Windmilling Propellers

HalfaDave Mon Apr 10, 2023 3:01 am

Hi All,
I got a school yard flight today on my Dad's electric 24in. span 6oz Baby Buzzard Bombshell. Smile

(sorry, no pictures yet, think of a long nose electro-turbo Buzzard)
The sunny thermals, at 5C were way stronger, than expected and down elevator was needed... Smile

( maybee 200ft up, 6oz goes way up very quickly... Smile

)
All the Cox engines I have run,
The props stop. I can glide down.
Idling, was never an issue.
The propellers stopped.
The stopped electric motors windmill and create huge amounts of drag.
To the point, I loose control of rudder/elevator. (not fun) Shocked

So,
I bring a 15min timer, and land before I 'run out of electric idle', if you know what I mean.
And miss +1hr thermal flights...
Any advice is appreciated.
With Respect,
Dave
P.S. I have scoped out a dozen urban small fields around here. My only problem has been unleashed dogs.
Everyone else, likes seeing a model airplane fly...

getback Mon Apr 10, 2023 7:19 am

Are folding props an option for less drag ? >> https://www.amazon.com/s?k=rc+folding+propellers&crid=1RDIPR6A9WH05&sprefix=folding+propellers%2Caps%2C89&ref=nb_sb_ss_ts-doa-p_2_18

andrew Mon Apr 10, 2023 7:47 am

Most ESC's are equipped with a "brake" function, however, this is usually turned off by default. Check your ESC setup guide to enable the function and how to set the necessary parameters.

Folding props are another option, but occasionally will need to work in conjunction with slowing or stopping the motor to get the prop to fold.

HalfaDave Mon Apr 10, 2023 8:15 am

Thanks getback and Andrew,
Older ESCs without instructions or markings to know what they are,
Have tried, do not think they have the brake function.
One is .020 size, other babybee.049 power.
Am thinking fuel tube hitting the TE of the prop,
Like making noise with hockey cards on bicycle wheel...
Just enough to stop the prop.
Still thinking,
Dave

GallopingGhostler Mon Apr 10, 2023 10:30 am

HalfaDave wrote:The stopped electric motors windmill and create huge amounts of drag. To the point, I loose control of rudder/elevator. (not fun)

Prop is most efficient when turning faster than the air. It's airfoil is properly shaped to create lift (thrust) in that mode. Windmilling it creates more drag, so yup, you are correct, Dave.

The rubber powered free flights had that problem. To overcome, there were braking mechanisms as far as back in the 1940's, that once rubber unwound, would by spring tension engage a pin and cog on the back of the bulkhead, stop the turning. Then blades would fold, further streamlining the aircraft. Some of the smaller models just let the propeller freely windmill, which I imagine could also act as a crude dethermalizer.

Sounds like you are using slower turning, larger diameter props on your planes. Like others have mentioned, a folding style prop, although more costly, would feather agains the fuselage and allow a good dead stick landing. Or, go to higher RPM electric motor and a smaller Cox sized prop, no? But then, wouldn't shortened battery life occur due to higher amperage? (Asking because so far, haven't done electric flight.)

HalfaDave Mon Apr 10, 2023 4:47 pm

Hi gg,

Rubber power was very Cool Cool

here.
Mankind was going to the Moon.
Cox engines showed up.
Moon? What Moon?
All the kids here were enjoying outsides, and having fun.
Going from rubber to a Cox engine was amazing...
We flew Cox.049s, 4hrs after we saw Niel put his foot down.
We all looked up...
I will solve my electric power problems,
When I grease up my slide rule,
Dave

https://willynillies.com/

sosam117 Mon Apr 10, 2023 8:03 pm

I could help you out if you can give me more information?

O.K. I know you have a Baby Buzzard Bombshell that is 24" wingspan and weights 6oz.
What Lithium polymer battery pack that you are using, is it a 2 cell 7.4volt pack and a capacity of 350mah?
Next is the size of the brushless motor. Is there any information you can get from/off the motor?
Now the prop size? Is it a 4 inch prop with a 3 inch pitch (4x3) it shoud have those number on the prop.

