Sources of thrust effectively calculated in BoS FDM....?

January 16, 2016

Apart from the evident - prop thrust - and depending on aircraft, what other sources of thrust are effectively calculated in BoS FDM ?

- is exaust thrust taken into consideration?

- is coolant / oil radiator thrust taken into consideration ?

Just wondering....

January 16, 2016

You will find out when/if they get round to modeling a Mustang.

January 16, 2016

We already have the 109s and the 190, as well as the p40... They all should be using it, and are probably, although I would like to know from the devs if it is really taken into account :-)

January 16, 2016

I only mention the P51 because, I understand, that it was only with this design that the thrust from the radiators became so significant that it started to disturb previous calculations about top speeds. But I am sure that you know this already.

Steps aside....

January 16, 2016

You're right unreasonable ;-)

January 16, 2016

Obvious fishing trip is obvious.....

Find out what is required in the physics to create significant amounts of exhaust thrust.

January 16, 2016

Obvious fishing trip is obvious.....

Find out what is required in the physics to create significant amounts of exhaust thrust.

Didn't get your idea Crump, can you please elaborate ?

I think I know what / where the sources should come from, but question is, how are they taken into account in the sim.

Thanks anyway

January 16, 2016

Exhaust thrust is about mass flow. That is how much air is moving thru the engine.

We are limited by the fuel to air ratio needed to achieve best power or around 12.5:1

The more horsepower we make.....the more fuel we burn....the more air we need. The higher the horsepower....the higher the mass flow....the larger the exhaust thrust benefit.

As for the radiator....it is very low drag and accounts for the low zero lift coefficient of the design. It is not a source of propulsion and does not create more thrust than it does drag.

To think it is jet engine puttering around is downright laughable. It is simply a fans fantasy.

Besides being a measured fact...

If that was case, NAA aviation would have patented that design innovation and such craft would be domination the commuter air market instead of expensive and very complicated Turboprop designs.

January 16, 2016

https://www.grc.nasa.gov/www/k-12/BGP/PAT/Fuel_and_Air2_act.htm

January 17, 2016

Exhaust thrust is about mass flow. That is how much air is moving thru the engine.

We are limited by the fuel to air ratio needed to achieve best power or around 12.5:1

The more horsepower we make.....the more fuel we burn....the more air we need. The higher the horsepower....the higher the mass flow....the larger the exhaust thrust benefit.

As for the radiator....it is very low drag and accounts for the low zero lift coefficient of the design. It is not a source of propulsion and does not create more thrust than it does drag.

To think it is jet engine puttering around is downright laughable. It is simply a fans fantasy.

Besides being a measured fact...

If that was case, NAA aviation would have patented that design innovation and such craft would be domination the commuter air market instead of expensive and very complicated Turboprop designs.

And of course no-one has said (here at any rate) that it did, if you read carefully. But a radiator provides (drag + thrust) = net drag. You can either model the two separately or simply model the net effect. Arguably, the Meredith effect function on the expelled airflow is an addition to the thrust, not a drag effect, hence my statement that the radiator produced thrust that measurably altered the speed. Not that it produced more thrust than drag.

Either way the radiator design added a significant degree of extra speed to the P51, compared to what it would have had if the design had been more traditional and had not separated the expelled airflow cleanly.

Adding a nasa reference would be much more useful if it actually addressed the specific issue.

So carry on Crump, life is too short to deal with any more of this.

January 17, 2016

Crump,

thx for your answer, and link, although I don't think you really understood what I was asking, because I was not actually starting a technical discussion about the relevance of these additive sources of thrust, which no matter how important or not, do indeed play their role, but rather if they were being separately taken into account in the simulation.

Unreasonable, thx for understanding and for your interesting points!

Edited January 17, 2016 by Herr_Target

January 17, 2016

And of course no-one has said (here at any rate) that it did, if you read carefully. But a radiator provides (drag + thrust) = net drag. You can either model the two separately or simply model the net effect. Arguably, the Meredith effect function on the expelled airflow is an addition to the thrust, not a drag effect, hence my statement that the radiator produced thrust that measurably altered the speed. Not that it produced more thrust than drag.

