Merlin 130 series vs other Merlins (frontal area)?

[BarnOwlLover]

It's been said that the Merlin 130 (used primarily in the DH Hornet) was designed for the Hornet to have as little frontal area as possible. Other than ancillaries being moved around, what else was done to reduce frontal area on the 130? I do assume that they do share the same block and head design as the other two-stage Merlins, or did those differ even?

 

[tomo pauk]

Paging W wuzak , D Deleted member 68059

 

[pbehn]

It's been said that the Merlin 130 (used primarily in the DH Hornet) was designed for the Hornet to have as little frontal area as possible. Other than ancillaries being moved around, what else was done to reduce frontal area on the 130? I do assume that they do share the same block and head design as the other two-stage Merlins, or did those differ even?

I dont think anything in the engine was substantially changed, the Spinner on a Hornet looks bigger in diameter, making the whole thing look smoother, there isnt a real transition between Spinner and engine.

 

[BarnOwlLover]

I've actually been wondering about the size of the Hornet's spinner compared to like a P-51 (Merlin powered) spinner. Both have smoother/more blended lines to them than a Merlin powered Spitfire. And the Griffon powered versions were so tightly cowled that the upper cowling had bulges to clear the valve covers.

 

[wuzak]

I believe the main difference in frontal area was using the downdraft carburetor rather than the updraft carby.

From http://www.wwiiaircraftperformance.org/Aircraft_Engines_of_the_World_Rolls-Royce_Merlin.pdf

 

[BarnOwlLover]

Good find and very interesting

 

[pbehn]

Good find and very interesting

There was around 5 years between the Spitfire and Mustang Mk ! and another 5 for the Hornet. Producing such cleaner designs starts at the drawing board, on a Spitfire, there is an oil tank in the fuselage under the engine for example.

 

[BarnOwlLover]

I do wonder what the frontal area between a Hornet nacelle and a Mustang nose was as far as if there was some similarities. It seems that the spinner size was similar, though the Mustang probably had a bit more frontal area ultimately due to having to accomodate a pilot behind it.

Also a case of what-if here, but what if the Spitfire was designed or redesigned to use a cowling with a larger spinner and was even more streamlined? The P-38K Lightning did something similar, though it never entered mass production (USAAF didn't really want it, were happy with the P-38J/L, as well as the P-47D and P-51B/C/D/K models, and worried about disrupting P-38 production).

And, what if the Hornet used updraft intakes instead of the downdraught ones? There's tradeoffs for both. The downdraft ones reduced frontal area (supercharger intakes were wing mounted), but the updraft ones probably could've made more power (straight shot into the carb/supercharger).

 

[pbehn]

I do wonder what the frontal area between a Hornet nacelle and a Mustang nose was as far as if there was some similarities. It seems that the spinner size was similar, though the Mustang probably had a bit more frontal area ultimately due to having to accomodate a pilot behind it.

Also a case of what-if here, but what if the Spitfire was designed or redesigned to use a cowling with a larger spinner and was even more streamlined? The P-38K Lightning did something similar, though it never entered mass production (USAAF didn't really want it, were happy with the P-38J/L, as well as the P-47D and P-51B/C/D/K models, and worried about disrupting P-38 production).

And, what if the Hornet used updraft intakes instead of the downdraught ones? There's tradeoffs for both. The downdraft ones reduced frontal area (supercharger intakes were wing mounted), but the updraft ones probably could've made more power (straight shot into the carb/supercharger).

The spinners on Spitfires have a history all to themselves, there were very round ones and pointed ones, but generally they got bigger because it went from two to three to four to five and finally to six blade contra rotating props.

 

[Deleted member 68059]

I believe the main difference in frontal area was using the downdraft carburetor rather than the updraft carby.

View attachment 693121


View attachment 693122

From http://www.wwiiaircraftperformance.org/Aircraft_Engines_of_the_World_Rolls-Royce_Merlin.pdf

The 66 has a bendix pressure carburettor (actually primitive single point injection) and the 130 has a proper single point fuel injection system. Just to get the semantics correct

 

[wuzak]

The 66 has a bendix pressure carburettor (actually primitive single point injection) and the 130 has a proper single point fuel injection system. Just to get the semantics correct

So updraft vs downdraft throttle bodies?

 

[Engineman]

It's been said that the Merlin 130 (used primarily in the DH Hornet) was designed for the Hornet to have as little frontal area as possible. Other than ancillaries being moved around, what else was done to reduce frontal area on the 130? I do assume that they do share the same block and head design as the other two-stage Merlins, or did those differ even?

Well, the differences are great, but it is a similar engine!
I strongly recommend that you purchase the RRHT book "The Merlin 100 Series" which is a fully illustrated encyclopedia of detail of the 100 series Merlin, including the 130 series for Hornet.
As far as profile cleaning-up goes, the coolant pump was moved up to the side and the engine air intake was made downdraught (with noted LE inlet) to allow reduction of depth at the rear. The throttle became a single semi-rectangular butterfly plate type, later changed to a Corliss type about 1946 onwards.
Overall, the changes were comprehensive and, the RRHT book is indispensible to anyone with interest in this subject.

Eng

 

[Engineman]

In addition, it is worth noting some of the advances that led to the Merlin 100 series. After starting production of the Merlin 66 with a max rating of +18lb Boost, it was decided to concentrate development on trying for an "Overload Test" of a straight 100 hours at maximum power, ie 3000rpm, +18lb Boost, 1750bhp, to be achieved at constant power, without any mechanical servicing. These overload tests started in Aug '43. Initially, the (Merlin 66) engines failed with faults like cracks in the crankcase at 27 hours. So, upgraded parts were designed and produced to overcome the failures and the test engine became more and more modified. Eventually, the full 100 hours at 3000, +18, was achieved in Nov '43. This engine formed the basis for Merlin 100 series.

Eng

 

[Engineman]

The information in the RRHT "Merlin 100" book is very detailed. I have just found that the single "rectangular" butterfly plate type throttle body that was used on earlier 100 Series Merlins, with the SU Single point injection system, was called the "VORTEX" throttle. This was designed to reduce intake losses compared to even the Bendix-Stromberg type installation on the Merlin 66, along with improved intake design and overhung supercharger impellor. Apparently, the Vortex throttle had issues with aerodynamic loads and operating torque in use and that was a reason for the adoption of the CORLISS type throttle, with it's single rotating plate that slides smoothly around, with notably low operating torque.
So, if this interests you, treat yourself to the book from RRHT!

Eng