Tail Wheel Colt Weight and Balance

[txfirefighter628]

Need some help on weight an balance for my colt. It has the tailwheel conversion that was done under STC SA45RM in 1987, which is now owned by Univair. I don't have any paper work for the STC other than the 337 showing it was installed. I called Univair and they wont give me anything with out buying the STC again for $535.78. What I really need to see if if the CG envelope changes with the tailwheel conversion. I wouldn't think that it would but would like some verification.

If I use the original Piper PA-22-108 chart I get an empty weight CG of 72" which is within specs. The problem is when I add pilot, passenger, fuel and baggage weight I go over the aft CG limit if I put more then 64 lbs in the baggage which is rated for 100 lbs.

When I weighed it I used the seat tube with a plum bob from the door post hole and also verified that the tail post and firewall were level. The tail was weighed at the tail spring to fuselage bolt.
Right main - 511 X 62.5 = 31,937.5
Left main - 505 X 62.5 = 31,562.5
Tail - 64 X 223 = 14,272
Total - 1080 X 72.01= 77,772 with 5 qts oil, fuel system empty



The center of the main gear axle is now 2.5" aft of the wing leading edge. The tail spring bolt is 163" aft of the wing leading edge.



View attachment PA-22-108 TCDS Weight and balance.pdf

 

[tnowak]

I would think the C&G position would have changed, but still be within the permitted range, as you have removed the weighty (?) nose wheel and support assembly.
That would most likely mean you have less payload to play with aft of the pilot and crew..
TonyN

 

[RickF]

You say that the tail was weighed at the tail spring bolt which is 163" aft of LE. But in your math you multiplied 64 times 223 for Tail.
What are those? I assume 64 is weight but what is 223?

As far as the STC, you can get all of the paperwork that the FAA has by ordering it on a disc or paper from them.
There may have a copy of the STC in it.

Good luck.

Rick

 

[txfirefighter628]

You say that the tail was weighed at the tail spring bolt which is 163" aft of LE. But in your math you multiplied 64 times 223 for Tail.
What are those? I assume 64 is weight but what is 223?

As far as the STC, you can get all of the paperwork that the FAA has by ordering it on a disc or paper from them.
There may have a copy of the STC in it.

Good luck.

Rick

The datum line is the front of the spinner. The leading edge of the wing is 60” aft of the datum line. So 60”+163”=223” is where the tailwheel spring bolt is from the datum line.

i have the FAA cd and a records search from aerospace reports. No STC data there other then the 337s which just say what was installed but no specific STC instructions.

 

[dgapilot]

Is there a required Flight Manual Supplement for the tailwheel STC? If there are any CG changes, they would be there. If there is no supplement then there are no changes from the stock airplane. Unless you need a big tailwheel, simplest solution is to go with a 6” tailwheel to reduce weight at the extreme aft end of your airplane.

Just looking at your numbers, assuming you only have one tank and 200 lb pilot and passenger, the most baggage you could carry is about 60 lbs without exceeding your gross weight (I didn’t check envelope), if you have 2 tanks and fill them you can’t even carry two 200 lb adults.

Sent from my iPad using Tapatalk

 

[txfirefighter628]

Is there a required Flight Manual Supplement for the tailwheel STC? If there are any CG changes, they would be there. If there is no supplement then there are no changes from the stock airplane. Unless you need a big tailwheel, simplest solution is to go with a 6” tailwheel to reduce weight at the extreme aft end of your airplane.

Just looking at your numbers, assuming you only have one tank and 200 lb pilot and passenger, the most baggage you could carry is about 60 lbs without exceeding your gross weight (I didn’t check envelope), if you have 2 tanks and fill them you can’t even carry two 200 lb adults.

Sent from my iPad using Tapatalk

Not sure on a flight manual supplement, that is why I'm asking on here. There have been 100's if not thousands of Tripacers or Colts converted using this STC. Was hoping someone on here may have more info. I have a stock size Scott 3200 tailwheel.

I have two 18 gallon tanks but only fill one for most flights. I would like to be able to travel solo with full fuel and 100 lbs baggage.

 

[dgapilot]

Just looked up the STC on DRS, you are required to have a Flight Manual Supplement per the STC. If you don't, then it is not legal to operate the aircraft. Unless you can find a copy of the FMS it looks like you need to write a check to Univair!

 

[28a]

I used the Univair STC to convert my PA-22-836 about 5 years ago. The 62.5 main gear calculation caught my eye. The STC weight and balance sketch shows the wheel centerline in line with wing leading edge, with the airframe leveled. That is exactly how mine was. Just for fun, I recalculated my W&B assuming that I did not correctly level the airframe. The result moved the cg 2.3” rearward. Assuming the WLE is 60” aft the Datum like mine was, I wonder where the difference is. Since the Tri Pacer landing gear mount becomes the new rear mount in the conversion, It would be hard to be 2.5” off. Were things like leveling points changed, were gear mounts or wing locations changed from the Tri Pacer to the Colt? Just some thoughts.

Phil

 

[txfirefighter628]

Just looked up the STC on DRS, you are required to have a Flight Manual Supplement per the STC. If you don't, then it is not legal to operate the aircraft. Unless you can find a copy of the FMS it looks like you need to write a check to Univair!

I didn't even know you could look up requirements like that for STCs through the DRS, good to know. I just looked all over the internet for the LPC-1033 flight manual supplement for STC SA45RM with no luck. Called Univair and they asked for the serial # to verify and a logbook entry. They said they would mail the flight manual supplement. Last time I called I was only asking for drawings, not a flight manual. By the way the drawings are on the short wing piper club CD, but no flight manual.

