Review Reports

Round 1

Reviewer 1 Report

The current paper presents the conceptual design optimization and assessment of a BWB using an engineering flight simulator. The core idea is interesting, as is the investigation in the flight simulator. Moreover, the article is well-written and the use of English language close to excellent.

However, there are some issues on a fundamental that need to be addressed if the article is to reach journal publication. The issues mostly refer to the design and optimization procedures, so the authors could possibly emphasize on the simulator study, stating that the BWB is more of a reference platform, rather than a designed / optimized BWB aircraft.

Most specific comments are listed as follows:

 

1. As a start, the design procedure is kept at a conceptual level, and a rather “early conceptual” one. That is, no trade studies are shown and no justification is made concerning the configuration layout selections. Perhaps the authors should present this part as the development of a reference platform, rather than an actual design procedure. More specifically

• The weights estimation methodology is not properly presented. Almost no analysis is made, no mission profile etc. Raymer’s approximations are mentioned, but it is unclear whether those approximations refer to general sizing methods or to the BWB-related coefficients.
• Concerning the wings and the corresponding parameters, almost o information is given on how those were selected. Same thing applies for the stabilizers. They are positioned at the winglets and almost no discussion is made for this option. A similar approach is followed by Panagiotou et al. (2018), but 1) they present some trade studies to support this selection and 2) they investigate a UAV configuration with different regulations e.g. for takeoff and landing performance. Is a winglet-mounted stabilizer acceptable (weights-, regulations-, or performance-wise) for a commercial airliner?
• How can the authors tell that the design has sufficient control surfaces? No information is given on trimming, from a designer’s perspective. This is even more crucial when it comes to flaps deflection – and trimming the effect of flaps is a serious issue for airliners with unconventional configurations.

 

2. The optimization procedure is also a bit confusing. I regret to say that the tools, the optimization data and the final result do not justify the claim for shape optimization.
   • Low fidelity methods for BWB, Qin has used RANS, how can the authors claim that the panel method is accurate.
   • The selected airfoil profiles are a bit too fundamental to be used on an optimized BWB (The research of Qin and the airfoils suggested there is a very good example). The use of symmetric airfoils can by no means lead to an optimized BWB.
   • Although an elliptical distribution has been achieved, it is not shown in any chart.
   • The biggest issue in this section, though, is the use of panel method on a BWB configuration. Given that no validation is presented, this optimization approach cannot be justified. The authors mention other studies that used RANS, whereas the need for RANS is also underlined in similar studies (Da Ronch et al. 2019, Panagiotou and Yakinthos 2017).
   • Figure 4 focuses more on aesthetics, rather on technical detail. For example, are the engines and landing gear taken into account through the design / optimization procedures?
   • In the comparison section (Table 4), no actual comparison is made – I would expect that you comment the various parameters between the different configurations.

 

3. The simulator setup is better justified. However, and even though the analysis for each of the examined cases is presented in detail, there are absolutely no figures or charts to support the comments in this Section. Indicatively I would suggest that the authors present some root locus diagrams as well the Bode or the corresponding Nyquist diagrams.

 

4. The conclusions is rather weak. Perhaps I missed a citation, but I would not claim that the BWBs are unstable – on the contrary most of the design in the literature are inherently stable.
   • Overall, I would expect the authors to clearly state what their work has to show against other, older studies with similar content.
   • As a general rule, the conclusions section does not include citations.

Author Response

Dear reviewer,

many thanks for reviewing our work and providing us the opportunity to enhance it based on your constructive feedback.

Please see the response as a pdf attachment.

Many regards

Author Response File: Author Response.pdf

Reviewer 2 Report

In this paper, a BWB airplane was conceptually designed and flying and handling quality was assessed with a flight simulator. The topic is very interesting. But the conceptual design process is not adequately presented. And much amount of input data for the flight simulator are missing in the article.

 

Page 4: 

 

2.1.2 : The wing geometry should be more elaborated. For example, the wing has two seep angles, one for the inboard wing and the other for the outboard wing. But the authors are mentioning only one sweep angle of 40 degrees. It appears to be the sweep angle for the outboard wing.

The design procedure to determine wing geometry presented in Table 2 should be explained with more details.

Also, no information is provided on the winglet geometry. 

 

2.2: the authors are using the term "optimization" but it seems like no actual "optimization" was performed in the study. It should be clarified how the design parameters are determined: empirically or through numerical optimization ?

The design airplane has a transonic cruise  condition at M 0.85, but there is no discussion on the wave drag component of the airplane. 

 

NACA sc0012 -> NACA 0012 ?

NACA sc2412 -> NACA2412 ?

 

Page 5 : Qin et al. [17], have determined using a RANS low fidelity optimization ... : Usually RANS simulations are considered to be high fidelity. What do you mean with "RANS low fidelity"?

How are the aerodynamic data obtained ? For flight simulator, much amount of aerodynamic data must be provided. The authors should explain how the aerodynamic data are calculated or obtained by any means.

 

Author Response

Dear reviewer,

many thanks for reviewing our work and providing us the opportunity to enhance it based on your constructive feedback.

Please see the response as a pdf attachment.

Many regards.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors' provided a much better version of their manuscript, following and answering all my comments.