Quantcast

10/23 Raptor Video

HomeBuiltAirplanes.com

Help Support HomeBuiltAirplanes.com:

pictsidhe

Well-Known Member
Joined
Jul 15, 2014
Messages
8,812
Location
North Carolina
Maybe he set it up to bleed cabin air pressurization from the second turbo at high altitude. In that case he wouldn't want to change anything, I suppose. Just speculation without knowing anything about his pressurization air source.
Even if he bled a ton of air, the turbos still need properly matching. The ratio of their size mostly depends on their pressure ratios.
 

BBerson

Light Plane Philosopher
HBA Supporter
Joined
Dec 16, 2007
Messages
14,441
Location
Port Townsend WA
Then explain how his combo engine boost/pressurization system works and can be properly matched to do both.
 

pictsidhe

Well-Known Member
Joined
Jul 15, 2014
Messages
8,812
Location
North Carolina
Then explain how his combo engine boost/pressurization system works and can be properly matched to do both.
It doesn't work...

Starting from scratch, determine required airflow and pressure ratios over the full flight range, then pick turbos that stay on the map everywhere.
The engine is going to use over 10 times more air than FAR requires for cabin air, so adjusting for pressurisation bleed shouldn't be a big deal.
 

pictsidhe

Well-Known Member
Joined
Jul 15, 2014
Messages
8,812
Location
North Carolina
Does he have onboard instrumentation to see if he is getting the desired boost?
He is measuring boost pressure. Boost pressure is set by two aftermarket car wastegates. They are not in flight adjustable and won't compensate for altitude. MAP will drop as he climbs.
 

Victor Bravo

Well-Known Member
HBA Supporter
Joined
Jul 30, 2014
Messages
8,421
Location
KWHP, Los Angeles CA, USA
Bashing and trashing Peter got us into trouble once or twice already. And I am not nearly sure I am understanding all of this correctly. My question is whether I am understanding the physics or pressures here correctly.

When I heard what he said in the video, it seemed like he was saying that the local pressure at the inlet of the second turbo was 1.5 PSI lower than it would have been without a first turbo hooked up in front of that (second turbo) inlet.

Did I get that correct... the first turbo is somehow preventing the second turbo from getting as much inlet pressure as it would have gotten if it was hanging outside in ambient air?
 

pictsidhe

Well-Known Member
Joined
Jul 15, 2014
Messages
8,812
Location
North Carolina
Bashing and trashing Peter got us into trouble once or twice already. And I am not nearly sure I am understanding all of this correctly. My question is whether I am understanding the physics or pressures here correctly.

When I heard what he said in the video, it seemed like he was saying that the local pressure at the inlet of the second turbo was 1.5 PSI lower than it would have been without a first turbo hooked up in front of that (second turbo) inlet.

Did I get that correct... the first turbo is somehow preventing the second turbo from getting as much inlet pressure as it would have gotten if it was hanging outside in ambient air?
What he was attempting to explain is that the first turbo develops slightly less boost when the 2nd turbo is running.
 

pictsidhe

Well-Known Member
Joined
Jul 15, 2014
Messages
8,812
Location
North Carolina
Up until the point where the cabin windows blow out ....


BJC
A smart design wound have something to restrict the amount of air flowing to the cabin. It doesn't need to be a complex device. I've used a calibrated hose to limit compressed air flow in an industrial situation. Hose/pipe works over a wider pressure range than an orifice.
 

wsimpso1

Super Moderator
Staff member
Log Member
Joined
Oct 18, 2003
Messages
7,641
Location
Saline Michigan
Did I hear this right... he said that he found that the first turbo was creating a 1.5 PSI vacuum in front of the second turbo... and then later at the end of the engine data portion of the video he said "I wouldn't change anything." ???

I think I recall one or more people here on this thread commenting on the idea that getting the turbo sizing and pairing (in a compound turbo installation like this) wrong could easily get everything all screwed up and reduce the available power. Is that not exactly what he just figured out in the Nov 13 video?
I heard it too. Seems he could uncrowd the engine bay and buy himself 1.5 psi boost at the same time...
 

rv6ejguy

Well-Known Member
Joined
Jun 26, 2012
Messages
4,079
Location
Calgary, Alberta, Canada
I just watched the November 13 video.

Did I hear this right... he said that he found that the first turbo was creating a 1.5 PSI vacuum in front of the second turbo... and then later at the end of the engine data portion of the video he said "I wouldn't change anything." ???

