Well, physics is physics. If they wanted more cooling margin then that would explain increasing airflow. Also, it seems if would perhaps be harder to get a very efficient duct shape to feed the cylinders with the extra clutter of the EFI bits on the top of the engine.
Van's Air Force
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RV-12iS Details
- Thread starter Tony_T
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Well, physics is physics. If they wanted more cooling margin then that would explain increasing airflow. Also, it seems if would perhaps be harder to get a very efficient duct shape to feed the cylinders with the extra clutter of the EFI bits on the top of the engine.
Crafting N112DR
Well Known Member
Ryan also said at the banquet that the engine is the 912iS Sport, because he said there was some problems with the iS.
Temperatures vs. Fuel Burn Rate
Perhaps the difference in temperatures is,one of the measurement technique(s) and procedures themselves and not a violation of physical theories. It is common that when measurement tools, sensors, etc. have become,better and more accurate earlier assumptions and beliefs start to be questioned. This may be just an apples and oranges type of problem and not a ripple in our widely accepted laws of thermodynamics.
-larosts
Perhaps the difference in temperatures is,one of the measurement technique(s) and procedures themselves and not a violation of physical theories. It is common that when measurement tools, sensors, etc. have become,better and more accurate earlier assumptions and beliefs start to be questioned. This may be just an apples and oranges type of problem and not a ripple in our widely accepted laws of thermodynamics.
-larosts
And chemistry is chemistry
Best power mixture is cooler, because you get about 3 times the heat making CO2 than CO. However, if you are O2 limited (rich) you can make twice as much CO as CO2 from the same amount of air - so you get your pressure (power) from more gas at a cooler temperature. The rest of the energy in the fuel goes out the exhaust as CO - it is never released as heat.
I did the calculations in this thread:
http://www.vansairforce.com/community/showpost.php?p=1177950&postcount=20
The bottom line is that 20% more fuel from peak EGT gives about 10% less heat with the same amount of air i.e. same RPM and manifold pressure.
And chemistry is chemistry
Best power mixture is cooler, because you get about 3 times the heat making CO2 than CO. However, if you are O2 limited (rich) you can make twice as much CO as CO2 from the same amount of air - so you get your pressure (power) from more gas at a cooler temperature. The rest of the energy in the fuel goes out the exhaust as CO - it is never released as heat.
I did the calculations in this thread:
http://www.vansairforce.com/community/showpost.php?p=1177950&postcount=20
The bottom line is that 20% more fuel from peak EGT gives about 10% less heat with the same amount of air i.e. same RPM and manifold pressure.
Ideally, we'd map the high rpm/ high MAP areas for around 12.5 AFR and the cruise conditions for around 17 to 1. You'll see from the graph I published that temps are roughly the same at 12.5 and 17 AFRs, although power is obviously less that far LOP. Yes, 12.5 is cooler for the same power but you'd never want to cruise here for fuel economy and the 912is clearly doesn't.
As far as the real world goes, more mpg at the same TAS means higher TE which means more fuel energy goes into turning the crank, less into the cooling system and exhaust stream. Higher TE means you can run the same TAS with a lower power setting which equals less heat. No way you need more cooling mass flow with a more efficient engine unless there are other factors at work here or you want more margin than before.
LOP operation has clearly showed 15-25% better mileage over best power mixtures while at the same time showing reduced CHTs and higher detonation margins than MBT AFRs.
More info and food for thought here: https://disciplesofflight.com/fuel-air-mixture-aircraft-engine/
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Yes, physics is physics. Refrigerators work on the principle that an evaporating liquid absorbs heat. When gasoline evaporates, it absorbs heat. The ULS engine wastes fuel. That evaporating fuel absorbs heat and it is expelled out the exhaust.
Since the iS engine does not waste fuel, the heat must be transferred to the air by some other means: via the water and oil coolers.
Since the iS engine does not waste fuel, the heat must be transferred to the air by some other means: via the water and oil coolers.
Surely for a valid comparison you need to compare the temperature at the same HP output?
Right, but the 912ULS might cruise in this range, especially since you don't have precise mixture control with the CV carbs.
If the fuel injection on the is allows more precise control, Rotax can run the engine leaner which means more heat at the same power setting. Potentially even at maximum power - Rotax presumably want to be very sure the carbed engine doesn't stray into dangerous territory at maximum power.
The effect of evaporating fuel is very small compared to the heat of combustion.
You have to be very rich before raw fuel is going out the exhaust. Excess fuel mainly means you are making CO instead of CO2.
The chemistry heat of reaction calculations DO factor the energy taken to go from liquid fuel to H2O, CO2 and CO gas.