Either way the radiator design added a significant degree of extra speed to the P51, compared to what it would have had if the design had been more traditional and had not separated the expelled airflow cleanly.

Adding a nasa reference would be much more useful if it actually addressed the specific issue.

So carry on Crump, life is too short to deal with any more of this.

Not short enough for you to put your 2 cents in the first place.

Your answer is a lot of goobledy gook and talking in circles trying to find an excuse on how to bend physics to increase your favorite airplane, the P-51's performance.

The short answer is no thrust is produced by the radiator and the more powerful the engine, the more powerful the exhaust thrust.

It is not my fault you do not understand the NASA link explaining how fuel to air ratio is the key to engine power production. It is not the first time you have been confused and unable to understand that concept so no surprise at all!!!

Crump,

thx for your answer, and link, although I don't think you really understood what I was asking, because I was not actually starting a technical discussion about the relevance of these additive sources of thrust, which no matter how important or not, do indeed play their role, but rather if they were being separately taken into account in the simulation.

Unreasonable, thx for understanding and for your interesting points!

Ok so you are interested in eating up cpu cycles and additional computing power for no reason at all.

You are right, I did not understand that is what your asking but it does not really make much sense.

January 17, 2016

Crump, see in DCS, for instance, how important it is for the P51d.

January 17, 2016

Crump, see in DCS, for instance, how important it is for the P51d.

I also see in star trek how important warp drive is to Captain Kirk. Both are on the same level of importance and representation of the physical world.

January 17, 2016

Honestly...

I think Yo-Yo has mistaken air inlet temperature with radiator inlet temperature on the information I gave him. With accusations of bias from moderators who cannot even figure the "schoolboy" math for simple pressure coefficient there is no productive conversation going to occur when people do not understand the basic science.

My advice wpuld be to run get your DCS Mustang and enjoy it. Ignoance can be bliss. Honestly...I wish I did not know this stuff sometimes.

Edited January 17, 2016 by Crump

January 17, 2016

. Honestly...I wish I did not know this stuff sometimes.

This made me laugh so hard, I think I've hurt myself!

January 17, 2016

http://spitfirevsbf109.com/files/19930093540_1993093540.pdf

http://www.sas1946.com/main/index.php?topic=28666.0

January 17, 2016

http://www.wwiiaircraftperformance.org/fw190/Jumo_213A_power_graph.jpg

Pasting graphs too...

Check it out, physics works!! The 2100 hp engine creates more exhaust thrust than the 1630hp engine!!

Of course all these facts and physic junk is just biased!!!

What a joke.

January 17, 2016

Of course all these facts and physic junk is just biased!!!

What a joke.

Well, thanks for the link, although I don't understand a word there ( will use google translate probably... )

But, who said this is physics junk, or biased ? My OP is a question to developers of il-2 BoS, asking if these is accounted for in the flightsim FDM ?

January 17, 2016

... although I don't understand a word there ...

This Jumo213A chart shows engine power in PS on top, exhaust thrust in kg (9.81N in SI) in the middle and specific fuel consumption in kg/PS per hour on the bottom. All this is done for several power settings, which I hope don't need a translation for the chart to be understood.

As for your original question, I'm pretty sure exhaust thrust is there (based on hearsay) and radiator thrust is included in the drag modelling for the radiator, which is an OK way to account for it in a game like that.

January 17, 2016

This Jumo213A chart shows engine power in PS on top, exhaust thrust in kg (9.81N in SI) in the middle and specific fuel consumption in kg/PS per hour on the bottom. All this is done for several power settings, which I hope don't need a translation for the chart to be understood.As for your original question, I'm pretty sure exhaust thrust is there (based on hearsay) and radiator thrust is included in the drag modelling for the radiator, which is an OK way to account for it in a game like that.

