduce auto displacement by squeezing out the hp at higher and higher RPMs.. but Rotax has done similarly and they use reduction gearing to get there and it hasn't been prohibitive in their proliferation. Automotive gearing has gotten quite efficient as well, with the elusive chase to higher and higher mpg, so the tech is out there

2) cars operate over a highly variable RPM range which makes their management for power and efficiency complex while aircraft operate predominately in a narrow and high (relative to the engine) RPM range (which can be easily optimized with simple mechanical systems)

This sort of makes my case though, you could optimize an already efficient auto engine and reduce much of the complexity and optimize out to one RPM range. Granted, you can't take an Audi engine (sorry raptor) and bolt it on to a plane and be done with it, but the tighter tolerances, laser cut and precision machined engines, etc., have yielded some remarkably efficient automotive engines out there... just imagine taking that and tweaking it as needed to get the desired performance

3) cars operate on average at a low percentage of rated power (10-20%?) while airplanes operate at a much higher level (75%+) for sustained periods

This is the part I disagree with though. At 33 hp per liter that Conti engine even at full tilt is not operating anywhere near the actual stress of what 85% to 100% power in a car would be, take this real world example:

Toyota: I have a Scangauge in my car and it shows that at highway speeds I'm using about 30% power.. this makes sense given that it's lifted, etc.. that 30% power works out to (.3*260)/4 = 20 hp per liter

Cirrus: At the typical 16.3 gph and 29.5 inches that works out to roughly "75% power"... so (.75*310)/9 = 26 hp per liter

.. that's fairly comparable in my book, and the FJ is relatively big displacement.. take the example even more extreme:

Toyota Celica: 180hp out of 1.8 liters... cruising on the highway works out to (0.25*180)/1.8 = 25 hp per liter... virtually identical to the Cirrus load

..realistically you could probably get 700 or 800 hp out of that Conti engine. It would disintegrate because of generally low tolerance sloppy build, but materially there are cars that are driven hard and put out *much* more than 33 hp/liter (even at "low" <30% power settings)

..but even just looking at the actual history... these engines have not had any real advancements made to them since the 1950's... they're still sand and die cast and handbuilt with large tolerances, each one operating a little different. Turbines on the other hand, thanks to commercial demand, etc., have advanced a long way since their genesis.. we didn't stop with the 1950's era turbines and say "well, that's it.. not much you can do at this point" - I mean even our fuel injection systems are a travesty, it's just a nozzle spraying fuel with abandon.. it's not actually timed out or metered the way they are in the auto world to hit cylinder chamber at the optimal point

 

[Tantalum]

There are definitely improvements that could be had but its not all disparaging

Is that a rotary engine rotor in your avatar?

 

[kyleb]

Aircraft engines have to run for 2000 hours at high power and the penalty for a major malfunction doesn't involve calling AAA. Other than in wartime conditions, you don't want highly stressed aircraft engines - reliability, not power, is the overriding consideration.

 

[Mtns2Skies]

If only we had an engine engineer... Oh wait!
@Ted DuPuis to the courtesy phone.

 

[SoonerAviator]

Aircraft engines have to run for 2000 hours at high power and the penalty for a major malfunction doesn't involve calling AAA. Other than in wartime conditions, you don't want highly stressed aircraft engines - reliability, not power, is the overriding consideration.

I don’t feel like 2,000 hours is exactly a high mark to hit with modern tech, and with many Lyco/Contis needing top end work inside that time, it’s not as if I’d call them Uber-reliable. It’s just that they’re about the only option save for a handful of other designs. A lightweight, liquid-cooled diesel is likely the best solution for most 4-6 person GA birds. Burns Jet A, will loaf along at low rpms without issue. Difficulty with them is the weight of traditional iron engine blocks and the power pulses are hard on gearboxes.

 

[GRG55]

That is an odd setback.. how often does your ECU in the car fail? Also, isn't there a limp mode, it's not like the thing would totally die...

How do you know it won't totally die? It is a completely untested and untried system in this application.

And what test pilot wants to risk the loss of the customer's airplane? It has no flight characteristics track record, so how to fly it in the event of a total engine failure is completely undocumented. So let's say the test pilot bails out. Just wait for the blame game and reputation damage to start. Who would want to put themselves in that situation over the lack of an extra box of transistors?

This is the part where I'll disagree a bit... the current crop of GA aircraft (Cirrus, Mako, most experimentals excluded) are effectively flying on 1950s technology.. wing, overall design, powerplant, etc. I fail to believe that the powerplants operating today's GA aircraft are "well optimized" .. I mean, take a Continental 550, you have a 9, NINE FREAKING LITERS, putting out a wimpy 300 horsepower. By comparison, my Toyota FJ has a 4 liter putting out 260 hp.. that put's out almost twice the power per liter than the Conti.. and that's a very basic Toyota engine that's gotten plenty of off road abuse.. and despite hauling around a box shape still manages about 19 mpg on the highway. If you get to into the performance car realm you can squeeze 100 hp out of a liter.. so Conti's putting out 33 hp per liter and AC engines still having a shoddy (at best) reliability record I'll say we're thoroughly in the dark ages on engine tech

I mean even looking at the experimental market you have very fast and capable machines with comparatively small engines sipping gas. I genuinely believe that this is one area where restrictive regulations have actually severely handicapped the advancement of safety


**I hope we continue to see innovation and bold claims.. in 1950's the average car could not boast the kind of performance specs a car built and sold today does... keep that in mind, the lion's share of GA aircraft flying are using 1950s tech.. or older, the engine tech is really 1930s era design. It's honestly completely pathetic

Here we go again...

If automotive engines could actually be converted to successful aircraft engines, in all the decades since Kitty Hawk wouldn't there be at least one technical & commercial success. We've had more than 110 years to do it. And it hasn't happened. Well, maybe the Ford Model A Pietenpol Aircamper engine might be considered a success.

Even the Merc-diesel based Diamond and Continental engines haven't proven particularly reliable or economical to own/operate so far. And I can't imagine the gobs of development money that have been spent on them so far, and continue to be invested to make them viable.

There's a reason Van Grunsven recommended RV builders stick with Lycomings (until he put a Rotax in the RV-12). There's a reason Cirrus uses that "old technology".

As for the Raptor, all this proved once again is designing, building and testing an airplane is an extremely challenging way to spend your time and money. There are far more failures than successes.

 

[Tantalum]

could actually be converted to successful aircraft engines, in all the decades since Kitty Hawk wouldn't there be at least one technical & commercial success

As for the Raptor, all this proved once again is designing, building and testing an airplane is an extremely challenging way to spend your time and money. There are far more failures than successes.

Without a doubt, I agree in general with all your points. But that doesn't mean we have to accept the status as quo and face this as the best we are going to get..

Automakers have had the luxury of billions of dollars of backing and an endless demand for their product and a competitive environment to refine what they're selling. The general aviation market by comparison is akin to maybe a small high-end boutique auto or yacht builder. Even the most successful organizations have limited funding and limited market forces to bring about change

I agree, you can't just take a car engine and put it on a plane and have it be it. But I do believe that are aircraft engines should have electronic fuel ignition and timing, tighter tolerances, and a host of other basic improvements.. it won't be the golden bullet so to speak, but we could probably squeeze some more reliability out of our engines and get 1 to 5 gallons per hour of efficiency out as well as some weight savings..

you brought up dimon too, they're actually a very good example, the da62 is comparable to the Cirrus and most performance specs, but burns a fraction of the gas and that's on two engines combined

 

[nauga]

Granted, redundancy in AC is critical, but don't test pilots wear parachutes, and doesn't the aircraft have it's own chute as well? Seems odd.

I'm not going to give you the full blast here but this strikes me as casual disregard for someone else's safety.

Also seems odd that they can't just get a second ECU on the thing with a simple arduino-type processor that could automatically fault to the redundant one if needed...

Fault tolerance and redundancy are seldom simple. It's easier to make a system less fault tolerant through redundancy than it is to make it more fault tolerant. Even making a manual switch adds new failure paths that must (OK, "should") be tested. I doubt the failure modes of the subject ECU in this kind of environment are well understood, and hope is not a good mitigation strategy.

I believe in the Diamond diesel FADEC you can cockpit select between ECU

Different ECU, different motor, different design environment, different level of testing for certification.

Nauga,
who has seen FADECs puke in flight.

 

[MtnMarcus]

While I can't speak to the finances, Velocity is cranking out the twin kits as fast as they can make them.

While I can't speak to the finances, Velocity is cranking out the twin kits as fast as they can make them.

So is CubCrafters and Kitfox.....over a 1 yr waiting list for some kits.

