P337 Intercooler Flight Test Comparison

[SkyKing]

Here's the American Aviation Intercooler flight test comparison data for a 1973 P337. Notice the difference in the servo inlet temperature with and without, as well as a nice increase in speed. Ours is a 1977 model and experience with the AA Intercoolers dictates the speeds are fairly close.

SkyKing

[Bob Cook]

Skyking

I am now a believer in magic... The intercoolers provide additional airspeed with no other drawbacks...... Right ?

(what is missing with the data Skyking is the Fuel Flow differences running similiar ROPs. None of the Intercooler mfgrs bothered to include these when selling intercoolers).

Basically it reduces the Upper deck air temp creating additional cooling and subsequent O2. But what about fuel flow figures.

If I try and run the AC using "book" figures it doesn't work. You are at least 1 gph richer / engine to run with same EGT/CHT. So where is the savings?

My feeling is they provide additional power on TO and climb, more reserve..........but..but.but ..... the rear engine oil temp or CHT is going to altimately create the limit.

It is kind of like that little coil that went into the top of the distributor (sold at carnivals).. you should remember eh DON?

Note for the newbies; Don't ever go by the POH or you will "cook" your engines!

Basically you are reducing density altitude... Anyone else want to jump in with a different thought ? <G>

Bob

[SkyKing]

Bob...

Were you able to successfully open the attachment.... I wasn't able to! Why is it that some items open within the message box and on others you have to click?

In any event, I'm going to try adding one additional item that might help you analyze the situation.

Regarding oil & cyl head temps... everything is much COOLER with the intercoolers.

BTW, does your P337 have intercoolers, or not?

SkyKing

[SkyKing]

Things seem to be hit and miss tonight... will try again to attach the fuel flow/power data for American Aviation Intercoolers. Hope this is enlightening Bob...

SkyKing

[SkyKing]

Things seem to be hit and miss tonight... will try again to attach the fuel flow/power data for American Aviation Intercoolers. Hope this is enlightening Bob...

SkyKing

[Bob Cook]

Yup

It has Riley intercoolers. ....... and no attachment. What kind of file are you trying to attach?

I seem to creep to 200 deg on the oil temp and I end up reducing the rate of climb. I usually am pulling 33/2500 to 2600 on the climb with approx 240 lbs/hr total fuel burn (full rich).


Bob

[Kevin McDole]

Skyking, I was able to download the chart you posted. I have not heard of the term "Servo Inlet Temp" previously. I assume they are referring to Induction Air Temp (IAT), which is the temp of the air entering the upper deck (after it's been intercooled).

I notice that even with medium power settings up high, you're getting a 100 degree F cooling benefit from the intercoolers - which is going to directly relate to a higher % HP output for the same RPM/MP. Some installations say that you should reduce the MP 1" for every 10C of intercooler effect. In your situation, that would be about a 5" to 6" reduction in MP to keep the same percentage HP.

How do you compensate for this?

[Bob Cook]

Kevin

HP = FF < losses (fricitional and otherwise).

Fuel flow is the only way to determine actual hp unless you work backwards knowing the Inlet air temp and using that to calc density altitude. Even that is tricky.

You can only assume you are accurate at two points; 1) full throttle take off, and cruise leaned to peak or thereabouts and then resorting to the engine mfg. charts.

The fact you are cooling the inlet air temp does NOT give you more hp, it provides you with better combustion characteristics. You still need the correct fuel/air mixture to maximize efficiency.

Get out the sliderule......... errr..... calculator! or, you run the engine within its temperature limits avoiding pre-ignition or detonation.

During world war II they used water and/or water methane injection to get emergency hp.
Limits ? strickly temps.
How much additonal hp ? > was theoretical based solely on density altitude from charts.

Compare the POH fuel flow leaned to peak and work backwards, using the correct rpm scale, you can see where the MP would be if there was no intercoolers. The difference is what the intercooler is contributing the performance. The amount of hp (%) remains the same for the given fuel flow.

GMAS ?? comments

Bob

[kevin]

FWIW, the advice I have been given (and have been following) is to reduce MP (or RPM I suppose, although that is not what I do) to get the book fuel flow. If you use book MP/RPM settings with intercoolers, you will be developing more HP, including higher cylinder pressures, than the engine was designed for. 'Course, if you use 65% power MP and get 75% power fuel flow, you are OK, you are still at or below 75% power.

