Propeller questions

[colmbo]

[Edit] Dale, do I remember correctly that you had a 180 at some point?

'57 182 which at that time was a 180 with a nosewheel.  The 180 in the video is the later model 180 that was pretty much an underpowered 185.  It has the big tail and an extra window/seat row but IIRC still had the same 230HP Continental of the 182/180 series.  The 185s have the 285 to 315 HP engines with the long 2-blade props that really make a racket.  Something I have seen quite often is guys on floats putting longer props on the 180s to help get them off the water -- the longer prop makes more noise.

[Tupac]

Quick semi-off topic question: Why does a cirrus use a 3 bladed prop with an IO360, but 172s running an IO360 only use a 2 blade?

[colmbo]

Quick semi-off topic question: Why does a cirrus use a 3 bladed prop with an IO360, but 172s running an IO360 only use a 2 blade?

Perhaps a matter of ground clearance?

[Stoney]

Quick semi-off topic question: Why does a cirrus use a 3 bladed prop with an IO360, but 172s running an IO360 only use a 2 blade?

Different design priorities.  Perhaps Cirrus wanted a better rate of climb, or more ground clearance, or needed shorter blades for tip speeds, or needed more blades for better power absorption, etc.  Maybe they thought it looked better...

[PJ_Godzilla]

I remember some of the experiments with swept blade props - NASA did some testing on that as well back in the 80s but it never seemed to go anywhere.  I also wondered why the Germans stuck with 3-bladed props on the 109K4 as well as on the 190D9 and TA152s. 

Actually, I was a wind tunnel test engineer at Ames in the late 80's. I remember an internal (principal investigator aws another NASA division) test we did on an unducted fan in the 14' TWT. That was basic research where we were mapping out the pressure distribution on the nacelles. Otherwise, IIRFC, the use of the fan is all about fuel. It's kind of ultra high bypass, if you like.

As for the swept blades, my recollection is that it's the same issue as with swept wings - delaying the onset of transonic wave drag - which goes something like the thickness/chord ratio. Apparent chord rises with sweep, thus t/c decreases. Also, and as an interesting aside, IIRC, the 262's sweep was all about c.g. - any other benefits were unintended.

[Stoney]

Also, and as an interesting aside, IIRC, the 262's sweep was all about c.g. - any other benefits were unintended.

I never knew that--very interesting...

[Ardy123]

I never knew that--very interesting...

The kommet had swept wings too, and was design in '41. At what point did they discover that property of swept wings?

[Tupac]

Maybe they thought it looked better...

That's the only thing I think it might be, maybe Wolfala has something to say about it, i know he owns a cirrus.

[Golfer]

Also, and as an interesting aside, IIRC, the 262's sweep was all about c.g. - any other benefits were unintended.

I'd heard that several times and I guess I never researched it.  To my eye it looks fantastic but I'd wondered if any significant advantages to that (relatively small) amount of sweep would be realized.

[PJ_Godzilla]

I never knew that--very interesting...

I said that from memory. I took a class i n advanced design with Ilan Kroo at SU back in '87. He cited it. I was able to find this very quickly in Wiki so perhaps, per usual, Kroo knew what he was talking about:

Although it is often stated the Me 262 is a "swept wing" design, the production Me 262 had a leading edge sweep of only 18.5°, too slight to achieve any significant advantage in increasing the critical Mach number.[15] Sweep was added after the initial design of the aircraft, when the engines proved to be heavier than originally expected, primarily to position the center of lift properly relative to the centre of mass.

<end snip>

As for the 163, I can make no claim but note that the genesis of the two designs is separated by a number of years of intense "learning" and "incentive".

[Stoney]

I'd heard that several times and I guess I never researched it.  To my eye it looks fantastic but I'd wondered if any significant advantages to that (relatively small) amount of sweep would be realized.

According to Raymer, sweep contributes a few advantages to different aspects of high-speed flight.  For supersonic flight, loss of lift associated with supersonic flow can be reduced by sweeping the wing leading edge aft of the Mach cone angle, where the mach cone angle = the arcsin(1/Mach #).  Since the 262 wasn't designed for supersonic speed, it gained no advantage from the designed sweep since at a Mach number of 1, no sweep is required.

On the other hand, wing sweep in the sub-sonic/transonic range increases the critical mach number of a wing, so it may have extended its critical mach number with the wing sweep that was designed.  According to Wiki, compared to the P-80 (which had basically no wing sweep), the USAF tested both aircraft and determined the 262 had a higher critical mach number, so perhaps the wing sweep created the advantage, although airfoil thickness and profile has an affect as well, and I don't know how those two aircraft compared in those respects.

[PJ_Godzilla]

According to Raymer, sweep contributes a few advantages to different aspects of high-speed flight.  For supersonic flight, loss of lift associated with supersonic flow can be reduced by sweeping the wing leading edge aft of the Mach cone angle, where the mach cone angle = the arcsin(1/Mach #).  Since the 262 wasn't designed for supersonic speed, it gained no advantage from the designed sweep since at a Mach number of 1, no sweep is required.

On the other hand, wing sweep in the sub-sonic/transonic range increases the critical mach number of a wing, so it may have extended its critical mach number with the wing sweep that was designed.  According to Wiki, compared to the P-80 (which had basically no wing sweep), the USAF tested both aircraft and determined the 262 had a higher critical mach number, so perhaps the wing sweep created the advantage, although airfoil thickness and profile has an affect as well, and I don't know how those two aircraft compared in those respects.

You could check it quickly and dirtily by comparing the relative increase in t/c for an 18.5 degree sweep.

[kvuo75]

To my eye it looks fantastic

Indeed! everytime I fly a 262 it reminds me of a boeing 737 wing. however a quick google search says the 737 is 25 degree sweep.. still looks the same to me!

[Stoney]

I wonder what its quarter chord sweep is compared to the leading edge sweep.  Does anyone have a scale drawing of the wing that measurements could be made off of?

[moot]

So.. do any AH props occasionally go supersonic?