 

[Tantalum]

I'm not going to give you the full blast here but this strikes me as casual disregard for someone else's safety.

Blast away! It was less an indictment on the test pilot (not my intention for it to read that way) and more a genuine question about what kind of safety standards safety pilots expect... I assume the very nature of the job has higher risks.. I seem to recall watching an A380 flutter test where they took it past Vne (?)... not for the faint of heart! When I saw the Vision Jet on tour out here many years ago the interior was remarkably spartan.. I had madd respect for the dude who flew it and did the fly by's for us. If it were my company I'd never expect a pilot to do something they didn't feel safe doing, it does seem weird though that they discover these "show stopper" issues so far along in the game. Does make you wonder if there were perhaps other politics that pushed the test pilot to say "you know what man, F it, I'm out!" I'd have thought with enough cad and computer testing, hell even in X-Plane, and talking with engineers, these concerns would have been dealt with

Even making a manual switch adds new failure paths that must (OK, "should") be tested. I doubt the failure modes of the subject ECU in this kind of environment are well understood, and hope is not a good mitigation strategy.

That speaks to just poor planning then by Raptor. The DA62 has dual ECU on each engine, and they're tested out.. they auto switch when one fails and can be manually tested. He had years to put that audi engine through it's paces... I would have one running on a test stand 24/7 having it run through all sorts of scenarios.. I mean, the guy's been doing this for SEVERAL years and he's had the engine picked since day 1

Different ECU, different motor, different design environment, different level of testing for certification.

Sure, but for Raptor to realize this is a show stopper now... considering that they've moved from vaporware to an actual physical product that is near flight... that's bananas!

Tantalum,
Who has an answer for everything

 

[MtnMarcus]

Interesting perspective. However, it's more about supporting a community of builders and relaying lessons learned, build choices, problems and challenges encountered during the project. Trying to build a plane for the first time in a proverbial bubble would be extremely challenging.

building an airplane is "more about supporting a community of builders...."?? I think you'd you'd be the one that has the more interesting perspective

 

[AA5Bman]

Thanks for biting, it's a fun area to geek out on


True, they've managed to reduce auto displacement by squeezing out the hp at higher and higher RPMs.. but Rotax has done similarly and they use reduction gearing to get there and it hasn't been prohibitive in their proliferation. Automotive gearing has gotten quite efficient as well, with the elusive chase to higher and higher mpg, so the tech is out there


This sort of makes my case though, you could optimize an already efficient auto engine and reduce much of the complexity and optimize out to one RPM range. Granted, you can't take an Audi engine (sorry raptor) and bolt it on to a plane and be done with it, but the tighter tolerances, laser cut and precision machined engines, etc., have yielded some remarkably efficient automotive engines out there... just imagine taking that and tweaking it as needed to get the desired performance


This is the part I disagree with though. At 33 hp per liter that Conti engine even at full tilt is not operating anywhere near the actual stress of what 85% to 100% power in a car would be, take this real world example:

Toyota: I have a Scangauge in my car and it shows that at highway speeds I'm using about 30% power.. this makes sense given that it's lifted, etc.. that 30% power works out to (.3*260)/4 = 20 hp per liter

Cirrus: At the typical 16.3 gph and 29.5 inches that works out to roughly "75% power"... so (.75*310)/9 = 26 hp per liter

.. that's fairly comparable in my book, and the FJ is relatively big displacement.. take the example even more extreme:

Toyota Celica: 180hp out of 1.8 liters... cruising on the highway works out to (0.25*180)/1.8 = 25 hp per liter... virtually identical to the Cirrus load

..realistically you could probably get 700 or 800 hp out of that Conti engine. It would disintegrate because of generally low tolerance sloppy build, but materially there are cars that are driven hard and put out *much* more than 33 hp/liter (even at "low" <30% power settings)

..but even just looking at the actual history... these engines have not had any real advancements made to them since the 1950's... they're still sand and die cast and handbuilt with large tolerances, each one operating a little different. Turbines on the other hand, thanks to commercial demand, etc., have advanced a long way since their genesis.. we didn't stop with the 1950's era turbines and say "well, that's it.. not much you can do at this point" - I mean even our fuel injection systems are a travesty, it's just a nozzle spraying fuel with abandon.. it's not actually timed out or metered the way they are in the auto world to hit cylinder chamber at the optimal point

Well shoot I’m convinced. Hook me up with that 900hp IO-550.

