V-1710 supercharger development potential

[tomo pauk]

The V-1710-143/145 (right/left turning) lacked 2 things the Merlin had: backfire screens and inter-cooler(s). The backfire screens were ceased to be installed in the V-1710s once the 'Madam Queen' intake manifold was introduced in winter of 1943/44; lack of the backfire screens 'earned' 1000-1500 ft of rated height in the war-time engines. That really backfired back (pun intended) once the greater manifold pressures were 'demanded' from the 2-stage V-1710 - there was no inter-cooler to cool the charge, and, once the detonation happened in one cylinder it was able to quickly spread in the intake manifold, due the lack of the backfire screens.
It seems that max manifold pressure was limited to 60 in Hg, at least it is so claimed by Edgar Schmued. 60 in Hg means measly power for a 27L engine post-war.

 

[gjs238]

The 9.6:1 supercharger V-1710s got a lot closer to Merlin 45 performance levels, but still a few thousand feet lower FTH. It's hard to say how much might have improved with larger impellers and/or diffusor casings allowed ... and the same things limiting those also limited the 2-speed gearing configuration I believe. The integral supercharger on the V-1710 didn't leave space to allow variable speed gearing or larger supercharger and initially even limited maximum single speed gear ratios. (the 8.8:1 speed was in part limited by the gearing they could manage to fit and how much strain it could take)

Excellent (or rather, Aha!) this is what I was looking for.
I suspected that there were inherent design limitations in the V-1710 that impeded growth.

 

[gjs238]

The aspect of the RR 2-stage approach that the V-1710 couldn't follow was a single shaft 2-stage design. Any added supercharger stages would be more or less used like a turbocharger, independently driven from the single-speed integral supercharger. This is fairly similar to the approach Pratt and Whitney took for their 2-stage designs, Allison just didn't have the funding or resources (internal or external) of P&W to carry out that development early on, and even most later developments were more primitive than what the superchargers on the R-2800 had developed into. (lack of intercooling was a big issue ... adapting a liquid intercooler arangement akin to the P-38J/L's -or Merlin's- would have made a world of difference)


That aside, the other limiting factor was supercharger design. Allison's own designs may have been reasonable enough, but paled in comparison to Rolls Royce's. Size/space constraints for the integral mounting point may have been a limiting factor too, but the roughly equivalent 9.5" diameter impeller used on the 'cropped' Merlin 50 series still performed significantly better than the Allison's at similar speed (the higher displacement of the engine made up for some of the difference -higher power at lower boost). With Merlin quality supercharger design, the single-stage Allison might have reasonably matched the Merlin 45 or 47 or even exceeded them a bit.

Didn't P&W call them the "sidewinder"?

 

[Piper106]

Couple of items to stir the pot.
1. In the fall of 1942 Allison proposed the F-24R engine which would have used "a newly designed integral two-stage supercharger". Dan Whitney "Vees for Victory" page 272. Asked if there were any further details over at AEHS, and unfortunity nothing more seems to have survived. I assume that this would have been something like the merlin 60 engines, but cannot prove it.
2. I seem to recall the problem with the historic Allison two stage engines was that the auxillary supercharger made the engine too long to fit into the Mustang B/C/D/K series airframe without serious center of gravity issue. In the P-51 F/G/H/J series the firewall was relocated further back, and the Allison two stage engine could be installed (as it was on the P-51J).
3. Backfire screens are a 'Band-Aid' fix on the real problem, that the mixture to that cylinder is too lean, and the combustion is way late (lean mixtures burn more slowly then a proper air/gas mixture) with the mixture stll burning when the intake valve reopens. I seem to recall reading that the problem with the V-1710-143/145 engine was that the speed density injection system ran the engine too lean causing backfires. Whether than was lack of development of the speed density injector (or as I believe) poor maintenance/incorrect replacement parts, has never been conclusively proved, nor may it ever be conclusively proved.

 

[Piper106]

Everyone gets on Allison's case for not having a intercooler on their two stage mechanical supercharged engines.

Well... on the Merlin 620 series commercial engines (with an intercooler) on North Atlantic flights, the mixture got so cold during cruise that the engines had trouble. (I assume fuel components condensing out, leading to problems very similar to those seen with the P-38 during WW2). Rolls Royce had to modify the engines to heat the intake charge for cruising conditions. While we like to talk about engines running hard pulling war emergency power, I think in reality even fighters spend most of there time at low cruise power. It could be argued that water injection for the few minutes when WEP is needed might be equal to hauling around an intercooler all the time for the few minutes it is needed.

 

[Shortround6]

Didn't P&W call them the "sidewinder"?

Yes and no.

