Speed to Cruise Gear Down

[201er]

I gotta fly my plane over to my mechanic 50 miles away to get work done on my alternator. If the alternator doesn't work on my ferry flight, I'm going to run minimal electrics off the battery and leave the gear down. What I'd like to know is what is the best speed and power setting to use doing this? Obviously the gear is going to make a ton of drag and I won't be going fast. But is it better to run 75% to have more power to overcome drag of the gear or is it better to fly 55% accepting the fact that I'll be going slow and just save some gas? I'm not really on top of what kind of power is needed just to keep it level and moving with the gear down. I just remember surviving an altrenator failure at night with my friend in his Bonanza and with 75% power and gear down barely pushing 100knots!

[jetdriven]

Our alternator quit and the opther partner ran it down to 8 volts.  Flew it 2.5 hours with everything on.  Nothing would work. Except the gear came down on its own and green light.   The air pulls it down, the motor has no load.     Rather than fly 50 miles with the gear down, I would put the gear up, kill the master switch for the 20 minutes it takes to fly 50 miles, and then make a normal landing.  I bet with only one NAV/COM turned on and a GPS, you can do it with everything on.  It is a theoretically 30 AH battery, figure half of that is usable, you have a realistic drain of 15A for an hour.  

 

But that is just me.  75-80 knots will be near your most fuel efficient speed for range with all that drag.  SWAG guess, around 65% power to get that.

[Immelman]

I would say use whatever power you want as long as you don't exceed Vle.

[Piloto]

Expect about 120kts IAS at about 65% power. You may need to keep the cowl flaps partially open to cool the engine. Just make sure not to retract the gear on landing.

 

José

[201er]

Quote: jetdriven

Our alternator quit and the opther partner ran it down to 8 volts.  Flew it 2.5 hours with everything on.  Nothing would work. Except the gear came down on its own and green light.   The air pulls it down, the motor has no load.     Rather than fly 50 miles with the gear down, I would put the gear up, kill the master switch for the 20 minutes it takes to fly 50 miles, and then make a normal landing.  I bet with only one NAV/COM turned on and a GPS, you can do it with everything on.  It is a theoretically 30 AH battery, figure half of that is usable, you have a realistic drain of 15A for an hour.  

 

But that is just me.  75-80 knots will be near your most fuel efficient speed for range with all that drag.  SWAG guess, around 65% power to get that.

[rob]

To your last sentence, I'd be sure to depart with as close to a fully charged battery as possible. Are you not able to get it on a trickle charger?

 

[jetdriven]

Worst case you crank the gear down. That indicator in the floor is primary, the green light is secondary. Again, Our partner got green down and locked with 8 volts.  It wouldnt power anything.

I have seen people crank an O-360 for a total of about ten solid minutes the battery was still doing it.  If you want, top it off with jumper cables for 20 mins then you got a fresh battery.  You will save a few gallons of 5$ fuel with the gear up.

You can run it with no lights, the transponder and one NAVCOM.  The amp draw there is around 1A on recieve, the KT76A transponder is 1A nominal, and ~2A with high activity.   The gear motor has a 25A CB, it runs for 6 seconds for a full cycle. Then the T/C has a 1/2A draw.  Now double that.  Your load is ~5-7A total.

[201er]

Quote: rob

To your last sentence, I'd be sure to depart with as close to a fully charged battery as possible. Are you not able to get it on a trickle charger?

[Ned Gravel]

My E model has the manual gear and the gear down limit speed is 120 mph.  But I can tell you that the airframe will not accelerate to faster than 140 mph with the gear down in level flight.  Don't ask me how I know this.

As for the flight to get your electrics looked after, good luck.  Been there too. How would you feel if the last thing you had to do on your walkaround was to cut the generator belt?  The generator was fried (long list of electrical issues back in 2005/6) and I was taking it to Clarence.  He discovered that it had apparently been mounted incorrectly.  Add to that that the regulator was not doing its job very well and it was also time to change to the Zephtronics regulator.

Stay safe.

[xftrplt]

Piloto and Immelman(n?) give excellent advice. 

Leave the gear DOWN. (Hell, I'd pin it down you can.)

