weight and balance

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Kenneth Aydt

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I have a 175 with the Lycoming conversion. the Constant Speed Prop is very heavy and makes the aircraft nose heavy. Has anyone gotten a Field Approval to add weight in the tail section to compensate?
 
Or just put a case or 2 of oil in the baggage area after you determine how much weight you need for correct W&B and CG.

Not in the tail, that impacts the structural integrity.
 
I recently flew with a pilot in his 175 with a Franklin engine/constant speed prop. It was so nose heavy that you ran out of elevator when you rounded out to land. We did a W & B & added two cases of water in the baggage compartment that weighed 104#. It made a huge difference in the handling characteristics of the airplane. With the water in the baggage compartment the CG was right in the center of the chart.
 
Kenneth Aydt said:
I have a 175 with the Lycoming conversion. the Constant Speed Prop is very heavy and makes the aircraft nose heavy. Has anyone gotten a Field Approval to add weight in the tail section to compensate?
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Not enough info. Is this for the empty weight or the loading weight? As mentioned, if for the loading weight adding temporary ballast in the baggage area will take care of things legally. However, if it is for the empty weight or you want a more permanent ballast solution then you shouldn't have a problem getting a field approval depending where you want to mount the ballast. Curious, what 360 mod do you have? I know of 2 175s with 360s and CS prop that don't have weight issues for their ops.
 
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Doc Holliday said:
Why not just place some weight in the baggage compartment?
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Why give up weight carrying capacity of up to 100 lbs when a 4 or 5 lb weight in the tail section will suffice?
murphey said:
Or just put a case or 2 of oil in the baggage area after you determine how much weight you need for correct W&B and CG.

Not in the tail, that impacts the structural integrity.
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seriously? A 4 or 5 lb weight in the tail will impact structural integrity ? This is a Cessna 175, not a wood s as d fabric home built
 
Kenneth Aydt said:
Why give up weight carrying capacity of up to 100 lbs when a 4 or 5 lb weight in the tail section will suffice?

seriously? A 4 or 5 lb weight in the tail will impact structural integrity ? This is a Cessna 175, not a wood s as d fabric home built
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If there’s a university with either an aerospace engineering dept or mechanical engineering dept in your area, please visit and discuss your experiment. Another option, contact the engineers at Cessna and discuss same.
 
murphey said:
If there’s a university with either an aerospace engineering dept or mechanical engineering dept in your area, please visit and discuss your experiment. Another option, contact the engineers at Cessna and discuss same.
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Pretty standard to use permanent ballast per page 7-8 of https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/media/FAA-H-8083-1.pdf with the usual paperwork for a minor mod. My experience of universities is that most of the staff would know diddly squat about this.
 
Mooney did this with a few of their big engine models, they call them Charlie weights.
Might want to find out how they did it and using same method should make approval process easier.
 
Some Swifts use permanent ballast.

235 Pawnees have the battery just in front of the tail wheel.

Do you have lightweight Starter and Alternator?

I think the 175 has the battery aft of baggage comp?

If not; consider relocating there.

Following Cessna’s method for similar aircraft would aid in Approval Process.
 
Navions typically have 9 or 12 lbs of weight at the very far end of the tail to keep the CG off the forward limit. Some have moved the battery (normally in the baggage area just behind the rear seat) further back into the tail cone as well.
 
The aircraft mentioned were designed for that - there’s a diff in just adding weight @ the end of a lever. True @ 1 G no problem, @: 3.8 now you have a whole another level of stress @ the end of that lever. But it might work.
 
Kenneth Aydt said:
Why give up weight carrying capacity of up to 100 lbs when a 4 or 5 lb weight in the tail section will suffice?

seriously? A 4 or 5 lb weight in the tail will impact structural integrity ? This is a Cessna 175, not a wood s as d fabric home built
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Duh?

Put the temp ballast there for everyday flying, and if you are going somewhere and need the load, remove the temp ballast and replace with baggage.

Otherwise, your airplane has another issue, and the additional weight in the tail is only a bandaid to cover for the real problem.
 
Kenneth Aydt said:
A 4 or 5 lb weight in the tail will impact structural integrity ?
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It's not about the weight. Even on an aircraft larger and more robust than your 175 it would require approved data to install as it's considered a major alteration per Part 43. Cessna did offer tailcone ballast kits for some models but regardless anytime you bolt in ballast it becomes part of the certified empty weight and you could cause a future problem on the other side of the CG envelop. However, for max flexibility on nose challenged Cessnas I usually recommend installing an extended baggage compartment kit and keep a fly-away kit of the appropriate weight stuffed in the back of it.
 
murphey said:
Not in the tail, that impacts the structural integrity.
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That would be my fear as well. That said, a pretty well-known aerobatic pilot back in the 1960s told me he added 10 pounds of weight in the tail of his Citabria to make it snap roll better.
 
