CrashedTrainer

Dear All!

As apparent from the topic of this post, can one use an APC prop that's been slightly bitten off from its tips due to a bumpy landing??

i use 10x6 or 11x6 prop size usually on my OS 46AX... I have a couple of props gathered over some time of flying now with their tips bitten off due to bumpy landings on my trainer plane(getting back to the hobby after a long break)... These props are made up of black APC material...

I have at times kept on flying on that same day using that same damaged prop and haven't had any issues such as extra vibrations or something...however i do change them afterwards thinking they might have an adverse effect over a longer period of use on my engine...

So I wanted to ask that if i balance these slightly damaged tips by filing the undamaged tip to balance the overall prop, can i continue to use these props?

Rodney

Depends on the degree of damage; if only slightly scuffed and you rebalance them, they should be okay. You want both, static balance and aerodynamic balance as you do not want one blade to be working harder than the other which can happen if there is a difference in blade area or pitch between the blades. An unbalance prop or one which has been damaged to the point it can shed a blade at high rpm can be very dangerous to anyone close to it.

daveopam

My Feedback: (9)

Some of the APC props get really thin at the tip. These are easy to break a tip off of. I have sanded both ends to match and rebalanced with no issues. At times making a better prop for that specific engine out of it.

A word of warning. The impact could have caused hidden stress cracks in the prop. It could come apart the next time you run it. If this was a hard impact THROW IT AWAY. If it broke off more than 3/8" THROW IT AWAY. Some will say throw it away no matter. There is some logic to that so sand them down at your own risk.

David

flyinwalenda

My Feedback: (5)

From the description it sounds like you have master airscrew props. As already stated if they are chipped you can clean-up and round off the damged end and then take the same amount off of the other end and then balance it. The composite  props can take a beating and also as stated if it took out a large chip,look over the prop carefully for other cracks as that can be very dangerous when it lets go on the engine.

da Rock

I've come back to edit this because the Greg Doe post a couple down from here is absolutely correct, and the original of this one gave bad advice as it was originally written.

I found that when repairing 'bitten off props' to keep them in service they were a lot more useful for me to do the following:

It's important to make sure you get a really good balance and the easiest way to do that is to insure that all blades are equal in length and the tip shapes are the same. THEN balance the sucker and that job will be easier, and the prop will be more apt to be useful after the repair with the models and engine sizes you're probably using. Most often, you want to make sure both blades produce the same amount of thrust AND they balance too.

Some of the best props for a specific plane/engine combination are ones that were shortened slightly to get enough rpm for the engine to hit it's stride.

As Greg says, one bladed props were used, and sometimes still are, in order to get that last bit of efficiency possible by using 'fewer prop tips'. They're used most often by speed flyers searching for extra mphs on very fast planes. However, since most of us are simply trying to save some money keeping as much blade area as possible is the order of the day. Few of us really have use for a prop that has half it's original blade area, and it really wouldn't be a smart move for most of us to try and balance a prop that has lost significant blade area. The same problem exists in that situation that causes up to warn everyone to carefully insure the remaining blade(s) have not been damaged. Shedding a blade is obviously a bad deal. Shedding a balance weight is just as bad a deal.

It was sloppy writing that caused me to say we needed to make the blades equal in area. We don't need to. But it has been the safest and easiest and most practical way for me over the years to keep a slightly bitten prop in useful service. It's been the advice I've given over the years to the average modeler who isn't very experienced.

Truth is, it's often bad advice for newer modelers to tell them to try and save bitten props unless YOU have personally inspected the prop to look for further damage. It's also bad to advise any new modeler to do anything that might require significant balance weight attachment if they're new to balancing props. Actually, it's not bad advice if you can spend the time to explain how to add that weight safely and get across all the different things that need be done. Truth is, almost all our advice should probably not be sound byte short but should include some classroom time and be followed by a quiz afterward.... Some things just need more time than we often give, and some advice loses the listener about halfway along.

kenh3497

Way back in the day when I was racing Quarter Midget planes we routinely cut and modified props. What ever you do to the damaged blade, do to the opposite blade also. Example... I would make one blade to the shape, length etc and then draw around it to make a tracing. I then would make the opposite blade match that tracing exactly. Then proceed to make the other changes match the first modified blade. After you do a couple you will find the process goes rather quickly. Of course a proper prop balancer is needed/required and I don't mean the kind you hold between your fingers

Ken

GREG DOE

Some more miss information in this post. There are several competition disciplines that use SINGLE BLADED PROPS. They must be balanced, but the blades DO NOT have to be identical: ie. equal in length or the tip shape the same. It's a myth that they have to produce the same amount of thrust. Years ago we raced two bladed props that were compression molded, continuous filament composit props. One blade was made of
glass filaments, and one blade was made from carbon fiber filaments. Guess what? We trimmed the glass blade 10% to 20% shorter than the lighter carbon blade. That was done to gain some of the benefits of a single bladed prop, which is more efficient than a multi bladed prop. The theory is that the trailing blade is encountering at least some wake turbulance behind the leading blade. During the '30's there was a small general aviation airplane flown all over the country on a single blade aeromatic prop, to promote the concept. There was no problem with the prop, or it's performance. The problem with the concept was the excessive side loads that were put on the crank shaft, and prop flange. Our modern model airplane engines are more than capable of handeling the side loads of single blade props, so without a doubt they can handle props where the blades are not exactly the same. Props still must be balanced. Try it. It works. Greg

CrashedTrainer

hmmm...thanks guys for the responses....especially the single bladed props info by Greg...that clears it out a lot...

so basically if the prop doesn't have any stress or impact damaged throughout its body and it is balanced by weight(by sanding off tips while staying in the safe operating limits of the engine) I shouldn't have any problems... right?

da Rock

Right

lopflyers

My Feedback: (12)

Wat??? A 10x6 , 11x6? Throw them away, they are very cheap. Don't risk a plane for a cheap prop.[:'(]

hugger-4641

My Feedback: (6)

I can say with no amount of pride that I have had many hard landings on pavement and damaged too many props to count. Master Air Screw props seem to be a little more resilient, but I generally prefer APC on my .46 sized glow engine planes. I have trimmed and balanced many damaged props and have yet to have one fly apart on a glow engine plane. I'm more concerned about plastic spinners flying apart than I am the prop. I've had several plastic spinners fly apart with no apparent damage prior.

CrashedTrainer

hugger4641... thats actually correct... just yesterday i had to go without the spinner because the spinner screws became free in their threads and were effective no more... thanks to the awesome 46AX which started in no more than two flips at maximum ... this another time the spinner broke off while i was spinning it with the starter motor...thankfully the engine didnt come to life during that attempt...

I was thinking to convert to a metal spinner... but my local hobby store guy said that that could do severe damage to the engine in case of a crash... your thoughts??

gsmarino2000

My Feedback: (2)

I would not worry about the difference in potential crash damage between a metal spinner and a plastic one. If you crash hard enough on concrete or asphault, your engine is probably toast regardless. I typically use plastic spinners (with metal back plates) on 40 - 50 size planes. Anything larger, I go with a metal spinner.

Greg

Rodney

While you can statically balance a one bladed prop, they are still harder on an engine/motor than a multibladed prop as they are not aerodynamically balanced; i.e. they tend to put a large strain on the prop shaft/bearings as it is trying to bend the shaft any time it is creating thrust. While this is not so damaging to low rpm props or rubber powered props, when you have a lot of power being used it can be very hard on the shaft and bearings. The Canadian government did a bit of research on single bladed props for aircraft during World War II and, while efficiency of the prop was improved with one blade, the other problems over road the advantages.

jefflangton

My Feedback: (23)

Wow! Really?? Just replace it

thepamster

A Master Airscrew prop is probably the only prop I would trust if chipped as they are very tough. I fly mostly APC props on glow engines and they can shatter if you just look at them wrong.
These props are just too cheap in price to risk possible injury. I always carry an extra prop with me and if one touches the ground it gets tossed.
Also I prefer spinner nuts instead of spinners on these smaller glow engines, easier to install and remove. I think they look cool.

