avi sirota

Hello,
Ill appreciate info about topics related to twins.
1. In a big planed twin project, powered by 2 DA85, how can I keep the platform relatively straight flight if one of the engines fail? Adding to the implemented rudder angles I thought using a gyro for rudders.

2. Is it posible to change rotation direction in a DA 85?

Thanks,
Avi

R8893

My Feedback: (20)

AVI,
I reversed the rotation of a DLE 35 and the method should work on any reed valve engine. If the Hall effect sensor is placed on the engine so that it is the same number of degrees after top dead center as the factory sensor is before top dead center the ignition will be timed for the engine to run in reverse. The reed valve doesn't know which way the engine is turning. Rather than try to drill new mounting holes for the sensor, I purchased an aftermarket Hall effect sensor that attaches to the crankcase with a worm drive clamp. I also made a small fixture to help accurately locate the new sensor.

One major drawback to this is that a pusher propellor is required and they are very hard to acquire.

I son't have any experience with gyros on my twins, so can't comment on that.

Chuck

RCFlyerDan

My Feedback: (54)

Avi,

Desert Aircraft is great with customer service. They may even do the mods for you for free. They normally only charge for parts.

A gyro may help on takeoff if it is on “Attitude Hold”, but in normal cruise flight, regular gyro setting is better. Attitude Hold wants to fly the plane in the last “attitude”, and doesn’t want to turn. Let’s say you want to turn left in the pattern. Giving left aileron for the turn, the rudder still wants to hold heading. So, you end up with cross control. Which on a single engine is a disaster. Putting a mix of aileron to rudder might help, but I am not sure.
You would be better off having a sensor that detects engine loss and reduces the good engine to idle and treating it as a dead stick. Most wreck their plane when trying to fly it out on takeoff. Loss of engine in cruise is easier for the one landing approach. Trying to do a go around is always a mistake. Watch YouTube.

avi sirota

Thank you both, Chuck and RCflyerDan.

I was thinking of using the gyro someway slaved to the RPM from both engines to be triggered only if one engine down.
Avi

avi sirota

Thank you both, Chuck and RCflyerDan.

I was thinking of using the gyro someway slaved to the RPM from both engines to be triggered only if one engine down.
Avi

RCFlyerDan

My Feedback: (54)

I think that it is Down and Lock that has a brake controller that does directional control with the brakes and gyro. It’s beyond me how to make it work with engines.

avi sirota

Any other aspects or things i should take under consideration with a big twin?
Avi

RCFlyerDan

My Feedback: (54)

If the plans don’t have it already built in, both engines should have out thrust. The right engine should have maybe a degree more right thrust, then the left engine thrust. Ex: Left engine has 2 degrees Left thrust, Right engine should have 3 degrees right thrust. This is to counteract P-Factor and loss of engine. This is all just....IMHO.
I’m sure others will chime in too.

R8893

My Feedback: (20)

Avi,
What is the model you are planning to build? If it is to be scale I would align engines the same as the full-size for appearance sake. I have built several twins, although no where near as big as you are planning, and have always set the engines straight ahead.

As the carnival barker says: "You pay your money, and you take your chances."

Chuck

avi sirota

Thanks guys.
It is a joint project with friends.A 1/4 P38 powered by 2 DA85. Don't remember the name of the designer. Ill have s look later.
Avi

RCFlyerDan

My Feedback: (54)

Avi,

I would strongly recommend a twin sync. Read up on the benefits. And the downside.

https://www.bigplanes.nl/contents/en...chronizer.html

avi sirota

Thanks RCFlyerDan.
Avi