LeO 451 Model du Vol

[viso]

En francais (par babelfish):
AvHistory essaye d'établir un modèle précis de vol pour le Lion 451. Cependant, les vitesses au niveau de la mer et à l'altitude ne semblent aucun raisonnable une fois comparées à l'autre avion. Nos données indiquent que le Lion a eu des moteurs de 2x Gnome le Rhône produisant 1.060 que la HP à la vitesse 4,800m. au niveau de la mer était 227 M/H et 298 M/H à 4,800m.
Ces données ne se comprennent pas. Le Lion devrait avoir eu aussi peu drague qu'un P-51 pour atteindre de telles vitesses. Est-ce que quelqu'un peut m'aider à obtenir des données précises ?

En anglais:
AvHistory is trying to build an accurate flight model for the LeO 451. However, the speeds at sea-level and altitude make no sense when compared to other aircraft. Our data indicates that the LeO had 2x Gnome Rhone engines producing 1,060 HP at 4,800m. Speed at sea-level was 227 MPH and 298 MPH at 4,800m.

These data do not make sense. The LeO would need to have had as little drag as a P-51 to reach such speeds. Can someone help me obtain accurate data?

[oli]

J'ai trouvé ça :
LeO 451
2 moteurs Gnome & Rhône 14N-48.
Puissance : 2 x 1140 ch
Poids en charge 11400 Kg
Vitesse maxi 495 Km/h à 4800 m
Plafond pratique 9000 m
Distance franchissable 2300 Km

[Pachy]

Everything below is from the official notice descriptive et d'utilisation de l'avion LeO.451 à moteurs Gnome-Rhône type 14N except when other source is given

I. AIRFRAME

A) General dimensions
Max wingspan: 22.52 m
Length: 17.2 m
Height (tail on the ground): 4.24 m
Height (inflight): 5.24 m
propeller clearance (tail on the ground): 1.32 m
propeller clearance (tail up): 0.72 m

B) wings
Dihedral angle: 6° 30'
built-in incidence angle: 3°
chord @ root: 4.826 m
chord @ wingtip: 1.374 m
area: 68 m2
Airfoil: "type 44 series, 15% max thickness, 11% min thickness" (This is from Jacques Lecarme's article "Triste campagne de France" in Icare magazine. I'm guessing this could mean NACA 4415 @ root and 4417 @ tip. It looks like a although 4-digit NACA 44xx was very common at wing tip, but it was more often in combination with something like a 23xxx at root.)

Ailerons:
lenght: 5.537 m
max chord: 0.84 m
individual surface: 5.5 m2
distance between center of aileron and aircraft axis: 8.057 m
max throwout angles: +12° 30' / -11°

Flaps:
lenght: 4.717 m
max chord: 1.388 m
individual surface: 5.5 m2
distance between center of aileron and aircraft axis: 3.01 m
angles: 18 ° (takeoff), 38° 30' (landing)

C) Fuselage
max height: 2.375 m
max width: 1.32 m
max frontal area: 2.812 m2

D) Tail surfaces
Vertical surfaces (1939 variant, smaller)
max height: 1.683 m
individual stabilizer surface: 0.58 m2
individual rudder surface: 1.44 m2
distance between rudder axis and main wing leading edge: 11.342 m
max throwout angles: 25° outer movement, 21°30' inner movement (symmetrical)

Horizontal surfaces
span: 6.924 m
dihedral angle: 13°
individual stabilizer surface: 3.16 m2
individual elevator surface: 2.10 m2
distance between elevator axis and main wing leading edge: 11.737 m2
max throwout angles: +25° / -20°

E) Landing gear
Main landing gear
tyre type: 1060x390
track width: 5.492 m
suspention max movement: 347 mm

Tail wheel
tyre type: 500*220
suspention max movement: 150 mm

II POWERPLANTS

A) Engines
Number: 2
Make: Gnôme et Rhône
Type: 14 N 38 (port) and 14 N 39 (starboard)
or 14 N 48 (port) and 14 N 49 (starboard)

(Pachy's comment: it is difficult to say when production switched from 38/39 to 48/49 subtypes of engines. They are very similar, the latter is very slighty more powerful at altitude)

