cordell staker

If you have nice engines and want them to last don't use dinked up or broken props.
If you have nice planes and want them to last, don't risk them on a dinked up or broken prop.
If you have good flying friends, and don't want them to pack up or get hurt when you fly...be wise.
I was flying one day at Cherry Creek in Denver and just before my plane rotated I heard a little prop nick sound from a bump or rock on the runway. I got up just fine, but my ear told me something was wrong. My ego said "fly on Oh Great One". So I flew on. About three minutes later on a pass the damn thing let go. Scared me. Startled my buddies. Hurt my plane more than the cost of a new prop. I could have landed easily right after the takeoff. Learned a good lesson.

airraptor

My Feedback: (66)

And what kind of prop was it.

we fly APC props all the time here and APC isnt to far away. minor nicks in the tips are of once blended out. The military and airlines blend the blade on the Jet Engines all the time. If you would have seen some of the nicks these things get from rocks and birds would scare you but once they are blended they are just fine. Same thing for props The APC props with start to turn white or show white stress marks. If you see them then for sure replace it. If you Do Not have the experience to tell if the prop is good then just buy a new one like these other guys suggest.

HoundDog

My Feedback: (49)

I'm sure that the lawyers at APC or any prop manufacrure would have a field with this thread and You if any one got hurt by a modified or broken prop you used oon your plane ... don't believe the AMA insurance would stand such an obvious violation of the safty code.

JohnBuckner

My Feedback: (1)

OK since we are obviously not talking about metal props here (yes they are spelled out in the AMA saferty code) Just where specifically in the safety code is propellor shortening, planform profiling, or even repitching spelled out and an 'obvious violation?

JohnBuckner

My Feedback: (1)

For all who are interested in the process of shortening and blade profiling Here is a safe, simple and cheap way to do so. Of course all safety caviets already extensively covered in this thread should be heeded concerning previous prop damage expecially around the root areas which is common damage from spinners and of course always balance after any prop work.

A quarter inch drill (or whatever your shaft size is) is drilled into a board then unchucked leaving the drill in the board. Some white paper is taped to the board in the tip area. Next after the short blade is reshaped or profiled as well as sanded smoothly then it is placed on the drill and a sharp pencil is used to follow the outline carefully.

Then just rotate the prop to the marked area and cut/sand to match. It is actually quite accurate and of course you will then balance the prop in the conventional way through light sanding on the heavy blades back side which is called the blade face.

This when done properly is safe, enjoyable and most important educational. To this day propellor blanks are avalible for those who wish to do their own propellor experimentation. Actually making your own props from scratch is viable an educational experiance that many to this day still enjoy.

John

Will post the pics later this server is being grumpy.

CrashedTrainer

that sounds quite interesting JohnBuckner...

this post is turning out to be quite informative.. i think its all about gaining knowledge...hence the reason for asking the question in the first place..

its always easy to throw away that cheap prop... but learning the reason to do so or anything for that matter is what matters IMHO... because otherwise there is no difference between you and that guy who is there just to enjoy the show...

da Rock

John just mapped out a safe process that will certainly work for anyone who follows it.

A bunch of us have worked props over for a very long time, and done it safely. How long have we done it? Well, since it was common to see handcarved props in regular use. And that predates the pylon racing boys' dabbling at making their own.

Reprofiling is done by many of us for more reasons than fixing bitten props, btw. Anyone who has experience testing props with some degree of accuracy has probably wished for 'half sizes' and thought seriously about modifying as a means to that end. Make yourself a tool or two (like the drill-in-a-board John described) and you'll discover how easy it is to do accurate work. You'll also be able to turn out all the half-sizes you ever wanted. You'd be surprised what having a paddle blade 10-6 can do when your model/engine doesn't like 11"ers and turns all the 10-6s you can buy at the LHS too fast. Make that paddle blade 10-6 from an 11-6. Or from an 11-5. If you ever used a pitch gauge, you'll understand why I can write those two previous sentences and both be possible.

I've got a tool in the shop that fits my band saw. I made it using a dowel instead of a drill bit. I bet it looks very much like John's suggestion. I've used it to make a bunch of 'magic props' that did what I needed and that couldn't be bought anywhere. And trust me, it's worth doing.

ovationdave

My Feedback: (16)

In the original post, CrashedTrainer stated "These props are made up of black APC material... "

Someone else mentioned that this may not be an actual "APC" brand propeller, which I have only seen in the light grey color, but a master airscrew prop, which are black.

I only mention this because they are different materials, APC props (APC Long Fiber Composite Per the website) are much stiffer, and more brittle, than a Master Airscrew (Glass Filled Nylon) which are more flexible. I would be cautions with APC only because they ARE so stiff (therfore more brittle), and I think I would toss it. I would be more inclined to re-balance a Master airscrew since it is more flexible, and seemingly less prone to Stress cracks.

Maybe I am all wet, but thats how I see it.

