pictsidhe
Well-Known Member
I'm going to second the no-wind idea. That thing needs dead calm conditions...
10/23 Raptor Video
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That much water-to-air radiator volume spread over 1.5 ft^2 instead of about 0.25 ft^2 would be way more effective. Let's get into the very real "whys".
Intercoolers have air powered through them by the turbocharger. To get scale on this whole issue, let's postulate this intercooler has a 1 psi drop across it at some useful unit of heat transfer. Stick this intercooler between a properly sized turbocharger and the intake valves, and that extra 1 psi is pretty easily obtained.
How fast do you have to go to make that 1 psi from the free air stream when using it as a radiator? Well, IF you have full pressure recovery at the radiator face (does not happen, but follow along), that 1 psi requires about 205 knots. With a more likely 80% pressure recovery, you need 230 knots. That is the reason why radiators for cars - and yes - planes need to have relatively thin sections and relatively large face areas to work well at the much lower q from lower airspeeds.
Seems to me that the auxiliary radiator had better be working well at 90 knots or this beast will never climb to any safe level off altitude. 90 knots is a q of about 28 lb/ft^2 or about 0.2 psi. Use 80% efficiency for the diffuser, and that is about 0.16 psi. Yeah, for our new hypothetical HX to work as well at 90 knots as the first hypothetical HX does at 230 knots, it needs to be about 1/6 as thick, which implies about 6 times the face area. Yeah, same radiator core volume, just arranged so we can get enough air through it at our speeds.
From looking at the space to work in on in the nose, I suspect a heater core, properly ducted could be fit and produce some real cooling improvements. Even a 6:1 diffuser on a 1.5 ft^2 HX would require a 7" diameter inlet, so it might all fit. If the HX had to be smaller, it could still be designed to make it work and effect the cooling in climb on this bird.
This intercooler as a radiator? You might be able to measure a difference at climb speed, but the difference will never be the significant improvement needed.
What would I do here if I were hired to fix it? Use the top inlet air split three ways for intercooler, aftercooler, and oil cooler, then add a P-51 style belly scoop with a pressure recovery inlet duct, velocity recovery throttleable outlet, and a substantial radiator, all shamelessly stolen from our own rv6ejguy (shoutout to Ross at SDS). The big deal would pertain to where you could package enough radiator. Probably need 800-900 in^3 of radiator core volume and 450 in^2. That is 11.5" deep by 40" wide, and 2" thick, so it is doable. It might look kind of pregnant, but if it cools... Making it pretty would require rearranging just about everything firewall aft, so that might have to wait for a second prototype.
Billski
Intercoolers have air powered through them by the turbocharger. To get scale on this whole issue, let's postulate this intercooler has a 1 psi drop across it at some useful unit of heat transfer. Stick this intercooler between a properly sized turbocharger and the intake valves, and that extra 1 psi is pretty easily obtained.
How fast do you have to go to make that 1 psi from the free air stream when using it as a radiator? Well, IF you have full pressure recovery at the radiator face (does not happen, but follow along), that 1 psi requires about 205 knots. With a more likely 80% pressure recovery, you need 230 knots. That is the reason why radiators for cars - and yes - planes need to have relatively thin sections and relatively large face areas to work well at the much lower q from lower airspeeds.
Seems to me that the auxiliary radiator had better be working well at 90 knots or this beast will never climb to any safe level off altitude. 90 knots is a q of about 28 lb/ft^2 or about 0.2 psi. Use 80% efficiency for the diffuser, and that is about 0.16 psi. Yeah, for our new hypothetical HX to work as well at 90 knots as the first hypothetical HX does at 230 knots, it needs to be about 1/6 as thick, which implies about 6 times the face area. Yeah, same radiator core volume, just arranged so we can get enough air through it at our speeds.
From looking at the space to work in on in the nose, I suspect a heater core, properly ducted could be fit and produce some real cooling improvements. Even a 6:1 diffuser on a 1.5 ft^2 HX would require a 7" diameter inlet, so it might all fit. If the HX had to be smaller, it could still be designed to make it work and effect the cooling in climb on this bird.
This intercooler as a radiator? You might be able to measure a difference at climb speed, but the difference will never be the significant improvement needed.
What would I do here if I were hired to fix it? Use the top inlet air split three ways for intercooler, aftercooler, and oil cooler, then add a P-51 style belly scoop with a pressure recovery inlet duct, velocity recovery throttleable outlet, and a substantial radiator, all shamelessly stolen from our own rv6ejguy (shoutout to Ross at SDS). The big deal would pertain to where you could package enough radiator. Probably need 800-900 in^3 of radiator core volume and 450 in^2. That is 11.5" deep by 40" wide, and 2" thick, so it is doable. It might look kind of pregnant, but if it cools... Making it pretty would require rearranging just about everything firewall aft, so that might have to wait for a second prototype.
