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08 Aug 2020, 21:42 [ UTC - 5; DST ]


Greenwich AeroGroup



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 Post subject: Re: Raptor Aircraft 5 Seat Pressurized 3,600 NM Range Die
PostPosted: 02 Dec 2019, 09:43 
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Citations have electrically heated panels on the inboard leading edge as well.


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 Post subject: Re: Raptor Aircraft 5 Seat Pressurized 3,600 NM Range Die
PostPosted: 02 Dec 2019, 10:49 
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Username Protected wrote:
That’s why we’re talking about using waste heat from the engine. For the VW diesel at stock power levels there’s at least 150kW of waste heat available.


I would guess the number is more like 250. Diesel auto engines are somewhere around 40% efficient. But I think the majority of the waste heat goes out the exhaust.


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 Post subject: Re: Raptor Aircraft 5 Seat Pressurized 3,600 NM Range Die
PostPosted: 02 Dec 2019, 11:39 
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Username Protected wrote:
That’s why we’re talking about using waste heat from the engine. For the VW diesel at stock power levels there’s at least 150kW of waste heat available.


I would guess the number is more like 250. Diesel auto engines are somewhere around 40% efficient. But I think the majority of the waste heat goes out the exhaust.


Plus you can only extract so much before you end up dropping the coolant temperature too low for the engine to function properly.

This whole thing is a hodge podge of interesting ideas without the deep rigorous engineering required to realize that they are just interesting ideas.

I'd rename it the Dunning-Kruger aircraft.
To be fair we are all capable of Dunning-Kruger.
As everyone continues to point out this just happens to be a good example.

Edit - I see that Michael M already brought up Dunning Kruger in this thread back in June.
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Last edited on 02 Dec 2019, 12:11, edited 2 times in total.

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 Post subject: Re: Raptor Aircraft 5 Seat Pressurized 3,600 NM Range Die
PostPosted: 02 Dec 2019, 11:45 
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Username Protected wrote:
That’s why we’re talking about using waste heat from the engine. For the VW diesel at stock power levels there’s at least 150kW of waste heat available.


I would guess the number is more like 250. Diesel auto engines are somewhere around 40% efficient. But I think the majority of the waste heat goes out the exhaust.


The general rule of thumb I’ve heard for liquid cooled diesels is that both exhaust waste heat and cooling waste heat are about equal to power output. So for 200hp of output you’d have roughly 149.1 kW of waste heat available. Even if I’m off by half you still have plenty available.
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 Post subject: Re: Raptor Aircraft 5 Seat Pressurized 3,600 NM Range Die
PostPosted: 02 Dec 2019, 11:49 
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Username Protected wrote:

Plus you can only extract so much before you end up dropping the coolant temperature too low for the engine to function properly.


In the steady state you have to remove all of the waste heat the engine produces or the coolant temperature will rise. The thermodynamics must balance so heat into the coolant from the engine must equal heat removed from the coolant by the rest of the system.

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 Post subject: Re: Raptor Aircraft 5 Seat Pressurized 3,600 NM Range Die
PostPosted: 02 Dec 2019, 11:50 
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Plus you can only extract so much before you end up dropping the coolant temperature too low for the engine to function properly.


In the steady state you have to remove all of the waste heat the engine produces or the coolant temperature will rise. The thermodynamics must balance so heat into the coolant from the engine must equal heat removed from the coolant by the rest of the system.


But the system has to work with reduced power for descent as well.

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 Post subject: Re: Raptor Aircraft 5 Seat Pressurized 3,600 NM Range Die
PostPosted: 02 Dec 2019, 13:07 
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Piping engine coolant to leading edges for anti-icing is certainly an attractive idea. I toyed with it myself in my days of drawing planes in study hall. But it gave me pause when I couldn't find any real airplanes that used this obvious idea. Surface radiators were used for racing planes (Schneider Cup, He 100, et al.) but not for anti-icing. Where heated wings were used against ice they used either exhaust or dedicated supplemental fuel burners. The Ju 88 had liquid-cooled engines but heated the wings against ice with exhaust heat, not coolant. It seems like such an obvious win, you have to wonder why no real airplane designers chose to use it.


