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RV 7 takeoff issue/question

Kofficer

Member
Having a takeoff issue with my RV7 (not A) and wondering if anyone else has encountered this problem. First let me say,I have have several hundred hours flying this plane with 100?s of takeoffs without any issues. I have had this problem occur on about 12-15 takeoffs over 4 years and not sure if it is a mechanical issue or just something I may be doing wrong. It has mainly occurred on a grass field (sometimes wet), but has occurred a couple times on pavement. My normal takeoff is to slowly add power, push stick forward to get tail up then plane basically flies off ground with a slight back pressure. Issue I am having is that the plane appears to stick to the ground and slight back pressure will not break ground. I keep applying back pressure and the plane will eventually ?leap? into the air with nose high attitude. It did it for 2 takeoffs in a row on wet grass the other day. Things I did to possibly correct , but didn?t help: I checked my elevator trim, made sure I wasn?t pressing brakes : tried not raising the tail so high, none of these helped/solved it. Went today and made several takeoffs from another field, no issues. Anyone else had this happen and found or discovered the issue?
 
Lots of drag from grass; lots more from wet grass. That will tend to pull the nose 'down' a bit, maybe making it feel like it's sticking to the ground. Are you using any flaps on takeoff? If not, try ~1/3 flaps. You should be able to use even full flaps, but not needed. First time I forgot to raise flaps after landing, & took off with full flaps, I thought I'd mistakenly gotten on an elevator. Not nose up climb; just levitation off the grass strip. And I fly off grass all the time; I'm based on grass.

I suppose you could have sticking brakes, but the idea of having both stick at the same time is a stretch.

edit: My experience is in a 160 HP -4, but I'd expect your characteristics would be similar.

Charlie
 
Visually verify that your trim tab is in trail with the elevator and note the position of your trim indicator. I have seen the trim indicators act up and show a false trim tab position. Most airplanes I have flown will need slight nose up trim just after liftoff when the takeoff is started with the tab in the trail position. I have forgotten to reset my trim for takeoff from what was used on the previous approach and it flys completely different.
 
Partial flaps for ?soft field?

Lots of drag from grass; lots more from wet grass. That will tend to pull the nose 'down' a bit, maybe making it feel like it's sticking to the ground. Are you using any flaps on takeoff? If not, try ~1/3 flaps. You should be able to use even full flaps, but not needed. First time I forgot to raise flaps after landing, & took off with full flaps, I thought I'd mistakenly gotten on an elevator. Not nose up climb; just levitation off the grass strip. And I fly off grass all the time; I'm based on grass.

I suppose you could have sticking brakes, but the idea of having both stick at the same time is a stretch.

edit: My experience is in a 160 HP -4, but I'd expect your characteristics would be similar.

Charlie

Mike Seager teaches using partial flaps for soft field takeoffs (no flaps for pavement or firm dry turf). Basically he recommends lining up the flaps with the ?down? aileron when the ailerons are fully delftected to gauge the correct amount of flap deployment.

Also, the typically recommended technique for taildragger soft field takeoff is to only lift the tail wheel ~ 1? off the ground during the takeoff roll, then hold it in that position until the mains lift off. When the mains are off the ground ease off the back pressure to allow the plane to accelerate in ground effect until Vx before starting the climb. Don?t forget to retract the flaps once airborne and accelerated.

Skylor
 
I/We assume yr CG is the same on all these t/off's?
As mentioned drag which comes in all forms can vary the requirements to break ground. I rarely use flaps in my 8 as it jumps off the deck like a scolded cat but do notice a slight difference when wet. I tried flaps one day on a soft surface and it levitated before I had all the horses on song.
As mentioned check trim tab position, usually a slight downwards deflection is needed for a normal t/off.
Hope you find what the issue is, seeing as it's not al the time something is different there on the odd occasion -:)
 
Thanks for replies. I have tried using a some flaps and seems to help, but still did it once. Have checked trim tab and appears proper, and I agree that I usually use a little down trim for takeoff. One thing I haven?t tried and not sure if this would be proper. I am pulling back on stick and it doesn?t come off like usually, so I keep pulling back further to where it literally breaks ground and jumps off nose high. Literally feels like it is stuck to ground. Wondering if I should not keep pulling back and eventually it will fly off or if it is sticking would it just pick up even more speed and eventually lift off or could this possibly damage gear,etc?
 
