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For those curious about the unusual overwing engine pods, Wikipedia says: "The HondaJet’s overwing engine mount configuration was designed to maximize cabin sp

For those curious about the unusual overwing engine pods, Wikipedia says: "The HondaJet’s overwing engine mount configuration was designed to maximize cabin space,[5] and achieve lower wave drag at a high Mach number." https://en.wikipedia.org/wiki/Honda_HA-420_HondaJet#Design https://en.wikipedia.org/wiki/Honda_HA-420_HondaJet#Design The source document has more discussion of the issues involved: http://www.hondajet.com/Content/pdf/FlightInternational_CoverStory.pdf http://www.hondajet.com/Content/pdf/FlightInternational_Cove...

pritambaral 8y ago
The source document is especially helpful. The overwing engine configuration is unusual because it has been an industry-accepted fact that flow interference (specifically, the conversion of the flow from laminar to turbulent) from the wing as the angle of attack increased beyond a few degrees — which happens during take-off, climb, and landing with wing-aerodynamic braking — would have significant-to-catastrophic effects on the engine's intake. Honda says they managed to find a sweet spot amidst the interference, using computational analysis and wind-tunnel testing. Computational analysis of turbulent flows is much more difficult than laminar flows, and wind-tunnel testing has been traditionally favoured over computational analysis for this reason. Honda also says they made their own airfoil and made the upper-skin extra smooth to keep the flow more laminar between the wing and the engine. This is impressive engineering. EDIT: Just noticed, the document claims the wing had to be made of metal instead of composites " to maintain the contour required for laminar flow".
cup-of-tea 8y ago
Is it normal to talk about a "high Mach number" for a subsonic aircraft?
- mseebach 8y ago
  Yes. At high (sub sonic) speed and high altitude, you get close enough to the speed of sound that this starts to matter a lot. https://aviation.stackexchange.com/questions/35408/what-is-the-reason-for-changing-the-speed-reference-ias-or-mach-number-with-al https://aviation.stackexchange.com/questions/35408/what-is-t...
- sandworm101 8y ago
  Mach is the better reference. If you quote standard speeds you get into the whole ground/indicated/actual speed/alt issue. Your numbers will always sound wrong to someone. Mach avoids the issue.

pritambaral 8y ago

The source document is especially helpful. The overwing engine configuration is unusual because it has been an industry-accepted fact that flow interference (specifically, the conversion of the flow from laminar to turbulent) from the wing as the angle of attack increased beyond a few degrees — which happens during take-off, climb, and landing with wing-aerodynamic braking — would have significant-to-catastrophic effects on the engine's intake. Honda says they managed to find a sweet spot amidst the interference, using computational analysis and wind-tunnel testing. Computational analysis of turbulent flows is much more difficult than laminar flows, and wind-tunnel testing has been traditionally favoured over computational analysis for this reason. Honda also says they made their own airfoil and made the upper-skin extra smooth to keep the flow more laminar between the wing and the engine. This is impressive engineering. EDIT: Just noticed, the document claims the wing had to be made of metal instead of composites " to maintain the contour required for laminar flow".

cup-of-tea 8y ago

Is it normal to talk about a "high Mach number" for a subsonic aircraft?

mseebach 8y ago
Yes. At high (sub sonic) speed and high altitude, you get close enough to the speed of sound that this starts to matter a lot. https://aviation.stackexchange.com/questions/35408/what-is-the-reason-for-changing-the-speed-reference-ias-or-mach-number-with-al https://aviation.stackexchange.com/questions/35408/what-is-t...
sandworm101 8y ago
Mach is the better reference. If you quote standard speeds you get into the whole ground/indicated/actual speed/alt issue. Your numbers will always sound wrong to someone. Mach avoids the issue.