Time to experiment

[mongo]

I have started building a new engine mount, firewall, and cowling.
I will be moving the thrustline up 8.5 degrees to + 2.5 nose up from -6.5 nose down, which it was before I started. I will also be moving the engine rearward 4.5" , this plus the removal of the starter/flywheel and a catto prop will put my empty cg at 16" or around what a 95hp supercub is.
Just some background info. I have an O-360 cub and the starting cg was 12.4 and the empty weight was 1237 when I started . It is now 1105 and the cg will be 16.0
As you can see below I had to move the horizontal tube connecting the top two engine mounts, and the firewall will have a large box to except the rear accessories.


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[180Marty]

Did you do the welding? Really looks nice.

[mongo]

I did, they are not perfect, but they look a lot better than any of the piper welds in my fuselage.

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[cgoldy]

Could you make a concave firewall?

[mongo]

It will have to be a box to clear the V, it has to go back 4"

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[D.A.]

Cool project. Sorry, I got to the party late - can you elaborate on what you're doing. Looks interesting. Please post pics and updates as the project progresses. Parallel valve 360?

Good on 'ya.

[mongo]

Yes on the O360
Should have the fire wall completed tomorrow.
I am most interested in the 2 degree nose up thrustline.






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[D.A.]

How much weight do you think you saved when you removed the original generator with all the attach bracketry and went to the little permanent magnet alternator?

[mongo]

I had an automotive style alternator, but an old style bendix starter.
starter flywheel and alt. 28lbs and almost as big of a change in cg as the engine mount will be.
and I actually really like hnd proping.

[NimpoCub]

Interesting (& ballsey) to tip the thrustline up 2*. Are you chasing STOL or speed?
Isn't it great to not be tied up by cert?
Good on ya!

[mongo]

STOL
No reason to look for speed in a cub
Everyone raves about going from nose down to zero so I figure I will test a bit of nose up. It will reduce the amount of nose up trim/elevator needed so the tail will be fighting the wing less. If I have no high speed nose down trim issues and I like the slow speed flight benifits I will continue testing more angle.

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[Dave Calkins]

Mongo, cool project. I am with you on what your empty CG change should do to slow flight performance.

What is your wing angle of incidence? (straight edge across bottom of spars at wing root relative to firewall, and relative to landing gear "bay" of fuselage)

Thanks for sharing!

[benflyn]

As your speed increases the aoa decreases, so trimmed out in cruise with the +2.5 deg on the engine, the trust line of the engine might be near 0.

[mongo]

Pictures of the firewall mod.
If this fits I will be making a new on out of CP2 Ti.

I will get the wing info for you Dave, but I have a Riblett airfoil not a USA35

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[mongo]

Wing incidence is 3.85 vs. the firewall.
And it is a 63" Riblett

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[Bobby Breeden]

Bravo, I am happy to say that you will be pleased with your CG change. I bet you will feel that extra engine incidence on take-off as it pulls you into the air.

Bobby

[mike mcs repair]

makes me get thinking on an inflight adjustable mount again, just need a guinea pig.... well and seeing the F-22 do it's thing this weekend...
hinge it at top(since mags and such are there),
maybe make the new lugs solid and thread them like nuts for bolt through fiewall & safety bolt on cabin end...
cowl & rails attach to engine mount, not firewall so the follow engine as it moves...
maybe a small hyd ram or two at bottom and small ski pump, but pump must not have a free flow position, maybe need a machanical 'lock' for once you position it?...
or a jackscrew set up...
muffler and tail pipe might need to point forward more if you go down more..
you could even have a nice indicator cable like the trim indicator....

[skukum12]

Look up Mike Skup in the dictionary and you will see "stinkin' genious' and 'not so mad scientist.' Keep on keepin' on MCS!!

[sierra bravo]

Centralized mass is a worthy pursuit. Reduce the divergence of moment and arm from the fulcrum. It isn't necessarily about CG. The thrust line thing? It'll be interesting to find out. Potential gains may be countered by losses in other parameters. Where a guy's point of compromise lies is subjective.

On the theoretical side, re: adjustable motor mounts, somebody may as well experiment with a helicopter's cyclic system on a forward facing propellor. Vectored thrust on a fixed wing propellor driven airplane. There's one to daydream about.

