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Hand propping with P-mags

N941WR

N941WR

Legacy Member
Over the years I have been asked how to hand prop a P-mag equipped engine with a dead battery.

It is a rather simple thing to connect a 9 volt battery to the P-mags and hand prop it. However, hand propping an airplane has some serious safety issues associated with it and if you have not been trained on how to hand prop an airplane, DO NOT try it until you receive the proper training.

Engines with wood or composite props are more difficult to hand prop due to the light weight of the propeller.

Tricycle geared airplanes and airplanes with high compression pistons both present unique challenges which I will not go into here.

Below is a simple diagram that shows how someone may opt to permanently wire a 9 volt battery connector to there ignition system. When NOT in use, remove the 9 volt battery and cover the terminals to keep them from shorting out.

I recommend you install the 9 volt battery terminals in the cockpit, in a place where it can be reached while sitting in the pilot's seat.

A simple option is to use a battery holder such as these:
9%2Bvolt%2Bbattery%2Bholders.JPG


Wiring diagram:
Standard%2520Pmag%2520wiring%2520with%25209%2520volt%2520battery.jpg


To hand prop your plane with this set up, put a competent pilot in the "pilot's seat", turn EVERYTHING off, prime the engine, set the throttle full aft for minimum power setting, pull the prop through a couple of times until it stops at the top of a compression stroke. Set the brakes, isolate the P-mag to be powered by the 9 volt battery by pulling its breaker, un-ground the P-mag, leave the master off, plug in the battery, carefully hand prop the plane. Remember, you have bypassed the mag switch, if the engine doesn't start, remove the battery before repositioning the prop or it WILL fire.

Once the airplane is running, return to the pilot's seat, increase RPM's to around 1,000 (something above the P-mag's self powering cutoff point), remove the 9 volt battery, turn on the other mag, turn on the master and let the airplane charge the battery.

This method is to be used in an emergency and should not be a normal operating procedure. It is much more desirable and safer to charge the aircraft battery than attempting to hand prop this or any airplane.

Thoughts, comments, etc.?
 
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Danny,

I Googled "9 Volt Battery Connector" and then checked the images.

Here are some links. I have never used any of these vendors, so I don't know if they are reputable or not.
Surface mount battery box

Clip in holder

Box with switch

There are a lot of different options. I'm torn between the first and last ones listed above. The first is nice because it can be mounted on your panel and you can insert a battery as needed. The one with the switch can hold a battery all year, with the switch off, and you just replace it every condition inspection. However, you will have to hide that one under the panel some place.

There is another option and that is to make a battery box with some alligator clips and just stick it on, when needed. The problem there is getting behind your panel to connect it to the breaker.
 
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Good technical procedure Bill, but I feel compelled to make a couple of comments regarding safety. Remember - I grew up hand-propping airplanes, as it was the only way we could start them (no electrical system). The first thing is that I would never want to hand start without someone competent being ON THE THROTTLE. I have just seen too many times when it is set higher than you expect. The second point is that not all RV's have parking brakes, but if they do, and even if they do - if the throttle is too high, the airplane can slip or crow hop. I'd recommend chocks and tying the airplane down via the tailwheel to something solid. Now go ahead and hand prop it, run it long enough to charge it, shut it down, untie, unchock, then do a new start - with P-mags, it should fire right off.

The thing is, unless I am being chased by a thousand Hootoo warriors with blow darts, I just can't see a need to crank it any faster if I am alone. If said warriors are closing in, take whatever risk you feel necessary. But there are just too many cases of airplanes getting away from hand proppers to ignore the fact that it DOES happen.

I love hand-propping the right airplane, and have done so with our RV's - but only with a qualified person on the throttle and holding the brakes.
 
Ironflight said:
Good technical procedure Bill, but I feel compelled to make a couple of comments regarding safety. Remember - I grew up hand-propping airplanes, as it was the only way we could start them (no electrical system). The first thing is that I would never want to hand start without someone competent being ON THE THROTTLE. I have just seen too many times when it is set higher than you expect. The second point is that not all RV's have parking brakes, but if they do, and even if they do - if the throttle is too high, the airplane can slip or crow hop. I'd recommend chocks and tying the airplane down via the tailwheel to something solid. Now go ahead and hand prop it, run it long enough to charge it, shut it down, untie, unchock, then do a new start - with P-mags, it should fire right off.

