Over-square Cruise Power Settings and Slipping with Flaps Husky A-1

[Alex McCulloch]

I've been a lurker for a while on here, thanks for reading my novel in advance. I've had my Husky for a few months and about 50 hours now and I thought I'd post up with two topics I've been curious about. I'd love to hear your opinions / impressions, especially the old-school heads on here with early wing experience.

Background

Airplane:
1995 Husky A-1 (old wing, old flaps)
180-HP O-360
Hartzel Metal Blade Prop 80"
Relatively Stock Example
Thomas's SGSs are the only real mod.
26" Goodyear Tires (23" in actual diameter)
29" ABWs on extra wheels I haven't mounted yet.

Pilot:
16,000 TT (ATP, CFI, CFII, MEI, CSEL) in a wide variety of aircraft types. 600hrs hang glider time not included (and as many off-airport landings).
200 Tailwheel Time, split evenly between STOL type aircraft (Piper J-3, PA-12, Husky A-1) and higher-performance experimentals (Mustang II, RVs, Thorpe T-18).
I am certainly not the ace of the base, but I'm a competent tailwheel pilot.
My attitude is one of humility; I'm keen on learning, improving and benefiting from those with more or less experience than myself.

My mission is a mix of cross-country operations and some back country stuff, virtually all of it in the high density altitudes of Colorado. I've flown the Husky through MT, ID, UT, and CO landing at medium-difficulty backcountry airports and other spots along the way.

Over-Square Cruise Power Settings

I've researched the posts on here about cruise power settings and running over-square seems to be the consensus. With the exception of a turbocharged platform, in the light training environment, I was always taught and have taught my students to keep your power settings under square to minimize strain on the engine. The consensus on here for the Husky is that going slightly over square is more efficient and keeps the engine better under load on descent. Experimenting with my own airplane, I came up with these numbers.

Conditions:
OAT: 60 degrees
Altitude: 6000'
Full Tanks
2 Passengers
At Max Gross Weight: 1800lbs (I'm an early A-1 without the 90lb mod).

Under Square:
RPM: 2350
MP: 20”
FF: 6 gph
IAS: 95 mph
CHT: low 300s

Over Square:
RPM: 1900
MP 20”
FF: 5 gph
IAS: 90 mph
CHT: low 300s

I've noticed a quieter ride at 1,900 / 20" than 2,350 / 20" but also more vibration (I could probably have the prop dynamically balanced for either power setting). I haven't pushed much further over square than 1900 / 20". In the mountains, especially if it's sporty, I'll cruise at 2,350 / 20" because the Husky feels like it has more energy if I need to react quickly to lift / sink or make a rapid course correction. In the flats, or a low-threat environment I have been preferring 1,900 / 20" for the fuel economy and noise.

What over-square cruise settings do you guys run?
And how far over-square are you comfortable with for max continuous cruise?
In the long term, is this bad for the engine / prop. What are the possible implications and things to look for?
I think I read in my engine book that there is a limitation of 1,850 RPM being the minimum continuous RPM.
Is running over-square unique to the Husky, since it is a relatively over-powered platform, so perhaps it isn't straining the engine / prop, like in a Cessna 172RG for example?

Slipping with Full Flaps

I couldn't find a limitation with about slipping with flaps. As a rule I have always avoided doing a slip with full flaps in any airplane due to the increased aerodynamic load on the flap and potential for elevator blanketing. Having flown a Husky A-1B with the new wing, MT Carbon prop, and 31" ABWs, the difference in descent rates is night and day between that and my A-1. I'm actually quite impressed at how well my early Husky glides even at idle power, full flaps and 26" Goodyears. I once wave soared it (clean, of course) on the lee-side of the Front Range at 15" of power (so I wouldn't shock cool the engine) from 11,500 to 14,000--granted the wave was nice that day. In order to fly a proper "back country" or relatively tight pattern, I've got slip it to get down and often quite aggressively (which is fun). Initially, slipping full flaps at 60-65 mph seems more productive than hanging it deep on the back side of the power curve at 50ish mph to get down. Depending on the scenario, I'll transition to that configuration prior to touch down. I have no problem widening out and flying an normal pattern, but I prefer to err on the tighter side.