I carry a toolbox in the baggage area, along with a case of oil, spare parts, etc.

Us old farts with old airplanes do this sort of thing.
 
My Sport has a balance weight in the tail. I think Beech had different weights available. Mine is 8 to 10lbs I think. Of course the manufacture did it so no 337 needed. The Sport is nose heavy.

If it were me I would do as others have said and load the baggage compartment until you find the happy spot. As @Doc Holliday mentioned, might be a good time to check rigging.
 
Doug Reid said:
I carry a toolbox in the baggage area, along with a case of oil, spare parts, etc.

Us old farts with old airplanes do this sort of thing.
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I can just picture it now...

"Can't depart because some part under the cowling broke and leaked a bunch oil"
followed by...
"Can't depart because we installed the spare parts and used the case of oil and now the CG is too far forward"
 
asicer said:
I can just picture it now...

"Can't depart because some part under the cowling broke and leaked a bunch oil"
followed by...
"Can't depart because we installed the spare parts and used the case of oil and now the CG is too far forward"
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Ok...I have been carrying tools, spare parts, oil, etc. for 50 years. Not only do I carry tools for my own use, but have helped others with issues while attending air shows and fly-ins.

I am A&P/IA.

My W&B is just fine with or without tools and such. If you fly a Classic or Antique, you better keep a few spares just in case. It is a long walk home.
 
asicer said:
I can just picture it now...

"Can't depart because some part under the cowling broke and leaked a bunch oil"
followed by...
"Can't depart because we installed the spare parts and used the case of oil and now the CG is too far forward"
Click to expand...


A thoughtful pilot would fill those empty bottles and boxes with sand or water or something and make it work! :)
 
Doc Holliday said:
Another culprit is aircraft flight control rigging. Has the elevator trim rigging been checked? How about elevator travel?
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Yep... all rigging has been checked. This is a well known and well documented issue with 175's that have had the lycoming mod with CS prop...
 
..umm, what's the difference of adding 5 lb in the tail versus the elevator constantly pushing down with an extra 5 pounds of force..?

Our GA planes already have such pathetic useful loads that sacrificing 100 lb seems like a complete travesty
 
Tantalum said:
..umm, what's the difference of adding 5 lb in the tail versus the elevator constantly pushing down with an extra 5 pounds of force..?

Our GA planes already have such pathetic useful loads that sacrificing 100 lb seems like a complete travesty
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What sacrifice? When you need the load, omit the ballast.
 
Tantalum said:
..umm, what's the difference of adding 5 lb in the tail versus the elevator constantly pushing down with an extra 5 pounds of force..?
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You're asking what's the difference between stability and trim. The most discernable differences are the amount of control surface deflection necessary to trim and the way the airplane behaves when it's disturbed from the condition you've trimmed for.

Nauga,
and his nose-up control power
 
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Half Fast said:
When you need the load, omit the ballast.
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nauga said:
You're asking what's the difference between stability and trim. The most discernable differences are the amount of control surface deflection necessary to trim and the way the airplane behaves when it's disturbed from the condition you've trimmed for.
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Thanks, I hadn't fully thought this one true
 
nauga said:
You're asking what's the difference between stability and trim. The most discernable differences are the amount of control surface deflection necessary to trim and the way the airplane behaves when it's disturbed from the condition you've trimmed for.

Nauga,
and his nose-up control power
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Well put Nauga...As it is now, I have to trim almost 1" up on my trim wheel to maintain straight and level flight. This has got to cost me a lot in range of control, drag, and accompanying fuel consumption/range.
 
Half Fast said:
What sacrifice? When you need the load, omit the ballast.
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You pay for every pound you carry in fuel/airspeed/range... that's why.

4 lbs in the tail (if approved) is better than carrying 100 lbs in the baggage compartment all the time.
 
Kenneth Aydt said:
Why give up weight carrying capacity of up to 100 lbs when a 4 or 5 lb weight in the tail section will suffice?

seriously? A 4 or 5 lb weight in the tail will impact structural integrity ? This is a Cessna 175, not a wood s as d fabric home built
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Good grief! Let's do a bit of math, shall we?

upload_2021-9-21_17-31-29.png

100 pounds at station 108, the farthest-aft point of the baggage compartment, gives us a moment of 10,900 inch-pounds.

A five-pound weight, as you recommend, at station 228.68, the tailcone bulkhead, the farthest-aft point we can attach anything, gives us a moment of 1143 inch-pounds, or about one-tenth of the CG correction of what the 100-pounder will do. We'd need 50 pounds back there. Not much room for that, even if it's all lead. That bulkhead is only about three inches wide, and maybe there's four inches of vertical space. The lower elevator cable runs through it. And it would be permanently stuck there, making a problem if we wanted to load the airplane with a bunch of baggage or freight or something. You'd lose 50 pounds of useful load (can't throw it out) and the CG might end up outside the aft end of the envelope.