The thing is, unless I am being chased by a thousand Hootoo warriors with blow darts, I just can't see a need to crank it any faster if I am alone. If said warriors are closing in, take whatever risk you feel necessary. But there are just too many cases of airplanes getting away from hand proppers to ignore the fact that it DOES happen.

I love hand-propping the right airplane, and have done so with our RV's - but only with a qualified person on the throttle and holding the brakes.
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Like you, I spent a lot of time hand propping Cub's, Champs, and T-Crafts. I even spent a few summers hand cranking the inertia starter on a friend's Stearman. (More time doing that than I ever want to admit!)

You are correct, you should not do this w/o a competent pilot at the controls and the airplane properly secured! That cannot be stressed enough! (I added "a pilot" to my first post, above.

It is much better and safer to pack a small battery charger for long trips as it is fairly easy to find an extension cord and simply plug the entire plane in and let it carge. However, some people operate in the "bush" and don't have access to the local power company.
 
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OK, I have been the "pilot" in the seat while someone has hand propped a Cub, also a C-172, but that makes me no expert whatsoever. In building my RV-9A I have installed an external power plug and I anticipate never having the 160 HP Lycomming hand propped. (I have dual P-Mags). But if I am really stuck and should rely on this method can you tell me if you have ever really DONE this procedure. Not trying to call you out, but you didn't mention actually performing this type of start even though from my readings it should work fine.
 
N941WR said:
Remember, you have bypassed the mag switch/QUOTE]

Bill, I don't understand the above statement. Does the 9-volt battery bypass the mag switch? Why not just turn the mags off if you have to reposition the prop?

Bevan
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N526JS said:
... But if I am really stuck and should rely on this method can you tell me if you have ever really DONE this procedure. Not trying to call you out, but you didn't mention actually performing this type of start even though from my readings it should work fine.
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To answer your question, Yes and No.

I received a call from a friend who was stuck and asked what to do. I talked him through how to temporarily wire up a 9 volt battery from his ANR headset. He was able to start the plane while his buddy was laying on his back, in the cockpit, holding the wires and battery in place. Definitely not an ideal solution.

If you have ever stopped by the E-mag booth at either OSH or SnF you will see that they have a P-mag powered by a 9 volt battery. Brad told me that the battery will last a day or two.

Like every thing else on a public forum, get some training, and try it yourself.
 
Bevan said:
N941WR said:
Remember, you have bypassed the mag switch
Click to expand...

Bill, I don't understand the above statement. Does the 9-volt battery bypass the mag switch? Why not just turn the mags off if you have to reposition the prop?

Bevan
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Bevan,

It is difficult to know how people wire their P-mags or hand prop an airplane so a good bit of caution is always needed. You are correct, the grounding of the P lead should still work, but if left on with the P lead and powered with a 9 volt battery with the Master OFF, the thing will fire.

BE CAREFUL!
 
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alternator field voltage?

Even if one were to get the engine running, the alternator will not charge the totally dead battery without a certain amount of voltage supplied to the field coil. IIRC, 5 volts is adequate to get the field coil working. Not sure a 9v transistor battery would do this. Field pulls about 5 amps.
-Roger
 
Are there small solar panel battery chargers available that might be a better option when no AC power is available for your battery charger?

Using the alternator to charge a dead battery is hard on them, or so I have been told.

Randall
 
RKellogg said:
Even if one were to get the engine running, the alternator will not charge the totally dead battery without a certain amount of voltage supplied to the field coil. IIRC, 5 volts is adequate to get the field coil working. Not sure a 9v transistor battery would do this. Field pulls about 5 amps.
-Roger
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The 9 volt battery isn't intended to excite the planes' alternator field, it only there to power the P-mag for hand propping. Above about 800 RPM's the P-mag's internal generator will power the ignitions so you can fly home. Remember, airplanes don't require radios, transponders, etc. to fly.

