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P38 Q & A?

Old 06-04-2003, 04:53 PM
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rottielover
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Default P38 Q & A?

Hello all,

I'm sure I could have found the answers to all my questoins by searching, so forgive me, I knew not what to search for exactly.

I'm planning on purchasing a KMP P-38 either late this year or early next year. I've been putting in alot of time on RealFlight G2 trying to fly the P38 on there with an engine out. I've found on the simulator that airspeed is a key. If your going too slow the plane will flat spin and crash, I found at altitude I could pull throttle to idle, rudder out of the roll point the nose down, increase throttle to full and pull out (once I had enough airspeed), then landing was just a matter of landing it "hot".

I'm hoping that someone could come up with a sticky thread for P38's. I know alot of people that would love to get into one, but are scared to death of them.

Please post any all info re: P38s for all of us that are thinking about getting one of those ARF's.

How to recover from engine failures, gyros ? , quirks of the plane etc.

THANK YOU ALL!
Old 06-04-2003, 08:02 PM
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William Robison
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Default P38 Q & A?

Rottie:

Go through this thread:
http://www.rcuniverse.com/showthread...77&forumid=220

If you still have questions post here and I'll try to answer, or send you to another thread. Or both.

Bill..
Old 06-04-2003, 09:20 PM
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rottielover
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Default P38 Q & A?

Actually that thread is the reason why I posted this thread

I'm not only interested in how to fly the P38 but also building issues, quirks of this plane, how-to's, should I bother with gyro's on a P38 etc.etc.

Here are some specifics to get going...

What is the best way to recover a P38 that has lost an engine and entered into a flat spin?

How do most kit's acomplish the rudder linkages since the rudders are on twin booms? (2 rudder servo's?)

What's the best website to get some pictures of P38's (preferably wartime pics, to get some paint ideas)?
Old 06-04-2003, 09:31 PM
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RangerVorian
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Default P38 Q & A?

Rottielover...

I too am interested in just what you're looking for. Bring on the info and pictures!!!

Old 06-04-2003, 10:09 PM
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William Robison
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Default P38 Q & A?

Rottie:

Flat spin? Same as with any other plane, except with the throttle at idle or cut off. With enough altitude you can recover, then bring the power back gently. If you are too low to recover we might send flowers to the funeral. But probably wont.

Best looking servo setup for the rudder is one servo in each boom, and this also allows differential rudder throw, the one on the inside of the turn has more deflection than the outer. Just like the real thing.

Although an external link could be used for the rudders with a single servo, and differential can still be setup in the linkage, it's not recommended.

Pictures: Using IE search with "Lockheed Lightning P-38 Picture" as the search data I got 426 hits, Google would probably give more.

I'm sure you've been here:
http://www.kmp.ca/esm/products/images/p-38.jpg

and there's not much info.

But Andrew Kondor is one of the good guys, his RCU username in "AKondor" and he'll answer your questions specific to the plane.

Bill.
Old 06-06-2003, 02:44 AM
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flying2bill
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Default P38 Q & A?

Pop over to rcwarbirds.com and check out twinman's colums on twins and gyro's, I believe he also has written quite a bit about P38's. Also check in the twins forum here for his thread on gyros
Old 06-06-2003, 12:20 PM
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rottielover
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Default P38 Q & A?

flying2bill,

It was actually twinman's thread on this board about gyro's that prompted me to ask about them specifically for the P38. He talks about them in a general sense, for any airplane, but I want to know specifically on a P38 what opinions are.

Thanks!
Old 06-06-2003, 04:07 PM
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William Robison
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Default P38 Q & A?

Rottie:

Twinman also had some comments specific to P-38 and gyro use, but you'll have to search for them.

Bill.
Old 06-08-2003, 01:08 PM
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flying2bill
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Default P38 Q & A?

On P38 he does suggest using two gyros (twinman correct me if I'm wrong) one for the ailerons but more importantantly one on the rudders. Like George says the gyros will not prevent the spin resulting from an engine out but they will slow down sudden snap and allow you time to react. I have been in the one engine tumble of death and know it happens in the blink of an eye!!
Old 06-08-2003, 05:31 PM
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JohnBuckner
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Default P38 Q & A?

The only P-38 that I have had experiance with is a Royal that was grossly overpowered (the worstcase senario for single engine handeling). This airplane was set up for warbird pylon racing and I only got perhaps twenty flights before it was lost not to an engine out but the result of a rather heavy wing loading and my over exuberance pulling G's at the #1 pylon with the resultantant instant snap roll into the ground. I only had one engine out on an occasion that happened at speed so was not a control issue.