O.K.
How does it fly?
At full throttle, does the Baby Buzzard want to climb at a 45 degree angle (and you might have to hold some down elevator)?
If it does, you might want to look for a smaller prop, so at full throttle it should climb at about a 30 degree angle (with no down elevator.)

Another reason for going to a smaller prop is that a smaller prop will be less drag (when spinning) that a larger prop.
Another plus with a smaller prop is that the amperage draw will be lower so that your flight time will be longer.

I have a Baby Buzzard Bombshell (36 inch wing span) that is built from an original 4K models kit.
It has a 2 cell 450mah lipo pack, Hobby King 10amp brushless controller (programed with brake "on")
Hacker A10-15S outrunner with a 4inch diameter Gemfan prop with a pitch of 2 (4x2)
And it folds: ** click on the link below **
4x2 Gemfan Folding prop

Below are photos of the Baby Buzzard for it's first flight of the season.
Ready to fly weight is 8.0 oz
See it climb at about a 30 degree angle at full throttle.
After it gets to a fair enough height, I'll throttle it back to about 1/2 throttle or shut the motor off altogether and glide around.

Member of SAM
President of the Chicagoland Buzzards chapter 117

HalfaDave Tue Apr 11, 2023 5:38 am

Thanks sosam117,
Beautiful Buzzard !
Dad scratch built this 24in span one ~2000 as far as we can remember. (he is 95 now)
A longer nose to get the battery fwd.
2C 800mah pack, 7/3.5 prop. Berg4ch rx.
No info on the ESC or 3/8th'' dia brushless motor.
Flies great. Easy 30deg climbs. 10 seconds to 200ft. Cruises at 1/8th throttle.
If I shut the motor off it windmills, I loose both rudder and elevator control and it dives -45deg...
My usual routine is set a 20min timer, use the throttle trim to get the motor on 'low idle', then launch.
Fun to fly, reacts to the slightest lift. Takes a tight spiral to get out of good lift... Very Happy

Then the timer goes off. Awww!, just when I'm having fun...
I should not complain.
Am curious how it would glide with the prop stopped.
In my 'CoxEngine' thinking, I am going to try a sliver of silicone fuel tube to touch the TE of the prop...

Hope your SAM flying season goes great....
Dad built a .40 size R/E/T BB in the 70s. 1hr flights on 2oz fuel.
Buzzard Bombshells are fun to fly...
Take care,
Have fun,
Dave

sosam117 Tue Apr 11, 2023 7:06 am

HalfaDave wrote:Thanks sosam117,
Beautiful Buzzard !
Dad scratch built this 24in span one ~2000 as far as we can remember. (he is 95 now)
A longer nose to get the battery fwd.
2C 800mah pack, 7/3.5 prop. Berg4ch rx.
No info on the ESC or 3/8th'' dia brushless motor.
Flies great. Easy 30deg climbs. 10 seconds to 200ft. Cruises at 1/8th throttle.
If I shut the motor off it windmills, I loose both rudder and elevator control and it dives -45deg...
My usual routine is set a 20min timer, use the throttle trim to get the motor on 'low idle', then launch.
Fun to fly, reacts to the slightest lift. Takes a tight spiral to get out of good lift...
Then the timer goes off. Awww!, just when I'm having fun...
I should not complain.
Am curious how it would glide with the prop stopped.
In my 'CoxEngine' thinking, I am going to try a sliver of silicone fuel tube to touch the TE of the prop...

Hope your SAM flying season goes great....
Dad built a .40 size R/E/T BB in the 70s. 1hr flights on 2oz fuel.
Buzzard Bombshells are fun to fly...
Take care,
Have fun,
Dave

Dave,
you might want to get and use a smaller prop.
That 7x3.5 prop is just too big and with it windmilling, I can see why you have a problem with the glide.

