Parkzone Ka-8 with Folding Prop - RC Groups
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Oct 17, 2017, 09:38 AM
rigibahn
Discussion

Parkzone Ka-8 with Folding Prop


Hi folks,
Just got two Park zone Ka-8 before they completely disappear form the market. One of the two i will use as a slope glider and the second one i will convert to a motor glider that i can use on our flying field.

First idea was to use a folding prop that has a nosecone that matches the shape of the fuselage. My thought was to use just the very tip of the fuselage where the shape is still pretty symmetrical or round. measuring all items and creating a CAD drawing it was obvious that this will not work out. Any round nosecone will not match up with the odd shaped fuselage. (see drawing below)

Looking throe the internet i could find just one other KA-8 with prop. In this case the prop was mounted without any nose cone. (See Pic below with yellow Ka-8)

Both solutions do not look that great, so I'm fishing for other solutions. If you made a similar conversion pleas ad pictures to this post
PJ
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Oct 17, 2017, 01:09 PM
B for Bruce
BMatthews's Avatar
Either way would work fine. But if you don't mind the extra work of building that small spinner to hide part of the folder's hub I think it looks great.

If you're worried about drag I'd suggest that the difference between what you drew and what you show in that picture amounts to no more than spitting into a rain storm. Either option is minimizing the drag by folding the blades. But the blades will produce more drag by far just by being there and folded compared to the hub treatment. So if you want to do the slick looking mod you show then fine. Or go with the easier option shown in the picture.

One other thing that I don't see in your picture which you WILL need is some amount of right and downthrust. That alone is going to mess up your neatly planned plot of flowing with the shapes since once you angle the motor and cut line it WILL look a little odd. Possibly less odd than what is shown in the picture.
Oct 17, 2017, 06:23 PM
Mesa AZ, it's a dry heat!

Ka8E


This is an interesting idea. I have a Ka8 which I have only flown off the slope at Eagle Butte in WA. It flew very well.
I am not sure if the weight of the model is conducive to good thermal performance.
Have you done any power calculations?

The motor you show has a high Kv, and you have a small diameter low pitch prop, and with a large bulbous fuselage the prop may not produce enough thrust to make it fly.
I consider 120W per pound to be minimum on a fairly high drag model and a thrust to weight ratio of about .75. Less may work, but I would prefer to have too much, at least to start with.

I will follow your progress with interest.

ESPRIT MODELS HAS THE SMALL YOKE. I HAVE ONE ON A SCALE DISCUS.

Iain
Oct 17, 2017, 09:38 PM
B for Bruce
BMatthews's Avatar
I dunno.... The nose is quite streamlined. Folks that fly GeeBees with only about 1/5 of the prop out past the edge of the cowling still do fine with them. The prop doesn't need to stick out past the fuselage. It just needs a smooth area behind the prop so the air doesn't load up. And the KA8 nose is certainly that.

Lately I've been flying some rather stubby sport models that I brought DOWN to just 65'ish watts/lb. I wanted to fly them in a more scale like manner and simply don't need a lot of power to do that. And even at that they still lift off at just a bit over half throttle and at full power they climb at around 45 to 50° in a very un-scale like manner given the designs. One is an E-Flite PT19 and the other an older Pilot ARF Stinson Voyager. Both are using 9 inch props. Needless to say neither one is as low drag a design as a sailplane style model. But the point is that we can still have a good time at less than 100W/lb if that is our thing.

So I'm thinking that if PJ can shift to using an 8" prop and go for a motor with just a little more power he'd likely climb at a reasonable rate. Just not a rocket like climb. Perhaps look at 75 to 80 watts/lb to hedge the bets on the smaller 8" prop? But even at 65 W/lb and an 8" prop he could expect a good solid 30 to 35° climb angle. But then he might find it takes a little over a minute to reach thermal hunting altitude.

Now, 28 oz is 1.75 lbs and at even 80 watt/lb that's only 140 watts total needed to fly in such a manner. The trick will be finding a smaller motor that has the wattage tolerance and Kv value to allow that power level on an 8x4 folding blade prop. On the other hand a pack and motor for this sort of power level would not be very heavy. So it should be practical to keep the weight for an electric version down to around 30 oz. And that assumes that the motor won't replace any built in nose weight. If that's the case it may come in dead on 28.