Do you early wing Husky guys slip with full flaps?
I experimented slipping with full flaps high up early on, and felt no aerodynamic buffeting other than on the flap itself, or blanketing of the elevator. Is that something to worry about (I remember the Border Patrol accidents)?
I'll often incorporate my slip into a continuous downwind, base and final turn (while being extremely cognizant of my AOA due to the stall / spin threat) if the situation warrants it, which could increase the aerodynamic load on the down-wing flap vs a non-turning slip. Thoughts?
Are there areas I should inspect more frequently due to slipping with full flaps?

Thanks for your experience and opinions in advance!

 

[Ak Kurt]

Hi Alex,

Welcome!

So much to tell ya and I am not a big typer so I will keep it short, however, feel free to give me a call any time and I would be happy to discuss anything Husky.

I love over square power settings. I am usually 60 percent power or below so no real danger in hurting anything. I run 1950 and up to 24 inches. I have the MT Ultra (amazing prop). I almost never run under square. I encourage you to try different power settings. Keep in mind that since you are not used to the sound and vibrations of these new to you power settings give them a few minutes before you give up on them due thinking the vibration levels are high, they may actually be lower but just different. Now, if they are obviously very shaky then adjust accordingly, you will know what is too much. Don’t forget to lean and don't worry about being too lean at the lower over power settings since you are pulling low percent power. Watch your CHT’s but from the sound of it I don't think you will have a problem if you are in the low 300’s. Stay below 400.

Slipping with flaps...
Go to altitude and get in an aggressive slip with full flaps, then without exiting the slip, staying in the slip, bleed off the flaps. You will automatically increase the slip! Experiment and see what works best for you. I usually never slip since I just don't need to but if I need to I wont hesitate to slip.

I too am an ex hang glider pilot, its fun to soar the Husky. I cooled the engine and then shut it off and stoped the prop one day and thermal soared for a half an hour until I got bored. I did this in New England over my grass strip with a cloud base of around 5,000’. I could have stayed until the lift shut off but I was hungry for lunch. Fun machine!

Feel free to PM me and I will give you my phone number.

Kurt

 

[tbienz]

I have a ‘95 A-1. My belief is that the whole concept of “over square” being a bad way to operate an engine is a wive’s tale with no science behind it. It needs to go the way of ROP vs LOP. It’s fairly clear that LOP is superior, if slightly slower.
I slip with full flaps regularly and have never felt that it blankets anything.
My set up is mostly stock...no VG’s just modified seaplanes’s AK un-faired gear and 31’s.

 

[Gust Kalatzes]

I will typically run 2330 and 17 to 19 inches depending on altitude. Sometimes that’s all the power I can make at altitudes I need to fly where I go. I’ve also run 1900-2000 and 20-22”...like the first setting best but second setting is quieter and very fuel efficient.

As to slipping. I went out with Mark Heiner (one of the former Husky test pilots at the factory) and he showed me how well the Husky slips with full flaps. I can get 1800-2200 fpm decent slipping when needed. We did have the discussion about effects on the aircraft etc. There were no issues with the slip from our conversation and I’ve been using them as needed for almost 20 years with full flaps. My B has VG’s, 31’s and MT prop. I’ve never felt or seen the aircraft do anything funny from slipping.

As to the Boarder Patrol accidents. I was cautioned several times when I bought the plane not to do tight slow circles close to the ground flying through my own wake. It is said the wake or prop wash could cause the plane to stall (maybe a moose stall...not sure). I was told not to do it and don’t see a purpose for it so I’ve stayed away from them.

Best,

Gust

 

[Alex McCulloch]

Thanks for the input guys!

AK Kurt, I actually have a 30 hour KBDL overnight on Saturday, I was looking forward to a little spring in the NE. Glad to hear from another HG pilot too. I'm still flying periodically in my decade old Wills Wing T2C. I actually thermalled my Husky two turns with a Baldy today climbing out of a buddy's field. Do you think having the MT prop (less rotational mass, etc) allows more aggressive over square power settings with less vibration? I would think it would. I'll try the full flaps / no flaps in the slip up high.

Thomas, what do you typically see for ground and take off rolls, assuming a relatively flat slop and moderately smooth surface (dirt or grass)? Without being too aggressive in my technique, I'm consistently around 500 feet take off and landing (ground roll, not 50' obstacle) with half tanks, closer to 600-700 near max gross weight. Density altitude is usually between 6000 and 7000. I ask since yours in an early wing. I can make my neighbor's late-wing, MT prop one fall out of the sky and have a significantly shorter (at least it feels that way) ground roll.