I would suggest that you try a smaller prop like a HQ 4x4.5 or a HQ 5x3 propellers.
Click on the links below:
HQ 4x4.5 prop
HQ 5x3 prop

That 7x3.5 prop I use on a much larger size Buzzard Bombshell with a wingspan of 46 inches and a wing area of 355sq.inches.
The motor is an old Graupner Speed 400 brushed motor direct drive and that prop doesn't fold and I get a good glide on that bigger Buzzard.
46" wingspan Buzzard Bombshell

You are flying a plane that is 1/2 that size on such a big 7x3.5 prop.
Reducing your prop size will reduce your prop drag because of the windmilling.
I'm guessing that the 800mah pack is being used for nose weight?
If it is not you can go to a pack that is 400mah to reduce the overall weight of the plane and then you can even go to a smaller prop as the plane weigh will be reduced?

Dave,
I have two planes just about like yours.
One with the "gull" wing is call a Spook and the other is an English old-timer design call a Tomboy.
Both have a wingspan of 24 inches and the ready to fly weight is a mere 4 oz.
So, they are either good for flying indoors or very early or late outdoors with a calm wind.

The Spook:

The Tomboy:

Now the detailed information:
Both planes have a small parkzone (PKZ3624) motor and gearbox: UM P-51
The servos, receiver and speed controller (without brake) is a Parkzone "brick" radio for Spektrum radio.
The battery is a one cell 180mah lipo.
Last is the prop which is a 5x3 prop from parkzone.
The plane flies for about 15~20 minutes depending on the how much throttle I use and how windy (over 3mph) the wind is?
The dummy engines are there for "nose" weight as I have round lead solder inside the dummy engines to balance the planes.

When the motor stops, the glide isn't like a sailplane but the planes do have a fairly good glide maybe a 5:1 glide ratio?
5 feet forward to 1 foot drop.

So, before you try using that surgical tubing idea try a smaller prop please?
Even with that stopped prop, the size of those blades will still give you a lot of drag.

rdw777 Tue Apr 11, 2023 1:55 pm

I think you have been given good advice Dave for a smaller prop or even a folder if you can source one…. If you went with a folder you could keep the larger diameter for efficiency in climb…. Nice you are able to fly your Dad’s plane and I hope he’s still involved….. My Dad is 86 and still tending his horses and goats….

Those are beautiful, Well built models sosam…. I’m sure they are pleasant to fly…. Thanks for sharing!!!

cmulder Tue Apr 11, 2023 2:04 pm

HalfaDave wrote:"I loose both rudder and elevator control and it dives -45deg...

have you still have working servo's once the motor stops running?
Also the use of a "'berg" reciever might imply that the esc could be a castle creations "phoenix" series.
Castle used to sell the berg recievers so it would be logical also buy the esc from them.

If you can post a close up picture then we can see if it looks like a phoenix and then we can guide you trough setting the brake function.

Also regarding the prop; choose a version that has the blades fold to the rear; the gemfan and dal "fold" prop does NOT fold to the back.
They are designed to fold to the side to make storing and transporting "quads" easier but do NOT help in making a plane glide better.
For example apc has a series of props especially for this purpose.
choose a "hub" that matches any spinner you use(the blade hinge point should be outside the spinner)
And then choose the blades based on the rpm and power of the motor.

My personal preference are the formely "Graupner" "cam" prop series and the also German "Aero-naut" folding props.

HalfaDave Wed Apr 12, 2023 7:08 am

Thanks sosam,
I found a 5-3 that fit. Will report when I try it. Springs are usually windy here.
Going to do a timed bench run at 1/3 throttle, see how much juice I have available...
Nice Spook and Tomboy ! Love the variety of designs of the era...
Have a box of Dad's various old GWS geared brushed/ nicad rigs to play with one day. Vintage electric ?

rdw, Dad likes having projects to do. Latest is going through the garage/workshop finding stuff to take to the scrap/recycle place.
Changing the old ballast/neon lights to Leds is going to be fun ! One box had old bent wire landing gears. I counted 30 of them, from various planes over the decades. With luck, the instructions for the esc/motor will show up ! Smile

cmulder, The servos work with the motor shut off. I have taped the prop still, given it healthy hand launches, good control.
Windmilling prop is the problem.
I got several (I like them) Berg rxs from a friend switching to 2.4 (when 2.4 was 'new')
Dad got the batt/esc/motor/prop from the hobby shop. I figured it was a 'matched' set.
Am probably just overpowered for a 24" Buzzard Bombshell. (with full downtrim, I can chase seagulls at full power! Laughing

)
At 1/8th power it is a joy to fly.
Not looking to buy any folding props/brake ESCs.... (mabee another battery or two!)
Just want the prop to stop.

