Unducted Fan engines are expected to be how many times the size of current turboprop engines?

Unducted Fan engines are expected to be how many times the size of current turboprop engines?

• A. Two to three times
• B. One to two times
• C. Four to five times
• D. Three to four times

Answer: (A)

The key idea is that an unducted fan relies on a very large front fan to move a lot of air efficiently at subsonic speeds, without a surrounding duct. To generate the needed thrust with a high bypass ratio, the fan must have a large disk area, which means a much larger overall engine diameter. To achieve comparable thrust and efficiency to current turboprops, this large front fan translates to an engine size roughly two to three times bigger than a typical turboprop propeller installation. If it were much smaller, there wouldn’t be enough bypass air to gain the desired efficiency; if it were much larger, the overall aircraft integration and structural penalties would outweigh the benefits. So two to three times is the practical range.

The key idea is that an unducted fan relies on a very large front fan to move a lot of air efficiently at subsonic speeds, without a surrounding duct. To generate the needed thrust with a high bypass ratio, the fan must have a large disk area, which means a much larger overall engine diameter. To achieve comparable thrust and efficiency to current turboprops, this large front fan translates to an engine size roughly two to three times bigger than a typical turboprop propeller installation. If it were much smaller, there wouldn’t be enough bypass air to gain the desired efficiency; if it were much larger, the overall aircraft integration and structural penalties would outweigh the benefits. So two to three times is the practical range.