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   Bonanza Defroster Ducting Mod by Old Bob


Old Bob Siegfried - Ancient Aviator


A few months ago, I decided I wanted my 530W box (installed to accept an Avidyne IFD540) mounted high up in the center panel of my Bonanza.


The place chosen was as high as it could go without it sticking up through the glareshield and just high enough to mount an Auracle engine management unit beneath the 530 box.


Everything worked out fine except that I found there was no longer enough room between the windshield and the radio to be able to remove the glareshield! On my 1978 V35B and most airplanes that came from the factory with the speed slope windshield, the defroster duct is affixed to the glare shield and it has to be removed with the glare shield.


What I did was remove the defroster duct from the glare shield and mount it separately in the same place it was before. Since it s no longer attached to the glare shield, the glare shield can now be easily removed without having to touch the defroster duct at all.


Hopefully my photos will show how I:


1. cut the defroster duct off the glare shield


2 fastened  it back on temporarily


3. made brackets to hold the cut off portion precisely where it had been while attached


4. I then took it apart, mounted and secured the defroster duct "permanently' in place


By placing those two struts at suitable angles it makes the left mount fully adjustable if anything moves. I think there is a better photo of that left hand brace among the photos sent.


I tried to figure a way of doing the same on the right side, but came up with a blank. What I did was as shown. With the duct in the desired position, I held the angle up against it and marked the spot on the firewall where I wanted the brace to mount. After the upper cross piece was in position, I added the angle brace as shown then drilled the holes in the strut and the defroster duct.


Sounds complicated, but actually quite easy to do. The angle to which all is fastened is kinda hidden in that photo. I took the insulation off the firewall to mount the attach angle, then put it back on after the angle was secured. The idea of the whole exercise is to just provide a means to hold the defroster duct in place after it has been separated from the glare shield. If needed I could move the upper arm and drill a couple new holes in the angle braces.


I am sure there are many more elegant solutions, but this one worked well for me. It does require that the panel area be well opened up to see what you are doing. I had all the radios and instruments out of the airplane and all removable panels off of the instrument panel so that I could position those braces properly.


One photo shows where I mounted my 496 GPS antenna in the duct and another shows the scat tube "permanently" attached to the duct. PS: These GPS and XM antenna pucks easily get good signal through plastic, fiberglass and wood materials. Metal materials are problematic.


When I want to remove the glare shield, I just take out the one screw on either side and lift it off. No need to disconnect anything else because it all stays in place.


What forced the issue was mounting the 530/540 box so high in the center panel. That made it impossible to remove the glare shield with the defroster attached. I am told that some folks have cut down the defroster duct to allow it to be removed with the 530 box installed, but my way works like a charm. I had intended to add a rubber strip to seal the joint with the glare shield, but it fits so perfectly that none is required.


I am very pleased with the result. Just another minor alteration. Here are Old Bob's photos of his project. Please click on them for larger images.











PS: Old Bob is an A&P and in his view this was a MINOR alteration and can be signed off by any A&P with a similar opinion!


Remember, A&Ps/IAs are like doctors, lawyers and accountants - opinions can and will vary on many matters.


Contact Old Bob if you have any questions about his modification!


Thanks Old Bob for this and all the many other contributions you have made to Beechcraft operation and ownership!



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