Elliptical vs Square Prop Tip?

J

JC150

Pre-takeoff checklist
Joined
Apr 22, 2013
Messages
491
Display Name
Display name:
JC150
Looking at different propeller options.. I did a google search but wanted to ask the experts here at POA. .

1) Is there a benefit to having an elliptical (round) vs square propeller tip?

2) Would it be worth adding a 3 blade propeller to my Piper Arrow III instead of 2?

3) Someone mentioned a Scimitar 2 blade prop for the arrow. Has anyone had any experience with this blade?

Thanks!
 
Can't speak to all your questions but a 3 blade is going to be noticeably smother than a 2 blade of similar material.
 
JC150 said:
2) Would it be worth adding a 3 blade propeller to my Piper Arrow III instead of 2?
Click to expand...
I can't address your other questions and I too am very curious about #1.

A 3 bladed propeller will give you better takeoff and climb performance but you'll cruise a bit slower. Everything will feel smoother and you'll also have better prop clearance since the blades are a bit shorter. The only downside to a 3 bladed prop is the loss of cruise speed and added weight. Of course many 3 bladed props are newer more efficient designs so you don't actually notice a loss in cruise speed.
 
Just a swag think about tip shape similar to wing tip shape.....
square = better power transmission, but loud
round = less noise and drag especially as tips approach super sonic speeds
If you are losing cruise speed moving to a three blade, the plane probably doesn't have enough horsepower to need a square tip and it would just be louder.
 
The three bladed prop looks much better,with a small decrease in cruise flight.
 
I had a passenger refuse to get on a plane I was flying that had Q-tip props.....

th
 
Maybe it's just me but a 3 blade seems to be a more effective speed brake when you yank the throttle and shove the prop.
 
Another consideration about the 3 bladed is that if you land gear up you are guaranteed a prop strike. If you have a 2 bladed prop and your gear is stuck up you can kill the engine and get it horizontal and save the engine.

Of course the above is hotly debated and generally advised as bad practice. It's still another difference between the props though.
 
FORANE said:
Can't speak to all your questions but a 3 blade is going to be noticeably smother than a 2 blade of similar material.
Click to expand...
Also, the 3 blade creates noise at a 50% higher frequency than the lower frequency pulses created by the 2 blade. The higher frequency is more effectively blocked by sound deadening material and ANR headsets.
 
I was under the impression that any prime numbered propeller will be "smoother" .. something like a 4 blade can get out of balance much more easily than 3 or 5. I've only flown about a dozen or so different planes, but I've never noticed a difference in 2 or 3 blade props. 4 vs 6 cylinder, yes for sure. Maybe I just haven't paid enough attention

Anyway, isn't technically a one bladed prop most efficient? http://www.ladieslovetaildraggers.com/blog/no-way-a-one-bladed-propeller/

upload_2018-7-17_14-11-15.png
 
Zeldman said:
I had a passenger refuse to get on a plane I was flying that had Q-tip props.....

th
Click to expand...
Seems logical to put winglets on these airfoils too. Any idea what kind of efficiency gains are expected?
 
jaymark6655 said:
Just a swag think about tip shape similar to wing tip shape.....
square = better power transmission, but loud
round = less noise and drag especially as tips approach super sonic speeds
If you are losing cruise speed moving to a three blade, the plane probably doesn't have enough horsepower to need a square tip and it would just be louder.
Click to expand...

So the square blades provide more power? So if i want speed, square is better than rounded prop tip?
 
I dunno... I had a sensenich aluminum and went to the schimatar carbon and its noticeable smoother and faster...
 
JC150 said:
So the square blades provide more power? So if i want speed, square is better than rounded prop tip?
Click to expand...
I think square can transfer more power, but the power has to be there. One reason that a three blade is slower is because the power isn't there to make a three blade prop necessary. I could be wrong though, just an educated guess. If I am wrong I would love to know.
 
Mtns2Skies said:
Another consideration about the 3 bladed is that if you land gear up you are guaranteed a prop strike. If you have a 2 bladed prop and your gear is stuck up you can kill the engine and get it horizontal and save the engine.

Of course the above is hotly debated and generally advised as bad practice. It's still another difference between the props though.
Click to expand...