Radial, 14 cylinders in two rows of 7, air-cooled, single-speed, single stage supercharger
cubic capacity: 38,670 cm3 (146 x 165 mm)
diameter: 1.290 m
"dry" weight: 620 kg
compression ratio: 6.8

rated RPM: 2,400
rated power at sea level:
990 (metric) hp (if 14N38/39)
920 (metric) hp (if 14N48/49)

rated power at 4,800 m:
1030 (metric) hp (if 14N38/39)
1060 (metric) hp (if 14N48/49)

rated IMAP: 800 mm Hg

take-off power:
1,100 (metric) hp (if 14N38/39)
1,180 (metric) hp (if 14N48/49)

take-off IMAP: 980 mm Hg

max RPM: 2,650

fuel type used: 87 octane

(B, C, D: blah blah)

E) Propellers
Make: Ratier series 1634 (starboard) / 1635 (port)
Type: 3-bladed, metallic, electric variable pitch, featherable
Diameter: 3.2 m
pitch angles: from 22 grad to 42 grad (19.8° to 37.8°)
reductor ratio: 2/3

(F, G, H, I: blah blah blah)

J) tanks

1) fuel tanks
Number: 4
Type: metallic (L2R), riveted, protected with Superflexit covering
(pachy's comment: Superflexit is a rubber-like material with self-sealing properties)
capacity:
main (inner wings): 2 x 880 l
secondary, front (outer wings): 2 x 300 l
secondary, aft (outer wings): 2 x 410 l
fuselage fuel cell: 45 l
total capacity: 3,225 l

2) oil tanks
Number: 2
Type: aluminium, sealed
(pachy's comment: they are located behind the engine firewalls, above the landing gear bay. The oil radiators are located on the outer side of the engine nacelles, between the exhausts and the firewalls, and are fed by the large air intakes you can see near on the wing trailing edge near this location. I'll post pics that show these radiators.)
total theoretical capacity: 2 x 77 l
practical capacity: 2 x 70 l

[Pachy]

(end manual quote...)

On the interesting subject of performance...

The LeO.45-01 prototype performed extensive performance tests in January 1939. While fitted with Gnôme-Rhône 14N20/21 engines (pratically identical to the 38/39) driving G&R propellers, and at a gross weight of 10560 kg, it achived the following results (source: Cuny & Danel's LeO 45, Amiot 350 et autres B4):

Max speed 500 km/h @ 5000 m

Time to altitude:

1000 m in 3' 01"
3000 m in 8' 27"
4000 m in 10' 56"
5000 m in 13' 31"
6000 m in 17' 26"
8000 m in 18'

Practical ceiling: 9100 m

Endurance @ 4000 m:
1675 km @ 2400 RPM (825 L/h)
2140 km @ 2185 RPM (600 L/h)
2900 km @ 1920 RPM (370 L/h)

However, there are several sources that state performance wasn't as good on main production examples. In Serge Joanne's book about the MB.152, an evaluation report for the early MB.152 (variant with the wide, draggy engine cowling) is quoted. It says that, while theoretically the early MB.152 should not have been able to intercept a running LeO.451 (as it max speed was only 480-something), it proved capable to do so during mockup interceptions. This was, of course, interpreted as the LeO underperforming and not the other way around, certainly due to experience with the LeO which was already in operational units.

Several reasons can explain the difference in performance between main production and the prototype. Cuny and Danel mention that the prototype had very well polished surfaces, and Lecarme (former test pilot) claims that the main production Ratier propellers were much less efficient than the prototype's Gnome-Rhône propellers (which were larger in diameter). These Ratier propellers were were chosen because they were already in production as they were fitted on an older aircraft model (MB.210 if memory serves).

Still according to Cuny and Danel, every LeO was flight tested out of the factory. A plane which didn't meet the acceptance criteria was to be rejected by the Armée de l'air. These criteria were:

* Gross weight to be 10625 kg with full fuel load
* Max speed to be at least 465 km/h at service altitude
* climb time to 5000 m to be at most 15'

So, these figures are a kind of worst-case scenario for a factory-fresh, unarmed planes (as weapons were fitted by the Armée de l'air not by the manufacturer). The detail of weights for this test case is given in the chart I did.

Main production plane serial number 242 was tested in 1941 and only reached 460 km/h. Cuny and Danel mention that the same plane was tested again in 1942, and scored better, but in either case the test conditions are not known.

