stunthanger.com
Design => Stunt design => Topic started by: Peter Germann on September 30, 2016, 04:26:23 AM
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Trying to investigate the influence of stabiliser vs. elevators thickness on altitude holding ability in level and inverted flight, turbulator strips of different thickness have been installed at the hingeline of the stabiliser. Repeated test flights have been conducted at governed constant RPM in calm conditions.
Test configuration:
Crossfire, electric, 64 oz.
Lines 0.4 mm x 18.0 m (0.014 x 59 ft)
RPM 9’240
Speed 5.0 sec/lap
A: No turbulators added
B: 4 ea. 254 mm (10 in long) 4 mm (0.16 in) thick and 4 mm wide triangular turbulator strips added
C: 4 ea. 254 mm (10 in long).1.5 mm (1/16”) thick and 10 mm wide triangular turbulator strips added
Findings
A: With stabiliser TE and elevators LE being equally thick, the airplane feels a bit touchy. Maintaining altitude in level and inverted flight requires constant attention. This is well manageable in level flight, but critical during the inverted laps. With crisp input, corners are snappy with clean exits.
B: With 4 mm thick turbulator strips added to stab at the hingeline, the airplane became extremely sluggish and tight corners could not be flown. While holding altitude in level and inverted was easy, this configuration would not allow competitive flying. Added drag reduced speed by 0.3 sec/lap.
C: With 1.5 mm thick turbulator strips added to stab at the hingeline, the airplane felt solid in level and inverted. Round manoeuvres looked fine, displaying kind of a nice flow. Holding altitude in level and inverted was manageable. Corners were a bit round. Moving back the by C.G. 3 mm (1/8”) brought back most (not all) of the cornering ability. Added drag reduced speed by 0.1 sec/lap.
Résumé
Equally thick stab TE and elev. LE may:
• Compromise altitude holding ability in level and (more so) inverted flight
• Reduce solid look & feel in round manoeuvres
• Improve cornering ability.
At hingeline thicker stabilisers may:
• Improve altitude holding ability in level and inverted flight
• Add solid look & feel in round manoeuvres
• (Critically) Decrease cornering ability
The above are strictly personal findings and must not be relevant to other airplanes and/or flyers. For the time being, I will continue flying as per configuration C and report here.
Update Oct. 1st 2916
When flying the 1.5 mm turbulator in 5m/sec (11 mph)wind, I found it critical to pull out accurately and low from square or triangular maneouvres. It seems that the reduced efficiency of the elevators was no longer sufficient to rotate the airplane and when I removed the turbulators on site, this brought back the original manoeuverability immediately.
While a thinner than 1.5 mm turbulator (or thickness difference) might be a valid compromise, I now do not believe that the stab-elev thickness difference, or the lack of it, is the key to explain or cure the level flight altitude holding problem (not hunting) of some electric stunt airplanes. With this conclusion, I will now terminate the above tests.
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Trying to investigate the influence of stabiliser vs. elevators thickness on altitude holding ability in level and inverted flight, turbulator strips of different thickness have been installed at the hingeline of the stabiliser. Repeated test flights have been conducted at governed constant RPM in calm conditions.
Test configuration:
Crossfire, electric, 64 oz.
Lines 0.4 mm x 18.0 m (0.014 x 59 ft)
RPM 9’240
Speed 5.0 sec/lap
A: No turbulators added
B: 4 ea. 254 mm (10 in long) 4 mm (0.16 in) thick and 4 mm wide triangular turbulator strips added
C: 4 ea. 254 mm (10 in long).1.5 mm (1/16”) thick and 10 mm wide triangular turbulator strips added
Findings
A: With stabiliser TE and elevators LE being equally thick, the airplane feels a bit touchy. Maintaining altitude in level and inverted flight requires constant attention. This is well manageable in level flight, but critical during the inverted laps. With crisp input, corners are snappy with clean exits.
