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10/23 Raptor Video

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rv6ejguy

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I'm amazed how long this guy will cling to an idea and try force it to work. I have tried and abandoned some things on my airplanes that "seemed" like good ideas, but didnt work in practice. My unconventional oil cooler duct is an example - didnt work out of the box, and now that I've thrown so many fixes at it to "make" it work, it no longer meets the original design goals. Instead of being a "clever" solution, now its just weird.

At some point, a designer needs that moment of clarity and admit his good idea...

...isnt very good!
My RV wears its many "development" patches as testament to how many of my ideas didn't pan out so well. Anyone who's done a lot of actual experimentation has had some fails along the way but hopefully can learn from others before them without having to make multiple mistakes themselves. Peter doesn't seem to apply even the most basic logic on his cooling system layout. Many of his same errors have been well documented by others years or decades ago...
 

PPLOnly

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Maybe I don’t understand the purpose of this test. Hasn’t he basically done a “simulated go around” every time he’s climbed 1,000 feet?
 
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flywheel1935

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Downham Market, Norfolk, UK.
This test was to determine what power setting I would be able to use in a go around in order to keep the oil temp in check.
Title of the latest 'yawn fest'
Just simply does not occur to get the cooling sorted from the get go :rolleyes:
 

Voidhawk9

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Nice of him to start off the video by mocking those who point out the problems with his test program as 'mansplainers'. 🙄 I guess this is evidence of why he's found himself alone (except for his adoring Youtube audience).
Ends the flight by insulting anyone who questions his admittedly low approaches, while making questionable claims about how it would be more dangerous to do anything else, based on his feelings.

Coolant temp appears to be stable 198F at 60% power. He now believes that adding a second cooler in the nose may eliminate the need for any coolant radiator in the cowl.
 

flywheel1935

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Nice of him to start off the video by mocking those who point out the problems with his test program as 'mansplainers'. 🙄 I guess this is evidence of why he's found himself alone (except for his adoring Youtube audience).
Ends the flight by insulting anyone who questions his admittedly low approaches, while making questionable claims about how it would be more dangerous to do anything else, based on his feelings.

Coolant temp appears to be stable 198F at 60% power. He now believes that adding a second cooler in the nose may eliminate the need for any coolant radiator in the cowl.
I, probably like many of us are trying not to follow this saga that just can't end well, but a bit like a moth to a flame I just can't help myself. I simply find myself having to comment on some of the uninformed nonsense that some of Lord Raptor disciples spurt out, then follows a protracted toing and froing, until you either win the argument, or in most cases just give up. If it wasn't for lockdown I'd have better things to do, but for a 'bit of sport' it's quite fun winding up some of the commentators 😉
 

wsimpso1

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In order to evaluate the "adequacy" of current situation of how much more heat rejection capability Raptor would need, we should cover a few principals.
  • Heat transfer from a heat exchanger is roughly proportional to air flow through and roughly proportional to temperature difference between heat source (coolant) and heat sink (ambient air);
  • Air flow through heat exchangers is roughly proportional to dynamic pressure across them, which means it is also roughly proportional to airspeed squared;
  • Heat rejected by an engine is roughly proportional to engine power;
  • Thermostats for car engines typically open and then regulate top water temperature at 192F;
  • If you have more than one effect, you multiply them together.
So how does this apply here? Well, we can postulate some numbers to get some ballpark estimates on each effect:
  • Dynamic pressure - If current version of Raptor is adequate at 120 knots cruise, it would need 144% of current capability at a 100 knot climb speed;
  • Ambient air effect - If Raptor is at 198F on a 50 F day, current delta T is 148F. If Raptor is to cool to 192 F (and thus be just barely regulating temperature) on a 100F day, it would need enough cooling when at a delta T of 92 F, or 161% of current capability;
  • If Raptor is to climb at 100% power, that is roughly 100/60 = 167% of current capability;
  • To do all of them simultaneously, that is 144%*161%*167% = 387%.
To climb at a reasonable airspeed, at full power, on a hot day, Raptor must have about four times the current ability.

But does PM need to do all that now? Well, if he is going to continue to climb on modest power, we can skip the higher power, but we have to keep the lower climb airspeed or it won't really climb. And he is going to have temperatures go up 50F over the next four months, so we have to keep the delta T. So that is still 232% of current heat rejection.