On the other hand the reviews I found from looking up what the Ka8 flies like to get an idea of the wing loading appear to make the model sound less than stellar. Lots of assembly issues and odd ways of doing things that result in a model that is difficult, or at least tricky, to set up and which might well prove to be quite damage prone. Also the way I saw the wings flexing like a wet noodle during an aerotow event gone bad indicates that this is a "no fast passes and no hi G maneuvers" sort of model.
Oct 18, 2017, 12:31 PM
rigibahn
Hi iain
If you go by the book you might be right with that prop size. however be aware that the diameter is more then 7.5 since i use a large alu bridge to mount the blades. I have the identical setup on my Multiplex easy star. It works great on that larger plane and it does not matter since i do not like to win any speed races. This prop and motor combination gives my easy star a nice climbing rate and that is what i care most fore.
By the way any larger prop would most probably destroy the glass of the canine.
regards PJ



Quote:
Originally Posted by rev.iain
This is an interesting idea. I have a Ka8 which I have only flown off the slope at Eagle Butte in WA. It flew very well.
I am not sure if the weight of the model is conducive to good thermal performance.
Have you done any power calculations?

The motor you show has a high Kv, and you have a small diameter low pitch prop, and with a large bulbous fuselage the prop may not produce enough thrust to make it fly.
I consider 120W per pound to be minimum on a fairly high drag model and a thrust to weight ratio of about .75. Less may work, but I would prefer to have too much, at least to start with.

I will follow your progress with interest.

ESPRIT MODELS HAS THE SMALL YOKE. I HAVE ONE ON A SCALE DISCUS.

Iain
Oct 18, 2017, 01:34 PM
B for Bruce
BMatthews's Avatar
Took me a few puzzled seconds to realise that autocorrect put in "glass of the canine" instead of "glass of the canopy"....
Oct 18, 2017, 10:33 PM
rigibahn
Mathew
The 2208/8 Motor has 260Watt wit a 3s 11.1v and 30a ESC, And even with that smaller prop i climb steady 35 Deg with my comparable Easy-star. The Ka-8 might even climb in a steeper angle since the weight is just around 30oz. By the way the motor specs call for a 7x3" or 6x4" Prop. If you go higher in prop size you might end up burning to much power for no reason taking away some of your flight time.
I used to distrust any motor specs and therefore i build a test stand where i measure Watt, RPM, temperature and Trust. So far i measured this way about 20 motors and astonishingly the specs aint that far off. My rule of thumb, thrust equal with model weight and you have for sure no lame duck.

The Ka-8 is a scale slope glider, the idea is not to have a racer.
I have a hard time understanding all the complains to how hard it is to take apart the main wing. One clip need to be released on the servo control horn, how bad is that really. Since i have a 4door Jeep i do not bother taking it a part every time i go fly. With the 2.25meter wingspan this plane fits even in my Fiat 500 that in one piece.

PJPJ



Quote:
Originally Posted by BMatthews
I dunno.... The nose is quite streamlined. Folks that fly GeeBees with only about 1/5 of the prop out past the edge of the cowling still do fine with them. The prop doesn't need to stick out past the fuselage. It just needs a smooth area behind the prop so the air doesn't load up. And the KA8 nose is certainly that.

Lately I've been flying some rather stubby sport models that I brought DOWN to just 65'ish watts/lb. I wanted to fly them in a more scale like manner and simply don't need a lot of power to do that. And even at that they still lift off at just a bit over half throttle and at full power they climb at around 45 to 50° in a very un-scale like manner given the designs. One is an E-Flite PT19 and the other an older Pilot ARF Stinson Voyager. Both are using 9 inch props. Needless to say neither one is as low drag a design as a sailplane style model. But the point is that we can still have a good time at less than 100W/lb if that is our thing.

So I'm thinking that if PJ can shift to using an 8" prop and go for a motor with just a little more power he'd likely climb at a reasonable rate. Just not a rocket like climb. Perhaps look at 75 to 80 watts/lb to hedge the bets on the smaller 8" prop? But even at 65 W/lb and an 8" prop he could expect a good solid 30 to 35° climb angle. But then he might find it takes a little over a minute to reach thermal hunting altitude.

Now, 28 oz is 1.75 lbs and at even 80 watt/lb that's only 140 watts total needed to fly in such a manner. The trick will be finding a smaller motor that has the wattage tolerance and Kv value to allow that power level on an 8x4 folding blade prop. On the other hand a pack and motor for this sort of power level would not be very heavy. So it should be practical to keep the weight for an electric version down to around 30 oz. And that assumes that the motor won't replace any built in nose weight. If that's the case it may come in dead on 28.

