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Soooo, new PA-18, prop strike

E

ExConPilot

Registered User
Oregon
I have been flying for 45 years, 747's to champs. 34,000 hours. Bought Cubcrafters PA-18-180.... did not realise how forward the CG was empty... hit the brakes, bagged the prop, now a new prop and OH engine later, flying again. Seems the Cubcrafters first 5 "Top Cubs" were very forward CG. I placed 60 # sand in tail, better. Still, when approaching at 50, no flare left, have to add power. Can approach 45, but have to add a lot of power. Told gap seals help, kit on the way.... what has been the experience for those with or without the gap seals? Also, this is a PA-18 - 180 Cubcrafters .... 180 HP with fixed Sensenich... lots of weight forward, add to that more incidence, and elevator stalls early... would like to land slow without a quick stab of power, what say you?????
 
Where is your trim??? Trim for touchdown airspeed on approach, I normally land with full nose up trim 14/1600 rpm to help prevent the situation you discribe. Landing like this you will have forward stick pressure on approach, not back pressure. Takes a while to get used to but now you horizontal stabilizer is helping hold the tail down and not fighting the elevator.
DENNY
 
You need Mark's ThrustLine mod. Also add VG's (Micro) to solve that early tail stall condition.
I had a widebody PA-18 with a O-360/180hp. It had the CC elevator and rudder gap seals. Worth the money. Good luck!
Lou
 
DENNY said:
Where is your trim??? Trim for touchdown airspeed on approach, I normally land with full nose up trim 14/1600 rpm to help prevent the situation you discribe. Landing like this you will have forward stick pressure on approach, not back pressure. Takes a while to get used to but now you horizontal stabilizer is helping hold the tail down and not fighting the elevator.
DENNY
Click to expand...
cUBCRAFTERS ADDED INCIDENCE, AND A STRAKE, BUT THE NORMAL CRUISE TRIM IS FAIRLY NOSE DOWN. eLEVATOR STALLS EARLY WITH FORWARD CG. STRAKE HELPS, BUT GOING TO TRY GAP SEALS ON RUDDER AND ELEVATOR. ALREADY HAVE VG'S ON WING. WISH ELEVATOR HELD ON A FEW SECONDS MORE....
 
Seals on the tail help elevator authority in my experience from two planes. Also VG's or side strake in back. Use back of the drag bucket power to keep the tail alive.

Gary
 
Dont land with full flaps, that will help, try half flap. Approach and stall speed will not increase much. Also, quickly dumping flaps on landing helps bring the tail down and allows for more braking without tipping up on the nose.

Kurt
 
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Yeah, I'll try that! I was new to the Top Cub, flying RV's, Commanders, and Boeings for 30 years.... Was taxiing to active runway, approaching hold short line... gosh, no toe brakes, got on the heel brakes (Boosters!!!!) foot slipped off...Tower yelled "STOP!!!!!!!" as I looked up, hit the heel brakes a bit too hard (Me in Top Cub, low fuel, very forward CG....) and the aircraft nosed over. I just finished a Major OH on the engine, used "Rick Romans" in Tulsa for parts inspection (Talk to Mike.. great guy, knows his stuff...) and bought a prop from Dennis Whittenberg (good guy, knows cubs...) and trying to see what works and what doesn't. Seems Cubcrafters placed more incidence in the wings on the first 5 prototype Top Cubs, and as a result, the Stab has to be trimmed fairly forward in cruise, elevator stalls out on landing... Have VG's on wing, Strake on HS; will put gap seals on elevator and rudder, see what happens. Will see how it flies with 1/2 flaps! Thanks for the info!!!

Gary
 
Don't try to land without adjusting trim. It is a cub, not a lot of things to play with on final SO ADJUST THE TRIM. don't touch the stick on final just add nose up until you have the TOUCHDOWN airspeed you want. You should not need 1/2 flaps, gap seals, or any weight in the back for most cubs even 180's. Get up high and do full flaps and full nose up trim at 1400-1600 RPM see what it does. That put the case of oil in the baggage stuff is when you only have a trim tab. A cubs tail will fly just let it do its job. Dumping flaps on touchdown is also a great ideal.
DENNY
 
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So it was on taxi, not landing. Any taildragger will go on its nose in a heartbeat at low taxi speed and full brake application.

I started hearing about experienced pilots going on their nose on the taxiway. Then what happened to you happened to me - almost identical, except by the time the tail was a foot in the air I was off the brakes, and not even embarrassed - just enlightened. A month later I started down the wrong alley in my Dec - panic brake, tail off the ground. Quick brake release again saved my ass. We are talking really slow speed here.

