Prop shapes - how to choose?

[Terry Caron]

Hi all -

I may be wanting to oversimplify a complex subject, but sizes and materials aside, these props all have different shapes, and there may be others I don't have on hand.
What dis/advantages do the different shapes have?
When to choose one over another?

Thanks.

Terry

[Dan McEntee]

  Hi Terry;
    This is one of those subjects that you can stay up all night and drink a lot of beer and argue about. If you fly stunt at any level of competition, you'll eventually learn that all props are not the same, some will work for this airplane/engine but not that one, and as soon as you settle on a prop for your best airplane, you'll never find another one! APC used to have a good bit of information about prop theory on their web site, so you might want to check that out. It explains why they make their props the way they do. You might want to check the other manufacturers also. All these different opinions and styles is good, give you a better chance to find what you want and need. I collect old props, just  because there were SO many neat designs, and they look cool! Back in the day, guys used to make their own props because they couldn't afford to buy the good ones after saving their pennies for the engine and they would copy what they saw or borrowed from their buddies. It is an interesting subject.
   Type at you later,
    Dan McEntee

[Howard Rush]

You will get a lot of bogus advice.  For the straight stuff,

Adkins, C.N. and Liebeck, R.H., Design of optimum propellers, AIAA Paper 1983-190,
January 1983, https://www.aiaa.org/IframeTwoColumn.aspx?id=4745

http://www.supercoolprops.com/

http://www.mh-aerotools.de/airfoils/javaprop.htm

[Terry Caron]

Theory is way past my intent. 

While I hope to rectify this soon, the last handle I had in my hand, about 10 years ago, had a Cox RTF Texan on the far end of some string.
If I fly to compete for anything, it'll be for one of those beers Dan mentioned. 

I had more in mind maybe rules-of-thumb sort of insight.
Example; I bought the scimitars because they are different from the others, but it may be pointless to consider this shape for, say, a Fox .35 on a Sig Banshee, "'cause they're for speed".

Again, I may be looking for an illusory simplicity; could be that the only things one can say with any certainty are the results of the equations in the theory.

Terry

[Dave_Trible]

Terry just to keep it simple,  my suggestion given what you have; Fox .35, Banshee and the props you have I think the best choice is that white Top Flight nylon prop.  Flexi nylon isn't the best material although it will take a lot of abuse.   However the wider rounded paddle blade works well with a lower rpm churner like the Fox on a lighter airplane.  For a higher rpm modern engine I'd go more with the APC.  The rest are great dope stir sticks.

Dave

Addendum..if buying new props which are available and low cost I'd get Top Flite wood 10-6 Power Props for that application.  Even MY LHS can get them.

[Terry Caron]

So is there then a general connection between blade shapes and rpm ranges?
And are the scimitars just a waste?

As an aside, those aren't my only props, nor my options for any particular engine/airframe combo, just a selection of illustrative shapes I have on hand.
But I do have a range of engines and (partially built) 'planes, including my example, that I hope to prop eventually.
With the Texan it was easy - the prop was on it.

Terry

[Dan McEntee]

  No, the scimitars are not a waste. They do work. There are a couple of APC props that seem to be the "go to" prop when nothing else work. When flying the larger models, line tension is your friend, and the prop has a lot to do with that. So does the altitude you live at! And the size and weight of the airplane. The APC and most of the off the shelf props are relatively inexpensive, so you can try a couple of different props as you go, then store the rest until next model. Then the process starts over. I have a big box or two of props from all the years I'v done this, and won't throw any away or sell them, because you never know when a certain prop might just be the ticket. I tried some Zinger Pro props with the scimitar shape on a couple of different engine/plane combinations, and just wasn't impressed. I put an OS.32 on my P-Force a year or two ago and started the prop dance to find what felt best, and the Zinger 11-4 Pro that didn't wake me up on other airplanes, was just the cat's pajamas on this model. I think you have the basic idea about the impotance or lack of on tip shape, but just to illustrate again, I was looking for a better prop for my Shark45 but in a smaller diameter so I could use shorter landing gear. I was using an APC 12.25-3.75 but wanted to get down to close to 11 inches in diameter. I made a tracing of the tip on one, cut it down, and carefully reshaped the cut-off tip to restore the original shape, and it seemed to work OK. Then, at a contest, I needed another one, and didn't have the time to goi through all the work of reshaping, and just cut it off square and accurately, balanced it and went flying and it was better!. Doesn't look as nice, but I don't worry about that as long as it keeps me from having to do a lot of back peddling with the airplane at 45 dgrees! I guess the short answer is, just get your hands dirty and see what feels good and performs the way you want it to. It's not always strictly about RPM on the ground, but how it feels  and performs in the air.
  Have fun,
  Dan McEntee

[Douglas Ames]

I think I still have scars from those damned flexible TF Nylon props. (1/2A)

I think the term is "coning".

