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Raptor Composite Aircraft

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BBerson

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My RC friend got addicted to the Raptor bi-weekly videos. He is retired and builds race cars and knows how to weld and rivet. The Raptor thing might get him interested in aviation and get him involved in Kitplanes. He said his wife is watching the Raptor videos now!!
 

pictsidhe

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My RC friend got addicted to the Raptor bi-weekly videos. He is retired and builds race cars and knows how to weld and rivet. The Raptor thing might get him interested in aviation and get him involved in Kitplanes. He said his wife is watching the Raptor videos now!!
That is what I like the least about the Raptor videos. New people to the hobby think that Peter is a shining example of how to build an aircraft.

His brainwashed fans occasionally chip in to this thread. It's horrifying just how they think he is a home building god and that the conventional homebuilders just don't have a clue. Yeah, the people with successful builds, designs and businesses behind them. Some of those Raptor fans are possibly going to build Raptor quality planes.

Anyone interested in kit planes after seeing the Raptor videos NEEDS to read this thread. Yes, that will take some time. Or, they can wait a few more years to see how the Raptor pans out in reality.
 

berridos

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Wasnt it jeff kerlo the one doing the composite work? He is supposed to be a well reputed composite expert. How is it that his eyesballs didnt became white when laying up the sheets for the keel. Maybe he thought he was laminating an U-Boot?
 

Deuelly

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Wasnt it jeff kerlo the one doing the composite work? He is supposed to be a well reputed composite expert. How is it that his eyesballs didnt became white when laying up the sheets for the keel. Maybe he thought he was laminating an U-Boot?
Jeff is on this site as "Canardlover". He has commented on the lack of input he had.

Brandon
 

cblink.007

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It's horrifying just how they think he is a home building god and that the conventional homebuilders just don't have a clue.
Before I was furloughed at American, I had a fellow pilot who defends this monstrosity as if it's the last best hope for General Aviation. He proudly admits that he was one of the first to place a deposit all those years ago, and openly admitted that he has donated more than $20,000, sent DIRECT to PM, because he "believes in the Raptor", and wants to see it fly. He actually believes in PM's bulls#!+ promises, and thinks the Raptor is "the finest GA aircraft ever developed".

What is scary is that this guy is a check pilot in my former airframe. He should absolutely know better, but he is an example that a sucker is born every day!
 

Mike0101

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Long time reader, first time posting.

Reading "jet guy's" comment on, 9:1 pressure ratio being required for this turbo diesel at 25,000 ft to maintain see level performance, peaked my curiosity.

Tried to quickly find base engine boost, then extrapolate out to 350 hp. Best I could do was find this http://www.volkspage.net/technik/ssp/ssp/SSP_350.pdf VW doc/pdf.

Of interest is, original engine had VNT turbo, believe Borg Warner. Other notable features include, laser honing, wide band 02, and Mass Air Flow (MAF)... Actually a reasonably impressive engine, too bad diesel-gate appears to have been it's demise.

Back to 9:1 pressure ratio, it is in the ballpark for 25,000 ft. That's PT6A turbo prop territory PR and final centrifugal compressor stage isn't aluminum (not sure what alloy, but likely something in high nickle super alloy family, some GE engines (turbo prop) are close to stainless steal metallurgy). Looking at videos when turbos are visible, the sizing at first glance is completely wrong. It may work (to some extent) on a truck where you are trying to get more boost and want to supercharge OE turbo. Density altitude appears to have been completely ignored. Then, flow path appear wrong too.It is very doubtful that this setup will get anywhere near 9:1 total pressure ration. I'd actually worry about bursting a compressor wheel, with any luck it will self govern due to sonic chock (the right hand side of compressor map).

Since this portion is about turbos;
* Bearing and seal losses aren't anywhere near 1%. Think an order of magnitude more. Some older designs incurred 30-40% losses and this has been documented in various tech articals/papers as well as text books.
* In theory turbos can be free, that's when your exhaust back pressure is lower than your boost pressure. It has been done in low boost and narrow window. If your backpressure exceeds boost pressure, then piston is doing negative work on exhaust stroke... Then get backpressure high enough and your VE (volumetric efficiency) plumets - too much residual gas trapped.
* VNT, depending on type is usually about optimizing velocity triangles in low speed region.

The redrive/PSRU to me is a bigger concern in not being directly coupled to engine. At best, he simply wipes out engine main bearings or thrust bearing, but likely both. Didn't spend much time looking at belt drive.

I'd actually pay money to see the tune/calibration... As others have mentioned, this/raptor isn't even half baked.
 

TFF

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There is 283 pages of this. I know the score. It’s overweight. So. Add another 1000 lbs. no rule says you can’t. You can add another 1000 after that. At some point either the physics of wing loading or structure wins and it can’t fly. Until then it can fly. How good is unimportant. Sounds like I’m defending this thing, but flying and flying well is two different things. No one is saying it’s going to fly well. It’s a joke, as Foghorn Leghorn would say.
 

jet guy

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Back to 9:1 pressure ratio, it is in the ballpark for 25,000 ft. That's PT6A turbo prop territory PR and final centrifugal compressor stage isn't aluminum (not sure what alloy, but likely something in high nickle super alloy family, some GE engines (turbo prop) are close to stainless steal metallurgy).
The PT6 and all turboprop and turboshaft turbines using a centrifugal compressor stage use a titanium wheel. No stainless or nickel alloy has ever been used for centrifugal wheels; the density is more than double that of titanium, and hence the centrifugal loads also.

