Kolb-List Digest Archive

Tue 04/24/18


Total Messages Posted: 1



Today's Message Index:
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     1. 05:44 AM - Re: Firestar 2 / HKS engine progress (Gary Aman)
 
 
 


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    Time: 05:44:14 AM PST US
    Subject: Re: Firestar 2 / HKS engine progress
    From: Gary Aman <zeprep251@aol.com>
    Bill, did the same exhaust mod on my MK3c.Be sure to plug the fuselage tube at either end.T he cabin will fill with exhaust gas very quickly if you dont seal it .G.Aman MK3C Jabiru 1100hrs > On Apr 23, 2018, at 4:03 PM, Bill Berle <victorbravo@sbcglobal.net> wrote: > > > Just a quick update on my HKS installation in the Firestar. After waiting months for the guy to be available, I finally had the last of the exhaust parts fabricated and welded! > > So now I have two 1.25" stainless exhaust pipes coming down from the engine exhaust ports, joining together and running down the rear of the fuselage cage, then a 2-into-1 collector at the right "tuning" location, then a 1.5" diameter "flex coupler", then a length of stainless tube that swings down and around to the bottom of the tailboom (fuselage tube), which then inserts into the front of the home made "Swiss Muffler" exhaust silencer. > > whew ! > > Now that the exhaust is complete, I will re-mount it on the aircraft and I can finally do a weight and balance to see where I have to mount the battery. I have waited to mo unt the battery because I literally have no idea whether it's nose-heavy or tail-heavy. > > With a little luck and no major obstacles, the Firestar should be ready for flight testing by this summer. > > Bill Berle > www.ezflaphandle.com - safety & performance upgrade for light aircraft > www.grantstar.net - winning proposals for non-profit and for-profit entities > > -------------------------------------------- > On Mon, 4/23/18, Charlie England <ceengland7@gmail.com> wrote: > > Subject: Re: Kolb-List: Re: Balance Master > To: kolb-list@matronics.com > Date: Monday, April 23, 2018, 11:45 AM > > What John described > is actually quite common in certified fixed wing a/c, as > well. Many that are equipped with metal constant speed props > have a 'yellow arc' (usually around 2000-2200 rpm on > an engine with max 2700 rpm). While not a problem to > transition through that range, continued operation there can > result in a broken crankshaft or prop. Remember, these are > FAA-blessed aircraft. > It's worth pointing out that just because you > don't feel it, doesn't necessarily mean it's not > there (might not be exciting the airfame so you're > feeling it at higher rpms, but still out of balance). But if > it's bad enough to be annoying, you probably want to > stay away from that speed range; you're probably > operating near the natural resonant frequency of the system > and stuff can sometimes break very quickly > there. > Have you tried *dynamically* balancing the prop? > It isn't cheap to pay an a&p to do it, but many EAA > chapters have one of the less expensive models you can > borrow or rent. > Charlie > > On Mon, Apr 23, 2018 > at 1:20 PM, John Hauck <jhauck@elmore.rr.com> > wrote: > "John Hauck" <jhauck@elmore.rr.com> > > > > Don't think I explained myself very well, as usual. > > > > I indicated the only numbers I could find were max power. > Could not find anything for cruise power. Was not > inferring the engine needed to be operated at max power. > > > > Not that familiar with fixed wing aircraft, but on several > of the Army helicopters I was privileged to fly there were > RPM areas to stay out of. When running up, don't > hesitate in these yellow zones. 4000 to 5200 may be a > similar zone with the 277. If it was me, I'd fly Hell > out of it and stay out of 4000 to 5200 except to transit > that rpm. > > > > Don't know if a 3 blade will solve your problem, but you > won't know until you try. > > > > john h > > mkIII > > Titus, Alabama > > > > > > > > > > -----Original Message----- > > From: owner-kolb-list-server@ > matronics.com [mailto:owner-kolb-list- > server@matronics.com] On Behalf Of Richard Pike > > Sent: Monday, April 23, 2018 1:00 PM > > To: kolb-list@matronics.com > > Subject: Kolb-List: Re: Balance Master > > > > <thegreybaron@charter.net> > > > > Jack Hart: What a prince! Thank you, can't wait to try > it out and see how it does. > > > > John Hauck: you are correct, I am sure that the Austrian > gnomes at Gunskirchen tuned the 277 for optimum power > between 6250 and 6500, and I am sure it would happily churn > away at that speed all day. However, while 6250 - 6500 rpm > is where the engine makes its rated power, that does not > necessitate the engine having to be consistently operated at > that rpm. > > > > Here is a very good website of tutorials by the Australian > light aircraft people - https://www. > recreationalflying.com/ tutorials/index.html > > and from their page on "Engines and Propellers", > > "Although aero-engines can quite happily operate > continually at their rated power, doing so is not good > practice. It is uneconomical in terms of fuel efficiency, > but more importantly it may shorten engine > life, if engine operating temperatures and pressures are > exceeded. Normally the maximum and optimum > power setting for continuous cruise operation is 75% of > rated power." > > > > Then they deal specifically with the 2-stroke; > "Two-strokes don't have very good volumetric > efficiency, and the engine is generally efficient only in > the upper 30% of its rpm and throttle opening range. In > fact, ultralight two-strokes tend to run very roughly at > speeds below 2500 rpm and achieve their rated power at > rotational speeds in the 5500 to 6500 rpm range. The three > most common two-strokes are two-cylinder models with > individual cylinder displacements around 250 cc; they > achieve their rated power at 6500 rpm and 75% power at > around 5300 rpm." > > > > Something else to consider is that running an engine slower > than its rated power does not lug it. Once again from the recreationalflying.com > tutorial page: "the power delivered by a propeller > varies in accordance with rpm cubed (if everything else is > kept constant)" Therefore, as rpm is decreased from the > engine/propeller maximum attainable rpm, the load reduction > on the engine decreases exponentially. (don't know the > right technical term for a decrease cubed, but you get the > idea) > > > > Back when I was flying a Maxair Hummer with a Rotax 277, it > spent most of its time around 54-5500 rpm. The 582 on my > MKIII spends most of its time around 54-5500 rpm solo, > 56-5700 rpm when I have a passenger. When I am in a hurry, > it runs at 6200 rpm and sucks gas like it was free. > > > > The 277 on the Firefly is still breaking in, but right now > it appears that the sweet spot is going to be around 5500 > rpm to run right and fly right. I have not been trying to > fly it at rpm's below 5100, it is that (possibly due to > still breaking in?) if it gets below 5100 down to around > 4000, as in when making a descent to land, it vibrates more > than it ought to. This is typically in a semi - unloaded > state, throttle retarded, engine providing minimal thrust. > Once it gets below 4000 rpm, the vibration goes away. > > > > David & I have discussed changing the two blade Ivo to a > three blade as a way to deal with the vibration, but only if > we have to. Right now we have an 800'/min climb rate, > and we would hate to have to give that up by going to a > smaller diameter prop. > > > > As always, appreciate your input, gives us all a chance to > think these things through and stimulate the old grey > matter. > > > > -------- > > Richard Pike > > Kolb MKIII N420P (420ldPoops) > > Kingsport, TN 3TN0 > > > > Forgiving is tough, being forgiven is wonderful, and > God's grace really is amazing. > > > > > > >




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