As for the alternator field, it has been my experience that usually we find the battery doesn't have enough power to turnover the engine but will have enough to excite the alternator field and thus, the battery can be recharged in flight.
 
field question

I concurr, a lame battery that won't quite spin the engine will provide adequate field voltage. But if the master contactor has been left on overnight and really flattened the battery, the alternator won't charge the battery, even if the engine is hand-propped to a running condition. Jumping from a jump cart and powering up the field for some short period of time while the jump cart is attached will get the alternator charging.
I understood the emergency nature of the initial question. Operating a low wing plane without a functional electric source means compromising the electric boost pump function. One more link in a chain....and these chains seem to form most rapidly on days when I have a dead battery and feel an urgent need to fly the airplane. I just don't feel as lucky as I did when I was younger.
-Roger
 
Ironflight said:
The thing is, unless I am being chased by a thousand Hootoo warriors with blow darts, I just can't see a need to crank it any faster if I am alone. If said warriors are closing in, take whatever risk you feel necessary. But there are just too many cases of airplanes getting away from hand proppers to ignore the fact that it DOES happen.

I love hand-propping the right airplane, and have done so with our RV's - but only with a qualified person on the throttle and holding the brakes.
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Here here.
What is the risk and what is the reward.

With that said, from a technical standpoint the information provided is good and useful.
 
xblueh2o said:
Here here.
What is the risk and what is the reward.

With that said, from a technical standpoint the information provided is good and useful.
Click to expand...

Here's the thing, someone may fly their plane into a remote strip to go camping for a weekend and leave the master on. This gives them a way to get home.

Or

Someone may build a very light plane and forego an electrical system and starter altogether and hand propping is the only way to start the engine. (I would probably use standard mags and not P-mags in this situation.)
 
Agreed, and in the kind of situation where there are very few other viable alternatives I think it is good you describe a valid technique to recover. On the other hand, picture this scenario. You show up at the hangar because the lunch bunch from various local airports are all meeting somewhere for a $100 hamburger. You find the master switch on and the battery dead. Is that worth the risk?
You just want people to examine the situation and decide, does the reward justify the risk.

I am not disagreeing with you in any form so please don't take it that way.
 
This is where "judgement" comes into play when dealing with a scenario like you describe Sam.

Plug in your charger and wait or hand prop? To hand prop, do you have someone qualified to sit at the controls and hold the brakes? Is it a tailwheel aircraft? (I won't hand prop a nosewheel.), finally and most importantly, is the person spinning the prop by hand experienced and trained in doing so?
 
P-Mag mag check?

I am just starting phase one on a dual P-Mag plane. Do you guys check that each P-Mag will run on its own internally generated power as part of the mag check? I have been surprised at how small the rpm drop is when grounding p-leads, typically 10-20 rpm. I typically ground both p-leads for a half second to verify that the p-leads are indeed intact. FWIW, panel is configured with two toggle switches for the p-lead grounding, and a single power switch that controls power to both P-Mags.
Need to update checklist.
 
N941WR said:
This is where "judgement" comes into play when dealing with a scenario like you describe Sam.

Plug in your charger and wait or hand prop? To hand prop, do you have someone qualified to sit at the controls and hold the brakes? Is it a tailwheel aircraft? (I won't hand prop a nosewheel.), finally and most importantly, is the person spinning the prop by hand experienced and trained in doing so?
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I agree, charging the battery is absolutely the best way to do this.

Not sure why you don't like hand propping nosewheels though, they are easier IMO than a tail wheel where the prop is much higher and harder to reach/less stable footing (I'm not a short guy either).
 
RKellogg said:
I am just starting phase one on a dual P-Mag plane. Do you guys check that each P-Mag will run on its own internally generated power as part of the mag check? I have been surprised at how small the rpm drop is when grounding p-leads, typically 10-20 rpm. I typically ground both p-leads for a half second to verify that the p-leads are indeed intact. FWIW, panel is configured with two toggle switches for the p-lead grounding, and a single power switch that controls power to both P-Mags.
Need to update checklist.
Click to expand...

With my dual P-Mag installation each P-Mag has a p-lead switch and a separate power switch with its own breaker. This way when doing the engine run up I check that each P-Mag runs off its' internal power. It also eliminates the single point of failure of running both Mags off of one switch/breaker.

:cool:
 
redundancy

GalinHdz said:
With my dual P-Mag installation each P-Mag has a p-lead switch and a separate power switch with its own breaker. This way when doing the engine run up I check that each P-Mag runs off its' internal power. It also eliminates the single point of failure of running both Mags off of one switch/breaker.

:cool:
Click to expand...

I thought about that, but concluded that the redundancy of two self-powering P-Mags downstream of the switch justified the savings in panel space and weight. I can still verify that each P-Mag is generating its own power by removing ship's power, then individually grounding p-leads.
- Roger
 
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