You think the prop is spinning "there" at the hub, but the tips are forward of that spinning "here" at your fingertips... as they slice thru your digits. 

Top Flite Super M's... Now there's a nice vintage Sport prop.

[Terry Caron]

Well, I don't have so many engines/planes/props that fly-n-try is out of the question, but I am old enough to not want to waste any more time than necessary.  

Dan, about cropping props - I have some old "gift" props trimmed to odd fractional inch diams that I've wondered about.
Does the average chord increase help, is it a matter of a non-commercial diam/pitch combo or what?

And Douglas, I'm currently healing from a minor brush with an old TF nylon on a Fox .15 myself.
But if your Super M comment is sincere, I have an 11x6 (wood) that might be a good cropping candidate for the Fox.  

Terry

[Howard Rush]

Again, I may be looking for an illusory simplicity; could be that the only things one can say with any certainty are the results of the equations in the theory.

I think so.  I fiddled with the theory some and got some insight, but my personal propeller selection technique is to go up to the guy who won the contest and ask him what prop he's using.  One rule of thumb is that for a given diameter and pitch, the APC prop will probably work best (once you get the hole centered).

[Steve Helmick]

I think what Dave is referring to as "Top Flite Power Props" is what is actually called "Top Flite Power Point" props...the current issue stuff. I will agree that the Power Point props work better than most other wood props you'll find at the LHS, tho they probably don't look any better. I've never found any happiness with any Master Airscrew, but you might, if you recognize the fact that the pitch is not as advertised. Try 1" higher pitch than your APC...maybe 2". 

Some do like the "Pro Zingers", but the standard Zingers are strictly prop kits, meaning that you need to strip the finish, repitch, thin, airfoil and reshape. Most guys start with a (standard) Zinger 1"-2" larger diameter than their goal, which makes them pretty expensive for a piece of wood. If you want really good wood props, RSM and Xoar are the best...and Xoar makes RSM props...in China. But the RSM 10-6 (5.5) is generally considered to be about as good a prop as you'll find for the Fox .35.

I've found limited success with CF props, but I don't have the patience or skill for repitching them, near as I can figure. But I can recarve an APC and make it work, and I've had great results with Thunder Tiger Cyclone and Graupner GRP props...both brands are consistent and reliable. The APC 10-5 will work very well on your Fox .35/Banshee. Thunder Tiger has a 10-5.5 that might be quite good. See Tower Hobby.  Steve 

[Dave_Trible]

These are some of the better classic style props I've found.  Most have the common traits of wider blade with rounded or elipse shape.  Those super thin nylon Grish three blades are amazingly effective.  The wonderful Rev Up is next.  Depending on airplane,  sometimes a gentle rounding of the tips was good.  The most amazing to me are the O&R props.  Really bite.  The Airflo and Y&O are pretty similar.  Somehow I think we've forgotten the 'magic' of low energy aerodynamics that they figured out in the 40s and 50s.  The dark mahogany Flo-Torque is pre and post WWII vintage.  Looks a lot like that APC sitting next to it, doesn't it?  The white nylon in this case is Soviet block.  A yes, Power POINT is on the right.

[Dave_Trible]

....

[Dave_Trible]

Another nice modern prop is this Falcon made of German Beechwood.  It's so accurate I think it's CNC machined, perfectly finished and beautiful.  Unfortunately I think this 13-4 is the smallest size.

[Terry Caron]

Since I haven't a clue about rebuilding a prop (and have no interest in learning  ), from Steve's comment I guess std Zingers are just a shot in the dark as to whether one will do well out-of-the-box.
At least they were cheap - and looked nice.
Good for display at least. 

In light of his comments, while I sure don't want to incite a pissing contest, when it comes to QC (or maybe QA these days), are some brands better or worse about giving you what you think you're buying?

And how about Grish yellow props?
I have a few of them also.

Terry

[Bill Little]

Hi Terry,

Be leery of the old nylon props.  Even with boiling them, they can throw a blade just from deterioration.  They can be 'brand new" old stock and still come apart.  Lots of stories of this happening.

As far as quality, the most disappointed I have been is the Master Airscrew line.  They are made just fine, but the pitch is always much lower than advertised when placed on a Prather Pitch Gauge (what is generally used as a "standard").  With that in mind, you can buy the props with an idea of what you are getting.  An example is the MAS 11-7 3bld.  It pitches out to about 5" pitch, across the board.

If you are at the highest levels of competition than you will experiment with props on your model while trimming it.  For the average sport flyer it can be fun and educational to change props and see the differences.  It can actually make your model fly better and thus give more enjoyment.

