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1:3 or 1:2.5 reductor


miromst
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Miro

Depends a bit on what you are trying to achieve. 3/1 will let the engine rev more than a 2-5/1 reduction. 3/1 might be better if you intend turning a big 130 prop, especially if the pitch is steep. Also, slower revving props tend to be quieter.

From my own experience with the 200 Simonini, and watching my friends with their Simmos struggle to get a fuel burn of less than 6 ltrs/ hour (2.5/1 reduction) I would plump for the 3/1 if using the Simonini 200. I used to average around 4 ltrs/hour and sometimes got down to less than 3.5.

Not sure if the above would apply to other motors but that's my experience with the Simmonini.

Pete was right really. You didn't need to know.....but now you do :)

Dave

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As Dave said if you want to get in to playing about with reductions it can be very time consuming and expensive due to having to have different props.

Paramotor manufactures have sort this out for you, it may not be ideal but it is close enough for what we need and use.

Pete

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Dear Dave and Pete,

Thank you both for your honest replies.

Dave, my6 weight is approx 85 kg. I want to do mostly cross country flying but prefer to have always a spare power. Don't have to use it all the time but want to have it.

So far I have some experiences with paragliding, 10 years gliding and little experience with microlights. I love flying and as I am very busy I can't afford to spend all days on the airfield or on the hill. Also affordability, I think that this is the most affordable motor flying financially and for the storage space too.

It is my nature to learn, understand and read about everything before I buy or do anything. That is the reason I have a lot of stupid questions sometimes.

Anyway, thank you again for your answers.

Miro

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  • 3 weeks later...

rpm, prop speed, engine output are all part of one equation.

When I ordered my motor I specified 3.1:1, but it was shipped with 2.34:1.

The result was the prop limited output to 16HP of the 26HP the engine was capable of.

While this is great for economy, it limits thrust and therefor climb rate.

Some manufacturers build their combinations for longevity, sacrificing some performance in doing so.

Owners can reprop to a lower pitched propeller to regain some of the HP hidden in lower rpm limited props, but even so it's a trade off and efficiencies vary simply due to how fast you fly on average (fast/slow trim).

I didn't check my redrive prior to first flight, assuming the manufacturer shipped what I asked for.

The result was inability to resist sink that would have been easily dealt with otherwise.

Thrust curves climb steepest toward the highest end of the rpm range due to the cube law, so whatever limits your rated engine rpm holds you back from using all your engine's power. Some people prefer this for economy, engine longevity and noise. Others feel cheated and dissapointed, and replace redrives, props or both to get all their engines can deliver with a squeeze of the throttle. Deciding which you are may not happen until you have some experience on several combinations to compare, and expect it to change as your skills do.

See for yourself:

[youtubevideo]

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