I think I recall one or more people here on this thread commenting on the idea that getting the turbo sizing and pairing (in a compound turbo installation like this) wrong could easily get everything all screwed up and reduce the available power. Is that not exactly what he just figured out in the Nov 13 video?
Peter hasn't listened to any advice on the improper turbo matching from several learned people over the last couple years. He doesn't even know what to look for frankly. Holding the one wastegate open is invalid. Not sure what he was hoping to learn there. The compressor is still in place and air has to get by that while it's turning very slowly now.

He has a tendency to guess what is causing a problem and then make another guess on how to remedy that problem. That doesn't work well as we've seen when you have no experience in that area. That approach has caused years of delays with this project. I wish he'd get some people with experience to help him out.

Compound turbocharging isn't for first time turbo system builders. Fundamentally, you can NEVER use the same size compressors on a compound turbo setup which is what Raptor has. Until he fixes that issue, Raptor will never get to 15,000 feet, let alone 25,000.
 
Last edited:

BBerson

Light Plane Philosopher
HBA Supporter
Joined
Dec 16, 2007
Messages
14,441
Location
Port Townsend WA
I think he confirmed that the staged compressors are not matched with his 1.5 psi vacuum comment.
So how did he measure this 1.5 vacuum at the first stage? Does he have a guage at each stage?

But does it matter much if the first stage isn't big enough if he can still get enough boost for rated power at sea level? It's not like the first stage is blocking the intake air like a choke plate. It should just spin a bit faster from the sucking vacuum from the second stage.
He only needs enough boost for sea level flights on this prototypes turbo setup.
 

pictsidhe

Well-Known Member
Joined
Jul 15, 2014
Messages
8,812
Location
North Carolina
The compressors are a long way from best efficiency. One is in choke, the other is close to surge. They are choking the exhaust and raising compressor outlet and EGT temps significantly. That will be causing a big power loss and unnecessary strain on the engine.

When Peter had the engine dyno tested, it developed less power than stock. He blamed that on a 'broken' dyno. The reality is that his 'upgraded' turbo system is largely responsible.

Along with subsequent injection tweaks and the redrive, it is a flying grenade.
 

wsimpso1

Super Moderator
Staff member
Log Member
Joined
Oct 18, 2003
Messages
7,641
Location
Saline Michigan
Did I hear this right... he said that he found that the first turbo was creating a 1.5 PSI vacuum in front of the second turbo... and then later at the end of the engine data portion of the video he said "I wouldn't change anything." ???
I would easily enough believe that the exhaust side is choked by the low pressure turbine, and even believe that the low pressure compressor might contribute little to manifold pressure, but it does sound uphill that the we would get a measurable drop across the low pressure turbine. Unless the bearings are coked up or the turbo is otherwise not turning. I would think that if the turbo were turning, you would get some boost no matter how poorly matched it is to the application.

I am also not above disbelieving data. Had too many instruments lie to me in my lifetime. In every type of statistical training I have received or given, the first step in working with data is to demonstrate validity of data and that the methods for obtaining the data are up to the task. Can not tell you how many times I have found the sensing system to be crap. A good engineer might start by checking that the turbines spin by hand, that all of the pressure instruments gybe with the barometer, and that all the temperature instruments gybe with OAT before starting. Then who knows if the gauges are reading correctly with air moving through the ducts? Probes angled into or away from the flow can mess them up too. Only after all of that is verified do we begin to believe an anecdote on a video.

IIRC, there was a video recently (when Peter was playing with the wastegate springs) showing some boost out of the low pressure compressor and bigger boost out of the high pressure turbine... Which conflicts with the latest video. It all makes me wonder what is going on.

Try not to take it all too much to heart.

Billski
 

pictsidhe

Well-Known Member
Joined
Jul 15, 2014
Messages
8,812
Location
North Carolina
Both turbines are way, way too small. He has hotrod turbos, sized to make low rpm boost.

If Peter set it to develop the bulk of the boost in the LP turbo and only a little in the HP turbo, he could move the LP compressor operating point actually onto the map. That would lower outlet temps noticeably. The HP turbo would probably still suck, but at a much lower pressure ratio, it wouldn't add much heat. It would also slightly help on the exhaust side, as the compressors would need less power. A slightly lower EGT. His experiments with boost were the wrong way.
I'm done giving him direct advice, let's see if he still lurks in this troll pit.
 
Top