Thanks fellow CEFers, for the help. Cool

I was going to go on an electric forum and ask, "my motor lacks compression?" Laughing

You guys understand. Smile

I'm thinking the new 400ft alt limit here will make Cox engines cool again. And S.M.A.L.L. planes.
I'll bring my RadioShack Db meter...
Those electric duckted(pun) fans are not quiet !
Take care,
Have fun,
Dave

P.S. I asked Dad why he likes Buzzard Bombshells. He likes the name, and they all flew great. Cool

sosam117 Wed Apr 12, 2023 3:50 pm

HalfaDave wrote:Thanks sosam,
I found a 5-3 that fit. Will report when I try it. Springs are usually windy here.
Going to do a timed bench run at 1/3 throttle, see how much juice I have available...
Nice Spook and Tomboy ! Love the variety of designs of the era...
Have a box of Dad's various old GWS geared brushed/ nicad rigs to play with one day. Vintage electric ?

rdw, Dad likes having projects to do. Latest is going through the garage/workshop finding stuff to take to the scrap/recycle place.
Changing the old ballast/neon lights to Leds is going to be fun ! One box had old bent wire landing gears. I counted 30 of them, from various planes over the decades. With luck, the instructions for the esc/motor will show up !

cmulder, The servos work with the motor shut off. I have taped the prop still, given it healthy hand launches, good control.
Windmilling prop is the problem.
I got several (I like them) Berg rxs from a friend switching to 2.4 (when 2.4 was 'new')
Dad got the batt/esc/motor/prop from the hobby shop. I figured it was a 'matched' set.
Am probably just overpowered for a 24" Buzzard Bombshell. (with full downtrim, I can chase seagulls at full power! )
At 1/8th power it is a joy to fly.
Not looking to buy any folding props/brake ESCs.... (mabee another battery or two!)
Just want the prop to stop.

Thanks fellow CEFers, for the help.
I was going to go on an electric forum and ask, "my motor lacks compression?"
You guys understand.

I'm thinking the new 400ft alt limit here will make Cox engines cool again. And S.M.A.L.L. planes.
I'll bring my RadioShack Db meter...
Those electric duckted(pun) fans are not quiet !
Take care,
Have fun,
Dave

P.S. I asked Dad why he likes Buzzard Bombshells. He likes the name, and they all flew great.

The one problem I have with my Buzzard Bombshell when I used a folder is that front wooden pin that the rubber bands go over.
If the folding prop is too long the blade got caught under the wooden dowel (wing hold down).
the other problem was when I started the motor back up the blade would also sometime catch under the dowel before it flipped out from being folded.
Just didn't want to take a chance of overloading my ESC doing that.
My receiver gets it power going through the speed controller (BEC) and if that goes, my receiver has no power.

HalfaDave Wed Apr 12, 2023 11:27 pm

Hi sosam,
I try for simple.
My fear is letting the 'magic smoke' out of this(these) electric powered planes.
Have you tried a sliver of fuel tube to stop the prop? Smile

I much prefer a half baked Cox.049 with fresh fuel and good glow.
That, I am comfortable with.

The electric stuff is to get the Neighbours used to me flying safely around here.
When I fire up a Cox engine,
Kids will like it, Karen's cannot complain.
Cox control line demos at High School Football half time will be cool again...
Marketing people like noise...
A Cox engine is perfect...

Take care,
Have fun,
Dave

sosam117 Thu Apr 13, 2023 7:49 am

HalfaDave wrote:Hi sosam,
I try for simple.
My fear is letting the 'magic smoke' out of this(these) electric powered planes.
Have you tried a sliver of fuel tube to stop the prop?

