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  #1  
Old 10-10-2016, 08:44 AM
TimO TimO is offline
 
Join Date: Feb 2005
Location: Wisconsin
Posts: 319
Default Heater Control cable "tightening"

I'm not sure what the best way to describe this is, but here goes...

I have 2 problems with the heater boxes and cables in the RV-14.

1) The doors don't seal well, so definitely take the time to put a very thin RTV seal bead on the firewall when you are building, to help those vents seal when closed. Mine leak and in the summer it isn't great because when it's 90F outside the last thing you need is more heat coming in.

2) Now that I'm into the season when I need to use cabin heat, I'm glad that it does seem to work well as far as the amount of heat available. But what isn't working for me is the push-pull cable. The way the heater boxes work, if you have the vent door 1/2 open, the airflow will try to shut your vent for you. The push-pull cable detents aren't enough to keep the vent in mid-travel position. Does anyone know a way to "tighten" that up? I don't think there's any adjustment but can something be wrapped around the shaft or maybe shoot some type of glue into the cable detent area that may help add some friction? It wasn't even that cold out the other night but ever 3 minutes I had to pull the heater open again to keep the cabin temp up. If there was some sort of friction adjustment, I think it would have been fine.

I'm going to have to get a fix for that in place within a month or it isn't going to be fun to fly up here in WI.
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Tim Olson - CFI
RV-10 N104CD - Flying 2/2006 - 1200+ hours http://www.MyRV10.com
RV-14 N14YT - Flying 6/2016 - 120+ hours http://www.MyRV14.com
RV-10/14 Transition Training: http://www.RVCFI.com
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  #2  
Old 10-10-2016, 09:15 AM
JHartline JHartline is offline
 
Join Date: Dec 2012
Location: Carrollton, GA 5GA2
Posts: 147
Default Sealing the doors

Tim,

Not specifc to the cables...

I'm nowhere near flying but I did try an experiment with the heater flapper doors. I attempted to seal the doors with a little RTV on the front side of the firewall. I put tape on the doors, squished them into the thin bead of RTV around their edges, and let it cure. Even though it was a very thin layer it made the doors not want to sit flush against the firewall when they were in the closed position. Im not sure how much pressure the cables apply to keep the doors shut, but they wanted to sit about 1/4" open with the RTV underneath. I assume even the thin layer was interfering with the hinge axis. I felt the results were neither satisfactory or safe compared to the fit without sealant.

A builder with more experience may have better results. Possibly a sliding door would be the ultimate fix but maybe they have their own issues. They work pretty good in my Maule.
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James Hartline
Carrollton, GA 5GA2
RV-14 - Finish and FWF in progress
T-Bolt IO-390
Maule MX7-180
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  #3  
Old 10-10-2016, 10:01 AM
gasman gasman is online now
 
Join Date: Mar 2007
Location: Sonoma County
Posts: 3,237
Default

Check out NAPA auto parts. They do have Beldon type cables that friction twist lock. They fit right in and work great.
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  #4  
Old 10-10-2016, 01:06 PM
TimO TimO is offline
 
Join Date: Feb 2005
Location: Wisconsin
Posts: 319
Default

Circling back to give a small update.

Gasman, thanks for the note. Napa's website kind of stinks, but it did lead me to find a few others on other websites that are potentially good.

James, thanks for the note on the RTV. How thin are you talking? I'm thinking of thin as in barely visible. Maybe if I only put it along the top and top 1" of the firewall door area it wouldn't push the door out too far?
And, of course smear it as thin as humanly possible?
I am just not looking forward to doing anything with it because whether I do it from inside the plane, stuffed into the footwell, or from outside, trying to weave my arms and fingers around the engine mount, it's not going to be fun. I highly recommend that builders fix the sealing issue before they hang the engine. You'll thank yourself later.

Regarding the cable, I did call ACSproducts, who while related isn't the same company as Aircraft Spruce, who makes the heater control cable Van's sells....the CT A-740 cable. That cable is made with detents that are controlled by a little spring clip on the cable. The lady said there's probably nothing that I can do that will fix it, but I should verify that the spring clip is there, and I could at least try to play with the spring clip and bend it and see if I could make it better.

But what they did have to offer is, there is a CT A-700 cable that rather than 3/8" hole mounted, is 7/16" hole mounted but a similar sized knob, that is pushbutton locking. The wire is also slightly thicker at .062 instead of .050, but otherwise the cable would fit into similar spaces and have a positive lock. She said it is good for at least 6 lbs of locking force.

