Potential Heater box issue easily resolved.

[Shadrach]

I flew my F model today for the first time since annual was completed last month.  My plan was to do a timed climb to 10k and gather speed data. It was 81° so I opened the vent in climb. To my surprise, I was blasted with high heat. It was like running a heat gun in the cockpit. I closed the center vent, but by 4500’ the heat radiating from the duct itself caused me to RTB. On the ground I started trouble shooting. It turns out, the cable mount was disturbed while reclocking the prop governor. This prevented the internal flapper valve from fully seating in either the open or closed position. A simple repositioning of the Adel clamp holding the cable rectified the situation. Those of you with heater issues would do well to simply ensure that the valve is moving over its full range of travel.  As you can see the heater box and the seal are in fine condition even at 57 years old. The seal material look like table tennis racket rubber.

Heat on

 

heat off

 

 

Adel clamp after repositioning.

[Ragsf15e]

@Shadrach Mine is a 68 but the valve looks totally different.  It’s a butterfly and the seal doesn’t look like it, well, seals as well.  They are pretty easy to adjust for best efficiency though.

I can’t wait for your time to climb and speed run numbers!

Edited April 15, 2024 by Ragsf15e

[Shadrach]

23 minutes ago, Ragsf15e said:

@Shadrach Mine is a 68 but the valve looks totally different.  It’s a butterfly and the seal doesn’t look like it, well, seals as well.  They are pretty easy to adjust for best efficiency though.

I can’t wait for your time to climb and speed run numbers!

This is what today looked like before I aborted due to the flying sauna. I was only 2200lbs but it was 81° and  the field DA >2100’. I stopped at 4500 and try again to see if adjusting the controls would do anything to reduce the heat. When it didn’t, I headed back. Speeds were well above Vy as I gave up on the idea Vy in favor of additional air through the side wemac and overhead. I bet the air coming out of the center console was over 200°.
 

All things considered she still performed better than expected. Perhaps there is a permanent up draft west of my drome…

 

 

 

[Shadrach]

Also on the subject of the heater box valve. On the 67 at least, the flapper is two discs with only the one that “seats” in the closed position having a seal. Also, the disc with the seal should float a bit which is to say it is not firmly tightened to the flapper arm so that it can articulate a bit to fully seal. The sealing disc is held fastened with a cotter keyed fastener to allow it to float. If you open your box to find the disc rigidly mounted, someone likely over tightened it.

[Shadrach]

1 hour ago, Ragsf15e said:

@Shadrach Mine is a 68 but the valve looks totally different.  It’s a butterfly and the seal doesn’t look like it, well, seals as well.  They are pretty easy to adjust for best efficiency though.

I can’t wait for your time to climb and speed run numbers!

I wonder if your box was “upgraded”. The 68 IPC looks identical to the 67.

[MikeOH]

@Shadrach @Ragsf15e

My 'system' looks like the IX labelled area I've outlined below and calls out air-box item 19, not like the area labeled "I" which calls out item 1 and looks like Shadrach's 'system'.  This seems to match the IPC for my '70F (and '69F)  The "I" configuration seems to apply to C models.  Perhaps the '67F matches "I" as well, but the IPC I have used doesn't cover before 1968.

[Shadrach]

9 hours ago, MikeOH said:

@Shadrach @Ragsf15e

My 'system' looks like the IX labelled area I've outlined below and calls out air-box item 19, not like the area labeled "I" which calls out item 1 and looks like Shadrach's 'system'.  This seems to match the IPC for my '70F (and '69F)  The "I" configuration seems to apply to C models.  Perhaps the '67F matches "I" as well, but the IPC I have used doesn't cover before 1968.

That is weird as the short bodies in 67 used a different set up from mine. You’d have thought there would be no need for distinct heater boxes from model to model.  

Ours has been very reliable with this clamp issue being the first issue that I know of.

[Ragsf15e]

19 hours ago, Shadrach said:

I flew my F model today for the first time since annual was completed last month.  My plan was to do a timed climb to 10k and gather speed data. It was 81 so I opened the vent in climb. To my surprise, I was blasted with high heat. It was like running a heat gun in the cockpit. I closed the center vent, but by 4500’ the heat radiating from the duct itself caused me to RTB. On the ground I started trouble shooting. It turns out, the cable mount was disturbed while reclocking the prop governor. This prevented the internal flapper valve from fully seating in either the open or closed position. A simple repositioning of the Adel clamp holding the cable rectified the situation. Those of you with heater issues would do well to simply ensure that the valve is moving over its full range of travel.  As you can see the heater box and the seal are in fine condition even at 57 years old. The seal material look like table tennis racket rubber.

Heat on

 

heat off

 

 

Adel clamp after repositioning.

Here’s mine… it’s a ‘68F but looks totally different, no?  Seems to have the same size flapper secured to a seal in the middle.  Looking down from the top.  I also have the large diameter scat tube in and out.  Maybe it’s just a different size sheet metal air box?  Yours is mounted much lower too.

My climb rates at lower altitudes were very similar to yours.  I didn’t start to drop off until above 5-6k…

[Shadrach]

2 hours ago, Ragsf15e said:

Here’s mine… it’s a ‘68F but looks totally different, no?  Seems to have the same size flapper secured to a seal in the middle.  Looking down from the top.  I also have the large diameter scat tube in and out.  Maybe it’s just a different size sheet metal air box?  Yours is mounted much lower too.

My climb rates at lower altitudes were very similar to yours.  I didn’t start to drop off until above 5-6k…

The valve in that box appears identical to mine. They just elected to box it out into a rectangle rather than a modified prism. Likely easier to manufacture with no difference in performance. The only advantage to mine is being able to get a visual on the seal. Looking at the position relative to the motor mount, I am pretty sure they are mounted in the same place.

[Echo]

I have the same issue, that I have NOT yet looked at as it is having panel upgrades that have resulted in plane being down for eight+ weeks.  Home stretch and then in for first annual.  Looking forward to getting plane back in the air.  This thread will likely help me resolve my blast furnace.  Thanks Ross.  I fly multiple multi hour flights with this going on...