You can do the calculations giving H20 in liquid or gas forms, and get different answers. I used gas of course, since water is a gas at combustion temperatures.
Higher thermal efficiency means more energy into the crank, less into the cooling system. How else could it burn 20% less fuel? The iS must be running leaner cruise mixtures and more optimized timing to get the same TAS on less fuel.
Are you referring to CHTs here? With regards to cooling, the EGTs have no impact.
We know the carbed engines do cruise in this range from my testing in 2007.
We're talking about the practical considerations of why Van's and Rotax increased the cooling system inlet and exit sizes. We don't know if actual cooling mass flow was increased by these changes but that's the assumption.
Assuming no airframe or cooling system drag increases, the aircraft requires the same hp for the same TAS at a given altitude. If we're burning less fuel for the same TAS, that means less heat into the cooling system since equal energy is going into the crankshaft. In any case, cruise cooling is rarely a limiting issue, climb is.
The EFI engine may make more power than the ULS at BMT AFRs and Rotax may be able to run leaner than BMT AFR, even at high power. In this case, they could trade a bit of hp for lower fuel consumption at climb power settings. This could be an explanation for the increased heat. We don't really know what they are doing with AFRs. It would be fascinating to instrument one with a wideband.
As I stated before, the carbed 912s have unequal mixture distribution and the EFI gets rid of that so all cylinders can run at the nearly same AFRs. This on its own, is more efficient.
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BillL
Well Known Member
Not enough information on this "heat"
Not necessarily - If you think about it, there a huge number of variables that affect the jacket water heat rejection. So, for the same bore/stroke, ring/bore package, valve events, intake/exhaust systems, cooling jackets, cooling jets, coolant/flow/temperature, and combustion chamber swirl/tumble (and more) that would be true. What other changes are in this engine vs the one it replaced?
As example, higher swirl and tumble will allow higher cr, faster heat release, resulting in better BSFC but will also increase heat rejection to the head and cylinder. 20% claim would have to be carefully defined, though.
One can drive better power to the crank with better expansion ratios, and might yield higher JW heat rejection at the same time, but with less exhaust energy content/losses through less blowdown energy.
Also, what are the comparisons of the earlier models' installation temperatures relative to ambient.
Not necessarily - If you think about it, there a huge number of variables that affect the jacket water heat rejection. So, for the same bore/stroke, ring/bore package, valve events, intake/exhaust systems, cooling jackets, cooling jets, coolant/flow/temperature, and combustion chamber swirl/tumble (and more) that would be true. What other changes are in this engine vs the one it replaced?
As example, higher swirl and tumble will allow higher cr, faster heat release, resulting in better BSFC but will also increase heat rejection to the head and cylinder. 20% claim would have to be carefully defined, though.
One can drive better power to the crank with better expansion ratios, and might yield higher JW heat rejection at the same time, but with less exhaust energy content/losses through less blowdown energy.
Also, what are the comparisons of the earlier models' installation temperatures relative to ambient.
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I agree, there could be multiple internal changes to the injected engine with regards to the chamber design, CR etc. All interesting questions.
Your last point follows my thinking- they may have done this to increase cooling margin on hot days.
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I was referring to the chart you referenced. Without seeing the source of the chart, I guess the thermal plug is the important temperature. If you want to compare temperatures at different mixtures, you need to keep power constant not airflow i.e. the IMEP line should be flat.
This is not correct. Yes the power into the crankshaft is the same, however the temperature is very different.
The increase in pressure in the combustion chamber comes from 2 sources when fuel is burnt - increase in temperature and increase in number of gas molecules.
Lean of stoich the temperature and power will be reasonably linear because you are converting all fuel to CO2.
Rich of stoich you start making CO instead. Combustion to CO gives you much less heat, but you get twice as many CO molecules per O2 as CO2.
So you are getting more of your power from the increase in gas molecules, and less from increase in heat.
From 14.7 -> 12.5 AFR you get much less heat released from the fuel, even though power increases. Less heat released means less cooling needed.
So if Rotax can control the AFR more precisely and as a result don't need to run as rich to give a margin for error, it is not surprising that more cooling is needed. Leaner will give you more heat at any equivalent power setting.
"The CHT drops more quickly on the lean-of-peak side of 15 GPH, than it does on the rich-of-peak side."
Superimpose this chart with my previous AFR vs. IMEP chart.
There is plenty of real world data from APS and others showing that your assertion is incorrect. Despite what chemical theory says, CHT vs. TAS tells us the actual story. If TAS is the same, power must be the same. If CHT is lower under these conditions, then there is less heat to dissipate from the cooling system. See the links below.