This ship had no gyros and twin 'Y' corded rudder servos with equal throws. As far as the full scale having rudder differential, perhaps but I doubt it. My thoughts on that is particularly with an aircraft with minimal vertical stabilizer and rudder area you certainly do not want one of those rudders in an asymetric thrust situation to be capable of only partial throw even if it is the one operating in the relative low energy air behind the dead engine.

As far as engine out recognition and control goes and this applies to any multi configuration to various degrees except 'inline thrust' there are four possible 'crutchs' or pilot aids if you will that serve the purpose of buying time for the pilot to recognize an engine out situation and to respond They are:

1. Closely spaced engines. Not always possible with scale.

2. Equal out thrust on both sides. Very effective method that is not hard to hide for scale purposes but in many cases this is prototypical for the full scale.

3. Rudder gyro. Absolutely a very effective device to buy time.

4. Horizontal stabilizer tip plates. A little known device while not as effective as the first three above for buying time but none the less does help and has been well tested on my Duelist. These are simply small plates on the tips of the stabilizer with a built in deflection built in i.e. right plate applies a right rudder imput and the left plate has a built in left rudder imput. Both plates are of equal and opposing deflection. Zero yaw in normal conditions. (yes there is a small total drag penilty to pay. When an engine is lost say the right one, there will be a loss of the high energy air flow over the the stab tip plate on that side which is behind the dead engine. This results in that plates inability to balence the left one and the result is always a yaw imput into that good left engine with no thought or reaction imput which is exactly what you want. Think what you may, this does buy that precious time and is well tested on my duelist and no it was not my idea.

Now having said all that I have never used gyros on a multi and simply because I was being cheap however I consider Twinmans rather rare research in the matter for our application solid gold.

One last thought after you are already in that grave yard spiral is not the time to start thinking about what to do and precisely why useing one or all of the above time 'crutchs' above are so very important.

Just returned this morning from a delightful flight with the Quad Kaydet.

John

Royal P-38, deceased.
Smallish UC-78 scratcher w/.25's.
World F-82, deceased from structural failure and wing folding in pylon racing.
Two bashed twins from trainers w/.20's and .25's.
A bashed quad from a trainer .25's.
My design eighty inch Stinson SM-6000 triple w/.25's (unfinished through cover).
Vintage Douglas B-26 Ukie, unthrottled Fugi .29's.
Duelist, Rossi .45's earlier now TT.46's.
Old 06-11-2003, 03:30 PM
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roadtrip
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Default P38 Q & A?

JohnBuckner,

If I understand what you said above, do you mean that you have, sort of, two small vertical plates acting as permanent rudders on each H/S tip? Each one permantly installed to deflect the air in the direction according to which side it is a part of? Kind of like the vertical tips on the wing tips of airliners? A nd if both engines are fine, there is equal force on each plate, which would create a bit of drag, but the result there being zero yaw, or equal deflection. Are we trackin' here, or am I de-railing?
Old 06-11-2003, 03:45 PM
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William Robison
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Default P38 Q & A?

JohnB:

In re your number four, the stab tip plates.

The differential rudder throw accomplishes exactly the same thing, without the straight away drag penalty.

Bill.
Old 06-11-2003, 04:09 PM
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Default P38 Q & A?

I have been with Twinman while he was testing the gyro effect on everything from at Ultrasport 1002 (Ultrasport with twin Supertigre 3000s on it) to a 96" Bobcat (Cessna 310 looking 60 size twin) with Supertigre 90s and his Zoroli P-38 (dont remember the motor size).

He will gladly tell you not to fly the 38 without gyros.

I will agree and funny things also happen when the Zoroli 38 gets far enough out to look like a forty size bird and you make a hard knife edge turn, I wont say anynore.

If you fly a 38 without at least a rudder gyro it is only a matter of time till a crash IMHO
Old 06-11-2003, 05:13 PM
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JohnBuckner
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Default P38 Q & A?

Roadtrip, yes you followed perfectly. Both fixed plates provide equal and opposite rudder imputs and when there is a loss of the high energy airflow on one side or the other the result will be a yaw imput in the proper direction to minimise but not eliminate the yaw resulting from the asymetric thrust.

There is of course a drag penilty just as there is a slight performance loss with say outhrust on the engines when not pointing in exactly the same direction the airplane is going. everything on an airplane is a compromise.

It has made an improvement on my dualist with no other changes in allowing the pilot the time to: recognize and respond appropriately The drag penilty has not proven noticible and this ship has been used as a pace plane in SWRA warbird racing and as a multi practice ship for the poles although of course it could not be raced since is not a scale airplane with documentation.

My only point in listing it is this method is little known and an effective aid among the others, besides the little triple tail is cool looking.

