914 power output

[Flyboy66]

I have seen comments about the 914 not being a linear power output or something of that nature. Can someone explain what this means? I have flown TSIO-360’s and TSIO-540’s before, so I am familiar with their characteristics and and wondering if the Rotax is similar or different.

Another comment said it had high power output for 5 minutes then fell off. Is that a time limit, a temp limit.......?

[Esser]

I’ve never been able to pin why the 115hp is a 5min limit but I suspect it’s heat.

Basically the 914UL is the core of a 912UlL which is an 80HP engine. The 914 turbos that engine and makes 100HP continuous at 100% power(36in). You can run 100% power all day on that engine if you wanted too. No matter how high you go in altitude, your engine makes that power until you are above 16,000’

The engine though has a 115% throttle setting. When you advance the throttle past 100% (this actually happens at 108%) the manifold pressure JUMPS to 40.5inches there is no I between 36 and 40.5. If you look at the power charts in the book, the manifold pressure line keeps going higher as you put in power but above 100%, that line shoots straight up. I think that’s what they mean by non linear.

You have to think of the engine as a 100hp engine at 100% throttle but had the ability to go to a 115HP at 115% throttle as a bonus for 5 minutes.

[Flyboy66]

So, if I had the throttle set for 100% and climbed, the manifold pressure stays constant unless I push the throttle in further? Is there any documentation that explains the system? I have looked in the Rotax Owners section and didn’t see anything other than charts, limits....


I think I did see that limit in the Rotax Owners stuff. Most of the engines I have operated (other than basic normally aspirated) have a 5 minute limit on takeoff thrust. As far why it is limited, that would be a question for the manufacturer.

[Ronin]

So, if I had the throttle set for 100% and climbed, the manifold pressure stays constant unless I push the throttle in further? Is there any documentation that explains the system? I have looked in the Rotax Owners section and didn’t see anything other than charts, limits....


I think I did see that limit in the Rotax Owners stuff. Most of the engines I have operated (other than basic normally aspirated) have a 5 minute limit on takeoff thrust. As far why it is limited, that would be a question for the manufacturer.
It is due to heat. I have run a 914 well over the five minute time limit, as long as the T&P's stay in the green the computer will not pull boost on you. Ivan Shaw of Europa used to run the Sun & Fun race wide open the whole time with a 914.

[Flyboy66]

It is due to heat. I have run a 914 well over the five minute time limit, as long as the T&P's stay in the green the computer will not pull boost on you. Ivan Shaw of Europa used to run the Sun & Fun race wide open the whole time with a 914.

Where did you find the information saying it is due to heat? The reason I ask is my current engine also has a 5 minute limit to takeoff. The temps are always within limits during takeoff and are not climbing during that period, so temperature does not appear to be the limiting factor. There may be other things that limit the time. If cylinder head temp was the only concern, there wouldn’t be a time limit, as a cylinder head temp limit would cover that concern.

[Esser]

The waste gate is controlled by the terminal control unit. It takes the data from all the sensors and constantly adjusts it to keep the MAP where it should be. As the intake manifold temps go up, the waste gate will slowly open making you lose power. This is the reason I put in my intercooler

[Flyboy66]

Josh,
I like to understand the systems on aircraft. Where can I find this information?

I would also like to see your intercooler. Is your engine a stock 914 that you have fitted with an intercooler, or did you buy an engine from Edge or other engine supplier?

[rv9ralph]

Go back to the Rotax-Owners website, look at the section on manuals, drill down to the 914 and look at the Operation Manual. The information on operating and limitations are there.

Ralph

[Esser]

Section 9-5 here:
http://www.aviasport.com/rotax/Documentacion_4T/Manuales/English/Manual_Ususario_914.pdf

I have a standard 914 with SDS fuel injection and an inter cooler I repurposed from a Subaru. I’m on my iPad at work and don’t have pictures with me. You can send me a private message with your phone number and I can text you some.

[Flyboy66]

Josh,

Thanks for the link. That is exactly what I wanted.

Steve

[Flyboy66]

Essex,

Can you tell me which intercooler you repurposed off a Subaru. Not sure if I will buy or build. Would like to see before and after.

Thx,

Steve

[Flyboy66]

Sorry, autocorrect struck again. That last message was for Esser.

[Esser]

It was off an EJ22R. If I were to do it again, I would buy something fromedge performance. Would have saved me a lot of time and cost about the same. Oh and lighter.