re worked props

[Bootlegger]

  First of all Happy New Year everyone,
 I remember somewhere reading about "prop kits" from Zinger props.
 I am putting together a model w/S T 60.
 Plan to try Zinger 12x6 and APC 12x6b on it, but my question is what is being done to the Zingers to get a better prop ?
        Thanks, Gil AKA Bootlegger

[Bill Little]

Hi Gil,

Mostly sanding down the LE and TE of the blades and thinning them out a little.

Being pretty thick wood they lend themselves to reshaping and all pretty good!

I have done the "scimitar" thingy to a few of them, reshaped them to look like the Top Flite paddle blades, etc.

Hope you're doing fine now.

Bill <><

[Richard Oliver]

Hey Gil. I have been carving props for 30 years. Props are one of, if not the most,  valuable element in why you have a good flying plane and one that is a dog. If you have lift and you have power, and this is a big if, then you have to match up your power to the right gear(prop) to drive your plane through the maneuvers. There are lots of things that come into play here. First is RPM! You must run your motor in the right RPM range. The type of motor run plays a big part in this. After you get RPM where it belongs you have to have the plane at the right speed for you and your plane. They go together! If the plane is heavy it will have to fly faster. If speed is something you do not like then you are going to have to compromise or build lighter or have more lift, ie. more flaps or bigger wing. All of the elements are in play all of the time. They are never separate from one another. Speed is pitch, period. Remember that RPM thing that I spoke of? It is married to this pitch thing. If the RPM is right and the pitch is right you are on your way. Prop Diameter is thrust. This is what drives your plane through the maneuvers, or should I say pull. Your motor will tell you, based on it's power, if you can get what you want. If you need more pitch(speed) and your motor can not pull more pitch (power) then you have to loose some of the diameter. Here is the conundrum. If you add pitch and have to cut you diameter and you loose your drive then you do not have enough power. Sounds simple but it is very complicated, sorry to say. Power can be increased but we will save that for another question.
Here is some of the compromises you can make to try and get what you want. First bases is RPM but the prop can be altered to get what you want, within reason. You can thin the blade thickness out at the tip and this will lighten the load a little. This will increase the RPM which means you can add the pitch you needed. See how we are compromising? We are trading a small amount of the drive in the blade thickness while keeping the blade sweep area(diameter) and adding a little pitch to gain a little more speed. Now the other question on your mind, how do I get more pitch. This is the prop kit you referred to. You sand in more pitch on a wooded prop, always from the back side, and test from there. A little goes a long way here. A tenth to 1/2° of pitch is a good starting point at maybe the last inch of the blade. This is so much easier to do with a carbon prop by heating and twisting that it is my biggest reason for spending the extra money. It is not that difficult to do with wood props but if you do it wrong the prop is most likely ruined, for this application. Step 2 might be to also thin the blade, chord wise, to lighten the load a little more. This is a bit more difficult because you have to sand the airfoil back in. These are all compromises but you get the idea. It is a process of cutting and trying. Your are looking for balance for you plane and power. Blade thickness is load. Think of it as a thicker wing that you have to pull through the air. Thinning it will lesson that load. Moving the high point of the airfoil of the prop blade will also change the characteristics. Adding or subtracting a little Phillips entry will also do things to get you what you are looking for. Underchamber helps to load the engine and I use it in the first half of the blade to keep down the wind up of the motor with out loosing substantial RPM.

