Christmas 2013 Build - KK Eaglet

Carving a prop sounds skillful

Can yo buy props

The Beard wrote: Carving a prop sounds skillful

It's like all modelling tasks, it's easy when you know how. All you need is the confidence to do it, which is why it might be worth putting it in another thread.

There are suitable commercial props available. The plastic ones are too heavy and not very efficient. The balsa ones are OK and they cost between £10 and £20 for the size I would need, but I still prefer to carve my own.

It's a similar story on the wheels. The plastic ones are either too heavy or too fat. I've not seen commercial balsa streamlined wheels, probably because the market for them is too small.

How about a styrofoam cup cut the prop shape at an angle, and you will get pitch and twist, wont you?

I didn't realise that free flight was so involved,
it's kind of uplifting.

yes please Andy, would love to see how one is made and carved.
Tis beautiful, when i grow up i want to build like you!

Thanks for that,really getting interested in this side of the hobby.

alan cantwell wrote: How about a styrofoam cup cut the prop shape at an angle, and you will get pitch and twist, wont you?

Cutting one out of a styrofoam cup is a good method for getting a quick propeller made for an Indoor or lightweight model. Such a prop would not be strong enough in respect of coping with both rubber torque and crash damage in respect of the Eaglet. You do get a twist on the blade, but it's not truly helical and in any event, it would only 'work' over the whole blade at one particular overall pitch.

Current thinking is that for maximum efficiency, prop blades should have slight washout at the root and the tip in the same way that a wing would. The shape of the blade is also critical to reduce drag. I'll not be going to such lengths on the Eaglet, however. My intention is to use a reduced size prop form similar to that shown on the plan of the Eaglet's big brother, the 32" Competitor.

Andy Sephton wrote: Thanks OF. They originate in the Czech Republic and are supplied by Flighthook, who'll be at Old Warden if they are trading this year. The pins are quite expensive at around £2.50 a small box (there's four boxes of 'em in my pin container in the pics), but they are fine (they don't split thin balsa) and extremely sharp (they go in a long way before you realise it if you stab yourself, the pain can only be described as exquisite!)

Are these the insect pins on Flitehook's website. If so, which size?

Modelflyer99 wrote:

Andy Sephton wrote: Thanks OF. They originate in the Czech Republic and are supplied by Flighthook, who'll be at Old Warden if they are trading this year. The pins are quite expensive at around £2.50 a small box (there's four boxes of 'em in my pin container in the pics), but they are fine (they don't split thin balsa) and extremely sharp (they go in a long way before you realise it if you stab yourself, the pain can only be described as exquisite!)

Are these the insect pins on Flitehook's website. If so, which size?

Sadly Mf99, they are neither. The insect pins are longer and thinner than the pins I use. Also, they don't have the large plastic head, only a standard pin-head.

Superb build Mr Sephton, I salute you.
It was also a real trip down memory lane. That model is sooo elegant and flies beautifully.
I also noted the tools you use and your pinning down methods. The balsa knife is ident to mine and my father's and I still use them today. I suppose they are still available but it was Swann Morten or nothing when Dad was building. I see that you use methods in some cases the same, and some totally different. There is nothing new under the sun and it is interesting to see alternative methods.
Best wishes for your build but I feel that your model will be impeccable anyway.

Gary

Many thanks for the kind words Gary, much appreciated.

For info, the brass knives and blades can be obtained through:

SAMS Models - www.samsmodels.com/acatalog/shop.html

And: Flighthook - flitehook.net/

I last bought a pack of blades two years ago at the London Model Engineering Exhibition which, coincidently, is this weekend (17th to 19th Jan) - www.londonmodelengineering.co.uk/ (I also got a good deal there on an A1 cutting mat and several sets of diamond files of various sizes.....)

Managed to get back into the model room this afternoon. Did some serious sanding on the model but nothing that would show up in a picture. Hopefully there will be something to show (as well as tell!) in the next couple of days!

Some 10 months after the last post, I had some time to spare in the workshop and had another look at this one. The sanding was almost complete, so in between work on another model (the Avro 707), I fitted some gussets to strengthen some perceived weak points:



As soon as they were dry, the sanding was finished off, the airframe doped and covering commenced:



The current state looks thus:



to be continued:

I forgot to add a plate to support the front of the fin for the DT system, so that was added this morning. The mechanics of the DT system should come clear as the build progresses.:




Covering was then completed and that is currently drying.

I'd planned a day in the garage today and so with a bandsaw at my disposal, I felt it time to start on the prop. Here's some calcs I did earlier for the propeller blank which I'll cut from balsa block:




Carving a prop is one of those jobs that requires a bit of skill, but it's easy to learn if you know the principals. The first thing to do is draw the edges of the prop blank onto some block balsa and cut it out. Most kits and plans will provide drawings for the blank, so it's not normally necessary to make up your own. This is not the case with the Eaglet, however, which is normally supplied with a plastic prop.

The prop diameter on a 24" vintage model such as this one is limited to 8" by SAM 35 rules, so that sets the diameter. The pitch is a little more difficult as it should match the aircraft speed and the power provided by the motor, both of which are unknowns until I've flown the model. Rubber models normally have a pitch equal to between one and two times the prop diameter, so I've chosen a mid value of 12" pitch for the 8" prop.