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Installed tunnel ramp flap on flying 14A - Report

Bsquared

Well Known Member
I have a 14A with the original 210 HP 390 and Vetterman crossover 4 into 2 exhaust so the ramp area is empty. When the OAT is less than 50 deg F I had a hard time keeping my CHTs above 300. With an OAT of 35 deg my CHTs ranged from 310 down to 285 in cruise at 8500 ft. I decided to add the optional tunnel close-out and cowl flap that is offered for the EXP119 engine. Most of the time you install a cowl flap to lower temps during high power operations. Because the tunnel close out greatly reduces the exit area of the cowl this mod actually can be used to increase temps in cruise.

The results of my first test flight post mod are encouraging. With the ramp flap in the open position I didn't notice any temp differences during climb. Once I reached 6500 ft (40 deg OAT) I allowed everything to stabilize and my lowest CHT was 285 deg. I then shut the flap and within a minute my lowest CHT increased to just over 300....a 15 deg improvement. I did notice that my oil temp increased 5 deg to 185 but that is not a concern. I also seemed to pick up a knot or two with the flap closed. I will get more data over the next few weeks.

Here are the lessons learned during the install:
- Total time required was about 25 hours. This was more than I expected.
- The forward edge of the close out panel had to be modified to fit around the FF-00003B cowl bracket.
- The kit comes with standard 2 leg nut plates but you need 2 one leg nut plates to secure the forward edge of the close out panel to the crossmember. There is not enough room to rivet the ones in the kit.
- The biggest pain was having to remove the stick boots and the floor panel they mount on to get access to rivet the 2 most aft nut plates.

There is a lot of debate on other threads weather low CHTs are really an issue. I feel better having some control over them so I am happy I did it.
 

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I have a 14 with the original 210 HP 390 and Vetterman crossover 4 into 2 exhaust. I also installed the cooling flap during the initial build. I find other than the most hot summer days that I can fly with the cooling flap closed. I used the original designed lower cowling, (not the EXP version) and therefore still have a large exit area for the lower cowl even with the cooling flap closed. I experience cooler than normal CHT's and contribute this to the fact that my lower cowl exit area is open between the two veterman tail pipes. On the EXP lower cowl this area is closed in up to the bottom skin of the fuselage. Therefore I see little effect with the cooling flap open versus closed.

Bsquared did you stay with the original lower cowl design? Did you close up the exit area? I have considered doing this but I now have a fresh Evoke paint job and do not want to mess with modifications.

In the first picture you can see my lower cowl design if you zoom in. In the 2nd picture you can compare my standard cowl to the Exp cowl.
 

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Bsquared did you stay with the original lower cowl design? Did you close up the exit area? I have considered doing this but I now have a fresh Evoke paint job and do not want to mess with modifications.

I have the original bottom cowl with the 'Chin" that provides clearance for the original Vans 4 into one exhaust. I have not closed up any additional exit area...waiting for more test results.
 
Thanks, Please keep us updated. There are not many who have installed the cooling flap with the original cowl.
 
I have an original cowl on my RV-14A. I have a Vetterman's dual exhaust, so I modified the cowl to clear the exhaust which resulted in a larger exit opening. I installed the cowl flap. On climb out I'm seeing CHT's around 340F. In cruise, at 60% power and running LOP my CHT's are usually 290-310F. I made an aluminum part to close off the center portion of the exit area which seems to have increased the CHT's by about 10F. Low CHT's seem to be common with RV-14's. What are typical CHT's with RV-14's with the newer cowl?
 
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