Breaking down the sources of cooling drag is fine if you are researching and developing cooling systems. Outside of that it just introduces unnecessary complexity and should never change measured known data points or the basic physical relationships. Doing so is a red flag.

January 18, 2016

Crump please check your PMs.

January 18, 2016

Crump,

thx for your answer, and link, although I don't think you really understood what I was asking, because I was not actually starting a technical discussion about the relevance of these additive sources of thrust, which no matter how important or not, do indeed play their role, but rather if they were being separately taken into account in the simulation.

Unreasonable, thx for understanding and for your interesting points!

Just trying to contribute constructively.

I have managed to dig out an old article about the P51 from Aeroplane magazine which discusses the radiator drag-thrust issue, but I see that you are more concerned with the specifics of how these issues are modeled in BoX. But I suspect that information will not come easily.... Should I post it here, or start a new post?

January 18, 2016

Please post here unreasonable.

I am in the very first place, an FM freak, so I really like to see that the simulators I use come as close as possible to modeling RW systems and flight dynamics, even if most of the systems are far from being well understood by me :-)

Just to make it clear, although it's probably evident :-), I used to appear as "jcomm" here at the forums, but changed tag to this new one which pretty much reflects my usual flight situation at the MP servers :-)

I use il-2 BoS / BoM and DCS World, and really like both sims ex-aequo, and actually find a lot more in common than different in the way, for instance, flight dynamics and overall physics modeling is done on both sims, although I prefer some aspects in one than in the other both ways :-)

Systems modeling is probably the same, even if in BoS / BoM we can't click the pitt ( but I am a "E" / "RALT-HOME" fan on both sims ... ), and in DCS the visual damage model is still very poor compared to BoS...

Edited January 18, 2016 by Herr_Target

January 18, 2016

Scratches head trying to remember how to post pictures...as you will see the author actually does have credibility is talking about these issues, and the article is about a technical subject but expressed in an admirably clear style.

January 18, 2016

Precious!

Thx for sharing unreasonable! Will read it carefully trying to "absorb" the most info out of it :-)

January 19, 2016

Aeroplane magazine is dedicated to offering the most in-depth and entertaining read on all historical aircraft.

http://www.aeroplanemonthly.com/about.asp

Here is something from the AAIA 9th Applied Aerodynamic Conference.

AIAA913288.pdf

January 19, 2016

What that essentially says is that the outlet air temperature has to go way up before the Mustang's radiator could begin to produce thrust.

A radiator just cannot raise the the heat of the outlet air to a high enough temperature to do it.

The NACA experimented with this quite extensively. They got it to work by using an electrical heater as a substitute for a radiator.

At the very least it would establish the Meredith effect as a major design factor at high speeds.

How to add heat at a high rate was our primary design problem. Combustion of fuel in the 8-foot tunnel was quite out of the question for many reasons. A search of the electrical heater catalogs with help from G. T. Strailman, Langley's principal electrical engineer, turned up no [164] high-output heater capable of being fitted into our 11-inch diameter duct. Baals and I therefore became high-capacity heater designers and produced a 160-kw, three-phase, 1500⁰ F heat exchanger with 32 square feet of surface area in the form of 1.5-inch-wide Nichrome ribbon woven on reinforced asbestos millboard supports. This heater produced air temperature rises of about 300⁰ F at high speeds with very small frictional losses. The rates of heat input were larger than those due to piston-engine cooling, but still only a small fraction of the heat of combustion of kerosene.

This heater produced air temperature rises of about 300⁰ F at high speeds with very small frictional losses.

Testing of the "heat model" started in February 1941, the first NACA wind tunnel investigation of a propulsive duct producing thrust. At a Mach number of about 0.5, the propulsive effect had become equal to the internal drag, and beyond this speed substantial net thrust was developed by the internal flow. At the highest test speed, Mach 0.75, the heated duct developed the respectable thermal efficiency of some 9.5 percent, close to the ideal theoretical value. As expected, the phenomena depended on the ratio of duct pressure to stream pressure, and was independent of heater surface temperatures per se. In all other respects, the careful measurements of these tests confirmed the calculations made by our engineering relations for analysis of this kind of internal flow system (ref.187).

http://history.nasa.gov/SP-445/ch5-5.htm

A radiator simply does not produce enough heat at the outlet to make net thrust.