You're already flying with an abnormal condition.  Why, on God's green Earth, would you want to raise it and look for trouble?

To save a few gallons on a 1/2 hour flight?

 

[201er]

Is there any good way of guessing how much juice I have judging by voltage? If I'm seeing 11volts, do you think that's enough for 30 minutes of normal flight exclusively off the battery?

Just my luck, the alternator will work and I'll have no problem getting there and mechanic will think I'm making it all up.

[jetdriven]

battery voltage an be approximated to state of charge.  We do this on sailboats. I will say that an old battery will have less capacity at a given voltage than a newer one.

 

When I fly, I have a plug in 12V digital meter and I monitor voltage all the time.  The regulator should be set to 14.0V +0 -.2 per the Mooney service and manitenance manual.

 

After you calculate your state of charge, take that value from half of the battery capacity. IE you cannot get 30AH our of a 30AH battery, only half that. The voltage gets too low and that spare capacity is unusable. If you have a 3 year old or older Gill G-35 then its going to be even less.

 

 

[Z W]

We use a solar panel battery trickle charger in our boat that plugs into the cigarette lighter. It actually puts out quite a bit of juice. You can buy them at reasonable prices at any marine store these days. Might be a good way to keep your battery topped at a field with no electrical, and to charge it for this flight. Put it in the sun inside the plane and it would even charge while you fly. Great for running the boat radio with the engine off in a cove.

 

Put me in the gear down camp. No reason to risk the plane and your own safety to save a few bucks on gas.

[201er]

I've been thinking about one of those charger things! However, my cigarette lighter port doesn't put out current unless the master is on. I think it's a good guess that it wouldn't recharge without leaving the master on (which I'm not going to do)? Is there any easy way to bypass the master for this kind of setup?

[MARZ]

Gear down -  portable com  you'll kinda look like a piper and still beat the 172 there.  Just don't go over Vle 

[FlyDave]

Quote: Piloto

Just make sure not to retract the gear on landing.

 

José

[M016576]

Quote: jetdriven

Worst case you crank the gear down. That indicator in the floor is primary, the green light is secondary. Again, Our partner got green down and locked with 8 volts.  It wouldnt power anything.

I have seen people crank an O-360 for a total of about ten solid minutes the battery was still doing it.  If you want, top it off with jumper cables for 20 mins then you got a fresh battery.  You will save a few gallons of 5$ fuel with the gear up.

You can run it with no lights, the transponder and one NAVCOM.  The amp draw there is around 1A on recieve, the KT76A transponder is 1A nominal, and ~2A with high activity.   The gear motor has a 25A CB, it runs for 6 seconds for a full cycle. Then the T/C has a 1/2A draw.  Now double that.  Your load is ~5-7A total.

[M016576]

Quote: xftrplt

Piloto and Immelman(n?) give excellent advice. 

Leave the gear DOWN. (Hell, I'd pin it down you can.)

You're already flying with an abnormal condition.  Why, on God's green Earth, would you want to raise it and look for trouble?

To save a few gallons on a 1/2 hour flight?

 

[FlyDave]

Quote: M016576

Out of curiosity- has anyone else done a manual extend to test their system or just out of curiosity, or am I the only one?  

[Immelman]

I have done manual extensions on the other complex airplanes I have flown prior to my J-bar Mooney in the context of training. That does not mean I would want to count on that system unnecessarily! I've heard enough stories about accident chains developing (admittedly, usually in more complicated airplanes like medium sized twins), where a small abnormal turns into a full-blown emergency.

Leave the gear down, unless you face some sort of emergency (need climb performance in a go around or something, or if the engine quits and you need to get rid of the drag to put the airplane somewhere habitable).

My very tongue-in-cheek answer is that one should only tempt fate in this circumstance if the insurance is paid up, engine near TBO, and airplane could use a new prop

 

[Ned Gravel]

Quote: Immelman

......My very tongue-in-cheek answer is that one should only tempt fate in this circumstance if the insurance is paid up, engine near TBO, and airplane could use a new prop .....