Gust, if I'm crossing the Front Range low (12,500') I'm usually around 19-21" at full throttle depending on the temperature. Thanks for the input about flying with Mark Heiner. I bet that was exponentially beneficial. I've been mindful of not doing any tight repetitive circles low since I got the Husky, but I always keep that thought in the back of my mind.

 

[Gust Kalatzes]

Yes the experience with Mark was a real treat. I was a fairly new pilot then and was worth getting tips from someone who really knew the plane well.

I also get 19-21 at full throttle but in cruise, depending on temps, 17-19” is about all the power I get. Did not mean to confuse full throttle with cruise.

 

[johnaz]

I see no issue with slips, but prefer just to slow it nose up to hit my spot. Do not like to approach any faster than needed, they hang pretty good without having nose down in slip, to me that tends to make one too fast and miss your spot. They float too well with flaps with any added speed.
I have an A1 and an A1B with C wing. A1 has VG's and flies slower, but does have the break at partial power all talk about, I just never seem to fly in that realm. Like the lower speed and control of the VG's on the A1.
Both are pretty light ones, 1300lb range for both, big tires and extended cub gear. A1 has pod.
Have one with Hartzell Trailblazer and one with MT ultra. Prefer the Trailblazer. Run with oversquare on both when wanting to be economical, up to 24" and 19-2000 rpm range. I think the Trailblazer is a bit smoother and more robust, but both close in performance near as I can tell. MT is like toothpick in comparison at tips, no scimitar shape like Hartzell which looks cool. Best improvement from metal prop one can make, good weight savings too.
John

 

[Alex McCulloch]

Gust, ah, got it.

Johnaz, are you based out of Central UT? I'm at 1280ish with the 26" Goodyears. I really want to do a carbon prop when I mount the 29" ABWs. It'll even out the extra weight and improve the CG. I dig the look of the trailblazer too, but I'd be happy with either. Both are out of my budget at present.

 

[Snowbirdxx]

Ovesquare @all power settings, prefer 23/2000 for cruise. Slipping not necessary I normal ops to loose altitude, just keep13 MP and fly 135 mph. There's not shock cooling if OAT is in a survivable range. That brings you down. Slipping pleas only with door closed, we had several side windows depart.
You may try to turn the flat pitch stop out on your Hartzell. That helps too. Let me know if you need instructions.

 

[johnaz]

Gust, ah, got it.

Johnaz, are you based out of Central UT? I'm at 1280ish with the 26" Goodyears. I really want to do a carbon prop when I mount the 29" ABWs. It'll even out the extra weight and improve the CG. I dig the look of the trailblazer too, but I'd be happy with either. Both are out of my budget at present.

Alex,
A1B is in Carefree, AZ, A1 in Anchorage, AK.
You have a light one, only adds to mine for added weight is the extended cub gear and AOSS, all else too weight off. Tried all we could to get weight lower, tough to do. Think my paint on A1 is too nice and heavy!
John

 

[flyingjack]

Nice post Alex. Good stuff.

 

[jkalus]

Lycoming is careful to state that we should not use a cruise RPM that they have not published data for, specifically they mention not exceeding the MP limits on a “curve from the Engine Operator’s Manual.” That statement may be directed at the larger engines, but the lowest RPM they publish manifold pressure data for on the O-360, either charted or tabulated is 2000 RPM. Our chart has pressures as high as 28” on the 2000 RPM curve.

They also state “Low manifold pressures, below an arbitrary point of perhaps 18" for continuous cruise, may cause excessive oil usage and oil buildup in the valve guides which could lead to sticking valves.”

In this discussion, they are using the O-540 for most of their examples.


My normal cruise power setting is 2000 RPM, 19.0” or full throttle MP which ever is less, and (5.8 gph at 19.0”). I have my MT prop dynamically balanced for 2100 rpm. I use about 0.1 qts of oil per hour, which may or may not be related to the low power cruise. It was frustrating with the stock Hartzel prop trying to operate around the RPM red arc.

With regard to slips, they have their place and I’m not aware of any unusual behaviors from the Husky doing so. I had an examiner show me once that an alternative is to push the nose over to the top of the white arc with full flaps. It works quite well, and there is so much induced drag created that it will slow down rather quickly when you return to a normal attitude.

