|
|
I know it's a tough sell. Hard to believe you have significant risk when
you are normally able to just throttle back, wait a while, and temps
start to drop. Tons of times I heard the same response in my
occupation...."If he just reacts to xxx, then the problem goes away".
Marginal systems place you closer to the boil over temp. It only takes a
20F rise in ambient temp to affect marginal system. It takes 80F rise to
affect robust system. If you heat soak a marginal system, that places you
right on the edge of boil over. Add a bubble of air to marginal system,
you are screwed. As your temps rise, your piloting skills drop off due to
anxiety. I've gotten a number of reports from guys who landed gear up
even though their warning horn was blasting away...just because they were
worried about the engine behavior. The incident I referred to was the guy that took off with marginal
cooling. Landed at Whyoming airport, changed to Evans, then took off and
bit it. Underlying root cause was marginal cooling. He never would have
changed to Evans if he had started out with robust system.
Our day to day problem solving skills set us up for failure. We are so
used to making marginal decisions, that we find it difficult to see the
significance of robust design. Easy to fly for years with marginal
system, then all of a sudden the other contributing factors stack against
you.......
High ambient temp, high altitude, heat soaked engine. Fortunately,
statistically it will only nail a few guys. A few for marginal cooling, a
few for marginal fuel delivery. One common cause....sys designed too
close to failure point.
Certainly agree, spray bar a good solution. -al wick
Cozy IV powered by Turbo Subaru 3.0R with variable valve lift and cam
timing. Artificial intelligence in cockpit, N9032U 240+ hours from Portland,
Oregon
Glass panel design, Subaru install, Prop construct, Risk assessment info:
http://www.maddyhome.com/canardpages/pages/alwick/index.html
On Tue, 15 May 2007 15:10:12 -0400 "Ed Anderson"
<eanderson@carolina.rr.com> writes:
Hi Al,
I would be interested in these other factors you mention referring to the crash. I have years of flying under cooling deficit conditions right after take off as do others as you mention - without any problem. Every study I have read on cooling indicates the designer strives for an optimum cooling system- for an operating regime - (frequently for the cruise regime) and then uses whatever, cowl flaps, exhaust augmentation, spray bars, to cool it under less than ideal conditions- like immediately after take off. I understand even the P51 faced that problem on taxi and take off on hot days.
You can certainly design your system to not have a "take off" cooling deficit but, you are now starting to talk bigger radiators (may have space constraints), more weight, cooling drag, etc. for some airframes and flight regimes a bit more would not be significant, but for other airframes and speeds these factors become more significant.
Perhaps we need to be as bit more specific as to what degree of "overheating" we are referring to. My limit on oil temp is 200F, my limit on coolant is 220F and those only for the short duration of launch and up to 120 MPH IAS at which time my system is on the good side of cooling. 10 years of flying with that limitation has not yet revealed any problem so far as I can tell. Now with a rotary, if your temps are going 240F on oil and similar on coolant then I personally would feel that is too high and something should be done.
A crash to which the overheating was apparently one of a set of factor is certainly something that I would be interested in. How bad was the overheating and how did it contribute to the crash? I (and I believe all of us) would be interested in the details of the crash you mention that was contributed to by marginal cooling - for lessons learned. A spray bar does indeed provide a considerable margin, Tracy flew with one for a bit (mainly for racing I believe), I've never experimented with one since I don't go racing and once airborne and 120 IAS and my system is happy. However, it might be interesting to see exactly how much benefit such a simple system would provide.
Gotta put that on my long list of "to do" things. Another thing I have been thinking more about is that my GM cores which have served well are approaching the 10 year point. They are really not designed for water flow as we know, so I would not be surprised that a custom made set of radiator cores might lower my coolant temps by 5-10F by simply providing improved coolant flow.
As always, appreciate your input and perspective, Al. Any risk we can eliminate or reduce is worth examining and taking action on. Again, would be interested in the details of the accident if you have them.
Best Regards
Ed
----- Original Message ----- From: "al p wick" <alwick@juno.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Tuesday, May 15, 2007 12:08 PM
Subject: [FlyRotary] Re: First Flight - Renesis in RV-7A
>I know a lot of you guys are flying with conditions similar to what Ed
> describes. It gets hot during climb, but cools off during cruise. It
> seems manageable. I encourage you to not tolerate such a design. This is
> a root cause for crashes. You have marginal system, normally easily
> managed, but suddenly other factors come into play. We had crash last
> year with marginal cooling as one of the root causes.
