B25 Landing Speed Calculator

This calculator estimates the landing speed of a North American B-25 Mitchell bomber based on its landing weight, wing area, and air density. You enter the aircraft’s weight in pounds, the wing area in square feet, and the air density ratio (or use the default sea-level value), and the calculator returns the stall speed in knots and the recommended landing speed (typically 1.3 times stall speed). The result is a theoretical figure; actual landing speeds vary with flap settings, pilot technique, and atmospheric conditions.

Formula

The stall speed is calculated using the standard lift equation solved for velocity:

V_stall = sqrt( 2 × W / (� × S × C_L,max) )

Where:

• W = landing weight in pounds (lb)
• Ï� = air density in slugs per cubic foot (slugs/ft³)
• S = wing area in square feet (ft²)
• C_L,max = maximum lift coefficient (assumed 1.5 for a flapped configuration)

The calculator uses the sea-level standard air density of 0.002378 slugs/ft³ and multiplies it by the density ratio you enter. The result is converted from feet per second to knots by dividing by 1.68781 (1 knot = 1.68781 ft/s).

Worked Example

Using the default values: weight = 25,000 lb, wing area = 610 ft², density ratio = 1.0 (sea level).

1. Air density � = 1.0 × 0.002378 = 0.002378 slugs/ft³
2. Lift numerator: 2 × 25,000 = 50,000 lb
3. Denominator: 0.002378 × 610 × 1.5 = 2.17687
4. Fraction: 50,000 / 2.17687 = 22,968.6
5. Square root: sqrt(22,968.6) = 151.55 ft/s
6. Convert to knots: 151.55 / 1.68781 = 89.8 knots
7. Landing speed (1.3 × stall): 89.8 × 1.3 = 116.7 knots

The calculator displays 89.8 knots stall and 116.7 knots landing speed, matching the above steps.

Why the B-25’s Landing Speed Matters

The B-25 Mitchell is a medium bomber with a relatively high wing loading compared to light aircraft. Its landing speed directly affects runway length requirements, approach angle, and safety margins. Knowing the approximate landing speed helps pilots plan approaches, especially when operating from short or rough airstrips common in Pacific theater operations. For modern operators of restored B-25s, this figure guides training and operational limits.

Factors That Affect the Real Landing Speed

The calculator gives a theoretical value, but actual landing speeds vary due to:

• Flap setting – Full flaps increase C_L,max and lower stall speed. The default assumes full flaps (C_L,max = 1.5). With no flaps, C_L,max drops to about 1.2, raising stall speed by roughly 12%.
• Weight – Heavier landings (more fuel, bombs, or cargo) increase stall speed proportionally to the square root of the weight change.
• Air density – Hot days or high-altitude airports reduce air density, increasing the required speed.
• Wind – A headwind reduces groundspeed but not indicated airspeed; the calculator gives true airspeed, not groundspeed.
• Pilot technique – Crossing the threshold too fast or flaring too high can add 10–20 knots to the touchdown speed.

How to Use the Calculator for Planning

To get a useful estimate, follow these steps:

1. Determine the landing weight – subtract fuel burned and any jettisoned ordnance from takeoff weight. A typical B-25J empty weight is about 20,000 lb; with fuel and crew, landings often occur around 24,000–28,000 lb.
2. Enter the wing area – 610 sq ft is standard for all B-25 variants.
3. Adjust density ratio – for sea level, use 1.0; for a 5,000 ft elevation airport, use about 0.86; for a hot day at 10,000 ft, use about 0.74. (These are approximate values from the standard atmosphere.)
4. Read the stall and landing speeds – the landing speed is 1.3 times stall, a typical safety margin for transport/bomber aircraft.

Common Mistakes and Misconceptions

One frequent error is confusing indicated airspeed (IAS) with true airspeed (TAS). The calculator outputs true airspeed. At sea level they are equal, but at altitude or on hot days, IAS will be lower than TAS. Pilots use IAS for the actual approach, so they must correct for density altitude.

