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Old 03-24-2015, 10:57 AM
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Default Aircraft Design and Aerodynamics

Hello everyone. I am currently working on a project that requires me to compare and contrast narrow body vs wide body aircraft. I am having a difficult time finding books and references that specifically talk about aerodynamic differences between both types of aircraft. What were some of the challenges for engineers when transitioning into wide body aircraft? Why are aircraft being designed wider instead of longer? What systems or technology had to be modified when designing a wide body aircraft?

Any references would be highly appreciated.

Thank you.
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Old 03-24-2015, 11:21 AM
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Originally Posted by tintin939 View Post
Hello everyone. I am currently working on a project that requires me to compare and contrast narrow body vs wide body aircraft. I am having a difficult time finding books and references that specifically talk about aerodynamic differences between both types of aircraft. What were some of the challenges for engineers when transitioning into wide body aircraft? Why are aircraft being designed wider instead of longer? What systems or technology had to be modified when designing a wide body aircraft?

Any references would be highly appreciated.

Thank you.

It sounds like you're a production intern at a "news" station and don't know anything about all that science stuff that makes 'em fly. Posting this on the day of fatal crash, all I can say is that your timing sucks.
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Old 03-24-2015, 11:25 AM
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Originally Posted by tintin939 View Post
Hello everyone. I am currently working on a project that requires me to compare and contrast narrow body vs wide body aircraft. I am having a difficult time finding books and references that specifically talk about aerodynamic differences between both types of aircraft...
Jan Roskam, Dan Raymer, and John Anderson are what I would check first.

...What were some of the challenges for engineers when transitioning into wide body aircraft?..
Any working aerodyamicist should be able to hit the main points of this question. You may wait a long time to hear from a 777 or 340 engineer who actually knows about the aero workup on that model.

...Why are aircraft being designed wider instead of longer?...
What makes you think there is atrend in this area? Not arguing, just a little surprised at your thesis.

... What systems or technology had to be modified when designing a wide body aircraft?...
This could get into a lot of sub-topics besides aerodyamics. How deep are you interested in going (what is the scope of the study)? The textbooks I mentioned above should have enough depth for preliminary studies.
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Old 03-24-2015, 11:36 AM
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Originally Posted by awax View Post
It sounds like you're a production intern at a "news" station and don't know anything about all that science stuff that makes 'em fly. Posting this on the day of fatal crash, all I can say is that your timing sucks.
We don't know that. They sound more like an undergraduate aerospace student to me.

OP- it would help if you reveal a little more about yourself. Even the difference between year 1 and 4 in an aerospace program makes a difference what matters. Give us an idea who-what-when-why and we'll try and come up with appropriate answers. It's a great question!
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Old 03-24-2015, 11:56 AM
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Originally Posted by Cubdriver View Post
We don't know that. They sound more like an undergraduate aerospace student to me.

OP- it would help if you reveal a little more about yourself. Even the difference between year 1 and 4 in an aerospace program makes a difference what matters. Give us an idea who-what-when-why and we'll try and come up with appropriate answers. It's a great question!

Really? An undergrad who can't draw conclusions about flat plate drag, weight, and thrust from available texts?

Why are aircraft being designed wider instead of longer?
Seriously?
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Old 03-24-2015, 06:24 PM
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I think the OP (if legit) is looking at the issue from the wrong angle.

Turn radius limits. See AC 150-XX series for airport design requirements. Size (wingspan and distance between main gear and nose gear) does matter with respect to runways and taxiways... Just look at the A-380... Several major airports needed to be "upgraded" to ensure the 380 would "fit"...

The "wide-body" has an amazing passenger pleasing feature not found in narrow body transports- The Double Aisle. Twice as efficient for in-flight service and potty break foot traffic
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Old 03-25-2015, 10:05 AM
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Hello everyone,

Sorry for not defining my problem more specifically. I am currently a senior in an aviation program not related to engineering. The class that I am currently taking is advanced aerodynamics course and I am required to present on cutting edge aerodynamics of the past, present, or future for narrow body and wide body aircraft. I am supposed to compare wide body vs narrow body aerodynamics. No other instructions were given to me other than stated above. I am supposed to come up with topics to talk about but I am not sure what. I belief my teacher wants me to talk about the fuselage specifically. Why go wider instead of longer? I know that if the narrow body tends to become very long, it may require a long heavy landing gear in order to permit the desired rotation angle on takeoff without scraping the rear end of the fuselage on the runway. This landing gear problem is alleviated by the shorter fuselage offered by the wide body. Are there any other factors that prevent engineers from designing aircraft longer? Maybe limited size of vertical and horizontal stabilizers affecting longitudinal stability?