[Ursa Major]

On the theoretical side, re: adjustable motor mounts, somebody may as well experiment with a helicopter's cyclic system on a forward facing propellor. Vectored thrust on a fixed wing propellor driven airplane. There's one to daydream about.

There is always this: V 22a.jpgV22 c.jpg

[sierra bravo]

There is always this: V 22a.jpgV22 c.jpg

How many R44s can a guy buy for the price of one tilt rotor?

( I googled the Bell Augusta civilian tilt rotor. Going now for $14 million. That's what, about 28 new R44s? )

Back to the topic, I'm always interested in why guys do mods to airplanes. It seems that some guys like to do thing TO airplanes. I prefer to do things WITH airplanes. No criticism, just observation. I no longer care to turn wrenches. I prefer to turn the key and go.

[Ursa Major]

I watched this Osprey for quite a while when he came into KCOE earlier this month. While it was impressive (speed wise) I was surprised at how small it seemed compared to a CH-47. Less capacity and about double the cost of a heavy lift helicopter. I'm all for the Marine Corps getting the tools they need, but I still wonder about the utility of the V-22.

[Dave Calkins]

Centralized mass is a worthy pursuit. Reduce the divergence of moment and arm from the fulcrum. It isn't necessarily about CG.

Stewart, centralized mass is a worthy pursuit, for certain. It gives snappy handling and quicker spin-recovery.

But also, moving the empty CG aft has been proven to open the slow-end of the flight envelope of Cub-type aircraft. In this case, it IS about CG

[sierra bravo]

If it was all about CG the kick-ass STOL mod would be to fly from the back seat.

No matter to me. I'm just a lowly Cessna driver. A happy one at that.

[sierra bravo]

So you aerospace engineer types are called upon again to correct me WHEN I'n wrong.

Let's make a teeter todder with perpendicular boards to make an airplane form and support it under the balance point. Leaving the representative "wings" alone let's add a hundred pounds at each end of the represented "fuselage". The balance remains the same. The CG, if you will. Now let's put a very accurate set of scales to detect the vertical weight, lateral deflection, and torque at the supporting base. For theoretical discussion let's assume that supporting structure is very thin. If I grab the tail and yank it up is there a detectable change in the supported weight? Deflection? What if the wings encounter disproportionate resistance either vertically or laterally. Is there a measurable change in weight, deflection, or torque at the base? Now let's reconfigure the two sacks of weight by moving them toward the balance point. Same gross weigh. Same CG. How would we expect the measured changes in weight, deflection, and torque to be different with the centralized mass (same CG)? Wouldn't any measurable increase in weight, deflection, and torque represent forces that are detrimental to flight? At least in the STOL category?

Moments and arms.

[Rob]

Wouldn't any measurable increase in weight, deflection, and torque represent forces that are detrimental to flight? At least in the STOL category?

Moments and arms.

Absolutely! And not only in STOL, but also on the opposite end of the spectrum. Which is why these cubs, and our Cessnas BTW, fly so much better with the CG aft.

You see, our tail is 'flying' down in as much as the engine, prop etc is 'pulling' down on the other side. The wings are tasked with lifting both of these downers... By sliding the CG aft, yet keeping the weight the same, the tail now needs to fly less down, thereby leaving less 'down' for the wing to lift.

Looks to me like you answered your own question

Works really well and gets a whole lot better the more aft you go... Right up until it gets really bad...

Take care, Rob

[mongo]

Why the canard is so efficient.

[sierra bravo]

Rob,

It isn't that simple. You're simply defining that your ideal balance point is aft of datum for your typical airspeeds. There's no secret there. The moment and arm exercise remains valid.

I guess another layer in the discussion is the relationship between center of gravity, which we control, and center of lift, which we do not.

[Rob]

Rob,

It isn't that simple. You're simply defining that your ideal balance point is aft of datum for your typical airspeeds. There's no secret there.

I probably should not have entered this conversation, as I am not an engineer type, and have nothing but seat of pants to make these claims is with... But... I believe you may have misstated this as well, because it's not just the slow end. Remember , the planes in question here also tend to fly faster with the aft CG as well.