Just remember it is a balancing act and sometimes the prop, balanced, right out of the bag will work.
When I start on a quest for the right prop it takes many, many flights. I cut (or twist) fly, cut (twist) some more till I get it right. This is another reason I like carbon, I can do this at the field and if I break one I can make another one quickly. All wood is not created the same (mostly because of density and grain) and it is near impossible to get 2 Identically carved wood props to work the same. This is only the pitch side. We still have to fine the right diameter and blade shape. At certain RPM a larger diameter prop will have too much GP and will resist turning to the point that you have to make other concessions. Like bigger handles spacing and aft CG. This again will come down to personal likes and dislikes for how a plane flies. I like mine just stable enough to give me a flat pull out and bottom. Al Rabe likes his very nose heavy with a big handle. His theory is to have underwinged airplanes that he like how they look with large flaps that generate lots of lift. They need to be deployed to get this lift and a forward CG forces you to deploy more control surface to get the maneuver done.
RPM, GP, Power, lift, weight, line length, handle spacing and more all figure into why you carve a prop and in what shape and size. Fine tuning is where you might want a little less drive coming out of the corners, or more. You might have to much power in the up lines and the plane is rushing you. You plane might do everything you want till you get to the hour glass. You might need more corner, or less. All of these can be obtained with props and tweaking or carving.
I plan to write a 2-3 part article for Control Line World on this very subject.
Are you confused?
RO

[Jerry Bohn]

Rich, Very good explanation about what the props do, how and why and the results of modifying them.
I use both wood and APC's and have always wondered how the extra wieght of the APC's comes into play. Could you reply a word on that?

[Joe Messinger]

Hi Richard,

Thanks for your thoughts and directions for tuning props.  I appreciate your advice.

As with most things that are tuned to as near perfect as we can make them, knowledge, practice and patience are always a part of the process.

I wonder, in the broad spectrum of c/l fliers, how many go to these lengths to tune their props to perfection?  I can only speak for myself and perhaps a handful of the fellows I fly with, but the extent of tuning I do with my props is pretty limited.  On synthetic props like those made by APC, Master Airscrew,etc, I sand the flash off the leading and trailing edges and balance them. Wooden props just get balanced.

My question is: "How important do you think precise prop tuning is to an average flier?" Provided the prop being used is reasonably well suited to the particular plane/engine set up, would you say precision prop tuning is of significant benefit for someone (like myself) who is, perhaps, in the middle of the learning process?

Thanks again and Happy New Year,

Joe

[Richard Oliver]

Hi Jerry, Yes they are very different in sooo many ways. Primary is weight. This first translates into more GP(gyroscopic precession) from the APC (heavier plastic)and a heavier feel on the handle.  This means it is trying to resist the turn. The APC is stiffer than most plastics and is more stable in pitch but many brands are not and will change pitch under load. Some pitch up and other will flatten.  Wood props because of their light blades tend to recover the transition of 2-4-2 quicker. The motor spools up and down faster with a lighter load or less flywheel effect. If a prop flattens (de-pitches) in the corners it will tend to richen and slow a little. If it pitches up under load it will lean out and jump out of the corners. When doing a vertical you want one thing but in a pull out in the bottom you want something else. The APC is a more efficient prop and in my way of thinking this is not good. In stunt you want a prop to be a little less efficient so it will tend to change speed less. When flying the APC you will notice that it speeds up a lot down wind and slows more into the wind.  When the wind blows it winds up more. The design is such that the faster you go the more efficient it gets and speed increases. I like for the prop to begin to slip when it tries to wind up and losses some efficiency and maintains a more constant speed.
If you look at the shape of the blade on the APC you will notice that it appears that it has a lot more pitch than most props. This is because most wood and plastic props do not work outside the hub thickness. The pitch in these props is never wider than the thickness of the hub. APC knows as many of us who raced for years that a Clark y airfoil works best when it has at least .2 to 1.2° angle of attack to be efficient. Most props are running at a neg angle of attack near the hub. This is because they do not have the material to increase the pitch with out making the hub much thicker with the added cost of material. This angle of attack is figured based on unloaded RPM in flight. Bill Lee ran the numbers for me when he worked for Shell Oil (almost 25 years ago) on their, at the time 235.00 hour, computer and we found nearly all of our racing props at the time were negative pitch for the first 4 stations on a Prather pitch gauge. This can be helped with a little Phillips entry but not solved. I still think for stunt you want this lower efficiency type prop. Also for a given speed and RPM the pitch is a descending number all the way to the tip.
Sorry I rambled a little.
RO