ALL P W 2 stage engines (at least production ones) used a single speed supercharger on the engine and a two speed drive plus neutral for the auxiliary supercharger. Take-off and low altitude was done with the Auxiliary supercharger in neutral, then as power fell off the supercharger was engaged in low gear and finally high gear was selected.

The "sidewinder" engine was ONLY used in the F4U-5 and used three impellers. TWO mounted sideways (Like a DB engine) with one on each side but operating in parallel. Both always ran at the same speed as each other and had the same neutral/low/high speed set up as the other P W engines. They feed the engine supercharger which was one speed.

 

[kool kitty89]

Excellent (or rather, Aha!) this is what I was looking for.
I suspected that there were inherent design limitations in the V-1710 that impeded growth.

Some of the details I summarized there, I hadn't actually seened confirmed until earlier in this very thread ... that said, actually looking at the physical supercharger installations on the merlin and V-1710 ... even comparing the single-stage single speed ones, I'm not sure the Allison engineers could have done much better even with the likes of Hooker's expertise. (the integral supercharger mounting is really cramped and doesn't make for much flexibility in terms of optimized diffusor arrangements, let alone increased impeller size)

The 8.8 and (especially) 9.6 supercharged engines were already limited pretty much to non-turbo installations (turbos were mated with lower blower ratio engines), so universal installation in that regard isn't much of a bonus (unless you're manufacturing nearly identical airframes with and without turbochargers) so the main issue would be standardized volume production ... IF keeping the supercharger/accessories section of the engine even streamlined manufacturing that much. (early V-1710s made some other significant changes like the reduction gearing on the long-nosed C vs short nosed F series)

And given all the trouble that seemed to go into auxiliary supercharger development, I'm not sure simply focusing on producting models that deleted the integal supercharger+carb intake placement entirely in favor of an arrangement that allowed a wider variety of superchargers would have been more practical. (from an engineering time + manufacturing time standpoint)

Pratt Whitney expanded development of BOTH their single-stage (single and 2-speed) superchargers as well as developing auxiliary systems and facilitating turbocharger arrangements ... Wright seems to have focused more specifically on single stage (fixed and 2-speed -maybe some 3-speed) with provisions for turbo installations (though the R-2600 seemed to have trouble).
It's hard to say what would have been the most effective for a smaller firm like Allison ... but most other manufactuers focused on single stage superchargers exclusively until they hit a wall and needed 2-stage (where single stages would have been unreasonably large). That was the situation in England, Germany, and Japan, including implementations of 3-speed single stage superchargers in some cases. (and sometimes single stages + aftercoolers)

2. I seem to recall the problem with the historic Allison two stage engines was that the auxillary supercharger made the engine too long to fit into the Mustang B/C/D/K series airframe without serious center of gravity issue. In the P-51 F/G/H/J series the firewall was relocated further back, and the Allison two stage engine could be installed (as it was on the P-51J).

Same for the P-39 forcing the more extensive redesign of the XP-39E (and P-63). Which again makes me wonder why a side-mounted arrangement wasn't attempted in able to keep the engine length closer, if even at the expense of some drag. (depending on the exact mounting position of the supercharger)

3. Backfire screens are a 'Band-Aid' fix on the real problem, that the mixture to that cylinder is too lean, and the combustion is way late (lean mixtures burn more slowly then a proper air/gas mixture) with the mixture stll burning when the intake valve reopens. I seem to recall reading that the problem with the V-1710-143/145 engine was that the speed density injection system ran the engine too lean causing backfires. Whether than was lack of development of the speed density injector (or as I believe) poor maintenance/incorrect replacement parts, has never been conclusively proved, nor may it ever be conclusively proved.

Backfires related to detonation would be pre-ignition and burning too quickly ... so a bit different /if/ detonation issues were even related to the backfiring ones. (it's possible detonation issues were a separate problem and backfire problems were limited to lean cruise conditions)

Granted, had Allison switched to a direct-injection arrangement for post-war developments that would have changed a number of issues too, backfiring and detonation included, but that's another topic. (just comes to mind with the R-3350 switching to that)

Well... on the Merlin 620 series commercial engines (with an intercooler) on North Atlantic flights, the mixture got so cold during cruise that the engines had trouble. (I assume fuel components condensing out, leading to problems very similar to those seen with the P-38 during WW2). Rolls Royce had to modify the engines to heat the intake charge for cruising conditions. While we like to talk about engines running hard pulling war emergency power, I think in reality even fighters spend most of there time at low cruise power. It could be argued that water injection for the few minutes when WEP is needed might be equal to hauling around an intercooler all the time for the few minutes it is needed.