 

[txfirefighter628]

I used the Univair STC to convert my PA-22-836 about 5 years ago. The 62.5 main gear calculation caught my eye. The STC weight and balance sketch shows the wheel centerline in line with wing leading edge, with the airframe leveled. That is exactly how mine was. Just for fun, I recalculated my W&B assuming that I did not correctly level the airframe. The result moved the cg 2.3” rearward. Assuming the WLE is 60” aft the Datum like mine was, I wonder where the difference is. Since the Tri Pacer landing gear mount becomes the new rear mount in the conversion, It would be hard to be 2.5” off. Were things like leveling points changed, were gear mounts or wing locations changed from the Tri Pacer to the Colt? Just some thoughts.

Phil

View attachment 23093

That's exactly what I need to see, THANK YOU! Turns out I was not using the correct hole to level with the seat frame and plum bob. I had the tail way to high. If I get the level correct, the center line of the axle matches the leading edge of the wing like yours. I will have to reweigh and calculate.

 

[dgapilot]

I didn't even know you could look up requirements like that for STCs through the DRS, good to know. I just looked all over the internet for the LPC-1033 flight manual supplement for STC SA45RM with no luck. Called Univair and they asked for the serial # to verify and a logbook entry. They said they would mail the flight manual supplement. Last time I called I was only asking for drawings, not a flight manual. By the way the drawings are on the short wing piper club CD, but no flight manual.

The DRS doesn't have all the STCs in pdf format, but the ones that do will tell you in the Limitations section if you need a Flight Manual Supplement. Glad Univair was nice enough to provide the FMS.

 

[txfirefighter628]

Just weighed it again using the plumb bob from the leading edge of the wing to the center line of the axle as level. Empty CG with oil is 70.856 which works out to where I can have 100lbs in the baggage and still be within the CG range. I thought that the original 64lbs i was getting on the tail seamed pretty light.
Right main - 499lbs X 60in = 29,940
Left main - 510lbs X 60in = 30,600
Tail - 72lbs X 223in = 16,056
Total - 1,081lbs X 70.8566 = 76,596

 

[RickF]

Tail - 64 X 223 = 14,272[/U]
Total - 1080 X 72.01= 77,772 with 5 qts oil, fuel system empty

View attachment 23087

Weighing it at the tail spring bolt and then calculating it at the tailwheel just does not sound right to me.
I think the scale should have been under the tailwheel.
With the scale under the spring bolt there is more weight further aft so the scale is going to read higher since it is supporting more forward weight.

Rick

 

[txfirefighter628]

Weighing it at the tail spring bolt and then calculating it at the tailwheel just does not sound right to me.
I think the scale should have been under the tailwheel.
With the scale under the spring bolt there is more weight further aft so the scale is going to read higher since it is supporting more forward weight.

Rick

I didn’t calculate it at the tail wheel. I calculated it at the spring bolt. I have it figured out now. Thank you.

 

[28a]

Just weighed it again using the plumb bob from the leading edge of the wing to the center line of the axle as level. Empty CG with oil is 70.856 which works out to where I can have 100lbs in the baggage and still be within the CG range. I thought that the original 64lbs i was getting on the tail seamed pretty light.
Right main - 499lbs X 60in = 29,940
Left main - 510lbs X 60in = 30,600
Tail - 72lbs X 223in = 16,056
Total - 1,081lbs X 70.8566 = 76,596

I didn’t mean to mislead you on my previous post. I first leveled the airframe using the door frame hole and dimple in the seat cross tube as described in the PA-22 op manual. The wheel being plumb with the wing root was confirmation of the landing gear correct position, not the method to level. Hopefully the two agree. Glad you’re making progress.

 

[txfirefighter628]

I didn’t mean to mislead you on my previous post. I first leveled the airframe using the door frame hole and dimple in the seat cross tube as described in the PA-22 op manual. The wheel being plumb with the wing root was confirmation of the landing gear correct position, not the method to level. Hopefully the two agree. Glad you’re making progress.

Not misleading at all, very helpful actually. I was using the a wrong hole for the top of the plum bob. Once I removed the trim piece I found the correct hole. Once leveled properly with the seat post, the axle lines up with the leading edge of the wing as well. Once I get the data from Univair I will verify that its correct but I'm pretty sure I have it right now.

I was using the trim piece screw hole to the left instead of the level hole that is just a few inches to the right, it was covered by the trim piece.

 

[RickF]

I didn’t calculate it at the tail wheel. I calculated it at the spring bolt. I have it figured out now. Thank you.

What I am saying is the scale needs to be under the tailwheel to get a correct weight for the calculations.
Put the scale under the tailwheel and it is going to be less than at the tailspring bolt.

Rick

 

[Jim Hann]

Rick, it doesn’t matter where the scale touches the airplane as long as the arm is correctly measured/computed. If the Tailwheel weight was lower then the mains would be correspondingly higher, total weight is unchanged. The most important thing for an accurate weight and balance is that the airframe is leveled IAW the manufacturer’s instructions AND the arms are correct. We had to weigh my airplane twice because we had the tail to low the first time. How much? The plum bob from the leading edge was just behind the axle, parallax error viewing the leveling mark on the cross tube. Three sets of eyes and we got it right. The total weight was +/- 1lb, the moment however, way different.