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Thread: Cruise rpm

  1. #31
    Senior Member av8rps's Avatar
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    Default Re: Cruise rpm

    Thanks for the compliment. Yeah, I love my little amphib too. The more I fly it the more impressed I am with it.

    Hopefully we can meet up next year at OSH.

  2. #32
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    Default Re: Cruise rpm

    Great information Paul

    Could you tell me what manifold pressures you find are acceptable both at high and low engine speeds. I have the same engine/prop combination on a Vixen but have not installed a manifold pressure gauge yet. Hopefully it will be in tomorrow`s mail.
    I do 118/120 mph at mid 5000`s on wheels and 1400 gross.

    Thanks for the info.

    Don

  3. #33
    Senior Member av8rps's Avatar
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    Smile Re: Cruise rpm

    In reply to Dons question about manifold pressure guages

    I'm sorry to have to tell you, but for the most part the vacuum manifold pressure gauge is useless. Mine will show 25" when the engine is loaded too light (prop pitch too flat) and only 27" when lugging overpitched at high throtttle settings. The range is so narrow that it is hard to tell a lot about how things are set.

    So I think to use one effectively a digital one with more accurate range readings would work better. But maybe there's something wrong with mine? Anyhow, it is still nice to have an idea of how you are generally set, but it sure doesn't work as effectively as the manifold pressure gauge on my lake amphib - that one works very well to help maximize the performance of the lycoming 0-360 and the hartzell constant speed prop. It will show manifold pressure readings from 15" to 30", so the readings make it quit obvious how things are set.

    All that said, in my opinion the best way to fly these IVO IFA's is to just pay attention to what your engine is telling you. You should be able to feel when the engine is lugging too much, and you can also tell when the prop is too flat. In reading some of the other posters rpm numbers and fuel burn, and knowing how my engine reacts to a variety of rpm and prop pitch settings, it is apparent there are a lot of guys flying around with props that are not pitched for maximum efficiency.

    More on the discussion about using lower rpms - I simply follow Rotax's information that says 5000 rpm is a 75% power setting, 4800 represents 65%, 5500 represents 100% cruise power, and 5800 is your max rpm for limited periods such as takeoff and max climbs. And that you should NEVER run a 912 more than 5800. (if you do Rotax highly recommends tearing it down to inspect for damage). All that said, I can't imagine Rotax supporting policies that would indicate you can only run their 912 at 75% or higher power settings. If that is true, it would amke their venerable 912 engine sale-proof when compared to other aircraft engine choices. Who would buy an engine with such limited operational requirements? Sure, a lot of aircraft have specific operational limitations, but to have an engine that shouldn't be operated at less than 75% power just doesn't sound right, or make sense to me. So however all that discussion got going, I'm sure somewhere along the line something was misunderstood or overstated. If this really bothers us (it doesn't bother me whatsoever fwiw), then should seek the advice of a qualified expert from Rotax. But since it doesn't bother me at all, I'm just going to keep all I've learned in this thread in the back of my mind should I ever need it. While I think it is unlikely that I will ever need it, I'm old enough to admit that I'm still always learning, and therefore sometimes wrong.

    Last subject - C'mon, we all just need to get along;
    Now I don't mean to stir the pot here, but we should all be able to speak on any subject while still being perceived as at least being civil to eachother. Face it, us aviators are a pretty small crowd, and getting smaller by the day. So we need to stick together and not let little issues divide us. So lets keep the discussions going while keeping them productive and civil. And when we disagree with each other, remember there is almost always something to be learned from other peoples opinions and experiences.

    Personally, I like people that challenge my thinking. And I hope they can appreciate when I challenge theirs. That's how we learn from eachother. And it's also half the fun of this forum. But let's not ruin the fun for our moderator by making him have to scold any of us - he's here to have fun too. I really appreciate that our moderators are willing to do all the work associated with this forum, so we don't have to. I'm sure the job is thankless enough, let's not make it any harder for them.

    So let's all just agree that regardless of our opinions, we will always remain buddies, and even though we may disagreee we will always treat one another with mutual respect...

    (There's my two cents worth)

    Paul S
    Central Wisconsin

  4. #34
    Senior Member av8rps's Avatar
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    Default Re: Cruise rpm

    Don,

    One last thought on the IVO IFA prop settings;

    If it were me rather than to focus on the manifold pressure gauge, I would rather install one of the navman fuel meters. That way you could watch your fuel burn rate, and that probably is one of the best ways to know how efficient your engine is operating at any given prop setting. I have one purchased for my kitfox but probably won't get around to installing it until next year. But I look forward to using it as I think it will be the cat's meow...

    Paul S
    Central Wisconsin

  5. #35
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    Default Re: Cruise rpm

    G`day Paul

    Thanks for the info and heads-up on the MP gauge. I plan on playing around with it and will keep the forum posted on results. Also appreciate your suggestion on the fuel flow meter. What type are you planning on installing?
    On another note, as a relatively new member of the KF community, I find this forum to be a wealth of information, especially on topics such as this whereby folks have the opportunity to disclose their ACTUAL operating performances and results. This is excellent material for us all!
    Let`s just have fun with it as well as LEARN from each other.

    Don

  6. #36
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    Smile Re: Cruise rpm

    Maybe I'm a little dense but I didn't find any problems with JetPilots remarks. Tone of ones voice is impossible to get across in these posts and I think sometimes we read into a remark a tone that was not intended. I've read my Rotax manual from cover to cover, over and over and I believe Jet Pilot gave good, solid facts that the Rotax manual backs up. Jet Pilot may have been a little blunt and straight forward but I don't believe any offence was intended. I almost got a little rattled when I read the post about the 5800 rpm cruise and the 6100 rpm full throttle. I fully expected to read some (are you crazy?) responces. I thought it myself but selfcontrol prevailed. Anyway, Jet Pilot, keep the posts coming. I, for one, understand where you're coming from and if quoting directly from the book offends someone, oh well!

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