I haz n ideeah

[Whirligig Girl]

Okay, this is probably stupid, but here's my idea. What if you put Propeller Blades on the intake fan? Extra thrust? Would the extra mass just make it worse?

[Andon]

That is, essentially, what the intake fans are for. I'm no engineer or physicist, but I think the mass would outweigh the gains on your traditional propeller.

[miracmert]

Okay, this is probably stupid, but here's my idea. What if you put Propeller Blades on the intake fan? Extra thrust? Would the extra mass just make it worse?

Student pilot and student engineer here! But I didn't understand your question. Do you mean what happens when you put propeller blades on the front of the jet engine?

[Kerbin Dallas Multipass]

Whats wrong with turbine blades?

[K^2]

Whats wrong with turbine blades?

I'm pretty sure the only real difference is that compressor blades are high RPM, low torque, and prop is going to be high torque, low RPM. So you'd need a gearbox if you want that prop to do something useful, just like normal turboprop. But otherwise, there is nothing really wrong with the idea. It's just that an extra compressor stage is going to be lighter and easier to make.

[miracmert]

Well I don't know if understood correct but I assume the question is about putting propeller blades on the front of jet engines. If that's the case, that pretty much useless because even though propellers are cheap and easy, there's a drawback about them. When you slow the engine down, propellers act just like a big circle shaped walls blocking the air so the aircraft slows down insanely. Also they are way, way bad at compressing air compared to jet compressors. However, there is an engine type called "turboprop" that works like both propeller andgine and jet engine. There are propellers to lead air into air intake channels in the engine and there are turbines at the end of the engine. After intake air gets burned up with fuel inside combustion chambers it turns the turbines at the back which turn the propellers on the front. Still, turboprops engines have the same problem as propeller engines have that they are not good at airflow, making them poor aerodynamically. Jet engines don't have these problems since the compressors are already inside the engine and they don't block the airflow, also compressing the air much better then any of those props.

[PakledHostage]

Okay, this is probably stupid, but here's my idea. What if you put Propeller Blades on the intake fan? Extra thrust? Would the extra mass just make it worse?

Like most respondents in this thread, I'm assuming that you're talking about mounting a propeller on the front of a turbofan engine. Something to keep in mind though is that turbofan engines are already optimized for peak efficiency over their typical operating range.

To put things in perspective, a 747-400 has a fuel capacity of ~375 000 pounds. Compare that to the empty weight of 400 000 pounds and a useful payload (with full fuel) of only 100 000 pounds. Flying a 747 on a return flight from LA to Sydney will burn almost two full tanks of fuel costing close to half a million dollars. Whatever you save in fuel burn not only saves you money, but it also increases useful payload (because you have to carry less fuel to reach your destination and can carry payload instead). Fuel costs money and useful payload pays the bills, so clearly there is a huge incentive to increase the efficiency of engines. Engine/airframe manufacturers already do everything that is technologically possible to increase efficiency.

[Giggleplex777]

Okay, this is probably stupid, but here's my idea. What if you put Propeller Blades on the intake fan? Extra thrust? Would the extra mass just make it worse?

Do you mean this:

Turboprop

Or this?

Propfan

The Propfan is pretty much a very high bypass turbofan, except more efficient.

Edited January 17, 2014 by Giggleplex777

[PakledHostage]

Interesting photo of the propfan. Looking up the registration, the aircraft is an Antonov 70. Only two were ever built according to Wikipedia. It cruises slower than typical turbofan powered aircraft so it is operating under different conditions than they do.

Something else that is interesting about it is that it appears to have counter rotating propfans. Propeller's accelerate the air that passes through them both axially and radially. The counter rotating props allow the recovery of some of the energy lost in radial velocity, thereby increasing the efficiency.

Edited January 17, 2014 by PakledHostage

[Traches]

Maybe I've spent too much time in the darker corners of the internet, but there's no way y'all are this easily trolled. I feel like people on this forum would have a lengthy, in depth discussion with links to wikipedia and carefully crafted arguments on the possible uses of "tist on a bool" if I asked nicely...

Edit: Anyway yeah, propfans are pretty cool. I'm more partial to turboprops myself though...

Edited January 17, 2014 by Traches

[PakledHostage]

Maybe I've spent too much time in the darker corners of the internet, but there's no way y'all are this easily trolled.

I don't think we are being trolled. GregroxMun is a regular on these forums. I don't have any sense of his/her age or background, but there are quite a few science minded kids here, and also several professional scientists and engineers. We do what we can to help out when someone has a question, even if it is a bit unusual (so long as they are polite about it).

[legoheli]

From how I understand the question, Gregrox is more or less suggesting another existing engine, but not a turboprop.

It's simply the high-bypass turbofan.

If you don't know what that means, here's the crash course (tee hee) in turbofan engines:

The central piece of the engine, the long tube with small diameter, is essentially a turbojet. This is the "classic" jet engine where a series of blades compress air, which is then mixed with fuel and ignited. Then at the back, said air passes over some turbine blades that drive the compressor blades in the front.

Now, in a turbojet, the first compressor blade is much larger than the other compressor blades. This is because this blade acts not only as a compressor, but also as a ducted fan, which is essentially a propeller with a casing. You will notice in the cutaway above that there is a large outer tube in the front. This is the "bypass", air that is simply pushed through the tube by the compressor, driven by the central turbojet, creating thrust. In a lot of cases, even most of the thrust of the engine!

This is much more effecient use of the jet engine than a traditional turbojet, and it is much less noisy too!

I hope this was what you meant.

[Traches]

I don't think we are being trolled. GregroxMun is a regular on these forums. I don't have any sense of his/her age or background, but there are quite a few science minded kids here, and also several professional scientists and engineers. We do what we can to help out when someone has a question, even if it is a bit unusual (so long as they are polite about it).

I'm poking goodhearted fun; I realize he's posted here before. You have to admit that the thought and effort put into his question makes this guy look like a go-getter: