Veloce 600, 6 seat pressurized twin auto-converted engines.

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Vigilant1

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Around 0.56 psi actually.
Yep. Unless we are talking about airspeeds near and above Mach 1 (compressible flow), the highest pressures we can get ("q") are at the stagnation point.
 

Dan Thomas

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Traditional Continental mechanical injection has a return line; traditional (Bendix style) Lycoming injection does not have a return line. At least one of the sellers of experimental Bendix style injection does offer a 'purge valve' option in its system design, but it is not intended as a full time return line. It's purely to purge the hot-side fuel lines of boiling fuel prior to engine start when doing a 'quick turn' requiring a 'hot start' (bane of most injected Lyc flyers). The valve is supposed to be closed prior to engine operation.
The RSA system had some problems with that in the 172R & S airplanes and Cessna put out an SB and MK to add a return line: https://support.cessna.com/custsupt/contacts/pubs/ourpdf.pdf?as_id=23006

That applied to earlier models of those airplanes; models after that had the return system installed. It works the same as the Continental system. It's passive; working all the time without pilot selection.

The T182T has the return system from the factory. The T206H does not. Both Lycoming-powered airplanes.
 
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Dan Thomas

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Of course, if one's diesel can run on JetA, it can run equally well on jetA1. I have run diesels on things you could not imagine - they can be the ultimate multi-fuel engine. BTW in the real world we start and run diesels down into the -50 range...without heating fuel or using additives. Refiners vary formulations with region and season. The days of D2 coming up from the deep South in a gelatinized ball are long gone.
The SMA aircraft diesel is only certified for Jet A. Something about diesel having too little lubricity for their pumps or something.

Airliners do things like running hydraulic cooling lines through their fuel tanks to heat the fuel at altitude. Sometimes something fails; remember the British Airways airplane that had its engines flame out on final in London? The fuel had entrained water (common) freeze at altitude and block filters when the fuel got too cold. British Airways Flight 38 - Wikipedia
 

rv7charlie

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Thanks for the Cessna link; hadn't seen that. But...
1630691219482.png
And it's a Cessna thing; not an RSA thing. In the Continental systems I've seen, the return is a designed-in thing. I don't think the Continental system will function properly without it, while the RSA system is designed without it. Do you have different info? My experience is limited to homebuilts, and a couple of older certified planes running Continentals.

Charlie
 

Dan Thomas

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Thanks for the Cessna link; hadn't seen that. But...
View attachment 115081
And it's a Cessna thing; not an RSA thing. In the Continental systems I've seen, the return is a designed-in thing. I don't think the Continental system will function properly without it, while the RSA system is designed without it. Do you have different info? My experience is limited to homebuilts, and a couple of older certified planes running Continentals.

Charlie
Lycoming uses a diaphragm pump. Continental uses a vane pump that can agitate the fuel enough to cause bubbles to form. Both systems use header tanks to remove air that enters the system through tank outlet unporting.
 

PMD

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The SMA aircraft diesel is only certified for Jet A. Something about diesel having too little lubricity for their pumps or something.

Airliners do things like running hydraulic cooling lines through their fuel tanks to heat the fuel at altitude. Sometimes something fails; remember the British Airways airplane that had its engines flame out on final in London? The fuel had entrained water (common) freeze at altitude and block filters when the fuel got too cold. British Airways Flight 38 - Wikipedia
The failure of Bosch CP4 pumps in VW HPCR systems is a shocking reminder of just how shakey lubricity can be in ULSD. I seldom think of lubricity in jet fuels as the specs normally quoted by refineries do not include a line for wear scar value, but overall jet fuel has HORRIBLE lubricity, as does ULSD or Euro V (due to desulfurizing process damaging other polar compounds and aeromatics). BUT: ULSD meets the ASTM (D275??) standard by adding lubricity additives at the rack tank farms near the end of distribution channels. My experience is that such things seldom get done well or some times at all. This has ceased to be as critical with B10, as the FAME (Fatty Acid Methyl Esters) are actually pretty decent lubricants as I understand it. Now you are getting me curious as to WHY SMA chooses only to use what should be an ever poorer lubricity fuel.

Many hydrocarbons are quite hygroscopic (good thing for me, I make a living out of taking gases and water out of oil) thus why the filtration used at airports to try to keep Jet A/A1 relatively dry. International air carriers probably get to fuel at the same places where pilots get their jobs based on "who's yur Daddy?" so no surprise that something could come back home to UK with more water in the tanks than we would expect.
 