On the other hand the reviews I found from looking up what the Ka8 flies like to get an idea of the wing loading appear to make the model sound less than stellar. Lots of assembly issues and odd ways of doing things that result in a model that is difficult, or at least tricky, to set up and which might well prove to be quite damage prone. Also the way I saw the wings flexing like a wet noodle during an aerotow event gone bad indicates that this is a "no fast passes and no hi G maneuvers" sort of model.
Last edited by PJ PJ PJ; Oct 18, 2017 at 11:07 PM.
Oct 18, 2017, 11:20 PM
Person of interest
KiwiKid's Avatar
Hi PJ, I hope you have success with the project. I have had good luck recently powering up a HK Hall Cherokee and a Habicht. The power option has given both models far more versatility and has had no noticeable effect on their slope soaring performance. I built the Cherokee set up with a yoke prop and the Habicht with a spinner.
Here's a vid of the Cherokee in park flying mode.

Hall Cherokee (2 min 17 sec)
Oct 18, 2017, 11:48 PM
B for Bruce
BMatthews's Avatar
PJ, from your last post it sounds like you have it all well in hand and have done your research. I foresee a good time with the Ka8 for you.

Ya know... if you just make it with the shaft sticking out for now but make the motor on a mount that allows for a future modification to do the spinner idea you would get into the air sooner and could work out any down and right thrust needs more easily. Then with that all in hand when you have some spare time convert to the spinner idea to clean up the nose cosmetically.
Oct 19, 2017, 09:42 AM
rigibahn
Hi kiwikid,
That is what I'm looking fore some ideas pictures of conversions. the video looks great, it is so refreshing to see something different then the usual slim sleek gliders. The Cherokee fits my taste it is right in the line with the Ka-8 or the new Hacker Habicht, or the MOA, or the Pilatus B4. As you can see on my pic the Cherokee is already on my my bench for a future project. Therefore i enjoyed your video with the Cherokee in particular.

In a few month we will move to our new home on top of a hill. Then i will have a place where i can slope soaring on 3 sides of a hill. However the slopes around are not cleared of shrub and i need to start and land from our street. So it must have a motor with folding prop. I liked your comment about no negative influence while soaring.
PJ


Sorry if my English is not perfect, i learned this language when i was forty years old and even i live now in the US i never managed to switch completely.
Oct 19, 2017, 10:01 AM
rigibahn
Matthew
I'm retired and all i have is a great time, or with other words just time for my hobbies. If I'm lucky i got another 10 years where my eyes allow me to fly planes. So lately i really went full speed ahead. I think that in the moment i have sixty RC planes ready to fly. I drive my wife nuts with it, she teases me now and then because our garages getting really crowded. Well maybe she is right, i will ad a few pics and you can be the judge of that.

By the way, i fly Rc planes for 45 years, so i think I'm not quite a novice.

PJ


Quote:
Originally Posted by BMatthews
PJ, from your last post it sounds like you have it all well in hand and have done your research. I foresee a good time with the Ka8 for you.

Ya know... if you just make it with the shaft sticking out for now but make the motor on a mount that allows for a future modification to do the spinner idea you would get into the air sooner and could work out any down and right thrust needs more easily. Then with that all in hand when you have some spare time convert to the spinner idea to clean up the nose cosmetically.
Last edited by PJ PJ PJ; Oct 19, 2017 at 10:07 AM.
Oct 19, 2017, 02:14 PM
B for Bruce
BMatthews's Avatar
You should have painted the garage walls before you loaded up with airplanes....

Quote:
....By the way, i fly Rc planes for 45 years, so i think I'm not quite a novice.
That's the problem with doing this stuff over the internet. It's tough to see who we are replying to or know their crafting abilities.

I too normally prefer to build then fly my own models. And other than old timer free flights I also prefer to design my own where I can. So I had to go to a couple of videos to see what the Ka8 flies like to see if my reply was going to make sense. A Flight Test channel video is the one where the guys were going on about how "tough" the model is to set up and work the wing. So that was what I passed on. But perhaps they were seeing it through the eyes of a typical short timer in the hobby. We tend to learn a few tricks after all those years of building and flying, eh?

Anyhow welcome to retirement. Like you I don't know how I ever found time to go to work! ! ! I'm 8 years in of being my own boss and I'm loving every moment. Built my own dream workshop for models, wood, bicycles, metal and motorcycles and now that it's all done it's like a slice of Heaven to work in the shop compared to the old "sardine can" size garage I had before.