 

[Tarheelpilot]

Blast away
Tantalum,
Who has an uninformed answer for everything

Fixed it for you. Lol.
Keep arguing with the guy that has all that pesky engineering and flight test experience.

Shoot man that sounds like something I would do. You’re slipping. Lol

 

[OkieAviator]

building an airplane is "more about supporting a community of builders...."?? I think you'd you'd be the one that has the more interesting perspective

Reading is hard....

 

[nauga]

I would have one running on a test stand 24/7 having it run through all sorts of scenarios..

I'm sure he's put a lot of time on the engine and ECU, but what kind of time and what kind of tests? Time alone is not an indicator of failure modes particularly in something software-driven, and a test stand (and test club?) never fully replicates the flight environment.

Sure, but for Raptor to realize this is a show stopper now... considering that they've moved from vaporware to an actual physical product that is near flight... that's bananas!

If I had a nickel for every first-flight readiness review I've been in where a showstopper has popped up I'd have...well, probably a good bit less than fifty cents, but it's not unheard of. In the civil experimental world it seems to be a lot more prevalent, and I think that is partly because of the lack of independent (non-advocate) inspections. Based solely on a single video (and therefore highly suspect) it sounds to me like expectations were perhaps a little unrealistic.

Nauga,
and the King's X

 

[nauga]

Does make you wonder if there were perhaps other politics that pushed the test pilot to say "you know what man, F it, I'm out!"

No, it does not make me wonder that in the slightest. I thought the video covered the technical issues well, even though it was clear he didn't agree with their severity.

Nauga,
who sees the design not the conspiracy

 

[Fallsrider]

He published another video yesterday. It looks like he's pressing on.

 

[jsstevens]

Thanks for biting, it's a fun area to geek out on


True, they've managed to reduce auto displacement by squeezing out the hp at higher and higher RPMs.. but Rotax has done similarly and they use reduction gearing to get there and it hasn't been prohibitive in their proliferation. Automotive gearing has gotten quite efficient as well, with the elusive chase to higher and higher mpg, so the tech is out there

Rotax's are small engines. What's the highest horsepower? 120? A reduction gear set for larger engines are much heavier, and have proven to be problematic. (GO-300, GTSIO-520 anyone?)

This sort of makes my case though, you could optimize an already efficient auto engine and reduce much of the complexity and optimize out to one RPM range. Granted, you can't take an Audi engine (sorry raptor) and bolt it on to a plane and be done with it, but the tighter tolerances, laser cut and precision machined engines, etc., have yielded some remarkably efficient automotive engines out there... just imagine taking that and tweaking it as needed to get the desired performance

The thing you're missing here is that the astonishing gains in efficiency and performance in auto engines are all about fixing compromises forced by the highly variable power & RMP range. If you're optimizing for a narrow band, you don't have to compromise - and, in fact, our piston aircraft engines are quite good in that regard.

This is the part I disagree with though. At 33 hp per liter that Conti engine even at full tilt is not operating anywhere near the actual stress of what 85% to 100% power in a car would be, take this real world example:

Toyota: I have a Scangauge in my car and it shows that at highway speeds I'm using about 30% power.. this makes sense given that it's lifted, etc.. that 30% power works out to (.3*260)/4 = 20 hp per liter

Cirrus: At the typical 16.3 gph and 29.5 inches that works out to roughly "75% power"... so (.75*310)/9 = 26 hp per liter

.. that's fairly comparable in my book, and the FJ is relatively big displacement.. take the example even more extreme:

Toyota Celica: 180hp out of 1.8 liters... cruising on the highway works out to (0.25*180)/1.8 = 25 hp per liter... virtually identical to the Cirrus load

..realistically you could probably get 700 or 800 hp out of that Conti engine. It would disintegrate because of generally low tolerance sloppy build, but materially there are cars that are driven hard and put out *much* more than 33 hp/liter (even at "low" <30% power settings)

First, you missed my point (maybe poorly communicated, I was typing on my phone): aircraft engines operate at a relatively high percentage (75%+) of rated power most of the time. Auto engines operate at a relatively low percentage of rated power (30% in your example) most of the time. Run that car engine at 75%+ of rated power and it's efficiency and longevity goes way down. They are not optimized for that case.