January 19, 2016

A radiator simply does not produce enough heat at the outlet to make net thrust.

Crump, how many times do I have to say that no-one here is saying that it produces net thrust! Please actually read what is written.

It - the P51 radiator - produces net drag, as the article clearly states. But it produces a large amount of thrust, especially at high airspeeds, (much more than other contemporary designs) sufficient to cancel out most of the drag.

The author of the article was part of the management team that actually built the thing - your attack on his credibility demeans only yourself.

Now I am putting you back on my ignore list - farewell.

January 19, 2016

Shouldn't one point out that other radiators like those on the Bf-109 did practically the same thing? The 109's radiators also featured a variable outlet:

i.e. the claim that Messerschmitt didn't know about it seems abit far fetched, esp. when they were first to introduce jets

Anywho since it only really proved beneficial at high speeds it would be a rather useless effect during a dogfight I'd imagine, as these usually take place at below 500 km/h. Also when the Mustang or any other aircraft started using overboost then the radiator outlets would open up anyway in order to better dissipate heat, removing the effect.

In short the benefits of the meredith effect were probably only really felt during straight flight at lower power levels.

January 19, 2016

Crump, how many times do I have to say that no-one here is saying that it produces net thrust! Please actually read what is written.

It - the P51 radiator - produces net drag, as the article clearly states. But it produces a large amount of thrust, especially at high airspeeds, (much more than other contemporary designs) sufficient to cancel out most of the drag.

The author of the article was part of the management team that actually built the thing - your attack on his credibility demeans only yourself.

Now I am putting you back on my ignore list - farewell.

Look, you posted a fanzine article and I posted a scientific investigation into the issue.

You turn that into "My attack" on his credibility??

Explain how we are to have an adult conversation with such silly accusations that is obviously nothing more than an attempt to suppress discussion?

The meredith effect was theoretical at the time and little was done in the way of engineering investigations to measure or explore its potential. When investigations were done, it was found that it did exist but required much more heat to occur than a radiator could impart on the inflowing air.

It is that simple.

In 1936, F. W. Meredith pointed out that the waste heat of a piston engine which is transferred to the cooling-air flow in a radiator is not all lost; it produces a small thrust provided the pressure at the exhaust of the radiator tubes is higher than the free static pressure of flight (ref. 192). This phenomenon became known as the "Meredith effect." Its mechanism was something of a mystery to many engineers of that period. A common fallacious notion was that the radial engine, because its fins were hotter than usual radiator temperatures of liquid-cooled engines, would enjoy greater benefits. (This mistaken notion still existed as late as 1949 and is stated by Schlaifer to constitute an "inherent advantage of the radial engine" (ref. 41).) The Meredith effect was so small at 1936 airspeeds that it could conveniently be neglected in performance estimates both by those who did not understand it and by those who doubted that such an effect really existed.

http://history.nasa.gov/SP-445/ch5-5.htm

It was simply a new theory and not a very well understood one either. North American Aviation is not the first engineering firm to develop a design based on theory that did not pan out.

Its designer reasoned that the drag, which is created by disturbed airflow near the tip of conventional wings, would be minimized by placing the propeller at the wing tip. By maintaining a uniform flow over the entire span, Mr. Zimmerman felt that it could take off and land at exceptionally low speeds and still have good high-speed performance. After pursuing this idea with NACA (NASA’s predecessor), he was encouraged to go to private industry and develop it further.

http://www.flightmuseum.com/exhibits/aircraft-3/aircraft-3/

January 19, 2016

Shouldn't one point out that other radiators like those on the Bf-109 did practically the same thing? The 109's radiators also featured a variable outlet:

i.e. the claim that Messerschmitt didn't know about it seems abit far fetched, esp. when they were first to introduce jets

Anywho since it only really proved beneficial at high speeds it would be a rather useless effect during a dogfight I'd imagine, as these usually take place at below 500 km/h. Also when the Mustang or any other aircraft started using overboost then the radiator outlets would open up anyway in order to better dissipate heat, removing the effect.