I much prefer a half baked Cox.049 with fresh fuel and good glow.
That, I am comfortable with.

The electric stuff is to get the Neighbours used to me flying safely around here.
When I fire up a Cox engine,
Kids will like it, Karen's cannot complain.
Cox control line demos at High School Football half time will be cool again...
Marketing people like noise...
A Cox engine is perfect...

Take care,
Have fun,
Dave

Problem with the small piece of fuel tubing tapping the bac of the prop is you have to get it just right.
Too much and you'll increase the amp draw because of the resistance to flip past the tubing.
Too little and it may not stop the prop.

I have also tried having a separate servo insert a piece of servo rod (plastic) into the spinning prop near the hub ( closest to the center of the prop -- next to the motor shaft.
How it worked was this:
Using the "gear" switch on the transmitter -- have it clear the prop hub when the switch was up (like when you landing gear was up) Now turn the motor on and fly until the batteries are discharger.
Then flip the switch to the down position (landing gear down position)
When in the down position the nyrod (plastic servo rod) would extend out and into the hub section of the spinning prop and stop it from spinning.

If you turn the motor on and off, you have to remember to retract/extend the nylon servo rod.
I have a computer radio that I have set-up and programed to do it for me so that I now don't have to remember to extend/retract the rod. I set it up in the program to extend and retract at about 10% on the throttle throw when the throttle is in the down (off) position.
The prop size for this is 16x12 carbon prop folder.
I tried the brake and the problem was the break would stop and fold the prop.
Then the blade hanging down would catch some air and start to spin the prop to where it was spinning 1/2 folded.
When there was enough of the motor producing some electric feed bac to the ESC, the brake would stop the prop.
Remember, the electric brushless motor becomes a generator when it is spinning, and the ESC senses the feedback and that how/why it activates the brake.
So, that is how I stop my very large prop on my 1800sq. in old timer plane.

getback Fri Apr 14, 2023 7:44 am

That's interesting to me since i don't know squat about the electric motor set up , what my plan will bee is a .049 bee engine on a what looks like 5' WS glider , I had thought .020 or .010 TD engine but I am not sure it would bee enough to pull it up .

GallopingGhostler Fri Apr 14, 2023 9:17 am

getback wrote:That's interesting to me since i don't know squat about the electric motor set up , what my plan will bee is a .049 bee engine on a what looks like 5' WS glider , I had thought .020 or .010 TD engine but I am not sure it would bee enough to pull it up .

The 48" (1220 mm) HOB Nomad R/O was about the limit to the diminuative .020 Tee Dee, IMO. I made the mistake of covering it in Monokote, too heavy a film for it. (Should have used lightweight silkspan or silk with sufficient clear dope to fill weave. 37 years ago, they did not have lightweight plastic film.) Never could get it to fly right.

Perhaps a Golden Bee or Babe Bee, Sure Start? You can always change props to adjust thrust.

HalfaDave Fri Apr 14, 2023 2:26 pm

Success !
Sunrise flight confirmed a 5-3 prop is way less drag than a 7-3 windmilling...
I still have control. ( and a needed nice -5deg 'dethermalizer' effect. Smile

)
Thanks so much sosam ! Cool

When I do a ground 'electic juice' left test, perhaps I can set my timer to +30 min. Smile

More flights this weekend...(weather window)
I'll try and take photos, and learn how to post them...
Take care,
Have fun,
Dave

sosam117 Fri Apr 14, 2023 4:30 pm

getback wrote:That's interesting to me since i don't know squat about the electric motor set up , what my plan will bee is a .049 bee engine on a what looks like 5' WS glider , I had thought .020 or .010 TD engine but I am not sure it would bee enough to pull it up .

A 5 foot wing span (1.5meter span), you would be better off with a .049 or .050/.051.
The .010 ---- NO WAY!
The .020 ---- Will really struggle to get it to climb, unless you build it 10oz or less?

