REFLECTOR: Interesting Gotcha this morning

Christopher Martin christophercmartin at earthlink.net
Sat Nov 6 20:22:07 CST 2004


A word of experience on the issue of water in the side ducts. I experienced this as well. Not only did the water come into my ducts from engine washing but I also got water into the skin of the fuselage. Most builders have antenna cable coming out of the ducts and running into the skin for glide slope and VOR antennas that are built into the floor of the plane. I had water migrate along the interior of the duct to the location where the antenna cables went into the skin of the fuselage. This resulted in water within the PVC foam of the fuselage floor. The is not a structural problem because it was localized to the antenna cable area only. The solution is to drill a few 1/8th inch weep holes in any area that is a possible spot for water retention.

I also thought it might help to plug up the ducts with expanding foam at the fire wall and front bulkhead. Bad idea! The duct on the pilot side, where I run my 1/2 inch oil lines got uncomfortably warm. So, I opened them up again and allowed that cool air, from the pressurized nose compartment, to flow through the duct and out at the fire wall. This will also help to ventilate the area to exhaust any possible dampness from the inevitable water penetration.

Little tiny water drain holes are very acceptable. I have them in the lowest point of the duct area. The lowest point of the fuselage bottom near antenna cables. I also drain the little storage area in the strake at the door. And, finally, make sure you drain the area around the top wing bolts so that there is no potential to pond water in the wing bolt cavity.

Christopher Martin
christophercmartin at earthlink.net



----- Original Message ----- 
From: Brian Michalk 
To: Velocity Aircraft Owners and Builders list
Sent: 11/6/2004 8:36:37 AM 
Subject: RE: REFLECTOR: Interesting Gotcha this morning


That's a good idea.  Do they make a non-flammable version of spray expand-a-foam?  Extra firewall protection.
Is the spray foam even flammable?  I'd imagine yes.

 Brian Michalk  <http://www.michalk.com>
Life is what you make of it ... never wish you had done something.
Aviator, experimental aircraft builder, motorcyclist, SCUBA diver
musician, home-brewer, entrepreneur and barely single
  
-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org]On Behalf Of robajohnson at comcast.net
Sent: Friday, November 05, 2004 7:00 PM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Interesting Gotcha this morning


I had put a shot of spray foam in each duct on each end. Easy to get out or punch through if you need to run something else through there but quick and eay way to keep the water and cold air out. 

Rob

-------------- Original message -------------- 

> After fixing the leak in my sump tank, I decided I would clean off my 
> engine and reinstall my dip stick tube as it had become loose. 
> 
> I used the spray on engine degreaser and hosed it off afterwards. It took 
> two applications to get it really clean as the loose dip stick tube had 
> been leaking oil. Rinsed it down real good and let it sit for an hour 
> before taxing back to the hanger from the wash rack. 
> 
> Fired her up this morning and taxied out to RW 13. About half the way 
> there I started getting a pop corn sound in my headset! It was pretty 
> loud. I turned the ANR off and on, no change. Tried EI or right mag, no 
> change. Changing the rpm did seem to increase the rate of popping but not 
> as much as the rpm was changing. Turned off the intercom, slightly less 
> volume. Turned off the strobes, no change.. changed comm's the quality of 
> pops changed but still there. 
> 
> All indications voltage and amperage looked within norm. 
> 
> I sadly taxied back to the hanger... Damn, and we were planning a trip to 
> Mesa Verde tomorrow..... 
> 
> At the hanger I cycled electrical power and no change. Cycled again(I'm 
> stubborn) and it stopped!! Hmmm... Now thats good and 
> bad... Intermittents can be real buggers.. I could not get it to come back. 
> 
> I got out , looked at the alternator wiring, as much as I can see with out 
> de-cowling.. Popped the nose door and canard hatch. Nothing obvious??? 
> 
> My friend the local A&P/AI wandered by, he said he got worried as he heard 
> me taxi out but not take off. I told him the story and he didn't have much 
> more to suggest, except that it may have been an external source, some 
> local transformer or someth ing. that got my hopes up a bit, but not much... 
> 
> I decided to fire up and see if it would come back by taxing 
> around. pushed out of the hanger, "prop clear!" and started the 
> engine. He got this funny look on his face and gave me the kill signal 
> while pointing back at the engine. I stopped it and bent out and looked 
> back. There was a puddle under the engine. I had not primed or ran the aux 
> fuel pump. 
> 
> I jumped out and went back, stuck my finger in the liquid, smelled, 
> tasted, it was water?? Wow, it was coming out of he gap in the cowling 
> where the vent and fuel whiffle valve lines are. 
> 
> It must be from washing the engine I said. Strange it didn't drain when 
> the cowling was off.. I went to the nose and lifted. Water gushed 
> out!!! Must have been 1/4 gallon or more! 
> 
> Then I realized there are gaps where the oil lines and wires go into the 
> two ducts on either side of the fuselage. In my quest to really rinse down 
> the engine and firewall to insure I got all the degreaser out I had sprayed 
> a bunch of water into the ducts! Who knows how many BNC and other 
> connectors are in there getting soaked. Not to mention the main big ol 
> wires for the starter/alternator. The shape of the fuselage is like a 
> banana and any liquid put in the firewall end of the duct would migrate to 
> the center of the fusalage... 
> 
> In fact I had noticed one time after I had changed the oil and really 
> bothched catching the oil from the filter, its mounted right above the left 
> duct. The oil poured all over that spot. A couple weeks later I had the 
> back seat out and there was an oil stain where there is access to the duct, 
> the pilled oil that got in the duct it had migrated up the duct to the 
> middle of teh fusalage. 
> 
> I held the nose up for about 5 minutes until all dripp ing stopped. 
> 
> Fired up and flew around for half an hour with no popping noise. Now I 
> don't know for sure if it was the water that caused the popping noise, but 
> I do know I don't want to get that water in there again! It could also 
> freeze and do who knows what? 
> 
> Scott 
> 
> "Those who sacrifice freedom to get security, deserve neither." 
> - Benjamin Franklin 
> 
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