Tracy wrote>>

The 'fix' I tried (and plan to try again) was to use the

wet wing fuel tanks as radiators (almost zero weight gain ).  This

of

course

requires that the fuel itself be used as the heat transfer medium

Marc wrote>

Tracy,
This sounds like the turbine engine fuel/oil heat exchanger. A

smallish

unit mounted alongside the turbine that contains the subject

exchanger,

which preheats the kerosine and cools the oil.

Marc Wiese

Mark wrote>

Not really what Tracy proposed. The Fuel/oil heat exchanger is dumping
engine oil heat into the fuel, but the fuel is not exchanging this heat

to

the air as Tracy proposes, rather just relies on the the huge flow rate

(A

GE90 usually exceeds 10 tons/hour fuel flow during take off) and dumps

this

heat with the fuel into the combustion chamber.

As others have pointed out, Tracy's plan sounds like airliners submerged
hydraulic system heat exchangers. Using this to add the extra cooling
capacity for the hot day climbs sounds good. How do you intend to

regulate

this so you are not increasing the vapor lock risk with nearly empty

tanks?

(Although looking at normal flight profiles - whenever you need power,

you

normally have either lots of fuel, and /or lots of airflow over the

wings).

What is the worst case?

Long taxi to a parking place at Oshkosh after a long x-country - no

safety

concern here?
Missed approach on hot day at high altitude airfield after long

X-xountry -

will this be an IFR RV-8?

Tracy, have you tried putting preheated or cooled fuel in you RV-4 and
getting some data on heat rejection rates? Would be interesting to know

how

much heat you can reject per gallon of fuel in your tank configuration

per

minute.

Do you intend using the stock RV cowl? When you add the weight and
complexity of oil lines to the tank plus the heat exchanger, it would

seem

easier to just use a larger radiator. The RV-8 cowl can't be that lmited

in

volume.

Mark Wrathall.

The taxi cooling problem I had was solved long ago.  No single change
involved, just many small incremental improvements.  All of them will be
incorporated into the -8 so I'm not worried about this.

The RV-8 is planned to be IFR equipped.  The missed approach should not be a
problem even without the 'fuel cooling' system.  Keep in mind that it is
mainly a maximum performance climb to cruise altitude that requires the
extra cooling in my scenario.  Even at its worst and on a hot day, my -4
cooling system would allow me to climb over 1500 feet at full throttle
before temps reached my conservative redline.  Backing off to 50% power
would quickly bring the temps down.

I did not do any extensive data gathering on the trial fuel cooling but I
got one indication that even minimum fuel situations would not cause a
problem.  Circulating about 1 gallon of fuel in the right tank (engine
running on left tank) through the oil pan heat exchanger at highest pan temp
(about 250 degrees) would cause an insignificant temperature rise in the
fuel from the tank.  I think the fuel might have been boiling in the heat
exchanger (anybody know the boiling point of auto fuel?).  If so, the fuel
vapor probably condensed on the cool skin of the tank and was back near
ambient by the time it got to the fuel pickup.  Unfortunately, the fuel flow
rate was not enough at the time to pull the oil pan temps down enough to
make it worth while.

I do plan on using the stock RV-8 cowl.  I would not add any oil lines to
the system to implement this system. (exchanger would be in oil pan)

Tracy Crook
tcrook@rotaryaviation.com
www.rotaryaviation.com

 
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