I am making an aircraft with an unducted fan design and I don’t know how big to make the fan.
This isn’t a super serious project, but I thought this would be an interesting topic to discuss nonetheless.
The aircraft is going to be about the same size as an E-190 or A220. (~120 ft wingspan, 110 pax) The idea is to make a next generation regional jet with an engine like the CFM rise. (mounted under the wing)
At first, I started out with a fan around 100 in, but it didn’t really look right. So I scaled up to a larger core and a 130 inch fan. It was at this point that I realized that 130 in. was about the size of a GE-9X fan! This setup actually looked okay since the props were hard to see whilst spinning, but it created obvious ground clearance issues. I then looked to the internet to find some real data.
According to Wikipedia, the PW-1900G on the E190-E2/A220 has a 73 inch fan. And the original E190’s CF34-10E has a 57 inch fan. However, I get the feeling a 60-70 inch propfan engine would look a skimpy on a regional jet. Also according to Wikipedia, the GE-36 engine designed for the Boeing 7J7 had a massive front fan diameter of 140 inches or 3.56 meters! And that aircraft was going to be around the size of a 757…
I know this is a weird topic, but hope this will stir up some interesting discussion. Unducted fan engines aren’t super well known. However, their efficiency could see them being introduced on new aircraft in the coming years. There are also few aircraft with these engines on SimplePlanes (at least I can’t find them). Do you have any builds (finished or planned) that use a propfan engine? Do you think we will see a real aircraft with a this engine soon?
NASA has some UDF footage that can be used as a reference if needed. It should be pretty easy to find on YouTube.
As far as fan diameter goes, I'd suggest maybe looking at some real-life propfan engines and figuring out the general ratio between the size of the prop and the size of the rest of the engine, and then go from there.