 

[Z W]

Quote: 201er

I've been thinking about one of those charger things! However, my cigarette lighter port doesn't put out current unless the master is on. I think it's a good guess that it wouldn't recharge without leaving the master on (which I'm not going to do)? Is there any easy way to bypass the master for this kind of setup?

[Hank]

201er--

Once upon a time, while training for Instruments, I had a complete electrical failure on a VOR approach to an airport on the bank of the Ohio River. Flying inbound at 2500 toward the VOR with Takeoff flaps at 105 mph [=90 kts] I started my descent 1½ dots high by dropping the gear and turning on the landing light. Boom! Dead.

Cycling the master did nothing. Pulling/resetting breakers did nothing. Leveled off around hilltop altitude [we were on the WV/OH line], cranked gear to verify fully down, ditched plates and foggles into the back, climbed back to 2500 and followed the river home. Vle is 120 mph, so I set the throttle for about 110 mph indicated, just a little more throttle than my training approach settings to maintain altitude [~19"/2300 dirty & level]. That left me a comfortable margin for variance as I headed home [~30 nm].

Lessons learned that would apply to your situation:  1) know your power settings; 2) carry a handheld radio [mine was safely in the hangar since I wasn't "on a trip"]; 3) review the Emergency section of your POH [mine is just 2 pages, it's a quick review!]; 4) get a headset adapter for your handheld, and plug it in.

Now my handheld lives in my flight bag in the plane with a spare set of batteries in a holder [swap the battery box, deal with a bunch of AAs on the ground], and the adapter cord stays plugged in except for the rare occasions I use it outside of the aircraft.

You'll be good flying gear down--just stay below Vle and have a handheld with good batteries ready to go.

[201er]

I had a complete electrical failure at night with an instructor on my first night cross country. We were getting a discharge light at the ground at our turn around destination and the radio wouldn't transmit below 1200RPM. I didn't know any better, the instructor was a moron. We flew back with a failed alternator not realizing we were going exclusively off the battery. Right after touchdown at home field the everything went out. For a moment I thought we crashed. Then I realized the electrics shut down and we had to taxi back in the dark with no landing light and barely any taxi/airport lights. What this made me realize was that if we had returned just 5 minutes later, we would not have been able to get the runway lights on cause neither of us had a hand held.

From then onward I have always carried a handheld in my bag. Then one time I wanted to use it just for listening to traffic on the ground and it didn't work. The battery discharged from lack of use and wouldn't recharge. So now I remember to recharge it from time to time but also I bought a AA battery adapter for it and keep a set of lithium batteries in the holder (those are rated for like 10+ years) and another set of AAs in the bag. The only thing I lack is a headset adapter, next on my list.

I also had partaken in an alternator failure at night with my friend in his Bonanaza and have had electrical issues in a cherokee and an arrow. I'm all too aware of flying without this stuff working. I'm used to flying gliders so the idea of flying without a radio (except in a substantial emergency) doesn't bother me too much in the daytime. Electrical failure at night is really bad and in IMC is catastrophic!

[AlexR]

While I would usually agree that bringing up the gear and then having to get it down manually (in severe clear VFR) would not be too challenging, in this case the short field arrival has me siding with the 'keep the gear down' crowd.  I would save as much juice as possible for getting the gear and full flaps back up in a hurry if you have go around at a short strip with obstacles.  While our Mooneys will climb a bit with gear and full flaps, the increase in interoccular-anal pressure would be alot to handle.  Land with the Master on just in case...gives you the option to get cleaned up in a hurry and ensures your gear and stall warning horns are backing you up.

Remember to pull your alternator field circuit breaker...should save you a few amps, and if you have a short circuit somwhere between that breaker and the alternator and regulator, it will decrease the chances of an in flight electrical fire.  Label the alternator 'INOP' in the off chance you get ramp checked...the electrical system is not required for day VFR under part 91 but anything inop needs to labeled as such.  After start up, check your amp load, if your electrical problem is a stuck starter (very high amp load) it will kill the entire system in a minute or two (Master on). 

Finally, I much rather freeze my butt off getting the battery out so can charge it overnight than deal with an unknown quantity in the air. 

Just my two cents.