My Amigo II 2.0 meter plane climbs well with a Cox Golden Bee.
Look on youtube for Amigo II with a Cox glow engine and you'll find one with a ,049 engine.

sosam117 Fri Apr 14, 2023 4:43 pm

HalfaDave wrote:Success !
Sunrise flight confirmed a 5-3 prop is way less drag than a 7-3 windmilling...
I still have control. ( and a needed nice -5deg 'dethermalizer' effect. )
Thanks so much sosam !
When I do a ground 'electic juice' left test, perhaps I can set my timer to +30 min.
More flights this weekend...(weather window)
I'll try and take photos, and learn how to post them...
Take care,
Have fun,
Dave

Glad to help out.
You could go down to a 4" prop with then a little more pitch --- say a 3.5 or 4
Just remember you go down one in diameter ~~ go up one in pitch.
You might be able to find a 4x4 prop
One other plus using the higher pitch.
The higher pitch will also reduce the drag (a very little bit) because it is almost like feathering your prop when you turn the power off.

Here is a place where you can get the 4x4 prop:
Click on the link below and it will take you to Hacker's website where they have GWS props and the 4x4 you might want to get?
Hacker / GWS props

Happy Landings! Flying

HalfaDave Fri Apr 14, 2023 5:27 pm

Hi sosam,
I am charging while typing this...
Perfect evening for sunset thermals...
Rare calm almost here, taking advantage of it.
I have a big ass camera,
I'll do my best, can you get Super 8 converted to video? Smile

Later,
Dave

HalfaDave Fri Apr 14, 2023 7:17 pm

Hi All,
I am back...perfect weather...
No cameras, beautiful evening.
Met many 'Niebours', dogs and kids.
They all like it.
No problem firing up a Cox engine here I think...
Will take a few more recharges...
But it will work,
No doubt the kids like noisy engines...
They like it,
More exciting than recharging stuff.
And getting outside,
Is more fun than the internet...
Take care,
Have fun,
Dave

HalfaDave Sat Apr 15, 2023 12:41 pm

Update,
Perfect weather here.
3rd recharge so far...
I get some yard work done while it recharges... Smile

Best yet,
A family walks by, the kids like it. I let them try the stick to steer it around.
Their Rotwieleirish dog gets excited.
I brought the Buzzard down low. They unleashed 'Roxy' ....Wow it was fun!
Dogs can jump high ! Total fun. Workout for me and the dog!
Too much fun to think about videos.
Zero problems asking people if I can fly a 'noisy' Cox engine here.
All would welcome it.
Battery is charged,
I am going out again,
To find a 'Karen' complainer,
And let her kids,
Try flying a Buzzard Bombshell.
Oh yeah,
You get greasy flying electric...
It is called 'sunscreen'... Smile

Later,
Dave

sosam117 Sat Apr 15, 2023 2:04 pm

HalfaDave wrote:Update,
Perfect weather here.
3rd recharge so far...
I get some yard work done while it recharges...
Best yet,
A family walks by, the kids like it. I let them try the stick to steer it around.
Their Rotwieleirish dog gets excited.
I brought the Buzzard down low. They unleashed 'Roxy' ....Wow it was fun!
Dogs can jump high ! Total fun. Workout for me and the dog!
Too much fun to think about videos.
Zero problems asking people if I can fly a 'noisy' Cox engine here.
All would welcome it.
Battery is charged,
I am going out again,
To find a 'Karen' complainer,
And let her kids,
Try flying a Buzzard Bombshell.
Oh yeah,
You get greasy flying electric...
It is called 'sunscreen'...
Later,
Dave

Fun to bring back a little fun in an airplane your dad built! Old Bugger

HalfaDave Fri Apr 21, 2023 7:31 pm

Hi sosam, (and All)
It is awesome flying my 95yr old Dad's planes.
(we are a tag team taking care of Mum with dementia)
Next up is a nice Peter Rake L19 BirdDog he built that just needs electric power figured out...
I have found several local fields,
No problems flying in.
Next step,
Firing up a Cox.049...
I doubt many people have not heard one.
Most will like it...
They will ask me where,
They can get one....
Take care,
Have fun,
Dave

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