Ed,
This throttle body size thing came as a surprise to me a couple of years ago when I first started my engine. I selected the 75MM size because that was what was in the RX-8 car. It pretty obviously is way too large for our application. Apparently even the 65 MM that Dennis is using appears to be too large. I suppose that is because in the car, the engine can rev to 8K+ rpms. We are only revving in the 5-6K range with an occasional outlier up in the low 7K range. The fact that the car can rev so high, I suppose, is the reason that there are no complaints about dead pedal in the car.
Thanks to you, I feel I now understand what is causing the phenomenon. I don’t see that it is a problem that should be fixed, at least, not yet. I just need to work on getting the engine to produce the most power it can and then, maybe, resize my prop to get rpms in a good power band for takeoff.
It seems that I remember someone on the list (probably Lynn) talking about a couple of carb throats being 44MM that he uses. If so, they (two of them) would have an area of about 3040 MM. A single 65 MM body would have an area of 3317 MM.. an increase of over 9%. A 75 MM body would have an area of 4415 MM…a whopping 45% increase!
Bill B
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Ed Anderson
Sent: Friday, February 12, 2010 4:38 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Throttle limits was Re: N.A. Renesis to turbo
Bill, if Dennis had a TB just big enough that it exactly provided 100% power at sea level, then as he increases in altitude, he will find more and more throttle travel that does nothing to increase power. This is because it takes less and less throttle plate opening to provide sufficient airflow for the pressure/air density in the manifold to reach the ambient pressure/air density (ambient density is decreasing with altitude). Since that air density is less than at sea level, it requires less throttle opening to reach than at sea level.
The position of the throttle plate affects only the air flow volume (not the density of that air airflow), but the amount of air flow volume does determine the air density in the manifold. The external atmospheric pressure is of course what is forcing the air through the throttle body – The less air pressure at altitude means less air is flowing through the TB as you gain altitude. Remember even though to simply the verbiage - we often talk of the engine “sucking” but of course it does not. The engine simply opens its ports and whatever pressure is in the manifold forces that air into the essentially empty combustion chamber.
Think of it this way, there are two ways you can have ambient air density in your intake manifold. Those two ways are with the throttle open or the throttle closed – a contradiction? Not, so. You may have ambient air pressure/density in the manifold when the engine is running and TB open sufficiently to provide ambient pressure in the manifold OR when the engine is not running.
When the engine is stopped - you also have ambient pressure in your intake even with your throttle 99.99 % closed because the engine is not “sucking” any air out of the manifold when stopped. So a small leak in the throttle bottle is sufficient for the manifold pressure to reach and maintain ambient when the engine is not running.
What Dennis has done with his DIE intake does not change this factor, but what the pulse in the intake does when it reaches the other end of the intake manifold (note how his intakes are tied together so the pulse can travel from one intake port of one rotor to the intake port of the second rotor) is briefly create a localized pressure increase in the intake manifold right at the intake port as it is open. This in effect shoves more mixture into the combustion chamber – in effect it is a very brief supercharger effect. It only lasts for milliseconds and therefore you don’t get the same power increase that you would if you had a turbocharger pushing in denser air the entire time the intake is open. On the other hand you don’t have 30-50 lbs more weight and for basically no more than fabricating your intake different – it’s basically a free lunch.
But, as Dennis will tell you - doing the analysis to get the equations so you get dimension correct for the effect – can give you a headache {:>) – right Dennis??.
So, anyhow, back the throttle travel, if your TB is larger than needed to reach 100% power at sea level, then you would also find “excess” throttle travel sitting on the ground with the engine running at WOT. Once the throttle is opened sufficient for manifold pressure to reach ambient, then opening it further will provide no increase in power. You have in the vernacular- “Maxed Out!” {:>)
Once the throttle plate is open sufficient to permit the manifold pressure/air density to reach ambient conditions – no further opening will produce any more power even though you may have 5” of throttle travel and 50% more throttle plate opening to go.
Ed
Ed Anderson
Rv-6A N494BW Rotary Powered
Matthews, NC
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Bill Bradburry
Sent: Friday, February 12, 2010 3:33 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: rpm vs Power was : Throttle limits was Re: N.A. Renesis to turbo
Thanks, Dennis,
It sounds like you still have a little unused throttle travel even with the new intake.
Can you provide design measurements for your new intake? I ask only if you have no plans to make and sell it.
Bill B
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Dennis Haverlah
Sent: Friday, February 12, 2010 2:20 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: rpm vs Power was : Throttle limits was Re: N.A. Renesis to turbo
I used the same 65 mm Mustang throttle body on both my original and new intakes. If I remember correctly, I believe I had a longer unused throttle travel with the original intake but I never measured it. I don't know the static rpm increase with the new intake - probably have that in my notes some where but my max. rpm at high altitude (8,000 - 10,000) increased 400-500 rpm. I estimated I went from 165 -170 HP with the old intake to about 185 HP with the new intake. This in in line with Ed Anderson's recent note that Mazda got about a 16% power increase at 6000 rpm with the DIE effect. I felt much improved acceleration the first time I took off with the new intake.
the new intake is based on dynamic intake effect (DIE) where the closing of an intake valve caused the moving intake air to bounce off the valve creating a pressure wave. The wave travels at the speed of sound to the other intake valve and arrives there just before that valve closes. This increases the amount of air and fuel that enters the combustion chamber. (As we know the rotary has no valves but uses the sides of the rotor for opening and closing the intakes.) I designed my intake to give max. performance at 6300 rpm.
If I had cut down my prop to 74" it would give me more clearance for the prop on my RV-7A and increase my top end rpm. Max rpm is about 6400 rpm with the new intake and the 76" prop. I'm really not needing higher RPM now.
Dennis Haverlah
Bill Bradburry wrote:
Dennis,
Did your static rpm increase with the new manifold? How much? Did you before and do you now have any unused throttle travel like Mike describes? Are you using the same throttle body on the new manifold? What is the MM opening of the Mustang body?
My manifold is very similar to your old one. My tubes are cut just above the injector bosses, which makes them a little (maybe an inch) shorter than your old ones. I have a 76 X 88 Performance prop which I am considering having cut down to 74” like Tracy and Ed when I send it in for final finish. I am using an aftermarket throttle body that is 75MM in throat diameter. This is the same size as the stock Renesis throttle body which is why I picked it. I had intended to use the Renesis body, but didn’t wait for Tracy to get the fly by wire done. I am not flying, but my static is 52-5300 rpm and I have a lot of throttle left at that rpm. The last probably ¼ of the travel is not used.
Bill B
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