 

[belloypilot]

I have a ‘95 A-1. My belief is that the whole concept of “over square” being a bad way to operate an engine is a wive’s tale with no science behind it. It needs to go the way of ROP vs LOP. It’s fairly clear that LOP is superior, if slightly slower.
I slip with full flaps regularly and have never felt that it blankets anything.
My set up is mostly stock...no VG’s just modified seaplanes’s AK un-faired gear and 31’s.

Multi point engine monitors and actual research on test stands like the ones at GAMI in Ada have pretty much put the OWT of over square to bed. Not that there aren’t ways to operate engines that are truly abusive, but in and of itself ‘over square’ isn’t one of them. It’s all about where the peak pressure event occurs in the cycle.

If trying to run over square and vibration starts occurring I’d look for changes in CHTs on one or two cylinders and see how it behaves with changes in mixture. It’s possible you have some cylinders running slightly ROP and some slightly LOP. If that’s the cause of the shakes its wise to get out of that zone fairly quickly.

 

[Meadowlark]

OK..... I've read all of this and kept quiet..... First, over square operations are nothing new. Jimmy Doolittle proved over square operations to be beneficial in radial engines over 80 years ago. Doing so, increased fuel economy and the longevity of those engines. Second, the ability to operate a naturally aspirated engine over square is entirely dependent on the ALTITUDE you are operating at. To change that fact..... you need a turbo charger or blower to force more air into the engine. So, percent of engine horsepower is in fact a moot point in these little naturally aspirated engines and bullshit in the operations manual. It is my desire to operate my engine over square ALL the time..... Of course, that is not possible. My oil consumption has fallen to one quart ~ every 20 - 25 hours. When my engine needs another quart of oil..... The oil gets changed. Third.......TO CORRECTLY SET THE AIR / FUEL RATIO..... YOU NEED TO INSTALL AN AIR / FUEL RATIO GAUGE AND EXHAUST PROBE!!!!!!!!!!!!!!!!!!!!!!!!!! Multi probe engine monitors be damned!

I have slipped my Husky in all flap configurations. I haven't wrecked one YET because of flap configuration while slipping the aircraft. I have made very small radius turns while low and slow. Yes, I bumped through my own wake. No, I didn't crash. Stop trying to apply Super Cub traits to a Husky. They may look alike, but that is about it.....

J/C GTF & P48

 

[Alex McCulloch]

Thanks for the continued feedback everyone.

I flew again yesterday and ran 1,900 RPM / 22" MP and saw nearly identical performance to 2,350 RPM / 20" MP with slightly less fuel burn. It was 15 gusting to the low 20s cross at my home airport and very textured down low, but down the pipe at the grass runway at 18V. I should clarify, I'm only slipping when necessary for glide slope corrections, or if the situation demands it, like a short or constricted approach. Love the Husky, it's highly versatile.

John, I was asking where you were because I think FlyingJack had mentioned you. I bet you guys are already kicking it if you are in AZ.

I wouldn't say any of the vibration I experienced running over square was abnormal, I'm just not used to it yet. I have a JPI EDM700 I just installed, so I've been able to watch my how even my cylinders are running and didn't see anything abnormal at any power settings.

 

[Ak Kurt]

Fantastic Alex, keep experimenting and let us know how it goes.

Kurt

 

[GreggMotonaga]

I fly a new wing A-1B. I operate frequently at 2100 rpm and 23” if I’m low enough to make that manifold pressure. If I want to go faster, I will run it up to 23 squared.

I slip when I need to. I have performed full flap, full rudder deflection slips without any issue.

 

[Joachim Wieland]

Slipping pleas only with door closed, we had several side windows depart.

Uh. Have you seen that happen only for slips to the right or also to the left?

 

[Snowbirdxx]

3 times the sliding window got blown out, once blown in. Be careful with that door open.

 

[David]

A-1 Husky. All of my previous experience and aircraft ownership has been with Citabria's. It actually was quite a shock for me when trying to forward slip in the Husky, to quickly reduce altitude, as I had in the Citabrias. The Husky does not slip nearly as effectively! It is due to the size and shape of the Husky's fuselage and the smaller effective rudder size of the Husky. A Citabria will fall like a brick. I used to slip a Citabria from altitude to flare often. I will not do this with the Husky. I have found that the Husky's flaps and the MT's prop's braking action to be highly effective. I have only had to slip a couple of times when I have made a miscalculation on an approach and I want to get down without going around.
David