Friends with your kind of experience have gone on their nose on the taxiway! The first thing I tell my students is how quick that can happen. I tell them that several times - I do not demo it.

Have never flown the Top Cub, but I have some pattern time in one of the 180CCs that Cub Crafters made from the Piper type certificate. It seemed to land normally, even with 26" blimp tires. It was a pig of an aircraft, but if coaxed it would go straight up. The 160 is a better Cub engine, in my opinion.
 
This begs the question for the need for excellent brakes. When are they required and what are the cautions? Think about when brakes made the day at low load and forward CG vs fat and heavy need to stop now ops. I've eaten a prop in a PA-18A because they are preloaded too much by the tech and I was ignorant what rising temps could do to the system. Stop on a dime and get 5 cents change has limits.

My PA-12-180 had forward CG and real double puck Cleveland toe brakes. Al Wright said "easy does it". He was right as always.

Gary
 
For myself I would like the best of everything! It is up to me as a pilot to make it work!!! I think brakes are a important and under utilized part of training/landing. They can save you from a lot of bad landing errors!! But as everything else in life too much of a good thing can be bad. If you need to use brakes consider only one at a time and wag the tail (this requires practice and is very effective) But it does slow the airplane. I do know a very good pilot that got a prop doing this so I would add the nose up trim also.
DENNY
 
To be clear, yours is a CC-18, not a PA-18?

The reason I ask is that they are two different planes. different GW, different mods available.

Lighter starter, alternator and such. The CC cubs are heavy. Big tailwheel also helps, but mostly you need to slow down and learn to fly that plane, it is different than the champ and citabria birds.
 
I believe large soft tires can forgive excessive braking. They compress under loads and flatten at ground contact absorbing energy versus rolling the airframe around harder tires and ultimately the axles.

Gary
 
What is your ACTUAL CG? What are your CG limitations? Is there a gross weight/CG slope on the forward limitation of the graph?

Your description makes it appear that you are operating outside the forward CG limit. Before you attempt to fix it with band aids, get your CG under control.

This is the type certificate for the CC18-180:
https://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/37ac4bb22eb2d2b18625804b0054758c/$FILE/A00006SE_Rev_8.pdf
 
I have a lot of time in one of the early CC180 cubs, in fact it was one before they were really CC180. It was legally a PA18 with 20 STC’s but it had all that, 180, strakes, VG, and I have to say it did not strike me as having any of the bad habits as described.

But, as Bob said if you jump on the brakes on many tail draggers you could have a problem. Saw a Husky with two guys in it go up on its nose at the hold short line.

Rich
 
It seems counterintuitive but your left hand should always be ready to blow the tail down.
Are you landing with cruise trim?

Glenn
 
I started out in J3 and the tail can be lifted with a pinky finger when at forward legal cg limit.. I taught myself to never brake both wheels at the same time. On landing if I needed to use max brake I did it pumping one than other rapidly, the tail never leaves the ground.. I always did this on turf though.. I have seen guys been put on nose taxing in strong winds, might have been combo of wrong stick position and light braking.. if youre taxing at slow safe speeds I dont think it will go on nose easy, taxi as if you dont have brakes.. that slow.
 
This was a ground incident, so while FLYING CG is not completely moot, it was probably not your issue...
The only modification cure for your 3pt CG is 3x3 gear, but the real cure is increasing your currency / proficiency. Knee jerk reactions are not mechanically cured, I'd rather have more brake I could control than not enough when I needed it.
Oh, and please lose the sand before you nose over again and it comes lose and kills you.
If you are still compelled to address the CG, start by trading in the hartzell for a composite sen.

Take care, Rob
 
. . . if youre taxing at slow safe speeds I dont think it will go on nose easy, taxi as if you dont have brakes.. that slow . . .

I disagree. This is insidious. I had been flying Cubs for almost a half century when I realized what was happening - we had a rash of taxiway noseovers. And it is not the fault of too much brake pad area or sophisticated double puck Clevelands and Dakota masters.

Here is the scenario: "Cub 123, cleared for immediate takeoff!" You are ten feet from the hold line, at a dead stop. Release the brakes, add power . . . "Cancel takeoff clearance, hold short . . ."

So you do what all of us do - power to idle, jump on the brakes. It is an automatic reflex. If you then do not immediately get off the brakes you will be on your nose. It doesn't make any difference how nose-heavy you are, or how good your brakes are, or how big your tires are. Don't jam on the brakes at slow taxi speeds.
 
What Rob said ^^^. I have some time in a very low serial number CC 18 180, and never found it to be unusually nose heavy. BUT, those airplanes all have the North River brake boosters, and they are very effective at increasing braking power.

