Roland D VIb – The ongoing saga.

[Akaalias]

Roland D VIb – The saga continues.

Sorry to do this to you, but I’m after more information on the performance figures of the Roland D VIb.

Hugh Cowin (German And Austrian Aviation Of World War 1 (Osprey Publishing)), on page 65, quotes a speed of 124 mph at sea level, decreasing to 113 mph at 2000 m. This is a rapid fall in performance, particularly when compared with other examples:

Hanriot HD1 115 mph at SL 111 mph at 2000 m
(JM Bruce, Warplanes Of The First World War)
Morane-Saulnier MoS 29 138 mph at SL 135 mph at 2000 m
(JM Bruce, Warplanes Of The First World War)
Nieuport 28 124 mph at SL 125 mph at 2000 m
(Ray Sanger, Nieuport Aircraft Of World War One)
SPAD XIII 130 mph at 1000 mtrs 129 mph at 2000 m
(Dan-San Abbott, The Aerodrome (4 June, 2003))


The climb rate for these aircraft to 2000 m and 3000 m are:

2000 m 3000 m
Hanriot HD1 6’03” 11’03”
Morane-Saulnier Mos 29 5’15” 8’40”
Nieuport 28 4’06” 8’10”
SPAD XIII 5’17” 8’45”

The post-war figures of the McCook Field flight test report (1920) are even more disparaging and show a decrease to 99 mph at 15,000 ft. The “corrected” McCook figures in “German Aircraft Of The First World War (Gray and Thetford) also reflect this, with a speed of 114 mph at approx 2000 m.

This sharp decrease is even more baffling given the very good climbing performance of the D VIb, as quoted from figures given by Dan-San Abbott in this forum (10 June, 2004) and the Windsock Datafile (#37):

Dan-San Abbott Windsock

To 1000 m 2’30” 2’30”
2000 m 4’54”
3000 m 7’44” 7’48”
4000 m 12’15”
5000 m 19’06”

These figures are similar and suggest that the general climbing performance was very good, particularly when compared to the four aircraft above, yet they don’t have the dramatic performance decrease ascribed to the Roland D VIb .

Peter Grosz states that the over-compressed Benz Bz 111av engine “possessed high-altitude capability similar to the BMW engine” (Windsock Datafile 37), but a speed of 113 mph or 114 mph at 2000 m seems at odds with this. Did the D VI with the Benz motor really have a good performance at altitude, or is the generally accepted figure of approx 114 mph incorrect?

Is anyone able to provide figures or reliable sources for speed and developed power at various heights up to 5000 m?

Any advice or assistance would be greatly appreciated.

[Greybeard]

From the figures on McCook Field flight test report you can guess how loss of speed with altitude was lower; making a rough comparison:

from 114 at SL to 111.5 at 6500' means -2.2%, that's to say 124 at SL become (124 - 0.022*124) 121 at 6500'.

How you can read on mentioned report, they haven't still fully understood overcompressed engines operation, thus tested not going beyond throttle stop as well as with a not fully suited propeller. I think actual max speed at SL in "emergency" (uber) was 124 mph and possibly a bit more (I estimated 127).

GB

[FlyXwire]

It is also quoted in the Windsock Datafile on the Roland D.VI, that of the 750 Benz Bz.IIIa engines ordered, which was nominally rated at 185 PS and mentioned as an "over compressed" version by Grosz, only 179 had been delivered by November 1, 1918.

How many Roland D.VIb airframes actually mounted the Benz Bz.IIIav as the McCook version is said to have, I wonder?

[Dan_San_Abbott]

Gentlemen:
The Rol.D.VIb with the BenzBzIIIav engine was the equal to the Fok.D.VII with the BMWIIIa engine. The Benz BzIIIav was rated at 197 Ps @ 1400 rpm at 2800 meters altitude. The Benz BzIIIav produced 243 Ps @ 1700 rpm. Its weight was 283 kg. dry, and BMWIIIa weight was 285 kg. dry. Both engines were referred to as "high Altitude" engines.
There were 200 Rol.D.VIb machines ordered and by 11 November 1918 all were delivered.
Blue skies,
Dan-San

[Akaalias]

Ok Greybeard, FlyXwire, Dan San. Thanks for that.

