Weight Loss Exercise

[Matt Piatkowski]

Hello,
In 2018, I have received the full-size F2B model named MPBee (attached).
Comment: somebody built this model for me and I paid for this.
The model flew well and I learned the pattern a bit better using it.

The RTF weight was 1862 grams (65.7 oz.).

During the next three years, I have made about 250 flights of this model, modifying the batteries, motors, ESCs, timers, and propellers. In the late Fall of 2021, I have made several flights using the configuration with the RTF weight of 1842 grams and shelved the model because I had already two competition stunt/F2B models flying the pattern better.

In December 2021, I started modifying MPBee by:
1. Increasing the Hinge-To-Hinge distance from 462 mm. ( 18.2") to 488 mm. (19.2")
2. Changing the airfoil of the horizontal stabilizer by modifying the LE area shape.
3. Increasing the surface area of the horizontal stabilizer by 3%
4. Removing the unnecessary connections, glue, plywood, and balsa from the fuselage and the vertical tail area.
    Comment: the model is taken apart and the interior of the fuselage is 80% accessible for Drehmel's work.

I am finishing the modifications right now by moving the CG of the RTF model 9 mm. AFT.
To do this, I had to slide the battery 27 mm. into the wing. Because the entire wing is removable, I had excellent access and could reinforce the newly created opening against stress concentrations. 

The RTF weight with 5S 3400 mAh. ThunderPower battery and Kv 820 motor (205 grams) will be 1780 grams. (62.8 oz.).
The RTF weight with 6S 2800 mAh. ThunderPower battery and Kv 650-700 motors (205 grams) will be 1755 grams (61.9 oz.).

The flight tests will take place in March and I expect good, sharp corners.

Happy Flying,
M

[Mike Alimov]

Hi Matt, at this weight, you could switch to the ThunderPower 6S 2200 mAh battery and shed another 2oz or so. I've tested it and it works up to 66' lines. If you prefer to fly on full length 70' lines, then it may not have enough charge. Good luck! I think you'll like the plane better when it's closer to 60 oz.

[Matt Piatkowski]

Hi Mike,
The flight tests will show the battery usage and then I will know if 6S 2200 is enough.
I will be flying this model on 64' eye-to-eye, 4 strand, Solomianikov's lines.
Igor's 12x5 narrow and wide blade carbon composite propellers will be used.

The target lap time is 5.3 sec.

60. oz is tempting but I always aim for the wing loading first. MP Bee total wing area (with flaps) is 690 sq.in. If the RTF weight is 1780 grams (62.8 oz.), the wings loading is WL= 62.8 / [690/144] = 62.8 / 4.792= 13.1 oz. / ft.^2. If the RTF weight is 1755 grams (61.9 oz.), the wings loading is 12.92 oz./ft.^2. Both are ok. for me and they fall within the so-called "Yatsenkos Range" for the full-size C/L stunt/F2B models. I prefer my models to have a little better wind penetration properties and this calls for a slightly larger wing loading.

I have one C/L stunter ( eParrot XL) that can be used with a single prop-single motor configuration ( wings loading 11.675 oz./ft.^2) and with the TMT contra (Himax 3516-1030, wing loading 12.69 oz./ft.^2). I like flying it with a single motor when the wind is 8 - 12 mph but with the wind exceeding 12 mph. I always use the TMT contra.

This brings an interesting question: shouldn't we all have two models with the same geometry: one for gentle winds and the other for stronger winds?
Regards,
M

 

[Ken Culbertson]

This brings an interesting question: shouldn't we all have two models with the same geometry: one for gentle winds and the other for stronger winds?

Interesting idea.  When I was competing regularly in soaring I had just that combination, but PA is not soaring.  I know that I have had planes that handled calm better than others and wind fliers that did poorly if the wind was under 5.  My current ride seems to be the guy in the middle - doesn't like either extreme!  My *question* is, given the amount of time it takes to get to know your plane well is it wise to not learn to fly the same one in both? 

Ken

[Matt Piatkowski]

Hi Ken,
We will probably never know which approach is better.
All we can do is try, fly, test, practice, crash, swear and...start again.
M

[Mike Alimov]

This brings an interesting question: shouldn't we all have two models with the same geometry: one for gentle winds and the other for stronger winds?
Regards,
M

 

... or one airplane that has a ballast compartment located on the CG... and a few pieces of ballast in your flight box to tune your wing loading to the "Yatsenko range" (did they patent 13 oz/sq.ft?)

[Matt Piatkowski]

Hi Mike,
I have not heard such an idea before but it is certainly interesting.
In my opinion, the ballast compartment should have top and bottom narrow rectangular openings, allowing to slide lead pieces along the wings sheeting and across the fuselage. 
In such a scenario, the position of the total ballast CG would be exactly in the X-Y plane of the model.
Comment: X-Y plane is the wings symmetry plane. The model's right-handed Cartesian coordinate system is as follows: (+)X is AFT, (+)Y is OUTSIDE, and then (+)Z is UP.

