Yesterday a P-51 got its maiden flight. It flew almost trim free requiring only a couple of clicks of roll trim and no pitch change but it required a lot of elevator to get it to rotate and hold the nose up on flare, especially with flaps. I was rotating only after a gaining very good speed.

It was sensitive to roll but not pitch. It is more sensitive to down elevator than up. Snap rolls are snappy. Roll rate was tamed by reducing to 80% and opting for 50% exponential and pitch was adjusted by reducing down to 80% and given differential with as much up as the hinges allow. It is an old design from the ''80s and is balanced right on the point shown on the plan though the point is up on the side of the fuselage and I balanced from under the wing, adding nine ounces forward in the cowling. An in flight balance check was not done but will be next outing.

It has a 64" wing with 685 inches and weighs 9 lbs 9 oz for about 33 oz of loading and is powered by a HB .61. I''m not very familiar with heavier wing loaded planes and my question, do heavier wing loaded designs typically require a lot of elevator to rotate or does it mean that the balance point should be questioned? It flies good other than hard to rotate and keep the nose up on flare.

One can appreciate that I don't want to enter the tail heavy world messing with this thing.

Most probably because the plane is nose heavy. Move the internal parts around to move the CG more aft. Best to do it a little bit at a time as if you get the CG to far back it will probably be your last flight until repairs are made. All other things being the same, added weight will only increase the stall speed.

I agree. I would look at the balance. Question ,will it stall and spin in flight? Is it hard to get it to stall? If so it is nose heavy,but don''t get it tail heavy to the point it stalls to easy.

Pitch response is basically the result of elevator authority. Elevator authority is limited by a number of things, but after the airplane is built, the only one we can affect it CG location. The elevator will be most efficient with the CG closer to the rear of it''s range. Move the CG forward and the efficiency goes away. Move it too far forward and the elevator gets sluggish. Farther forward still and it''s close to worthless and the airplane is closer to it''s expiration date.

Lot''s of beginners and even some experienced modelers think they''re making their models safer by moving the CG an extra bit forward. They are not. They''re simply taking away the elevator''s ability to make pitch changes.

You''re seeing just that.

The weight sounds reasonable for a 60 size model. Higher weight only means the CG has more effect for what you''re talking about. And amplifies the CG location effects even more the slower the airspeed.

Not much you can do to lighten most completed models significantly. Lots of ways to move the CG back. Before you do it however, it''s sensible to know more about the airplane, so check it''s measurements out on geistware.com. That''ll tell you a lot about what''s really going on with the model.

Speed is your friend. Horsing a plane off at the minimum speed it can fly at is fraught with difficulties, tipstalls being Enemy #1.
It needn't require a lot of elevator to take off.

Thanks to all for the responses. Very good words from da Rock on clarifying the dynamics of pitch authority and how it is affected by balance and speed.

It is of course possible that the plan illustrated a very conservative balance point.

I think my next step is to do an in flight balance check... straight and level at half power to a 45 degree down glide and watch for any upturn. If it does, I will start to remove some of that nose weight in one oz increments and report back the outcome.

Paul... I hear ya. I''ve been flying RC since ''75 and this plane was given to me in ''82 by a then pilot for Walmart. H''ed partially built it and I painted it and was preparing it to fly when the wing sheeting joints started curling up. It was set aside in the barn for many years and deserve to fly and some effort saved it but no further heroic measures will be given. It has a foam core wing and fibergass fuselage so wont get any major repairs. Plus, I''ve fairly well shifted to gas models and hate cleaning up after a .60 size 2 stroke glow motor but I just couldn''t stand to see this plane not have its day.

Yes... I didn''t try to rotate until boogying well and then was surprised by how much elevator was required. Course, this is the world of scale and it simply may not have enough elevator. I guess I''m saying, I''m assuming nothing and not going to jump to conclusions it is nose heavy.

And... it just occurred to me that there is one more issue that could have a bearing on this. As I said, the sheeting joints curled on this thing and I removed and replaced all the wing sheeting. The stab is foiled and was also sheeted and it has one joint that curled only very slightly. The stab was of course fitted and faired to the fiberglass fuselage and replacing the sheeting on it would have been very difficult and the bump very minor in appearance. It could however be that the bump causes physical issues however as a contributing factor, ie scale plane and minimum elevator and reduced elevator authority because of airflow disturbance.

In that dive test SOME up pitch to come back to level is desireable. It''s just that you want it to me moderate, nor extreme. For a model of that size look for a first rotation to level from a 45 degree nose down attitude to take about a 100 to 120 foot loss. If it rotates to level in less than that then you are nose heavy. If around that to 150 I''d say you''re in good shape.

