Wooden Watts prop: Identical on Spitfire and Hurricane?

[Doc72]

I just realized that I have two 1/72 Airfix Hurrys with fabric wings, but none of the two kits include the wooden 2-blade prop I want to use. However, I have the prop from Airfix's early Spitfire. Now the question ist: Are the props identical? I know the spinner on the Hurricane wooden prop is more pointed than the one fitted to the earliest Spitfires, but otherwise the props itself should be identical, shouldn't they?

 

Thanks in advance!

Ole

[Sturmovik]

@Troy Smith is your man for this question.

[gingerbob]

I don't believe that they are, in terms of original items.  At the very least, the pitch would probably be different to suit the top speed of the two types.  There might also be a difference in diameter, but I'm just thinking out loud.

[Fifer54]

The real question here is whether anyone would be able to call you out for the wrong Watts Airscrew in 1/72 if you didn't tell them!

Just say it's "from the spares box"!

Of course, you've already given it away, and now every Britmodeller and his dog will call you out on it . . .

[Troy Smith]

1 hour ago, Doc72 said:

Now the question ist: Are the props identical? I know the spinner on the Hurricane wooden prop is more pointed than the one fitted to the earliest Spitfires, but otherwise the props itself should be identical, shouldn't they?

 

No.

the Hurricane has a smaller nose ring than a Spitfire, which is why the 'classic. BoB Hurricane Spinner,  which is a Spitfire Rotol unit, is too big for the nose ring.as seen here

 

If you put a Spitfire Watts on a Hurricane,  the same thing should happen, and it will be noticeable.  

note in the case of the Hurricane Watts prop, it look slightly too small for the nose ring

 

see here for more details

compare

 

[Doc72]

Ok, thanks for the quick response. I have already started to reshape the spinner. I noticed that the diameter at the base ist bigger for the Spit and I might be able to reshape this, too. If the final shape doesn't satisfy me, I can still get me an Airfix Hurricane on Ebay that includes the 2-blade prop.

But what about the diameter and shape of the prop itself? Both planes should be very close in terms of speed and engine power.

[Troy Smith]

27 minutes ago, Doc72 said:

I have already started to reshape the spinner. I noticed that the diameter at the base ist bigger for the Spit and I might be able to reshape this, too. If the final shape doesn't satisfy me,

I'd suggest trying to add the Spitfire Watts blades to a cut down Hurricane DH spinner in the kit , it's a bit too long and pointy for what it supposed to be., but might work.

I'd aim to sand the back down,  till it looks like the photos, and add the blades, but.. sort of thing that can be tricky to get a good result.

Quote

 

I can still get me an Airfix Hurricane on Ebay that includes the 2-blade prop.

Or ask about for spares. We have a wanted section.     I'd suggest it would be easier to get the kit. 

Note Sword also did/do a fabric wing Hurricane and that has a two blade prop in all the boxings.

Again, if you don't ask....

Quote

But what about the diameter and shape of the prop itself? Both planes should be very close in terms of speed and engine power.

Don't know, never seen any data.   They look pretty similar and I'd be surprised if they were very different. 

[Seahawk]

1 hour ago, Doc72 said:

But what about the diameter and shape of the prop itself? Both planes should be very close in terms of speed and engine power.

In the old Aerodata International series there are 1/72 drawings by Alf Granger of the Spitfire and Hurricane, both featuring the early Watts propellers.  The Hurricane's is described as 11' 0.25" and I measure the diameter in 1/72 as 47mm.  No diameter is given for the Spitfire's but it measures 46mm.  The Hurricane prop has a markedly more pointed spinner.  BTW given diameters for other Hurricane props are: De Havilland 11' 0" and Rotol 10' 10".

[Selwyn]

The Spitfire and Hurricane were not fitted with a "Watts Propeller."  Its named after , Dr H C Watts M.B.E., D.Sc., M.Inst. C.E., F.R.Ae.S. who I understand worked at the RAE and came up with  design parameters for  fixed pitch props. He was never involved in the manufacture of  propellers or was employed by a company that did.

