Best Glide speed/ Max demonstrated crosswind

[Jch]

I am putting together my POH for my SS7 and would like to add these numbers. What numbers have others used? Jch

[n85ae]

Not really any answers to your questions, but -

It's an interesting issue for me, I glide tested my Series 5 (IO-240B) quite a
bit, and my glide is virtually the same at any speed from 55-85 mph. I tested
several passes at each 5 mph increment for 2000 feet of descent and there's
virtually no differences and it glides very well at each speed.

To me it explains also the issue where on landing, if I don't get the plane
really slowed down, and then I hit ground effect it floats for a million miles.

For summer fun flying I often drop 11 degrees flaperons, and power back to
a 65-70 mph 2-300 fpm descent, and pretend I'm flying a glider, and go
thermal hunting. Great fun, and burns very little fuel.

Regards,
Jeff Hays

[Dave S]

Jeff,

Each of our planes is different since they do not come off an assembly line like a commercially manufactured model. Certainly there are design values, but they might not match the actual given variations among different KFs.

First off, there are 7 different basic kitfoxes........then each one, for instance the S7, have different features such as hoerner wingtips vs the short wingtips, manual tab trim vs electric HS trim, differences in W/B, rigging, ASI calibration, landing gear etc. So many differences that it is not feasable to pick an average or standard number which can be used for the POH for a specific EXP KF without actually testing the specific aircraft.

Max demonstrated Xwind is interesting....if it hasn't been demonstrated on a specific experimental, well, it isn't "demonstrated". If I am correct (and that is certainly subject to review:o)..... Max demonstrated Xwind in production aircraft has to meet a defined % of the Vso.....so a cessna might have a Max demonstrated Xwind which has been established as meeting the minimum spec required by regulations, but it is not limiting......a better than average pilot with a lot of experience can often better the MDXW published value for a plane.

One reason I would be reluctant to put a value in the POH that had not been tested and found true for the particular plane is liability......regulatory liability if you want to get specific. The luck of the draw might be someday, for some reason, the FAA may end up getting curious about how the data was established....where's the testing log?

By regulation, we are required to establish Vso, Vx and Vy by testing an experimental aircraft and state the weight and balance under which those values were determined and enter it in the aircraft logbook.

The POH is sort of a legal document in a way. if you don't put something in the POH that wasn't tested or required....pretty hard to find fault with it. If you put it in, you should be confident it is correct for the particular aircraft through testing procedures.

Sincerely,

Dave S
KF7 Trigear
912ULS Warp Drive

[av8rps]

I am putting together my POH for my SS7 and would like to add these numbers. What numbers have others used? Jch

I've always used 60 mph for under 625 lb empty weight, and 65 for over 625 lb ew Avid, Kitfoxes, and Highlanders.

And I know that number works well as I've experienced 3 engine failures over the years where I had to dead stick land the airplane (2 were engine failure on takeoff). Every time I made sure to maintain at least 60 mph, which is pretty much minimum needed to be able to arrest the sink rate and flare. Not any of those times did I damage any of the planes, so I know 60 plus works in real life. For a Super Sport I'd put best glide at 65 mph.

Not sure if I recall correctly on max crosswind, but I know 15 to 20 is doable in real life without any trouble, so if it were me I'd use 20 mph. If you have concerns about that number if ever selling it, then I'd put it at 15 mph.

Not scientific, just my opinon based on real life numbers experienced.

Paul Seehafer
kfv4 amphib, early Avids, and a Highlander.
2000+ hrs in these aircraft

[n85ae]

Dave -

I'm not sure your point here ...

I don't believe I made any suggestion that they were even remotely the same
from one to the next, I was merely commenting on my experience with my plane.

Regards,
Jeff


Jeff,

Each of our planes is different....

[Jch]

Thanks for your replies. The posts got me thinking. I hope to be "Phase II" eligible in about two weeks and during those first 40 hours I will be thinking "How far can I glide if I have to?" constantly. Having some idea of what to set the airspeed at is very helpful. So I appreciated someone giving me a number to use until I come up with my own more precise one. I have some gliding experience and one of the things I day dreamed about while building my SS7 was...I wonder if I could thermal? Gliders I have flown are 600-1000lbs, of course more aerodynamic, but what if you had an 800-1000ft/min updraft? and lets say I was right over the airport...could I shut the engine off and stay aloft? Fun to think about. My last plane had a Max crosswind of 17 or 18mph. Never having flown an SS7 I wondered if it would be more or less than the 3400lb plane. Maybe because it was so light it would be alot less. Maybe it would be more...I had no idea. So all of your responses were relevant.

[jiott]

For the particular SS7 I trained in in Boise (Stick & Rudder) the best glide was stated as 65 mph; and max demonstrated xwind was 18 mph. I know 18 is conservative because I saw firsthand Paul Leadabrand land it in about 25 mph xwind. The airplane is capable but the pilot may or may not be.

[Jch]

That helps!

