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Camillo

Well Known Member
Hi.

I'm trying to obtain an IFR VMC permit to fly for my RV9A.

Italian amateur build regulation states that the builder has to comply to CS-VLA rules (subparts E and F).

§CS-VLA 1093 states as follows (from subpart E):

CS-VLA 1093 Induction system icing
protection
(a) The reciprocating engine air induction
system must have means to prevent and
eliminate icing. Unless this is done by other
means, it must be shown that, in air free of
visible moisture at a temperature of -1°C –
(1) Each aeroplane with a sea-level
engine using a conventional venturi carburetorhas a preheater that can provide a heat rise of
50°C with the engine at 75% of maximum
continuous power;
(2) Each aeroplane with an altitude
engine using a conventional venturi
carburettor has a preheater that can provide a
heat rise of 67°C with the engine at 75% of
maximum continuous power;
(3) Each aeroplane with an altitude
engine using a carburettor tending to prevent
icing has a preheater that, with the engine at
60% of maximum continuous power, can
provide a heat rise of 56°C;
(4) Each aeroplane with a sea-level
engine using a carburettor tending to prevent
icing has a sheltered alternate source of air
with a preheat of not less than that provided
by the engine cooling air downstream of the
cylinders.

Now, I installed a muffler - bought on Wicks aircraft (EC100-020) - much bigger than that which Van's catalog supplies, but I seriously doubt that it can rise temperature of 50°C (see point #1 above).

The engineer says that I will have to give evidence of that temperature rise OR give evidence that our carburetor falls in the #4 point (carburetor tending to prevent icing).

Does someone know if the Precision carburetor which comes with the stock Lycoming O-320 D1A is "a conventional venturi carburetor" (point #1) or a "carburetor tending to prevent icing" (point #2)? I may answer yes to #1, but maybe its particular displacement (attached to the wet sump) makes possible to answer yes also to #2.

Second question. If the answer to the first question is only 1, is the particular position of the carburetor in the O-320 (attached to the wet sump) and the narrow gap with the cowl enough to state that: "(a) The reciprocating engine air induction system has means to prevent and eliminate icing"?

Thanks a lot.
Camillo

Edit: sorry for the angry smile. It came out for mistake
 
All I can say............is that the fact, the the Lycoming carbs are attached directly to the oil sump, does have an effect on pre-heating the carb. This is why older Cessna's with Continentals always used carb heat for landing, while Pipers with Lycomings..........specified using carb heat only when required. There is also reference to this in Lycoming manuals.

L.Adamson --- RV6A

edit: A bit of additional info...

http://www.sacskyranch.com/crbice.htm
 
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Thank-you.

I searched on the web but found nothing more.
On Saturday I will look at my engine manual.

Ciao.
Camillo
 
What is the absolute carburetor temperature you are measuring? Some probes installed in the location provided in the Marvel/Precision carb read higher than the ambient air, due to the heating of the carb throat by contact with the oil sump. If this is the case then maybe you could use this information as evidence that your carb "tends to prevent icing"?
 
Camillo,

I also have the Wicks SS heat muff and I think with some minor modification it could produce much more heat. I have thought about fabricating a baffle blocking off a large part of the gap so that air would be drawn in from smaller gaps at each end. This means that incoming air would be forced to travel around a greater length of exhaust pipe. The baffle could be a piece of sheet SS or aluminum that attaches to the outside of the heat muff with screws/nutplates.

Another thing you could do is to increase the surface area that heats the air by wrapping a stretched spring all around the exhaust pipe in the whole area covered by the heat muff. You can make your own long "spring" by coiling 0.041" SS safety wire (lockwire) around some rod or dowel. Obviously the spring must be secured at each end to keep it firmly wrapped around the exhaust pipe.

Finally, for the purposes of measuring the temp rise with carb heat, I suggest you temporally install the temperature probe so it is measuring the temperature of the air before it enters the carb. I suggest securing the entire probe in the carb air filter box just in front of the air filter (on the outside of the filter so it can't get sucked into the carb). Don't forget to block off the hole for the carb temp probe in the carb body. :)

Fin 9A
 
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Camillo,

Have a look at what Vern Little did to seal his carb heat valve to stop cold air being mixed with the hot air. See the last 3 photos at the bottom of the page HERE

Fin
9A
 
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Have a look at what Vern Little did to seal his carb heat valve to stop cold air being mixed with the hot air. See the last 3 photos at the bottom of the page HERE

\
Click to expand...

I do believe that the flange for additional air from the sides, was added after this accident. I'd leave as is...


"According to the Van's Aircraft construction and operating manual, one method of building the
internal carburetor heat system is to "run a 2-inch air hose from a heat muff and position it to
feed into the alternative air inlet of the carb[uretor] air box without being attached and closed."
According to the FAA inspector who examined the aircraft following the accident, this is the
method by which the pilot constructed the airplane. According to the inspector, the 2-inch hose is
not large enough to adequately supply enough heat to the carburetor to sufficiently melt the ice."

