HPA

I did some more work on the latest build today while waiting for the balsa to turn up, which it has now done, so this was an efficient use of time.

Today's task was to make the prop blank.  Here's a photo.
Prop blank.jpg

The wood is paulownia.  Since I had a block 300mm long to hand, I made the 400mm length by splicing 2 pieces 300mm x 38mm x 32mm together with about a 87mm long splice.  Then I remembered to wait for the glue to dry and to then drill the hole in the post drill before shaping the blank.  On my calculations this should give a 400mm pitch (i.e. P/D of 1.0).

Here's a start on the fuselage.  It's a bit different in that all sides are 0.8mm sheet and the "spacers" or "bulkheads" are glued to the sides first.

Here are a couple of pictures:
Fuse bulk holder 1.jpg
fuse bulk holder 2.jpg

To hold them down while the glue sets (I like using aliphatic) without putting holes in the spacers or the sides, I made some little plastic holders with the 3D printer which are held in place by pins and which just push down enough on the spacers to make a good contact with the balsa side.

Here's a photo of a couple of those little gizmos:
fuse bulk holder 3.jpg

Some more progress - wings and fins built and ready for sanding
Wings and fins.jpg

I attach a picture of the Mystery model's tailplane plan.  I can't work out what the plan means.  Is it:
1.    sheet on bottom with a little triangle of balsa on top?
2.    sheet on top with extra triangle on top?
3.    sheets on bottom and top and extra triangle on top?
4.    something else?


Mystery TP.jpg

5.   little triangle let into the top sheeting (change of grain direction)?

Sorry Jeremy, sat here for half an hour trying to make sense of it.  The plan definitely shows sheeting on the top and I think the extra piece is laid over the top, Is that the L.E. could it be to reinforce the L.E. Joint. ???

Is it held on by rubber bands? If so, it might be for strength.

Quote from: dputt7 on Aug 14, 2026, 06:12 PMThe plan definitely shows sheeting on the top and I think the extra piece is laid over the top...

Yup.

All I can think of is that it's to provide a 1/16" thick panel for not much extra tail weight to give a rigid/robust mounting point for the fin. Perhaps also allowing the fitting of the fin with the LE offset to port or starboard.

Thanks for the replies, chaps.

The tailplane is held on by rubber bands, according to the article.  But I'm not going to use bands but will use a wire and tube hinge to hold the TP on and for the DT.

I think that the first time I saw this was a picture in a 1950's AeroModeller showing a fitting made by Jim Fullarton - I couldn't find it in the excel index, but it's a bit like Dave Hipperson's hinge for Senator but the tail tips rather than the fuselage.

The sheeting can't be a fin thing - it has twin fins stuck on the TP tips!

Today I carved the prop for this model. 

Here are some of the tools I used - Sloyd carving knife, staight carving knife, razor saw and Liogier (French woodworking rasps).
Mystery Prop 4.jpg

The carving knives are from woodcarving times and are good and rigid in the blade and hold an edge much better than "hobby" knives. 

The French rasps are hand-stitched (the process of making the teeth is called stitching) and are much more effective than the machine stitched rasps that are usually available.  The main reason is that they are slightly out of perfect line and size so that they don't create tracks in the wood which is what happens when each tooth goes along the same line.  So the finish strangely is much better.
Mystery Prop 2.jpgMystery prop 3.jpg

I have two of them - a bigger and a finer each in tapered half-round shape.

The other tool that I find very useful when making the saw cuts is a carver's vice - the jaws swivel to hold the workpiece which makes it much easier to hold the prop still while sawing it.

Mystery Prop 1.jpg

The eagle-eyes will notice that the prop is balsa not paulownia.  When I was carving the paulownia blank shown earlier in this thread, I wasn't using my woodcarving knoves and  trying to hold it still using a "hobby" knife, I snapped that blank and did it so comprehensively that the prop couldn't even be rescued by gluing it back together.

Hmmm - the Carver's vice and the French rasps - never heard of these. I feel they ought to be in my toolkit. Thanks.

Stephen.

Jeremy,

Thanks for the propeller carving information. More details of the process would be appreciated.

Tim

That's interesting Jeremy - an insight into wood carving and associated tools. That vice does sound interesting.

Thanks and more info on your prop carving would be appreciated.

John

Thanks for all the very kind comments. I am by no means an expert at prop carving, but I have done it a few times and I find it easier every time I do it. The first couple of attempts were frankly pretty bad, but one learns quickly. If doing this the first time, buy enough material to make three or four props. It is almost certain that you will have to throw away the first and one or other of them will be broken as you go along.