Nickel alloy blades have been used in the last couple of stages of very high pressure modern turbofans, and here we are talking of pressure ratios of over 40. Those blades are so much smaller at that level flow density that the material weight can be tolerated. But even here we now have the latest titanium alloys that can go up to 600 C, so those are taking over and the latest engines have no nickel compressor blades at all. Titanium makes up about a third of total engine weight in modern turbofans.

As for the 9 to 1 pressure ratio in Peter's engine. It is straightforward to find the pressure ratio required to hold SL pressure at altitude. At 25,000 ft the atmospheric pressure on an ISA standard day is 0.37 that of SL, ie the pressure delta. The inverse of that is 2.7 so that is the pressure ratio you need to hold the same manifold pressure as SL. Plus he already has a PR of about 3 at sea level to begin with, so you are going to be in the region of 9.

But here is another problem with Peter's setup. He doesn't have intercooling between the two stages, which you absolutely need, because you can't just dump air that is compressed at 3 to 1 into that second compressor without cooling it. The air compressed to 3 is going to be over 150 C.

And even if that second compressor had a titanium wheel that could take the temp, it would have a very difficult time reaching its own 2 or 3 pressure ratio, because hot air is much more difficult to compress than cold air. The compressor turning at a given rpm at standard temp [15 C] will be doing the equivalent work of a much lower rotor rpm, when the air temperature is elevated.

The corrected for temperature shaft speed varies by the square root of the temperature, so at 150 C you have about a 20 percent lower corrected shaft speed, with the compressor now putting out the same kind of actual performance as it would at say 80,000 rpm versus its actual rotation speed of 100,000. so it will also be flowing less, since the compressor map is now shifted down.

But all of that assumes that the two turbo stages are even sized properly, which is not the case. He even has the cold side plumbing on *backwards* taking in ambient air on the high pressure turbo. It's pretty 'unique' to say the least.

This is in fact a bigger problem than it may seem at first glance, since it's not just the fact that he won't see anywhere near the high pressure ratios he needs at altitude. Those jumbled turbos are now creating a huge backpressure and exhaust valve temps because the cylinder is not being evacuated properly. Also the turbos themselves are being stressed, not just on the hot side, but also on the cold side, where that flow mismatch is just as bad and is causing the second compressor to operate in surge [it's too big for the corrected flow coming out of the first one, so it is operating in the surge area of the map; that is very hard on the compressor wheel].

The figure of one percent for shaft bearing losses I gave is the industry norm for turbine aircraft engines with much longer shafts than turbos. The ball bearing turbos should be in this range also, although the journal bearing older style turbos are going to be higher. Not sure just how high since I'm not really a turbocharger expert, but I think I have heard something like about 5 percent. I would think ten percent might be too high.
 

pictsidhe

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Ooooh, that explains why we keep mixing up HP and LP turbos in this thread. They are both HP and LP! This is not normally done as it makes matching turbine to compressor much harder But since Peter is using 2 almost identical turbos, it doesn't really matter here...

When I looked at some rare numbers that Peter gave out, the LP compressor was in choke, the HP compressor was near surge. I haven't tried extrapolating for altitude, but they aren't going to work any better. Either surge problems or excess IAT are going to spoil Peter's fun at moderate altitude. The current system is a weighty downgrade on the stock turbo.

Something that really frightens me is the intercooling. Peter is using the fuel to do that. The intercooler heat load is getting dissipated through the wing skins. We don't know what his epoxy Tg is. What the surface area is or the conductivity of the skins (Jeff?) You can safely bet Peter has not run the numbers on this. With the low fuel load required to stay under gross with a pilot aboard, fuel heating could be a serious problem, especially with the very inefficient turbo system. Peter has not put a gauge in the tank to monitor temp. Instead, he has said that it will be 'fine'... Are the fuel tanks in contact with the spar?
 
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jet guy

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Peter is using the fuel to do that. The intercooler heat load is getting dissipated through the wing skins.
That's just bizarre. His cooling system is already a big problem. I didn't even know he was running anything but engine coolant through his heat exchangers.

This is getting ridiculous.
 

wsimpso1

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Did anybody else look at the way his temps rose when he put the fuel to the engine in the most recent video, where he was trying to assess cooling?

I did. He had applied full power, whatever that currently is, and then we could watch the various temperatures change. They seemed to change quickly and a lot during the few seconds he was at takeoff power. Scary? Could be. Tough to tell...

What can we expect to see from runs like these?

