Frontal area vs. drag vs. wetted area vs

[Nicknick]

Flying wings with jet engines was the coolest stuff in those times, but this combination was neither suitable for maximum range or speed. Flying wings offer very good glide numbers and a high lift (at low speeds) but they have a large frontal area (=> high parasitic drag).

Flying wings would have been well suited for a propeller driven extremely long range bomber, since you can take off and fly with a very high payload (even load distribution with low stress in the airframe, high wing area, low drag) and relative small engine power.

When Northrop switched to jet engines in his flying wings, he lost halve of the range and couldn’t compete with the B-47.

 

[HoHun]

Hi Nicknick,

Flying wings with jet engines was the coolest stuff in those times, but this combination was neither suitable for maximum range or speed. Flying wings offer very good glide numbers and a high lift (at low speeds) but they have a large frontal area (=> high parasitic drag).

Hm, what's the source for that opinion? I'm not sure I follow ...

Regards,

Henning (HoHun)

 

[Nicknick]

What are you questioning, the glide numbers or the frontal area?

 

[HoHun]

Hi Nicknick,

What are you questioning, the glide numbers or the frontal area?

I am asking for a source, because I thing that would help me to understand what you're trying to say. Aerodynamicists normally don't consider frontal area as the key parameter of a wing, but actually wing area and wetted area, so I'm curious where you've got that from.

Regards,

Henning (HoHun)

 

[Nicknick]

Taking a look on YB-35 and the B47 will make it clear. Aerodynamics will always consider the frontal aera as very important, the Cw value (there is a equivalent value for planes, but is has a somewhat different name) is related to the frontal area vs. drag. The parasitic drag of aircrafts depends on aerodynamic quality and frontal area.

It can easily be seen, that very fast aircrafts tend to have low cross sections in combination with small thin wings. Flying wings need thicker wings for storage of fuel, propulsion and payload, this will (almost) always result in a high cross section with high parasitic drag.

The flying wing really shines when it comes to induced drag, or even in the parasitic drag vs. frontal area (Cw value), so it is very efficient for slow flying heavy airplanes.

You should compare the YB-35, YB-49 and B-47, this makes clear, why flying wings were great for long range at low speed, but unsuited for high speeds. Jet engines only make sense for high speed applications, thats why the combination failed.

 

[HoHun]

Hi Nicknick,

Taking a look on YB-35 and the B47 will make it clear.

So you're not relying on a NACA report or a Messerschmitt document here, but merely eye-balling the three view?

Regards,

Henning (HoHun)

 

[Nicknick]

I’m not your google servant, there is no need to verify things which can easily be seen, will you doubt, that the frontal area of the YB-49 is larger than that of the B-47?

This is not the first thread about this topic, please inform yourself.

 

[HoHun]

Hi Nicknick,

I’m not your google servant, there is no need to verify things which can easily be seen, will you doubt, that the frontal area of the YB-49 is larger than that of the B-47?

I was asking for your source, not for an explanation, which I think is perfectly reasonable, and would have deserved a polite answer.

I'd be quite interested in reading up if you'd be able to provide pointers. Seems you aren't ... well, call that a missed opportunity.

Regards,

Henning (HoHun)

 

[Nicknick]

Well, this forum isn’t the first and only one where we had a discussion that’s why I don’t want to invest a lot of effort in answering you. It was your decision to block me over there, so why should you expect a friendly answer?

 

[Nicknick]

I’m totally calm, I haven’t insulted anyone or said something mean, so what?

The larger frontal area, wing span and wetted area of the YB-49 compared to the B47 is not a personal opinion, it is obvious. I choosed three airplanes as example to prove my thesis and this should be sufficient. The B47 was competing to the YB49 and won for good reasons (higher speed, longer range)

 

[sienar]

I think you are getting things mixed up with Raymers comparison of the B-47 and Avro Vulcan. You are also getting a few other things wrong - frontal area is largely irrelevant subsonically, Swet and avoiding separation are whats important.