What about the increase in drag for wide body aircraft vs narrow body? What are engineers doing to reduce this increase in drag on the wide body fuselage? I found tons of books on fluid dynamics but they have a lot of intense math that is difficult to understand. I found a book titled Design of Aircraft by Thomas C. Corke and it gave me good information on aerodynamic considerations when designing a fuselage. For example, effects of fuselage fineness ratio on viscous and wave drag, formulas in estimating drag, and a number of quantitative fuselage shapes.

The reason why I asked for help in this forum is because I thought maybe there would be someone out there that might be able to help me think about ideas of what to include in my 20 minute presentation and what books to look in. Specifically topics that will help me compare wide body vs narrow body aircraft aerodynamics. I picked up Fundamentals of Aerodynamics by John D. Anderson, Jr and I will be looking it over today. I will definitely be picking up books from the other authors that were suggested as well.

Any help would be greatly appreciated.
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Old 03-25-2015, 10:20 AM
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Originally Posted by tintin939 View Post
I know that if the narrow body tends to become very long, it may require a long heavy landing gear in order to permit the desired rotation angle on takeoff without scraping the rear end of the fuselage on the runway. This landing gear problem is alleviated by the shorter fuselage offered by the wide body. Are there any other factors that prevent engineers from designing aircraft longer? Maybe limited size of vertical and horizontal stabilizers affecting longitudinal stability?
It sounds like you're on the right track with the "longer vs. wider" design problem. If you use the current 737-900 narrow body as an example, Boeing has stretched it to the point that take off and landing speeds are unusually high to avoid tail strikes during take off and landing (the higher the speed, the lower the AOA, which in turn lowers the deck angle). The higher speeds reduce the stopping performance for rejected takeoffs, and increase landing distance, or both.

Aircraft are designed around specific routes, so range and payload play heavily into the design process.

I think you'll find this book interesting, read the article on page 64:

https://books.google.com/books?id=N4...page&q&f=false
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Old 03-25-2015, 12:23 PM
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Assuming you want to stay within the aerodynamic aspect of the topic, you need to look at some preliminary aircraft design books and see what the fineness ratio discussion leads you to. You'll get some quick and approximate ideas from preliminary design books because the subject is for ballpark estimation. The Jan Roskam books are great for this purpose, he spent many years collecting bits and pieces that a preliminary designer needs to do the job. His most popular collection is titled Aircraft Design I-VIII. I do not have my collection handy, but one of the books has the data you need. It will tell you what the tradeoffs are for a wider body in a general way. Right off hand, I recall that lower fineness ratio has very modest drag penalties in the subsonic regime, which is why we see a lot of high subsonic wide-bodies. You can go very fat in relation to the wings, and still have pretty low drag. However, the cheaper way to get more seats in a derivative airplane is to add a "fuselage plug" which is just the addition of an additional body segment. That's why we see so many of them (DC9 derivatives, CRJ and ERJ series, Dash 8 derivatives, 737 series, etc.)

I am told there was a proposal by FedEx for a Cessna Caravan that would be able to carry a standard 757 cargo container to save time sorting cargo into smaller groups. That would have been one fat looking airplane.

Fineness ratio - Wikipedia, the free encyclopedia
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Old 03-26-2015, 06:25 AM
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Cubdriver suggested some good books. I found the following in, "Airplane Design: Part II, Preliminary Configuration Design and Integration of the Propulsion System".

On page 110 is a table of historical data on fineness ratio based on category of aircraft. The Jet Transport category shows a fineness ratio (Length Fuselage/Diameter Fuselage) of 6.8 - 11.5.

The Roskam series is based on using empirical data from past aircraft to do preliminary design of new aircraft. These cited numbers include a huge range so it might not help much.

I think the Anderson book will teach you more about the fundamental physics but it will have some serious math. One contribution to total drag is a function of the surface area (aka wetted area). By playing with some geometry, you will see that adding length to a fuselage will not increase the interior volume as efficiently as increasing the diameter of the fuselage with respect to wetted area. However, the surface area when viewed from the front is a competing factor that also contributes to drag. Part of the problem is in optimizing this fineness ratio. This is very simplified and there are other complexities to incorporate as the speed increases into the transonic regime.

As Awax explained about the growth of the 737, sometimes the reason for a design decision isn’t really based on optimizing the physics. It could be that a decision is based on financial constraints or the need to incorporate existing technology. For example, the super long 737 allows airlines have one group of pilots with common “type rating” fly a larger variety of aircraft. An engineer would probably never design the 737-900 if it were a “clean sheet” design. It only makes sense when you include the financial, regulatory, historical environment.
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