APS recommends adding back a bit of MAP in turbo engines to restore speed lost from leaning. The CHTs are still lower, FFs are way down and TAS is the same.
Many of our clients climb LOP as well to keep CHTs down and in cruise at altitude, LOP can sometimes result in the CHTs getting down near the minimum allowed on Lycoming engines.
I have trouble buying theory when it's contradicted by actual real world data.
http://www.gami.com/paulferraris_leanofpeaksaga.pdf
http://www.gami.com/articles/bttfpart1.php
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I understand what you are saying, John. There apparently are people with fully completed forward fuselages who are selling them and presumably using the tail, rear fuselage, and wings as the basis the what they are building, so I would call that an upgrade. But it certainly makes more sense to me for Van to start from scratch and sell his existing RV-12. I would probably want to do the same thing.
I really like the improvements they have made. I do think being able to lock up the canopy is important. They probably had a reason for leaving out that feature, however. Someone who became locked in could quickly die in the heat.
I really like the improvements they have made. I do think being able to lock up the canopy is important. They probably had a reason for leaving out that feature, however. Someone who became locked in could quickly die in the heat.
Alan,
There is/has been an excellent after-market lock available by Aircraft Specialties:
I don't think it's possible to lock yourself in with this lock.
Crafting N112DR
Well Known Member
That's me, I'm selling my old style fuselage. (feels funny saying that) Will use the wings (will need to install a landing light in the Left wing) and the empennage.
Driftdown
Well Known Member
Good for you Dave. I would do the same thing if I were in your position.
IMHO, the new deal maker is the new engine, fuel tank and reworked landing gear support structure.
Good luck selling your 'legacy' fuselage and moving forward.
WolfgangMN
I'm New Here
Next Step (Hopefully)
After having achived this a replacement of the 912iS with a 915iS for a EAB version of of RV12iS would lead to my dream machine. I hope Van's will "just" do it!
After having achived this a replacement of the 912iS with a 915iS for a EAB version of of RV12iS would lead to my dream machine. I hope Van's will "just" do it!
Crafting N112DR
Well Known Member
I put down the 25% at Oshkosh, looking for Oct shipping
Crafting N112DR
Well Known Member
$6,238.00 + $50.00 for iS option and you can also use the new fuselage with the ULS engine for $75.00.
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According to the order form on the website, the ULS option is $75.00.
http://vansaircraft.com/pdf/order_forms/RV-12/RV-12-order-form.pdf
Did they tell you at the booth what parts are different between the two options and at what stage during construction you need to install them?
Crafting N112DR
Well Known Member
Yes your correct about the $75, missed that. I did not ask that because my only interest was the iS option.
Real world experience.......
Van's engineering department was as interested as anyone, in what the actual fuel economy benefit of the iS engine is.
Well now we know.
The red prototype (N412RV) piloted by Proto shop guy Tony Kirk and the new iS airplane (N912VA) Piloted by Mitch Lock made the trip to OSH together.
They flew at close to the same weights and flew the same distance and flight profiles (together).
Total fuel for the trip east....
N412RV with ULS engine - 60 Gal
N912VA with iS engine - 45 Gal (A 25% reduction in fuel burn)
The prop pitch is set on both airplanes to values that we feel provides an equal level of speed performance (both airplanes achieve the same TAS at any given altitude when operated within the max. continuous RPM limitation of 5500 RPM)
What is interesting is that to get equal speed performance, the iS engine has its prop pitch set .4 degrees courser than that of the ULS airplane, but when both airplanes are flown side by side in a climb test at exactly the same weight, the iS airplane climbs 100 FPM faster.
We attribute this to the peak torque output of the engine being right at the RPM value that is typical in a Vy climb with the fixed pitch prop on an RV-12. In fact, even with .4 degrees more pitch, the iS engine is turning a higher RPM climbing at Vy than the ULS RV-12 does. Another factor likely having some influence is the iS having cold air induction fed via a NACA scoop on the right side of the cowl, vs the ULS ingesting ambient engine compartment air.
Van's engineering department was as interested as anyone, in what the actual fuel economy benefit of the iS engine is.
Well now we know.
The red prototype (N412RV) piloted by Proto shop guy Tony Kirk and the new iS airplane (N912VA) Piloted by Mitch Lock made the trip to OSH together.
They flew at close to the same weights and flew the same distance and flight profiles (together).
Total fuel for the trip east....