 

[Nicknick]

No, I didn’t mix up something with the Avro Vulcan, the YB35 was developed as a long-range bomber in competition with the B36, but when Northrop switched to jet engines it lost its long rage capabilities but gained a higher speed. With that changes it had to compete with the B47 which showed more potential than Northrop’s flying wings (higher speed, longer range).

With similar proportions, physics don’t care it you are using the larger wing area with a smaller drag coefficient or the smaller frontal area with a higher coefficient to describe the total drag. If an increase the wing area, you increase the frontal area as well and so does the absolute drag. For good reasons, aircraft designers are used to the wing area as reference and car designers are used to frontal areas, both approaches lead to the same results. By the way, do you believe, the Superguppies or the Airbus Belugas weren’t affected by the large frontal area?

The wings of theYB35/Yb49 weren’t thin at all, according to this thread ( https://www.secretprojects.co.uk/threads/northrop-xb-yb-35-yb-49-and-yrb-49.9969/page-2 ) they must have been around two meters in the center section. Thick wings tend to have higher cd values which corresponds to theire higher frontal area.

Focusing on the wing area blurs the reasons for drag, folding wing aircrafts reduce the frontal area at high speeds by folding its wings (which also helps to improve the aera rule) and reduce drag.

Flying wings could become great tanker aircrafts, were high lift to drag ratios are important (low induced drag) but they don’t do well suited to minimize parasitic drag at high speeds. Flying wings tend to be much larger planes in terms of wing area or frontal area compared to conventional planes which do the same job (please compare the YB49 with the B47 or the B1 with the B2)

 

[HoHun]

Hi Nicknick,

If an increase the wing area, you increase the frontal area as well and so does the absolute drag. For good reasons, aircraft designers are used to the wing area as reference and car designers are used to frontal areas, both approaches lead to the same results.

Since there's no direct link between wing frontal area and drag, aerodynamicists have a good reason not to include "frontal area" of wings in their calculations. If you get the same results, then only by investing a lot more "physics" into this than you have done so far. What you're doing is called "arm waving".

I just checked NACA-TN-1477 "Generalized Performance Report on Large Conventional, Tail-Boom and Tail-less Airplanes", a an 85-page report dealing with the topic, and they don't even care to define a symbol for wing frontal area. They do use a symbol for total frontal area of fuselage, tail-boom and nacelle, though.

Regards,

Henning (HoHun)

 

[Nicknick]

There is no direct link between the frontal area and the drag either, both depends on the shape. If the projected wing area seen from above is 10 times bigger than seen from the front, the cd value is 1/10 th that of the Cw value, that’s all.

The parasitic drag is:

F = 1/2 *Cw*A(Frontal)*v²=1/2*Cd*A(wing area)*v²

It doesn’t make any difference, but of course it makes more sense to refer the lift value Ca to the wing area than to the front area. As long as you don’t change the type of profile, the proportions of frontal area vs. wing area is the same as Cw/cd.

You gathered a lot of knowledge, but you tend to overlook simple relationships. Slim profiles with low cd values also have low frontal areas which explains why these values are low. Fat profiles (like the ones used in the YB49) have high cd values and a large frontal area. There is a connection you are unable to see.

 

[sienar]

Here is raymers famous comparison.


Note the complete irrelavence of wing thickness, frontal area, ect on final L/D. Aircraft are a sum of their parts and any breakdown that ignores this is largely worthless.

I think you are still confusing things too. You say stuff like "There is no direct link between the frontal area and the drag either, both depends on the shape." - NO at subsonic speeds it depends on wetted area provided no separation is occurring.

 

[HoHun]

Hi Nicknick

The parasitic drag is:

F = 1/2 *Cw*A(Frontal)*v²=1/2*Cd*A(wing area)*v²

As you can't predict either coefficient from the frontal area, how does that help you? You got the formulae wrong, by the way.

And please don't lose sight of your original point:

Flying wings offer very good glide numbers and a high lift (at low speeds) but they have a large frontal area (=> high parasitic drag).

