Safety Alert: Excessively Rich MA3-SPA Jetting.

Please Read the Comments section for further information. Scott Romey in the comments is a technician at D&G. His information can be directly followed on this matter. Applicability now contains list of individual carbs. 

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DATE and REVISION:  23 June 2017. – Original Safety Alert on this subject.

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SUBJECT:      Some MA3-SPA carburetors remanufactured for Corvair builders by D&G Supply in Niles MI, were jetted excessively rich. While done with good intention, testing and operation has conclusively shown that the stock, original jetting for a 10-4894 model works on all displacement Corvair engines from 2,700 – 3,300 cc.

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APPLICABILITY:      Recommendation for inspection, MA3-SPA carbs rebuilt by D&G Supply

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Below is a file, listing all the individual carbs believed to be affected by this safety alert. Any builder with a question should directly contact D&G rather than make an assumption

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From Scott at D&G: “I just got done making what I think is a complete list.  All we ask is to please call or email us before sending the carb in. so we can confirm it has a modified nozzle and not waste time and money on shipping”

https://docs.google.com/spreadsheets/d/1NP6szGNgx4C9cXVRAbWVo0usHuQgHA77HeJtg6aP-fg/pubhtml#

 

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EXCLUSION:     This does NOT apply to any MA3-SPA carb which is known to have original model 10-4894 jetting.  NOTE: We have never sold carbs. I have just recommended models and suggested jetting and suppliers. Thus, any comment that starts with “My Carb came from WW” is not a factual statement.

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COMMENTARY:         Over the last several months, I have gradually become aware that some Corvair builders utilizing MA3-SPA carbs rebuilt by D&G supply had excessively rich carbs. This prompted a survey of builders, revealing that a number of builders had excessively rich carbs, but had not spoken with either myself nor D&G. Without such contact, the scope of the issue was not previously known. Today, I believe we are speaking of 35-40 carbs.

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Dan Weseman and myself have always used MA3-SPA carbs with stock jetting on all of our Corvairs. My run stand, which has operated several hundred Corvair engines has a completely stock MA3-SPA on it. This exact carb was used for the extensive computerized dyno testing we did in 2015 at John’s Speed Shop in Jacksonville Florida. Dan’s 3.3L Corvair ran one test to 147HP, and the instrumentation and data logging showed that the stock jetting on the carb worked perfectly. Jetting requirements are not directly displacement nor output related. All displacement and output Corvairs with MA3-SPA carbs in my work and testing have been shown to run well with stock jetting.

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The erroneous rich jetting was generated by one builder in Michigan, and his mechanic, supplying ‘information’ to D&G, without speaking to me about our testing. D&G, mistaking the supplied ‘information’ as typical data, made other rebuilt carbs richer. This misunderstanding has now been corrected, D&G is absolutely willing to re-jet the carbs, and it is up to builders to do their part to make sure their carb is jetted correctly. 

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If  you are running your engine at a density altitude of 5,000′ or less, the engine should run without issue with the mixture set at full rich. If the engine only runs cleanly with the mixture pulled back significantly, this is an indication that the carb is probably excessively rich.

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This excessively rich condition is a safety issue for three reasons: 1) The engine will not make full power if it is excessively rich, 2) It will have a significantly higher fuel burn, it will have reduced range and duration. 3) in the event of a go-around, pilots are taught to instinctively push the throttle carb heat and mixture full forward. If the plane will not run correctly with the mixture full rich, it will be an issue just when the pilots full attention needs to be on flying.

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Builders should not assume their carb is jetted correctly without verification. I recently spoke with a builder who was selling the Corvair he had removed from his flying Zenith after about 15 hours.  He never called to discuss the issue, but he was convinced that he had been experiencing “Carb Ice” , and claimed that he knew this because when he had the throttle pulled back for some length of time, the engine ran rough. He never tried pulling the mixture, or calling, he just decided to remove the engine and replace it with a fuel injected one. I have spoke with the current owner of the engine, and can say the issue was simply an excessively rich mixture. The plane was not experiencing carb ice at all. It just needed the carb re-jetted. Instead, it got a completely different engine. Calling us when you have an issue can save a lot of time and money.

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SUGGESTED ACTION:     I highly recommend that all Corvair engines with MA3-SPA carbs verify they have stock jetting.  Carbs rebuilt by D&G came with paperwork which indicates the jetting. If the jetting can not be positively verified as stock, then the carb should be returned to D&G  for inspection. If the carb was jetted richer than stock, this will be corrected by D&G. I have spoken with the owner on this, and he is more than willing to rectify this issue for builders. There is no excuse why any builder would continue to operate an excessively rich carb. Already having 10, 20, or even 100 hours of operation with excessively rich jetting without does not justify their further use without correction.

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http://www.dgsupply.com/contact-us

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This is a “Safety Alert” and I am issuing a “Suggested Action” because Corvairs are experimental engines, and as such, do not have Airworthiness Directives and Service Bulletins in the same form as certified engines do. I cannot require any builder to take any action, I can only appeal to his better judgment by making a serious recommendation. Airworthiness Directives are only issued by the federal government, and Service Bulletins are issued by certified part manufacturers, thus the difference in the Safety Alert.

