A049

MAKE: SynchroLite ~ Engine

General

Orientation:

Degrees off the 3 planes for engines.

X-axis	YZ plane (for-aft) (roll)	12.5 degrees
Y-axis	XZ plane (side-side) (pitch)	0.0 degrees?
Z-axis	XY plane (vertical) (yaw)	22 degrees (approx.)

The carburetors must be vertical.

Mounting carburetor on 90 degree elbow below engine

Note Ultrasport has horizontal engine cylinders and extended manifold on one.

John Alevaras questioned-

1/ will oil, which is heavier, get to crank &

2/ may change operation (possible leaner) because of greater distance of carburetor from engine.

Look into Tuned intake manifold / Tuned induction

Fuel Injection

I read somewhere that fuel injection reduces fuel consumption by up to 25%. With the ultralight 5-gallon limitation this might be a big deal. It was mentioned that the engines will run cooler also, but if the mix is leaner won't the engines run hotter?

The Hirth 2706 can now be purchased as fuel injected. This is the engine used on the Ultrasport 331. The F-33 is has the same head, cylinder and piston as the 2704. All 3 engines have cylinders of 313 cc. Perhaps the fuel injection could be adapted to the F-33?

Make & Model

Hirth F-33

Hirth F-33B

Power (max.) 25 hp @ 6000 rpm w/ 21 ft-lb of torque

May be more at later date, with tuned exhaust etc. See Hirth South Africa web page.

September 29, 1999

Based on Sportscopter 254 w/ Hirth 2703

Minimum Mean Maximum

Engine RPM 4800 57-5800 6503 (114%)

Consider buying 1 or 2 of the shrouds that is used on the 2704 or 2706 engine, and modifying it.

Note: The Hirth F-33B has a larger head and does not need a fan if mounted in front of or behind a prop.

Sportscopter said that they went for Hirth's engine over Rotax's since the Hirth's power curve was flatter at the top and was therefore easier for the pilot to pick up loss rpm.

Zanzottera MZ34

Zanzottera MZ34i

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Newsletter exchange:

from Eric Braeden:

> I don't know if this applies for a scaled down ship, but a rule-of-thumb for large dual engine helicopters I have heard is that the remaining engine in a single engine failure code is required to provide 75% of the power required of BOTH engines in full gross weight takeoff configuration. If your design required 22 HP from each F-33 for takeoff, you would need on the order of 33 HP from the remaining engine. The Hirth HP curves for the F-33 would seem to show that's not possible.

my Reply

The full gross weight takeoff horsepower from blade element calculations is 34.8hp. 75% of this will be 26.1hp. The new version of the F-33 is 25hp so this does not seem to be too bad.

Further thoughts:

This works out to (550/34.8) = 15.8 lb/hp. Ultrasport says that they have a high rotor efficiency and get 14 lbs of lift for each horsepower, partially due to low disk loading. Their disk loading is 1.5158 lb/ft2 and the SynchroLite effective disk loading is slightly higher at 1.6248 lb/ft2. This brings my above calculations into question. The lack of a tail rotor on the SynchroLite will help a little. Note: The old Kaman K-225 had a maximum gross weight of 3000 lbs and 225 horsepower for 13.33 lbs of lift for each horsepower.

Mounts:

Engines should be on rubber mounts; I think. Lord mounts?

The following was in a newsgroup;

Stan Robinson's engine vibration dampening technique for the Rotax work on your Hirth?

Coupling:

Engine should have device to isolate transmission from engine radial (rotational) shock (spikes). If V-belt and pulleys are used, then this should do. It looks like the Goodyear EAGLE is to be used and it offers no shock absorption therefore spring and dampening must be incorporated in the driven sheave.

Potential Damage:

Could cold rain hitting the hot engine crack the head or cylinder?

Last Revised: July 21, 2001