My approach is based upon my reading of, mainly, the following:

• R. H Warring, Airscrews (in the Plan Gallery);
• R. G. Moulton, Modern Aeromodelling;
• R Coleman: Airscrews en masse (Aeromodeller 1973); and
• Andy Sefton's article in April 2026 Aeromodeller (number 1067).

I don't exactly follow any one of these. There is no single "right" way to do this. What matters is not how you do it, but getting a good propeller out of the process.

I won't go into prop design or layout of the prop blank.  For that, go to the material above and the articles by John O'Donnell in early relaunched Aeromodellers (2014 - 16).

Also, the block specifications and blank layout are often set out on the plan or in the instructions/article accompanying the plan.

So assuming you have the dimensions for your blank,

• mark the dimensions onto your block,
• glue the ply reinforcement plate on the front centre of the blank,
• drill the hole for the prop shaft (it's much easier to get it plumb when you do it at this stage!)
• mark the blank to show the areas that need to be sawn away before starting to shape the blades
• cut those areas away with a tenon saw or bandsaw if you have one
• mark the blank now on the bottom and the front of both blades - to work out the front, I find it easier to put the blank down on the bench with the ply plate up and treat the further vertical side for the right hand blade as the front and then rotate the blank 180° so the left blade is now the right blade and mark the further vertical side for that blade as front as well.  So the bottom near corner of the blank is the trailing edge of the blade and the top further corner is the leading edge. 
• the next stages are to carve away the back of each blade so that at each radius of the prop, you have a right triangle with a straight line between the leading edge and trailing edge as the hypotenuse and the top and near sides as the "square" sides).Do each stage to one blade and then the other and then move on to the next stage   The first stage is to make saw cuts with a razor saw through the back triangle starting with the right angle and cutting down to the hypotenuse line at radius points along the blade - I tend to space the radius points between 8 and 10mm - the idea is to in effect mark the hypotenuse at each radius point. 
• The second stage is to carve the sawn material away using your knife - I always find I need at least two knives per blade and sharpen them, before starting and whenever the blade feels harder to sweep through the wood.  The saw cuts make the job easier because they make it easier for chips to separate from the blank, they make it simpler  to stop the blade following the grain into areas that you want to preserve, and, if you have made them nice and straight (i.e have marked the hypotenuse accurately) they show you when you are getting close to the correct depth and make it easier to see if you are creating a straight line from LE to TE or putting a convex curve on it.
• When I think I'm about 1.5mm from the hypotenuse I stop carving and use the larger and then finer rasp and then a slot sander to finish the back down to the blank corners.

Next step is to mark the thickness down to that to which you wish to carve the front of each blade. I create guidelines by making by drawing a line on the leading edge and trailing edge 4mm back from the leading edge and 4mm up from the trailing edge. That should create a blade which is about 3.5mm thick when you carve down to those lines.

I repeat the process that I used for the back -  saw cuts across the blade to connect the guidelines, carve by knife close to the guidelines trying to keep the surface flat and to avoid  convexity, and finishing up with the rasps and the slot sander.

Having done that to both blades, draw on your preferred blade shape. I must admit to trying to use more of a Larrabee blade shape (the very useful article by John O'Donnell from AMI is now available in the Plans Gallery, I notice) rather than the more traditional "paddle" blade that is often shown on the plan. I maintain that it is as authentic as any other blade shape since "dagger blade" propellers were used in the "golden age" and everyone was experimenting with everything at that time, so some of the blades used then are likely to have been very close to the Larrabee shape.

Once you have the blade shape as close as you can get it to your desired shape, it is time to shape in the desired airfoil. I tend to use something close to the ARAD 6  airfoil that I have mentioned before (there is an article on this in the Plans Gallery with the theory and also the coordinates). One reason for this is that I have created a set of 3D printed plastic templates for upper and lower surfaces of various chords and changing airfoil would require a new set of templates. For that shaping I only use the fine rasp and sandpaper.

Some final hints:

• always carve away from yourself ;
• if you are not using a vice to hold the blank while carving, remember to hold the blank not to push it into the bench - pushing hard tends to lead to blank breakage; and
• the moment the blade of your carving knife feels at all blunt, take it to your sharpening station and put a new edge on it -carving balsa or paulownia is much easier if you are using a sharp tool; it is also much safer since you don't need to apply so much force to make the blade move through the wood.

phew!  That took longer than carving a prop!