Another interesting document is a little offical data sheet from the Musée de l'air, dated 11th April 1940. It gives the following performance figures (from test flights not estimated):

with a gross weight of 10850 kg:
370 km/h @ sea level
470 km/h @ 5000 m
Climb to 4000m in 11'
take-off field length 690 m (with 8 m screen height)
landing in 550 m (with 8 m screen height)
Endurance 2200 km @ 5000 m @ 2100 RPM

That's about all I have...

[Gerfaut]

Holly cow ! Gael, 1st class advisor as always !

[Pachy]

These data do not make sense. The LeO would need to have had as little drag as a P-51 to reach such speeds. Can someone help me obtain accurate data?

My data isn't in major disagreement with the figures you quoted. I'm not sure about the comparison with the P-51, but one has to realize the LeO 451 design sacrificed everything to aerodynamical efficiency:

* the Mercier engine cowlings had very little drag (but were a maintenance nightmare...)

* the dorsal gun mounting is technically similar to a conventional motorized turret, except the gunner sits outside the turret... because a conventional turret ring would have been larger, and therefore impossible to fit inside such a narrow fuselage. The downsides were limited traverse and awful accessibility to the cannon (not good for a magazine-fed weapon...)

* instead of one large, versatile bomb bay, like the one aboard the "fat-bellied" and slower Amiot 351, the LeO had one medium sized bay in the fuselage, and two small bays in the wing roots. Because of this, it could not carry torpedoes or large (1000 kg-class) bombs. Even if the LeO would have been capable of lifting at least three (perhaps even four in overloaded condition) 500 kg-class bombs, there was room for two, period!

* the wing bomb bays and tanks took a lot of room, so the wing structure was overly complicated. The G-tolerance wasn't probably too bad, but the ability to sustain structural damage was.

* the landing gear was overly complicated too, so as to retract the wheels as close to the engines as possible, and limit the nacelles' wetted surface. Compare with the DB-7's much longer nacelles.

* then of course, the vertical tail surfaces were much too small. This was even problematic on bombing runs, for lining up over the target. The combination of small rudders, fragile landing gear, and fragile wing structure was nasty: a minor pilot error on takeoff generally ended up in a ground loop, destroyed undercarriage, and damage to the wing structure. And of course an engine problem on takeoff meant four killed.

So yes, the LeO.451 was really fast, it came at a price, though.

[Pachy]

...au fait, je suis désolé d'avoir tapé tout ça en Anglais, mais je suggère aux francophones de lire Léo 45, Amiot 350 et autres B4, par Raymond Danel et Jean Cuny, Docavia n°23 - Editions Larivière. Ces gars-là savaient de quoi ils parlaient...

[Gerfaut]

Bien vu, Gael.
Alors je vais me le procurer dare-dare celui-là.

Le LéO est pour le moment en IA dans CFS3. Qu'il bénéficie d'un MDV 1% est un gros plus pour envisager de le rendre pilotable mais pas à court terme, quand on voit déjà la somme de taf 3D/textures pour le cockpit du D.520 (d'une qualité équivalente aux cockpits allemands de Mathias Pommerien).

[moi1000]

L'avantage du MdV 1% sur un avion IA est d'avoir des adversaires (et coéquipiers) qui volent de façon réaliste

[jeanba]

I have a performance curve from the docavia , but no scanner

Performances data for the number 242 from 1941 tests :
0 m, max vel = 362 km/h
1000 m : 381 km/h,
2000 m : 400 km/h,
3000 m : 420 km/h
4000 m : 440 km/h
5000 m : 460 km/h
6000 m : 450 km/h
7000 m : 440 km/h
8000 m : 422 km/h

For the number 1 (1938 test) :

0 m, max vel = 389 km/h roc = 5.4 m/s
1000 m : 410 km/h, 5.7 m/s
2000 m : 400 km/h, 6.1 m/s
3000 m : 432 km/h, 6.5 m/s
4000 m : 478 km/h, 6.7 m/s
5000 m : 500 km/h, 5.7 m/s
6000 m : 490 km/h, 4.5 m/s
7000 m : 478 km/h, 3.0 m/s
8000 m : 460 km/h, 2.0 m/s
9000 m : 432 km/h, 0.7 m/s

Absolute ceiling seems to be around 9400 m roc = 0, max speed = 420 km/h

[viso]

Chouette! Merci boucoup pour tout les reseignments.