 

The early spit prototype was fitted with a prop described as the "weybridge." I believe that the first production  spitfires were fitted with an aeroproducts two bladed propeller  using the  Watts perameters, possibly the Hurricane was fitted with a prop by the same manufacturer,   it may  be the same,  but the watts system  allowed the prop to be manufactured to match the engine / airframe so it possibly was  a different item.

 

Selwyn.

[dogsbody]

You could ask if anyone who bought this kit, but didn't use the Watts prop, if they might let you have it. This kit comes with both two and 3 blade props.

 

 

 

 

Chris

[gingerbob]

Quoting a comment on a FlyPast thread: (with slight edit for clarity)

 

Quote

Hurricane diameter is... 11.25 (11'3").

Production Spitfire props were 10.67 [or 10' 8"] and had a distinctive cut out on the trailing edge near the hub.

 

[72modeler]

PJ Productions does  a resin Hurricane 2-blade prop/spinner in both 1/72 and 1/48. The big H at Lowestoft has them in stock, if you are interested.

Mike

[Doc72]

16 hours ago, gingerbob said:

Quoting a comment on a FlyPast thread: (with slight edit for clarity)

 

 

Good point! I didn't notice the cut on the trailing edge so far.

[303sqn]

The so called “Watts Propeller” takes its name from the the designer, Dr H C Watts M.B.E., D.Sc., M.Inst. C.E., F.R.Ae.S. He never manufactured propellers or owned a company that did but he was involved in the manufacture.

 

After obtaining his degree from Bristol University, from 1911-14, he worked as a Technical Assistant for the Bristol Aeroplane Company. From 1914 until 1919 he was in charge of design and supply of aircraft propellers at the Air Ministry. From 1919 until 1925 a director of Ogilvie and Partners, consultant Aeronautical Engineers. From 1928 until 1932 he worked as an independent consulting engineer. In 1932 he joined the Airscrew Company, Weybridge, Surrey, as technical director. The Airscrew Company manufactured the two blade propellers for the early Hurricanes and Spitfires. So they can be called Watts or Weybridge.

 

He was the author of The Design of Screw Propellers: With Special Reference to Their Adaptation for Aircraft

 

[Junchan]

The early Hurricanes and Spitfires used the different two-blade props.

On page 141 of "The Hawker Hurricane", Francis K. Mason wrote the prop of the early Mk. I as "Propeller: WattS two-blade right-hand wooden Type Z38. Diameter 11 ft. 3 in. Weight, 79 lb.

While, Alfred Price wrote on page 81 of "The Spitfire Story" that the first production Mk. I, K9787 used the Airscrew Company two-bladed fixed pitch wooden, 10 ft 8 ins diameter.

 

Hope this will help.

 

Jun in Tokyo

https://www.flickr.com/photos/horaburo/albums

[Work In Progress]

I realise nobody else knows or cares but they are both approximately 22 feet pitch. Which is a REMARKABLY high pitch to diameter ratio for a fixed pitch prop, and the main reason why the two-position VP props, and then constant-speed props, made such a remarkable difference to the take-off and initial climb. . We rarely get over 1:1 "square" P:D ratios in full size light aviation, same with or i.c. or electric models, and even low-revving rubber power is rarely more than about 1.5:1 P;D ratio

 

Why so coarse? Partly because of the high top speeds but partlicularly because of high top speeds being realised at, for the time, very high altitudes. As the air gets thinner a finer pitch prop would have unloaded too much and would have over-revved the engine at full throttle, even though the pwoer available has also reduced. I didn't realise how considerable this effect was until one day in an ill-spent youth when I dragged a fixed-pitch PA-28 up to 12,000 feet over East Anglia. As the climb rate sagged below 100 FPM I leveled it, and at 80 knots IAS, and full throttle, properly leaned for height, it was at the 2700 rpm red line for the engine (conservative though that is).   At 1000 feet, 80 KIAS in the full power climb only took about 2300 rpm

[JosephLalor]

Thanks for that, Work In Progress.  Quick question, hopefully quick answer then back to the topic of the thread.  Is a propeller at coarse or fine pitch when feathered?

