DH Hornet and counter rotating props

[kitnut617]

Originally, these props turn the same as the XP-82's did (the port engine being a Merlin 131), that is they turned outwards from the top. Then after quite a few test flights in this configuration trying to solve numerous problems, (one being severe buffeting of the tail-plane which no matter what they did, wasn't cured), they swapped the engines over. Most problems went away after this was done and all Hornets then had the props turning from the top towards the fuselage.

Interesting.  

I wonder if the problems were for the same reason as the XP-82's, i.e. the inner wing sections stalling, but perhaps on only one side?

There wasn't a problem like that Kit, reading 'The Hornet File' it flew very well from the start. Buffeting around the tail was the main problem, another was during gun firing trials, the empties were being drawn up towards the fuselage underside causing damage.  They spent a lot of time reshaping the engine nacelles, especially towards the rear end of them to get the air flow to not cause the buffeting, swapping the engines over remedied the whole thing.

The Hornet was specifically designed around the Merlin 130/131. Sticking Griffons (bigger and heavier) on would have upset the balance of the entire design. And it didn't need Griffons because it was blazingly fast and powerful with the Merlins.

That is correct, the Hornet was specifically designed around the 'cleaned up' Merlin 130's, the Merlin 131 came later, as I said in the other post, there was a requirement to go to contra-rotating props so I think the design did take this into consideration, weight wise. I'm going to build one of my Hornets with a pair of Shackleton props on it.

IMHO, if De Havilland decided to put Griffons on it, they would have built a bigger aircraft to size it so that the Griffon would fit into the nacelle shape they developed.  I'm using the Mosquito development as an example here, when they designed the DH.101 to take Napier Sabres, they scaled the whole aircraft up (1.2 times to be exact) so that the engine would fit inside the Mosquito shaped nacelle, but when they were told they wouldn't be getting the Sabres and to use Griffon instead, De Havilland just scaled the DH.101 down so the engines would fit into the nacelles. This produced the DH.102 which wasn't a DH.98 with Griffons, it was a scaled down DH.101 but still bigger than a Mosquito.  Just out of interest, the DH.101, DH.102 and DH.103 (Hornet), all would have had single side leg undercarriage.  Of the drawings I have seen, the only thing common with all three designs, was that they all had a Mosquito canopy (the bomber version)

Incidently, the DH.101 was to have contra-props, with the propellers being Tempest diameter.  Another aside, the so called 'Jet Mosquito' was really a development of the DH.102, so was also bigger than a Mosquito.

[wuzak]

Incidentally, the XP-82, P-82B,C,D had Packard license built Merlin 130/131's (BTW, the P-51H had a Packard license built Merlin 130) the only difference apart from American nuts & bolts, was the Merlin 130/131 had down-draft carburetors, and the Packard equivalent had up-draft ones (like all previous Merlins)

Packard built Merlins had British standard nuts and bolts - Whitworth and BA. The bulk of the Merlins built by Packard went to the RAF, so needed common fasteners, and it made little sense to change the fasteners for V-1650s.

There were differences, however. The two stage versions used an epicyclic gear drive for the supercharger, instead of the Farman type used by Rolls-Royce, and Packards used the American Bendix injection carburettor in place of a British type.

V-1650s used an SAE (American) standard spline for the prop shaft, while Merlins for the British used Society of British Aircraft Manufacturers (SBAC) splines.

[wuzak]

In his book and in other places I have read about the terrible takeoff tendencies of the Mosquito; it did not have counter rotating props and could be a real handful.  This begs the question; Why did the RAF not insist on counter rotating props on the Mossie; it could not have cost that much, and would have saved many aircraft from being written off

I haven't seen this before.

But the handling in the air and landing would be, I think, far more important. On that score the Mosquito handled very well, even when flying with one dead engine.

In fact, Geoffrey de Havilland Jnr would often perform aerobatics with one engine shut down during demonstrations of the Mosquito.

Counter rotating props could be done in one of two ways:

• By adding an idler in the reduction gear (for inlines with spur reduction gear)
  
• Reverse the rotation of the entire engine
  

The former is the method used for the Merlin 131.

The latter is the method used for the V-1710. It was also used for a version of the Peregrine used in a Whirlwind prototype, which was tried with counter rotating propellors.

The V-1710 is, I suppose, a special case in that it was desigend from the outset to rotate in both directions, and in fact was designed to be reversible in flight (for air ship use). To reverse the rotation a few components would have to be changed around, and an idler gear put into the supercharger drive train.

The Peregrine was eversed by building a completely handed engine, from what I understand. This was, unsurprisingly, impractical from a production point of view, and in any case pilots could not tell the difference in handling between the Whirlwind with counter rotating propellors and one without. So they did without.

