You’re welcome, Bill.

 

Yes, I think with the smaller primary injectors I would not recommend two-injector flight as a norm.  I would rather recommend on removing the bog at staging or minimizing it (as Tracy suggests) by moving it a bit higher in manifold pressure.

 

I fly an RV-6A so my approaches are quite a bit slower than 90 knots.  More around 70 knots on final.  I don’t know the manifold pressure, that is one gauge I do not recall looking at in the pattern.  My rpm (2.85:1 gear box) in the pattern downwind  is around 3800 rpm at around 85 knots and then back to 3200 rpm (80 kts)  turning base and back to 2800 on short final (65-70 kts) to full idle across the threshold (don’t look at the rpm gauge or airspeed at that point , but its probably around 2100 rpm and 55-57 kts).  I fly with a few more knots on final that a lot of RV aircraft as I am bit heavier and my philosophy is I would rather go off the far end of the runway at 15 knots than end up 5 knots too slow on approach end.

 

 

Ed

 

 

 

From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Ed Anderson
Sent: Wednesday, February 18, 2009 6:02 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: staging

Hi Bill,

 

Two 295 cc/min injectors would provide a total of 2*295 * 0.8 = 472 cc/min combined flow at 80%.  So converting to something I can handle better than metric - that gives approx 0.1307652 gallon/min * 60 = 7.845912 gallons/hr * 6lb/gallon = 47.075 lbs/hr.  Using a conservative BSFC of 0.55 that gives Hp = 47.075/0.55 = 85.49 HP.  An RV will fly quite well (once airborne) on that flow rate.  I normally fly (cruise) at 7.5 – 9 gallons/hr.  85HP will get an RV launched as well – but need a longer runway for sure.

 

 But, I will be a very leery trying to get a heavily load RV out of a short strip on a hot day on that kind of power – in fact, I would not attempt it.  But, then my RV-6A is a bit on the heavy side.

 

However,  Dave’s use of two injectors for cruise works just fine – the primary reason is that he is using two 460 cc/min (I think, either that or 550 cc/min) injectors as primary, but taking the lower estimate.  That would give Dave 2 * 460 *0.8 = 1150 cc/min or 0.3037979 gallon/min * 60 = 18.2278 gallon/hr * 6 = 109.36 lb/hr and finally

 Hp = 109.36 lb/hr / 0.55 = 198 HP.  So due to the larger injectors Dave can fly with impunity (almost) on two injectors throughout his flight profile – except when he want to run boost and race {:>).

 

So if you wanted to do the same, I would strongly suggest you go to larger than the stock Renesis injectors.  Although, you might consider swapping your injector electrical connections so that your EC2 primary drives your secondary (larger injectors) and secondary your primary injectors – Naw probably not the best idea.

 

Best Regards

 

Ed

 

 

 

 

Ed, You are good at this kind of thing..

 

The Renesis primary (red) injectors are 295 cc/min flow rate.  At say, 80% duty cycle, what HP would these injectors support if you moved the staging point to higher RPMs?

 

Bill B

 

Tracy and all,

Looking back at the data I was using when thinking about my “staging bog”, I realize that the manifold pressures I am looking at are values I calculate from the EC2 data.  My conversion to units of inches Hg may not be correct.  Either my EC2 manifold pressure sensor may have changed calibration or I may have never had this conversion correct to begin with.  I have only one program to do this and may not have it right.  How Tracy keeps track of all the versions of EC’s is beyond me.

In any case, I can NOT say with certainty that my EC2 is internally inconsistent as I stated in my previous message.  I apologize if this has caused you to waste any of your valuable time and energy over this.

The reason I am concerned with staging more than many others might be is that at the ground level density altitudes of my home airport, the maximum manifold pressure I see is about 23 inches and of course it gradually drops off from there as I climb.  This results in staging taking place during critical flight regimes.  Encountering an extended “bog” right after take off is not my idea of fun.  If I cannot get the staging to work well using mode 6, I am considering David Leonard’s suggestion of moving the staging point to a higher manifold pressure where I will not normally encounter it.  In my case this is need not be much of a change.  The manual indicates that some modes are active only when the engine is running.  Is this the case with mode 7?  I’m trying to make sure I can set the staging point with a pressure source other than the engine.

This does generate the potential for my next trip to lower altitudes to be memorable.  I just have to remember that this is venturing into unknown territory again and that full throttle operation may not be reliable until tuning at the higher power settings accessible at lower altitudes has been accomplished.

Again, my apologies to especially to Tracy and also the rest of you.

Steve Boese

  

 

    

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