L.Adamson --- RV6A
 
Why not

Check with others there and see what they did in order to certify their aircraft. Check the experimental and the certified aircraft in your area.

I suggest that you make friends with a certified aircraft mechanic - maybe they can help you. Please let us know what you find out.:cool:
 
Alan Carroll said:
What is the absolute carburetor temperature you are measuring? Some probes installed in the location provided in the Marvel/Precision carb read higher than the ambient air, due to the heating of the carb throat by contact with the oil sump. If this is the case then maybe you could use this information as evidence that your carb "tends to prevent icing"?
Click to expand...

Alan, yes, that what I thaught, even if I would like to be sure and reach the 50? rise, too. When OAT was +2?C carburetor temperature was +17?C. After carburetor heat was applied, temperature was +27?C.
 
Finley, thanks for your ideas.

I believe that reducing the central part of the gap on the muff would be an improvement.

In addition, I may use the Vern's remedy. My only concern is that in such way hot air will always be in contact with:
- the aluminium plate which closes/opens the passage for the hot air to the airbox;
- the airbox itself.
I hope this will not tend to ruin the airbox, after a few hours.
Anyway, I will ask Vern if his airbox is still there...

I will try shortly to make this mods.
Ciao.
Camillo
 
Ok. I made some more research and found some possible solutions.

First of all I have a question for you, since I didn't understand the following message (from an old thread on this forum http://www.vansairforce.com/community/showthread.php?t=2391&highlight=carburetor+heat&page=2). It is not clear to me if John solved the problem or not:

"When I installed carb heat on a FAB-equipped 7, I used the beer can Van's sells for the pick-off, knowing full well that sucking air across only 2" of exhaust isn't going to warm all that air all that much. No high math involved here; it doesn't pass the smell test. Yet I persisted. What I did do different was NOT use the Van's Carb Heat Connector because it is perched up on Z-brackets above the FAB hot air opening. This leaves a huge gap that will allow unheated air into the engine. I installed a spun aluminum 2" pick-off that Spruce sells to achieve a no-leak path from beer can (the plane's, not mine) to the intake (the plane's, not mine). It, incidently is rugged compared to the Van's offering. I removed the Z-brackets from the Van's connector to use it as the cabin air pick-off. The wimpy tack welds snapped within 20 hours; I remember others have posted similar failures. It's a piece of **** no matter the application.

I think I'll have a beer.

John Siebold"

My idea is to buy a second muff and install it on the left (side) exhaust pipe (as for the cabin heat muff) and connect it to the existing muff on the crossover pipe via a scat tube. In such way, I will have a muff preheating the air which enters in the second muff. This will produce much hotter air at the base of the scat tube, just before entering in the FAB.

In addition, I would like to seal the side flanges, if this will not melt something or reduce significantly air flow into the carburetor.

A similar solution to the second muff should be the following (from Garnt.piper on this thread: http://www.vansairforce.com/community/showthread.php?t=2391&highlight=carburetor+heat), but I have no idea where buying a muff which encloses both crossover pipes or how building it:

"Hi, some practical experience on my carb heat set-up for you all to digest. I installed the FAB-360 airbox and carb heat flapper door as per Van's instructions. I built my own exhaust pipe muff that fitted over both exhaust pipes that pass in front of the sump. On the ground, and in flight, I get a noticeable RPM drop when selecting carb heat on. I installed an airbox temperature probe, one of those cheap Radio Shack indoor/outdoor dual sensor thermometers. During initial flight testing I had no trouble getting 50-70?C temp rises at 75% power. The max temp I saw in testing was 89?C in the airbox. I thought this was good enough, the cheap thermometer has since failed, but I know my system works."

What seems certain is that Van's setup (the one with the short 2'' pipe) is NOT good for IFR installations as reported from Bruce Reynolds (extracted from this thread http://www.vansairforce.com/community/showthread.php?t=26712&highlight=carburetor+heat&page=2 ):

"The alternate air door on the top of the air box was originally there without
any heat muff of any kind. The theory was that warm air in the lower half of
the cowl was adequate to prevent carb ice. It was never thought to be warm
enough to melt ice in the carb. Since then we have offered a small muff and
connection to enhance the heat supplied to the carb. It is still our contention
that this is to be used to prevent carb ice, not melt ice that has already
formed. Since the heat door does not bypass the filter, you are always
getting filtered air unlike the carb heat system on some factory planes. It is
OK to fly with the carb heat on any time that you think that there may be a
chance of carb ice."

"Yes, the Vent DL-07 is to be used to connect the EA CARB HEAT MUFF with a short piece of 2" SCAT tube. That is the only combination of parts that we have for that purpose. This arrangement was never intended to provide hot air to melt ice and should not be used for IFR operations."

Thanks.
Camillo
 
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