This said, I appeal to builders to follow this recommendation. The most frequent form of push back on suggestions of this kind is a builder who is myopically looking at his one plane and making a conclusion based on his impression of his own plane. Conversely I get to see all the data, understand the extenuating or aggravating conditions, I had world class training in statistical decision making at Embry-Riddle, and I always further consider what still works, not just looking at what broke.  I am not a genius, but for the above reasons, my recommendations on Corvair flight engines carry more weight than those of one guy with a flying plane, even a well intentioned one. We don’t have to speak of opinions of internet personalities that have no direct personal involvement nor experience with flying Corvairs.

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DISTRIBUTION:    I ask that this information be shared with others who personally involved in building a Corvair flight engine. This should be done just by people who have read and understood the information themselves, who also are Corvair builders.  For this safety message to have efficient, accurate and timely distribution, it should not be forwarded in part, nor by anonymous sources. I issue Safety Alerts very infrequently, and they need to be taken seriously. Any impediment to their accurate transmission to builders is an act contrary to the safety of builders.

 

William Wynne

WilliamTCA@flycorvair.com

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Fall Corvair Colleges: sign in now open

Builders:

Here are the sign up links for the next two Corvair Colleges, #40 in Texas, and #41 in South Carolina. The links are active, and you can sign up at any time, they will close automatically when the events are full. Special thanks to Shelley Tumino for handling all of the on-line work for these events, and also for Co-hosting #40 in Texas.

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Corvair College #40 Wisener-Mineola Airport, (Tyler) TX 29 September 31 October 2 2017: This college has Shelley Tumino and Kevin Purtee as hosts the same couple who brought you the four colleges in Austin TX, Read about them here:The Cherry Grove Trophy and here: Kevin Purtee and “The Hat of Power”

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CC #40 is a medium sized 40 person Corvair College, at a real grass roots airport, hosted by two very experienced hosts. Both Dan Weseman and Myself are going to be on hand for technical support, in addition to a number of returning builders to assist. The required sign up fee covers the catered food and drinks. I expect this to be a very productive college. We will have several Corvair powered planes on hand for demonstration and inspection. Unlike other aviation “technical seminars” Corvair College is a total immersion experience, we pack a great deal into a very short time window.

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Corvair College #41, Barnwell SC, 10-12 November 2017:  This is a return to our flagship College at it normal time of the year. For a look at the 2015 Barnwell College, check this out: Corvair College #35 Barnwell builders video.

For a look at the EAA film about the 2013 Barnwell College, click here: New EAA video on Corvair College#27, Barnwell 2013.

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Barnwell has been the home of eight previous Corvair College. P.F. Beck and crew have the logistics down so well that we have no difficulty having a productive event for 90 builders. If you are planning on going, do not delay in signing up, as I expect the event to be full by labor Day

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here is the link for CC41:

https://eventregistration2017.wufoo.com/forms/cc41/

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Thank you,
William Wynne

 

Carb Ice

Carb Ice
By Grace Ellen

 

wwpiete

Grace Ellen is a freelance writer and pilot. She was a newspaper journalist for 10 years but left the profession upon finally conceding that it was morally bankrupt. A three-day open cockpit trip home from AirVenture 2001 in N1777W crystallized her love of aviation and formal training followed in a 1943 Taylorcraft L2-M. Tutored by CFIIs Chuck Nelson and Ken Terry, she also received aerobatic training. Grace Ellen earned her IAC Smooth Patch flying Ken’s Christen Eagle. A member of local IAC and EAA chapters, she is close to completing her instrument and commercial ratings. MCM

William Wynne was the passenger in his Corvair powered Pietenpol when it crashed north of Tampa, Florida, on July 14, 2001. The engine cut off at 700′ AGL, which gave only 60 seconds to attempt a restart and execute a forced landing. To avoid people on the ground, the pilot tried a sharp bank and the plane spun in from 80′. The impact destroyed the airframe.

When freeing the trapped pilot, a fire started and ignited William’s fuel-soaked clothes. While extensively burned, both William and the pilot survived the accident. An investigation into the engine stoppage has indicated that carb ice  almost certainly was the cause. Because a few of the engine components were incinerated in the fire, no one will ever be able to say with 100% certainty that carb ice was the cause. The engine was recovered from a wrecking yard where it sat for months, placed on a test stand, and runs well. The remaining wreckage was examined very closely and no evidence of any kind of failure was found.

This mechanical integrity and clues such as visible condensation on the exposed intake manifold just prior to the engine quitting leaves carb ice as the only probable cause fitting not most, but all of the evidence, William said.

A single incident of carb ice hardly seems newsworthy. Most pilots and flight instructors feel they have an adequate knowledge of the subject. However, William’s extensive discussions with pilots and builders after the accident revealed that most traditionally trained pilots have little understanding of the subject. The rote memorization of a technique that works on a single aircraft and atmospheric setting does not constitute an adequate understanding of the topic. Further, experimental aircraft may have quite different engine management requirements.

