wonwinglo
SMF Supporter
- Joined
- Apr 18, 2004
- Messages
- 6,754
- Points
- 113
- First Name
- Barry
The propeller is such an important item to our aircraft models but it is also one of the most abused,we throw them into our tool boxes as if they were a screwdriver ! but really they deserve much better care and attention,lets consider a few points-
Today we can go into any model shop and buy propellers off the shelf to almost any specification that we want,things have not always been that way and it is only within the past ten years that really efficent propellers have evolved,this is partly due to new materials becoming available and also new manufacturering techniques being found.
The most recent revolution has been the computer configured prop,to gain the most efficency every aspect from the root to the tip has to be considered,noise also emits from the prop to a far greater extent than first imagined,fine tipped props may be super efficent but they produce a lot of noise into the equation.
Four stroke engines and good old diesels require a much broader blade to work better at the lower revolution scale,in all cases the hub has to be adequate to support the blades so compromise number one has to be taken into account.
When you first buy a prop the first thing that should be done is to boil it for a few minutes in order to remove the built in moulding stresses,the best way to do this is to get hold of one of those old alloy saucepans and bash the edges making it more easy to accept the long prop,it looks a bit odd but it does the trick ! another problem in the mouldings can be air pockets which can be detected by holding the blades up to a strong light,if you find any of these then take thm back for a replacement straight away as they are not only un-acceptable but dangerous as well.
Once the stresses have been removed now it is time to balance the prop,if you do not have a commercial balancer then two razor blades stuck into a block of balsa together with an accurate shafting material will do the job,the best commercial ballancers have magnetic coned spacers where the prop is held and balanced.
To achieve a proper balance use clear varnish or similar on the light tip,be wary about excessive trimming of blades as further problems could occur,if the blade is so far out then it is scrap,or another case for its return for replacement.
Also make sure the blades are in track as well,only use a proper prop reamer to bore out the centre and work from either end of the hub itself.
Fixed wing modellers tend to get blase about propellers,when you operate helicopters and know the problems a small amount of out of tracking and blade indifference is then it makes you more aware of what is involved.
Whilst in service constantly check the propeller for any damage that could make it dangerous in operation,I have seen props shed their blades and stick into the ground,please do not take them for granted but give them the respect they deserve,you probably will get away with it for years then bang it happens,the motor will shake itself and the model to pieces within seconds.
Spare props are best stored in pop wrap to protect them until you need them.
Wooden props deserve special attention something that I will cover in a future tutorial.
Today we can go into any model shop and buy propellers off the shelf to almost any specification that we want,things have not always been that way and it is only within the past ten years that really efficent propellers have evolved,this is partly due to new materials becoming available and also new manufacturering techniques being found.
The most recent revolution has been the computer configured prop,to gain the most efficency every aspect from the root to the tip has to be considered,noise also emits from the prop to a far greater extent than first imagined,fine tipped props may be super efficent but they produce a lot of noise into the equation.
Four stroke engines and good old diesels require a much broader blade to work better at the lower revolution scale,in all cases the hub has to be adequate to support the blades so compromise number one has to be taken into account.
When you first buy a prop the first thing that should be done is to boil it for a few minutes in order to remove the built in moulding stresses,the best way to do this is to get hold of one of those old alloy saucepans and bash the edges making it more easy to accept the long prop,it looks a bit odd but it does the trick ! another problem in the mouldings can be air pockets which can be detected by holding the blades up to a strong light,if you find any of these then take thm back for a replacement straight away as they are not only un-acceptable but dangerous as well.
Once the stresses have been removed now it is time to balance the prop,if you do not have a commercial balancer then two razor blades stuck into a block of balsa together with an accurate shafting material will do the job,the best commercial ballancers have magnetic coned spacers where the prop is held and balanced.
To achieve a proper balance use clear varnish or similar on the light tip,be wary about excessive trimming of blades as further problems could occur,if the blade is so far out then it is scrap,or another case for its return for replacement.
Also make sure the blades are in track as well,only use a proper prop reamer to bore out the centre and work from either end of the hub itself.
Fixed wing modellers tend to get blase about propellers,when you operate helicopters and know the problems a small amount of out of tracking and blade indifference is then it makes you more aware of what is involved.
Whilst in service constantly check the propeller for any damage that could make it dangerous in operation,I have seen props shed their blades and stick into the ground,please do not take them for granted but give them the respect they deserve,you probably will get away with it for years then bang it happens,the motor will shake itself and the model to pieces within seconds.
Spare props are best stored in pop wrap to protect them until you need them.
Wooden props deserve special attention something that I will cover in a future tutorial.