IFLYBVM2

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Hi Guys-Need some opinions-I have a Ziroli P-38 ready for a maiden voyage. I am using those very nice but very heavy Glennis wheels/brakes. The plans call for CG at 5.5" back on the side root of the center wing pod, with gear EXTENDED. My question is this : I have always been told to CG this type of bird with rear folding retracts with the gear UP. I am currently balanced slightly nose down with gear in the UP position, at the 5.5" mark. Of course, with the weight of those wheels, with gear down, it is fairly nose heavy. I am not questioning Nick, but rather wondering if he envisioned those super heavy wheels when the plans were laid out. Should I leave it as I have it ? Opinions, advice warnings, and all other comments welcome. Thanks-Mike Oberst

Mustang51

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Hi Mike,
I'm building(almost done) a CBA P38 which is 122.25" ws. I am also using the glennis wheels along with the Sierra gear, so I'll be interested in hearing how your 38 flies. What motors\props? I'm using 3W competion 50s' with 22x12 3blades, custom mufflers.

Now on to your prob. ALWAYS ballance an airplane that has retracts, in the extended(down) position. With the wheels down, you should have a SLIGHTLY nose heavy condition. When the gear retracts you should be right on the cg. If you are nose heavy with the gear up, you are going to be grossly nose heavy with the gear down, that's not good either because you'll have to come in(landing) faster then needed, not to mention rotation issues on take off. Don't know where you heard about gear up ballancing, but maybe these are the same guys that talk about F4Us' and P40s ballooning with gear retraction. I had a Ziroli Corsair for years that was ballanced in the manner which I described and never budged one bit with either gear up or down.

As with full scale aircraft. There are a few reasons the test pilots don't retract landing gear on the maidens. One of which is CG issues. Take a note from them. Get the plane up(leave the gear down), fly it around a little, get to know it. Do some slow flight tests flaps(and of course gear) in the down position. Find out where she stalls(at altitude of course). After you have a flight or two on her. Take her up again and at altitude, retract the gear, see what happens both at cruising speed and at slower flight.
Remember this... the gear retraction is optional.
Good luck, I know you'll do fine.

-Dave

Hellcat716

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For Corsair's,P-40's and Hellcat's, you always balance the plane with the gear in the up position since the gear swings back on rotation. It even say's this in the manual's.

IFLYBVM2

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Looks as if I have two differing opinions on the first two posts. My thoughts are that if I balance gear down to a slightly nose down position, the weight of those heavy Glennis wheels on retraction with make me tail heavy. I will stay tuned for more input. Thanks-Mike O

Connery

It's a well known fact that if you have an aircraft that the gear retracts aft and crosses the CG, you balance the plane with the gear retracted. If you don't, you will be tail heavy during flight, and could possible loose the plane. Being slightly nose heavy with the gear extended is not a problem. This is the same reason that if your fuel tank is mounted ahead of the CG, you balance the plane with the tank empty. When you fill it with fuel, it will be slightly nose heavy....a much better condition than being tail heavy after you fly for 10 minutes using up your fuel and then try to land.

BIGDAMMODELS

JUST JOINED AND WAS JUST TRYING TO POST

Mustang51

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It's also a well known fact that a P38 has tricycle landing gear that when retracted, even though the weight of the struts and wheels are shifted rearward, It does not cross the cg, hence , not effecting a P38 in the same manner as a F4U, or P40..As I stated before. When the gear is down, the plane should be slightly nose heavy, when the gear is retracted, the plane should be "ON THE CG".