Hot Wings

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Well, with the similarity of preposterous claims, perhaps this new twin should be named... wait for it... the Veloce-Raptor !
So, what is the HBA record for number of likes for a single post?
...............Just started to read this thread.................can't get to sleep tonight.
 

rv7charlie

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Lycoming uses a diaphragm pump. Continental uses a vane pump that can agitate the fuel enough to cause bubbles to form. Both systems use header tanks to remove air that enters the system through tank outlet unporting.
Agree on the 1st statement (for a typical stock Lyc; carb or injection). Never seen an the guts of a Continental engine-driven pump, so I can't really comment on that other than to say that it seems counter-productive to use a pump that actually causes aeration of the fuel. I know for a fact that Lycoming (assuming that means Bendix style injection) does not require a header tank. There are some *aircraft* that may have a header tank, chosen by the *aircraft designer* to meet his/her needs in the design of the airframe, but that's not an engine/injection requirement. None of the Globe/Temco Swifts STC-converted to Continental IO360s that I've seen have any sort of header tank. The return goes to one tank, and the pilot must manage fuel to be sure that he doesn't pump fuel overboard when running off the other tank(s).

My experience with other certified airframes is basically nonexistent, but I am fairly familiar with how the Bendix style injection system works (Lyc powered Swift & Lyc powered RV6). A bit less with the Continental; just several friends' Continental powered Swifts, a couple of whom had random engine stoppages for years before finding the cause; air getting into the fuel via aging & failing flexible lines *on the suction side of the fuel pump*. The lines never leaked fuel, but would pass air into the line when under suction by the pump.
 

rv6ejguy

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The big difference between Raptor and this project are the men behind them. PM had zero background in Aero, engines, structures, systems etc. Mark is an actual engineer who has a huge engine background, aero background, having designed other aircraft before and has worked in the industry for many years. He also listens to others and runs his ideas past other engineers for their ideas and critical thoughts.

No design is proven to perform to projections until it flies no matter who is behind the design process but this is a very innovative design by someone who has the background to actually do it properly. I'm skeptical if it will meet all of the specs but let's sit back and see how it does perform.
 

lelievre12

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Really, before you post, I'd suggest you research what's already been done for years now...
Errrr. We are talking about using auto engines at 35,000 feet and NOBODY is doing that now nor ever did. Even the 'high altitude' B29 Stratofortress was only certified to 32K.

The research and papers I presented clearly show that there WILL be serious issues with using volatile fuels at 35K and its simply dreaming to expect Mogas with a vapor pressure of up to 14PSI could ever operate at 3PSIA. It wont. It will boil away. If it was easy, everyone would have done it and you would have seen B29's flying at 40K. Its not easy which is why Avgas is specially formulated to have a higher vapor pressure and even with this high octane, still is altitude restricted.

Of course when flying at 25K/7PSIA or lower, Avgas and maybe even some Mogas is stable and wont boil. At these altitudes EFI systems work just fine. We are not debating that. We are looking at what happens when you go higher. I know as I have done it and a T210M will readily develop serious fuel pressure fluctuations when attempting to operate near its ceiling (27K). The POH even has an emergency procedure and I quote:

EXCESSIVE FUEL VAPOR - Fuel flow stabilization procedures
1. Aux pump on (to pressurize the suction side of the main engine fuel pump)
2. Mixture Reset
3. Change tanks (to select the cooler head tank where return fuel has not heated incoming fuel).

And this engine has a fuel pump specially designed to handle vapor.

If you think you can simply port all the hot return fuel from your EFI regulator back to the main tank and shoot straight up to 35K, then good luck with that. Any heating of the fuel at 35K will simply boil it away faster than the lapse rate already will. And any pump, even auto EFI pumps will have a suction side trying to take a feed from that boiling fuel. Since none of these have vapor handling systems its not unreasonable to expect trouble.
 
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Vigilant1

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Of course when flying at 25K/7PSIA or lower, Avgas and maybe even some Mogas is stable and wont boil. At these altitudes EFI systems work just fine. We are not debating that.
It seems useful to acknowledge that we were debating that, and now the goalposts/positions have shifted, which is fine and good. But before it was:

As a start, it's not possible to use Avgas at above 22,000 feet easily as its Reid vapor pressure range is only 5.5 to 7 psi. At 35,000 feet, standard pressure is only 3.5 psi so all your Avgas just boiled out of the tank and turned to vapor.
As a practical operational matter, the performance difference (range, TAS, weather, etc) is only slightly different between 25k MSL and 35k MSL. It would be useful to explore the challenges/ tradeoffs needed to go to 35k, and for Mark to consider them. It is a good discussion to have. If it costs a lot of weight, money, complexity/reliability, then flying a bit lower will be the obvious choice, and won't extract a big penalty.
The modern examples of aircraft successfully using mogas and avgas at altitudes well above 22k can be a useful guide.
 
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Dan Thomas

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Agree on the 1st statement (for a typical stock Lyc; carb or injection). Never seen an the guts of a Continental engine-driven pump, so I can't really comment on that other than to say that it seems counter-productive to use a pump that actually causes aeration of the fuel. I know for a fact that Lycoming (assuming that means Bendix style injection) does not require a header tank. There are some *aircraft* that may have a header tank, chosen by the *aircraft designer* to meet his/her needs in the design of the airframe, but that's not an engine/injection requirement. None of the Globe/Temco Swifts STC-converted to Continental IO360s that I've seen have any sort of header tank. The return goes to one tank, and the pilot must manage fuel to be sure that he doesn't pump fuel overboard when running off the other tank(s).