As PM puts in throttle, the temps will go through some sort of initial transients as the pump comes up to speed, the thermostat opens, etc. Then a highly predictable pattern of temperature rise and asymptotic approach to a new steady state temperature develops. The math is simple and well known. The difference between start point and the steady state temp is called the deltaT and is usually linear with the engine power and otherwise related to how good the system is at dumping heat to the heat sink - usually ambient air. If the system will overtemp at 100% power, lesser power settings can be used that will go steady state within allowable ranges. You also get a pretty good idea of the time constant tau is for the system time base. Between delta T (at known power settings) and tau, you can predict the time vs temperature curve for any power application vs time curve that you have.

Trouble with what Peter did was the thermal response of the system we saw during the runs were all those upward curving temp rises - that is just the initial transients. We saw little if any slowly flattening of the thermal response as it approached the new steady state except for after throttle was taken to idle, and so we have nothing much but guesses as the eventual temperature things will settle down at. We also learned little about how fast the settling on the steady state values would occur. He learned little other than the fact that full power for a few seconds plus a low power to hold his speed for a few more seconds did not overheat the engine.

Now it is true that he did not get to flight speed, with its somewhat better cooling, but we still know nothing about how the cooling system temperatures will run beyond the few seconds to get to 75 mph. Power reductions after takeoff are rarely to less than 75%, and we saw no runs at intermediate power settings. Other ways to get a look at how it will run further out after power application is to hold brakes and run up to whatever power for this run for a few seconds then release brakes and you will see a later section of the warm up curve. That was not done in our view of the system.

I do not see any evidence that would make me comfortable with the current cooling system. From the steepness of the temps shown, I expect that there will be overheat alarms shortly after climb is commenced. No, I have no idea if it will be 10 seconds or a two minutes after they commence climb. I also have only the short term transient data for guidance on how high 100% power would take temps, although there did appear to be a pretty big temperature rise for such a short event. How bad or good is it? I do not know, we do not have any usable data.

Billski
 

pictsidhe

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Peter's testing looks more like showmanship to me. It is rare to get useful data from his tests. As billski says, they are mostly just too short and transient in nature. All we can safely deduce is that the cooling and TIT will go into the red quite quickly at high power settings. If he released hard data, a slew of mathematically more capable people would analyse it in less time than he likes to waffle about it.

He could stick a hose into the radiator inlet to cool it down and hold high power settings, but seems averse to doing that. He could also measure weight transfer on the mains to derive prop torque and hp, but thinks that would be pointless. Without an HP figure, he won't be able to calculate accurate aero drag and potential performance from a proper engine from dimensions, climb and speed numbers.

I can only think of unflattering reasons he doesn't want to hold high power or measure hp.

Far too many critical things are being left to flight test that could easily be tested on the ground. Yeah, we get it, the cooling may not be up to scratch on the ground, but be ok in the air. That does need a wind tunnel or flight test to verify. But it is foolish not to verify that the engine/redrive can sustain high power with ample cooling.

The air intake to the turbo could be throttled to see how the cold sides react to higher pressure ratios. On the ground, one turbo is near surge, the other is in choke. That won't be a good test for the hot sides, but it is a simple test that may show a trend. If a compressor surges or IATs go too high, that will suggest a hard altitude limit until he fixes the turbo system.

So many things he should be testing before flight.
 

cheapracer

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The prototype is overweight by 1000 pounds, won't be pressurized, and won't get 230kts at 7kph. If the contraption driving up and down the Georgia runways ever flies, it won't be the airplane advertised to investors/deposit holders.

Yeps, been saying just that, as others have, for the last 5 or so years.


Wasnt it Jeff Kerlo the one doing the composite work? He is supposed to be a well reputed composite expert. How is it that his eyesballs didnt became white when laying up the sheets for the keel. Maybe he thought he was laminating an U-Boot?
He mentioned that he made numbers of suggestions, only to constantly be rebuffed, so in the end he just did what he was told to do. The money is the same at the end of the week, and without the stress.

This moving to the airport video is compelling to his apparent controlling nature, it appears the workers, including Jeff, are just limp, doing the bare minimum when requested, while Raptor guy runs around controlling everything.

 

SuperSpinach

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Hello,

This moving to the airport video is compelling to his apparent controlling nature, it appears the workers, including Jeff, are just limp, doing the bare minimum when requested, while Raptor guy runs around controlling everything.
And after watching the latest video, it appears he will also be taking care of the flight testing himself !

All those ground tests seem pretty pointless to me. Hardly any interesting data comes out of these tests and I feel like Peter doesn't know what he is looking for.
Even after all that extensive taxiing no significant change or thought seem to be put in the design.

It's really sad that he doesn't want to admit the flaws of the aircraft (but I believe he is somewhat aware of them in the back of his mind).
Let's hope (atleast) that the first "flights" or hops will be uneventful and everything goes fine.
 

pictsidhe

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To be fair. If you are precision moving a big or heavy thing with several people, you can only have one person in charge. The grunts are limited to doing what they are told and telling the foreman about things he cannot see. We take turns at being foreman at work moving big, heavy awkward things. Though it rarely seems to go too well when the current boss is the boss...
That didn't look very awkward. It went straight through with many, many inches to spare. A fun one involves twisting and turning to get through.
 
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