I challenge you to a duel.

vvH8WBd.jpg
 
I went through this exercise a few years ago on my Piper Arrow when my original 2 blade prop was condemned by the prop shop. I went with a 3 blade prop. It climbs noticeably better. This was important to me so I can get to an altitude that turn back to the airport is available as an option should the engine decide to give up the ghost. I haven't noticed a loss in cruise speed. Also, as mentioned by another poster, its a great speed brake. The 3 blade looks better in my opinion. Not that looks make a difference in performance, but it is nice.

There is the option for a 2 blade scimitar prop. I looked at it briefly. It doesn't seem as popular of a choice. I didn't want to worry about support if I was one of the few with it.

My though on a gear up incident is if I cant get the gear down, I am not going to mess with stopping the prop and bumping the starter. That's asking for more trouble. The plane is insured for stuff like that.
 
Adam Weiss said:
Seems logical to put winglets on these airfoils too. Any idea what kind of efficiency gains are expected?
Click to expand...
Apparently not enough to make a difference given that the idea seems to have faded away.
They were supposed to be quieter though - hence the name "Q-Tip".
http://aviationweek.com/bca/remember-q-tip-prop

JC150 said:
So the square blades provide more power? So if i want speed, square is better than rounded prop tip?
Click to expand...
The most efficient lift distribution for any wingish thing is elliptical - minimizes induced drag. But, there are many ways to adjust the lift distribution - one is the planform, another is to put in some twist, and a third is to change the airfoil between the root and the tip. All these methods work. Also you have to consider practical limitations such as diameter / ground clearance etc. And, when you get into propellers - the details of the twist get interesting when you try to compensate for the fact that some of the prop is in front of the cowl and some is out in the free stream. Then you get into variable pitch propellers - the ideal twist varies with the pitch setting, so at best, you get a compromise.

To make a blanket statement that one type of tip is better or worse than some other is pretty much like arguing that Ford is better than Chevy. Mostly, they just be different. And, if you want to compare prop A vs. prop B., all the other things that are likely to change in the design are going to make as much as, if not more, of a difference than a square vs. round tip.
 
Adam Weiss said:
Seems logical to put winglets on these airfoils too. Any idea what kind of efficiency gains are expected?
Click to expand...

On the ground, as the propeller turns, a small vortex will build between the prop and the ground. That will suck up small gravel into the prop. When operating on non-paved surfaces we were told that the Q-tip reduced that vortex thereby reducing damage to the prop while on gravel surfaces. I could see the vortex when idling, and it still picked up very tiny pieces of gravel into the prop so I don't really know if the Q-tip did any good or not. I could not even tell any difference in prop noise between the two props.
 
Adam Weiss said:
Seems logical to put winglets on these airfoils too. Any idea what kind of efficiency gains are expected?
Click to expand...

I thought so too at one time. I bought a Prince prop with "P-tips" which are in effect the same as the Q-tipped props. But then I started reading some things by Paul Lipps. His props have been taking first place for years at Reno, particularly in the Bi-Plane division. His material can be found in Contact! magazine and quite a lot on Van's Air Force forums under the username "Elippse". It's very interesting prop information and I'll leave those who want to dig into it with those links. Also, just Googling his name will get you to some of the essentials. To give you a quick and dirty take on Paul's work, sticking an airfoil at the tip of a prop reduces prop efficiency by a very significant amount. The best design for prop tips is what you'll see with Catto props, Bruce Catto having worked with Paul for years prior to his (Paul's) passing a few years ago. The prop on Paul's Lancair had tips so pointed you could stab yourself if not careful, as are the tips on his Reno props. His designs made use of the prop angle next to the hub, a section wasted (actually worse than that . . . it's drag producing) with most prop/cowling installations. His props have a very sharp angle near the hub for driving air into the cowl for better cooling. They widen out to a broad mid-section then taper to a tiny tip - where velocity and drag is greatest. Google the race plane Phantom owned by Tom Aberle to see an extreme (and winning) example of Paul Lipp's designs. In short, a broad squared tip is horrible, drag wise - although one does see them on turbine powered aircraft like the Convair 580 and others. Maybe turbine-powered props have different aerodynamics, but I doubt it. I suspect Paul would say they are terrible aerodynamically but practical for some other reason - for instance, to provide sufficient airfoil surface to absorb the power of a turbine given the restriction of prop diameter. . . dunno. I do know that listening to a T-6 take off was an excruciating experience to Paul's engineer mind. All that noise. Pure wasted power and nothing more. Anyway . . . read Paul Lipps on the subject. You'll learn a tremendous amount about props if you do.
 
Last edited:
You must log in or register to reply here.
Back
Top