That also sounds like a problem with ability to regulate airflow to the intercooler ... the same problem can happen with oil and collant radiators (overcooling situations). Radiator duct/flap designs are a big part of this. (along with simply using larger radiator area than needed or operating in colder environments than intended)

 

[GregP]

Hi gjs 238,

Yeah, I get the feeling that if Bill and I could sit and talk, we'd agree on a lot of things. Tough to have realistic conversations on a forum when it gets into argument so easily. It's less easy to misunderstand each other face to face.

I don't think there was anything especially wrong with the Allison and aux stage, but it was too long and heavy for what it was. Still, it could have been made to play well in an airframe had the time been spent to DO it. The P-63 wasn't bad at all ... we just didn't buy many, probably because of the superficial resemblance to the P-39. The Soviets liked them well enough.

Hi koolkitty,

Not sure if the situation was all of them or a combination of one or two. The Allison G-series I have seen run great and are reliable. That sort if flies in the face of what gets said in many places, but it is a fact from the ones I've seen in service today. I'd really like to know.

Heck, I hadn't heard the term "kinner time bomb" in 20 years until Harrison Ford went down, and now it's in the news again. Fickle people. They don't remember the years of good service, they remember the first failure. It's like the restaurant business ... only as good as the last meal.

Couple of weeks ago I said I'd get pics of the V-1650-7 and Merlin 224 we have at the museum. I got them and will try to post tomorrow when I have time to mess with it. Unrelated to THIS thread, but you can at least see the case differences between a single-stage and a 2-stage Merlin. I'll title the post "Single and Two-Stage Merlin pics."

 

[wuzak]

Interestingly the V-3420 used a 10.0" diameter supercharger impeller for single stage models. Only 1/2" larger than the V-1710, despite being twice the capacity.

 

[GregP]

Hi Wayne,

Though Joe has two V-3420's, he hasn't gotten around to getting one running yet. Something about selling Allison and making money versus spending money to get a show engine running keeps getting in the way.

I have not invested the time yet to look at the altitude performance of the V-3420 but, if it didn't have a turbo ... I don't see how it could be a high-altitude engine. The standard V-1710 wasn't without a turbo.

 

[kool kitty89]

I don't think there was anything especially wrong with the Allison and aux stage, but it was too long and heavy for what it was. Still, it could have been made to play well in an airframe had the time been spent to DO it. The P-63 wasn't bad at all ... we just didn't buy many, probably because of the superficial resemblance to the P-39. The Soviets liked them well enough.

Unfortunate delays to development, initial targets for more of an interceptor and medium-range fighter (and thus not exploiting added wing space for fuel) and said delays putting it too far back to make it worthwhile delying things further for a redesigned wing. (more or less making an american counterpart to the Spitfire/109 ... or maybe Tempest/190 -kind of somewhere in between all those in terms of speed, power, range, armament, and sheer weight/size)

Rather than trying to correct the P-39's major flaws of altitude performance and range. (along with easier maintinence -which the P-63 did aim address)

That and canceling the less ambitious XP-39E outright. (which didn't suffer quite the same delays in testing as the XP-63, so might have made it into service early enough to actually be attractive to the USAAF)

Sticking so heavily with the 37 mm cannon was odd too, using a 20 mm on more than just the P-400 and a limited number of early P-39s and then no more limited its usefulness.

I have not invested the time yet to look at the altitude performance of the V-3420 but, if it didn't have a turbo ... I don't see how it could be a high-altitude engine. The standard V-1710 wasn't without a turbo.

The integral stage on the V-3420 seems a fairly similar installation to the 1710's, though the 2-stage mounting on the 3420 seems a fair bit more compact given the size/capacity. At a glance, the bell housing for the integral stage appears proportionally larger for just a 1/2" gain in impeller size, so possibly more space used for the diffusor.

http://www.michaelp.org/photos/fantasy_of_flight/allison_v-3420_engine_2.jpg

http://svsm.org/albums/Allison-V-3420/P1340676.jpg

http://svsm.org/albums/Allison-V-3420/P1340677.jpg

http://gallery.oldholden.com/d/95762-1/Allison+V-3420+_amp_+drive.JPG




Huh, and the supercharger placement (and housing) in the F series V-1710 chaged more than I'd assumed compared to the older C15 series. Plane Talking - HyperScale's Aircraft Scale Model Discussion Forum: Allison V-1710 photos?

Whatever the changes, it didn't seem to make the supercharger on the -39 (F3R) any better performing than the -33 (C15). Take-off and Mil power were higher, but at similar boost (or overboosting) they had virtually identical power and identical critical altitudes.

