Product Alert- Heat Muff

sprucemoose · #1 03-29-2009, 02:03 AM

I found this today while doing the annual on the Spruce Moose. As many of you have no doubt learned, the standard Van's carb heat muff is a pretty cheesy, ineffective affair. During my quest for a better solution, I came across this unit from Aircraft Spruce:

http://www.aircraftspruce.com/catalo...peheatmuff.php

I bought one and installed it. It works much better than the stock Van's unit, in that it actually produces a noticable RPM drop on run-up. I have extolled the virtues of this unit and have talked to many of you about it, and up until today I recommended it.

Well, here's what I found today:

This unit had about 150 hours in service. Three of the six stainless mounting ears had broken off entirely and were only held in place by the hose clamp. One of the remaining three ears had shed one of it's two rivets, and was hanging on by a thread. The final two ears just barely managed to hold the unit in place. However, it shifted enough to allow it to rub vigorously on the adjoining exhuast pipe, where it rubbed about 2/3 of the way through (the muff, not the pipe.)

I do like the idea of a wrap around carb heat muff over the stock Van's unit. However, based upon all this, I have serious doubts about this particular unit. I encourage everyone who has one (especially all those who I talked into buying and installing one) to take a close look at it.

Geico266 · #2 03-29-2009, 04:56 AM

Carb icing can occur, but is almost non existant on carbed RV's that I'm aware of anyway. Was there a problem that lead you to looking for a better "solution"?

DennisRhodes · #3 03-29-2009, 05:45 AM

I ran a 0235 L2C for years without Carb heat available. never had a problem. The 0320 seems to be just as forgiving. What about placing a screen between the heat muf and carb intake? That may provide better assurance that the parts don't reach the throat.

Rick6a · #4 03-29-2009, 05:48 AM

Quote:

Originally Posted by Geico266

Carb icing can occur, but is almost non existant on carbed RV's that I'm aware of anyway. Was there a problem that lead you to looking for a better "solution"?

The following is a real world example:

Christmas 2002: A transient pilot, his carburated RV-6A fitted with Van's stock "heat muff" was enroute to visit family and happened to be passing through our general area, a few miles southeast of Scott Air Force Base. He found himself flying through light snow and experienced in-flight icing and engine stoppage. God was with him because as he broke out of the low level clouds with little room to manuever, he was presented with an uncommon gift....an open field. Within the course of a few heartstopping moments, he dead-sticked onto the cornfield's frozen bumpy surface. Luckily, he was spared injury. In fact his RV suffered only minor wheel pant damage as the plane rolled to a stop. A few of our local EAA Chapter 32 members turned out to help him after responding to a general on-line plea issued by his distressed mother.

The builder/pilot's words, not mine: "It didn't have enough heat to melt the snow/ice that was starving my engine of air, and it doesn't provide an alternate air path if the filter is blocked. I'm going to change that design (alternate air) when I get home."

Geico266 · #5 03-29-2009, 06:05 AM

Good example Rick, but that was an example of the filter becoming clogged with snow, not carb icing. Would not the alternate air source be a better solution for that problem? If the carb heat was on (even the Van's heat muff) during the flight in snow there would not have been as sever a snow build up on the filter. The majority of the air feeding the carb would be coming from the engine cowling, not the outside air intake. Once the engine stops making heat any carb heat system is pretty much useless. Actual carb icing in RV's is a rare event, which may have lead this pilot not to use the carb heat in the first place?

Note to self: Turn carb heat on in snowy conditions.

JMHO

bhester · #6 03-29-2009, 07:57 AM

Here is the one I installed it has 280 hrs. with no problems and yes the carb temp does rise with it.

http://www.robbinswings.com/Carb_Heat_Muff.htm
http://www.robbinswings.com/FAB_Connection_Housing.htm

If you type Carb Heat Muff in Google it's the first thing that pops up,
just like typing in Bobby Hester my RV site is the first thing :-)

Rick6a · #7 03-29-2009, 09:59 AM

COMPARISON SHOPPING

The one piece Wicks carb heat muff is quickly secured with 2 (included) band clamps.

The Robbins Wings muff is designed more like a scaled down version of a traditional cabin heat muff. By that I mean it is assembled using several parts including (2) through-rods and two 2-piece end caps secured with nuts/washers. A band clamp secures each of the muff's end caps to the exhaust pipe and completes its basic assembly.

Both muffs are designed with an open area along the length allowing ambient air in. Cost aside, is one design inherently better than the other? As always, that is for you to decide. Obviously, I happen to possess both designs but have only used the Wicks muff. With it, I observe a 30-40 RPM drop when carb heat is applied.

sprucemoose · #8 03-29-2009, 12:31 PM

Quote:

Originally Posted by Geico266

Was there a problem that lead you to looking for a better "solution"?

Not really a problem, just looking for a better system. Many people have noted that they see almost no drop in RPM on runnup with the application of carb heat. RVs are not prone to carb icing, but that doesn't mean it can't occur. I've experienced it, and I wanted a more robust carb heat system.

Quote:

Originally Posted by Geico266

Note to self: Turn carb heat on in snowy conditions.

This is not just a good note to self, it is Van's recommended procedure. The carb heat on a carbed RV is not carb heat in the traditional sense, in that it does not bypass the filter. Van's recommends that application of full carb heat while flying in any frozen precip (snow) to avoid snow getting in the air box and choking the filter. This is not what most pilots are used to, and it is what lead to the service bulletin to install the filter by-pass mechanism. If one uses the correct procedure and applies full carb heat at the first sign of snow, then there is no need for the by-pass system.

There was an RVator article on the subject several years ago but I don't have it handy.

RV6_flyer · #9 03-29-2009, 02:11 PM

Quote:

Originally Posted by bhester

Here is the one I installed it has 280 hrs. with no problems and yes the carb temp does rise with it.

http://www.robbinswings.com/Carb_Heat_Muff.htm
http://www.robbinswings.com/FAB_Connection_Housing.htm

If you type Carb Heat Muff in Google it's the first thing that pops up,
just like typing in Bobby Hester my RV site is the first thing :-)

Over 2,000 hours on the Robin's Wings Heat Muff. First flight was without it. Installed it around the 100 hour mark. Now have over 2,200 hours. Reinstalled the SAME Robbin's Wings heat muff on new exhaust system with new cylinders.

The Robbin's Wing heat muff was recommended with my original Vetterman Exhaust system that was purchased from Vetterman before Van's sold the same system.

BTW. My Vetterman exhaust was replaced at overhaul time only because of the number of heat cool cycles and not becasue it was broken.

MrNomad · #10 03-29-2009, 03:50 PM

Jeff:

BIG THANK YOU for pointing out a potential problem. I use carb heat whenever it's indicated, and I'm in Tucson (warm country). I also use it to speed up the warming of the oil temp before flight. The warmer air reduces the time to get the engine up to operating speed.

Please disregard thread hijacks that change the conversation from the reliability of the product into whether we should or should not be using carb heat at all.

Your intent was to alert your fellow pilots to an obvious product hazard and for that I offer my THANKS.