Capstrips

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Postby daffy1029 » Sun Oct 26, 2008 1:36 pm

Hi all,
I have capstrips mounted on the top of my wings, along with some other mods such as larger (44" dia. ) props, Solo engines with 2.5:1 ratio redrives. It's a series 2 Lazair with wide gear and I weight about 205 lbs. Also factory enclosure. I find with both engines off, the plane has very poor glide. When I flew it back in the early 80's, it never bothered me to shut my 185"s off and glide in. When close to the ground it would "float" in ground effect before settling onto the ground. Now it just drops like a stone, and I have to flare at the last second and it's on the ground. It's now scary to land without power! I know extra drag from props and extra weight would lower the glide, but this much? I would expect at least 8:1 glide ratio as the plane is now (but it seems much worse). The balance of the plane is ok as well. I want to blame the capstrips for the poor performance, am I right? Daffy
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Postby Shannon » Sun Oct 26, 2008 3:16 pm

Personally I don't think the capstrips have anything to do with it. Think back to your plane when it had "good glide". Lets look at the weight difference then vs. now. Be sure to add any weight difference of yourself then vs. now (if any). I'd bet if you really get down to crunching the numbers there is a fairly good weight difference.

Make sure your ailerons are adjusted properly. "Properly" would mean adjusted so that they "reflex" evenly with the trailing edge. "Reflex" meaning take into account the slack in the control system and adjust the ailerons so the wind can push them up just a tad to be in line with the trailing edge in flight. I recall reading something about out of adjustment ailerons spoiling glide numbers during a flight test.

Last are you seeing a great difference between engines at idle glide and engines off glide ?
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Postby sustainflight » Sun Oct 26, 2008 10:07 pm

Is it the glide angle that is worse now, or just the rate of descent? What speed are you flying?

Weight shouldn't degrade the glide angle; it just causes you to fly down the glide-slope faster (higher sink rate).

For an enclosed Series III with a 200-lb pilot, does anyone have data (manual or experimental) indicating what the best glide (shallowest glide angle) speed is?

What about speed for lowest sink rate (slower airspeed than above, but worse glide angle)?

Craig
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Postby daffy1029 » Mon Oct 27, 2008 8:52 pm

Hi Shannon, sustainflight,
How does a two seater perform with both engines out? I know it has a slightly longer wingspan, but it has to carry much more weight.
How do I know for sure that the balance is good? I have the trim tabs down about 15-20 degrees to fly hands off at about 40mph airspeed. Would more weight in the nose or tail make it fly better?
The last time I landed without power, I purposely pointed the nose down to keep the airspeed up, then flared, but the response was quit sluggish, and I landed a little hard. I had a few other landings and they were a bit hard too. If I land with power on, I can land smoothly.
I will look at the ailerons first, to see if they need adjusting. Thanks for your input, Daffy
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Postby Shannon » Mon Oct 27, 2008 11:03 pm

Daffy I think Dave, Shorty, or Tyler could more accurately describe 2 seat engine off performance. Last time I flew in a 2 seat was many moons ago and the engines were always running. I'll make a wild guess that glide is of the rock variety.

If you have hands off at 40 then trim is good. Ideally you wouldn't want to add weight.

You may have answered your own question. You may be getting much more drag with the 44" props than you were accustomed to with the 28" Bi-props. This may explain why holding a little power produces a better landing. Additionally the 185's do produce a few pounds of thrust at idle.

I have always wondered about any negative aspects of switching to re-drives and 44's on 185's. One question in particular I never could get an answer for was engine at idle sink rate.
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Postby JPXman » Tue Oct 28, 2008 4:12 pm

there is no need for a comparison of engine off/engine idle glide speed comparison with a 2-seater. as soon as you come off cruise power,you can look between your legs and that's pretty much where you'll go :)

sustainflight - i don't think there is a lazairhead out there who would know any particular performance speed numbers for a lazair, nor stares at their ASI during any phase of flight.

the two seater has one speed - 40mph. you climb at 30, thats about the only different one. cruise 40, approach 40, full power maybe you see 45 :)

i think a lazair just needs two positions on an ASI
1. flying
2. not flying

its a perfect day to fly here and i'm stuck at work - booooooo

Tyler
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Postby uscgairdale » Sat Nov 01, 2008 7:25 am

Hey Guys,

I just got back from two week of doing Coast Guard checkrides in New England. I don't even want to guess what the glide ration would be on a two seater. Is it possible for it to be a negative number?....Seriously, a dead stick landing would be more like a helicopter autorotation!

I haven't messed to much with single engine work, but I can climb. I haven't measured it yet, but I don't think that it's very fast. My Lazair's performance numbers are similar to Tyler's:

Takeoff and climb at 30.
Power off stall at 25.
Cruise at 40.
Approach at 40.

The only difference is that I can definitely exceed VNE if I were to firewall the throttles in level flight.

I should have some new props to install next Monday....sweet.

Dave
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