Start with the "general" recommendations for your engine (ie; 10-6 for a Fox .35) and experiment with similar props from different makers and try different pitches such as a 10-5 from the same maker, etc..

Billy Werwage has a binder with tracings of his "best prop", with notes, for each one that ends up being the "contest" prop on each of his models.  It can become a very important factor.

BIG Bear

[Terry Caron]

Thanks Bill - that's a real eye-opener about the MAs.

I just looked and most of the props under 8" I've recently bought are Windsor, in a variety of sizes and series designations, some marked MA, others not.
I suppose the pitch caveat applies across the board to them?

I barely rate as a beginner flier, so I warmly thank all of you who have contributed thus far to my further education.

Terry

[Kim Doherty]

Hi all -

I may be wanting to oversimplify a complex subject, but sizes and materials aside, these props all have different shapes, and there may be others I don't have on hand.
What dis/advantages do the different shapes have?
When to choose one over another?

Thanks.

Terry

Terry,

I would further what Howard says and add this:

Does the prop clear the ground with the fuselage sitting level? If it does try that prop.

Did the engine start fairly quickly (under five minutes) ? If it did that is a good enough engine.

When the engine started was there a lot of air coming from the back side of the engine? If it was that is a good setting and good prop.

Did you get it into the air for more than a few laps? If you did, that was a good flight.


Do not try to over think this just because someone will attempt to provide you with an answer. Enjoy the experience!! The rest does not matter.

Kim.

[Terry Caron]

Thanks for your input Kim.

But rather than overthinking, I see my questions as avoiding reinventing the wheel.
Though I'm older than almost everyone who's responded, I've very little experience with c/l beyond going in circles, and almost all of that about 55 years ago.
I haven't gotten together with any local fliers yet and I see forums such as this as the best way ever invented to access information learned through no doubt thousands of years (just think about that) of accumulated experience.

I assure you I'll get something in the air as soon as I can. 
I don't even know of a flying site close by so, among other preparations, I'll need to clear a lot of trees and brush just to fly the Cox Texan again.
After I build a stooge (found the how-to on a forum).
So it may be a while

Terry

[mike londke]

Terry, I see you are from Mid TN. Close to Nashville? There are 7 of us who fly regularly.  Mike

[Terry Caron]

Mike - PM sent.

Thanks.

Terry

[Andrew Hathaway]

Old nylon props are dangerous.  The newest Grish Tornado prop is at least 8 years old.  They'd be the white and black variety.  The yellow and silver versions are even older (by decades), along with the white Top Flite props.  Most of the time these old props will snap in your hands if you give them a good flex.  Sometimes you can see the stress cracks in the nylon before they break, but not always.  The same applies to vintage Cox nylon props.  It's best to throw them in the nostalgia box, or use them for static display only, where they can't hurt someone.

Zinger and Master Airscrew props may not perform the best, but they're safe and consistent, fine for sport use.  Thunder Tiger props are dirt cheap and seem to work well.  APC props are probably the best commonly available prop.

Don't get hung up on the shape.  Buy a variety of props sized for the engine you're running and try them and see if one or another works better for you.  Unless you're looking for maximum performance and pushing the limits, you might never notice a difference between a Zinger, Master Airscrew, or APC.   

[Steve Helmick]

Even when they were newly released from TF, their nylon props were suspect. One of our guys (late 1950's) had a 10-6 nylon throw a blade, yank the engine off the nose of his Berkley "Grumman Guardian" Stunter and smash the McCoy .36 "Super Stunt" against the concrete (inside) wall of the WSC "Field House". He was unhappy! TF sent him a new prop, OBTW. I don't think he ever used another TF Nylon.

About 10-12 years ago, I saw a yellow Tornado nylon throw a blade, when the engine backfired while the owner was trying to start the McCoy .19RH. But maybe it's just a McCoy thing?  Steve

[Terry Caron]

Well I certainly feel justified in asking about props.
My flying in the last few decades has been scratch-built sport rubber FF, with very little danger involved, so I know Super Duper Zilch about power props.
I've only recently caught the c/l bug again and have no idea how or when I acquired the stack of old props I have.
While I've bought a handful new in the last few weeks, I have been bench running engines (including a couple old McCoys Steve!) with some of these oldies, and one of the TFs let go both blades just a few days ago on a Forster .29 (most of my stuff is older than dirt - received an O&R .23 FRV just today).
Ignorance is bliss (I was having fun) and, thankfully, no harm done.
But I'll definitely heed the wisdom imparted here and retire the nylons to display or something.
It's also good to know I haven't unwittingly thrown away money on useless props.

I again thank all who kindly took the time to reply - it's a real pleasure to "netsociate" with you.
With a huge THANKS! to Mike, I look forward to soon meeting some experienced local fliers who can show me the error of my ways.

regards,

Terry