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Old Sep 11, 2007, 07:37 AM
I'm not flying backwards!
Tony65x55's Avatar
Oshawa, Canada
Joined Sep 2004
3,753 Posts
Quote:
Originally Posted by warhead_71
Here's my 48" KFm BluBaby... I blew up the 33" plans to make the most of a single sheet of FFF (actually, 1 sheet plus about 5" of another for the KFm step.)

I modified the monobloc a bit so I could cap the ends with BluCor for aesthetic reasons... and I modified the nose to accept a 1-quart oil bottle as the cowl - which turned out pretty good I think. I also built in an air vent under the cowl to allow air to vent from the bottom. All up I'm at about 28oz... but a full 6oz of that is the heavy LG - so I may need to build something a bit lighter. I think the BP21 with a 10x3.8 on 3S ought to pull it nice and slow.

My Rx is in another plane right now so I won't maiden it right away... but I can't wait to test her out.
That's a seriously spiffy looking Baby. She should fly very nicely. The cowl looks great.

Tony
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Old Sep 11, 2007, 07:41 AM
I'm not flying backwards!
Tony65x55's Avatar
Oshawa, Canada
Joined Sep 2004
3,753 Posts
Quote:
Originally Posted by Pongo
Started my BB over the weekend. This is my first scratchbuild foamy, so I'm sure I have lots to learn. (I've built and flown several balsa gas models, but it's been quite a few years) I'm going with a 33 inch sport wing version.

The Lowes near me has the blue fan fold (Protection board I believe), but it looked terribly warped and wavy, and I'm concerned about building it straight, so I'm using Elmer's foam core board for the foam instead. Tonight I stripped the paper off the pieces, and it went much easier than I was expecting. Last night I was skimming the threads about that and it was sounding like a major pain. I used hot water in a shallow plastic tray (found at the hardware store, used normally for under water softeners or washers I think) after just a few minutes, the paper practically fell off. Hot water was really the key for me, since when it cooled down I had to rub a bit. A new batch of hot water and things went smoothly again.

Anyways, the weight of the foam with the paper was 9.25 oz, and now after stripping the paper off, the same components weigh 2.95 oz! I wasn't expecting that much of a change. Now I've got to go get some balsa or carbon to strengthen it again.
Hi Pongo, welcome to the BB thread. Your foam board should be fine. Don't sweat about the blu-core waviness. Sometimes if you sift through the bundles you'll find one that's a little better but it's all usable. The BB structure will straighten out the foam board. Just remember to build it straight and don't banana the fuselage.

Tony
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Old Sep 11, 2007, 07:54 AM
I'm not flying backwards!
Tony65x55's Avatar
Oshawa, Canada
Joined Sep 2004
3,753 Posts
Quote:
Originally Posted by tuppertn
A couple final shots of my BBAP1 BluEndurance. Moving the servos got my CG without batts to 38% cord--pretty darn close!

EDIT: Do you think she'll need spoilerons?
Spoilerons? Good Lord, Kendall, that sucker is going to need a 88mm anti-aircraft gun to make it come down. While flying the BBAP2 last night (60" 2 step KFm) I made the observation that it glides better than my Dynaflite Daydream 72" sailplane. Seriously. (I'm gonna have to make a new wing for the sailplane!)

Seriously though, I would go with flaps/flaperons before I used spoilers. You can use them to customize your lift for heavy loads as well as add drag. Slows your landing speeds too and that's important with an expensive camera on board. Easier on your LG too.

I have a minor concern about your power plant (as a friend). The little BP21 is going to have to pull a LOT of airplane through the air and while the KFm has pretty low drag, that's still a lot of wing.. It'll fly fine, but with a 6-8 oz payload you might need a little more power... Maybe... I'm sure we'll know soon enough.

When's the maiden?

Tony
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Old Sep 11, 2007, 09:50 AM
Postcards From The Purple Edge
tuppertn's Avatar
United States, OK, Sand Springs
Joined May 2007
3,919 Posts
Ended up not using the BP21. Went with the lower kV KDA 20-22L (see post #1132). What do you think? I think I could prop up certainly to 11x4.7 and maybe even 11x6 if I went with a GWS HD. There's always the HXT35-36-1000 (AXI 2814 Eq.) to fall back on.