On my airplane, this results in book fuel flow at 63% power being 2" MP lower than book. This is operating 50 degrees rich of peak on the first cylinder to reach peak (#5 on my airplane, both engines). Fuel flow is verified by actual fuel consumption, not just fuel flow indicator. So I use 27"/2500 RPM for 63% power cruise.

Kevin

[Bob Cook]

Kevin et al ?

Question:

1) How do you know 2"s is appliceable ?
2) if OAT -10 deg. is 2" applicable at 5kft ? 10 or 19k ft?
3) what parameters does the POH use for fuel flow settings?
4) what density altitude does the engine see with turbos? without turbos? assuming std temp and pressure.
5) What fuel flow does the TCM manual say for same settings as the one you just mentioned?
6) is 50 ROP developing same HP as PEAK ?
7) what ROP settings does TCM give for there mean effective brake hp figures ?
8) would the 2" hold if the OAT was 105 deg F ?
9)So what is the common denominator for HP?
10)How does JPI calculate the % of HP on their engine guage ?

Do you have the TCM manual on the TSIO360C or CB?

What happens if your tach or MP guage is out by 10 or 20% ?



Interesting discussion.

BTW Kevin what is your actual fuel flow for this power setting?

Bob

[kevin]

Bob,

To answer some of your questions:

I developed the 2" based on experimentation at various altitudes and temperatures, and measuring actual fuel consumption (with a dip stick). So cockpit instrumentation is irrelevant.

I fly from 13 - 20,000 feet most of the time, I didn't experiment at the lower altitudes. For 13 - 20K, OAT from -35 to +20 C, I did not detect a signifcant difference in fuel consumption. I suspect there was one, but I think the difference is buried in the basic inaccuracy of my measurements, i.e. +/- 1 gallon per tank.

My MP gauges may be both out the same amount in the same direction, but I doubt it. One guage does seem to be about 1/2" off based on indication at sea level. But again, I don't care what the indication is, I just want to run my engines at 63-67% power.

TCM manual is at the hangar.

50 ROP is of course not the same horsepower as peak, and you know that, this must be one of your stalking horse questions.

Rear tach IS out by 50 RPM, checked using ground instrument. If either tach or MP gauge goes out of adjustment, I will detect the difference in unusual fuel flow, low or high, and investigate.

I agree, an interesting discussion

Kevin

[kevin]

Actual fuel flow is 23 gph at 27/2400 50 ROP.

Kevin

[SkyKing]

Kevin, Bob, et al.,

Okay, maybe the following chart will help in the discussion, which shows recommended cruise-climb as well as normal cruise power settings.

Bob, your oil temps don't sound right... we very rarely see them approach 180 degrees unless it's a ++ISA day, and the rear engine always runs slightly cooler than the front with everything buttoned up. Maybe the Riley type intercoolers don't offer the same amount of "inter" cooling - ha! I've not seen the Riley up close, but from pictures it appears the radiator surface is somewhat smaller than the American Aviation units.

Another chart I attempted to scan wouldn't go, but basically the MAX POWER limitation is 35.3" MAP @ 2800 RPM for NORMAL takeoffs. For Density Altitudes above ISA, the chart reflects the correct MAP for a given condition, but in any event max is 37". Today, for instance, our OAT is 90 degrees at sea-level and the chart shows a MAP for takeoff of 36.3".

We normally cruise at 27" & 2300 RPM, and as you can see by the chart, that equates to approximately 55% power with a fuel flow of 57PPH each end using peak EGT for Best Economy, or 64PPH each end for Best Power. At this low cruise power setting, we opt for peak EGT or right in the middle, around 60PPH each end, so Kevin... you're burning more fuel than you need to -- if you have the AA intercoolers. We have the standard Cessna gauges and the dual Economy Mixture Indicator (EGT), which because of the probe placement in the exhaust stream is actually reading TIT. And note what the POH says... "Continuous operation at peak EGT is authorized only at 65% power or less."

SkyKing

[Bob Cook]

I always run at 29/2450 or 31/2450 for cruise. Burn is about 27 gph at 50 rop for 68-70% hp (29").

re temps. rear engine does run warm based on OAT being isa++ with the air conditioning on. Normal front temp is 160 and rear is about 180. they would run a lot cooler if i ran at 55% power.

My humble opinion is try power is based on fuel flow at peak EGT then consulting the tcm manual and correlating to rpm curve.