MTV
 
bob turner said:
. . . if youre taxing at slow safe speeds I dont think it will go on nose easy, taxi as if you dont have brakes.. that slow . . .

I disagree. This is insidious. I had been flying Cubs for almost a half century when I realized what was happening - we had a rash of taxiway noseovers. And it is not the fault of too much brake pad area or sophisticated double puck Clevelands and Dakota masters.

Here is the scenario: "Cub 123, cleared for immediate takeoff!" You are ten feet from the hold line, at a dead stop. Release the brakes, add power . . . "Cancel takeoff clearance, hold short . . ."

So you do what all of us do - power to idle, jump on the brakes. It is an automatic reflex. If you then do not immediately get off the brakes you will be on your nose. It doesn't make any difference how nose-heavy you are, or how good your brakes are, or how big your tires are. Don't jam on the brakes at slow taxi speeds.
Click to expand...

I have never put one on its nose, 2000 hours Super Cub time, I have seen it done a couple times but I have always been careful I guess. The only time I did get a little nervous was in a J3 and strong surface winds and a downwind taxi, I just taxied at walking speed and no issue.
If you need to use heavy brake than ONE at a time, it cannot go on its nose. Firm pressure one side than the other, you do it fast left heel than right heel.
 
ExConPilot said:
..... Still, when approaching at 50, no flare left, have to add power. Can approach 45, but have to add a lot of power. Told gap seals help, kit on the way.... what has been the experience for those with or without the gap seals? Also, this is a PA-18 - 180 Cubcrafters .... 180 HP with fixed Sensenich... lots of weight forward, add to that more incidence, and elevator stalls early... would like to land slow without a quick stab of power, what say you?????
Click to expand...

Rob said:
This was a ground incident, so while FLYING CG is not completely moot, it was probably not your issue...

Take care, Rob
Click to expand...
Rob, The damage was done during a ground incident. However, there is also a complaint about not enough up elevator control in flight. That is very likely a CG issue and could contribute to the nose over incident.
 
Simple things first. Confirm the plane's controls and trim including stick movement (front and rear) conform to the TCDS or Service Manual's specs.

Gary
 
BC12D-4-85 said:
I believe large soft tires can forgive excessive braking. They compress under loads and flatten at ground contact absorbing energy versus rolling the airframe around harder tires and ultimately the axles.

Gary
Click to expand...
Which maybe almost offsets the increased moment arm from the taller footprint. Big tires help, until they hurt...
 
+1 on alternating brakes. It’s easy to say that here at my table, but another thing to do it when ATC tells you to stop right now. I imagine it would be REALLY hard to do when you’re going against 34,000 hours of braking experience. [aside: I’d love to sit down with a 34,000-hour pilot some time. Please let me know if you’re ever in the Midwest!]

Is there a way you could remove weight from the nose rather than add some to the tail?
 
As an experiment try lifting the tail for planes of close to equal weight equipped with small tires like 8:00x6 vs 29-31-35"x6. From what I've noticed the bigger the tire (or taller the axle) the heavier the tail in 3-point.

Gary
 
That is sort of true, but the higher center of gravity is what you are dealing with. The angle changes very little, but the length of the seesaw goes up as you extend the gear and enlarge the tires. Train yourself to not jump on the brakes at low speed. You can screech the tires at high speed, because of airflow over the empennage, but get off them at slower speeds.

Also consider - folks who go for big tires also go for other heavy mods. It is really rare to see a stock Cub with anything bigger than 26" tires. I can no longer lift any Super Cub by the tail handle.
 
BC12D-4-85 said:
As an experiment try lifting the tail for planes of close to equal weight equipped with small tires like 8:00x6 vs 29-31-35"x6. From what I've noticed the bigger the tire (or taller the axle) the heavier the tail in 3-point.

Gary
Click to expand...
Wouldn't disagree but you also have additional force to overcome when you have to arrest that forward motion that is created by the longer moment arm when you hop on those boosted brake prop- flatteners.
 
I have a lot of CC-18 time. Basically the first 70 aircraft they produced of that stamp were before the type certificate had been awarded, so there are a bunch of PA-18-180 aircraft that are functionally identical to the CC-18.

There is a huge difference between the behavior of the brakes with 31" Bushwheels and the smaller 8.50x6s. The brakes seem fairly optimized for the larger tires, and feel right. They are extremely touchy with the smaller tires, and minimal application is necessary or they completely grab.

Whether this is germaine to the OP is not clear to me, but that is my experience in the CC-18.
 
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