Engineering an Inclined Wind Tunnel: Designing Airflow at 30°–45°
How an inclined wind tunnel works: flow decomposition, working-zone length, turning vanes at non-standard angles, safety systems and what drives the cost.
For thirty years, indoor flight meant one thing: a vertical column of air holding a body against gravity. You could fall beautifully, but you could not go anywhere.
The inclined wind tunnel changes that. Tilt the flow, and the same aerodynamic trick that supports a body in free fall also reproduces forward glide — which is the entire point of a wingsuit. It is the youngest branch of the industry, there are only a handful of facilities worldwide, and most of the engineering questions are still genuinely open.
This article is about those questions.
1. The physics: one vector, two jobs
In a vertical tunnel, drag balances weight and the flyer's horizontal velocity is zero. Tilt the flow by an angle and it decomposes into two components that do different work:
- the vertical component still carries the flyer's weight, exactly as before;
- the horizontal component supplies the relative wind of forward flight, so a wingsuit pilot can hold a glide instead of merely falling.
The tilt required is not arbitrary — it follows from the glide performance of the wingsuit. A suit flying at a glide ratio of roughly 2:1 to 3:1 needs a flow inclination consistent with that ratio for the flyer to sit in a stable, natural body position. Which means an inclined tunnel is not "a vertical tunnel on a slope": the angle is a design parameter tied to the discipline it serves, and adjustable-angle designs exist precisely because different suits and skill levels want different conditions.
For reference, the world's first inclined facility — Inclined Labs' Indoor Wingsuit Stockholm at Bromma — operates a flight chamber 16.5 ft wide and 33 ft long, with flyers typically working at 90–130 km/h, and with both speed and incline adjustable. The first indoor wingsuit flight there took place in April 2016 in a full-scale prototype chamber, and the facility opened to customers in September 2017.
2. Why it is harder than a vertical tunnel
The working zone has to be long. A glide needs space along the flight path, not just above the flyer. That single requirement drives the building: the chamber becomes a long inclined volume rather than a compact column, and every metre of it has to hold flow quality.
Wall boundary layers grow along that length. In a long test volume, the effective flow area shrinks as boundary layers thicken, and the free-stream accelerates if the duct is prismatic. Getting a uniform speed from entry to exit usually means deliberately shaping the section along the working zone.
Corner vanes work at angles they were never tabulated for. Vertical tunnel circuits are built from well-understood 90° corners with cascade turning vanes whose loss coefficients are known. Incline the circuit and the corner angles change, the flow arrives at the cascade differently, and the vane chord, spacing and camber all have to be re-solved rather than copied. Get it wrong and you pay twice: in pressure loss, hence fan power forever, and in flow non-uniformity that the flyer feels directly.
Safety systems exist in more than one plane. In a vertical tunnel, the net is below and the flyer's failure mode is a controlled landing. In an inclined chamber, a flyer who loses lift moves along the incline as well as down it — so catch systems, netting and access have to be solved at both ends of the working zone and along its length.
Entry and exit are a design problem, not a door. Getting a pilot in wingsuit gear into a moving inclined flow, and out again, without stopping the tunnel for every flyer, defines the commercial throughput of the whole facility.
3. The decisions that shape the project
- Fixed or adjustable incline. Adjustable geometry widens the addressable market — different suits, beginner and expert conditions, non-wingsuit disciplines — and adds mechanical complexity, sealing challenges and cost.
- Chamber cross-section. Sets the maximum wingspan in flight, the number of simultaneous flyers, and directly drives fan power.
- Speed range and stability. The controlled range matters more than the top number: coaching happens at the low end, and step changes must be smooth.
- Circuit architecture. Closed loop for energy and temperature control, with all the vane questions above; open circuit is simpler and rarely economic at these run hours.
- Cooling. Fan energy becomes heat in the air. The strategies are the same as elsewhere — passive ventilation where climate allows, active heat exchange where it does not — and the trade-offs are in
.
- Instrumentation for coaching. Camera coverage, telemetry and video review are not extras here: in a discipline this young, the instruction product is a large part of the revenue.
4. What it does to the building
An inclined tunnel is the most demanding of the three architectures to site, because it needs both length and height — a vertical tunnel's structural depth combined with a horizontal tunnel's footprint. Two consequences follow.
First, site selection precedes design . Ceiling height, span, foundation capacity and available electrical power constrain the achievable chamber before any aerodynamic work starts.
Second, existing industrial buildings are a real option . The Stockholm facility is housed in a Bromma structure originally built for military aviation research in the 1930s-1940s — a reminder that large old halls with generous height and heavy floors are exactly the stock this industry can reuse. The retrofit path has its own trade-offs, which we cover in
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5. Where the cost actually sits
Broadly, the cost drivers are the same as for a large vertical tunnel — drive power, ducting, structure, safety systems — with two additions specific to the inclined case: the longer working zone (more duct, more structure, more area to keep uniform) and the vane and geometry engineering that cannot be inherited from an existing product line.
What that means commercially: inclined tunnels reward custom engineering and punish catalogue thinking. There is no standard model to scale up or down, because there is not yet a standard. That is a risk for a buyer who wants a fixed price on day one, and an advantage for one who wants a facility differentiated from every other attraction in the market.
For where an inclined facility sits against the other architectures, see our
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6. What we ask before quoting
Five inputs decide the concept: the available building envelope, the target flyer profile (beginners, sport wingsuit pilots, professional or military training), whether the incline must be adjustable, the number of simultaneous flyers, and the target throughput per day. Everything else — power, chamber dimensions, vane design, cooling strategy — follows from those.
We design, manufacture, install and commission custom wind tunnel systems, including inclined configurations, with single-point responsibility from concept to handover. Send us your building and your flyer profile and we will come back with a concept layout and a power estimate. Related reading: our articles on
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[Article not found: indoor-wingsuit-facility-economics].
Sources and notes
- Reference facility data — chamber 16.5 ft wide × 33 ft long, typical flight speeds 90–130 km/h, adjustable speed and incline, first indoor wingsuit flight April 2016, opening to customers September 2017, Bromma building originally constructed for military aviation R&D in the 1930s-1940s: Indoor Wingsuit Flying Stockholm, Indoor Skydiving Source, Indoor Wingsuit Flying Just Became a Reality, Inclined Labs.
- Wingsuit glide ratios of roughly 2:1 to 3:1 are the commonly quoted performance band for modern suits and vary widely with suit, pilot and technique; treat as indicative, not as a design specification.
- Engineering discussion (working-zone length, boundary-layer growth, vane redesign at non-standard corner angles, multi-plane safety systems) is TunnelTech engineering practice.
- Earlier internal drafts quoted a horizontal component of 100–160 km/h and working-zone lengths of 8–15 m. The published reference facility operates at 90–130 km/h in a 10 m chamber; use the verified figures.