Here's the point to all of this...
The cg "IS" the cg. It's not movable although there is a slight "range" to which it falls.
I would think that if a builder\flyer is going to try something as complex\expensive as a P38, he would have the intelligence to keep his aircraft in the cg range. That means (in the case of the P38) that he would ballance the plane so that it is on the cg in flight configuration, and as close to the cg in landing configuration as possible, and that usually means a slightly nose heavy condition(which is always more desireable then a tail heavy one). No one in their right mind would build a P38, ballance it with the gear down, and NOT check it with the gear up to see where the ballance falls, hance avoiding a wheels up, tail heavy airplane.
Mike, I think you know what you're doing here. I would suggest however that you try to get the nose heavyness with the wheels up out of the airplane. With the added weight of two full fuel tanks and an already nose heavy airplane, you're aproaching a grossly nose heavy situation.
Get the plane wheels up, no fuel and ballanced on the cg, you'll be fine. The weight of the Glennis wheels is nominal

-Dave

OldScaleGuy

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I agree with the theory of balancing with the gear up. Certainly it is going to be more nose heavy with the gear down but better that than a tail heavy subject on your hands with the gear retracted. I balanced my B-25 to be slightly nose heavy with the gear up and never had any overly nose heavy issues with the gear down. Better to be safe than sorry.

Chad Veich

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Mike, I think you're best bet would be to shoot an email off to Nick himself. I understand what the guys are saying here but, if Nick shows the CG where he thinks it should be with the gear extended and you balance it at that point with the gear retracted, you're going to be way nose heavy with full fuel and the gear extended. I don't know why Nick would draw it that way as he obviously can't account for the different hardware that people are going to use on his designs but you never know.

longeze

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Balance the Ziroli P-38 with the gear down just as Nick calls for. I also questioned this to myself when balancing mine before the first flight but decided to go with gear down. It flew perfectly balanced.

Glenn

IFLYBVM2

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Thanks to all-Maiden happens on Thursday, Feb 8th, Lord willing and the creek don't rise ! -Mike O

zipnz1

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i too had concerns with the c/g dilema before my maiden flight. at that time there were some posts from other people discussing the proper c/g position. i ended up going with the c/g location on the plans, gear down with the tanks empty. slightly nose heavy is good on a warbird to avoid the tail dropping when the flaps are down and the approach speed gets too slow. the plane flys like a dream. with the p-38 you have to learn to use the rudder on turns to avoid pylon type turns, because of the engine torque or the right hand engine out thrust the nose does not like to drop when going into a left hand turn. my rudder is set on low rates in flight and are very effective on the p-38. with flaps down my elevator has about 2 clicks of down programed in to the landing switch. i myself like to make my p-38 final approach higher than a normal landing position, low power on landing decent and controlling the decent with the throttle and not touching the elevator until the flair.

best of luck on your maiden flight.

mike

jkeze

My Feedback: (36)

I too have Glennis wheels and brakes on mine. Just do what the old master Nick says and all will be fine. I have G-62's on mine and it flies great. My 2 cents.
Jack

kram

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IFLYBVM2:

First of all, Best of Luck on the maiden! We all know how much sweat and blood you have invested, but No Hangar Queens!, right?

Best advice I ever got on a P-38 maiden is Remember to Breathe sometime in the first 20 seconds after takeoff. Hypoxia can wreck your reflexes!

I have owned and flown three big 38's and two P-61's (different animal). I balance them with a 3-scale technique, which is extremely accurate. I have noted that the CG moves back about 1/4" when Robart wheels are retracted. Glennis wheels (13 oz each on my Z-61) change CG about 1/2" on my Z-61. Sorry to say that and the extra air it takes to cycle them influenced me to fly with Robart wheels, display with the Glennis.

Bottom Line: If Ziroli says CG is "here" with gear down, then fly it that way for maiden, don't cycle the gear, get a feel for it.

I have found all P-38's to be very stable flyers as long as both engines are running and you keep your airspeed up. They actually tolerate "pylon turns" and gear retraction (CG back) pretty darn well. Engine-out? Well, I don't wanna talk about that!

Good Luck! Post pics!


mt

kram

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Mustang51

Now that I've portrayed myself as an expert, please help me dispel that a little.

Where do the instructions on your CBA say to put the CG?

Mine is a joy to fly and the "baddest" bird I own, and has survived 7 years and two previous owners, but it requires the nerves of a NASCAR driver to land. Anything under about 1/3 throttle (40 mph?) and it flops on the runway like a manhole cover.

