# Power-augmented ram (PAR)

> What is power-augmented ram (PAR) take-off?

- Category: Aircraft design › Ground-effect design
- Kind: Standard part
- Basis: Design rules and figures from the cited sources; example geometry by Xem Studio
- Page: https://xemstudio.com/objects/power-augmented-ram-par/ · JSON: https://xemstudio.com/api/geometry?object=power-augmented-ram-par · Plain text: https://xemstudio.com/objects/power-augmented-ram-par/sheet.txt
- License: dimension sheet CC BY 4.0 (Xem Studio); files Xem Studio Design License (free to use and sell from, not to redistribute as files: https://xemstudio.com/license/)
- Use in every chat: add https://xemstudio.com/mcp as a connector (https://xemstudio.com/use-with-ai/)

**Exact dimensions.** True size, with no printing tolerance added.

## Notes

- PAR aims engine exhaust under the wing so it is trapped by endplates and a deflected flap, forming an air cushion that lifts the craft off the water before it reaches flying speed; near the ground lift comes mainly from that cushion (NASA TM-78793).
- In NASA tests, flap deflection beyond about 20 deg dropped the flap trailing edge below the endplates and lost the cushion; trapped efflux cut forward thrust to about two-thirds of fan thrust (NASA TM-78793).
- Soviet craft used dedicated PAR engines: Orlyonok had two 10 t PAR engines plus a 16 t cruise turboprop; Kaien-2 reached take-off CLmax 1.9 at 15 deg pitch-up, about four times cruise (Rozhdestvensky).
- Used on: Orlyonok, KM (Caspian Sea Monster), Loon, Kaien-2.
- The file is a reference example built by Xem Studio from the numbers above. Sizes the sources do not fix are illustrative; scale the example to your own vehicle.

## Sizes

| parameter | value or range | source |
|---|---|---|
| NASA model wing | 1 m chord x 2 m span (AR 2), Clark-Y 12% | NASA TM-78793 |
| Fan position | about 0.76 chord ahead of LE (4 exit diameters) | NASA TM-78793 |
| Flap limit for cushion trapping | ~20 deg (flap TE meets endplate bottom) | NASA TM-78793 |
| CL with 19 deg nacelle, 10 deg flap, CT 1.6 | ~3.5 at ~20 deg AoA | NASA TM-78793 |
| Forward thrust with trapped efflux | ~2/3 of fan thrust | NASA TM-78793 |
| Test heights | 0.08-0.50 spans | NASA TM-78793 |
| Kaien-2 take-off CLmax | 1.9 at 15 deg | Rozhdestvensky 2006 |
| Reference build | span 400, chord 200 (1:5 of NASA model), endplates 30 | computed |

## Where the files are

- NASA Langley / DTNSRDC (Thomas, Paulson & Margason): [Powered Low-Aspect-Ratio Wing in Ground Effect (WIG) Aerodynamic Characteristics, NASA TM-78793 (1979)](https://ntrs.nasa.gov/api/citations/19790022970/downloads/19790022970.pdf) — web — Publisher's page; dimensions are facts
- Progress in Aerospace Sciences (K.V. Rozhdestvensky, 2006): [Wing-in-ground effect vehicles (review)](https://www.hassanhameed.com/wp-content/uploads/2016/01/wingingroundeffectvehicles-130120003005-phpapp01.pdf) — web — Publisher's page; dimensions are facts

## Free STEP/STL (1 parts, Xem Studio Design License, Xem Studio)

Index: https://xemstudio.com/files/hardware/power-augmented-ram-par/index.json · license: https://xemstudio.com/files/hardware/power-augmented-ram-par/LICENSE.md

- power-augmented-ram-par-wing: [STEP](https://xemstudio.com/files/hardware/power-augmented-ram-par/power-augmented-ram-par-wing.step) · [STL](https://xemstudio.com/files/hardware/power-augmented-ram-par/power-augmented-ram-par-wing.stl) — power augmented ram: span 400, chord 200 mm, anhedral 0°, endplates 30 mm (scale to your craft)

## Questions

**How much flap for PAR?**

About 20 deg in NASA's tests; more lets the flap drop below the endplates and spill the cushion (TM-78793).

## Fits with

- [Ground effect: height/span ratio and induced-drag reduction](https://xemstudio.com/objects/ground-effect-height-span-ratio/)
- [Ground effect: height/chord ratio (ram / chord-dominated regime)](https://xemstudio.com/objects/ground-effect-height-chord-ratio/)
- [Lippisch reverse-delta ground-effect craft](https://xemstudio.com/objects/lippisch-reverse-delta-wig/)
- [Ekranoplan layout (low wing + high tailplane out of ground effect)](https://xemstudio.com/objects/ekranoplan-wing-tail-layout/)
- [Tandem-wing ground-effect craft (Jorg type)](https://xemstudio.com/objects/tandem-wig-configuration/)
- [Endplates on ground-effect wings](https://xemstudio.com/objects/wig-endplates/)