All my ca hinges are correct except the elevator, it has a 1/8” gap or more. the plane is a PT-40MKII with a .49NT Evolution engine it’s my first plane and will flying it slow will this gap effect the plane?

As long as the hinges are glued in securely I'd just use covering or clear tape to seal the gap.

Ditto

just use some scotch tape along the top and bottom of the gap

I always hear about filling a large gap with covering, or tape. Can someone explain why a 1/8" gap between the wing and the control surface is a bad thing. I know I am new to this, I just don't understand how that could really affect the performance of the plane.

Thanks

P.S. Not questioning your expertise or advice, just seeking a better understanding of the hobby.

Good question it's only 1/8th inch and it's on a slow trainer

Without getting into a bunch of the math, the hobbyist's answer is pretty much this:

Pretty much any calculation pr presumption made about an airplane's behaviour presumes, first, that airflow over, under, and around any surfaces is uninterrupted...that is to say, for example, that the wings are treated, for purposes of such calculations, as a solid unbroken surface.

A gap in any surface results in air not 'successfully" completing the trip, as it were, for a variety of reasons. Probably most significant are the disruption of the flow (in terms of both direction and speed) and the drag created both by the disruption and by the impact of the air with whatever "flat surface" might be exposed by the gap.

Why can/does this cause problems on some airplanes? Simple...it causes the surface in question to behave differently than designed. Perhaps it's a bit more draggy, thus raising the overall drag of the aircraft, which then raises the power required to overcome said drag, which of course has the resultant change in angle of attack for a given power setting, blah blah blah blah. In short...the plane 'ain't right" *heh*

How MUCH difference it'll make will depend on a great many things. How "slick" is the airframe supposed to be? What's the airplane supposed to do? how precise is the airplane in its 'correct" configuration? How skilled/experienced is the pilot?

Take a VERY precise sleek pattern airplane with an experienced pilot....even a small change to the airflow can make a notable difference to such a pilot.

On the other hand, as wzak suggested...a less experienced pilot on a more 'soft" airplane like a trainer? 1/8" gap probably won't EVER be noticeable...though covering the gap as suggested above is still good practice simply because it's good to be in the habit of 'getting it right", as it were.

If air can escape between the wing (or fin or stabilizer) and the control surface, it reduces the effectiveness of the surface because air that should be deflected is escaping through the gap. Also, the airflow around the gap can cause turbulence that makes the control surface flutter. If a surface flutters, the vibration can rip it apart.

These may not be huge issues on a trainer, but a two foot strip of tape is cheap insurance.

I experienced elevator flutter with a SIG Astro Hog (not a really fast plane) and it ripped the stabilizer and fin off of the plane. It rolled inverted and glided around for a while before crashing nd destroying the fuselage. I still have the wing.

Since I'm here I'll chime in on this one. On something like a trainer it will probably not make a noticeable difference unless you put it in a high speed dive. But what happens with a large gap is a vortex (turbulence) is created by the change in the surface between the stabilizer and the elevator. This results in more drag on the control surface. At higher speed this is a real problem because it will cause flutter and eratic performance of the elevator and can cause the hinges or elevator itself to come apart. You can guess what happens after that. MinnFlyer or someone will correct me if I have explained this incorrectly, but I should be close. Hope this answers your question.

I just taped the elevator took all of 10min. THANK'S

When in doubt, make it right. good choice.

Ok, here's why:

When you deflect a control surface UP, the surface creates a high-pressure area on the top side and a low-pressure area on the bottom.

If there is a gap, the low pressure will suck the high pressure right through. This will make the control surface less efficient. In most cases, it's not too big of a deal, but I have seen people with a large gap talk about wanting more aileron throw and I tell them to seal the gap before they change anything - the next thing you know, they want LESS aileron throw.

I keep my gaps small and haven't sealed one in years, but if you're performing precise areobatics (Like pattern fliers do) you would want to seel it - not so much to make them more effective, but to make them equal to each other.

MinnFlyer's a great source of knowledge... and he has a picture for everything.

Just make sure when you've sealed your gap you still get full flex from the control surface. Best way to achieve this is extend the surface fully downwards then seal the top, then flip the plane and reverse the process so the two layers of sealing medium actually stick to each other through the gap along the hinge line.

There is really no need to do both sides

If you're using tape or something else that's sticky and you only do one side, won't the gap end up full of dirt stuck to the tape?

Geeze, how much dirt do you fly through?

I fly off a grass strip in a country that's had seven years of drought and water restrictions. I get dirt, dead bugs, dead grass and all sorts of yuck stuck to the castor oil slick on the skins of my planes... I can't imagine trying to dig it out of an elevator gap.

In that case, use covering. It's not sticky

Or just do both sides. It helps a lot when it's time to clean up your plane. Engine snot gets into everything!!

Minn and the others, thanks for the great explanations. I never considered that it could cause flutter, although I have never experienced flutter or the after effects either.

I sure never said anything about flutter. It is not true that sealing a gap will reduce flutter - in fact, it can also make it worse.

Flutter is a chapter all its own. Don't relate it to whether or not there is a gap.

Minn is correct. Many people will claim that gaps in control surfaces will cause flutter. This is not true. As Minn eluded to, the gaps can add to a fluttering problem. But it will not cause flutter. And yes, flutter is an entirely seperate discussion.

Ken