Here are the actual frontal area values from NACA TN 1477 (frontal area is represented by symbol F):



Not to say flying wings are the greatest thing since sliced bread, but at least the NACA guys know what they're doing.

Regards,

Henning (HoHun)

 

[Nicknick]

There was a discussion in theFlugzeugforum (well known by both of us, at least I’m pretty I read it over there) where someone tells a story of an automotive development company presented their results for an helicopter calculation. At first glance, their results seemed to be horrible wrong, until someone found out, that they related everything to the projected front area and not to the rotor area. Finally, it turned out to be pretty accurate. You an choose any area as reference and get the right results, but for comparing different wings, the wing area is the most useful one.

I’m sure it is an interesting quotation, but I don’t get what it is referring exactly, what is St/S? I guess you are not going to tell me, that the frontal area of a fyling wing “wing” is lower that the frontal area of the pure wing from a conventional airplane.

The large wing area of flying wings could produce much more lift than ever needed at high speed (as long as not flying extremely high), that why the best glide ratios is of little value il you have either a large wing area or frontal area (which goes hand in hand in a flying wing). For flying fast and efficient in a flying wing, you need to make use of the high lift and fly extremely high, until you match the perfect angle of attac and glide ratio (remember our discussion about the Otto Celera…)

 

[HoHun]

I’m sure it is an interesting quotation, but I don’t get what it is referring exactly, what is St/S?

I’m not your google servant

 

[sienar]

You an choose any area as reference and get the right results, but for comparing different wings, the wing area is the most useful one.

Its not. Wings stopped being used as reference area for Cd ages ago. Its been Swet since a bit after ww2. Also keep in mind that L/D is important at every speed, because it is total lift/total drag.

I think you are also possibly confusing flate plate equivalent area with frontal area.

 

[Nicknick]

You can take any reference area you like, as long as you correspond the measurements of lift and drag correctly, even the projected area of the pilots cap will do. But with a silly definition, you can’t compare different wings with each other that’s why it is wise to choose something like wing area.

As you said, only the total drag and lift values are finally important, you don’t even have to know anything about the wing area or any other given geometry to use them. If frontal area didn’t matter, the Concorde would have been a wide body plane with lot of room and comfort for its passengers…

 

[sienar]

That is not true at all though. Wings were used as reference area in the early days of aviation. This works well enough if you are comparing similar configuration aircraft. But this doesnt work out if you are comparing dissimilar designs, like a B-47 and and flying wing B-35. This is why total wetted area is now used instead.

And the concorde is supersonic, is it not? I've repeatedly said frontal area is meaningless subsonically.

 

[Nicknick]

If frontal areas wouldn’t matter, the Airbus Belugas would be as fast as their basis (A330) which is definitely not the case (735 km/h vs. 870 km/h). You can as well compare the cruise speed of the B-377 (547 km/h) with the derived Pregnant Guppe (361 km/h). The only significant difference ist the increased frontal area. Frontal areas will always matter subsonic or supersonic, it you increase the front area by a given aerodynamic efficiency you will always increase drag. There are good reasons why aircraft tend to be so cramped in the inside, but indeed, of you increase the aerodynamic efficiency by laminar flow you can use a bigger fuselage diameter without a severe drag penalty (see Otto Celera).

Of course, I have to compare dissimilar designs to point out, which one is better suited for the job. The B47 killed the YB49 because a sleek plane with swept wings was faster and had a longer range than the YB49.

 

[sienar]

The only significant difference ist the increased frontal area.

The increase in wetted area is significantly greate. I really don't get how you can't see that. Do you understand that wetted area is simply the surface area of the aircraft exposed to the airstream?