It could also be drag in the gear, causing the nose over tendency. You said it flew well in the air. With warbirds, you don''t want to be able to stall or snap, so having a forward CG is a good thing. You can pull full up elevator and nothing bad will happen. But you do want to be able to get maximum lift. Try a power off stall in level flight, gradually pulling the elevator back. If it stalls, then you have enough elevator throw. If not, you can move the CG back a little or increase the up elevator travel, if possible.

P-51''s have a long nose and therefore tend to be noseheavy. I have proven this from a 3.6 oz Strega EPP Mustang to the 60 size WM P-51.

I wanted to also add that not only is elevator efficiency lost with a nose heavy airplane, but a key factor in wing efficiency is lost as well.

The center of lift and center of gravity must be fairly close. My 2c

Thanks again for the additional comments. I may get a chance to fly it again tomorrow.

Interesting point about the long nose and it caused me to think perhaps the fuel load has greater leverage than typical and as others have pointed out, with greater wing loading comes more distinctive effects of fore and aft locations. I don''t recall what size tank it has, probably a 14 0z. I may try a half tank and note any difference. it was of course balanced with no fuel load and all of the landings were with a fair amount of fuel left. I didn''t set a timer and certainly didn''t want to run out of fuel and it has been many years since running a .60 size glow engine.

I did get altitude and test for any tip stalling nastiness with elevator at slow speeds and did not get any in both normal and position one of the flaps. It can be induced to do some brisk snap rolls and recovers from them easily with neutral sticks. I didn''t spin it as it was getting dusk and I want it way up there when doing that the first time.

Will report more after flying again.

I woke in the night and thought on the plane a bit and recalled an experience back in the 1970''s when foam airplanes were first introduced by Sure Flight if I recall. I built a Spitfire and gosh it flew well... that is until the fuel tank got low and it turned wicked with an increasingly sensitive elevator and pitch became so unstable that the plane was lost late on its maiden flight.

So, the thoughts about long noses and fuel load leverage on war birds is applicable.

Outing #2 report. I wasn''t up to full power yet and the plane rotated on its own and lurched about twelve feet up before I could react and get the pitch leveled. It was fortunate it didn''t snap. What in the world was going on?

As the P-51 climbed for altitude, I was mystified that Sunday it required great amounts of elevator to break ground and now it broke on its own and no changes had been made. I''d discussed the Sunday issue with the few guys gathered at the field and they all concurred that the plane could be nose heavy and some flight observations were in order.

One of the guys hollered... I thought you said that it was hard to get up. Before reaching safe altitude to relax a bit... it hit me. There was only one thing that could possibly have changed between Sunday and Tuesday.... the wing incidence.

The wing is bolted at the front. The back of the wing is trapped under the P-51''s radiator scoop, which is part of the fiberglass fuselage on this kit. It had to be a variance in how tight the wing had been seated to the saddle, which could change the incidence slightly. The incidence had been checked about a year ago after re-sheating the wing and drilling and tapping for the hold down bolts and was satisfied that every thing was zeroed.

Evidently, the wing bolts had not been adequately tightened on Sunday and overtightened today. About four clicks of down were needed to trim whereas Sunday, no pitch had been needed.

I hollered back at the guys that it had to be incidence changes due to the wing hold down bolts. Flipping to low rate on the elevator, the plane flew fine. With plenty of altitude, stall test showed that the plane is not forgiving and will stall a wing if the elevator is horsed too much at slow speeds.

The center section leading edge of the wing is faired to the fuselage underpan and after landing was checked. I''d tightened the bolts so that the fairing was perhaps 1/32 - 1/16 beyond the belly section whereas perhaps on Sunday it had been left short of reaching flush.

Loosening the screws very slightly so that the leading edge fairing was flush with the underbelly produced a sweet spot where the plane required a small amount of elevator to break ground and climb out beautifully and experience no nose dropping issues on landings. My great surprise is how such a little bit of change in those hold down bolts effects the flight character.

Guys... forgive my carelessness in not considering this before laying this on the group. This is the only plane I've had with forward wing bolts and the pitfalls that can result.

our pleasure

I''d add that the CG is obviously not too far forward. We rung it out a bit and it will do wild snap rolls and the lumcevak. Left spins are fairly typical spin rate but right spins really wind up. It recovers from spins about one spin later than most birds but does otherwise come out with neutral sticks.

Rolls were smoother with the incidence better set.

We again had a fair headwind so only the first flap position was used for landings. It requires a very fast idle or perhaps even slightly more to maintain landing glide slope. I''d prefer to never land it dead stick.

What is very interesting is that the airplane ... flew almost trim free requiring only a couple of clicks of roll trim and no pitch change the first flights with the incidence "screwed up". And after the incidence reduction, you didn''t mention elevator pitch trim at all.