A shame they didn't take advantage of that redesign to work in provisions for more variable configuration of the integral supercharger stage. (including aerodynamics of the carb intake and supercharger ducting)

 

[Shortround6]

XP-39E was longer because it was designed to to fit that war winning wonder engine, the army designed and Continental built, the V/O/IV-1430.

They used the two stage Allison when the Army/Continental failed to be ready on time.

 

[kool kitty89]

XP-39E was longer because it was designed to to fit that war winning wonder engine, the army designed and Continental built, the V/O/IV-1430.

They used the two stage Allison when the Army/Continental failed to be ready on time.

Which also happened to need a longer engine compartment and couldn't be fitted to existing P-39 airframes. (otherwise the XP-39E itself might have stayed engineless and a more straightforward conversion of the P-39 to a 2-stage V-1710 may have taken place)

 

[Koopernic]

I think there was no technical reason why Allison could not have built a two stage supercharger like the Rolls-Royce designs.

Why they didn't is probably more to do with the philosophy of Allison, particularly with regards to modularity and the ease of manufacture.

To do a 2 stage design like Rolls-Royce would require a complete new supercharger design. In the case of Allison's two stage design, the engine stage supercharger remained the same, while the Auxiliary stage supercharger was, essentially, a bolt on module. The core of the two stage engines with the carbuerretor attached to the engine stage supercharger, instead of the auxiliary stage, were identical, or near enough to, the equivalent turbocharged version.

From memory the Two stage Merlins impellers came from the vulture and peregrine both of which achieved production but were abandoned.

 

[wuzak]

From memory the Two stage Merlins impellers came from the vulture and peregrine both of which achieved production but were abandoned.

No, that is incorrect.

The first stage for early two stage Merlins was 11.5" compared to the 12.0" of the Vulture (per RRHT). Later versions were 12.0". The second stage was 10.1", compared to 10.25" for single stage Merlins.

 

[Shortround6]

I believe the story may have it's roots in the fact that they used a Vulture impeller in the first test rig. It was handy, it was about the right size (desired airflow) and gave them something to go on. I haven't read anything about using a Peregrine impeller though. I would guess it was too small. You have to deal with both pressure and volume.

 

[GregP]

Everyone we spoke with at Joe Yancey's said they were running them at 75 inches in late production models. By "everyone" I mean former pilots, since usually only owners, former pilots, and former crew chiefs came by the shop when we were breaking in newly-overhauled Allisons. Joe usually had anywhere from zero to 4 visitor during engine runs, and we usually ran them for anywhere from 2 - 6 hours on the test stand before the rings seated sifficiently for Joe to be happy with it going flying.

The backfire screens are effective only at startup if you aren't well trained on how to start the engine. Once it is running, the backfire screens are useless and cost intake manifold flow. Unless you are a ham-handed idiot, nobody backfires an engine after it is running, assuming the carburetor isn't WAY out of tune. If it is that far out, you have no business trying to run it. Carbs typically last 5 years before needding overhaul, but they NEED it after 5 years.

If anyone wants a pic, I have an Allison backfire sceen in pristine condition. It isn't needed once you can start the engine and really isn't needed once it is running, but it makes for a nice piece of engine bit in your display case.

 

[BiffF15]

GregP,

Just post it!

Cheers,
Biff

 

[wuzak]

I believe the story may have it's roots in the fact that they used a Vulture impeller in the first test rig. It was handy, it was about the right size (desired airflow) and gave them something to go on. I haven't read anything about using a Peregrine impeller though. I would guess it was too small. You have to deal with both pressure and volume.

The second stage in the original test rig may have been the standard Merlin impeller.

 

[GregP]

Hi Biff,

OK. Here are some allison parts. If you look at the rods, the one with the cut in the middle is a fork rod. The rod in the middle is a blade rod.:

Here is a closeup of the Allison Backfire Screen. It goes into the intake manifold where it bolts onto the cylinder head, but is not needed at all once you can start an Allison. If you get to WER power, you will be in auto-rich anyway ... or you will be walking home.:

Here are some early and late model wrist pins. The one with the thin end is early and experienced some cracks in service, so they eliminated the champfer and just went with cylindrical wrist pins:

Here are some valves. Naturally the larger valve is intake and the smaller valve is exhaust. The valve stems are Sodium filled and the material is Stellite:

And, finally, here are a couple of heavily modified pistons. These come out of one of Guy Lombardo's Championship-winning hydroplanes. He had the bottom rim cut off and modified the remaining bottom slot to be the new bottom ring. Unsurprisingly, these "slapped" at idle and had lower lifespans. The holes in the sides were for lightening and they don't really work. Stock pistons really work better than these!:

All for now.