flyrotary@lancaironline.net Mailing List Archive

That's curious. Are you saying that fuel flow *decreased* as rpm *increased* above 6750 rpm? And airspeed decreased, as well? The only way fuel flow should decrease as rpm increases is if the load on the engine is going down.

Is the prop running out of pitch (or ability to absorb the HP) as you get faster? Is the airframe hitting a drag wall due to cooling drag (still shouldn't show a reduction in fuel flow; it just wouldn't go any faster)?

What actual speeds are you achieving when this is happening?

Refresh my memory; who's prop (what blades) is it?

Do engine temps go up as you get above 6750 rpm?

Think about the 'airplane as dyno' thing: If rpm continues to go up, and the drag (our substitute for torque on the engine brake in a real dyno) stays the same or increases, then power *must* be increasing, and so must fuel flow. Simple math; (torque*rpm)/5252. So, was the plane going downhill, or was the prop unable to absorb the additional power and decoupling, unloading the engine?

Charlie

On Fri, Aug 7, 2020 at 9:01 AM Stephen Izett stephen.izett@gmail.com <flyrotary@lancaironline.net> wrote:

Hi Guys.

Today we did some engine data analysis at 9500, 7500, 6000 and 4500 feet agl.
WOT with constant best power mixture of 0.9 Lambda.
We looked at Fuel Flow and IAS at 5500,5750,6000,6250,6500,6750 & 7000rpm.
The data revealed a very slight peak in both IAS and Fuel Flow at the 6750rpm point at basically all altitudes.
I think what this is suggesting is that increasing rpm beyond 6750 is only increasing wear and has no benefit given the current intake/exhaust configuration.

With the current Prop Fine Pitch Limit, on initial WOT at Takeoff the engine consistently hits 6900rpm within ~6 seconds and 7000rpm by liftoff at 70 KIAS.
It then generally builds to 7400rpm (With no pitch adjustment - We presently don't have a Constant Speed Controller) before throttling back as we turn downwind.

I think this would suggest we ought adjust the props fine limit marginally so that takeoff WOT yields approx 6700rpm and keeping the rpm as close to 6750rpm as
possible when seeking maximum power by manual prop pitch adjustment.
A Constant Speed Controller would be nice!

I’m now thinking we have enough data to tune the Mixture Correction Table of the EC2’s computers for climbing at 6750rpm and as Bill suggested cruising at 6000rpm.

Next step in tuning in the Glasair Super IIRG will be playing with the cowl flaps and cooling drag. Presently the flaps are wide open and draggy.
I’m in the process of completing a little box of 5 differential pressure transducers (MPX10DP’s) mounted under the cowl.
I worked out that they interface quite nicely without any other circuitry with the Dynon Skyview's surplus EGT inputs via a new Polynomial in the sensor config settings.
So hoping in the next few weeks to ascertain how the inlets, diffusers and outlets are functioning or not.
What I like about the MPX10 interface with the Skyview EFIS is the simplicity of displaying the pressure data inflight while its all logged along with engine and flight data
for analysis on the ground.

I’ve got 7 more hours of Phase #1 testing.
So far both aircraft and engine are really great.

My friend and test pilot Dawie also demonstrated at the end of todays flight - a Lazy Eight, a Roll and Wingover.
I felt sick for the next 3 hours. I don't think aerobatics will be in my future.

Thanks for all the help you guys.

Steve Izett
Perth Western Australia
Glasair Super IIRG Renesis 4 port RD1C EC2 EM3

> On 7 Aug 2020, at 2:25 pm, William Jepson wrjjrs@gmail.com <flyrotary@lancaironline.net> wrote:
>
> Stephen,
> The answer to one of your questions is easy. A fast cruise RPM should be 6000. Mazda did many instrumented runs and found that 6000 rpm was a sweet spot where the dynamics balanced perfectly. At 6000 there is almost no load on the bearings. The rotary would run at that RPM indefinitely. If you have more power at higher speeds you can use that for maximum speed. Those RPMs are eshaft RPMs not propeller.
> Bill
>
> On Thu, Aug 6, 2020 at 4:15 PM Stephen Izett stephen.izett@gmail.com <flyrotary@lancaironline.net> wrote:
> Hi Guys
>
> Thanks for all the feedback.
> I think I didn’t explain my objective clearly enough.
>
> Some questions:
> 1. Given I have variable pitch, what combination of MAP and RPM should I climb or cruise at? With fixed pitch I dont suppose you think in these terms.
> So should I be Climbings at WOT & 7000rpm OR WOT & 6300rpm Best Power Mixture.
>
> I think Lynn best understood my intention of trying to use the flight as a dyne - I didn’t realise the complexity of the relationship of mixture and timing at various settings, thanks Lynn.
> I thought by keeping WOT and mixture constant I might ascertain a maximum efficiency combination for MAP/RPM.
>
> I’d like a combination for max power. I’m thinking identified by higher fuel burn and IAS for the climb, and
> a max efficiency/ecconomy combination for cruise identified by best miles per gallon.
>
> I thought our Renesis with our modified OEM (shortened) manifold but no variable intake valves etc. would have a distinctive peak at ~6400-6600rpm.
>
> 2. I’m finding tuning the EC2 (objective being EC provides constant mixture across the flight envelope) is dependant on the combination I choose to tune it at.
> Eg. Tune EC2 MCT for one MAP/RPM combination, say a cruise of 18” AND 5000 rpm, then the EC will not be able to provide a constant mixture if I then choose 18” at 6000rpm.
> My EC2 has Tracy’s 8 table setup but fueling requirements given the extra permutations provided by the variable pitch prop (climbing that hill - which gear should I use - 3rd 4th or 5th??)
> appears to stretch its inherent capabilities. So I want a plan for what MAP/RPM I will use and then adjust/tune the EC MCT for that combination.
>
> Thanks again guys.
>
> Steve Izett
>
>
> all is nice if you fly that combination. If I then choose ab
>
> > On 7 Aug 2020, at 6:16 am, lehanover lehanover@aol.com <flyrotary@lancaironline.net> wrote:
> >
> > Your thinking is correct. Control full throttle RPM with load. Then experiment always at that particular RPM until you have whatever data point you were after. Everything affects everything so it may be that (for example) advancing ignition timing at one RPM adds power but at another RPM reduces power. A rich mixture at one RPM may increase power but reduce power at another RPM. To recover even similar data on consecutive days is difficult. The SAE has some charts that produce a multiplier to account for density temperature and so on. Required to compare results day to day. It takes a long time to collect good data..........
> >
> > Lynn E. Hanover
> >
> >
> >
> > https://search.aol.com/aol/image?p=dyno+sheets+for+stock+rx-7+engines&s_it=img-ans&v_t=loki-keyword&fr=loki-keyword&imgurl=http%3A%2F%2Fwww.rx7club.com%2Fattachments%2Ftime-slips-dyno-128%2F346326d1243952257-anyone-have-stock-turbo-ii-dyno-graph-stock-s4-t2.jpg#id=19&iurl=http%3A%2F%2Fwww.rx7club.com%2Fattachments%2Ftime-slips-dyno-128%2F346326d1243952257-anyone-have-stock-turbo-ii-dyno-graph-stock-s4-t2.jpg&action=click
>
>
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