A strong warning needs to be voiced here. If the amount you tighten the wing hold down bolts affects the wing incidence, you''ve got a major problem with that sucker. The wing underneath the hold down bolts should be rock solid. The bolts should snug up to something that has no give at all. Once securely tightened, the wing should be at the incidence that flies best. Your descriptions so far suggest that you can tune the incidence with the hold down bolts. That really should lead to one of two things. Death of the airplane when the wing wears around the bolts and rips off, or an airplane that needs elevator trim about every outing.

Changing the incidence of the wing actually changes the AOA the tail has to work with. The pilot directs the airplane''s pitch with the elevator. At whatever speed the pilot chooses he winds up needing elevator deflection to maintain level flight. We usually trim that amount of elevator so the plane holds level flight hands off. At that state, the wing will be at whatever AOA it needs. And the rest of the airplane winds up pitched however the wing incidence pitches the fuselage etc. And we wind up having elevator trim adjusted for all that. That elevator trim is really a result of what AOA the stab/elevator was pushed into by the wing/speed/pilot/etc. So........ If you fly an airplane with let''s say 5degrees too much incidence and then fly it with that 5degrees removed, what the tail has seen is a difference in it''s AOA between the two flight being 5 degrees. Tails generate a bunch different lift when their AOA changes that much. One would really expect the elevator trim to be quite different between the two flights in the example.

But bottom line isn''t the difference in elevator trim. It''s having a model with a rubber wing that is the bottom line.

BTW, the strong pitch on takeoff after the wing was screwed down more is not a surprise. Trim for level flight with extra wing incidence, then reduce the incidence and what happens? Next flight, after the incidence change, the wing is going to go to about the same AOA as before, and that''''s going to change the tails AOA. It''s going to try to correct the pitch that doesn''t need correction and it''ll do it wrong until the trim is changed.

It''''d be surprising if you didn''''t need a fair amount of elevator trim to fly level after tightening the wing on tighter.

I worked up a little show and tell. It shows what should have happened from your description. It might help to see how AOA of the wing and tail works.

The model at #1 is with the everything as designed and the airplane flying along in trim at full throttle. The wing is being asked to carry the weight at that speed and basically finds what AOA gets the job done. It's pitch decides how the fuselage pitches and the fuselage decides how the tail pitches. Since the tail design was figured for all the rest, you see the elevator trim is about zero.

The model at #2 has the wing bolts loose and the wing is hanging down in back. The airplane hasn't taken off yet.

The model at #3 has taken off and the wing has the same weight to carry and very close to the same speed so it'll assume the same AOA. This pitches the fuselage and the attached tail up and what happens to the tail. It's now forced into a negative AOA by the more powerful wing. So it lifts down. If you don't do anything on the TX, the airplane won't fly level. So you trim the elevator so the lift back there doesn't keep pushing the airplane out of level flight. You've got to get rid of some of the excess down, so you trim the elevator. It winds up looking like it does now in #3. (Basically the airplane is screwed up in terms of drag. The fuselage isn't at it's best drag angle, and the tail is now less than a slick, low drag symmetrical profile.)

So you decide to fly again but now screw the wing in to it's design incidence angle. The plane starts to fly and #4 is what the air sees. It sees basically the airplane in #1 but with elevator trim that wants to push the tail up.

This make it easier to see????

The P-51 configuration in my experience is quite intolerant of even "normal" elevator deflections!
I''ve always had to reduce the elevator throws to less than what is used on similar planes.

da Rock, your right it did require 4-5 clicks of down trim on the first flight yesterday to get in trim. After coming down, I noted the elevator was down slightly so the bolts were eased just slightly to line up the fairing with the under pan and two clicks of up were put back. At that point it took off beautiful with just a little up elevator needed to lift off.

You are of course absolutely right about the importance of the stability of the wing and I can see that these forward bolts are not ideal (other than dialing in the wing incidence for best flight characteristics) but the wing really seats well into the larger portion of the wing saddle with a slight space forward. The bolts were very snug in both instances when flying. I expect the difference was about 1/8 inch, which is really surprising to me that elevator authority would vary that much with such little difference in incidence angle. 1/8 inch in the 14.5 inches of chord is not much angular incidence change. I''m left to think that the additional tightening warped the wing a bit.

At any rate, once it is dialed in I will lay some silicone on the forward sections of the wing fairings were the slight gap existed and wax paper the wing where contact is made to firm it all up a bit. It is also unlikely that this plane will get a lot of flight time, at least from me for several reasons. I''m spoiled by gas and don''t like cleaning up after a .60 size glow engine any more, plus I''ve grown fond of a little larger plane than this and those lighter loaded and finally, this thing is silver and too frigging hard for old eyes to see except in the best of sky conditions and it is too fast and goes out too far. This plane was given to me 25 years ago and I took pity on it and decided it deserved to fly... and it has.

Here is the plane and I just noted that one can see the slight gap forward on the fairing.

http://pages.suddenlink.net/arlyn/P0002824.JPG