[Richard Oliver]

Joe, It is HUGE. If you are fighting your plane and motor set up it only slows down your progress. If you are making concessions to your prop choice then you are not giving the judges their best look at your maneuvers. If competition is not your thing then it is about a pleasant flight or one that keeps you jumping instead of just leaning back on your heels and drawing pictures with you stunter.
I have watched people that fought their set up and struggled to get in a good flight and wonder if they really had the talent or not. I let one of my flying buddies fly one of my ARFs that I had spent a lot of time changing from RC 3D to CL. After the flight I figured out he had a lot more talent than we had seen from him before this flight. Part of it was the trim of the plane but a huge part of it was the power and the prop set-up. He commented after the flight that he did not know that flying the pattern could be that easy to do. I think I may have spoiled him.
It sounds like a lot of work and it can be but if you have friends that know some of this and will help it goes a long way. There are stock props that will work. I discovered one before going to VSC last year that I felt would really work well in the thin air in Tucson. The Tunder Tiger 11x4.5 Cyclon(sp) was great there on my 40! Here in thicker air it is a little agressive but plastic can be heated and de-pitched. I did a couple of these for some of the guys here and it worked great. We are at sea level and have everything from great air to the pits. This is another part of the equation and I will go into detail in the article for CLW.
RO

[Joe Messinger]

Thanks, Richard.  I'll look forward to reading your article in CLW.

Regards,

Joe

[Richard Oliver]

Hey Joe, sorry if I left the impression that anyone should wait for the article to ask questions or post their ideas or findings. Conversation is by far the best tool for learning a subject. Reading an article will leave holes and questions you can't ask the piece of paper in your hand. Some areas will need the article to cover in depth but some need questions and answers from dialogue.
RO

[Bob Reeves]

I think prop selection like trimming are black arts, being very difficult to explain/teach with just the written word. I applaud Richard for trying to help us understand an important part of the trimming process. Thank you Richard, looking forward to your article.

[phil c]

" I am putting together a model w/S T 60.
 Plan to try Zinger 12x6 and APC 12x6b on it, but my question is what is being done to the Zingers to get a better prop ?"

You kinda answered part of your own question Gil.  Try it first and see if it suits, stock.  Then try some modifications, if you can figure out what is not quite right.  You'll see that that is a key part of RO's posts.  Identifying a problem and selecting the correct fix are key things to learn.  Fly the plane.  See what the motor/prop/plane are doing.  Figure out what isn't quite right, and then determine if changing the prop is the appropriate fix.

As an example, I had an LA40 that had been running quite well in the fall of 2005.  This year it started out OK, but later in the summer, when we went flying in some really hot weather it seemed to lose some of its punch and started to run away towards the end of the tank.  In this case, a larger venturi, to get back the power lost from heat, and a clipping 1/4 in. off the tips to reduce the load worked wonders.  The motor was back in its sweet spot, 10,400 rpm at launch, with a much steadier, more even run through the tank.  On the plus side, the changes still work fine in 45 deg. weather now, over the winter.  Next summer I'll probably experiment with some higher nitro to see if I can keep the extra power and cooler running from the winter even in the summer heat.

[Richard Oliver]

Black Art is a very good way to describe it. There are days when I scratch my head and wonder if I am as stupid as I am feeling at the moment. When you are looking for the right flying characteristics it is a process of elimination and compromise. Compromises come from your equipment choices. If your motor is too small, plane too heavy( or light believe it or not), wrong fuel, venturi, compression, control throw geometry, and on and on. The one biggie if you have to live with all the others is the prop choice for what you have. I can almost always find a better prop for a given set up if I am willing to do the work and or find and get the props. Again this is why carbon is so valuable. It is repeatable! I like the wood props when they work as much or more than carbon but worry about chipping and breaking. Wood ages fast, compresses at the hub gets chipped from debris and soaks up fuel. They even dry out and wet up (if that is a term) based on climate. Interesting fact is that carbon props will also get out of balance from water absorption. We used to store them in bags with silica gel packs to keep them from getting out of balance. A small amount of out of balance will cause big problems in racing but in stunt it is not as serious, but needs your attention. It can foam your fuel in the tank, wear out the bearings and more. Just something to remember. It also makes it harder to set your needle. On the ground it is different than in the air where it will smooth up some. This means the needle changes and you chase it all day.
RO

[Jerry Bohn]

Rich, Great replies about props. These are the thing I wish  knew 10 years ago.
Thanks to you and the forum, I feel I'm back in school again and loving it.