Second, hp/liter is not a measure of percentage of rated power (nor a measure of efficiency, really). Power is limited by how much oxygen you can pump through and engine. Remember the Renault turbo charged F1 engines that got 1,500 hp out of 1.5 liters (at 15,000RMP)? That was 100% of rated power and they lasted just about long enough for an F1 race (1-2 hours). Brake Specific Fuel Consumption (BSFC: https://en.wikipedia.org/wiki/Brake-specific_fuel_consumption) is a much better efficiency comparison. (@will44s cited in post #133).

Could you get some small level of improvement with tighter tolerances, EFI, etc? Maybe, but you're having to add weight & complexity (like water cooling-those "sloppy" tolerances are partly to accommodate wide temp swings in normal operation, gear reduction systems- getting the RPM up is key to lower displacement /higher power).

..but even just looking at the actual history... these engines have not had any real advancements made to them since the 1950's... they're still sand and die cast and handbuilt with large tolerances, each one operating a little different. Turbines on the other hand, thanks to commercial demand, etc., have advanced a long way since their genesis.. we didn't stop with the 1950's era turbines and say "well, that's it.. not much you can do at this point" - I mean even our fuel injection systems are a travesty, it's just a nozzle spraying fuel with abandon.. it's not actually timed out or metered the way they are in the auto world to hit cylinder chamber at the optimal point

I'll also add that turbines also benefit from being developed in a period of much better technology in related fields-and EVEN WITH THAT, turbines proved to be poorly matched to automobiles. What works in one arean does not necessarily translate to the other.

John

 

[SoonerAviator]

I always wonder about the gearbox issues. I mean, Volvo and Mercruiser have been making outdrives on boats for the better part of a century which run for several thousand hours without issues, in arguably a much harsher environment with higher horsepower/tq, and they have to shift to reverse as well! I realize they weigh a ton, but most of that weight has little to do with the gearset. I just find it odd that it's such a pain point for aircraft manufacturers.

 

[Tantalum]

Keep arguing with the guy that has all that pesky engineering and flight test experience

haha not trying to be argumentative, just genuinely curious about what kind of risk levels test pilots accept as "typical" .. I assume they're higher than what you and I would tolerate. Disappointed in Raptor that these show stoppers were discovered now.. crazy

 

[Grum.Man]

Not to further derail the topic but car engines are trending towards aircraft engine characteristics. I have hope that in a few years there will be a flood of car based options. Displacement is coming down due to turbo charging which also means the engines are incredibly light now. A lot of newer engines have exhaust and intake manifolds integrated into the aluminum head saving weight and bulk. Modern engines are designed to operate in a much narrower and lower power band often producing peak tq at 2k rpm or less. With CVT and 9-10 speed autos being common place now the engines are designed to operate in that 2500 rpm sweet spot that most 4 cylinder cars seem to cruise at on the hwy.

My GMC Terrain has a very compact 1.5T that produces peak TQ of 207 ft/lb at like 1800 rpm. I would bet at reduced rpm it would be a good match for something designed around a Rotax 914.

The downside of all of this is car engine prices are creeping up as well to the point where the delta between aero and auto is getting too narrow to justify.

 

[Tantalum]

he didn't agree with their severity

Thanks, that's the part that bugs. You should work with your engineer and flight test team, not "against" - especially when you're as small as he is. Anyway, thanks!

 

[nauga]

You should work with your engineer and flight test team, not "against" - especially when you're as small as he is.

Thanks, I’ll keep that in mind, but in any team with more than one person you will never have 100% concurrence on severity.

Nauga,
and his Part I**

 

[FormerHangie]

<SNIP>

This is the part where I'll disagree a bit... the current crop of GA aircraft (Cirrus, Mako, most experimentals excluded) are effectively flying on 1950s technology.. wing, overall design, powerplant, etc. I fail to believe that the powerplants operating today's GA aircraft are "well optimized" .. I mean, take a Continental 550, you have a 9, NINE FREAKING LITERS, putting out a wimpy 300 horsepower. By comparison, my Toyota FJ has a 4 liter putting out 260 hp.. that put's out almost twice the power per liter than the Conti.. and that's a very basic Toyota engine that's gotten plenty of off road abuse.. and despite hauling around a box shape still manages about 19 mpg on the highway. If you get to into the performance car realm you can squeeze 100 hp out of a liter.. so Conti's putting out 33 hp per liter and AC engines still having a shoddy (at best) reliability record I'll say we're thoroughly in the dark ages on engine tech