BTW
The vice (which I now see is called a pattern maker/luthiers vice) is available in Australia at Carbatec  (https://www.carbatec.com.au/products/pattern-vise)and Timbecon (http://above-bench-luthier-vise-145mm-capacity?utm_source=google&utm_medium=organic&utm_campaign=Timbecon+Primary+Feed&utm_content=Torquata+Patternmaker%27s+Vice+Above+Bench+Luthier+Vise+145mm+Capacity&gad_source=1&gad_campaignid=21372031412&gbraid=). Lie-Nielsen (https://lienielsen.com.au/shaping-tool/rasp/) in Adelaide have Auriou hand stitched rasps which are equivalent to the Liogier rasps I have.

I must say, the prices have gone up quite a bit in the decade since I got mine!

As for Sloyd knives, these can be obtained on FleaBay pretty easily for a pretty reasonable amount.

I imagine that in the UK, Axminster, and in the US, Lee Valley, would be likely places to look for these kinds of tools.

Thanks for the detailed explanation Jeremy. I consider carving props to be a nessesary skill to possess to be able to consider onself a well rounded aeromodeller.

Quote from: Piecost. . .carving props to be a nessesary skill to possess to be able to consider onself a well rounded aeromodeller.

Blimey, that's me out, then.

Thanks for the artisan tool info Jeremy - yes, writing these things up does eat into overall modelling time available, but I think people appreciate the effort, by and large - and it's what keeps forums like this alive and relevant and entertaining.

Stephen.

I completely agree Prosper. I have not yet been able to carve a wooden propeller. It is on my to-do list, in which case; this information will proove invaluable.

Thanks for that Jeremy. I have carved one balsa prop, but haven't used it yet! my approach was similar - basically razor saw and knife.

Good luck with your Mystery Model.

John

Quote from: OZPAF on Aug 28, 2026, 03:40 AMThanks for that Jeremy. I have carved one balsa prop, but haven't used it yet! my approach was similar - basically razor saw and knife.

Good luck with your Mystery Model.

John

Thanks John.
Prop carving is one of those things that is shrouded with unnecessary mystery and is not as hard as some think.  It is a skill that is acquired by doing and made better by doing it again

Another reference, by David Dodge:
The Idiot's Guide to Prop Carving v2.02
https://gryffinaero.com/models/ffpages/tips/propcarve.html (https://gryffinaero.com/models/ffpages/tips/propcarve.html)
I don't recall if I actually used it, but it's memorable for the quote from dannysoar at the beginning. "It is a source of national shame
that a single citizen should have to go
to bed unable to carve a propeller."

Prop carving isn't that hard, especially if you relax your standards. ;-) I've made several, including a right and left pair for a twin pusher. However, they are not Larrabee style, or paddle style. More like wider versions of the Wright Brothers' props from 1903. That is, too wide at the tips. I wanted to quit while I was ahead, and they worked fine. 1:30 on an all-sheet model is probably good enough, anyway. I've made a tiny prop for an indoor rc plane and a small one for a Parlor Fly, too. They all worked ok.

I want Paulownia! Not so much for props as for building a really light boat that I can carry around. Just the thing for flying rubber models off water.  Paulownia is hard to find in the USA. Illegal to grow in this state because they're invasive. Three or four years to get a lifetime supply. I wonder if it's ever used for pallets.

Lincoln

Not sure of your state  - the details just say USA.  Paulownia is used by wooden surfboard makers, so if there are any of them near where you live, they may have it.

It is also used in Australia by wooden boat builders, so that's another trail to follow.  It is very good for a light timber.

There aren't very many surfboard builders in Massachusetts! I haven't heard of any boat builders using it, but that's an idea. Down south, there are vendors with pre-primed, finger jointed siding imported from China. Allegedly, it's made from Paulownia. I think boat people usually use cedar for light wood, but that's much denser. On eBay, though, it's cheap enough for model airplanes.

Covering almost complete:

All parts except port wing & vert stab/fin fully doped with banana oil over to remove the nitrate dope blush (which is why the port wing looks lighter than the starboard one).
MM covering.jpg

Any guesses as to what model it is?

Okay chaps.

Here she is roughly assembled.  Any guesses?

Yes there are still things to do, such as:

• freewheel clutch and thrust washer for prop
• bend front rubber hook
• fit rotary damper DT

and probably several other things I can't think of yet.  But at least you can see what she looks like.

PS  I've never seen one in the wild before....

Very neat!

Goo9d news - trimming glides in the backyard were  successful.

What is the model?  Here's the answer:
1938 05 MODEL AEROPLANE CONSTRUCTOR Thumbnail.jpg

The magazine (including the plan) are available in the Plans Gallery.

Good luck with the trimming.
John

Zaic's designs always have a certain design flair to my eyes.

John