Dave

thepamster

Cutting, shaping, and reforming a propeller in a controlled manner to customize a propeller is one thing.
I am an "experienced"  pilot, builder, mechanic, and my field of expertise is electronics, but I DO NOT need a degree in aerospace engineering to tell me whether a prop is bad or not.
If there is a chunk missing  it  is bad. Period. Though technically just my opinion due to the lack of a degree in aerowhatever and no access to an x-ray machine, I am not risking ANYTHING over a 2.00 propeller.

ovationdave

My Feedback: (16)

I wish all my props were only $2.00...........

hugger-4641

My Feedback: (6)

The pro and the con of coming to a forum like this and asking a question like the Op asked is the spectrum of answers you get. There are always a couple posters who think that everyone who asks such a question is a completely inept and clueless newbie, so they give them the textbook "safe" answer, even though they may or may not exactly follow their own advice.  Then there are those who have tons of knowledge and experience that enables them to safely manage taking more risks than the average person and are willing to share that knowledge with those who ask. Both ends of the spectrum are the right advice for the right person, and the wrong advice for the wrong person. 

Gray Beard

My Feedback: (-1)

I think most of us have repaired more then one prop at some point. Once in a while I still do it and toss the prop in my box for those days when I need one of a certain size and don't have one. Back when I was using the smaller engines, like under .60 I repaired quite a few without any problems. If this is just a trainer plane with a .46 I wouldn't bother, I would just buy a couple new props. If it is a trainer I use the Master Air Screw props, they are about bullet proof and perfect for trainers and new pilots. They handle the dreaded ground strike way better then any other make I have used. Groupner is another good one for new pilots that have the prop strikes once in a while. For the price of the small props why bother repairing them. I know how but I don't fool with them very often these days.

GREG DOE

Who remembers when the first nylon props were introduced in the 50's, and standard procedure was to boil them in water for a few minutes to relieve the stresses? I don't remember the manufacturer, but they were 1/2 A props, and they were 100% guaranteed. For $0.25 they would replace ANY damaged prop. I think
Top Flight was next to have a line of nylon props, which were white, or opaque ( about the color of uncooked fish). Then Grish made Tornado props which were dyed yellow, but still not fiber filled nylon. The first Cox nylon props were black. Later they made the gray nylon props, which I believe were the first fiber filled nylon props. Someone might correct me on that one?

Here's another neat story: At one time the FAI combat guys used a nylon prop that would stretch near the prop hub. This would load up the engine, and the RPM's would drop off, but they didn't separate.

Occassionally air bubbles will get in a prop hub. I guess I've seen it twice. The reason I saw it was because a prop blade separated. There may be many more props out there with air bubbles in them, but they haven't come apart. I've also seen brand new wood props shed a blade. I've never seen a Master Airscrew, or APC prop that had a tip strike, and was rebalanced, come apart. Certainley that doesn't mean it can't happen, so if it makes you feel better to toss a dammaged prop, by all means do so. Greg

tony0707

I use only APC props on my two cycle glo engines from 46 to 1.08 for top performance ( vertical )- mostly wood above that size
Always balance all props to prevent airframe and electronics damage from vibrations
The APC props do not splinter from my experience
Measure the both sides of the prop with a ruler and make them equalthen finish the tips as desired and rebalance the prop
If a tip gets damaged - remove the prop as soon as is possible to take to the air again
Do prop repair home
The prop will be smaller , so it will turn more RPMS on the same engine ( not always good ) or use it on a smaller engine in the future

It is possible to work with a given size prop to get your engine to run at the suggested peak RPM of the manufacturer
by changing the props size

If you run a 10/6 prop -( as stated in the early post ) you should go to an 11/5 prop to run at the same RPM and develop more vertical torque from the same engine
An 11/6 could be a tad more prop than desired - base that on the RPMS the engine turns on a tachometer
Torque is what pulls you through your maneuver
My rule is to run the largest prop with the least pitch I can on a given two cycle glo engine- after flying a lot for 23years
I do run 11/5 APCS on my 46-51 size engines for top performance
Try it you should like it

I am always propping airframes-for the very best vertical performance while keeping the engine running at it sweet place regarding engine RPMS and power output
This is usually done in the first 10 flights of a new plane

JohnBuckner

My Feedback: (1)

Finally got some pics up this evening after the My post #30 with the full description of the the very simple and safe method to shorten or reprofile propellor tips.

Propellor care and modification done the right way is a far better way to help our new folks than the to clam up and refuse information with a blanket dismissal. That certainly can cause safety problems for them when left hanging.

John

HighPlains

My Feedback: (1)

Ah props. The most complex object on the entire aircraft. I worked for a model prop manufacturer (Chris Machin of Rev-up) part time in college (must have made over 200,000 of them during my time there because you guys can't land), and knew Fred Burgdorf pretty well to during his early days at APC.