 

[Nicknick]

if the wetted area would be the main issue, all planes would look like that:

View: https://www.youtube.com/watch?v=4GdbIVATKoQ&ab_channel=stephanbre


All planes would have short wide bodies fuselages to reduce the wetted area. In reality, the best results for drag is that of a sleek teardrop shape:

Does unity drag coefficient have special meaning?

gives examples of drag coefficients of assorted shapes from 0.045 to 1.28. I understand that $C_D=\large{\frac F{\frac 12Av^2\rho}}$. Does a drag coefficient of exactly one correspond to any signi...

physics.stackexchange.com

The Reynold Numbers of airplanes are in the 10^7 range, that implies that pure air friction (increases linear with speed) is very low compared to shape dependen drag (nevertheless, for boundary layer, flow seperation an turbolence, the friction still matters).

 

[HoHun]

Hi Nicknick,

if the wetted area would be the main issue, all planes would look like that:

View: https://www.youtube.com/watch?v=4GdbIVATKoQ&ab_channel=stephanbre

The tail has wetted area as well, and the shorter the moment arm, the more wetted area it needs to be effective.

If you don't need a horizontal tail, you have more freedom ... have a look at the Me 163 for a real-world egg-plane.

From Dan Raymer, "Conceptual Aircraft Design for Homebuilders":

"There is considerable debate about the best value for fuselage fineness ratio (length/diamter). Numerous design books such as the classic Hoerner Fluid Dynamic Drag say that the lowest drag occurs when the fineness ratio is around three. However, most airplanes including homebuilts have much higher fineness ratios.

Analysis indicates that the best fineness ratio really is about three if your design needs to have a pretty large cross-section area, and it is not tight on volume (in other words, you can make it as short as you want). This is typical for a small airplane, especially one with side-by-side seating as shown below. [Photo of Questair Venture]

The shortness of such a design requires larger tail areas to get the desired tail volume coefficient, which increases wetted area. Also some people just don't like the egg-like apparerance, or are scared about controllability despite favorable analysis and flight test. [...]

If the cross-section area is not so much of a problem, but you need to enclose a certain amount of volume, then a fineness ratio of around six will have less drag. This is more typical for larger aircraft or for smaller aircraft with tandem seating."

Questair Venture: https://img1.wsimg.com/isteam/ip/be322e30-6ffe-4326-8ef5-e0c6f169dc90/1.png/:/

And here's a graph from Hoerner's Fluid Dynamic Drag, showing airship drag - based on wetted area, of course:



Regards,

Henning (HoHun)

 

[Nicknick]

If the airship would have had a ball shape, the wetted area would have been reduced significantly (and so the drag???) You might know, how important a low frontal area has been during engine development in WWII, im pretty sure you can also find one of there charts which show the drag penalty in horsepower corresponding to the frontal area (I’ve seen them a couple of times).

There is nothing to stop you from building a ball like fuselage with a thin tail to the rudder...

As said, the wetter area is just a reference, you can as well choose any other reference (wing area, frontal area...)

 

[Nicknick]

Here is raymers famous comparison.
View attachment 673677

Note the complete irrelavence of wing thickness, frontal area, ect on final L/D. Aircraft are a sum of their parts and any breakdown that ignores this is largely worthless.

I think you are still confusing things too. You say stuff like "There is no direct link between the frontal area and the drag either, both depends on the shape." - NO at subsonic speeds it depends on wetted area provided no separation is occurring.

The Avro Vulcan had a very low aspect ratio, unlike the YB35/49, this helps to reduce frontal area as well as wetted area.

There is always a turbulance wake field behind every body, with the same shape and reynolds number, the size of it directly corresponds to the frontal area.

 

[sienar]

If the airship would have had a ball shape, the wetted area would have been reduced significantly (and so the drag???) You might know, how important a low frontal area has been during engine development in WWII, im pretty sure you can also find one of there charts which show the drag penalty in horsepower corresponding to the frontal area (I’ve seen them a couple of times).

There is nothing to stop you from building a ball like fuselage with a thin tail to the rudder...

As said, the wetter area is just a reference, you can as well choose any other reference (wing area, frontal area...)

Ball shape doesnt work because of separation. If no separation is occurring then what matters is wetted area. This happens around a fineness ratio of ~3-3.5 depending on reynolds number.