[Junchan]

29 minutes ago, JosephLalor said:

Thanks for that, Work In Progress.  Quick question, hopefully quick answer then back to the topic of the thread.  Is a propeller at coarse or fine pitch when feathered?

See this.

Jun in Tokyo

https://www.flickr.com/photos/horaburo/albums

[Work In Progress]

If people don't mind a digression from Spitfires and Hurricanes --

 

Correct: feathered is a VP blade moved in the direction of coarser pitch all the way to where it ceases to be a prop at all, blades lined up with the front to rear flow of air past the engine to minimise drag on a dead engine.

 

If you go the other way, and make the pitch finer and finer, past the normal fine-pitch stops and back towards to the point where the powered rotating prop provides no thrust forwards or backwards, that's normally a trick only available on turboprops and its called "beta range". It's useful when you're taxiing on a turboprop because the engines run at basically constant speed so the normal fine pitch stop gives you a lot more thrust than you want for meandering around the airfield at a walking pace.  On some types you are also allowed to select beta in the air, and then you can use the drag to create truly heroic rates of descent in steep but safely speed-limited approaches to airfields with high obstacles around them (like London City airport). Further back from beta gets you actual reverse thrust which is mainly for getting off the stand without having to wait for a tractor, or for three-point turns on narrow runways (but be careful because you can't see where you;re going, so ideally have a crewman in the back with the ramp down talking to you on intercom, or relay on a competent marshaller).

 

On a piston-engined type you don't need beta range for taxiing speed control as you just throttle back to a low RPM idle once you're moving.

Edited March 6, 2019 by Work In Progress

[dogsbody]

Feathering also stops rotation of the engine during flight. Before feathering became available, many a damaged engine tore itself from the mounts or caught fire from overheated bearings.

 

 

 

Chris

[Work In Progress]

Very true, mainly in cases where the engine failure was associated with all the oil having fallen out (broken pipe, bullet hole through the oil tank, lower cylinder blown off, and so on) with the result that rotation continues with no lubrication

 

One of the paradoxes of fixed pitch props is that, in flight, if they are rotating it is surprisingly difficult to stop them, and if they are stationary it is surprisingly difficult to start them moving.

 

On yer average fixed pitch single you can switch it off at a safe height and will generally have to get right back into the stall buffet to stop the prop. Conversely when it stops on its own (when stall-turning a Tiger Moth in my case) then you might well need a near vertical dive to almost Vne followed by a sharp pull up to make it turn over again (no self-starter on most Tigers).  A feathering prop helps air starts as well as stopping the prop in flight , As the blades just start to come out of feather they turn the engine very slowly, but they turn it with a lot of force - and as soon as you get over one compression, the others usually follow.

[ClaudioN]

On 3/5/2019 at 4:13 PM, Work In Progress said:

I realise nobody else knows or cares but they are both approximately 22 feet pitch.

I may be wrong, but I'd expect pitch to be given in degrees (i.e., angle)?

Sorry, my fault. Pitch is actually feet , though the relationship to the propeller blade angle is still obscure to me. 

Thanks for the very interesting discussion, I knew very little about effects of pitch variation.

Edited March 6, 2019 by ClaudioN

[Work In Progress]

The angle varies all the way along the blade. If you want to convert easily between blade angle at a given distance out from the hub, and the pitch that represents, there's a neat little Excel spreadsheet for it here

https://www.lightaircraftassociation.co.uk/2010/Engineering/Design/Calculators/Prop blade pitch angle converter.xls