I have heard the name "Yatsenkos Range" in 2019 Wierzawice (Poland) F2B contest. When the wings with flaps loading fall between 11.8-13.5 oz. / ft.^2, the wings loading suppose to be optimal.
When you make, say, 500 pattern flights in ALL weather conditions and you feel that the model flew well, it is in the Yatsenkos Range.

[Ken Culbertson]

Hi Mike,
I have not heard such an idea before but it is certainly interesting.
In my opinion, the ballast compartment should have top and bottom narrow rectangular openings, allowing to slide lead pieces along the wings sheeting and across the fuselage. 
In such a scenario, the position of the total ballast CG would be exactly in the X-Y plane of the model.
Comment: X-Y plane is the wings symmetry plane. The model's right-handed Cartesian coordinate system is as follows: (+)X is AFT, (+)Y is OUTSIDE, and then (+)Z is UP.

I have heard the name "Yatsenkos Range" in 2019 Wierzawice (Poland) F2B contest. When the wings with flaps loading fall between 11.8-13.5 oz. / ft.^2, the wings loading suppose to be optimal.
When you make, say, 500 pattern flights in ALL weather conditions and you feel that the model flew well, it is in the Yatsenkos Range.

I am a 12.9.  Does that mean those sloppy patterns are not the planes fault?   Na...

Ken

[Matt Piatkowski]

Hello,
I have finished the modified model.

There are four configurations that will be flight-tested:

1. Cobra Kv 820 motor, TP 5S 3400 battery, Pol-Prop 11x6x3, 60+ ESC and KR Governor: RTF weight=1777 grams (62.7 oz.)
    This configuration had the RTF weight=1842 grams (~65 oz.) before the weight loss exercise and the lap time was 5.0-5.1 sec.
 
2. Cobra Kv 820 motor, TP 5S 3400 battery, Igor's 12x5x3 wide blade propeller, 60+ESC, and KR Governor: RTF weight = 1775 grams (62.6 oz.)
3. Cobra Kv 820 motor, TP 6S 2800 battery, Igor's 12x5x3 wide blade propeller, 60+ESC, and KR Governor: RTF weight = 1750 grams (61.7 oz.)
4. BadAss Kv 710 motor, TP 6S 2800 battery, Igor's 12x5x3 wide blade propeller, 60+ESC, and KR Governor: RTF weight=1725 grams (60.8 oz.)

Static tests, each 30 seconds long, delivered the following results:
Configuration 1 develops 630 Watts at 33 static Amperes at 9140 RPM. The voltage at load was 19.1 V (no-load voltage: 5x3.9=19.5 V).
Configuration 2 develops 640 Watts at 35 static Amperes at 9140 RPM. The voltage at load was  18.3 V (no-load voltage: 5x3.9=19.5 V).
Configuration 4 develops 660 Watts at 32 static Amperes at 9140 RPM. The voltage at load was 20.63 V (no-load voltage: 6x3.9=23.4 V).

I anticipate that the lighter model will be able to maintain the lines tension overhead flying slower. The target lap time is, like I wrote before, 5.3 sec.

Will I be able to control the lightest model when it is windy? The flight tests will show.

M

[Steve Helmick]

Pushing yourself away from the table is the best weight loss exercise. If you want your model to weigh less, holding it very close to the sandpaper is the equivalent.  Steve

[Avaiojet]

Hello,
I have finished the modified model.

There are four configurations that will be flight-tested:

1. Cobra Kv 820 motor, TP 5S 3400 battery, Pol-Prop 11x6x3, 60+ ESC and KR Governor: RTF weight=1777 grams (62.7 oz.)
    This configuration had the RTF weight=1842 grams (~65 oz.) before the weight loss exercise and the lap time was 5.0-5.1 sec.
 
2. Cobra Kv 820 motor, TP 5S 3400 battery, Igor's 12x5x3 wide blade propeller, 60+ESC, and KR Governor: RTF weight = 1775 grams (62.6 oz.)
3. Cobra Kv 820 motor, TP 6S 2800 battery, Igor's 12x5x3 wide blade propeller, 60+ESC, and KR Governor: RTF weight = 1750 grams (61.7 oz.)
4. BadAss Kv 710 motor, TP 6S 2800 battery, Igor's 12x5x3 wide blade propeller, 60+ESC, and KR Governor: RTF weight=1725 grams (60.8 oz.)