Water will freeze in cold weather, splits the containers, and then saturate everything once it melts.

In the flight school we made up ballast bags. We used old truck inner tubes, sections about 30" long, wired one end shut, filled them with rice, and wired the other end shut. Not going to freeze. Easy to tie down. And if we were forced down in the middle of nowhere on some long cross-country into the sparsely-settled areas (lots of that up here) we had lots of food. Just need some water, a container from the survival kit, and a fire. It was an idea from one of our MAF guys that had flown in Africa, where there are plenty of places to disappear if something quits.
 
Dan Thomas said:
Good grief! Let's do a bit of math, shall we?

View attachment 100294

100 pounds at station 108, the farthest-aft point of the baggage compartment, gives us a moment of 10,900 inch-pounds.

A five-pound weight, as you recommend, at station 228.68, the tailcone bulkhead, the farthest-aft point we can attach anything, gives us a moment of 1143 inch-pounds, or about one-tenth of the CG correction of what the 100-pounder will do. We'd need 50 pounds back there. Not much room for that, even if it's all lead. That bulkhead is only about three inches wide, and maybe there's four inches of vertical space. The lower elevator cable runs through it. And it would be permanently stuck there, making a problem if we wanted to load the airplane with a bunch of baggage or freight or something. You'd lose 50 pounds of useful load (can't throw it out) and the CG might end up outside the aft end of the envelope.

Water will freeze in cold weather, splits the containers, and then saturate everything once it melts.

In the flight school we made up ballast bags. We used old truck inner tubes, sections about 30" long, wired one end shut, filled them with rice, and wired the other end shut. Not going to freeze. Easy to tie down. And if we were forced down in the middle of nowhere on some long cross-country into the sparsely-settled areas (lots of that up here) we had lots of food. Just need some water, a container from the survival kit, and a fire. It was an idea from one of our MAF guys that had flown in Africa, where there are plenty of places to disappear if something quits.
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That math is correct, but if you assume the CG is at the 44 inch station, it would be 100x68=6800 vs 5x184=920 for the actual effect at/on CG.
 
MauleSkinner said:
That math is correct, but if you assume the CG is at the 44 inch station, it would be 100x68=6800 vs 5x184=920 for the actual effect at/on CG.
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Cessna uses the lower front face of the firewall for the datum for all CG calculations (Station 0), with the CG (empty) normally being at around 37 or 38 inches. You have to use the initial empty weight and moment to get the actual CG shift. I just pointed out that the moment of a five-pound weight, as far back as it could go, had a small fraction of the moment of a 100-pound weight in the aft end of the baggage compartment. The tail is just not that far aft of the baggage compartment, that's all.

The CG range for a 1963 172D is from about 36 inches to about 47.3 inches aft of datum. The 175 will be pretty close to that.
 
I learned this a little different but end result would be about the same.

From memory ; I think it’s from AC 43.13-1 ( CAM 18 in my case)

It sounds like you are forward of the Forward Limit (FL) when loaded.

If we calculate the distance from the FL to the Loaded CG and multiply

by the Loaded Weight We then have the Nose Heavy Moment ( NHM).

The FL is the fulcrum here.

We want to move the CG aft so we must have Tail Heavy Moment (THM) that

equals the NHM.

Since we know the THM needed; we can divide by the Arm from the FL

to the proposed ballast location to obtain the amount of Weight needed.

Since this changes the EWCG; recalculating it with the ballast will assure accuracy.


btw. It seems that per TCDS some aircraft had a movable ballast system optional.

I believe it was called a CG Adjuster or similar.
 
Our 57 172 is nose heavy as well. We put 100 pounds of rocks in the back. We bought a couple of tool bags from Harbor Freight and put the rocks in there so we can take one or both out easily if we have a rear passenger to make the W&B work. The other thing we do to get it in the envelope if necessary and you have heavier people up front is have the passenger sit with the seat back several inches.
 
Now, if this was a taildragger we could just adjust it using a lead tailwheel.
 
If this happened to the crew of a reality tv car show, they'd cut the aircraft in two just in front of the tail, and lengthen it about 8". You'll need some aluminum tubing, a mig welder with a spool gun, and a LOT of high speed duct tape.

I'd try a 25lb barbell weight in the baggage compartment. It might improve things enough that it flies fine. Or 50. I doubt you'd notice the performance hit from either. If, on the other hand, you put the weight in the tail, you'll be reducing your limit for the baggage compartment by 100lbs, unless your baggage compartment is weight vs cg limited.
 
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