We now have a data based engineering estimate that Raptor will require the cooling of 2-1/2 to 4 times the current cooling. Put another way, the Raptor currently has 25% to 40% of the needed cooling right now, depending upon how you view the mission and power needs. Big shortfall to correct.

Now we can evaluate the idea of a second little heat exchanger in the nose. Yes, it might double the current forward heat exchanger capability, but what does it do to the whole system. Will that be enough? Hmmm, doubling 40% is 80% of needed rejection. Nope, it will still overheat.

Doubtless the heat exchangers aft, while inadequate, were doing something. Let's say the first forward heat exchanger is as capable as the aft stuff. We are at 40% of needed capacity now with both, so we were about at 20% before. Hmm adding another of those exchangers will add another 20% of needed capacity. That does not sound like much, does it? That would put Raptor at 60% of needed capacity to climb on 60% power on a hot day. Way inadequate....

Now are these numbers really accurate? Nope, not intended to be either. But as an indicator towards how much additional cooling is required, I think it points the way.

Billski
 

Voidhawk9

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Additional cooling adds weight. What's the solution?
I say air cooling.
It already has air cooling. :)
The solution is to rip out the current cooling system entirely and start over with one properly engineered to provide adequate cooling. It certainly can be done, and in a way that is lighter and simpler than the current patches on patches system. Such recommendations have been discussed on this site in detail more than once, and even directed at Peter on Youtube. But apparently that's mansplaining...
 
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FTEstudent

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Anyone know did he ever demonstrate it's "cruise" speed? Has he admitted yet that it's no where near the performance of a SR-22? I stopped following his progress because well, we all know it's an inevitable train wreck.
 

BBerson

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It certainly can be done, and in a way that is lighter and simpler than the current patches on patches system.
The front patches didn't add much weight, it replaced ballast. A new larger system aft would make it heavier and tail heavy.
 

5761RF

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Nov 26, 2020
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Any additional cooling capacity made available by installing a larger front mounted HX is limited by the amount of coolant that can be carried in the existing plumbing. I believe the lines are 1" diameter. He could, of course, install larger hoses, but that will produce more problems.

I don't recall the specifics of the additional pump capacity Muller has added or how robust the changes are. It astounds me he has not applied any objectivity and calculations to the matter. One would think he might use facts and reasoning to solve the issues, but there seems to be no attempt to do so.

Muller's comments about leaking AN fittings in the oiling plumbing, "grit", and applying more force to the fittings in efforts to stop the leaks are appalling. His faulty logic on this and other issues is astounding. It's quite comical that he attributes the leaks to contaminates in the oil, yet after draining it to clean the joint surfaces, he pours that oil back into the engine.
 
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Voidhawk9

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The front patches didn't add much weight, it replaced ballast. A new larger system aft would make it heavier and tail heavy.
The ballast itself is a patch for the grossly overweight engine and airframe producing an aft CG. Patches on patches...
Maybe for this version he could remove all the water cooling from the engine bay and put a properly sized and ducted radiator in the nose - it would look a bit like an F-86 then! More sales! (not a serious suggestion, in case you wondered, though theoretically could work... with unknown aerodynamic stability effects to add to the existing ones)
 

BBerson

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Maybe for this version he could remove all the water cooling from the engine bay and put a properly sized and ducted radiator in the nose
Right. He can do whatever is needed for this research version. He may only want to get a bit more cooling to get to the cooler altitudes. Nobody knows what the testing goals are. It may be limited to winter flights only.
 

Aesquire

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Re: whole airframe parachute testing.

You go on faith it works and preflight with the manual in hand.

The builder in question didn't design or sew it himself, so you treat it like a seat belt. Buy one good enough, install per directions, strictly, carefully, and hope you never need it.

Testing a whole airframe chute is highly likely to destroy the craft, even if everything works perfectly. The odds of personal injury are very high. So that's pretty much the Final flight test of a prototype, after everything else is fixed.

There's a reason in pre-critter-safety days they used animals in ejection seat development. The film I really want to see is how they strapped a Bear into a seat. Did they strap it in, then install the seat w/Bear? Or hoisted the Bear up into the plane and strapped him in? What tranquilizers? Custom jock straps for ground crew? ;)
 
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