Griffon powered P-38?

[gjs238]

Would the Rolls-Royce Griffon been a good choice/evolutionary step for the P-38?

 

[herman1rg]

I think perhaps it may have been to big?

 

[wuzak]

I think maybe it would have been possible. The Griffon fit in a space designed for a Merlin, and the Merlin fit in a place designed for a V-1710.

The Griffon was 6in deeper than the Merlin/V-1710, but much the same width and shorter than both (single stage V-1710, single and two stage Merlins with 2 speed drive). One issue may be the extra 600lbs over the V-1710, though this is partially compensated by the turbo, intercooler and ducting. But it will change the centre of gravity.

 

[wuzak]

Here is a P-38 with Griffon engines (from a Spitfire XIV nose)

 

[GregP]

Could easily have been if the Griffon had bneen made ion counter-rotating models. It wasn't as far as I know.

The P-38 proved conclusively it needed counter-rotating props in the initial British order.

Today, we could fix the aerodynamics that made the P-38 a dangerous diving machine. Back then, maybe not. But the Griffons would have considerably increased the climb which was already pretty good. With Griffons, I think we would have seen 5,500 fpm climb or better and 440+ mph.

 

[wuzak]

The Griffon could easily have been made in left and right hand turning models - chnging the reduction gear setup, as per the opposit rotating Merlins.

Or, they could have chose to put the contra-props on them.

 

[Readie]

Wouldn't the extra fuel consumption be an issue though?
If the Lightning was too be a long range fighter then engine design in that department was pretty important. Maybe more than sheer power?
The Allison had the mpg edge with the Turbo charger over RR. Maybe if the engineers could turbo a Griffon, then you could have the best of both worlds.
Does anyone know if there were plans to move away from SC to TC'ers ?
Cheers
John

 

[claidemore]

If replacing the Allison in the Mustang with a Merlin worked out so well, I would think doing the same in the P-38 would do the same. Seems to me I remember that being done on a test model or prototype? Or was it just an idea?

 

[post76]

True..
But Allison pluss turbo might yeild different results than Griffon + turbo?
Maybe the Griffon lends itself better to supercharging, hard to say.

 

[davebender]

I don't think so.

P-38 and P-47 airframe designs were dictated by turbocharger system space requirements. If you want to power an aircraft with a supercharged engine then there's no reason for such a large and heavy airframe.

 

[tomo pauk]

If replacing the Allison in the Mustang with a Merlin worked out so well, I would think doing the same in the P-38 would do the same. Seems to me I remember that being done on a test model or prototype? Or was it just an idea?

Two-stage supercharged, properly intercoled engine replaced single-stage engine in P-51 (offering cca 70-80% more power from 15kft up).
In P-38 case, we talk about turboed engine being replaced by two-stage one: up to 20-25 kft the difference see-saws within couple of %, while above tat height turboed Allison has slight edge vs 1610-7, but barely any vs. 1610-3. Granted, Merlin yields decent exhaust thrust here (the higher faster, the better;1710 yields none in P-38), so it's a toss up in my eyes.
The major shortcoming re. such a replacement is that by mid 1943 there is almost none of two stage Packard Merlins to choose, and P-51 was far better airframe to use those (along with already mentioned 'weaker' 1710 aboard, as a reason).

 

[helmitsmit]

P-38 didn't need it. Too much power for minimal benefit

 

[wuzak]

I don't think so.

P-38 and P-47 airframe designs were dictated by turbocharger system space requirements. If you want to power an aircraft with a supercharged engine then there's no reason for such a large and heavy airframe.

The twin engined airframe of the P-38 was designed to give the desired performance on the then available engines. A single engined aircraft could not meet the performance requirements.

 

[wuzak]

Lockheed did various studies of installing the Merlin in the P-38 during the war.

Data from Dan Whitney, Vee's For Victory - The Story of the Allison V-1710 Aircraft Engine 1929-1948:

Lockheed estimates of a Merlin XX powered P-38.