Kevin, I wasn't trying to bait you. my argument is cooling the inlet air can can help to run the engine cooler and develop more potential output based on hot and heavy climbs. Fuel flow still dictates % power regardless of OAT or intercooler temperature.

Skyking, I do not have my poh with me but what is the cessna spec pwr based on same RPM and FUEL FLOW in your chart. Must be a couple of inches difference ? just a guess.

Bob

[SkyKing]

Bob,

Sorry that chart was so BIG... guess I need to learn how to make it "fit the window".

If it wasn't readily apparent after looking at the AA Intercooler Power Settings, as you can discern, the basic idea is to remember three power settings for any altitude based on 55%, 65% or 75%... e.g., it's always going to be 33" and 2400 RPM for 75%; 31" and 2300 RPM for 65%; and, 27" and 2300 RPM for 55% -- and their corresponding fuel flows, i.e., 88, 76 and 64 for Best Power (50 ROP), and if at or below 65%, peak EGT's resulting in 67 or 57 PPH respectfully.

Now, with respect to Cessna's POH... the chart for a stock airplane seems to have finite differences in BHP and Total PPH for a given altitude, ISA. So, let's just pick 10,000' and 18,000' for comparison and arbitrarily use 2400 RPM and 33".

At 10,000', Cessna POH shows 72% Best Power (50 ROP) with a fuel burn of 153 Total PPH for 2400 RPM and 33", and a TAS of 184 Knots. With the intercoolers the chart shows this same power setting giving 75% Best Power (50 ROP) and a fuel burn of 176 Total PPH, or 23 additional PPH (3.83 gallons per hour). BUT, the airplane equipped with the intercoolers is giving 195 KTAS instead of 184 KTAS as in the POH.

AHhhh, but drop the intercooled airplane down to 65% at the same altitude (30"/2400 RPM) where you can run lean peak EGT and your fuel burn is now 134 Total PPH with no penalty in airspeed... your speed is the same as the stock airplane at its slightly higher power setting... 184 KTAS ... and beating the stock airplane fuel flow by 19 PPH, or 3.16 gallons per hour. This latter figure isn't quite comparing apples to apples, because if you compare to the stock airplane's comparative per cent of power setting, the difference is only about a gallon per hour. So, it depends on how you want to skew the numbers.

OK, for 18,000' the stock airplane Cessna POH shows 71% Best Power (50 ROP) being developed with 33" and 2400 RPM, with a fuel burn of 150 Total PPH, resulting in 198 KTAS. With the AA intercoolers for the same altitude, 2400 RPM and 33" nets out 75% power and a fuel burn of 176 Total PPH- but you might need an extra 50 RPM spool depending on ISA conditions to keep MP steady, turbos spooled and pressurization happy, so running 32.5" and 2450 nets the same 75%. Again fuel burn will be 176 Total PPH, but speed will be 211 KTAS instead of the stock airplane's 198 KTAS, a distinct 13 knot advantage. Dropping the intercooled airplane down to 65% power results in 202 KTAS, and a fuel burn of 134 Total PPH, which is still better than the stock airplane at 150 Total PPH for 71% in addition to a slight speed benefit.

We very rarely run 75%... and unless we're going long, it really isn't economical to climb to the teens... but we like the pressurization and the turbos for mountain flying, and so we usually run 55% to 65%. At these power settings we can run lean and at peak EGT, thereby grabbing the fuel flow savings and also gaining speed over the stock airplane, at least at the higher altitudes.

If we run around local, say 5000' for a hop, we generally run 55% power which gets us down into the 114 Total PPH range, or 19 Gallons per hour and generally gives us about 160-165 KTAS on ISA days. Besides, we like to enjoy the ride, and these lower power settings are easier on the pocketbook and the noise levels are reduced too.

I beleive the intercoolers were probably the best investment on the P337 as it enables the engines to run cooler and promotes longer engine life. And there's virtually no maintenance to this item, as long as the rubber connection hoses maintain their integrity. Above all, as with any add-on equipment, if someone was in the market for a P337, I'd strongly suggest getting one with the goodies that you want already installed, as aftermarket installs now would be QUITE expensive, almost to the point of being cost-prohibitive. (Same with boots, RSTOL, etc.) And speaking of RSTOL, last time we checked it was around $14K+ for Robertson.

Well, there you have my nickel.

SkyKing