Is a lot of elevator needed to rotate, typical of heavier wingloading?

Is a lot of elevator needed to rotate, typical of heavier wingloading?
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All Forums >> RC Airplanes >> Aerodynamics >> Is a lot of elevator needed to rotate, typical of heavier wingloading?

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Is a lot of elevator needed to rotate, typical of heavi... - 4/14/2008 3:29:33 PM

AA5BY

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From: White Oak, TX, USA
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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.

< Message edited by AA5BY -- 4/14/2008 7:32:54 PM >

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RE: Is a lot of elevator needed to rotate, typical of ... - 4/14/2008 3:35:31 PM

Rodney

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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.

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RE: Is a lot of elevator needed to rotate, typical of ... - 4/14/2008 4:54:01 PM

crasherboy

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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.

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RE: Is a lot of elevator needed to rotate, typical of ... - 4/14/2008 6:59:22 PM

da Rock

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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.

quote:

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.

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.

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RE: Is a lot of elevator needed to rotate, typical of ... - 4/14/2008 7:44:22 PM

Tall Paul

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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.

< Message edited by Tall Paul -- 4/14/2008 7:45:09 PM >

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RE: Is a lot of elevator needed to rotate, typical of ... - 4/14/2008 7:49:38 PM

AA5BY

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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.

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RE: Is a lot of elevator needed to rotate, typical of ... - 4/14/2008 8:11:18 PM

AA5BY

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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.

< Message edited by AA5BY -- 4/14/2008 8:21:34 PM >

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RE: Is a lot of elevator needed to rotate, typical of ... - 4/14/2008 8:54:38 PM

BMatthews

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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.

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RE: Is a lot of elevator needed to rotate, typical of ... - 4/14/2008 8:57:35 PM

wellss

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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.

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RE: Is a lot of elevator needed to rotate, typical of ... - 4/15/2008 1:08:58 AM

MustangAce

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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

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RE: Is a lot of elevator needed to rotate, typical of ... - 4/15/2008 4:27:30 AM

AA5BY

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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.

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RE: Is a lot of elevator needed to rotate, typical of ... - 4/15/2008 11:42:34 AM

AA5BY

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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.

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RE: Is a lot of elevator needed to rotate, typical of ... - 4/16/2008 4:11:57 AM

AA5BY

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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.

< Message edited by AA5BY -- 4/16/2008 1:07:27 PM >

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