N412RV with ULS engine - 60 Gal
N912VA with iS engine - 45 Gal (A 25% reduction in fuel burn)
The prop pitch is set on both airplanes to values that we feel provides an equal level of speed performance (both airplanes achieve the same TAS at any given altitude when operated within the max. continuous RPM limitation of 5500 RPM)
What is interesting is that to get equal speed performance, the iS engine has its prop pitch set .4 degrees courser than that of the ULS airplane, but when both airplanes are flown side by side in a climb test at exactly the same weight, the iS airplane climbs 100 FPM faster.
We attribute this to the peak torque output of the engine being right at the RPM value that is typical in a Vy climb with the fixed pitch prop on an RV-12. In fact, even with .4 degrees more pitch, the iS engine is turning a higher RPM climbing at Vy than the ULS RV-12 does. Another factor likely having some influence is the iS having cold air induction fed via a NACA scoop on the right side of the cowl, vs the ULS ingesting ambient engine compartment air.
Were they taking orders on the S-LSA -12?
But not that the engine has higher cooling demands......
BTW, I even brought up this thread in a meeting at OSH with one of the Rotax engineering reps visiting from Austria, the Distributer Rep. for Canada, and distributer Rep. for the U.S. and suggested they contribute. All I got was a smile and a firm NO. But once again a verbal confirmation that all airplanes converting from the ULS have had to make adjustments to cooling......
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But not that he engine has higher cooling demands......
BTW, I even brought up this thread in a meeting at OSH with one of the Rotax engineering reps visiting from Austria, the Distributer Rep. for Canada, and distributer Rep. for the U.S. and suggested they contribute. All I got was a smile and a firm NO. But once again a verbal confirmation that all airplanes converting from the ULS have had to make adjustments to cooling......
It doesn't help us understand why without technical details. It seems none of these folks you talked to knows or is willing to say so I'll let this one rest until a knowledgeable Rotax engineer tells us why this is so- which may never happen.
subpar_bucker
Well Known Member
I sent in my check for the new fuselage this week. I'm curious if anyone has any idea what the lead time will be for delivery? I check Vans lead time page and it says 12 weeks for the -12 fuselage. I was really surprised to see that the wing kit lead time is now 20 weeks! Is that due to the OSH announcement or some other reason?
I agree on the not understanding why part (and know one has tried to provide an explanation to me).
At one point the discussion in the thread seemed to be leaning towards it defying the laws of physics so it must not be true.
I can assure you it is.
The current goal is to try and begin shipping fuselage kits in October.
The listed lead time for wing kits is because of a back on parts deliveries by a vendor.
Same power with less fuel is a leaner mixture, and a leaner mixture is hotter - it's as simple as that. This is exactly what the chemistry (and physics) predicts. No laws are defied. No-one should be surprised.
I haven't seen any charts showing leaner mixtures are cooler where the power has been kept constant. They always compare e.g. 100hp LOP with 120hp ROP.
Or they define peak EGT (which is already on the lean side of stoich) as the starting point for their definition of "cooler".
Nice figures though!
XOverZero
Well Known Member
Well, foo! There goes my theory about dilithium crystals.
JwWright57
Well Known Member
....to follow up, when is Rotax coming out with the dilithium engine? And what is the HP? LOL
Nonsense. I've posted several charts and links from respected sources and your statement flies in the face of what many people flying observe every day with digital engine monitors. Stoich is essentially at peak EGT, give or take about 1%. CHT reduction increases more rapidly than power loss LOP in the 16-17 AFR range where most folks cruise LOP.
Read more on APS and running LOP with turbocharged engines where a bit more MAP is added to regain the lost power. CHTs are substantially lower at the same power/ TAS when running LOP. We can do the same with an atmo engine where we have some more throttle available to add an inch or 2 of MAP.
CHT and FF become the essential factors as described in the latest APS recommendations which I linked to. EGT is just referenced to know that we are LOP.
Piper J3
Well Known Member
I'm pretty sure Van's was referring to residual heat once the engine is shut off. Electronics on top of the engine are OK when in flight and cool air is moving vertically down through the engine and exiting the cowl flap at the bottom. When sitting on the ground with engine stopped heat travels up through the engine and cooks the electronics. Louvers on top of the cowling allow heat to escape. I leave my oil door open after engine stop for same reason.
That was one of the factors that had to be dealt with, but temps with the engine operating were a factor also.
The base price difference between the ULS and iS engines is $5000.
The price difference between the fuselage kit for each is only $25, but the base price for the new fuselage kit is ~ $500 more than the Gen. 1 fuselage kit.
rcarsey
Well Known Member
Hey, just curious what happened with this feature. IIRC, the tube in my iS kit was black.
The translucent hose was very stiff and difficult to install, and once a bunch of time in service was accumulated the longevity with exposure to auto fuel became suspect so a change was made to the black hose.