Bill rudder differential will not do the same thing. The tail plates require no response from the pilot like rudder does and the effect happens the instant the asymetric thrust begins. I do not believe Rudder differential is any advantage in any asymetric situation. In that situation I want the maximum rudder authority in both directions from both rudders even if one of the rudders is operating in the relatively low energy air behind the dead engine. Reducing The total rudder authority by artificial means like differential will always result in a higher VMC (velocity minimum control) speed.


John
Old 06-11-2003, 06:22 PM
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MajorTomski
 
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Default P38 Q & A?

A few more items to consider when flying twins.

The phenomenon that rottilover hinted at is called Minimum Controllable Airspeed. On a twin this airspeed may or may not be the same as the aircrafts's stalling speed. By definition it is the lowest airspeed that the aircraft can maintain straight flight with the critical engine inoperative. His experiencing flat spins in the computer P-38 is caused by this effect. The single engine with its displace thrust line is producing too much yaw for the fin(s) and rudder(s) to correct. So the simple solution, as he has indicated is to either throttle back so that the engine is pulling less or fly and land hotter to keep the rudder(s) effective.

And
put your weakest engine on the right wing.
And
Get both engines to idle and accelerate reliably.
And
Set peak power on each engine as if the airplane were a single engine model. If you try to exactly match high end on both engines one or the other is going to be running rich or lean setting the foundation for an engine quitting. The small differential thrust you are going to get at the high end because of slightly different rpms will not be a factor in the air.
Old 06-15-2003, 09:04 PM
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AmishWarlord
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Default P38 Q & A?

Another problem with twins. A nice power train for a Ziroli P-51 cost $700 on average. Wile the power train for the Ziroli P-38 is $1,400. I'm still running data though the computer to account for this phenomena. There has got to be an answer to why twins cost twice the price to power.
Old 06-15-2003, 09:16 PM
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William Robison
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Default P38 Q & A?

AWL:

Duh!!!

Bill.
Old 06-17-2003, 01:43 AM
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twinman
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Default P-38's

The problem I have seen with the four P-38's I have owned, and flown (Number five is on the table)
The engines are very widely spaced, very small rudders, high wing loading, and small surface area on the side of the booms.
If even slightly underpowered or slow, loop, or over do the elevator throw.....snap roll!!!! NOW!!!....and let's not even discuss the engine out snap roll!!!!!
My two cents is to use two gyros. One for the rudders, and yes, use two servos for the rudders, and two for the elevator. ( Note, using one servo for the rudder guarantees flutter!!!)
The second gyro for the ailerons.
Using only one gyro on the plane, for the rudders is not enough to counteract the yaw of an engine out.,,,,they are too small. OK If the plane is flying really fast, yes they could hold it, but that never happens.
The aileron gyro to dampen the roll over into the snap roll. The combination, will not stop a gentle roll during engine out, but will dampen it to a level that you have time to react, and throttle down to idle NOW!!!. My two cents, is to not try to power back up with the P-38 unless you have a great deal of experience. It will go to a snap roll again, even if you have it under control.
I have also used the two gyro set up, and ( Dumb move) flown combat. The gyros also stopped the snap roll in very high speed and violent manuvers.
The problem is that we are not in the seat of the plane and are always behind the problems and adverse effects of engine out or impending stall. Then it is too late to fix it or correct. The gyros assist in this area.
Never turn the gyros off on a P-38.......ever!!! It take too long to find the switch as the plane spirals down.
Good Luck,
Twinman

Having said this.......did I mention how cool the P-38 looks and sounds in the air!!!!!!! Nothing else comes close!!!!
Old 06-17-2003, 01:53 AM
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AmishWarlord
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Default P38 Q & A?

LOL Twinman,


That post reminded me of a line from AL Bundey on Classic cars, "Do they run good? No, They run like crap, they aren't reliable and they drive like trucks. Then why? Because they are COOL."
Old 06-20-2003, 11:20 AM
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twinman
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Default P38 Q & A?

To AmishWarlord.
I am sooooooo unworthy to be in your presence. Truer words have never been spoken.......particularly about flying the P-38.
Old 04-10-2004, 12:03 AM
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Default RE: P38 Q & A?

Twinman -
I'd really appreciate some advice on engine selection.
I have been working on my one and only Z P-38 (you have FIVE!! How in the world ...?) for quite a while now, and made the mistake early on of buying US 41's for it. I've since sold them, at a small loss, but am once again in the engine market. I do not want to screw it up this time around. I've looked into the BME50, and can fork over the money for them, but I'm wondering if this makes sense. I understand that the wood version comes out tail heavy, and needs weight in the nose. The very light weight (3.0 lbs) of the engine would seem make this even worse.
Would you mind sharing what engines you use?
Old 04-11-2004, 02:32 AM
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scale dail
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Default RE: P38 Q & A?