>
> One simple solution that provides extra safety margin is to just add a
> spray bar in front of radiator. It just takes a tiny mist of water to
> dramatically improve cooling. Strongly encourage spray bar at a minimum.
> Great solution for initial testing.
>
> Even then, I would seek improvements that eliminate need for spray bar.
> There are simple improvements out there. There are guys flying exact same
> hp as you, yet they have 10 to 20% better cooling efficiency. Find out
> what they are doing right.
>
> If you had everyone flying record their temp as they climb out from sea
> level to 12k ft, you would find a couple guys with better efficiency than
> the others. You'd have to record outside air temp. Coolant, oil temp at
> start and end of climb. Everyone would have to climb at same rate, say 80
> mph, then 90mph. Compare area of radiators. With some facts like this you
> could end up with some genuine breakthroughs. Speculations do not lead to
> breakthroughs.
>
>
> -al wick
> Cozy IV powered by Turbo Subaru 3.0R with variable valve lift and cam
> timing.
> Artificial intelligence in cockpit, N9032U 240+ hours from Portland,
> Oregon
> Glass panel design, Subaru install, Prop construct, Risk assessment info:
> http://www.maddyhome.com/canardpages/pages/alwick/index.html
>
>
> On Tue, 15 May 2007 07:47:09 -0400 "Ed Anderson"
> <eanderson@carolina.rr.com> writes:
>> Congratulations, Dennis. A great day for sure! A lot of work and $$
>> coming
>> to successful launch. Unless you make the cooling system capacity
>> considerably greater than you need at cruise, you will always run a
>> cooling
>> deficit during climb - high power, low airspeed. So long as it
>> doesn't
>> exceed your limits and cools off once sufficient airspeed is reach,
>> you
>> should be fine
>>
>> Ed
>> ----- Original Message ----- >> From: "Dennis Haverlah" <clouduster@austin.rr.com>
>> To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
>> Sent: Monday, May 14, 2007 10:23 PM
>> Subject: [FlyRotary] First Flight - Renesis in RV-7A
>>
>>
>> >I made my first flight this evening!! All systems worked fine -
>> cooling
>> >was marginal in climb but we had a good inversion and the outside
>> air
>> >temperature was quite warm. Several neighbors videoed the flight
>> and I
>> >heard several comments about how quiet the rotary plane was when we
>> played
>> >the video. We had a 180 hp RV-7A flying chase and on the video it
>> was much
>> >louder!! Only flew about 10 minutes but made an acceptable landing
>>
>> >considering there were about 50 people watching. I'll post some
>> picures of
>> >the plane later tonight.
>> >
>> > Dennis Haverlah
>> > RV-7A, Renesis, James Cowl
>> > Radiators under engine
>> > Catto 76 in dia- 8 in pitch
>> > EC-2, Em-2, RD1-C
>> >
>> > --
>> > Homepage: http://www.flyrotary.com/
>> > Archive and UnSub:
>> > http://mail.lancaironline.net:81/lists/flyrotary/List.html
>>
>>
>> --
>> Homepage: http://www.flyrotary.com/
>> Archive and UnSub:
>> http://mail.lancaironline.net:81/lists/flyrotary/List.html
>>
>>
>
>
> -al wick
> Cozy IV powered by Turbo Subaru 3.0R with variable valve lift and cam
> timing.
> Artificial intelligence in cockpit, N9032U 240+ hours from Portland,
> Oregon
> Glass panel design, Subaru install, Prop construct, Risk assessment info:
> http://www.maddyhome.com/canardpages/pages/alwick/index.html
>
> --
> Homepage: http://www.flyrotary.com/
> Archive and UnSub: > http://mail.lancaironline.net:81/lists/flyrotary/List.html --
Homepage: http://www.flyrotary.com/
Archive and UnSub: http://mail.lancaironline.net:81/lists/flyrotary/List.html
-al wick
Cozy IV powered by Turbo Subaru 3.0R with variable valve lift and cam
timing. Artificial intelligence in cockpit, N9032U 240+ hours from Portland,
Oregon
Glass panel design, Subaru install, Prop construct, Risk assessment info:
http://
|
|