I have seen a'64 cherokee has I am intersted in which has a simple unheated pitot tube rather than a mast. Is this right? Also,the electrical supply is from a generator and can't cope with full load at at 2350 rpm- VOR/DME/VHF/ADF/navs/cockpit and anticol (it was just an exercise as I could loadshed). Could it support a heated mast which I assume would be 10A? The cockpit has no CB or switch for pitot heat so is is fair to assume it was never fitted?
I would say your assumption is correct. I would check the equipment list that you should have in your records.
10 additional amps on a maxed out generator probably wouldn't help the situation.
I understand the limitations of the Gen- As I don't intend to really IFR,I'm loathed change the gen. My aim would be to climb through the cloud and descend through it to VFR below at destination. If its worse then that, I ain't going. I would accept turning off other items to power the heaterin these conditions. Any thoughts on the pitot tube versus mast?
You said your intent was not to fly IFR, but then you said you want to penetrate cloud on climb and descent. That's IMC in my books which means you need pitot heat and must file IFR.
Ice can build up surprisingly quickly depending on how saturated and thick the clouds are, the OAT, and what part of the cloud you're flying thru.
And I don't think you would want to turn off things in IMC - you want to have everything working for you.
OK guys, I don't fly in the USA. I can get a local radar service to penetrate cloud without filing. In the summer the weather is such that a layer of scattered or broken strato-cumulus often sits around 2000ft to about 3500ft and clear above. The airspace is crowded below with microlights and gliders. So rather than mixing with them or circling in a hole and killing climb perf in the process, I could climb en route for about 2 mins IMC if It were possible to get parity on the gen load when powering a pitot heat perhaps at the expense of a non essential electrics. I know ice can build up quickly, hence my technical question on elec load. Continious IFR on one engine is a recipe I won't consider for the peiod. For others the risk is ok, so that's fine. Anyway, any technically based opinions out there...
Sorry Mark, I did assume you were in N.Am. I'm actually in canada, but our regs are pretty much the same as the US. So I was befuddled by the scenario you provided.
I guess I really don't understand your question.
You say that your current generator can't support full load at 2350rpm, but want to know if it can support an additional 10A for a heated mast?
Well sure it could, if you turn off at least 10A of other load, change the unheated tube for a heated mast, and have a circuit breaker and switch installed. It's all doable.
You say changing the generator to a higher power alternator (the best solution in my mind) is not something you want to do, so what other choice do you have? You have to offload the generator while you have pitot heat on or you don't put a heated pitot on and take your chances penetrating cloud. You've pretty much answered your own question as far as I can tell.
Is there a specific question you wanted a technical answer for?
Has anyone got experieince of running a pitot heat as a retro fit on an old style generator as opposed to an alternator? I thought I might add up the current (bad pun) equipment fuse ratings that would give me a clue but i'm not an electrician. Any pointers?
Is the pitot tube on this aircraft a genuine Piper component it looks experimental, just a tube really. I've only ever seem either heated or unheated masts? It one of the really early ones- 1964 I beleive but could be older.
If you look in the POH there should be a load calculation that specifies what the actual loads are of the various electrical bits.
If that's not there, or is not complete or up-to-date, then you need to put an ammeter on the battery (or alternator if the engine's running at high rpm) and measure the total load on the generator with everything running. Remember, the big difference between generators and alternators is that generators don't develop full power capability at low rpm.
Adding up the breaker values is not useful as they are not based directly on the current draw of the box, but on the current-carrying capacity of the wiring that feeds the box - in other words, they're set to protect the wiring, not the box. So adding those values up would take you well above the capability of your generator.
And 10A for pitot heat is what the breaker might be, but it's not what it draws. I've never measured it, but it's likely closer to half that.
As for whether it's a genuine part or not, have a look at the attached sheet from the Piper part catalog. Is this what it looks like? If so, it's genuine.
Hope this helps.
Pete
PS> You can also see that there is a separate static port used with the pitot tube on the earlier Cherokees. So you'd have to have that covered/removed/addressed in any upgrade to a mast - but I'm sure it's all doable. Best to talk to your mechanic.
Edited 1 time(s). Last edit at 02/19/2008 04:05PM by PilotPete.
Talk to your mechanic about whether that can be upgraded to a heated mast. He should also be able to tell you whether your generator can handle the increased load or not.