I guess another layer in the discussion is the relationship between center of gravity, which we control, and center of lift, which we do not.

Actually, I disagree here too pretty sure we change the center of lift every time we pull flaps / slats, etc... Although I also believe it depends what kind of wing we started with, and what we have for flaps, in respect to where and how much that change is.


Engineer types? What say you?

BTW SB, Any chance you will replace the '12 with an experimental?

Take care, Rob

[Rob]

I watched this Osprey for quite a while when he came into KCOE earlier this month. While it was impressive (speed wise) I was surprised at how small it seemed compared to a CH-47. Less capacity and about double the cost of a heavy lift helicopter. I'm all for the Marine Corps getting the tools they need, but I still wonder about the utility of the V-22.

Hi mike, I find ospreys intimidating to fly around while in the cub, and since I was in the only squadron in the Marine Corps to have '46s, 53's, and 53E's, at the same time,I always kinda resented them.

Having said all that, I just thought while I was being antagonistic on this thread I would remind you that the CH46 ( the bird the Osprey is supposed to replace ) is not a heavy lift like the CH47 or CH53. It looks a ton like a 47, but it's pint sized in comparison... As in less than half the GW... It is a Medium lift helicopter, and a pretty darned good one

Take care, Rob

[Ursa Major]

Having said all that, I just thought while I was being antagonistic on this thread I would remind you that the CH46 ( the bird the Osprey is supposed to replace ) is not a heavy lift like the CH47 or CH53. It looks a ton like a 47, but it's pint sized in comparison... As in less than half the GW... It is a Medium lift helicopter, and a pretty darned good one

Take care, Rob

Thanks for the clarification Rob, I didn't realize the 46 and 47 were so different. I was confused since I saw a CH-47 land here the week before and noted the much larger apparent size than the V-22.

[mongo]

New pics, firewall complete.
Now I am just waiting on Backcountry cubs to send me my cowling kit.





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[mongo]

I have finished the cowling and have started on a new exhaust system I had Burn's stainless design using their proprietary software.






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[Bobby Breeden]

Looks great!!! That exhaust and welding work looks really well put together. Moving the C.G. aft will lower your stall speed and give you a quicker responding plane, as I am aware you already know. How soon until the maiden flight? I am really curious how that positive thrust-line angle will work out.....

I hope it is even better than you hoped it to be.

Bobby

[mongo]

My goal is to make it to John Graham's flyin.....
The header is going to be a tight fit with the short engine mount but it will be a nice power gain from my old Sutton system I estimate 15hp.
I also made a larger carbbox as I found the stock unit was restrictive, it is not deep enough. I made a series of static pulls with and without the air filter and with and without the stock airbox, I found that without the filter the airbox is still a restriction about 30 revs the new unit is not and Yardley has a drop with the filter installed.
The new one is 4.5" deep and all of the air filter is used unlike the stock unit.

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[Superpacer]

Mongo,
All looks great! You have been busy. I'm also interested in the relative restriction that comes from stock size airboxes. Do you have a photo of your prototype air box. Did you keep the carb flange - drop section (about 3/4") where the "X" vaines straighten out the air flow into the carb? Or did you deepen the whole airbox and bolt it flush to the carb base? I'm building a new cowl, airscoop & airbox for my 180 Pacer and am always looking for data that comes from actual testing, etc. Again, great looking project.
John, Utah Pacer

[mongo]

I deepened the entire box by bolting it to the carb and adding to the bottom.
No need for the vanes the butterfly will straighten the airflow, my air cleaner flange is also different, I can send you the CAD drawings I made but I don't think it will fit a stock cub.

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[Superpacer]

Mongo,

Thanks for the quick response, the CAD file would be great. The one photo above looks like you are using a flat aircleaner, so am I, a Donaldson one, next size larger than the stock one used on O-320 Pacers etc. The attached PDF is a box that came with my engine STC and I'm planning to enlarge it a bit.
Thanks for the info, if you get a chance, please send the CAD file to john.f.kobbeman@boeing.com

John

[mongo]

I will send it Monday
I am using a round K&N filter, I had the flat filter before this change, the new filter mounting plate is not shown in the pic.

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[mongo]

Here is the exhuast design it is for a stock O-360 only