I mean even looking at the experimental market you have very fast and capable machines with comparatively small engines sipping gas. I genuinely believe that this is one area where restrictive regulations have actually severely handicapped the advancement of safety

**I hope we continue to see innovation and bold claims.. in 1950's the average car could not boast the kind of performance specs a car built and sold today does... keep that in mind, the lion's share of GA aircraft flying are using 1950s tech.. or older, the engine tech is really 1930s era design. It's honestly completely pathetic

I was really thinking more of aerodynamics, such as the claims he's making for the Raptor, but as long as we're talking engines..
What's important in an aero engine:

1. Reliable
2. Fuel efficient
3. Reliable
4. Reasonable acquisition cost
5. Reliable
6. Field serviceable

Oh, did I mention that they need to be reliable? As others have mentioned, the currrent low speed, direct drive, air cooled engines do their jobs pretty well, which is why they don't change much. Continental tried making engines that produced more power for their displacement, remember the Tiara series? Don't worry, no one else does either. One of their significant drawbacks were that they used more fuel than did the direct drive engine. If you look at the most efficient internal combustion engines, they are the very low speed diesels that power ships. These typically turn around 100 rpm, and are very large displacement. I don't doubt you could get a little better fuel specifics by adding electronic ignition and a better fuel injection system, but apparently not much, or else the existing manufacturers would have done so.

Don't forget about development cost. The total number of aero engines produced is very low, a modest sized automotive engine plant produces more engines in one day than the entirety of general aviation consumes in a year, there are not a lot of development dollars to be had.

I don’t feel like 2,000 hours is exactly a high mark to hit with modern tech, and with many Lyco/Contis needing top end work inside that time, it’s not as if I’d call them Uber-reliable. It’s just that they’re about the only option save for a handful of other designs. A lightweight, liquid-cooled diesel is likely the best solution for most 4-6 person GA birds. Burns Jet A, will loaf along at low rpms without issue. Difficulty with them is the weight of traditional iron engine blocks and the power pulses are hard on gearboxes.

An aero diesel really needs to be a clean sheet design, and the combination of low potential sales and a relatively low price per engine conspire against this happening. That general aviation seems content with flying its legacy fleet doesn't help either.

Not to further derail the topic but car engines are trending towards aircraft engine characteristics. I have hope that in a few years there will be a flood of car based options. Displacement is coming down due to turbo charging which also means the engines are incredibly light now. A lot of newer engines have exhaust and intake manifolds integrated into the aluminum head saving weight and bulk. Modern engines are designed to operate in a much narrower and lower power band often producing peak tq at 2k rpm or less. With CVT and 9-10 speed autos being common place now the engines are designed to operate in that 2500 rpm sweet spot that most 4 cylinder cars seem to cruise at on the hwy.

My GMC Terrain has a very compact 1.5T that produces peak TQ of 207 ft/lb at like 1800 rpm. I would bet at reduced rpm it would be a good match for something designed around a Rotax 914.

The downside of all of this is car engine prices are creeping up as well to the point where the delta between aero and auto is getting too narrow to justify.

While it's true that the turbo engines do produce peak torque at propeller friendly engine speeds, they don't make much power there. You might be able to get Rotax 912 kind of power out of that engine, but I bet it would be a good bit heavier than the Rotax as well

He published another video yesterday. It looks like he's pressing on.

I watched that. Now, not only would I not fly in that airplane, should it ever get aloft, I'd rather it not fly over my house. What are the principal's qualifications as an aircraft designer? It sounds like he's using the "that looks about right" method of design. He's at the point where he's looking for a test pilot and the prototype is shredding parts on a taxi test??

 

[Tantalum]

Now, not only would I not fly in that airplane, should it ever get aloft, I'd rather it not fly over my house. What are the principal's qualifications as an aircraft designer? It sounds like he's using the "that looks about right" method of design. He's at the point where he's looking for a test pilot and the prototype is shredding parts on a taxi test??

this is starting to remind me of a thread I read on sailinganarchy a couple years ago about a guy who planned to build a 20,000 square foot catamaran all by himself and sail it around the world.. the guy has zero qualifications but had apparently read "hundreds" of books on boat design.. needless to say the thing sank 20 miles off the coast of San Francisco..

 

[Tantalum]

Edit: it was 3,200 square feet and he studied "THOUSANDS" of boat designs: http://forums.sailinganarchy.com/in...y-32-foot-catamaran-3200sqft-of-living-space/