Raining today. Maiden will have to wait until I have less moisture and a higher ceiling (lost my Simple Fokker in a low cloud yesterday ).

kendall
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Old Sep 11, 2007, 01:11 PM
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Truglodite's Avatar
Carmichael, CA
Joined Feb 2007
3,523 Posts
pongo, if it's the waviness you're worried about, all blucor has a wave to it (as do all of our blucor planes if you look closely ). like tony said, the construction will remove most of the warp, however you need an unwarped flat piece to make a good wing & tail.

omg kendall!!! now THAT, is one big hi aspect ratio wing. when you get that bad boy flying well it should easily swallow up bb endurance records.

the 20-22L is a good step up from the bp21 for max thrust, which is better for lifting payloads & recoveries.

regarding endurance: while you're cruising around level the 20-22 will require more power to lift the extra weight of the motor, and it will be spinning farther below it's peak efficiency than a bp21. with a bp21, you get less max lifting power, but it would take less current to maintain level flight (ie: a bp21 will probably give more endurance).

then again, i have a UC wing, & i'm not sure how much more power a kfm would require, & i'd hate to see you stuck with an "s2". (fyi: s2 = aviation terminology for an airspeed that is below stall, and a ground speed that is too fast to stop before the runway ends).

cheers, & gl with the maiden,
kev
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Old Sep 11, 2007, 01:32 PM
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Carmichael, CA
Joined Feb 2007
3,523 Posts
Quote:
Originally Posted by Tony65x55
OK Kev, I'll bite. What is selitac?

Tony
hehe, funny pic tony.

here's a link to selitac sold at rcfoam:
http://www.rcfoam.com/cart.php?targe...category_id=85

it's has a directional grain, so it can be used to make very stiff & light monocoque's. perfect for airfoiled foamies, but not sure how durable it is. it's been around for a while, but here's the first post i read where someone actually used it to build something.

http://www.rcgroups.com/forums/showp...postcount=1786

after seeing the fuse, i'm thinking a hybrid is a better approach. ie: use normal epp/depron/fff construction, but with selitac as a wing skin. here's another usefull post in the same thread with data comparing the weights of depron, epp, & selitac.

http://www.rcgroups.com/forums/showp...postcount=1800

as you can see, the stuff is hard to beat for monocoque airfoil wings.

kev
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Old Sep 11, 2007, 03:17 PM
Postcards From The Purple Edge
tuppertn's Avatar
United States, OK, Sand Springs
Joined May 2007
3,919 Posts
Quote:
Originally Posted by Truglodite
...regarding endurance: while you're cruising around level the 20-22 will require more power to lift the extra weight of the motor, and it will be spinning farther below it's peak efficiency than a bp21.
The difference in motor weight is only 6g. I can fiddle with the prop selection and see how flight times change, but I don't have the tools to actually measure efficiency.

Quote:
Originally Posted by Truglodite
...with a bp21, you get less max lifting power, but it would take less current to maintain level flight (ie: a bp21 will probably give more endurance).
I guess I don't fully understand. Compared to the BP21 I get more output(W) for less current at any given throttle setting as the voltage doesn't drop as much. But then that's swinging the same prop. I guess I need to experiment with more prop combos. This is the motor/prop combo the gives me 32-34 minute flight times on my BB32 on a 2s/1320. Not sure if it will translate to the bigger plane on 3s, though.
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Old Sep 11, 2007, 04:32 PM
I'm not flying backwards!
Tony65x55's Avatar
Oshawa, Canada
Joined Sep 2004
3,753 Posts
Quote:
Originally Posted by tuppertn
Ended up not using the BP21. Went with the lower kV KDA 20-22L (see post #1132). What do you think? I think I could prop up certainly to 11x4.7 and maybe even 11x6 if I went with a GWS HD. There's always the HXT35-36-1000 (AXI 2814 Eq.) to fall back on.

Raining today. Maiden will have to wait until I have less moisture and a higher ceiling (lost my Simple Fokker in a low cloud yesterday ).

kendall
That motor sounds really good Kendall. Let me know how it works out. I'd like to try it. The price is certainly right.

Tony
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Old Sep 11, 2007, 07:00 PM
Out the Window
High Flyin''s Avatar
United States, FL, Alachua
Joined Jul 2004
1,287 Posts
Thanks all for your recommendations on my poorly built warped fuse. I think I will build another as the glue joints are also not very attractive. I am going to try the gorilla glue for the joints. I used it to combine the monobloc and the sides and liked the way it worked. It gave some time to move it about and I could quickly sand off the little that oozed out.

I am building the 32 inch version and I used all of the 1/2 inch foam I had to build the monobloc. I have a lot of the 3/4 inch foam. Would there be a problem with making the monobloc one and a half inches wide? I don't think it will add much weight and may look more three dimensional. Also where are you running the wireing from the motor to the esc to the battery as they seem to be in different compartments in the monobloc?

Thanks again,
Ray
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Old Sep 11, 2007, 07:30 PM
Postcards From The Purple Edge
tuppertn's Avatar
United States, OK, Sand Springs
Joined May 2007
3,919 Posts
I used one chunk of 2" pink foam for my monoblock. Works fine, looks good. I used a 1/2' round file to drill and widen a hole through the planes "chin" straight through to the electronics bay that doubles as a vent. You could also cut a channel down one side of the monoblock before gluing on the fuse sides.
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Old Sep 11, 2007, 09:20 PM
I'm not flying backwards!
Tony65x55's Avatar
Oshawa, Canada
Joined Sep 2004
3,753 Posts
Quote:
Originally Posted by High Flyin'
Thanks all for your recommendations on my poorly built warped fuse. I think I will build another as the glue joints are also not very attractive. I am going to try the gorilla glue for the joints. I used it to combine the monobloc and the sides and liked the way it worked. It gave some time to move it about and I could quickly sand off the little that oozed out.

