Mode C on battery??

[Bluebeard777]

Regulatory pressure is pushing me to reluctantly consider a Mode C transponder, however with no electrical system in my aircraft
this will have to run off the 12v 7Ah battery.

Anyone any experience of a transponder with minimum power requirements? Microair's has power requirements of 400 mA TX/80 mA RX.

[LowNSlow]

Where are you operating from Bluebeard ? The strip I operate from is right under Luton Zone and they are happy to accept non transponder equipped aircraft. Are you planning to operate into the Channel Islands on a regular basis?

There is a fan driven generator available to PFA type aircraft which will give you more than enough power to run a transponder. Çan't fit one to a Tiger or an Auster though without reams of expensive paperwork being generated also.

PS Unless the PFA, AOPA etc are successful, we will all have to use Mode S in the not to distant future..........

[Bluebeard777]

The aircraft in question is in Ireland, where non-transponder equipped flight in controlled airspace is no longer permitted, subject to some limited exceptions.

Battery operation, if feasible, seems a simpler power source than adding a generator.

The future of the Mode S requirement for light aircraft seems very unclear, from what I have read. Could be 2008, or could be way off into the future. This is a deterrent to spending money now on Mode C.

[FlyingForFun]

Sorry, no practical experience.

But it sounds like it should be ok, in theory, from the figures you give. Assume that you're transmitting pretty much constantly (which is probably reasonable, given the number of airliners with TCAS that'll be interogating you if you fly anywhere even vaguely busy). That gives you a total consumption of 480mA. Round up to 500mA, and your 7Ah battery should, in theory at least, be able to keep it running for 14 hours. Even given that the battery will loose its capacity over time, and there'll be other imperfections in the system that will reduce this, it should still last longer than your bladder, as long as you ensure the battery is charged prior to flight.

My uneducated opinion is to go for it - and give it a nice long test-flight outside controlled airspace before you use it anywhere you actually need it, just to make sure.

FFF
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[PPRuNe Towers]

A scratch around with a search engine might show some impending news. Qinetic and the CAA completed trials earlier this year - subject: lightweight battery operated transponder.

Rob

[Circuit Basher]

Have a feeling that this is a long way from regulatory approval. Interim solution (that I'd use) is a sealed lead acid battery such as you can find on the CPC Web site (http://custom1.farnell.com/cpc/product.asp?catalog%5Fname=CPC+Catalogue&product%5Fid=258212). Some quick calculations (based on a 4:1 Rx:Tx ratio) based on the stated current figures indicate that average current drain will be 0.144A. Assuming a maximum flight endurance of 5 hrs and adding 100% safety margin means that you should be looking at a 12V 2.2Ah model, such as the BT0267266, which wieghs 1.0 kg and measures 60x34x178 mm (H * W * D). One of these costs £6.62, so should hardly break the bank. Downside is that you may want to buy 2, so that one can be on charge and the other in use on the aircraft.

Just a thought.

[Bluebeard777]

Thanks guys. My battery is 7 Ah, enough currently to keep my radio going for weeks of summer flying.

Rob, I will follow up about Qinetic.

Regarding how long a battery will last with a transponder, this item would only be on when legally required. I wonder though what will happen when I announce "Now in Class G airspace, transponder off" on the radio (!).

[IO540]

Now in Class G airspace, transponder off

I think you will find that a lot of people do that already without announcing it. It's a good way to avoid busting the 2500ft LTMA by flying at say 2800ft :yuk:

[andyb79]

i see why that might be done but where i fly it wouldnt be a wise idea the airfield is right in the midlle of glasgow and edinburgh and under the scottish TMA even with mode c on i have had heavy aircraft divert around me because hight couldnt be confirmed ( just taken off and not changed frequency yet) it doesnt make your airfield very popular with the approach controllers

[Circuit Basher]

A precis of the response from a contact of mine in QinetiQ is as follows:

I don't believe that QinetiQ have developed a lightweight transponder, but QinetiQ did get involved in testing a "demonstrator" for the CAA to prove the concept.

The CAA was/is concerned about the usefulness of a low power transponder before they make it mandatory. The trials went well using the QinetiQ Harvard and a BAC1-11 target but it is suspected that it will be a few years before they are mandatedby the CAA. The kit they used was a one off and is a long way from being suitable for production and marketing.

The guess is that any manufacturer will combine it with other capability (eg GPS) and will make it a lot smaller than the unit tested. A big problem is likely to be where to position the aerial as the Harvard had several black spots even when the aerial was mounted on the airframe.

I will be in the presence of CAA SRG representatives on Thursday evening (a GA Safety evening), so will try to raise the subject there.

[Edited to correctly paste all relevant info]

[IO540]

andyb79

I have been told by various ATCOs that if there is no height info, they assume it is UNDER the CAS.

Unless, presumably, the CAS extends down to ground, in which case they're going to panic.