Bill, I think Richard deserves kudos for his great replies on this subject. What is the method to give members get kudos?

[Al Rabe]

OK, but what I haven't seen so far is someone stating the obvious.  Unless you have a pitch Gage and prop balancer you can't begin to apply all of Richard's suggestions regarding how props work.

I heartily agree with Richard regarding the importance of having a good prop.  A good prop can possibly be the difference between your airplane being a competition ship or a Sunday flyer.  I am constantly surprised at how airplanes "come alive" when you happen to hit on that "magic" prop.

I seriously doubt that any of the NATs top 20 are running stock props "out of the box".  I suspect they all have pitch gages and prop balancers.  If you are really interested in getting the most from your airplane, first get the equipment you need.  Then you will be able to effectively use information published here.

Finally, a very good reworked wood prop can match the performance of a repitched and balanced carbon, but the carbon props are easier to get quickly into the "Ball park" of top performance.

The importance of good props can't be overstated.  I've collected a fair number in the last couple of years since returning to stunt.

If I were really desperate for a "magic' prop, even the workshop clock wouldn't be safe.

Al

[Randy Powell]

Richard's explanation is a very good one. When I have new plane, I take a whole box full of props to the field. Every prop, knowing that line length I'm going to start with and power, that could feasibly work. And I start to go through them one at a time. Each prop is of a different, hm, maybe catagory. Long and narrow with a thin airfoil. Sorter with wider blades and a fat airfoil, etc., etc. whatever. Once I get a prop that is at least in the ballpark, I come back with a bunch of props in that general catagory and start going through those. Once I fine one that is pretty close (or occasionally THE prop), I'll start to modify those to get that last little bit out. Sometimes it's a composite prop, sometime a wooden one. I try to come up with The best general prop for the plane. As time goes on, I try to develop certain props for certain conditions. I might end up with a general prop that works over a range of conditions and maybe one that works best in hot, dry and low wind conditions and perhaps another that works best in windy, cold or rainy conditions. Sometimes that's the same prop, other times it's three different ones. And of course, you are always experimenting. As Richard note, it's probably the single most important trimming tool you have.

Gil,

I've referred to the Zinger props as a "prop kit" because they are seldom in balance out of the box, they usually have a very thick airfoil and squared off leading and trailing edges and are generally very inefficient in their stock form. But a bit of clean up, thinning of the airfoil (espcecially toward the tips), sharpening of the trailing edge and rounding off of the leading edge and they can make a decent prop. With tweaks they can be very good props.

Zinger props are a great way for someome to learn what happens when you do this or that to a prop. They are pretty cheap and if you mess one up; oh well, throw it away and go to the next one. Try different things and see what you get. You will quickly learn what helps and what hurts. Just be careful not to damage the integrity of the wood by thinning the airfoil too much or by carving too deeply at the hub. You don't want the thing to fly apart when you start the engine.   

[Bill Little]

Thanks, Randy.  That's pretty much what I told Gil in the first reply to this thread.. 

Thanks, also, to Richard and Al for their comments on the importance of finding the correct prop. 

Having known Gil for 15 or so years, I know he is very cognizant of what a good prop can do to an airplane, but a lot of readers here have not experienced that, yet.

What I like is that a fairly comprehensive answer to the whole "perfect prop" question has grown out of "what do most people do to the Zingers". 

The experience of Richard and Mr. Rabe in their years of working with model airplanes, and engines, qualifies as great information!

Bill <><