Since we're showing off our shops here's a shot of the model area and two of the metal area taken right after the benches were done. They've never been this clean since....
Oct 19, 2017, 08:11 PM
rigibahn
Hi Matthew,
Nice shop you have there, I like all the counter tops and all the cabinets or drawers. Just recently i started with wood turning. Woodworking in a metal shop is just a bad idea. The dust settles everywhere even on my planes. Luckily I'm on my way out of this home and the new home which we are building at the moment has a even bigger garage (2350Sqft). The walls will be textured and painted this time even in the garage. And i will have a proper dust collecting system where every equipment is hooked up to it.

I was my own boss for the last 16 years. I worked from home I owned a machine shop. My specialty was micro mechanics i was working mostly for the semiconductor industries. Since i retired I sold most of the equipment and at the moment I'm just finishing up a Deckel GK-21 Engraver/Milling machine that i sold. I will keep one milling machine and a smaller lathe a surface grinder and some other smaller metal working equipment since i do make Model engines like the 7Cylinder four stroke radial engine.
Next to airplanes I'm in to mahogany runabouts, my all time favorites are Dumas boats. Like you i work on bikes i have my 230cc dual sport but here in Phoenix the streets are to straight and to crowded and it is to hot to drive any bike. Sitting on a bike here in PHX feels like sitting in front of a giant hair dryer. I have two Honda XL200 for sale, they are a part and need some engine work to be finished.

Yeah, i think i have to many hobbies and not enough time to do everything i like. The good news I'm never board unlike some other folks who are 65 and still working because they find nothing to do, no challenges that keep them busy.
PJ

Quote:
Originally Posted by BMatthews
You should have painted the garage walls before you loaded up with airplanes....



That's the problem with doing this stuff over the internet. It's tough to see who we are replying to or know their crafting abilities.

I too normally prefer to build then fly my own models. And other than old timer free flights I also prefer to design my own where I can. So I had to go to a couple of videos to see what the Ka8 flies like to see if my reply was going to make sense. A Flight Test channel video is the one where the guys were going on about how "tough" the model is to set up and work the wing. So that was what I passed on. But perhaps they were seeing it through the eyes of a typical short timer in the hobby. We tend to learn a few tricks after all those years of building and flying, eh?

Anyhow welcome to retirement. Like you I don't know how I ever found time to go to work! ! ! I'm 8 years in of being my own boss and I'm loving every moment. Built my own dream workshop for models, wood, bicycles, metal and motorcycles and now that it's all done it's like a slice of Heaven to work in the shop compared to the old "sardine can" size garage I had before.

Since we're showing off our shops here's a shot of the model area and two of the metal area taken right after the benches were done. They've never been this clean since....
Last edited by PJ PJ PJ; Oct 20, 2017 at 09:17 AM.
Oct 19, 2017, 08:34 PM
Person of interest
KiwiKid's Avatar
Very interesting stuff guys.

Love your collection BJ. I think I spied an OGAR there - they also are a really neat sloper.

SZD-45 Ogar (3 min 58 sec)


I also like vintage type gliders and have had a lot of fun with the larger Ka-8B from Phoenix (available from Tower Hobbies) - also a versatile model and makes a great club and park flyer, thermaler and sloper:

Ka-8B ridge soaring (2 min 55 sec)
Oct 19, 2017, 11:06 PM
rigibahn
Cool videos thanks for showing us. It must be great to soar on the coast. To bad it takes me 7Hrs car driving to get to the Californian coast. When i was a younger dude i went frequently with my friends from my Swiss RC club up to the Swiss alps. I guess it must be a similar feeling like flying on the coast. I remember how it was when you launch your glider over a cliff where it went down straight for several hundred yards.

Your video of the OGAR plane motivates me to maiden mine. I still have to ad on the decorative covers but other then that it is for month ready to fly.

Regards PJ


Quote:
Originally Posted by KiwiKid
Very interesting stuff guys.

Love your collection BJ. I think I spied an OGAR there - they also are a really neat sloper.

https://vimeo.com/120276110

I also like vintage type gliders and have had a lot of fun with the larger Ka-8B from Phoenix (available from Tower Hobbies) - also a versatile model and makes a great club and park flyer, thermaler and sloper:

https://vimeo.com/115836314


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