A modern sailplane is basically an egg fuselage with a boom to give the tail enough moment arm to stay small while countering the high pitching moment of the wings airfoil.

If you think other reference areas like wing or frontal work better, then I'd suggest you do the math to see. You keep making certain claims about the B-47 and B-35 but not a single number to back anything up.

 

[Nicknick]

Here is raymers famous comparison.
View attachment 673677

Note the complete irrelavence of wing thickness, frontal area, ect on final L/D. Aircraft are a sum of their parts and any breakdown that ignores this is largely worthless.

I think you are still confusing things too. You say stuff like "There is no direct link between the frontal area and the drag either, both depends on the shape." - NO at subsonic speeds it depends on wetted area provided no separation is occurring.

As we see in this example, the B47 had a wetted area of 11300 square feet. I haven’t found anything about the wetted area of the Yb49, but the wing area was 4000 square feet. The wetted area must have been more than twice as much, I guess something between 10.000 sq ft und 12.000 sq feet, which is quite similar to that of the B47.

The combined trust of the yb49 was 136 KN, that of the B47 was slightly higher 160,2 KN. The starting weight was (YB 49 88 t:, B47 93.75 t), so that the B47 had about 10 % better power to weight ration. Despite the advantages of flying wings in respect to mechanical loads, the B47 had surprisingly a lower empty weight 35 t instead of 40 t).

The slightly better power to weight ratio of the B47 doesn’t explain why it was that much faster (977 km/h vs 789 km/h). The much longer operational range (3240 km vs. 2600 km) of the B47 compared to the YB49 also shows, that this plane must have had a much more efficient aerodynamic. As we see, the wetted area of both planes was quite similar (I would like to have exact values of the YB 49) but the frontal area of the B47 was significant smaller.


Edit: according to this graph (the scan is of low quality): https://books.google.de/books?id=bSq-cEf0EWsC&pg=PA188&lpg=PA188&dq=yb+49+wetted+area&source=bl&ots=iHNwxPNwvJ&sig=ACfU3U2FX-tuR6BL6fuF9gPcr0DJkBWLcw&hl=de&sa=X&ved=2ahUKEwiixsei8u_1AhU6RfEDHdCPBC84ChDoAXoECCMQAw#v=onepage&q=yb 49 wetted area&f=false

the wetted wind area of the YB49 and B47 was similar, but the B47 had significantly less drag than the YB49 (about 24 sq ft vs 56sq ft equivalent drag area).

 

[Nicknick]

The frontal area and wetted areas are not independent from each other. Whenever a fixed geometry is compared (like a wing profile, or a Nacal), the wetted area is proportional to the frontal area. In these cases, the frontal area dictates the wetted area. Its different, if you compare different versions of a plane with a longer or shorter fuselage, in if the rest is the same, an elongation of the fuselage will have very minor effects on the drag, but some on the wetted area.

As said, you can use any reference area you like, there is nothing wrong about choosing the frontal area or wetted area as reference. You should keep in mind, that choosing a reference does not change or explain anything about drag. You can as well find many examples were the frontal area with zero lift drag was chosen to determine the parasitic drag, but all calculations can be done with frontal area, wing area, wetted area or whatever area.

 

[sienar]

The frontal area and wetted areas are not independent from each other. Whenever a fixed geometry is compared (like a wing profile, or a Nacal), the wetted area is proportional to the frontal area.

Of course this is true, but I don't know why you think this is important. Aircraft have radically different geometries from each other. If you want to use frontal area for comparing wings, sure I guess, but I don't know why you would ever do that for aircraft. And then you are just using a different system of measuring wings - for what gain?

As said, you can use any reference area you like, there is nothing wrong about choosing the frontal area or wetted area as reference.

No, there is something wrong with using frontal area as a reference area - it just doesnt work unless the aircraft being compared are of similar configuration. You are the one saying you can use any reference are you like, I am not.

