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Thread: Custom Ducts Information

  1. #1

    Custom Ducts Information

    1974 Sport B19,

    I was not happy with the appearance of my FWF NON-Custom Ducts, functional but not pretty. The Custom Ducts are absolutely beautiful.

    There is some missing information here on the last duct, fresh air duct RH Lower Cowl (NACA Scoop) to Cabin Heat Valve The dimensions are missing on the website for this duct, they should be 3" X 22".

    If you are running the Power Flow Exhaust STC the 2.5" Muffler shroud air inlet from the oval engine baffle needs to be 22 inches long minimum. I have used the 2.5" X 15.5" shroud inlet duct for the muffler shroud to carb heat duct. And expanded the 2.5" X 18" duct to 2.5" X 22" for the muffler shroud air inlet duct. This is what worked best for me.

    I hope this helps, saves you some money and is not to confusing.



    "Technical Editor:

    These are the air ducts needed for a 1970 and later Sport.


    115167DXX121063 Carb filtered inlet air, 3 by 26.5, standard cuffs both ends, 1 each

    115167DXX100723 Carb heat duct, 2.5 by 18, standard cuffs both ends, 1 each

    115167EXX121363 Muffler shroud to cabin heat valve, 3 by 34, standard cuffs both ends, 1 each

    115167EXX100623 Muffler shroud inlet air, 2.5 by 15.5, standard cuffs both ends, 1 each

    115167EXX080623 Cabin heat valve to defroster valve, 2 by 15.5, standard cuff one end, 2.125 cuff on defroster end, 1 each

    115167EXX080803 Fresh air duct from lower RH cowl to cabin heat valve, standard cuff one end, 3.125 cuff other end, 1 each"

    Just as a foot note, I am de-modifying my aircraft from the AD 73-23-03 (if I remember correctly) which removed these double walled ducts from under our engine cowls. Mike R. had posted a very long time ago that the construction of Custom Ducts should avoid the delamination and air blockage of the other double walled ducts which the AD removed. I will be watching closely. And you should as well, if you are running these double walled ducts.

  2. #2
    I also have just installed all my firewall forward ducting in my 1973 B19. The quality of Custom Ducts product is wonderful!! All the ducts that we had the numbers for fit like a glove and functioned perfectly!! Below is a quote from the email that I sent to Jon.

    I installed my firewall forward ducts yesterday and they worked great!! Even my AME said that they were the best custom ducts that he has seen from any company. He's a finicky fellow so this means that he was really impressed!!

    You said once I knew the length for the fresh air duct to let you know. I need the following:

    115167EXX120803 Fresh air duct from lower RH cowl to cabin heat valve, 3" by 19", standard cuff one end, 3.125" cuff other end, 1 each
    My original fresh air duct actually measured 3" diameter and 18" in length. The length by the part number is 80 quarters or 20" and I've asked Jon for a 19" version. I note from Siscoe's post that he had to go with a 22" version in his application. You will also notice that by the part number on the website the diameter would be 08 quarters or 2". In my parts manual I found the 115167EXX120803 part number from which the diameter would be 12 quarters or 3". After discussions with Mike and Jon about the two different part numbers, it was decided to wait until I could determine the diameter and length during the installation. Mike indicated that this particular duct may be different year to year and model to model due to various reasons and I should check it before I ordered one.
    I think Siscoe's disclaimer "This is what worked best for me" also applies in my case. My aircraft is stock under the hood and all the ducts as shown in the website worked as advertised. The only one I had to measure to confirm was the fresh air duct and Jon is sending that one out to me today along with an additional radio cooling duct. I noticed that the left cheek plenum had a duct going to the back of the avionics in the radio stack, but the right cheek had nothing attached to it at all. So because I have a fairly extensive amount of radios and nav gear located in both the stack and the right side panel I decided to put an additional duct from the right plenum to the back of the avionics in the right panel. As a beech pilot I guess you can never be TOO cool.....LOL.

    Anyway, "this is what worked for me" (my disclaimer) and I echo Siscoe's comment. Jon's Custom Ducts "Rock"!

  3. #3

    The preferred length for the 3" by 3.125" cabin air inlet duct, for the 1970 and later lower cowls having the NACA RH side air inlet, is 19". The original specification is for a 20" length, including a 3/4" cuff on each end. The ducts have usually been shortened in service, both to trim the ragged end and to prevent chafing on the brake reservoir line. Once they have to go under 18" or so, they are too difficult to get on and keep attached, to the cowling flange.

    Some replacements were made longer, most likely to leave 'trim stock' as the attachment end gets torn up during cowling R&R. The 3.125" molded cuff puts an end to that problem.

    I have encountered cowling flanges that have been damaged by the over-tightening of screwdriver-type worm clamps; then repaired using fiberglass wraps around the OD, rather than proper internal reinforcement. It might be a good idea to measure your cowling flange before ordering this particular duct. If you need it, Jon might be able to make it a bit larger than 3.125" for you. Of course, the other alternative is to properly fix the flange, so that it is the correct size (and to use the proper thumbscrew clamp).

    These Custom Ducts, when properly installed and with proper chafe protection, should last virtually the remaining life of the airframe.

    It's my opinion that the lined duct delamination experienced with some of the early FF ducting occurred when field technicians used standard duct stock to replace factory original ducting. They probably used the cheapest stock, rather than the molded and cuffed ducts from Beech; and (naturally) installed it with plain cut ends. It is very easy to leave the inner liner unsecured, and folded back into the duct; particularly on flanges where the duct is a very tight fit. In turn, that made it very easy for the lining to obstruct the duct. In contrast, the lined SCEET used for the Custom Duct parts that Jon makes for us is the heaviest quality on the market. The lining and the outer jacket are bonded together into a properly fitting cuff on both ends. I cannot imagine the airflow and suction it would take to cause the inner liner to detach from the outer jacket and from the spiral reinforcement wire.

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