In short the benefits of the meredith effect were probably only really felt during straight flight at lower power levels.

This could all be quite right, but my impressions are:

1) The article notes that the effect was indeed very small at low speeds, but built up considerably. A good cruise speed for a P51 would be 350-390 mph, I believe, within the range that the article notes a significant effect. If you are trying to fly a single engined escort fighter from Britain to Berlin and back I imagine that a 20 mph speed improvement for a given fuel usage would be extremely valuable. Whether it would somehow dissipate in a dogfight is another matter - if I were flying a P51 (not that I ever have, even virtually) I would not be slowing down for a turnfight if I could avoid it.

2) The only comment I have on the "why not think of the 109 radiator outlets in the same way" issue would be to look at the size of them - by eye, the two outlets appear to have a much greater area than the single outlet of the P 51 so I imagine it would have been harder to maintain a high pressure gradient, but that is just a guess. Spitfire radiators also attempted to harness the effect - but failed because of the details of the design - so clearly there was more to it than just having a variable outlet.

January 19, 2016

I just thought I would extract a couple of points from Crump's reference materials since I know some people who read threads like this never actually read them... (sometimes, I suspect, including the poster....)

http://history.nasa.gov/SP-445/ch5-5.htm

"Clearly, the insignificant "Meredith effect" had the potential to become a primary jet-propulsion system."

"Testing of the "heat model" started in February 1941, the first NACA wind tunnel investigation of a propulsive duct producing thrust. At a Mach number of about 0.5, the propulsive effect had become equal to the internal drag, and beyond this speed substantial net thrust was developed by the internal flow."

Speed of sound 769 mph. This was an experiment dumping heat to a system using electric heat sources so it dumped heat faster than a normal radiator system, although the authors do not say how much more, only that it was nowhere near the heat of burning fuel directly.

So according to these source materials the effect can be considerable under the right conditions. Nowhere in these sources is there a calculation or even a statement that the P-51 radiator was incapable of producing enough thrust to measurably change the plane's performance at high speeds.

January 19, 2016

I do not get the excitement over the P-51 coolant jet thrust, it was a well known phenomenon by WW2, perfected by many, it may even be that the 51s designers got the furthest with that - but its all a lot of guesswork without figures. Messerschmitt certainly tried a single radiator fuselage scoop for the 109 but there were no benefits to be found.

The idea was not new though, nor it was Meredith or Messerschmitt for that matter the first to think about it - Hugo Junkers was, who patented it in 1915. However speed were too slow back then to show real gain until the 1940s saw an increase of top speeds into the 350-400 mph range.

Edited January 19, 2016 by VO101Kurfurst

January 19, 2016

So according to these source materials the effect can be considerable under the right conditions. Nowhere in these sources is there a calculation or even a statement that the P-51 radiator was incapable of producing enough thrust to measurably change the plane's performance at high speeds.

I haven't read it all either but couldn't your comment be re-written as:-

"So according to these source materials the effect can be considerable under the right conditions. Nowhere in these sources is there a calculation or even a statement that the P-51 radiator was capable of producing enough thrust to measurably change the plane's performance at high speeds"

If there is no facts to disprove it surely there are none to prove it or am i missing the point

There is no question that correctly designed and decent radiator ducting can have hugely beneficial effect in reducing drag and thus almost getting 'free/less costly' cooling however I can only remember reading once a figure quoted as 10Ibs thrust being generated and that was not confirmed

Was not this all started and patented? demonstrated in 1915 by Junkers anyway, and used in an aircraft then

I am no expert in this field and this is probably the limit of my contribution

*EDIT* written before the above post

Cheers Dakpilot

Edited January 19, 2016 by Dakpilot

January 19, 2016

I just thought I would extract a couple of points from Crump's reference materials since I know some people who read threads like this never actually read them... (sometimes, I suspect, including the poster....)

unreasonable, I do read through it, and try to digest every piece of info, and to balance the scientific data with the remaining thoughts all contribute..