Not for the original poster question but:

Here is a taiwheel technique me and my buddy like to teach and practice.

We believe forcing the tail up is good for a couple good reasons.

1) Zero AOA on wing to prevent "skipping" as airplane accelerates up to flying speed.

2) Less drag than tail low, allows faster acceleration

3) Rudder is in clean air helping with effectiveness if a cross wind gust is encountered.

Tail low lift off is ok mainly in calm winds.

You can also begin your takeoff roll Zero flap and pop in a short burst to get you airborne below Vs in ground affect. As stated, don't forget to accellerated to Vx or Vy before you begin your climb out to ground effect.

It happens quick but my friends and I believe this is the fastest way out of a strip with the least amount of runway needed.

Lastly you can begin your power application facing 180 away from your runway. While turning to line up, add full power. The left tuning tendencies will help bring your airplane around the last 90 deg and you will be at full power with the least amount of propeller slippage.

YMMV
 
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Here is a taiwheel technique me and my buddy like to teach and practice.

We believe forcing the tail up is good for a couple good reasons.

1) Zero AOA on wing to prevent "skipping" as airplane accelerates up to flying speed.

2) Less drag than tail low, allows faster acceleration

3) Rudder is in clean air helping with effectiveness if a cross wind gust is encountered.

Tail low lift off is ok mainly in calm winds.

You can also begin your takeoff roll Zero flap and pop in a short burst to get you airborne below Vs in ground affect. As stated, don't forget to accellerated to Vx or Vy before you begin your climb out to ground effect.

It happens quick but my friends and I believe this is the fastest way out of a strip with the least amount of runway needed.

Lastly you can begin your power application facing 180 away from your runway. While turning to line up, add full power. The left tuning tendencies will help bring your airplane around the last 90 deg and you will be at full power with the least amount of propeller slippage.

YMMV

Respectfully, with 45 years of flying over 30 different types, I find all the techniques mentioned above to be hyper aggressive lacking emphasis on good airmenship skill set.
Believing of course you have a recomended engine and not a 85 horsepower VW engine requiring 3000? of runway. ?Pop a short burst...? ....interesting.
R
 
sorry. should have specified. Pop the flaps (if you have manual) is what I meant to say.

here is a good article. Not RVs but a fun read: "pop the flaps" is a little past the half way point.

https://backcountrypilot.org/stol-tips/stol-tips-takeoff/32-stol-tips-takeoff

I have electric on my 6 and set to in line with the aileron as others have mentioned.

Those techniques come from my missionary pilot bud who flys the rivers and jungles in Peru. Lots of max wt / DA issues with one way in / one way out types of places where inches count.

When he rotates back to the US (no pun intended) every few years, we have our own STOL contest on as many grass strips as we can find around here in TX.

The great news is that RVs fly so good, we should never have to use most of that stuff. But if you want to practice it, it may come in handy someday.
 
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Ok...thanks for clarifying. Your buddy is applying special skills to meet demanding unusual conditions. Here, with very limited understanding as to what is perplexing the thread ops, we?re offering ideas to try to improve his chances of solving a riddle.
My first take is he is preventing the aircraft from flying with pitch. Maybe he learned in a 65hp J3 and thinks the 7 should be flown the same way.
I recommend explaining to and working with a RV instructor to solving the mystifying ?sticking?.
I?m ready to learn more things.

R
 
Hopefully the Original Poster discovers it's something simple like trim that Titanhawk mentioned.

Great thing about VAF is everyone is always learning from each other.
 
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I had a weird problem with my RV-4 was not accelerating and taking off as quickly as expected. Brake pads were worn, caliper pucks were sticking out so far, they were binding and brakes dragged. On asphalt ramp I tried moving the plane by hand, could feel it. New pads solved the issue.

Not to get into the pilot technique of how to takeoff in an RV w/ conventional gear, the OP may consider conditions at takeoff (winds, temp, AC weight, runway condition "wet grass" or not) and note airspeed when it became unstuck. It may be performance related issue, meaning normal. I know flying my RV-4 at gross with passenger it flew very differently than solo.
 