Last year at the Multi-Meet in Ames in a 40 mph headwind, the airspeed computer in my brain miscalculated ground effect and it fell the last 4 feet or so, ripping out my nosegear. Several Wisemen were present and suggested my CG is too far forward, and I'm inclined to try to move it back a little, although I suspect it's just about size and weight (53#)

What do you think?


mt

Mustang51

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Hi Kram,
Glad to hear there's another CBA alive somewhere. Never let it be said that composite planes are easy to put together, that's for sure.
There were no instructions with the kit. None that I know of anyway. I had spoken to Bob Antonell(owner of CBA) about 5 weeks ago. I asked him that very same question(CG). He said the cg was
5 1\2" from the leading edge.

Bare in mind too. At the typical flying field, the grass of the threshold of the field is usually pretty thick and high(sometimes 3 or 4 feet). Alot of warmer turbulent air is rising off of that grass and your flying off of its ground effect. Suddenly, you've crossed the threshold and you're over the nice low cut grass of the field and your ground effect just fell out beneath you and the plane gets real ugly for a second. I see this happen every year, usually in the mid and late Summer months when the sun is really heating things up(especially after rains when the grass is wet and the water is evaporating and you add all that humidity rising as well). As long as you're aware of it, and ready for it, you won't get hurt.
Sounds to me though that you may be nose heavy.

-Dave

kram

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IFLYBVM2:

Suspense is killin' me!!

How's it go?

Pictures, at least?

Let me guess....the usual "P-38 Ballet"? (That is, take it out to the field, spend a coupla hours checking stuff out and standing on your head tuning the engines, find something that makes you vaguely uneasy and the batteries are run down, pack it up and take it home).

I wish I had half as much 38 flight time as I have that kind of time!


Mustang 51:

Yep, here's proof of life, in all her war-torn glory.

There's better (in flight) pictures on RCWarbirds.com under "Events, Multi-Fly."

Yes, there was dramatic turbulence and ground-effect transition that day due to 40 mph winds, but I flew another 38 that day no problem, and the CBA is by far the heaviest lander of all my collection regardless of wind.

IFLYBVM2

My Feedback: (360)

Ok Guys-GREAT News-Three successful flights yesterday. What a GREAT flying aircraft. This one's a keeper for sure. The most realistic takeoffs I've ever flown.
For the record, I left her balanced as I had it, that is, slightly nose down with Glennis wheels in UP postion. CG seemed spot on. Twin G-62's provided MORE than ample power. Full flap landings were un-eventful, with about 1/8" of down programmed in on the 10X. Started out with 4 or 5 clicks or ail. trim (nervous pilot) and ended up back in neutral by the third flight.
Many Thanks to my crew chief and partner on this project, Billy Skipper-He has put many hours in the plane and burnt the midnight oil countless nights-it would not have happened if it were'nt for him.
The pics are in my buddy's digicam-Will post later today hopefully. Thanks again to everyone. RCU is a wealth of info and an asset to modelers.

Mustang51

My Feedback: (25)

WAHOO!!!!
GREAT!!!!
CONGRATS!!!!
[sm=thumbup.gif][sm=thumbup.gif]

Glad to heart it! Hope you wore your "brown" pants.

-M51

kram-RCU

Great Job!!

Welcome to the Brother Hood of the P-38 and all the joy and sorrow that entails!

Didya remember to breathe?

Anything vibrate loose?


mt

IFLYBVM2

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Yes-We have the usual screws here and there that need looking after-My experience is that it takes 6-or 8 'shakedown' flights to see what will come loose and get things sorted for the long run. -Mike O

IFLYBVM2

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One pic for starters-

BOLTMAN

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IFLYBVM2

GORGEOUS, Absolutely GORGEOUS!!!!!!!!!

Glad to hear she flies well.

I would like to tackle one of these myself one day.

Cheers

OldScaleGuy

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Congratulations! It's a beauty!

GlennisAircraft

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Nothing like a '38' - really nice

Glad the flight went well

Dennis