Static tests, each 30 seconds long, delivered the following results:
Configuration 1 develops 630 Watts at 33 static Amperes at 9140 RPM. The voltage at load was 19.1 V (no-load voltage: 5x3.9=19.5 V).
Configuration 2 develops 640 Watts at 35 static Amperes at 9140 RPM. The voltage at load was  18.3 V (no-load voltage: 5x3.9=19.5 V).
Configuration 4 develops 660 Watts at 32 static Amperes at 9140 RPM. The voltage at load was 20.63 V (no-load voltage: 6x3.9=23.4 V).

I anticipate that the lighter model will be able to maintain the lines tension overhead flying slower. The target lap time is, like I wrote before, 5.3 sec.

Will I be able to control the lightest model when it is windy? The flight tests will show.

M

M,

Nice information.

Your ESC? I looked on line, says it's for R/C cars? Any information you could share on this item would be appreciated.

Charles

[Matt Piatkowski]

My ESC is Cobra 60+ Amps. It is sold by https://innov8tivedesigns.com.
This ESC works well with Keith Renecle's governor.
It will not work with Fiorotti's and Igor's active timers.

Regards,
M

[Matt Piatkowski]

Hello,
I have flight-tested configuration 2 (RTF weight 1775 grams) in 12 miles of steady wind with + 3 MPH gusts.
Exceptional performance in square eight, triangle, hourglass, and cloverleaf.
The horizontal lap time was 5.15 seconds.
Lines length was 64 feet e-t-e.

Next step:  I will increase the length of the lines by 35-40 cm.
                  This will give me laps of about 5.25 seconds.
                  This is probably slow enough to have much better control of the sharp corners.

TP 5S 3400 battery use after the pattern with 5.15 sec. per horizontal lap was 79%.
I am charging these batteries to 4.19 Volts per cell.

The tests will continue.

M

[Matt Piatkowski]

5.25 sec./horizontal lap has been achieved in ideal conditions - light, steady wind, and partial sun.

I usually test any change flying the triangles, hourglass, horizontal eight, and the overhead eight.

They all looked better when I flew slower.

With increased lap time, the model will also speed up less in maneuvers in wind.
                 
My next step: flying this model in moderate and strong wind.

Can I reach 5.35 sec./ lap and still improve the maneuvers?

The contra-powered stunt and F2B full-size planes can have a lap time 5.45-5.5 sec.
One more reason to get Polish Contras: geared and TMT.
There is a catch, though: the model itself must be built using a very light balsa and all the tricks to remove weight.

The covered, completely finished structure with everything except the contra power plant, propellers, ESC/ESCs, timers, cable harness, and battery must weigh 1020 -1030 grams ( ~36.2 oz.) for geared and 920-930 grams (32.6 oz.) for TMT contra

Difficult? Yes. But not impossible, considering that almost everybody builts their planes too strong for the pattern.

Interested in details? Talk to me.
M

 



I will see soon.

M

[Matt Piatkowski]

Five flights yesterday.
The first four flights with 11x6x3 PolProp to check if the RPM change from 9140 to 8950-9000 still allows flying full pattern on this propeller.

Comment: Keith Renecle's governors have a poor resolution of RPM: it is somewhere between 50 and 100 RPM. This RPM resolution was sufficient for me four years ago but it is not now.
                 I will probably switch to timers providing a more precise RPM selection. The average RPM in flight is also affected by the Gain parameter. I am using Gain=3 and the RPM in flight fluctuates audibly.
 
The lines length is now 65 feet eye-to-eye (it was 64' before using this propeller and 9140 RPM, with lap time 5.0 -5.1 sec).
The lap time on 11x6x3 PolProp and 65' long lines was 5.15 seconds and the pattern looks good except for the 9th. and 10th. corner of the horizontal eight and second corner of the hourglass.

Wind: 10 miles/hour with gusts of 3-4 miles/hour and some turbulence overhead.

Flight #5 was done using 12x5x3 Igor's wide blade propeller, turning at ~9800 RPM. The lap time is 5.25 sec., lines 65' e-t-e.

Wind: 10 miles/hour with gusts of 4-5 miles/hour and strong turbulence overhead.

Al corners in all maneuvers looked ok. Despite the fact that the model was flying slower (5.25 sec. v/s 5.15 sec./lap), the larger diameter propeller delivered sufficient power to execute the critical corners properly.

TP 5S 3400 batteries use after pattern: to 3.76 Volts/cell on average for 11x6x3 PolProp and 3.78 Volts/cell for 12x5x3 Igor's wide blade prop.  Capacity in: 2700-2750 mAh. (79.4 - 81%).

The tests will continue.

Comment: I will not extend the lines anymore. I am tall, I have a long reach and the total distance from my body center to the outside wing tip is now 73.7 ' (22.3 m.). There are flying circles, especially in Europe, having fences that may cause catastrophe while landing. These circles were built in the fifties and/or sixties: for example, the Hradec Kralove F2B circle is somewhat "tight" and limits the safe length of the lines to 64', restricting also the pilot's movement while landing.