I have been flying my royal P-38 on special occations for a few years now, and have yet to have an engine out. 2-K&B .48s and about 12 pounds. I have made dam sure the engines are running perfect before taking off, but----you never know... now you guys have me really nervous about single engine flight with a p-38. just what happens when a gyro equipped P-38 loses an engine? I also have a Tigercat 2-OS .46s 62" and about 12 pounds. and have purposly filled ether tank only partially to have controlled single engine flight,and it is quite scary even at altitude,but once that immediate roll toward the dead engine is checked with both aileron and rudder it is controllable with at least some speed. but what about the P-38,the legend? is it imposable to save?
Old 04-11-2004, 05:22 PM
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twinman
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Default RE: P38 Q & A?

Is the P-38 single engine flight impossible to save......Yes, and no. ( Just what you needed....a smart a_ _)
It, like all twins, depends upon MANY things.
1.You, personally, seem to be able to handle twins. Others have no idea what the left stick is for, other than throttle. For them, yes, it will crash.
2. When did the engine fail? On climb out, from take off, at full power, with other engine running? Almost impossible. (Personal experience). VQ number two is back in the air....yes, two gyros!!
3. How is it balanced? Nose heavy for more controled landing...Very difficult to handle. Here, it takes more power to pull out and that causes the snap roll. Too tail heavy for better landing and the added instability, causes a snap roll faster. Talk to the three D guys on that one, but they have far more power than we do and control surfaces......And only one engine.
4. At level flight and good airspeed...will try to snap roll almost instantly, but with airspeed and instant throttle back, can be caught. Do not suggest trying to power back up, due to small rudders!!!

The problem is very high wing loading, (I would suppose much higher than your Tigercat), by design, wide engine spacing ( Some models are worse than others here. Go for the more scale closer spacing)
The plane also has very small rudders. Make sure your set rudder control for maximum deflection. Remember on your Tigercat, you were expecting an engine out. It is the surprise that kills you.
Here is where, (In my opinion) the gyro(s) comes in. It is not an auto pilot, but significantly dampens the unexpected tendency to snap roll and gives you the extra edge to react before the spin of death really gets started. We are always "behind the unexpected" in our planes, as we are not in the seat of the plane.
Do I have gyros on all my twins?,,,,,no, only the P-38's. Yes, they are the most expensive in terms of money and time.
My two cents, it is cheap insurance. Can I fly most of my twins on a single engine? Yes, but I have a lot of practice. You do not want that kind of practice!!!
Hope that helps.
Twinman
Old 04-11-2004, 05:41 PM
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Default RE: P38 Q & A?

Lightning Fan
What engines to use. Here again, there is no right or wrong. I have seen pictures of Zeroli's with G-38's, and you can see them at rcwarbirds.com and the fighter section. There are also power plant specialists and builder specialists there to answer questions. The Zeroli plans ( Yes, I have the plans, but will never live long enough or have the building skills to built it) call for the G-62.
Now, my personal thoughts, (which of course are open to comment.)
What do YOU want? If you only want to put around the sky in a some what scale manner, it will fly with such low horsepower engines as the G-38's and US 41's. Do not plan on ANY possiblity to fly on a single engine!!
The G-62, while reliable, is not a particularly powerful engine, but reliable. ( Do not get confident in ANY engine reliabilty on a P-38. There was a gentleman, approx one year ago, with a Yellow P-38 and G-38's, and lost one engine and the plane, on the maiden flight)
Do you want scale three blade propellors? ( Personal favorite) Due to the loss of efficiency, you need more horsepower to pull 24" three blade props on your scale plane. I would think more than the G-62's could provide. Do you want a very scale look, without the carb sticking out of the cowels? Now you are into rear induction engines such as 3W and ZDZ. From personal experience, the rear induction engines are far more powerful, but a challenge to install and control.
Do you want the WOW factor of loops rolls and none scale take off? You need power for that........now that does not mean that too much is just right. You can get into a bunch of trouble with too much power.
Balance, Yes, the P-38 almost always comes out tail heavy. Look how much of the plane is back there. Personally, I would not buy heavy engines only to counter balance the plane. You would add far less weight to the plane, by adding weight to the nose of the center pod, for balance, due to the fact it is farther forward, than to balance with the engines, which are much farther back and much nearer the CG.
Best of luck and keep us posted.
Twinman
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Old 04-12-2004, 05:42 PM
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scale dail
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Default RE: P38 Q & A?

Some day when I get my VQ P-38 done I will start experimenting with the royal P-38 way up high!

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