Rev-up's were first produced in 1949, so they developed with the hobby industry, and were almost all made from rock hard maple. Being a natural fiber, there was large variation in wood density and strength. The first thing you should do with any wood prop is to firmly grasp the hub and flex the blade at the tip. Good wood will allow flexing of 1/4 to 3/8" of the tip on a 10-12" prop with no cracking sound. Do both tips this way to test the prop's strength before using it or after a strike. If it breaks or makes a cracking sound, go ahead and break the prop in half so no one will fish it out of the trash. About the only other safety concern is the hub. Do not force a wood prop onto a tight fit on the crankshaft. This can fracture the hub and allow the blades to blow off. A correct fit is a hole that is 0.002-0.003" oversize. It takes a lot of steps to make a wood prop, but I like that they are very light weight and easier on engine bearings than plastics. They are also easier to modify in all aspects, and so you can mod and fly in very short order if you use thin CA to seal the wood. A couple applications using a paper towel and 600 paper will give a good finish.

By the 90's Fred and his brother Otto were developing the APC line. Both men were very smart, high tech savy, driven people. They wrote over 30,000 lines of code to control the CNC machining of the molds to make the props. While the physics and aerodynamics of a prop is quite complex, the hardest part of the design is the hub to blade interface. Production was vary simple when compared to making wood props however. Pretty much load the molds, fill the hopper, put empty bins at the mold machine's output, and turn off the lights on the way out for the day.

APC prop's color makes seeing distress areas pretty easy to see. I don't know how sensitive they are to notches if chunks are knocked out, but sharp corners tend to be stress concentrators for most materials. But we have all seen fliers get a tip strike on a touch and go and keep on flying with no advise effect. But it is a good idea to pay close attention to your prop and engine. For instance while plastic is fairly stable once mounted, wood can shrink or expand and may be loose on the engine if conditions have dried out for several months in areas that have high humidity seasons and low humidity seasons. Of course this assumes that you don't break many props, so just forget I mention it if a three point landing means the nosegear and two prop blades.

JohnBuckner

My Feedback: (1)

Thank you so much HP, I was hoping you would join in and share on this thread. I love hearing about Mr. Freds early history and whom I did have the good fortune to meet as well as had many wonderful conversations with during his later years. I will never forget the classic sight of that Cowboy hardhat out on the course towering above the other teams as he delt out dose's of humility but back in the pits freely passed out the latest and greatest 'magic' props.

To the newer fellows I though I would pass on these photos of a direct comparison of the same model and size of APC props with the one on the right being an example of a very dangerous prop. It is severely sun damaged and lost far to much moisture. This is of course extreme but gives a good idea of how the color and gloss will disappear as this happens making it easy to detect what is unsafe.

All forms of plastic props are subject to this sun damage/drying. The black masters do not show it as well unfortunately. Early pure nylon props as already mentioned in this thread even required boiling when new. I have whole cards of those over forty years old brand new and would never run them on an engine.

Which brings up the thought about the pure nylon bolts so many of us use use for wing bolts. On low wing airplanes I don,t normally bother but on high winger aircraft that use: one, two, three or four nylon bolts that hold the wing on and carry all flight loads I am in the habit that has been deeply ingrained of boiling those bolts new or old for about fifteen minutes. Sorry for the digression away from props

John

GREG DOE

This thread has been quiet for a couple of days, so I thought I'd throw in some more dangerous stuff to comtimplate.
In the 30's, 40's, and 50's there was a company called the American Junior Aircraft Company, or A.J. Aircraft Company for short. A lot of people who weren't around then know that it was Jim Walkers company, and it was responsible for many inovations, as well as inexpensive models that were afforadable. This included the Interseptor Folding Wing Glider that was used to train marksman during the Second World War.
In the 50's they had a 1/2 A controline model called a "Firebaby" which was actually an ARF. We just didn't call it one back then! You could buy just the airplane, or a combo that included an engine. Now we get to the safety issue. Included in the kit was a stamped aluminum propeller, which was revolutionary because if you bent in a crash, you could just straighten it out, and fly it again! That was a selling point. What will they think of next? P.S. Even back then I never flew with one of them, but only because the nylon 1/2 A props gave better performance, and oh did I mention they were fully guaranteed.
There is a web site about A.J. Aircraft Company, and Jim Walker, but you will have to Google it, because I have forgotten it. I can remember the stuff from 60 years ago, but not from yesterday! Greg

aspeed

I can remember taking a 6-3" yellow Tornado prop and grinding it on the pavement to shave it down to 5&1/4" dia.  and then trimming the burr off.  May that wasn't safe either?  I have thrown a few old plastic ones away that got grainy and soft.  Some snap off when you bend them back and forth.  I always check the old ones before I use them, and don't use them on stronger motors at all.  The glass reinforced ones are a different story.  I will carefully trim them a bit if needed.  Say you want a 10-6" with more blade area, you cut down and balance a 11-6" for example.  Of course, you have to use uncommon sense.

GREG DOE

I like that, uncommon sense! It's common today.