Another misconception is that the B-25 has a “fixed� landing speed. In reality, it varies with weight and configuration. For example, a lightly loaded B-25 at 22,000 lb with full flaps stalls at about 84 knots, while a heavily loaded one at 30,000 lb stalls near 98 knots. The difference is significant for runway planning.

Also, the calculator assumes a maximum lift coefficient of 1.5, which is typical for a flapped aircraft but not exact for every B-25. The actual C_L,max may be slightly higher or lower depending on the specific airframe and flap design.

Comparison with Other WWII Bombers

To give context, here are approximate stall speeds (full flaps, sea level, typical landing weight) for similar aircraft:

• B-25 Mitchell (25,000 lb) – ~90 knots
• B-26 Marauder (27,000 lb) – ~95 knots (known for higher wing loading)
• A-20 Havoc (18,000 lb) – ~85 knots
• B-17 Flying Fortress (45,000 lb) – ~95 knots (much heavier but larger wing)

The B-25’s landing speed is moderate for its class, but its relatively short wingspan (67 ft) gives it a higher wing loading than the B-17, making approaches slightly faster and requiring more attention to speed control.

Safety and Operational Limits

Landing speed directly affects safety margins. Exceeding the calculated landing speed by even 10 knots increases the landing distance significantly – roughly 20% more runway needed. For B-25 operators, the POH (Pilot’s Operating Handbook) provides specific speed schedules; this calculator is a planning aid, not a substitute for official data. Always consult the aircraft’s manual and check the actual airspeed indicator during approach.

Also note that the calculator does not account for ground effect, which reduces induced drag and can allow a slightly lower touchdown speed. However, the effect is small (1–3 knots) and not critical for planning.

Frequently Asked Questions

What is the normal landing speed of a B-25?

At a typical landing weight of 25,000 lb, full flaps, sea level, the stall speed is about 90 knots and the recommended landing speed is about 117 knots (135 mph). Many pilots report touching down at 100–110 knots indicated, depending on weight and wind.

Does flap setting change the landing speed?

Yes. With no flaps, the maximum lift coefficient drops to about 1.2, which raises the stall speed by roughly 12%. For the same weight, stall speed would be about 101 knots instead of 90, and landing speed about 131 knots. Full flaps are standard for landing.

How does altitude affect the landing speed?

At higher altitude, air density is lower, so the aircraft must fly faster to generate the same lift. At 10,000 feet density altitude, the air density is about 74% of sea level, which increases stall speed by about 16%. For the B-25, that means stall speed goes from 90 to about 104 knots.

Why does the calculator ask for wing area when all B-25s have the same?

While all B-25 variants share the same 610 sq ft wing, including the wing area as an input makes the calculator generalizable. If you are working with a similar aircraft or a modified airframe, you can change it. For the B-25, you can leave it at 610.

Is the landing speed the same as approach speed?

No. Approach speed is typically 1.3 times stall speed, which is what the calculator outputs as “Landing speed.� The actual touchdown speed may be slightly lower because the pilot flares, reducing the descent rate and allowing the aircraft to settle just above stall. The 1.3 factor is a safety buffer for controllability and gust response.

Can I use this calculator for other aircraft?

Yes, if you know the weight, wing area, and adjust the maximum lift coefficient (not exposed here) to match the aircraft’s flap configuration. For most flapped aircraft, 1.5 is a reasonable default, but for unflapped or highly modified planes, results may be off by 10–15%.

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in weight | Landing weight (lb) | lb | 25000 | 0
in wing_area | Wing area (sq ft) | sq ft | 610 | 0
in rho_ratio | Air density ratio (sea level = 1) | - | 1 | 0.5
out stall_kts | Stall speed (knots) | kts | sqrt((2 * weight / (rho_ratio * 0.002378 * wing_area)) / 1.68781^2) | 1
out landing_kts | Landing speed (1.3 x stall) | kts | sqrt((2 * weight / (rho_ratio * 0.002378 * wing_area)) / 1.68781^2) * 1.3 | 1