My experience with other certified airframes is basically nonexistent, but I am fairly familiar with how the Bendix style injection system works (Lyc powered Swift & Lyc powered RV6). A bit less with the Continental; just several friends' Continental powered Swifts, a couple of whom had random engine stoppages for years before finding the cause; air getting into the fuel via aging & failing flexible lines *on the suction side of the fuel pump*. The lines never leaked fuel, but would pass air into the line when under suction by the pump.
The Continental fuel pump:

1630773533169.png

How it fits in the system. Note that the pump is facing the other way in this pic:

1630773814100.png

Somewhere here I have a better schematic of the system, with the vane pump shown end-on and how it moves the fuel. Continental uses that pump as one of the means of metering the flow; more engine RPM means more fuel delivered, with the fuel control taking inputs from the throttle and mixture controls to have the final say as to what the injectors get. A vane pump is a positive-displacement pump, delivering more fuel for more RPM.

Lycoming's diaphragm pump is also positive displacement, but not as precise due to the flex of the diaphragm. And it produces fuel flow in pulses, not so steadily. Lycoming (RSA) uses a big bunch of other stuff to control fuel flow before the fuel controller has the final adjustments made by the throttle and mixture.

1630774184463.png

The detail at top left is actually the mechanism at the bottom right; attached to the throttle body.

A good article on the RSA: Bendix and Beyond
 
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rv7charlie

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On 1st look at the RSA drawing with that split drawing of the throttle body assy, I thought we were talking about different systems. :) The Lyc pump's diaphragm spring regulates pressure, so there's no return line. The various boost pumps used with the Bendix system have internal bypass regulators which return the bypassed fuel to the pump's inlet. So with 'stock' systems, there's no return line to a tank.

Thanks for the Continental drawing; I frequently seem to learn stuff when I disagree with someone. (again, :) ) I am confused by the 2nd drawing of the pump, though. It looks as if the inlet (purple), feeds the same chamber in the pump assy as the fuel return line, the 'low pressure bypass', and the 'vapor return' (which I assume means the return to the tank). Is that correct?

(You high flying 6 seat guys, just ignore the conversation going on over here in the corner...)
 

Toobuilder

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There are rotary fuel pumps used on some Lycoming/Bendix models. The turbo 540 used on some Aztec models is one example
 

Toobuilder

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There is a pad on the accessory case. I really would like to figure out a way to build one up for EFI use to make the airplane "less" electrically dependent. But in reality, EFI is all or nothing. Its like being "a little" pregnant.
 

rv7charlie

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I haven't tried to prove it, but I strongly suspect you could go up a size or two on the electronic injectors and run the stock 20-30 psi Lyc engine driven pump. Spray pattern would probably still be better than a lead-clogged Bendix injector. ;-)

The injectors still suck a bit of current, but nothing like the injection pump. At that point, a little vac pad driven B&C PM alt could be the 'magneto' for all engine electrics, with the main a/c alt as the backup. If the rotary had an accessory pad to drive a fuel pump, I'd certainly use a mechanical pump.
 

rv6ejguy

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About 5% of Bendix equipped Lycs have the rotary Lear type pumps and some folks have used them with EFI, same with the Conti pumps. Here though, we are talking auto engines and EFI which pretty much exclusively use electric pumps and certainly won't be using certified type mechanical pumps or metering units.
 

rv7charlie

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I was just responding to Toobuilder's desire to reduce current consumption, possibly by using regular Lyc diaphragm pump.
 

Dan Thomas

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(again, :) ) I am confused by the 2nd drawing of the pump, though. It looks as if the inlet (purple), feeds the same chamber in the pump assy as the fuel return line, the 'low pressure bypass', and the 'vapor return' (which I assume means the return to the tank). Is that correct?
Found the pump schematics in my old textbooks.

1630795120411.png

1630795179464.png

The fuel is centrifuged to remove any bubbles. I had to look it up and review it. Last studied it a long time ago. Any vapor generated by the pump can still get into the injection system. The bypass valve at the bottom opens if the pump fails, letting the boost pump provide fuel under pressure.

And that boost pump, at least in the Cessnas, has a variable-speed function controlled by a couple of adjustable power resistors in the supply circuit, with a microswitch on the throttle body to short one of the resistors when the MP goes past 19" or so, and the other resistor is shorted by the Emergency side of the boost pump switch. Getting those resistors adjusted right is a pain, as is setting the low and high unmetered fuel pressures. The Lycoming/RSA is so much simpler, since its mechanisms sort it all out.
 
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