A073

A073

DESIGN: UniCopter ~ Landing Gear

Stability:

The US Army requires the helicopter to have the ability to land on a 15º slope.

Drag:

Consider making one or all the legs retractable.

For information on leg and wheel faring see Kitplanes May 2004 page 58. Have hard copy.

Parallel Skids:

The two legs have a streamline profile. The larger size results in a lower Reynolds' number.

The legs and skids are fiberglass and both flex.

The top of the leg is in the same location where the pilots forces are concentrated and possible bracing from the power train is concentrated.

The extra strength of the larger legs will be (partially?) offset by the reduced strength that must be taken out to the nose to accommodate a tripod arraignment.

The parasitic drag and negative pitching moment of the fuselage (& landing gear) will be reduced if the landing gear is retractable.

Tripod:

General Notes:

Have the rear legs support approximately 73% of the GW and the single front leg support 27%. The track and wheel base dimensions must give an overturn angle at less than 63º from the horizontal. [Source ~ CV p.52]

See temporary drawing Web Page / Working Data / CalVert.dc

See section below [Information for Determining the Location of Tripod Supports:]

A thought 8/15/04 Give the rear skids greater strength and perhaps 80% of the load, They would be fixed whereas the front skid would retract. The rear skids must extend back fare enough to stop the craft from tipping backward during a gust when the cockpit and fuel tank are empty .

Wheels:

Consider three wheels in lieu of skids. Two or all three could later be fully or partially retractable, should the UniCopter prove viable at high speed. The retractable wheels will also help improve Speed Stability. The nose wheel could be stored under the pilot's knees. In fact, all three wheels might go under the pilots knees. This may take the center of gravity too far forward.

Also consider 1 wheel and 2 skids or 1 skid and 2 wheels.

Extended wheels are said to have twice the drag of streamlined skids.

Information for Determining the Location of the Rear Tripod Supports:

From CH-83 Condor Report: http://web.nps.navy.mil/~brutzman/Savage/AircraftHelicopters/JhlHeavyLift-NPS/JointHeavyLiftHelicopterDesignReportMarch2003.pdf LANDING GEAR Section 3.4

Landing gear data was calculated using Roskam’s Airplane Design text (volume II, chapter 9). The basic layout of the landing gear will be a tricycle configuration, with a nose gear and a pair of main gears. Longitudinal tip-over criteria states that the main landing gear must be located behind the most aft c.g. location, usually at an angle of 15°. (See figure 3.4.1.) The most aft c.g. location of the Condor is in its empty condition (no fuel and no payload), in which case the c.g. is at FS 55. This puts the longitudinal position of the main landing gear at FS 56.5.

Figure 3.4.1: Longitudinal Tip-Over Criterion

Lateral tip-over criteria states that the main landing gear must be located such that the angle ψ is less than or equal to 55°. (See figure 3.4.2.) By placing the nose gear at FS8, this puts the lateral position of the main gear at 8.5 feet off the centerline, resulting in the main gear being located underneath the aft section of each sponson.

Figure 3.4.2: Lateral Tip-Over Criterion

Front: Arbitrarily placed at 60" ahead of the center of the masts.

Rear: Calculating using the above information:

At GW, the CG is 1" ahead of the masts.

At GW, the CG is 69.5" [ground to ctr.. of hubs] - 24.5" [below ctr. of hubs] = 45" above ground level.

At empty weight, the CG is 5214 in-lb / 769 in = 6.78" behind the masts.

At empty weight, the CG is 69.5" [ground to ctr. of hubs] - 19.06" [below ctr. of hubs] = 50.43" above ground level.

Figure 3.4.1: Longitudinal Tip-Over Criterion ~ Location behind centerline of masts = 6.78" + tan(15) * 50.43" = 20.3"

Figure 3.4.2: Lateral Tip-Over Criterion

tan(90-55) * 50.43 = 35.3"

Front skid contact point is 60" ahead of the center of the masts therefore the front skid contact point is 60" + 6.78" = 66.78" ahead of the CG.

Angle at nose is 90º - arcsin(35.3/66.78) = 31.9º

Rear skid lateral distance from the centerline is tan(31.9) * (60 + 20.3) = 50.0"

Note that the further ahead the nose wheel/skid is or the wider it is the less the tread width at the rear.

Interleaving with Wheels:

Consider mounting the main legs in the aerodynamic brace to the rotorhubs. Then consider having the wheels at the fuselage ende of the respective strut, or in the bottom of the fuselage.

General:

The rigid rotor will not provide forward thrust on the ground and therefor the craft will not ground-taxi.

The craft can be lowered from the 20.5" dimension and the support legs can be shorter because the propeller will be folding. This should be particularly good for the front leg.

Same Page ~ Different Craft: ~ SynchroLite

Last Revised: August 25, 2008