The day of the accident was overcast with the cloud base at 800′ and dropping. The OAT was about 70F. The dew point was within 5 degrees. The trip had been 90 miles and the flight was within 2 miles of the destination. The plane had been throttled back to 60mph to allow traffic at the destination to clear. The carb heat control was in the rear cockpit and was not applied.

The engine, a direct drive Corvair fed by a Stromberg carb from a C-85, was  turning about 2,200rpm. It had at least 13 gallons of 100LL in the wing tank. Within one minute of the power reduction, the engine quit, William said.  It had dual ignition and a restart was attempted on each one. The engine  cranked normally, but did not light. Carb heat was not used. The impact broke  up the airframe and severed the 3/8″ fuel lines to the wing tank.

The  airframe ignited about a minute later when fumes from the spilling lines  reached a shorting wire. The fire burned for more than 20 minutes, consuming  most of the airframe but leaving the engine largely intact.

Many pilots interviewed later expressed the following thoughts:
1) Carb ice cannot form at 70F, and certainly not in Florida.
2) It would take longer than a minute for ice to block off the 34mm venturi.
3) The engine would “run rough” for a while before quitting.
4) Ice could not form at 2,200rpm.
5) Auto fuel would have about the same potential to ice as 100LL.

All five of the above thoughts are wrong. If you believe any of them,
you are a giant step closer to having your own version of William’s accident.
Here’s why:

1) Ice can form on warm days. Anytime a gas expands from high pressure to  low it will consume energy from its environment. In this case, the gas is the  air the engine is consuming and the pressure drop is from ambient to manifold  pressure, about 30″map to 12″map. The energy it consumes is ancarbicey form of     available heat. Most of the heat comes out of the air. This temperature drop  is instantaneous and can easily be more than 40F. Shoot a thermometer with a  CO2 extinguisher and learn.

 

 

 

2) Carb ice forms at the pressure drop point, which occurs at the
restriction to flow. At a reduced power setting, the throttle plate is the
restriction, not the venturi. At 2,200rpm and 12″map, the throttle plate is
barely cracked open. Right at this crack is the idle fuel port, a tiny hole.
A minute film of ice could cover it in an instant. The engine will stop
running because at power settings like these, most of its fuel comes from the idle circuit.

3) A certified four-cylinder engine of 7 to 1 compression and 190cid
swinging a 25-pound metal prop generally will sputter for a while when it is
experiencing carb ice. By contrast, a 9.5 to 1 six-cylinder 164cid engine
with a 6-pound prop will quit nearly outright. Many Lycoming pilots said
their engines gave warning. Lycoming carbs are bolted to the oil sump and
experience the onset of icing at a slower rate.

4) Icing has nothing to do with rpm; it results from the pressure drop.
Granted, an A-65 Cub with a certified prop is very unlikely to ice at
2,200rpm, but this is because 2,200rpm usually is associated with nearly open
throttle on this plane, and consequently very little pressure drop in the
carb.  However, any motor experiencing a large pressure drop in the carb is prone to ice, regardless of rpm. The motor in N1777W had a static rpm of 2,650. Any motor that has a prop that will allow a similarly high static rpm will be running low map at an rpm like 2,200. A manifold pressure gauge provides
useful information that a tachometer by itself does not.

5) Although auto fuel was not being used the day of the accident, pilots
need to understand how it can contribute to carb icing. Remember that at a
reduced power setting, the restriction is the throttle plate. And when
operating at reduced power, there is a large pressure drop at the plate, with
its accompanying temperature decrease. Fuel flows out of the idle port in a
mist. Misted fuel is still a liquid, not a vapor. 100LL under these
conditions remains a mist until reaching the combustion chamber. Contrast
this with auto fuel, which by design will vaporize readily under these
circumstances. It is a fact of physics that when the fuel changes from a
liquid mist to a gaseous vapor, it takes further heat from the surrounding
air. This is the cooling one feels when gas evaporates off the skin. This
additional temperature drop can produce icing when the same engine under
identical circumstances would not ice with 100LL.

In the past five years, N1777W flew with more than a dozen pilots and  logged hundreds of hours that included several very long trips. William  briefed pilots who flew the plane to use carb heat before any substantial  power reduction. The carb heat system on the plane was so effective that it  produced a 200rpm drop at idle, but still had to be employed as anti-ice, not
de-ice. The pilot involved in the accident only had about two hours in the  plane, including the final flight. Click here to view the NTSB accident report.

Although much of the physics of icing can be found in textbooks and  technical publications, William’s observations on the subject are based upon  years of work and actual flight testing. It is the nature of some to debate  anything and offer opinions extracted out of context from technical  publications. But William adamantly believes that this is a safety of flight  issue and people without flight testing experience debating esoteric details  dilutes the risk management message. William deems any commentary that  hinders the delivery of the message as amoral.

To reduce the possibility of a similar accident, William suggests that  potential pilots get a better understanding of icing, more thorough  briefings, a panel placard about when to use carb heat, and carb air  temperature gauges. William is working on a combined throttle/carb heat lever
which would move in concert and have calibrated linkages, but could be  manipulated separately for run ups. All of these are small efforts when the  price can be the destruction of aircraft and the loss of life.