Topic: Transponder

[David H]

If all goes well, I'll be buying my friends Chipmunk and he'll be getting one with the correct FAA paperwork for the standard certificate - it's been a bit of a painful learning experience for him but it should work out in the end.    

The chippie does not have a transponder.   It has a small portable comm connected to the airplanes electrical system and an external antenna.  It also has a portabable intercom.  Both of these items are mounted in the front cockpit on the right side.    I've seen other chipmunks where the front compass has been removed for the radio installation.   I'd prefer to keep the original compass so I'm looking for ideas on where to mount the transponder and encoder.   My home airport is under the KPHL mode C veil so I must have one.    Becker and Microair make really small units for installation in an instrument hole.   I'm wondering if a standard transponder wouldn't be a better choice if it could be secured just below the instrument panel or off to the side somehow.   Any suggestions or photos would be great.

thanks
Dave

[ACL]

I have flow one with radio and xponder mounted on a bracket between the compass mount and the bottom of the instrument panel - set back a bit so you could see the compass (just). For a tall pilot it meant ducking down in order to see the radio's display, and the intercom which was mounted on top of them was all but invisible.

I have a panel-top mounted compass - original fit in my aircraft, so radio/xponder sit where the big compass would have been mounted - easy to see and operate. However, the intercom is attached to the bottom edge of the instrument panel on the right hand side, and I always hit it with my knee when climbing in... so be careful mounting things under the panel.

If you take a good look at the path your legs take when you get in and out of a Chipmunk, you will realise that there is very little space between the seat and panel that some bit of your anatomy doesnt pass through. I realised this when thinking about where to fit a mounting bracket for a GPS. (In the end I fitted some elastic to the GPS and strap it to my knee AFTER I've got into the aircraft.

The microair type units might fit against the fuselage side, but you'd have to find a bit not occupied by flap levers, etc.

Space is at a premium. Good luck in finding a bit of it spare!

Enjoy your forthcoming Chipmunk ownership.

James

[Bob]

We have the radio (old Narco 720) and intercom (sigtronic) mounted on a tray forward of the compass, and I agree i'ts not the best place but It does allow you to keep the original compass. we are thinking about changing to Microair and sputting them on the right side of the panel then mounting the instruments on a pod on the right, but it will take some thought and cheching what space is available with the biggest pilot in the seat!
Bob

[Rod Blievers]

For what it’s worth, here’s what I did to accommodate radios, intercomm and a GPS in my Chipmunk – though I must stress I’m not saying these are the best solutions!

Radio/intercomm – my “package” comprises a King KY-96A VHF radio (which incorporates an intercomm) and a King Transponder. These are mounted on a tray below and forward of the instrument panel, and forward of the floor-mounted P.11 compass. The VHF is mounted below the Transponder, I find this easy to see though to sight the Transponder requires some minor head-ducking (I’m 5’11” tall).

GPS – originally I used to wear my trusty Garmin GPS 92 on a cord around my neck, though I soon got mightily fed up with the inconvenience of this arrangement. Inspired by Mike Hannell (Chipmunk VH-ZIZ), I mounted my GPS using an “L” shaped plate, twisted to align with the lower surface of the coaming. A RAM plastic GPS holder is fitted to the lower arm of the plate. Initially, I had planned to remove the GPS for any flights other than cross-country trips (there are two wing-nuts on the coaming upper surface for this purpose) but it has proved so convenient and generally space-efficient that it’s become a permanent fixture. Subsequently I’ve had a GPS power supply installed, via a cigarette lighter fitted on the RH rear of the seat pan.

Whatever you do, check and check again as to what space you have available for BOTH you’re seated and (equally important) entry and egress from the seat. I’ve just installed a 1.5Kg BCF fire extinguisher, mounted vertically to the front of the seat and as far to the RHS as possible – while when seated the extinguisher is well out of the way below my right knee, I wish I’d thought more about the “mounting/dismounting” exercise, as I now have to be very careful where I place my right foot!

I hope this helps,

Rod.

[Dick Gower]

The radio rack on mine (VH-DCZ) is similar to Rod's as illustrated.

It is suspended from the underside of the radio rack which was stressed to hold a 36 lb STR9X VHF COMM so structurally it is sound.  It picks up the same four bolts positions that held the original radio so is easy to remove for access.  Of course it is essential to have all of the wiring (including the things usually forgotten like dial lights) via a decent connector.  The antennae are via connectors on the RHS.

It all comes out very easily and can be tested as one unit on a bench.

The compass stays where it is.

[David H]

Thanks for the suggestions and especially the pictures.   I think I'll make up some cardboard dummies of some different size transponders and see what works.   Forward of the compass looks like the best bet.    What about the encoder?   Behind the rear cockpit or behind the front intrument panel?

Rod, your fire extinguisher idea made me wonder.   Could a transponder fit vertically against the seat below my right knee?   Might be too difficult to use.   This particular chippie has a fire extinguisher bracket mounted on the right side of the forward cockpit above the rudder pedals.   The fire extinguisher is missing.

Dave

[Rod Blievers]

Dave:

Yes, your transponder would fit there but it would be terribly vulnerable to being stepped on every time you got in and out.

Encoder? I know I have one, not sure where it's fitted (my Chipmunk lives 50 miles away from here). I'll get back...

Cheers,

Rod.

[Dick Gower]

Thanks for the suggestions and especially the pictures.   I think I'll make up some cardboard dummies of some different size transponders and see what works.   Forward of the compass looks like the best bet.    What about the encoder?   Behind the rear cockpit or behind the front intrument panel?

Rod, your fire extinguisher idea made me wonder.   Could a transponder fit vertically against the seat below my right knee?   Might be too difficult to use.   This particular chippie has a fire extinguisher bracket mounted on the right side of the forward cockpit above the rudder pedals.   The fire extinguisher is missing.

Dave

Best to have the encoder as close to the transponder as possible; ideally on the same removable frame as the transponder so they can be remnoved and tested together.  It is often difficult to know whether a fault lies in teh transponder, the encoder or the wiring between.  The encoder  also needs connection to the static plumbing.

(Rod's encoder is behind the front instrument panel!)

[Rod Blievers]

Thank you, Dick! Embaressed that you, 800 miles away, know more about my aircraft than I do...

Cheers,

Rod.

[Dick Gower]

Thank you, Dick! Embaressed that you, 800 miles away, know more about my aircraft than I do...

Cheers,

Rod.

Thought you would be amused Rod!