Author Topic: Performance of IO-550 versus IO-520  (Read 25675 times)

Scott Newpower

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Re: Performance of IO-550 versus IO-520
« Reply #45 on: October 27, 2012, 09:06:00 PM »
You lost 25 MPH by reducing fuel flow 2.5 GPH? That can't be right.  I might lose a few MPH for that.

Thomas Pelz

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Re: Performance of IO-550 versus IO-520
« Reply #46 on: November 05, 2012, 07:16:16 AM »
Scott,

When I am burning 12.1 GPH, I am developing 180.29 HP.  This is 60% power.

When I am burning 14.6 GPH, I am developing 217.54 HP.  This is 72.5 % power.

I obtained these numbers by the formula:   P= 14.9 X FF

I may be using these calculations incorrectly.   However, these were the formulas posted by someone somewhere.  They kind of make sense to me.

Tom

Lance Fisher

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Re: Performance of IO-550 versus IO-520
« Reply #47 on: November 16, 2012, 08:32:37 PM »
I obtained these numbers by the formula:   P= 14.9 X FF

I may be using these calculations incorrectly.   However, these were the formulas posted by someone somewhere.  They kind of make sense to me
That formula works for a "high compression" engine (i.e. 8.6:1) when it's running somewhat lean of peak.  (e.g. 10-20 LOP at 65%) Since there's excess air the BFSC is relatively unaffected by mixture.  If you're running ROP the ratio is different (less HP/gph) and varies considerably with mixture.  IOW when ROP increasing the fuel flow 10% while maintaining RPM and MP has very little effect on power produced but when LOP, the power drops off at about the same rate as the fuel flow.

Ernie Ganas

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Re: Performance of IO-550 versus IO-520
« Reply #48 on: November 16, 2012, 09:06:53 PM »
Scott,

When I am burning 12.1 GPH, I am developing 180.29 HP.  This is 60% power.

When I am burning 14.6 GPH, I am developing 217.54 HP.  This is 72.5 % power.

I obtained these numbers by the formula:   P= 14.9 X FF

I may be using these calculations incorrectly.   However, these were the formulas posted by someone somewhere.  They kind of make sense to me.

Tom

Tom You are losing far too much IAS when going LOP you should be losing less than 7 MPH at those power setting.

From the APS seminar, the power at the ROP settings you mentioned (21"/2300 RPM) on a standard day would equal 62% power.

The formula they gave us to compute ROP power was 100-((Max RPM/100-SetRPM/100*2.5 + (maxMP-SetMP)*3.5) =%HP

or 100-((2700/100-2300/100)*2.5+(29-21)*3.5)=62

FYI in my Model 36 with the IO-550B I'm within one knot or so of the published Oct 83 POH Performance data on pages 5-26(ROP) and 5-27 (LOP). I lose about 6KTAS, sometimes 7KTAS, (173KTAS-167LOP) going from ROP to LOP and use just a little over 2 GPH less.

 I generally run WOTLOP 2500 about 20 degrees LOP at 7500 to 9500.

Ernie
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John Ramsey

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Re: Performance of IO-550 versus IO-520
« Reply #49 on: March 01, 2013, 06:22:13 PM »
I put an IO 550 on a v35B and while I did get 8-10knots more TAS at 8-10K altitude, I found that the higher fuel burn reduced my range and on long leg trips it wasnt worth the extra speed to have to stop for fuel if I had a significant headwind.  I had a routine trip of 696 nautical miles which I flew probably 50 times and I could make it easily with an IO 520 even with a 20 kt headwind but it became marginal with the IO 550.  I would have preferred to have the IO 520 back for the type of flying I was doing.  Also, I put on a scimitar prop and I swear I lost a couple of knots of TAS.

Robert Siegfried

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Re: Performance of IO-550 versus IO-520
« Reply #50 on: March 02, 2013, 08:08:37 AM »
Hi John-

My experience with the IO550 differs somewhat from yours. Since the IO550 has the same specific fuel consumption as the IO520, if you wish to duplicate the performance that you had with the IO520, all you need do is adjust the power so that you have the same fuel flow at the same HP. I typically operate LOP if I am at altitudes below about 13,000, so it is easy to dial the mixture back to achieve whatever fuel flow I desire. However, I find that I can usually make a trip using less fuel that I did with the IO520 by climbing 2 to 4 thousand feet higher and obtaining a higher TAS at the same fuel flow.

Regards,

Bob Siegfried, II

Paul Safran

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Re: Performance of IO-550 versus IO-520
« Reply #51 on: March 02, 2013, 09:23:29 AM »
Hey John,

To add to what Bob II said, even with my puny IO470N and 2 blade in an N35, (a bit more efficient than a 550 w/ 3 blade), I routinely slow down to make 750+nm trips non-stop.

Just did, going to FL from Upstate NY via Tullahoma for weather. I'm very lucky my wife & kids tolerate the long legs.

Lust after a 550 still, to get higher faster into smooth air and go faster when the mission calls for it.

Are you running LOP and getting all the fuel out of the tanks?

Timothy Hutchison

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Re: Performance of IO-550 versus IO-520
« Reply #52 on: March 03, 2013, 05:18:54 PM »
I just had an interesting conversation with a sales rep I met at the airport.  He happened to park next to my A-36 with a past TBO iO-520.  He was in a late model A-36 with an iO-550.  He was bringing the plane for a potential customer.  Of coarse I had to have a look and asked his opinion of replacing my 520 for another 520 vs a 550.  He says that he flies both renditions on a daily basis and, while the 550 is a little faster he doubts that I would notice any real difference warranting the $10k price difference.  In my soul I want the 550. But, that 10K would pay for the paint job I really want to.  What to do?