Billski
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rv6ejguy
Well-Known Member
I think for the rad, he could get by on 300 in2 of face area and 750 in3 of volume. That would fit ok with a long belly scoop. This assumes best ROC would be at 100+ knots. The problem is he also needs an oil cooler of at least 250 in3 of volume and two intercooler cores (one after each compressor) of around 1000 in3 EACH. It would indeed look pregnant. He can't get by with one intercooler because the charge temp would be over 500F after the 2nd stage compressor which exceeds the safe temp limits for the silicone hose couplers.
Improperly managed, the sheer amount of mass flow required for all these HXs would create huge drag and this is a consequence of choosing a diesel for high altitude flight. The intercooler requirements are much higher than an SI engine due to the high pressure ratios the diesel requires to make hp. 6-7 to 1 vs. around 3 to 3.5.
Also, up at FL250, a relight would be challenging on the diesel.
Improperly managed, the sheer amount of mass flow required for all these HXs would create huge drag and this is a consequence of choosing a diesel for high altitude flight. The intercooler requirements are much higher than an SI engine due to the high pressure ratios the diesel requires to make hp. 6-7 to 1 vs. around 3 to 3.5.
Also, up at FL250, a relight would be challenging on the diesel.
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rv6ejguy
Well-Known Member
This is an example of a properly implemented radiator setup. Turbocharged Subaru. Note variable geometry exit door which is a must for good cooling on the ground and climb plus low drag in cruise. Bluntly, Raptor's cooling system layout breaks every rule of good design which has been understood since about 1940.
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rv6ejguy
Well-Known Member
And, an improperly implemented one:
flywheel1935
Well-Known Member
Been following and commenting on the Raptor YT channel for a couple of years now (Using my real name). Despite your attempts to take on board your concerns I see the latest 'Fix' is another bodge on top of the previous bodge, an infinitum. I also see that us HBA members are getting verbal abuse for our attempts to save the project & PM, Can't really see it panning out to well, so from now on I'll keep my thoughts to myself, and view from a distance.
rv6ejguy
Well-Known Member
Physics never takes a vacation as they say. Peter really needs some professional help in several areas if he ever wants Raptor to become what he intended.Been following and commenting on the Raptor YT channel for a couple of years now (Using my real name). Despite your attempts to take on board your concerns I see the latest 'Fix' is another bodge on top of the previous bodge, an infinitum. I also see that us HBA members are getting verbal abuse for our attempts to save the project & PM, Can't really see it panning out to well, so from now on I'll keep my thoughts to myself, and view from a distance.
flywheel1935
Well-Known Member
I think one issue is that Peter does not know what he really wants and has less idea on what his 'customers' want. All us grey haired pilots with prostate issues would only want to travel a couple of hours before a comfort break, etc. If a prospective Rapor buyer has no confidence in its creator, (Would you buy/build one ???) then what's the point .
TarDevil
Well-Known Member
Yepper, that's pretty much where I am. Just watching the snowball grow.I'll keep my thoughts to myself, and view from a distance.
I'm concerned about the 2nd flight. Very concerned. My gut says he'll push too many edges.
Does diesel cooling drag at altitude negate diesel fuel efficiency?
Looks like he will eventually have more cooling drag then air cooled Cirrus.
Looks like he will eventually have more cooling drag then air cooled Cirrus.
pictsidhe
Well-Known Member
A very well designed cooling system need have little drag.
Throwing unverified ideas at the wall is never going to work, though.
Jet787
Active Member
Raptor will never become what Peter intended as stated in his spec sheet. It’s like my 8yr old designing an airplane. Physics won’t allow it.
At this point I think it is fair to say that Raptor is no longer an airplane project but is more of a syndrome and a social construct--and most likely a symbiotic aggregation of those two.
Of course, there is still a lot of value to be had in discussing the relative merits of the various solutions and mitigations undertaken to address the shortcomings in the airplane in question. However, at this point it should be clear that any such discussion has value only to the degree that it applies to our own projects. We should probably assume that Raptor is, in the words of David Bowie, "immune to our consultations."
Beyond that, Raptor remains a fascinating topic from a psychological and sociological perspective. But that falls outside the bounds of homebuilt airplane discussion, and we would probably do well to limit our forays into that realm.
TarDevil
Well-Known Member
I've probably learned more from the Raptor discussion than everything else combined.
Richard Schubert
Well-Known Member
Men make mistakes. A smart man learns from his mistakes. A wise man learns from the mistakes of others.
jedi
Well-Known Member
Warning: I have resisted posting to this thread till now with only one exception. Once again the temptation has overcome me.
Peter is a doer. A doer recovers from mistakes as best he can. I want to help doers. When he ask months ago "What I would do prior to flight test," I answered. He has not ask yet, but the big question now is what to do next. I think it may be time to start an online auction for the famous Raptor SN/1.
Do I have $100?
Peter is a doer. A doer recovers from mistakes as best he can. I want to help doers. When he ask months ago "What I would do prior to flight test," I answered. He has not ask yet, but the big question now is what to do next. I think it may be time to start an online auction for the famous Raptor SN/1.
Do I have $100?
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?
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?
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.
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This is gonna give the turbo encabulator a run for its money.