B: With 4 mm thick turbulator strips added to stab at the hingeline, the airplane became extremely sluggish and tight corners could not be flown. While holding altitude in level and inverted was easy, this configuration would not allow competitive flying. Added drag reduced speed by 0.3 sec/lap.
C: With 1.5 mm thick turbulator strips added to stab at the hingeline, the airplane felt solid in level and inverted. Round manoeuvres looked fine, displaying kind of a nice flow. Holding altitude in level and inverted was manageable. Corners were a bit round. Moving back the by C.G. 3 mm (1/8”) brought back most (not all) of the cornering ability. Added drag reduced speed by 0.1 sec/lap.
Résumé
Equally thick stab TE and elev. LE may:
• Compromise altitude holding ability in level and (more so) inverted flight
• Reduce solid look & feel in round manoeuvres
• Improve cornering ability.
At hingeline thicker stabilisers may:
• Improve altitude holding ability in level and inverted flight
• Add solid look & feel in round manoeuvres
• Decrease cornering ability
The above are strictly personal findings and must not be relevant to other airplanes and/or flyers. For the time being, I will continue flying as per configuration C and report here.
WOW! Great job Peter! Thank you very much for doing this experiment.
Jerry
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Trying to investigate the influence of stabiliser vs. elevators thickness on altitude holding ability in level and inverted flight, turbulator strips of different thickness have been installed at the hingeline of the stabiliser. Repeated test flights have been conducted at governed constant RPM in calm conditions.
Peter, have you tried the conventional hinge line setup with the corners knocked off? Anything I did along the lines of what you are doing made it worse rather than better. Also, what tail incidence are you using?
Brett
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With the smaller wedge seeming to be better, but for cornering, would a slight reduction in flap chord help? Or a sharper LE on the stab? D>K
In earlier tests I have found that, contrary to what I thought before, increasing the flap throw has brought tighter corner. I started flying the Crossfire in 2015 with the elevators deflecting to 45° and the flaps to 30° and later found it turning substantially tighter with a 45° / 45° setting. Since 2016 it now turns "Skark" style and seems to do better what judges like to see... However, it is still a challenge to keep it level in inverted.
Following Paul Walkers advice here, the stab leading edge was sharpened to a knife edge lately and this did in fact improve the altitude holding ability a bit.
As the airplane still requires constant attention to maintain altitude, a problem virtually unknown to me in 40 years flying all kinds of IC motors and having surfaced repeatedly during the past 6 years of competing with various electric F2B models, the search for the cause of this phenomenon must go on.
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Peter, have you tried the conventional hinge line setup with the corners knocked off? Anything I did along the lines of what you are doing made it worse rather than better. Also, what tail incidence are you using?
Brett
Interesting to learn, Brett. It seems that my findings on aerodynamic hingeline modifications support what you have experienced before.
As I am still uncertain whether to use left or right turning props, the airplane has zero tail and motor incidence. While this requires a bit of constant trim input at the handle for either level (as I do) or inverted flight, I dont know whether it could be the cause of the airplane wandering off from the initiall level flight. altitude.
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As I am still uncertain whether to use left or right turning props, the airplane has zero tail and motor incidence. While this requires a bit of constant trim input at the handle for either level (as I do) or inverted flight, I dont know whether it could be the cause of the airplane wandering off from the initiall level flight. altitude.
Some combination of rigging the elevator to trail a bit up or down and biasing the handle should fix this. It certainly has for me on at least one 0-0 setup.
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Peter,
Do you have the same problem when using a tractor prop?
Also, being aware of old dogs and new tricks, I just say that sometimes position in which you hold the handle during inverted flight can cause tracking problems. L
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Do you have the same problem when using a tractor prop?
Also, being aware of old dogs and new tricks, I just say that sometimes position in which you hold the handle during inverted flight can cause tracking problems. L
Its a while since I flew a tractor and I just dont remember... I will of course try, checking the handle position, too