[wuzak]

At least they avoided the problems that the Twin Mustang had. When it was first built it wouldn't fly until they reversed the rotation of BOTH engines, then it was OK. 

What they actually did was swap the engines and props from one fuselage to the other of course.

A similar situation occured with the P-38.

The XP-38 had the engines in opposite rotation to those in the YP-38s and subsequent production versions. In the P-38 it was a case of how the aircraft flew on a single engine - ie not very well in the case of the XP-38.

[wuzak]

Might it have suffered the same fate as the Hughes XF-11?

I think that to be unlikely, at least with a Rotol contra-prop.

Ths article by Flight describes the operation of Rotol's contra-prop hub.

Page 3 shows the Rotol contra-prop system in a cutaway.

Pitch control is by an hydraulic piston at the front of the hub, connected to the blades via mechanical links, both to the front and rear props.

I'm not sure with the Hamilton-Standard unit in the XF-11, but my understanding is that the contra-prop experienced an hydraulic failure which lead to one of the hubs going into reverse pitch. This doesn't seem possible for the Rotol unit, unless the links break at which there would be no pitch control whatsoever.

It may be possible with the de Havilland system. de Havilland built the Hamilton-Standard constant speed prop unit under licence, so their contra-prop is likely to be related to Hamilton-Standard's.

I saw the title of this and thought that the Hornet had contrarotating props, not handed turning, but contrarotating props, that is,, two props per engine, but, after reading through the thread, realized my mistake.

But then, why not? Didn't the Shackleton have contraprops? And how successful was that?

Instead of the Merlin engines, what would have been the performance of the Hornet with Griffons and contraprop?

There were Merlins built and tested during WW2 with contra-props. A few Spitfires were fitted with Merlins and contra-props, including JK535, a Mk VIII fitted with a Merlin 63.

http://www.svensktmodellflyg.se/users/4210/MkIXconter.jpg

Also, the Short Sturgeon was a contemporary of the Hornet (but differnt role) and used Merlins with contra-props. So it would quite feasible for the Hornet to have contr-aprops too.

[kitnut617]

Incidentally, the XP-82, P-82B,C,D had Packard license built Merlin 130/131's (BTW, the P-51H had a Packard license built Merlin 130) the only difference apart from American nuts & bolts, was the Merlin 130/131 had down-draft carburetors, and the Packard equivalent had up-draft ones (like all previous Merlins)

Packard built Merlins had British standard nuts and bolts - Whitworth and BA.

Packard built engines had American fasteners according to the Rolls Royce books I have, although the complete engines were interchangeable with aircraft using RR Merlins, parts in the engines weren't interchangeable. My Dad was an Instrument Fitter on Lancasters, and he had a complete set of AF wrenches (Across Flats spanners) for this purpose in his tool box for occasions when he had to help out else where when he wasn't busy doing his job.

[kitbasher]

There were Merlins built and tested during WW2 with contra-props. A few Spitfires were fitted with Merlins and contra-props, including JK535, a Mk VIII fitted with a Merlin 63.

http://www.svensktmodellflyg.se/users/4210/MkIXconter.jpg

I think I've seen that picture before but never noticed it has what what clearly looks to me like a Mk 14 fin and rudder.  Now that would make for an interesting model - it'd get heads scratching, I reckon.

They look like the broad (Jablo I think) Mk V prop blades too.

[The Wooksta!]

I've done something similar, twice, as part of The Plan.  Airfix IXc with a complete PRXIX tail unit.

[kitnut617]

There were Merlins built and tested during WW2 with contra-props. A few Spitfires were fitted with Merlins and contra-props, including JK535, a Mk VIII fitted with a Merlin 63.

http://www.svensktmodellflyg.se/users/4210/MkIXconter.jpg

I think I've seen that picture before but never noticed it has what what clearly looks to me like a Mk 14 fin and rudder.  Now that would make for an interesting model - it'd get heads scratching, I reckon.

They look like the broad (Jablo I think) Mk V prop blades too.

The same photo appears in the Morgan/Shacklady book, the caption says it's a Rotol contra-prop, it wasn't the only one converted to the Merlin 63 engine though. Under this photo is another photo of a Mk.VIII fitted with a Griffon which also has a contra-prop. The broader fin was designed for the Mk.VIII, but used on later variants too, and as you say the Mk.XIV

[dogsbody]

I thought all Merlins were updraft carbureted. I've never heard of a down-draft carb fitted to any Merlin.


Chris

[kitnut617]

I thought all Merlins were updraft carbureted. I've never heard of a down-draft carb fitted to any Merlin.


Chris

Yes -- except the Merlin 130/131's.  The air intakes for the Hornet are the openings in each outer wing leading edge, the air being ducted to the down draft carbs. Also whenever the u/c came down, the intake air was redirected through a filter before entering the carb.