That may be a good way to go. I did find that if I kept pushing the heater knob in the summer and kept force on it, I could keep the leakage down. And so perhaps by giving it a little extra travel I can use the locking effect to keep the vent both locked closed or locked open part way.

So tonight I'll see if I can tweak the spring clips but probably will end up ordering new cables tomorrow. The Van's cables are over $30, so if this works, it may be something that you want to leave out of your kit and just order the A-700 cable from Spruce.
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Tim Olson - CFI
RV-10 N104CD - Flying 2/2006 - 1200+ hours http://www.MyRV10.com
RV-14 N14YT - Flying 6/2016 - 120+ hours http://www.MyRV14.com
RV-10/14 Transition Training: http://www.RVCFI.com
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  #5  
Old 10-10-2016, 03:02 PM
rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
Posts: 6,676
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We haven't had any problem with the standard cable installations in the two RV-14 prototypes and I have heard any negative feedback from Mitch either.
We do have the cables installed using the standard aircraft practice of adjusting so there is some cushion gap under the knob when the control is in the off position (pushed all the way in)
There is a method of increasing the friction to reduce position creep if anyone decides their installation requires that.
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  #6  
Old 10-10-2016, 04:18 PM
Aussieflyer Aussieflyer is offline
 
Join Date: Jan 2015
Location: Redcliffe, Queensland, Australia
Posts: 42
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I agree with Tim O. Both my heater vents leak and I live in the "Sun Shine State" of Australia (similar to Florida). I don't need or want the heat inside the cabin. I thought my vents looked pretty good when I built them and installed them and I'm very surprised to find they leak.

I wish I knew what Tim O and I now know when we were building. Its a minor issue but most annoying in warmer weather

I am considering removing the scat hoses for summer to alleviate the problem. Does anyone see any problems with removing the hoses?

Tim thanks for the research into the cables, I'm very tempted to buy a new set of cables.
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  #7  
Old 10-10-2016, 06:21 PM
JHartline JHartline is offline
 
Join Date: Dec 2012
Location: Carrollton, GA 5GA2
Posts: 147
Default RTV seal

Tim,

The layer between the door and the firewall was pretty thin. I tried for enough thickness for the door to seat against but when I peeled it back off it was paper thin. Since I don't know how much tension the cable will keep on the door in the closed position I'm back at the stock installation.

Again, a smart person may have better luck.
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James Hartline
Carrollton, GA 5GA2
RV-14 - Finish and FWF in progress
T-Bolt IO-390
Maule MX7-180
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  #8  
Old 10-10-2016, 06:55 PM
sibriggs sibriggs is offline
 
Join Date: Nov 2014
Location: Concord, NH
Posts: 90
Default Tighten cable

The way to tighten a cable that is used for the heat flapper is to make a small (not to sharpe) bend in the cable. This will increase the friction on the wire inside the spiral wound core and stop wire inside the cable from sliding due to vibration.
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  #9  
Old 10-10-2016, 08:37 PM
KeithB KeithB is offline
 
Join Date: Mar 2014
Location: Granbury, TX
Posts: 84
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After seeing Tim's problems with the heater doors not fully closing, and observing a tendency of one of my doors to "gap", I opted to get the A-700 cables hoping they would exert more pressure in the closed position. Unfortunately, I'm not flying yet (in fact not yet installed) so can't offer a PIREP.
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RV-14A Builder - kit #136
N314KC - First flight Mar 8, 2017, Phase I compl Apr 3, 2017
RV-6A sold
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Dues paid 12/2016
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  #10  
Old 10-10-2016, 10:40 PM
TimO TimO is offline
 
Join Date: Feb 2005
Location: Wisconsin
Posts: 319
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Keith, do you have a pic of the cables you ordered? How do you like the looks of them? Any reason that you think I shouldn't go for it?

BTW: I did add a slight cushion to the cable so that it doesn't bottom out but you can push it and get the heater door closed and still have a tiny bit of travel left. That wasn't enough to get it to stay closed and sealed though.

I may try to kink mine and see how it goes, but I have a feeling the A-700's are in my future. We use the heat from now thru May and on many higher altitude flights, so that's a long time to screw around without things being just right.
If you don't live in the midwest (or north of here), you really don't know what true cold is. It's not worth having the heater valves close on me for any length of time. The leakage issue can wait until spring now.
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Tim Olson - CFI
RV-10 N104CD - Flying 2/2006 - 1200+ hours http://www.MyRV10.com
RV-14 N14YT - Flying 6/2016 - 120+ hours http://www.MyRV14.com
RV-10/14 Transition Training: http://www.RVCFI.com
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