1st flt Avid - impressions

56 posts in this topic

Posted

Turbo

 

Congrats on your first flight.

I flew with the Rotax 2 stroke for over 1,000 hours before switching to the Jabiru 2200 on my model B.

Here is my input on some of the questions you have...

I don't recommend a prop clutch. As was mentioned it will limit your glide ration about 20% and you can not hand start the Rotax, which you WILL do one day.

I had the E box on my Rotax.

I totaled my B model so I will be referring to my MK4 in this response.

My IAS at stall is 40 MPH clean and 35 MPH with 13 degrees of flaperon. Stall is just a bob up and down. I have a Dynon D10 in the panel and it has an AOA indicator with audio alarm for stall indication.

If you have a wing low trim you can adjust the rear left wing lolly pop attachment to raise or lower the rear part of the left wing to get the trim right. It doesn't take much.

Don't put more than 15 degrees as your flaperon down angle. On your model, the roll rate gets slower and if you put in too much down flaperon you can get reverse control. You put in left stick and the right wing drops and visa versa.

As concerns your rough low RPM you will need to be sure your carbs are balanced and your idle jets are clear. You should be able to idle at 2000 very smoothly.

It is easy to flood the upside down engine on the Avids. To prevent this, don't use the primer until you are actually cranking the engine.

Make sure the flange on your thermostat has a couple holes drilled in it if you have a grey head engine. Here is why. If you are on a loooong final with the throttle pulled back the water in the radiator will cool down quite a bit, especially in winter flights. Then as you are landing you decide you need to go around. You put in full throttle and on climb out your thermostat opens and floods your hot engine with cold water. Could cause a problem.

I ran a 70" wood two blade prop and cruised at about 75 -80 MPH at 5800 RPM.

I ran 100% synthetic oil at 100:1 ratio so I disabled the oil injector. 

I used to get 300-500 hours TBO on my engine.

I had VGs on my model B, but have determined not to put them on my MK4. You can get a bit slower touch down, but the angle is so high that the tail wheel touches first and then the mains slam down. The flaperons do a great job without the VG. I also use a bit of flaperon for nose down trim while in cruise.

With the Jabiru I cruse ar 90-95 TAS at 2900 RPM burning 3.0 GPH. Since it is direct drive the max prop length is 66".

That's all I can think of at present.

I now have over 3,000 hours in Avids and am completely satisfied with my MK4.

We fly to the Idaho backcountry each year where the Avid really excels. I flew it to OSH two years ago.

Have fun flying your avid.

 

John M

 

 

 

 

1 person likes this

Share this post


Link to post
Share on other sites

Posted

Thanks, John.  Lots of sage advice there.  My bird seems to get 80mph IAS on 4500 rpm, yet it doesn't seem so clean aerodynamically, although it is lightweight.  Lower altitude (3k) maybe?  I have no interest in VGs, as they also reduce maneuvering speed, along with stall speed.  Will have to take a look at the thermostat.  Engine seems quite healthy, but the carbs are the old variety with no drilling for venturi pressure, so I have relied on measurements of throat opening for balance.  I'm sure if i could tune to equalize pressures I could do a better job of balancing them, and perhaps improve smoothness. 

It seems I need to use a spark plug wrench and paper towel to clean one or more plugs before it will start.  Is there a work-around for this?  - Art

Share this post


Link to post
Share on other sites

Posted

If you haven't ran the plane in a while, this may help you. it did for me.  Give it full throttle, mags on and crank a couple of revolutions.  Doubtfull  that it would start, but be ready to pull the throttle back.  That will help to blast the old gas out of the plugs.  If you are scared of the full throttle, do it at idle.  After that, then prime it and start as usual.  If the plugs are full of old gas and oil, and then you blast in some more with the primer, you are much more likely to flood the engine.  JImChuk  

Share this post


Link to post
Share on other sites

Posted

Yeah, Jimchuk, I am skeered of full throttle!  That 582 is a mighty little bugger!  Maybe all this excess of oil will become a nonproblem once the OI system is back up?  Or at least mitigated to some extent.

Share this post


Link to post
Share on other sites

Posted

Checked wing incidences with inclinometer & found them to be equal to within 1/10 of a degree, the precision limit of  my tool.  Also found an area on the port aileron where the trailing edge had been bent up, likely hangar rash.  That could explain the roll moment.  Bent it back down as best I could.  We'll see if I got all of the roll moment out.  This may take several iterations.  Turns out I have the older f7 mixer arms.  No matter; Just need more airtime.  If my new, stiffer trim spring works with some flap, I'll be tickled silly!

What is the best way to accurately measure my wing incidence?

Share this post


Link to post
Share on other sites

Posted

The zero-lift angle of the airfoil itself can be estimated using a simple approximate method due to Pankhurst in the front of Abbot & Von Doenhoff Theory of Wing Sections.  I did that calculation, getting -5.64 degrees relative to the max-length line, but that may not be what you're after.  (BTW, the max length line is 1.76 deg above a line between the TE and the lowest point on the lower surface.)  I believe the term "incidence" refers to the angle of the root airfoil with respect to the fuselage reference direction.  To measure the wing's washout I simply found a straight piece of wood longer than the chord length, but thin enough to fit between the wing trailing edge and the flaperon.  I simply pressed an inclinometer up against the board, which in turn was pressed up against the wing's lower surface.  I measured this at the root and out at the tip, just inboard of the fiberglass wingtip.  For my bird, the washout was a whopping 4.5 degrees, which I think is in accordance with Dean Wilson's design.  Lots of folks, myself included, think this was a bit excessive.  Maybe Dean was trying to save us hosers from killing ourselves.  Every aerodynamicist worth his salt knows an untwisted Hershey bar wing will initiate stall at the root in rectilinear flight.  But things could be different in a tight turn, like when trying to escape a box canyon.  If you want the wing incidence relative to the fuselage reference line, that line is parallel to the door sill, so make that measurement too, and do some subtracting.

I occurs to me that Dean was a great designer, but missed the following point:  To properly design a wing using the same airfoil shape from root to tip, it's necessary to make sure the chosen airfoil isn't coming up out of its drag bucket at 0 CL, which is what you get at the tip.  The lift always falls to 0 at the tip!  The Avid's fiberglass wingtips help, but what's going on just inboard of them?  The combination of that much washout and an airfoil with concave lower-surface camber pretty much guarantees the tips are out of their drag buckets on the low CL side, and adding a fair amount of drag.  You might want to tuft the wing there, to see if and where the flow's separated.  If it is, VGs might be called for locally!  It might reduce lift a little, but not by much, so close to the tip.  Flow separation means pressure drag! 

Hey, Merry Christmas, my friends!   Turbo

1 person likes this

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now