GREG DOE

Rodney, What you say is very true, but full scale aircraft engines are built to a different standard. If a full scale engine has a prop strike, it's mandatory tear-down, even if the prop tips are only curled. Model airplane engines are routinely crashed without any damage. Also, the side forces on a full scale engine are much greater, than on our model engines. If full scale aircraft engines were built to withstand the same punishment that our model airplane engines are, they would be so heavy they couldn't get off the ground! Just imagine the difference in impact of a 5 pound airplane striking the ground at 100 mph. and a 2000 pound airplane striking the ground at the same speed.

The most important thing to take away from what Da Rock said in his most recent post (the long one) is that many of the questions posted here do not always have a simple answere. In fact sometimes the answere for a new-bee modeler is different from the answere for an experienced modeler.

Finally on the subject of spinners. They are a big help when using a starter, but the best reason for using a spinner is to protect your crankshaft. Spinners absorb a lot of energy in a crash, and often provide enough protection to prevent engine damage. Most aluminum spinners are of better quality than plastic spinners, but
lately plastic spinner quality seems to be improving. The wall thickness on aluminum spinners is less than on
plastic spinners, to keep the weight down, so I have to believe that crashing with an aluminum spinner is no more likely to damage an engine, than crashing with a plastic spinner. Personal experience reinforces that
opinion, as I've probably punched well over a 100 aluminum spinners into the ground with no serious engine
damage except in a few of the worst crashes. Greg

airraptor

My Feedback: (66)

All you guys saying throw away chiped props send them to me I know how you use them and balance them. Yor guys thoughts only apply to wood props where they can splinter. on of normal engines and sport props you can keep cutting/sanding them down to what ever size you want as long as they balance. if a 10x6 is now a 9x6 then use it on a smaller engine. I rework all of the APC props as there is usually 500-1,000 more rpm in these props with no change in length or pitch.....

hugger-4641

My Feedback: (6)

I do have a few planes that have nylon spinners with aluminum back plates and so far they have served well, but for the most part I have started changing out any plastic spinners on my planes to metal spinners. They actually help in a crash as some other posters have mentioned asside from making it easier to use an electric starter.

straitnickel

I would never fill or add to a prop.
I have sanded off gouges with no problems afterwards

DAMBUSTER

I seriously considered leaving this alone,but then thought that maybe new comers/learners would read the thread and become dangerous too.
This is a no brainer.....throw the things in the bin,no second thoughts,throw them !!!!
Explain how you could/would determine if they are damaged internally or stress fractured ? One way to find out is to run them at full revs in the pits and if a blade shears and injures some one...then it was damaged !!!
Please don't come fly with me,bravery is not my strong point.
Dambuster.

GREG DOE

And I know of people who won't fly in an airplane, because they crash. Safety is in the eyes of the beholder!

dirtyoldman00

My Feedback: (100)

PROPS ARE CHEAP EYES AREN'T TRASH THEM

airraptor

My Feedback: (66)

If you have enough experience then you know it its bad or not.

kochj

If it was a chip or a nick, and it was my only prop, then use it... untill you get a chance to order some more....

Chiping a prop due to a bumpy runway...and if it was APC... I wouldn't worry... wood props get more risky..

I have many chiped APC props for that size engine...and I always get new ones, becuase it just isn't worth the risk..

I would forever have regrets if I caused harm to myself or worse someone else... It would dam near kill me inside....
If I caused someone else to loose a eye because I tried to save a few bucks..

I would would say there is some very good info about props though..