Here is raymers famous comparison.
View attachment 673677

Note the complete irrelavence of wing thickness, frontal area, ect on final L/D. Aircraft are a sum of their parts and any breakdown that ignores this is largely worthless.

I think you are still confusing things too. You say stuff like "There is no direct link between the frontal area and the drag either, both depends on the shape." - NO at subsonic speeds it depends on wetted area provided no separation is occurring.

As we see in this example, the B47 had a wetted area of 11300 square feet. I haven’t found anything about the wetted area of the Yb49, but the wing area was 4000 square feet. The wetted area must have been more than twice as much, I guess something between 10.000 sq ft und 12.000 sq feet, which is quite similar to that of the B47.

The combined trust of the yb49 was 136 KN, that of the B47 was slightly higher 160,2 KN. The starting weight was (YB 49 88 t:, B47 93.75 t), so that the B47 had about 10 % better power to weight ration. Despite the advantages of flying wings in respect to mechanical loads, the B47 had surprisingly a lower empty weight 35 t instead of 40 t).

The slightly better power to weight ratio of the B47 doesn’t explain why it was that much faster (977 km/h vs 789 km/h). The much longer operational range (3240 km vs. 2600 km) of the B47 compared to the YB49 also shows, that this plane must have had a much more efficient aerodynamic. As we see, the wetted area of both planes was quite similar (I would like to have exact values of the YB 49) but the frontal area of the B47 was significant smaller.


Edit: according to this graph (the scan is of low quality): https://books.google.de/books?id=bSq-cEf0EWsC&pg=PA188&lpg=PA188&dq=yb+49+wetted+area&source=bl&ots=iHNwxPNwvJ&sig=ACfU3U2FX-tuR6BL6fuF9gPcr0DJkBWLcw&hl=de&sa=X&ved=2ahUKEwiixsei8u_1AhU6RfEDHdCPBC84ChDoAXoECCMQAw#v=onepage&q=yb 49 wetted area&f=false

the wetted wind area of the YB49 and B47 was similar, but the B47 had significantly less drag than the YB49 (about 24 sq ft vs 56sq ft equivalent drag area).
View attachment 673788

This isn't really saying much.

Power to weight ratio has nothing to do with predicting the drag of an aircraft. You are also comparing an aircraft designed to operate in a transonic regime to one designed for piston power. These are very different regimes and this is why there is a big speed difference.

You are also making a big mistake by thinking that range explains this either. What is the amount of fuel each aircraft carries? What is the lb/lb/hr of the engines? If you don't take things into account the comparison is meaningless.

If you want to actually compare them, then do this; take a speed/alt perf for each aircraft, as well as the engine thrust at that alt+mach. Now you can calculate the equivalent flat plate area. And guess what? They aren't that far off, probably within ~15%.

And if you really aren't getting this, here is a simple hypothetical. You have two wings;

Wing A = 1ft chord and 25% thick
Wing B = 2ft chord and 8% thick

Which wing has higher drag? Keep in mind wing A has ~56% more frontal area than wing B.

 

[Nicknick]

We should go back to my first posting and the beginning discussions. I said, the YB49 wasn’t suitable as a medium range bomber because it had much more drag than the competing B47 due to its high frontal area. You said, the frontal area doesn’t matter, it’s only the wetted area. It turned out, the wetted area o the YB49 is identical to the B47, but the YB49 has more than twice the drag

So drag only depends on the wetted area?

The frontal area of the YB49 is indeed much bigger (maybe I will invest some effort to determine it) I would estimate about twice as much as the frontal area of the B47, this fits very well to the differences in drag

So frontal area really doesn’t matter?

I guess it hurts, but I proved all my theses. The YB 49 had much more drag than the B47 which can’t be explained with the wetted area but very well with the frontal area.

Now you are saying yourself, that comparing different types of airplanes just by the wetted area doesn’t make sense, that what I’m saying all the time. You cant expect that two planes match in the diagram if one has twice the frontal area than the other.