                                         Merlin XX    V-1710-F2 (-27/29)
                                        Reprt 2036           YP-38
Takeoff BHP                              1280/3000       1150/3000
Critical Altitude Military bhp                1170            1150 
Critical Altitude, feet                      21000           25000
Critical Altitiude max speed, mph              431             405
P-38 weight, pounds                          14500           14348
Sea level rate of climb, ft/min               3160
Sea level max speed, mph                       354
High speed cruise, bhp/rpm                875/2650       1000/2600
High Speed cruise mph/Alt ft             393/20000          /25000
High Speed cruise fuel use lb/bhp/hr         0.485
Range at high speed cruise, miles/gal         2.78             310*
Service Ceiling, feet                        38100           38000
Engine, with turbo  ducts, pounds            1430            1590
Normal range, miles                            640             650
Normal fuel capacity, gallons                  230             210

* This figure is clearly not right. If it was 3.10 it would suggest the high cruise speed of the YP-38 was lower than the Merlin XX powered aircraft.


By the time Merlin production had begun in the US RR were making two stage Merlins. Packard soon changed to the V-1650-3 in production, and that pretty much put paid to the idea of a Merlin XX powered P-38.

However, Lockheed prepared some estimates of a Merlin 61 powered P-38....

                                   V-1710-F17 (-89/91)           Merlin 61
                                    Military   Normal       Military   Normal
Altitude for max speed, ft             27000    25000          27300    30200
Maximum speed, mph                       418      395            423      403
Sea level                                360      326            343      326
5000ft                                   365      342            365      345
10000ft                                  382      358            386      364
15000ft                                  396      374            406      381
20000ft                                  408      386            406      395
25000ft                                  416      395            414      388
30000ft                                  414      383            419      402
Absolute ceiling, feet                 42300    38500          42300    41200
Service Ceiling, feet                  41600    37800          41600    40400
Climb in 5 minutes, feet               17800                   17800
Climb to 20000ft, minutes                6.2                     5.9
Climb to 25000ft, minutes                8.7                     8.4
Climb to 30000ft, minutes               12.2                    11.8
Distance to takeoff 
of 50ft obstacle, feet                  1640                    1770

Clearly there wasn't sufficient margin to warrant pushing hard for the Merlin 61 option, especially considering the disruption to production it would cause. The V-1710-F17 (89/91) was first used in the P-38J.

In 1944 Lockheed prepared further estimates involving an advanced V1710 engine (maybe the V-1710-G1) with the same reduction ratio as the P-38K and the same high activity propellor. It was compared with a late model Merlin (100 series with WEP of 2000hp dry?).

                                    Standard  Advanced   Advanced      
                                       P-38J   Allison    Allison        Merlin
War Emrgency Power, bhp                 1600      1725       2000(wet)     2000
WER engine, rpm                         3000      3200       3400           n/a
Engine?propellor gear ratio           2.00:1    2.36:1     2.36:1        2.36:1
Propellor diameter, feet                11.5      11.5       12.5          12.5
Turbosupercharger, GE Type              B-33      B-39       B-38       Jet Exh
Fuel grade                               130       140        140       Special
Propellor activity factor               89.3      89.3        110           110
Propellor weight increase, lbs             0         0         51            51
Per engine weight increase, lbs            0         0         45           n/a
P-38 operational weight, lbs           16200     16200      17250         16500
Increase in maximum speed, mph             0        12         16            38
Increase in maximum climb, fpm             0       490        850          1300
Impact om manoueverability %               0        0?         -5            -1
Maximum sea level speed, mph             356       364        382           398
Maximm speed @ 30000ft, mph              436       448        452           468
Maximum climb in 5 minutes, feet       18700     21600      23000         25600
Timb to climb to 30000ft, minutes        8.7       7.2        6.2           6.2
Absolute ceiling, feet                 43900     43900      43700         43900

Also thought was given to installing a two stage V-1710 in the P-38. An sketch of a possible intsallation was produced, and it looks pretty slick.

The estimated performance numbers above include hp equivalent for the jet thrust exhaust.

 

[MikeGazdik]

I think the biggest thing that could have been done to improve the Lightning, would have been to redesign the wing into either a thinner airfoil, or a laminar airfoil. I think that would have addressed how soon it came into the compressability situation as well. The regular single stage supercharged Allison is great at lower altitudes, but that is it. It has a reputation as a poor engine but really the only problem was a lack of a good 2 stage supercharger, as compared to the Merlin. Turbocharging the Allison more than makes up for any deficiancy, in my view.