Thx for your comments and links!

January 19, 2016

Dakpilot, the context of my post was that I had presented a brief qualitative account of the workings of the system, based on an account by one of the men who was directly involved in the project. You are free to believe that he was an idiot, lying, or just wrong, but personally I see no reason not to at least take what he says as a good starting place.

After a complete misunderstanding of what I was stating by another forumite - sources are produced as rebuttal evidence. When I read the sources, it is quite clear that not only do they not contradict anything I have said, but they actually support it. Ie the radiator could produce substantial thrust to offset most of the radiator drag, given the right conditions.

This is not completely qualitative either - as the article states the effect grows with speed, so earlier efforts at much lower speeds would have seen no measurable effects: even if the design of the radiator system were exactly right. Hence the irrelevance of Junker's earlier efforts. Not only that but other attempts at the right speeds failed to harness the effects - eg the Spitfire. So you have to get two things right, the speed and the details of the design.

This is nothing to do with who thought of the idea first: it is about it's successful execution.

If someone wants to demonstrate that the ideas outlined in the article are incorrect, go ahead. Nothing presented so far has even addressed the substance: all we have had is the misunderstanding that I have claimed that the radiator produces net thrust, and claims that other designs got there first. (Whoops, edited).

I really have no axe to grind here, the P-51 means nothing to me. Or if you just want to ignore it all, or prefer to believe something else, I care not. But I do not see why I should shut up and not answer mis-representations of what I said.

Edited January 19, 2016 by unreasonable

January 19, 2016

For me the thread provided exactly what I needed to know unreasonable, from what you posted and explained so well, but also from the documents I was able to read, posted by you and crump.

It is clear that there is indeed a benefit, from well designed exhaust systems, and they can play their role overcoming the parasite drag created by the radiators, if not for more, at least by providing a "compensatory" thrust, which will be significative at higher speeds.

I just wondered, in my OP, if this was being taken into account in aircraft like the 109s, C.202, P40... in il-2 BoS / BoM.

January 19, 2016

i.e. the radiator could produce substantial thrust to offset most of the radiator drag, given the right conditions.

But is it actually producing thrust ..or just reducing the amount of drag the radiator is creating

Don't worry this is not an entirely serious question

Cheers Dakpilot

January 19, 2016

I do not get the excitement over the P-51 coolant jet thrust, it was a well known phenomenon by WW2, perfected by many, it may even be that the 51s designers got the furthest with that - but its all a lot of guesswork without figures. Messerschmitt certainly tried a single radiator fuselage scoop for the 109 but there were no benefits to be found.

The idea was not new though, nor it was Meredith or Messerschmitt for that matter the first to think about it - Hugo Junkers was, who patented it in 1915. However speed were too slow back then to show real gain until the 1940s saw an increase of top speeds into the 350-400 mph range.

Is it this patent? (US version)? https://www.google.com/patents/US1464765

This is a ventral radiator with a regulator, to be sure, but I wonder if he had thought about the issues we are discussing? They are not mentioned in this patent.

Nice photo though.

Sources of thrust effectively calculated in BoS FDM....?

Recommended Posts

Guest deleted@50488

unreasonable

Guest deleted@50488

unreasonable

Guest deleted@50488

Crump

Guest deleted@50488

Crump

Crump

unreasonable

Guest deleted@50488

Crump

Guest deleted@50488

Crump

Crump

DD_Arthur

Guest deleted@50488

Crump

Guest deleted@50488

JtD

Crump

Bearcat

unreasonable

Guest deleted@50488

unreasonable

Guest deleted@50488

Crump

Crump

unreasonable

Panthera

Crump

unreasonable

unreasonable

Kurfurst

Dakpilot

Guest deleted@50488

unreasonable

Guest deleted@50488

Dakpilot

unreasonable

Browse All

Activity