I am building the 32 inch version and I used all of the 1/2 inch foam I had to build the monobloc. I have a lot of the 3/4 inch foam. Would there be a problem with making the monobloc one and a half inches wide? I don't think it will add much weight and may look more three dimensional. Also where are you running the wireing from the motor to the esc to the battery as they seem to be in different compartments in the monobloc?

Thanks again,
Ray
I 1/2" should be fine but remember to widen the pieces for the top and bottom decks for the fuse rear. When's the maiden?

Tony
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Old Sep 11, 2007, 09:28 PM
Out the Window
High Flyin''s Avatar
United States, FL, Alachua
Joined Jul 2004
1,287 Posts
Quote:
Originally Posted by Tony65x55
I 1/2" should be fine but remember to widen the pieces for the top and bottom decks for the fuse rear. When's the maiden?

Tony
Tony

My wife and I are getting ready to spend about a month in a motor home, so it may be a while before I get the Blu-Baby finished and flying. I am very slow in my building. I do plan to stop by a electric fly-in in Tennessee on the trip, so at least I will get to look at some model planes. Also my stop by the Wright/Patterson Air Museum in Daton, Ohio so will get to see some full sized aircraft!

Thanks,
Ray
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Old Sep 11, 2007, 09:40 PM
I'm not flying backwards!
Tony65x55's Avatar
Oshawa, Canada
Joined Sep 2004
3,753 Posts
Ahhh, traveling the I-75 I see. I've done it many times myself. My sister has a place in Port Charlotte and we make the pilgrimage annually to escape the cold winter snows. Have been to W-P AFB twice to see the air museum. FANTASTIC!!!! Have fun!

Tony
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Old Sep 11, 2007, 10:20 PM
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Truglodite's Avatar
Carmichael, CA
Joined Feb 2007
3,523 Posts
Quote:
Originally Posted by tuppertn
The difference in motor weight is only 6g. I can fiddle with the prop selection and see how flight times change, but I don't have the tools to actually measure efficiency.


I guess I don't fully understand. Compared to the BP21 I get more output(W) for less current at any given throttle setting as the voltage doesn't drop as much. But then that's swinging the same prop. I guess I need to experiment with more prop combos. This is the motor/prop combo the gives me 32-34 minute flight times on my BB32 on a 2s/1320. Not sure if it will translate to the bigger plane on 3s, though.
sorry kendall, i can see how my post was confusing. to help clarify my thoughts: watts in is not equal to watts out (wattmeter->watts in / tachometer->watts out). efficiency is defined as watts out/watts in. while the 20-22 may have used less watts in, the rpm may have been less so the watts out could be less. typically you get the best efficiency/endurance using a motor that is in the middle of it's "power band" (ie efficiency curve) during level flight. this peak typically occurs around 80-90% of WOT. assuming the weight is the same, the power output required for level flight is the same for both motors. therefore if a "larger" motor is way overpowered, then rpms will typically be low on its efficiency curve during level flight, so it will be somewhat less efficient compared to a smaller motor that is turning 85% of it's max power output. of course the limiting factor to how small you can go is the amount of excess power required for climbing & recoveries (these moves are not part of a true endurance flight profile, so they are somewhat unimportant when shooting for time records).

the reason tony (& i) prefer having gobs of excess power is payload. too much power is also fun for aerobatics, but these larger bb's are designed for payloads, and power required for flight is directly proportional to weight.

at a mere 6gm difference, you can pretty much ignore the added weight. the funny thing is, it doesn't take much more power to lift a 60"bb versus a 32"bb. the reason is the weight doesn't increase very much as you go up in size (my bb32" weighed only 7oz less than my bbap1-60"). you should expect only slightly less flight times using that same motor & lipo on the bigger bird, and with a bigger lipo flight times could go past 34min. your 20-22 could also be more efficient than a bp21. if so, it's likely a win win situation.

kev
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Old Sep 12, 2007, 02:59 AM
Registered User
Ipoh, Perak Malaysia
Joined Jul 2006
4,011 Posts
I have two of these motors (20-22L). They are pretty good. I have them swinging GWS 9x7.5HD props and I supposed it is a bit under utilized. It can easily swing a 10" diam. prop.no problem. One thing about these made in China motors: Take the manuf. recommendations with a large grain of salt. Down-size it at least 1 step if you don't have the means to measure the actual current drawn or you may burn out a motor.

I am stuck with a max 9" prop because of ht restrictions caused by the landing gear. I would have preferred a 10". I HAVE tried it with a 10"x3.8" SF prob without problem

chewy
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