[av8rps]

snip, snip.... I have some gliding experience and one of the things I day dreamed about while building my SS7 was...I wonder if I could thermal? Gliders I have flown are 600-1000lbs, of course more aerodynamic, but what if you had an 800-1000ft/min updraft? and lets say I was right over the airport...could I shut the engine off and stay aloft? Fun to think about..... snip

When I bought my first Avid Flyer, it was Dean Wilson's prototype. And consequently powered with a scorpion snowmobile (Cuyuna 430) engine with a home made gear reduction unit from a Ford C3 transmission (no one was using gear reductions on small aircraft, and Rotax didn't get into aircraft engines until a few years later). I was having a blast flying that little 360 lb Avid around. Then one day at Oshkosh while I was thanking Dean for designing such a great airplane, I went on to tell him about how much fun I was having with his first Avid. I'm sure out of concern for me he reminded me of how potentially unreliable that engine could be and suggested I climb it to 10,000 ft one day over an airport, shut the engine off, and glide it around for a while so I would know how it flys with the engine off (should it ever fail :eek:). And he said to be mentally prepared to land engine off if for some reason it doesn't start. So I did what he asked me to.

And of course...it didn't restart. But landing it was uneventful, and in fact I found dead sticking it was so much fun that I did it repeatedly. I actually logged my gliding time back then, and have 2.3 hrs of engine off time in an Avid Flyer. Longest glide I had was 22 minutes when at 8800 agl. Later I read up on real soaring, and then started finding thermals. Never got really good with that, but it sure was fun to get in some of those elevator like updrafts that would give me more altitude. I even glided around and landed dead stick on floats repeatedly (even have video somewhere). I also have glided my 800lb Kitfox 4 amphib and that too is fun. In fact, I think the Fox glides better than the Avid did, probably mostly due to the cleaner Riblett airfoil vs the early undercambered Wilson airfoil.

So, with all that said, I think it is safe to say you can attain your dream with your SS7. I think it will make one heck of a fun motorglider. BUT...just be mentally prepared to land with the engine off if it doesn't restart ;)

[n85ae]

Okay this is getting off-topic, but the discussion is a good one

If you aren't obsessed with turning the motor off, running at a very low power
setting easily simulates a glider (i.e. 70 mph 2-300 fpm descent rate). This
burns little fuel, and challenges you to fly efficiently and find lift. Then when
you have dropped down enough you just gently ease the power back in and
climb back up. Thermal flying a truly engine out Fox is not going to work very
well unless you have some of them really dark concave bottomed clouds above
you ... Which reminds me of when I flew a C-152 under one out in Colorado
one day ... (that's one of my "Never Again" experiences")

Regards,
Jeff

[av8rps]

I don't think we are off topic at all, knowing how to fly your Kitfox engine off in a real glide is very pertinent to the "best glide" discussion.

Your advice about flying at idle is good, as it for sure is a more safe option. But, I will say with these gear reduced rotax engines they glide significantly better than they do with engine at idle, because the prop stops. No windmilling braking effect like most other engines have.

So, to all those that are practicing emergency engine outs with a gear reduced engine just remember in a real engine out you will most likely glide further than when in practice. You don't want to overshoot :)

Of course, if you are all practiced up on slips, that won't be an issue in a Kitfox.

[n85ae]

That's still not quite what I meant. I have flown sailplanes a few times, and typically
they glide along in about a 2-300fpm descent, unless you find lift. Lacking
wings and decent aerodynamics the Fox can't do that with the power off.
BUT you can simulate
a glider by flying at a power setting that simulates a glider. In
my plane this is a notch of flaperons and about 1500-1700 rpm.
That gives me a nice mellow 65-70'ish 200-300 fpm descent which is very
much like for example a Blanik.

So what is the point? Well lacking a sailplane to fly I do it as a personal
challenge to see how well I can do at finding and flying in lift, and more
or less it's a way to fly cheaply without shooting along from point A to B
burning fuel for no reason. My fuel consumption is around 3gph with the
IO-240B doing this. So I can literally fly twice as long on the same fuel
I would burn by going places.

I started doing it a couple years ago, and now it's my way of enjoying
flying without doing a billion takeoff's and landings, or going no place
with no purpose. Basically it's just a fun activity in the plane.

Another thing I do, I fly almost always with the GPS turned off, and I just
use a map. I think it makes you a better pilot when the moving map display
is what you see out the window.

Regards,
Jeff


I don't think we are off topic at all, knowing how to fly your Kitfox engine off in a real glide is very pertinent to the "best glide" discussion.

Your advice about flying at idle is good, as it for sure is a more safe option. But, I will say with these gear reduced rotax engines they glide significantly better than they do with engine at idle, because the prop stops. No windmilling braking effect like most other engines have.

So, to all those that are practicing emergency engine outs with a gear reduced engine just remember in a real engine out you will most likely glide further than when in practice. You don't want to overshoot :)

Of course, if you are all practiced up on slips, that won't be an issue in a Kitfox.