Avionic compartment weight to change CG

[PilotX]

Good morning. I can't remember what day it is or whether I have asked this question already. My initial idea was to put 6 extra pounds of Charlie weights because that is the most bang for my buck but Mooney engineers didn't want to touch that idea.

My avionics compartment is empty. Because of the forward CG shift I put 50lbs of sand in the luggage compartment. That would equate to about 35lbs of fixed weight in the avionics compartment. Seem like owner level stuff if I can fabricate a box with some weight and attach it using the existing holes on the avionics tray. Saving 15lbs and an aft CG = 2kts 

Thoughts? Be gentle.

[N201MKTurbo]

35 Lbs seems like a lot to put there, but what do I know.

A friend of mine got FAA approval to put up to 110 Lbs in the tail of a rocket. He made nice drawings, hired a DER for an approval and it slid right through the FAA with no issues. He has said he would do another for about $5K. If you wanted to pursue it yourself, He may be willing to sell the drawings and the DER approval. These were replacement charlie weights in the back of the tail. There was additional structure and mounting brackets added. Because it is a different model, it would probably need another DER approval.

[LANCECASPER]

2 hours ago, PilotX said:

Good morning. I can't remember what day it is or whether I have asked this question already. My initial idea was to put 6 extra pounds of Charlie weights because that is the most bang for my buck but Mooney engineers didn't want to touch that idea.

My avionics compartment is empty. Because of the forward CG shift I put 50lbs of sand in the luggage compartment. That would equate to about 35lbs of fixed weight in the avionics compartment. Seem like owner level stuff if I can fabricate a box with some weight and attach it using the existing holes on the avionics tray. Saving 15lbs and an aft CG = 2kts 

Thoughts? Be gentle.

There's a big difference in the eyes of the FAA in carrying 50 pounds of "cargo" in the luggage compartment compared to "installing" a box. From a practical point of view if you need the extra useful load it's a lot more flexible to remove the 50 lbs. of cargo. Plus the cargo could be something easier to work with than a bag of sand, such as a couple of 25 lb dumbbell weights, strapped down. 

https://www.walmart.com/ip/CAP-Barbell-25lb-Rubber-Hex-Dumbbell-Single/397310225?wmlspartner=wlpa&selectedSellerId=0&wl13=508&adid=22222222277397310225_117755028669_12420145346&wmlspartner=wmtlabs&wl0=&wl1=g&wl2=c&wl3=501107745824&wl4=pla-294505072980&wl5=9028241&wl6=&wl7=&wl8=&wl9=pla&wl10=8175035&wl11=local&wl12=397310225&wl13=508&veh=sem_LIA&gclid=Cj0KCQjwlumhBhClARIsABO6p-xIAkV3CbkTKMPNv8QOYOaW_l6qb8UhoEcZCXa9EkxNVey9FDxzx20aApHNEALw_wcB&gclsrc=aw.ds

[Niko182]

3 hours ago, PilotX said:

Good morning. I can't remember what day it is or whether I have asked this question already. My initial idea was to put 6 extra pounds of Charlie weights because that is the most bang for my buck but Mooney engineers didn't want to touch that idea.

My avionics compartment is empty. Because of the forward CG shift I put 50lbs of sand in the luggage compartment. That would equate to about 35lbs of fixed weight in the avionics compartment. Seem like owner level stuff if I can fabricate a box with some weight and attach it using the existing holes on the avionics tray. Saving 15lbs and an aft CG = 2kts 

Thoughts? Be gentle.

what did your CG and empty weight end up at?

Edited April 15, 2023 by Niko182

[PilotX]

10 hours ago, Niko182 said:

what did your CG and empty weight end up at?

41.86 - 2315 - UL 1053. 

@N201MKTurbo How much weight do you think was in (my now empty) avionics bay? Stormscope (7#), signal generator (14#), static inverter (.3#), miscellaneous trays for all of the equipment. Also replaced the old ELT with something a few pounds lighter, not to mention what had to be 1.5 tons of cannon plugs.

@LANCECASPER I wasn't thinking entirely practically. I consider the sand, which is a gym bag, more or less permanent. I thought was I would gain 15# overall which is currently taken up by deadweight, if I put something in a space that already had carried around 25#.

[N201MKTurbo]

The weight of all that should be in your weight and balance records, but just eyeballing it, I doubt ti all weighs more than 10 Lbs.

[Niko182]

Going through the entire hassle of hiring a DER and all, might just be easier to get an MT prop, or the acclaim type S prop might knock off 5 to 10 pounds aswell.

[PilotX]

8 hours ago, N201MKTurbo said:

The weight of all that should be in your weight and balance records, but just eyeballing it, I doubt ti all weighs more than 10 Lbs.

Stormscope (7#), signal generator (14#), static inverter (.3#), miscellaneous trays for all of the equipment. I looked up the weights when I removed them.

That's 21.3

[PilotX]

5 hours ago, Niko182 said:

Going through the entire hassle of hiring a DER and all, might just be easier to get an MT prop, or the acclaim type S prop might knock off 5 to 10 pounds aswell.

Gained 78.5# UL (already been argued) during the 2021 avionics install but the CG shifted 2.24" (44.1 - 41.86). I am certain the 2022 avionics upgrade was a wash W&B-wise. An MT prop might be the only thing that saves me (emotionally not financially). I'll do the weight because getting approval for an extra 6# of junk in her trunk sounds as about 1/3 as expensive as a beautiful four bladed propellor but with more bang for my buck. Hugz Mooniacs.

The avionics rack.

[LANCECASPER]

2 hours ago, PilotX said:

Gained 78.5# UL (already been argued) during the 2021 avionics install but the CG shifted 2.24" (44.1 - 41.86). I am certain the 2022 avionics upgrade was a wash W&B-wise. An MT prop might be the only thing that saves me (emotionally not financially). I'll do the weight because getting approval for an extra 6# of junk in her trunk sounds as about 1/3 as expensive as a beautiful four bladed propellor but with more bang for my buck. Hugz Mooniacs.

The avionics rack.

Just buy back an inop WX-1000 Stormscope processor (6.5 pounds) and use the same mounting holes and call it a day.

[N201MKTurbo]

We all know the biggest bang for the buck, CG wise, is putting the weight as far back as possible. This will give the biggest CG change with the smallest weight gain. The Charlie Weight thing is your best bet. 

[Steve Dietrich]

After the MB conversion to my 231 I added a Charlie weight which would stay within  the envelope with me alone in the left seat and a 180 pounder alone in back. 

For a long flight alone or with 1 in the front I would carry two  2.5 gallon water jugs in the baggage compartment as added ballast  and a nice thing to have should I end up off field.  Unlike carrying lead ballast in the baggage compartment I could dump the water on the ramp if I was carrying folks or cargo .