[jeanba]

Chouette! Merci boucoup pour tout les reseignments.

Viso, check your viso gmail account, I sent you information.

[TOPOLO]

Juste une ou deux questions (n'ayant pas le Docavia sous la main et etant peu familier des perf des avions de cette époque),
1 - les vitesses que vous donnez pour chaque altitude, ce sont des vitesse Indiquées (IAS), ou des "vitesses vraies" (TAS)
2- Roc = Rate of Climb ?, c'est supposé être équivalent à l'Excess Specific Power ?

[Pachy]

Juste une ou deux questions (n'ayant pas le Docavia sous la main et etant peu familier des perf des avions de cette époque),
1 - les vitesses que vous donnez pour chaque altitude, ce sont des vitesse Indiquées (IAS), ou des "vitesses vraies" (TAS)

Autant que je sache, les perfs des avions français de l'époque sont données en vitesses vraies, sauf dans les consignes particulières à telle ou telle phase du vol, du genre "ne pas entamer une boucle à moins de 300 km/h au badin".

2- Roc = Rate of Climb ?, c'est supposé être équivalent à l'Excess Specific Power ?

Pour moi c'est un taux de montée en m/s.

[viso]

I have a performance curve from the docavia , but no scanner

Performances data for the number 242 from 1941 tests :
0 m, max vel = 362 km/h
1000 m : 381 km/h,
2000 m : 400 km/h,
3000 m : 420 km/h
4000 m : 440 km/h
5000 m : 460 km/h
6000 m : 450 km/h
7000 m : 440 km/h
8000 m : 422 km/h

For the number 1 (1938 test) :

0 m, max vel = 389 km/h roc = 5.4 m/s
1000 m : 410 km/h, 5.7 m/s
2000 m : 400 km/h, 6.1 m/s
3000 m : 432 km/h, 6.5 m/s
4000 m : 478 km/h, 6.7 m/s
5000 m : 500 km/h, 5.7 m/s
6000 m : 490 km/h, 4.5 m/s
7000 m : 478 km/h, 3.0 m/s
8000 m : 460 km/h, 2.0 m/s
9000 m : 432 km/h, 0.7 m/s

Absolute ceiling seems to be around 9400 m roc = 0, max speed = 420 km/h

The difference between the two speed trials is very interesting. The 1941 data confirms to the aerodynamics formulas and results in a drag profile that is similar to a P-38. Such a drag profile suggests a very streamlined design for a medium twin-engine bomber. By comparison, a Ju-88 has almost twice as much drag.

Unless someone can propose a compelling argument, I think that the 1% flight model should incorporate the 1941 speeds of 362 KMH at sea-level and 460 KMH at altitude.

[Pachy]

Such a drag profile suggests a very streamlined design for a medium twin-engine bomber. By comparison, a Ju-88 has almost twice as much drag.

Not surprising, the protruding canopy and bombardier gondola must generate a lot of parasitic drag. The LeO is comparable, but much cleaner.

Unless someone can propose a compelling argument, I think that the 1% flight model should incorporate the 1941 speeds of 362 KMH at sea-level and 460 KMH at altitude.

My only problem is that this specific test, done a on a 2 year-old, battle-weary example, falls below acceptance test criteria. If a brand new example exhibited such poor performance, it was in theory to be sent back to the factory for fixing...

[Gerfaut]

Hmmm... He's not wrong, Craig.
Well, if not, at least it looks like an admissible argument. One could hardly imagine servicing such a brand new bomber aircraft not fulfilling its acceptance criteria close to theoretical bombing altitude.
Do you think that it might be a major concern for AvH guys to take into account fresh from factory specs ? I mean, even given the atypical drag seen on the LeO ?

[viso]

The fundamental problem is that the physics just don't make sense at the higher speeds. To achieve 500 KMH, either the LeO needed 1500 HP engines or it had to have had a drag profile something like the darts they use in pubs. At 460 KMH, we see a combination of HP, speed, and drag that makes sense.

All of this keeps reminding me of the MS-406 speed issue. All of the 'official' data said 305 MPH but the real top speed was more like 285 MPH. It came down to pilot accounts (from Finland), which were definitely real world measurements. The same might be said of the 1941 measurements.

Well, what are the alternatives? Can we find any other documented facts such as pilot accounts perhaps?

----------------------------------------

By the way, AvHistory was very appreciative of (and very impressed with) the other detailed LeO data that was posted. They'd love to get their hands on similar data for the Br-693, Po-63.11, and Po-631. I'll make separate posts for these requests. Looks like we could have 1% flight models for most French aircraft in 2007.

[Pachy]

The fundamental problem is that the physics just don't make sense at the higher speeds. To achieve 500 KMH, either the LeO needed 1500 HP engines or it had to have had a drag profile something like the darts they use in pubs.

Are you sure you don't trust your computational model too much? Anyway, I am not suggesting we use the values from the prototype...

Personally, I like this little data sheet from the MAE a lot:

with a gross weight of 10850 kg:
370 km/h @ sea level
470 km/h @ 5000 m
Climb to 4000m in 11'

It just sounds "right" considering the comparative tests with the early MB.152 and the memoirs of test pilot Jacques Lecarme, who is very much qualified since he trained pilots on the type and also flew in combat with it!

Ideally, the 1941 and 1942 data mentioned by Cuny and Danel would be interesting to have a look at, but unfortunately none of them are with us still, and many of their personal archives were lost... so finding the original data may be either very painful, or downright impossible.

[moi1000]

The fundamental problem is that the physics just don't make sense at the higher speeds. To achieve 500 KMH, either the LeO needed 1500 HP engines or it had to have had a drag profile something like the darts they use in pubs. At 460 KMH, we see a combination of HP, speed, and drag that makes sense.

All of this keeps reminding me of the MS-406 speed issue. All of the 'official' data said 305 MPH but the real top speed was more like 285 MPH. It came down to pilot accounts (from Finland), which were definitely real world measurements. The same might be said of the 1941 measurements.

Well, what are the alternatives? Can we find any other documented facts such as pilot accounts perhaps?

----------------------------------------

By the way, AvHistory was very appreciative of (and very impressed with) the other detailed LeO data that was posted. They'd love to get their hands on similar data for the Br-693, Po-63.11, and Po-631. I'll make separate posts for these requests. Looks like we could have 1% flight models for most French aircraft in 2007.

I'm not surprised by these data. The Bloch MB157 (with a Gnome-Rhône 14R) reached 712 km/h in 1942 !!!
The first german aircraft with this speed was probably the Fw190D, 2 years later.

[moi1000]

Peut-être serait-il bon de faire un topic sur le forum Aviation Passion ?
Qu'en pensez-vous ?

[viso]

Update: AvHistory continues to wrestle with this one. The speed issue remains unresolved but they are very interested in some of the historical factors set forth so far. Excellent discussion.

[Pachy]

Update: AvHistory continues to wrestle with this one. The speed issue remains unresolved but they are very interested in some of the historical factors set forth so far. Excellent discussion.

How can we take part in their discussion?

[viso]

How can we take part in their discussion?

Actually, you already are - although not directly.

The current discussion occurs in the Desert Rats forum, which unfortunately is not a public forum. The MAW members use it to communicate regarding the project. Thus far, I've been swapping info between that forum and this one. 95% of the discussion is going on at Check-Six and I'm keeping you updated on the other 5%.

[jeanba]

All of this keeps reminding me of the MS-406 speed issue. All of the 'official' data said 305 MPH but the real top speed was more like 285 MPH. It came down to pilot accounts (from Finland), which were definitely real world measurements. The same might be said of the 1941 measurements.

As to the MS-406 issues :
Switz figures give 475 km/h for numbers 601 and 602 (J1 & J2 according to switz names).
The D-3800 (license built MS406) gives the same figures (but there may be some differences on the design of the D-3800) : maybe some "switz values" can be obtained to help and understand ?
The available aerodynamical data are consistant with those values.
On the other hand, if you use the "finnish values" to compute the aerodynamical and engine characteristics, you will find some inconsistancies.
My two cents of € hypothesis is that the theoretical maximum values are the highest ones (they are ok for aerodynamics values), but due to cowling problems, the engine could not maintain its maximum power for long enough in a "clean" (ie : radiator retracted) configuration to reach this maximum value.
This hypothesis is based on repetitive accounts of this type of problems for most french aircraft and particularily on the Morane by various sources, including finnish pilots.