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 Post subject: Re: Raptor Aircraft 5 Seat Pressurized 3,600 NM Range Die
PostPosted: 02 Dec 2019, 14:13 
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Username Protected wrote:
But the system has to work with reduced power for descent as well.


So set a minimum power in icing conditions in the AFMS just like jets have.

Lots of diesels in vehicles have ways to restrict their exhaust so that the engine can produce excess power to keep itself warm while not doing anything useful with it.

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 Post subject: Re: Raptor Aircraft 5 Seat Pressurized 3,600 NM Range Die
PostPosted: 02 Dec 2019, 14:41 
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It seems like such an obvious win, you have to wonder why no real airplane designers chose to use it.

Increased complexity and weight of a (pressurized) liquid cooling system and the increased risks of bad things happening in the event of a leak.

Using waste heat from the exhaust is probably lower weight, less complex and lower risk in the event of a leak.

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 Post subject: Re: Raptor Aircraft 5 Seat Pressurized 3,600 NM Range Die
PostPosted: 02 Dec 2019, 15:02 
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1940 NACA report on using exhaust for anti-icing
https://ntrs.nasa.gov/archive/nasa/casi ... 014183.pdf

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 Post subject: Re: Raptor Aircraft 5 Seat Pressurized 3,600 NM Range Die
PostPosted: 02 Dec 2019, 15:11 
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I fly liquid cooled airplanes quite a bit, and it is the Achilles heel of the airplane. If you are flying a Mustang and not thinking about the cooling system, you're not doing your job.

Having a cooling system with 1 pipe to and 1 from the radiator is scary. Having a system where the radiator plumbing carries coolant all over the airplane and the radiator is subjected to flexing and bird strikes is terrifying....

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 Post subject: Re: Raptor Aircraft 5 Seat Pressurized 3,600 NM Range Die
PostPosted: 02 Dec 2019, 15:49 
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What that would do is drastically increase the volume of the cooling system. Water is heavy, heat exchangers are heavy, pipes are heavy. Water pump would have to be sized up, that is heavy. It's a fundamentally flawed idea.


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 Post subject: Re: Raptor Aircraft 5 Seat Pressurized 3,600 NM Range Die
PostPosted: 02 Dec 2019, 15:52 
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Username Protected wrote:
I fly liquid cooled airplanes quite a bit, and it is the Achilles heel of the airplane. If you are flying a Mustang and not thinking about the cooling system, you're not doing your job.

Having a cooling system with 1 pipe to and 1 from the radiator is scary. Having a system where the radiator plumbing carries coolant all over the airplane and the radiator is subjected to flexing and bird strikes is terrifying....

my grandfather always said, if one was sending a picture home to a girl it was better to have a mustang or spitfire but for people shooting at you, stick with the P47


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 Post subject: Re: Raptor Aircraft 5 Seat Pressurized 3,600 NM Range Die
PostPosted: 02 Dec 2019, 16:57 
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my grandfather always said, if one was sending a picture home to a girl it was better to have a mustang or spitfire but for people shooting at you, stick with the P47


Or, "a water cooled airplane makes as much sense as an air-cooled submarine."

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 Post subject: Re: Raptor Aircraft 5 Seat Pressurized 3,600 NM Range Die
PostPosted: 02 Dec 2019, 17:11 
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The common feature of electric de-ice systems on the 787, ThermaWing and Villinger is that they cycle the heat in sections. It would take too much power to heat the entire leading edge continuously, as Raptor intends. The alternator for the system on my plane puts out over 17 kW and that's with 20% less wing area to protect than the Raptor.

17KW?? You sure about that? A 17 KW generator will power a house....

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