No, not smart enough for that. But hope to make some small improvements that will give me better flying aircraft. There was pretty big smile on my face during my last test flight. So, I am almost were I want to be without redesigning anything.You are talking about redesigning the airplane... Are you ready to do that?Billski
When you don't have sufficient control authority in your most critical condition. For many aircraft, this is flaring in ground effect, with full flaps, at the most forward c.g. location. Or is there any point in your flight envelope where the AOA would cause the tail to stall, with our without elevator deflection?Question is this: - when aircraft designer should stop increasing stabilizer angle and start thinking about increasing horizontal tail volume?
When you don't have sufficient control authority in your most critical condition. For many aircraft, this is flaring
I don't think you're confused on this point! That sounds like the correct conclusion.I am confused a little again and need someone to straighten me out.
The way I see it, during stalling or flaring with passenger I am running out of elevator all the time. Stick is all the way back and you just sitting there and waiting for touchdown. Stabilizer is not helping at this point and maybe working against elevator, looking at my picture above. So I am making conclusion that elevator too small or tail arm too short.
The tail volume does appear to be too small. The challenge, as you're finding out, is what to do about it now.So, this is standard Skyboy in level flight and 2 people. As I see it, stabilizer is doing all needed work and elevator is trying to help. Stabilizer is already installed at neg. - 5.7°and it's not enough. So, what is right thing to do here? Drop stabilizer down to neg. - 6.5°and try? Or should we start thinking about larger stabilizer? Maybe horizontal tail volume of 0.34 not really working here? And when is that cut out line? Is it 5°, 7°, 9°? Or should designer get this message as soon as he needed to go below 4° mark? Do we have airplanes we know with stabilizer set at 6-8°?
I have a few possibilities for you.
- Document current airplane:
- Weigh the airplane, determine and record its exact empty CG, figure out the loaded CG. You will want to know what it was, and how much you change it;
- Record speed at which it runs out of elevator at both low and high seat weights, both aloft and in ground effect, and at idle speed and high power - that is eight conditions;
- Make the tail more effective;
- VG's on the underside of the tail will increase tail authority a noticable amount;
- Add gap seals on the horizontal tail;
- Shift CG:
- Where is the battery? If forward, shift it aft;
- Is the engine mount a separate assembly? If it is, you can build another that shifts the engine aft an inch or two;
- This thing of strengthening the tail boom will add weight aft - the stuff that is added, keep track of its weight and position;
- Test fly each change:
- Read up on test flying and looking for pitch stability issues, how to spot them, what to do about them, etc. Neither I nor anyone else on here can educate you adequately as a test pilot;
- If you are shifting CG aft it can be a sensitive thing. Aft CG is nothing to play with. While it sounds like you have a forward CG and can adjust it quite a bit, move the CG aft in small increments. Some folks talk about having a bag of shot aft and way to pull a handle and dump it. Done properly, that lets you adjust in small increments and go back to a known good CG with the tug of a handle;
- Calculate the new flight CG position and record it;
- Taxi test, first slow, then at increasing speeds. You should be able to set the stick and have the nose settle on a pitch attitude, nice and steady with the nose wheel off the ground. If it wants to bang the tail skid or bang the nose wheel on, the CG got too far aft - record that CG and resolve yourself to not flying that far aft again;
- If you get any indications, either on the ground or in flight of it not wanting to set a steady pitch attitude based on a fixed stick, land as soon as practicable. If it does it right after breaking ground, close the throttle and land - record that CG and resolve yourself to not flying that far aft again;
- Carefully test fly looking to see if you raised or lowered the speed at which you run out of elevator in all eight cases;
- Check out the rest of the envelope - if it gets touchy, record that CG and resolve yourself to not flying that far aft again;
- Read up on test flying and looking for pitch stability issues, how to spot them, what to do about them, etc. Neither I nor anyone else on here can educate you adequately as a test pilot. Yeah, I said it twice. That is selective redundancy, and we do that because the repeated topic is really important.
Why experiment with it? Because you keep making observations about undesirable behavior, like this:But from CG stand point why I need to experiment with it? As long as I stay inside of this 21-36.6% window = I am safe!
And this:Aircraft can not be trimmed for level flight and hunting up and down by 300-500 ft apart. And aircraft with passenger feels like filled with lead.
These are indications that the aircraft is not fully controllable across the entire c.g. range. Is it safe, but just annoying? Possibly.Stick is all the way back and you just sitting there and waiting for touchdown.
Yes! Thank you!2. Modify the aircraft to make it behave well across the currently specified c.g. range.
The fact that you opened this thread in the first place would indicate you want to pursue option 2.