At what minimum height (in Europe) could maximum power be safely applied with the Benz?

Cheers,
Me

[FlyXwire]

Dan San,

In addition to Akaalias's question above, is it known how many Benz BzIIIav engines were actually produced and mounted in the Rolands, as opposed to the BzIIIa?

[Dan_San_Abbott]

FlyXwire:
After further study I found there were three engines, The BzIIIa rated at 185 Ps @1400 rpm @ and maximum Ps is 208 @ 1700 rpm at sea level. The bore is 130mm an the stroke is 190mm. Compreession ratio is 4.93 :1. There were 218 built in 1917.
The second is the BZIIIav rated @ 197 Ps @ 2800 meters altitude and 260 Ps at 1700 rpm at 2800 meters altitude. The bore is 140mm and the stroke is 190mm. Compression ratio is 5.65:1.
The third is the BZIIIaü rated @ 225 Ps 1400rpm, and 239 @ 1600 rpm. The the bore and stroke is the same as the BZIIIav engine, I would surmise the compression ratio was most likely increased to achieved the greater horse power. I have no further data on the BZIIIaü engine.
Blue skies,
Dan-San

[Akaalias]

Ok. Thank you for that.

Cheers,
Me

[Bletchley]

Akaalias, the information that I have on maximum power in engines with altitude compsensation devices in British aircraft is that it could 'safely' be used at over 3000 ft, but it would not produce much noticeable effect, accept for an improvement in fuel economy, until about 5000-6000 ft. British altitude compensation devices used a semi-automatic pilot controlled 'vacuum' device to reduce the fuel in the fuel/air mixture, whereas the German altitude compensators used the opposite approach, increasing the air in the mixture - but the effective altitudes should have been the same, I think. In both cases the altitude compensator could have been engaged for 'emergency power' at a lower altitude 'safely' for 'a few minutes only' (5 minutes, according to one report that I have seen), but not for continuous running as the engine would soon start to overheat, cylinders crack, etc. Also, I doubt if the throttle could be fully advanced by the pilot for emergency power at an altitude much below 3000 ft, because when the British RAE tested a German altitude compensating carburettor (albeit a Mercedes one) they could not fully open the throttle at ground level without the engine cutting out, and had to substitute a 'standard' Mercedes carburettor to induce full power at ground level.

Short answer to your question: the 'high altitude' throttle setting could probably be engaged and then partially advanced, safely, at above 3000 ft, and fully advanced at altitudes of above 5000 ft.

I believe that pilots may also have had access to a similar (but reduced, and officially frowned upon) 'emergency power' throttle advance for 'a few minutes only' in some, possibly all other WWI aero engines, even without altitude compensators, as well - but I am still at the stage of looking into this so I can't say that this was so for certain. Anyone else know?

Bletchley

[FlyXwire]

Thanks Dan San for your research!

Perhaps the compression ratio for the BzIIIau was 5.8 to 1, as this is what Glenn Angle list in his book for the BzIIIav, albeit with the power figures you list for the BzIIIau (Angle: 221.5 hp at 1400 r.p.m., and 239 hp at 1600 rpm).

So the Benz BzIII engine series contained:

BzIII 160 PS
BzIIIa 185 PS
BzIIIav (approx. 200 PS) ???
BzIIIau 225 PS

(and perhaps a BzIII of 150 PS)

The second German fighter trials in May-June 1918, list the subject Roland D.VIb being evaulated with the Benz IIIa u, while the evaluation flights in July list Roland D.VIb (types) being flown with the Benz BzIII a v.

The question that remains (in my mind at least), is which Benz engine was the predominant installation for the Roland D.VIb? Was the BzIIIav the standard engine, or perhaps the BzIIIa, or even the BzIIIau?

Are the production specifications for the Roland D.VI series definitive enough in this regards I wonder?