Landing Gear Drag

[Peter Germann]

Battery re-charge after flying the FAI pattern with a.) the gear locked down and b.)  gear up after 10"s and down 3 secs after motor stop has shown a difference of 5% or 1'922 mAh gear down vs. 1'824 with gear retracted.

Airplane: F2B 683 sq.in  64 oz
Gear type: Fuselage mounted 2-legs 1/8 piano wire, 2 in wheels, folding backward (Cessna Cardinal like).
Lines: 0.015 x 64 ft
Speed: 5.25 sec/lap
Motor: Hacker A40 A40-14SV2 14 Pole 530 RPM/Volt
Battery: 5S/2700
Propeller: AeroNaut CAM carbon light 14 x 6 L
Retract Drive: two ea. e-flite EFLG 101 
RPM set, Gear retracting: 8'976
RPM set, Gear locked down: 9'042
ESC: Castle Edge in high gov.mode
Timer:Hubin FM-9 LG

[Tim Wescott]

Pictures of the gear?  And maybe a movie of the thing retracting?

Does it turn and retract into the fuselage like the Cessna 177RG?

Not for any practical purpose -- I'm just a retract junkie.

[Peter Germann]

Yes, it folds back like Cessna 177 RG. Looks cool, indeed

[Tim Wescott]

Peter sent me a video.  I posted it:

[Trostle]

I had no idea that a fixed gear could waste so many electrons.

Keith

[FLOYD CARTER]

I have a full body P-51, built from an RSM kit.  OS LA46.  It has retracting L.G.  the gear retracts inward, so no change in CG with wheels up.

I can't measure wheel drag, but the plane flies much smoother wheels up.  Most improvement seems to be in corners, where it changes direction with less "wobble" with no sign of "hunting".

Besides, it looks a bunch better!

Floyd

[Brett Buck]

I had no idea that a fixed gear could waste so many electrons.

    You could probably use the data to figure out what fraction of the total drag the landing gear represents. I wouldn't be surprised if it was 1/3 the entire drag load of the airplane in level flight.
 
     Brett

[Tim Wescott]

A thorough investigation would take account of any weight added by the landing gear, and the extra battery drain caused by it in maneuvers.  One would have to rely on estimates, though -- my plane with fixed gear would probably be heavier than anyone else's with retracts!

[Howard Rush]

    You could probably use the data to figure out what fraction of the total drag the landing gear represents. I wouldn't be surprised if it was 1/3 the entire drag load of the airplane in level flight.

I wouldn't have been surprised either.  Landing gear drag is less than I expected, however.  I calculated landing gear drag energy, which is pretty easy if you can guess wheel c_d, particularly when Peter went to the effort to express his data in our quaint units, not to mention our language.  Divide landing gear drag energy by prop and electrical efficiencies to get battery energy increment due to extended landing gear. 

Peter gave us the real data, but I include the calculation for your amusement anyhow.  Enter numbers in the yellow cells.  I assumed Zürich airport elevation, 70 degrees F temperature, 50 degrees F dew point, baro set 29.97 inches Hg, to get air density and viscosity.  Behold that this calculates extended-gear drag energy, but Peter measured extended-gear drag energy - retracted-gear drag energy.  A retractable-gear airplane with gear retracted probably has more drag than a clean airplane.

[Igor Burger]

My spread sheet says that Max II has landing gear drag aproximately 0,15N and whole airplane drag in level flight is proximtely 6,5N (including lines) in the same conditions.

[Tim Wescott]

A retractable-gear airplane with gear retracted probably has more drag than a clean airplane.

If Peter really wanted to be thorough (I just love suggesting work for other people) he could tape off the wheel wells, and maybe even scab on some quickie wheel pants, and get some more measurements.

Dunno if it matters for stunt, unless you could either make a lighter stunter or if the LG & whatnot actually generated enough turbulence to prevent really smooth, controlled maneuvers.

[Trostle]

My spread sheet says that Max II has landing gear drag aproximately 0,15N and whole airplane drag in level flight is proximtely 6,5N (including lines) in the same conditions.

Igor,

Can you approximate the line drag component of that total 6.5N airplane drag in level flight?  I think the number is surprisingly high.

Keith

[Igor Burger]

Yes, line drag is aproximately 2,5N means little less then 1/2 of whole drag. But again, it is in level flight, the drag in corners goes up.

[Peter Germann]

If Peter really wanted to be thorough (I just love suggesting work for other people) he could tape off the wheel wells, and maybe even scab on some quickie wheel pants, and get some more measurements.

I am sorry to report, Tim, that tinkering with wheel well taping and/or pants will have to wait until the "Symmetria" airplane will have its new nose. This is because the original fuselage nose disintegrated when a multicopter carbon filled prop said to be built for 12 kRPM lost a blade at 8'750 RPM...

However, from learning how little energy the gear consumes and from experiencing (for me, that is) the almost unnoticable change in flight characteristics (trim) caused by the gear being up or down, I might in fact decide to trade-in the (really sharp looking) retractable gear for a 2 oz lighter fixed gear.

[Tim Wescott]

I am sorry to report, Tim, that tinkering with wheel well taping and/or pants will have to wait until the "Symmetria" airplane will have its new nose. This is because the original fuselage nose disintegrated when a multicopter carbon filled prop said to be built for 12 kRPM lost a blade at 8'750 RPM...

Y'know, that's the second report I've heard in this forum of a quad prop throwing a blade on a stunter.  Both happened in Europe, though -- perhaps the laws of physics are different here, and we're safe.

[Scientifiction .]

Anyone building a electrowhizzery thatll fire a  solenoid or two , to release spring loaded gear up or down ( up & Down actually - Two Seperate springs , the down rather taut )
that only needs a weeny little battery and weighs stuff all .  ?

 

[Howard Rush]

Both happened in Europe, though -- perhaps the laws of physics are different here, and we're safe.

The vegetation of the Arlington, WA flying field approximates that of Włocławek.  If you would like to repeat that experiment, I'd be happy to witness it, although from a greater distance.