Thorp Air Command - T18.net

The 10th post of this thread shows my EarthX battery in a firewall mounted box that utilizes existing structure behind the firewall.

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Scott Emery
EAA Chapter 326
T-18 N18TE

EEGADS!! - that almost looks like 14/2 romex wire next to that air conditioner discombobulator! One of my airplane dweeb friends has one of those lightweight batterys in his IO-360 biplane - says it's got plenty of oomph and him likes it.

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Fraser MacPhee
N926WM
Serial #279-1
Angel Fire, NM (KAXX)

It was all aircraft wire around it. I was able to reuse most of it although the lead to the master switch ended up being too short. Tha black wire above the contactor is coax.

It was recommended to me to install a diode on the solenoid. I know what a diode does but not the “why” behind installing a diode as a jumper from the battery terminal and the switch post on the master solenoid. The old setup didn’t use a diode but I know some, if not all, production aircraft do. Can anyone here enlighten me as to “why”?

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Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

The "Flyback Diode" has a purpose:
When you open the switch to the contactor (turn off Master Switch) the hold-in coil magnetic field collapses.
This causes a high voltage spike (of very low current) that can eventually damage the switch, the contactor's contacts and anything else that is turned on, like avionics.
The diode sinks this voltage spike.
https://en.wikipedia.org/wiki/Flyback_diode
I always have to study this before installing, or I might put the diode in backwards and burn it out as soon as I turn on the switch...
(let the smoke out, as they say)
A Flyback Diode is also used on the Starter Solenoid.

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Scott Emery
EAA Chapter 326
T-18 N18TE

Scott, all electrical motors, switches, etc. have smoke built inside and sometime in their life the smoke will come out, happens to me all the time

Scott, Thanks for the info and the link. It makes a lot more sense to me now than the “to protect against reverse polarity” reason I had been given. No stores around here to buy that kind of stuff but Ebay has everything.

The battery is finally moved and the last of the lead ballast (3.7 pounds today, 8.1 total) has been removed from the engine. Everything powered up without generating any smoke or wires getting hot so all I need to do is the paperwork (w&b revision/log entry) to call the job finished.

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Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

After I installed my solenoids I found this site that had the diode stuff . Even has pics to make it caveman simple ! Verticalpower.com/media/attachments/2017/07/20/contactor_wiring.PDF

RB

Thanks Rich, there is a lot of good info on that site too. I downloaded and saved their documents for future reference.

I knew the CG would move forward with the battery but the final tally surprised me a little bit. Removing the lead and moving the battery brought the CG 1 inch forward which is a bigger change than what adding the lead made. Working backwards from last year's scale weight, it appears the new empty CG is now 1.4 inches ahead of where it was before the lead was added.

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Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

Most empty CGs come in right at, or forward, of the forward limit. It is not until adding pilot weight that you get in the envelope.
Cubes

Currently at 7.6" aft of the wing leading edge but I have other things I want to do. Most items on the list will move the CG forward in very small increments and will likely be negated when I install the baggage compartment.

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Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

I performed a w&b last weekend on mine. I had a flight with full fuel and just myself with no baggage and noticed that I was full aft stick and the plane had little to no flare at 85 mph on landing. It just sat straight down onto the runway. I was concerned that I was forward cg. After performing w&b It appears I have removed over 40lbs when I took out vac system and moved battery to firewall. Switched to dynon for instruments. I'm 918lbs dry with 63.4" cg. So it's within envelope completely empty and right in the middle with full fuel and myself. Not sure why I'm running out of back stick with this setup. Put 10lb bag in the baggage and all felt better.

After looking at previous w&b it showed my tail as 82lbs and my mains at 52" datum. I had mine leveled (and performed it with an a&p) and I had a 53lb tail with 54" main. The tail wheel was also at 214.25" on the previous and I measured (6 times to make sure I didn't mess it up) to 216.5". Nothing in logs about a change in tail wheel for entire history of aircraft. I think previous w&b was performed in 3 point instead of level which would change the weight of the tail that much.

Anyone else with a scott 3200 tail wheel know their distance? I measured from wing leading edge and used the plans distance of 55" for wing leading edge to calculate the distance.

How do the flight control measurements match the plans? Sounds as though the stab travel is not right.

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Bob Highley
N711SH
SN 835
KLAL

How does your tailwheel position look in relation to mine? Mine figures out to 213.8" from a nose datum. In addition to control throws, has your spinner, engine model or engine mount ever been changed. If it has or the original w&b did not account for variations then simply dropping a plumb bob from the spinner will give you bad measurements although the difference shouldn’t be enough to give you the excessive landing speed. To verify a nose datum it must be measured forward from a fixed point on the airframe to find it.

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Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

I have same spring but scott 3200 assembly so it looks slightly different in that respect.

I did all of my measuremens off of the wing leading edge at the fuselage which should be exactly to plans. Per plans it is 55" from plans datum at spinner. Using the wing removes the issue of changed prop or spinner since the build.

Fytrplt, I think bob highley said something about moving my stops at the fly in yesterday. He thinks I need to increase my travel for the stops. I did find that I wasn't close to maxed on my trim. I had full fuel and single pilot yesterday and I just held my trim down quite a bit longer to give more rear stick. My motor is dead slow on movements so I think I wasn't getting it far enough back. My plans are microfische so I haven't had a way to look through them to make adjustments. Since my w&b is within the envelope I'm not too worried about it and just have to trim for a longer period before getting to final approach. Seemed fine at KY dam when doing this. It's more pitch than I need on final so I just hold a little front pressure with more up trim then in the flare I have plenty of room to pull the stick back.

I haven't seen a 3200 on one of these yet and was just trying to get a feel for your tailwheel location. I agree trim and/or control travel issues are the most likely cause of what you are seeing. The control throw drawing and a good discussion can be found here: viewtopic.php?f=36&t=7954&p=18339&hilit=travel#p18339

I would have liked to have flown over for the gathering but we pretty much had thunderstorms thurs-sat and rain all day yesterday. If the weather had been good I would have had to work Friday and Sat anyway.

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Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson