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Closing the tunnel for EXP Mod

Jetmart

Well Known Member
Wondering if anyone with dual exhaust is considering closing in the tunnel and adding the pilot controlled exhaust ramp cooling flap and associated cable/bracket that comes with the RV-14 EXP version.

It is too late for me to do the entire EXP but like the idea of a pilot controlled cowl flap and understand that closing the tunnel reduces a fair amount of drag.

Does anyone have any insight on what would be involved in doing this? I am in late stages of my build and trying to understand if there is sufficient benefit to incorporate closing the tunnel and adding the cooling flap now.
 
Wondering if anyone with dual exhaust is considering closing in the tunnel and adding the pilot controlled exhaust ramp cooling flap and associated cable/bracket that comes with the RV-14 EXP version.

It is too late for me to do the entire EXP but like the idea of a pilot controlled cowl flap and understand that closing the tunnel reduces a fair amount of drag.

Does anyone have any insight on what would be involved in doing this? I am in late stages of my build and trying to understand if there is sufficient benefit to incorporate closing the tunnel and adding the cooling flap now.

Hi Glenn:

I have a flying RV14A and I am definitely considering a tunnel mod without the engine change. My plane is slightly faster than the official numbers, has excellent cooling (290s - 310s on CHTs), has Vetterman 2x 2-into-1 trombone exhausts, so I consider it a good candidate. I’m planning to benchmark the current performance well and then do a test run with the tunnel closed off, much like the pictures shown by Vans for the first prototype (webinar by Greg Hughes). Based on the results, I’ll decide if it’s worth investigating a retrofit of the tunnel “cowl flap” air box. I may even be able to just close it off with no mechanism. I’m also patiently waiting to see if anyone else pioneers it, or if Vans brings out a retrofit option. I’d also like to see the final version to make my designing easier.
 
Hi Glenn:

I have a flying RV14A and I am definitely considering a tunnel mod without the engine change. My plane is slightly faster than the official numbers, has excellent cooling (290s - 310s on CHTs), has Vetterman 2x 2-into-1 trombone exhausts, so I consider it a good candidate. I’m planning to benchmark the current performance well and then do a test run with the tunnel closed off, much like the pictures shown by Vans for the first prototype (webinar by Greg Hughes). Based on the results, I’ll decide if it’s worth investigating a retrofit of the tunnel “cowl flap” air box. I may even be able to just close it off with no mechanism. I’m also patiently waiting to see if anyone else pioneers it, or if Vans brings out a retrofit option. I’d also like to see the final version to make my designing easier.

I think there will almost have to be at retro kit available soon from Van’s to close off the tunnel. There are likely many builders that have taken delivery of the fuselage kit and still have the opportunity to do the engine upgrade when ordering the engine and firewall forward kit
 
I would also like to see the outcome of what you are planning.
Hi Glenn:

I have a flying RV14A and I am definitely considering a tunnel mod without the engine change. My plane is slightly faster than the official numbers, has excellent cooling (290s - 310s on CHTs), has Vetterman 2x 2-into-1 trombone exhausts, so I consider it a good candidate. I’m planning to benchmark the current performance well and then do a test run with the tunnel closed off, much like the pictures shown by Vans for the first prototype (webinar by Greg Hughes). Based on the results, I’ll decide if it’s worth investigating a retrofit of the tunnel “cowl flap” air box. I may even be able to just close it off with no mechanism. I’m also patiently waiting to see if anyone else pioneers it, or if Vans brings out a retrofit option. I’d also like to see the final version to make my designing easier.
 
I have installed the kit onto my QB fuselage. Not too bad of a job. It took about 8 hrs. to do. I understand this mod is more about drag reduction than cooling. If I had a flying airplane to benchmark against I would try to temporarily close off the tunnel completely and go fly. Monitor temps and assess whether the cooling flap is necessary at all. The entire kit with everything you need from Van's is $250.
 

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I think there will almost have to be at retro kit available soon from Van’s to close off the tunnel. There are likely many builders that have taken delivery of the fuselage kit and still have the opportunity to do the engine upgrade when ordering the engine and firewall forward kit

There is a retro kit available from VANs and it is not too hard to add it if one really wants to. What it would be involved is to install 8 nut plates (four on each side of the tunnel) which would not be much work. You will also need to poke a new firewall pass thru for the cable that operates the cowl flap. But this will not work with the VANs single pipe exhaust or the Vetterman dual pipe, if they go thru the tunnel.
One other concern would be temp control for the oil. Nearly all RV14s do very well with CHT but the oil temp can be marginal. As you close the exit airflow, this will have an impact on the cooling but by how much, I could not tell.
 
Add me to the list of interested parties. I too have a stock 390 (34 hrs TTSN) with the Vetterman 2 into 1 pipes that exit through the lower cowl leaving the tunnel empty. Like others have stated my engine temps are fine and my oil temp seldom goes above 190 F even in a hard climb (I installed the 5” oil cooler scat tube flanges). Even if the mod only adds a knot or two it will pay for itself over the life of the airplane. If anyone test flys before and after the mod PLEASE post the results
 
Reactivating this thread

<SNIP> Has anyone added the tunnel cowl flap to a flying airplane with the original 210 HP engine? If yes, was there a speed improvement? Also, On colder days my CHTs can drop down to the 280 range in cruise at altitude. Does this mod help to modulate CHTs?
 
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<SNIP> Has anyone added the tunnel cowl flap to a flying airplane with the original 210 HP engine? If yes, was there a speed improvement? Also, On colder days my CHTs can drop down to the 280 range in cruise at altitude. Does this mod help to modulate CHTs?

You get about 2-3 knots of speed. You can expect both your CHT and oil temp go up but on warm days, 75+ OAT your oil temp will be high, perhaps uncomfortably.
One other benefit is that your cabin heat will be working really well because all the pressure and warm air inside of the engine will be rushing thru. Make sure you don't have any exhaust leak within the engine compartment.
 
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I have a non-EXP with dual Vetterman exhaust. I installed the cooling flap during the initial build so I don't have any before versus after data. I didn't reduce the outflow area any of the original style cowl and now feel I could have. My CHT's are cool and my oil runs 187-191F with the cooling flap closed even on the hottest days. I find myself only opening the flap on hot days for landing to reduce under cowl heat and reduce fuel vapour idle loping. I would not expect you to have any heat problems with this type of set up. As mentioned my oil temps are fine with the cowl flap closed. I do have the 5" scat tube to the oil cooler. I have over 110 hours on this setup. If I were doing it again I would close up the exit area of the original NON-EXP cowl.
 
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2nVvMGJ


I have an IO-39O thunderbolt - not the exp. Redesigned the cowl for more speed and had some initial issues with high oil temps. As part of this process I tested Vans cowl flap (the assembly covers the entire tunnel area). With or without it - I saw no change in top speed (221 mph). I did see a 7 degree drop in oil temps without the assembly - compared to with it and the flap door open.
 
A little bit of a side twist on the subject, but has anyone installed the Antisplat cowl flaps along with the center tunnel flap?
 
-14 tunnel cowl flap kit part# ?

-14 tunnel cowl flap kit part# ?

I've searched through vansaircraft site and cannot find the entire kit part number, price, and a installation instruction download.

can anyone point me to that information?
 
The Kit P/N is F-14190 INSTALL KIT. If you contact Vans tech service they will send you the instructions.
 
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