I also totally agree that the problem of the YB49 was that it was designes as a fuselage of a slow flying heavy loaded propeller plane, that’s what I said right from the beginning!

So now its you turn to explain the high parasitic drag of the YB49 if neither the wetted area nor the frontal area should be the reason.

 

[Nicknick]

I would like to point out, that the airframe of the YB35/YB49 weren’t inefficient, just because they look so on the chart. I’m convinced that this shape offered great glide angles and lift, so that the YB35 could have flown very efficiently with lot of fuel, at medium speed in relative thin air. They just appear to be inefficient in this diagram, because their small wetted area. These airplanes had a wingspan of 52 m which could produce much more lift, than the YB49 ever needed (which is, why the YB49 failed).

If the stabilizer fins of the YB49 would have been elongated by, let’s say 10 m, it would have added a lot of wetted area but little additional drag and they would have looked much better in the diagram (despite becoming less efficient).

The Horten Flying wings look much more suitable for higher speeds, since the have a much lower AR ratio, thus decreasing both, frontal area and wetted area.

 

[HoHun]

Hi Nicknick,

We should go back to my first posting and the beginning discussions. I said, the YB49 wasn’t suitable as a medium range bomber because it had much more drag than the competing B47 due to its high frontal area. You said, the frontal area doesn’t matter, it’s only the wetted area. It turned out, the wetted area o the YB49 is identical to the B47, but the YB49 has more than twice the drag

You have finally provided some data, but you haven't validated your methodology.

In fact, the overview diagrams you found do not show "frontal area" (which is not what the NACA report I quoted considers frontal area, anyway), but flat plate area, which is a calculated value that has an area dimension, but no link to the real geometry.

That the diagrams you found link flat plate area to wetted area by means of a coefficient that is considered an expression of aerodynamic quality is in fact a confirmation that the wetted area, just as sienar pointed out, plays a more important role than "what Nicknick considers frontral area".

I didn't question your statement that the B-47 shows lower drag than the YB-49, I questioned your methodology and asked for your sources. I'm happy to see that after being questioned hard enough, you actually went and tried to back up your claims with actual data. Great work, that should have been in your first post!

With regard to the drag comparison ... as I said, flying wings probably are not the greatest thing since sliced bread, but picking the YB-49 as a basis for comparison to the B-47 isn't particularly enlightening, as the B-47 was a purpose-built jet-bomber based on the post-war state-of-the art, flying well into the transonic realm where "captured" German knowledge made a big difference. The YB-49 on the other hand was a slightly modified YB-35, and that had been a propeller bomber designed for much lower operational speeds, mostly based on the pre-war state of the art.

It would make more sense to compare the YB-49 to the B-29A, and as they both come out with a Cf in the neighbourhood of 0.006 in the graphs you linked, I don't think that even coincedentally supports your "frontral area" methodology.

Regards,

Henning (HoHun)

 

[Nicknick]

I never claimed that this diagram showed the frontal area, but I added a picture of both planes in the same scale which should make clear, that the B47 has a much lower frontal area than the YB49. A said, my link showed the drag equivalent area vs. the wetted area. When I will be back in the office (I’m doing fine, but I’m having Corona…) I will try to scan the frontal sketches and try to determine the frontal area with CAD.

If two planes with similar wetted areas can differ by a factor of more than two in terms of drag and the “worse” plane is a very clean design, than this shows clearly there is something wrong with the criteria. As said, the YB35 (which had an almost identical structure) was a very efficient plane which outcompeted the B36 prototype. It appears to be an inefficient airplane in this diagram, but this is just because flying wings don’t have a lot of wetted area. I’m sure, from its lift capacity and internal volume it would have competed against planes which are much more up on the X axis.

The YB49 was an oversized plane with unused lift capabilities and unnecessary drag as a consequence of an oversized wingspan.

This example shows, that wetted area is just one of many factors and drag cannot be predicted by this alone. Logarithmic charts tend to bring things closer together than the actually are, when we talk about aerodynamics a difference of more than two is a huge factor.