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Great point about brakes.

I forgot to mention something I include in every Flight Review. The 70 / 50 rule. A few years ago we had a double fatality at our airport where this may have saved them. When I flew the Falcon 2000, we would do an accelleration check on every takeoff. So in high weight situations taking off from Aspen in the summer with an 8 knot tail wind, you could see if everything was going as planned.

In GA I heard about the 70 / 50 rule and begin teaching to everyone I've flown with. Here is a good link. It's great for shorter runways and evaluating engine health during takeoff while things are happening fast.

https://www.boldmethod.com/learn-to...he-50-70-rule-of-thumb-for-your-safe-takeoff/

I encourage everyone I fly with to round up to their 70% of rotation speed and verbally call it out during takeoff. If I don't have that speed by the fuel pumps or whatever a 50% down the runway point than thats the abort decision.

We have a decision speed in 121. My buddies who fly bush do it. And I hope all the flight review people I sign off do it. 70/50 may have saved 2 folks at our airport who didn't make it.
 
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Great point about brakes.

I forgot to mention something I include in every Flight Review. The 70 / 50 rule. A few years ago we had a double fatality at our airport where this may have saved them. When I flew the Falcon 2000, we would do an accelleration check on every takeoff. So in high weight situations taking off from Aspen in the summer with an 8 knot tail wind, you could see if everything was going as planned.

In GA I heard about the 70 / 50 rule and begin teaching to everyone I've flown with. Here is a good link. It's great for shorter runways and evaluating engine health during takeoff while things are happening fast.

https://www.boldmethod.com/learn-to...he-50-70-rule-of-thumb-for-your-safe-takeoff/

I encourage everyone I fly with to round up to their 70% of rotation speed and verbally call it out during takeoff. If I don't have that speed by the fuel pumps or whatever a 50% down the runway point than thats the abort decision.

We have a decision speed in 121. My buddies who fly bush do it. And I hope all the flight review people I sign off do it. 70/50 may have saved 2 folks at our airport who didn't make it.
Excellent. While I understand the Jet world has a published abort protocol, why not apply something simple like this to us. This is easy to wrap ones head around.
 
I/We assume yr CG is the same on all these t/off's?
As mentioned drag which comes in all forms can vary the requirements to break ground. I rarely use flaps in my 8 as it jumps off the deck like a scolded cat but do notice a slight difference when wet. I tried flaps one day on a soft surface and it levitated before I had all the horses on song.
As mentioned check trim tab position, usually a slight downwards deflection is needed for a normal t/off.
Hope you find what the issue is, seeing as it's not al the time something is different there on the odd occasion -:)

It has been proven that "popping" the flaps during the takeoff roll actually lengthens the takeoff roll because your other hand bobbles the stick. Set the flaps before the start of the take off run. It has the benefit of reducing the weight on the tires sooner, reducing rolling resistance.

Also, DO NOT touch the flaps or anything else until you have climbed above any surrounding trees! I had the "pleasure" of watching a friend get blown into the trees while he was reaching down to retract the flaps. He got really lucky and only lost his wingtip.
 
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Sticky brakes

My brakes stuck with me once and as soon as I got airborne it leaped forward like you are describing. Just a data point....
 
Takeoff

Hey Kurt, when your brakes stuck, did it feel like it did not want to leave the ground and took a lot of back pressure to get it to break ground? I am thinking that may be the issue and currently doing new brakes , bearings and cleaning. I tend to feel it is a mechanical issue or wet grass since I have had hundreds of good takeoffs and only a handful of these jumps. Has happened with different cg ?s and no shortage of power with my 195hp. Also has happened with tail low or tail high and with flaps and no flaps.
This forum is great to help solve issues,thanks again everyone!
 
As you go through the brakes, make SURE that the brake pedals are fully retracting every time you release the brakes. There are numerous posts on the forum about the master cylinders on the rudder pedals not fully retracting. this can cause brakes to drag.

It goes without saying that you need to make sure your feet are fully off the brakes during takeoff, but I said it anyway!:rolleyes:
 
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