So, when wetted area is the decisive factor and both planes having the same wetted area, but total different drag, what is your explanation? I think we can agree that the YB49 would have had the same dot in the diagram.

 

[Nicknick]

Having a lot of time to spend (due to quarantine) I found some more about the YB35:

“Stazer et al. [11] compared the minimum drag coefficients of
the XB-35 flying wing with a wingspan of 52 m and the C-5 con-
ventionally configured military transport aircraft with a span of
68 m. The result indicate a 47% decrease in the zero lift drag from
0.023 for the conventionally configured C-5 aircraft to 0.012 for
the XB-35 flying wing Bomber”

https://www.researchgate.net/public...design/link/5adaf0afaca272fdaf83f5ed/download (I wasn t able to open the primary source)

This means, that it was very likely that the YB35/49 had excellent best glide ratios but of course not at the max. speed of the YB49. It also indicates, that the YB35 was potentially a very efficient design which shows how misleading it is just to look on the equivalent drag/wetted area chart.

 

[HoHun]

Hi Nicknick,

unfourtunally some of my postings went missing with establishing this new thread.

There seems to be a second thread with the same title that has the missing posts:

https://www.secretprojects.co.uk/threads/frontal-area-vs-drag-vs-wetted-area-vs.38868/

Regards,

Henning (HoHun)

 

[HoHun]

Hi Nicknick,

“Stazer et al. [11] compared the minimum drag coefficients of
the XB-35 flying wing with a wingspan of 52 m and the C-5 con-
ventionally configured military transport aircraft with a span of
68 m. The result indicate a 47% decrease in the zero lift drag from
0.023 for the conventionally configured C-5 aircraft to 0.012 for
the XB-35 flying wing Bomber”

Well, that's again comparing two quite different aircraft from very different eras. NACA report I mentioned before is more interesting ... it compares conventional, tail-boom and flying wing aircraft built with the same technology and for the same purpose to each other.



So at least as long as we're not dealing with transonic drag rise, I don't see any reason to assume that a flying wing would have higher drag than a conventional aircraft if designed to the same key parameters, as outlined in NACA TN 1477.

Regards,

Henning (HoHun)

 

[Nik]

Fascinating...

Having been blown off my feet at our camp-site near Holyhead by a Vulcan doing a low pass prior to 'Bump & Go' at RAF Valley, I remember staring at underside of its vast delta for what seemed a very long time...

 

[Nicknick]

Interesting document, in my view it fits very well to my argumentation. The YB35 could have been (without the mechanical issues) a very capable airplane which is confirmed by this report. The reason behind this is, that it offers low induced drag and high lift by its “fat” wing with an high wingspan. The parasitic drag of this design tends to be high, when related to the typical small wetted area of flying wings, but surly low when related to the high lift capacity (unfourtunally I haven’t found the L/D of this plane).

The B47 was the better design for a fast, medium range bomber as it is confirmed by your document. The high wing load and sleek body was surly the reason for having a much lower drag despite the equal wetted area.

With 52 m Wingspan and a maximum thickness in the middle the frontal area of the YB35/49 can easily be calculated (two triangles describe the geometry very well), so that the frontal was about 52 m. The drag equivalent area was about 56 sq. ft = 5,2 m² so the Cw value was about 0.1. This is about twice as much as an ideal body, which is not sensational low, but quite realistic for a real life airplane with fins, openings, doors, rivets and so on. I doubt, that a significant lower Cw value could be achieved for an airplane with the same fabrication technics. For sure, super smooth surfaces or partially surfaces with “shark skin”, more detail optimization with a lot of CFD could help to reduce it further, but I haven’t found a single example of anything with practical use which offers a lower drag. The best values I found were some extremely optimized fully enclosed Velomobiles with a drag as low as 0.1 I’m saying that, because it indicates, that there seams to be a technical limit for Cw values in the range of let’s say 0,7 – 0.1. If this is the case, frontal area alone will result in a minimum drag which cant technically be undercut.