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-   -   Speedbrakes on the RV-10 (https://vansairforce.net/community/showthread.php?t=154854)

RV10inOz 12-22-2017 05:55 AM

Quote:

Originally Posted by DanH (Post 1226734)
Come on guys, skip the 'learn to fly" lecture. Scott's RV-10 is not like yours, he understands speed management, and he has a reason for asking.

Well maybe in future he should articulate that. :confused::mad::cool:

Not everyone is a mind reader.

DanH 12-22-2017 08:17 AM

Perhaps an analogy; we have a few readers old enough to have flown the early turbojets. Recall that many of those airplanes deployed drag devices for the approach, with the specific goal of enabling a higher power setting while flying a descent.

This photo illustrates a similar aspect of flight management with the 200-series diesel. Here Scott is turning base for KFFC's R31, elevation 807 ft. Remember, he cannot dip below 30" MP, or allow CHT below 212F.



Can't chop and drop (minimal prop braking, and it's already near minimum power anyway). Can't push the nose down (the RV-10 is slicker than a Skylane). To make a normal pattern size work in KFFC's traffic, Scott started descent at midfield; we're at 700 AGL in the downwind to base turn. He keeps it nailed dead on 500 FPM with the speed creeping back, all the way to the flare. On the runway, CHT is a little less than 230. No problem for a pro.

The catch? This was a 70F day in Atlanta. Consider a 0F day in Chicago or Calgary. Given the OAT, it's going to be hard to fly an approach at the required 45" MP.

It's not a problem. it's just an engineering task, developmental work to match an airframe to an engine.

Ron RV8 12-22-2017 08:19 AM

If you like I can expand a bit on the characteristics of the Precise Flight brakes I had on the Mooney. YMMV on the -10...

They came with the plane and I quite liked them. When I looked at them for the -8 I could not justify the additional cost and figured I could add them later if I really missed the functionality. You really want to keep your diesel warm, so another "tool" in your kit would be useful...

Sorry but I never really made note of speed change in level flight as I was usually throttling back as well or joining up with someone else and not really looking inside. The button was right beside the throttle so I did not have to look for it. I do miss them for that function and end up reducing power a lot more to compensate...

As I said before, at cruise power, popping the brakes gave 1500fpm down instantly.

Having one brake stick up was a "non event", happened only a couple of times on landing due to pre-takeoff water which had frozen.

Taking off or making a go around with the brakes accidentally extended was also a "non event". Eventually you notice the drag as you try to accelerate and slap yourself on the forehead... Not even noticeable on initial climb out...

It was explained to me that the brakes were far enough back on the wing to have little affect at low speeds and high angles of attack, thus the small impact when landing and taking off...

The brakes on the Mooney had been installed by a previous owner and did not look too difficult.

They were deployable at any speed. Nice when you're cresting a mountain ridge or even just getting down to flap speed...

Overall I was impressed with their product and was always amazed at how effective those little blades were at cruise speed... If I had a need I would not hesitate to install them again, but so far with the -8 I'm happy without...

Hope this helps...

KatanaPilot 12-22-2017 08:31 AM

Quote:

Originally Posted by DanH (Post 1227196)
Perhaps an analogy; we have a few readers old enough to have flown the early turbojets. Recall that many of those airplanes deployed drag devices for the approach, with the specific goal of enabling a higher power setting while flying a descent.

This photo illustrates a similar aspect of flight management with the 200-series diesel. Here Scott is turning base for KFFC's R31, elevation 807 ft. Remember, he cannot dip below 30" MP, or allow CHT below 212F.



Can't chop and drop (minimal prop braking, and it's already near minimum power anyway). Can't push the nose down (the RV-10 is slicker than a Skylane). To make a normal pattern size work in KFFC's traffic, Scott started descent at midfield; we're at 700 AGL in the downwind to base turn. He keeps it nailed dead on 500 FPM with the speed creeping back, all the way to the flare. On the runway, CHT is a little less than 230. No problem for a pro.

The catch? This was a 70F day in Atlanta. Consider a 0F day in Chicago or Calgary. Given the OAT, it's going to be hard to fly an approach at the required 45" MP.

It's not a problem. it's just an engineering task, developmental work to match an airframe to an engine.

Today's high bypass turbofans all have high idle thrust. Some have a "flight idle" mode triggered by flap extension. Primary reason is to meet Part 25 requirements for an 8 second limit from idle to go around thrust. The 787 is a model of efficiency - and yet it has speedbrakes to assist with energy management, as do all of the Boeings and Airbuses. The use of speedbrakes is often necessary and not an indictment of the pilot's skills.

If I recall correctly from articles published years ago when Cessna was flight testing the SMA diesel on the 182, one of the issues was low power descents and their effect on engine temperatures. The diesels on the Diamonds (Thielert/Continental/Austro) have operational limitations too and they are liquid cooled.

So Scott's request for information on speedbrakes seems perfectly logical to me.

rocketman1988 12-22-2017 09:17 AM

Yep
 
"...The use of speedbrakes is often necessary and not an indictment of the pilot's skills..."

You would be surprised at the number of people I work with that do not understand this point...

It always cracks me up when they refuse to use everything available because of a perceived deficiency in their skills...

woxofswa 12-22-2017 09:45 AM

In the spirit of the learning value of discussion, I would like to further expound.
I’ve flown airliners with speed brakes for almost 30 years. Yes airliners have to have them and there are certain situations, usually (but not always) attributed to sloppy controller and/or pilot work where they are necessary. They are also necessary to meet requirements for emergency descents. (Something not a player in the RV world). I’ve flown with crewmembers who use them every leg and others who might deploy them once or twice over a four day sequence. I tend to fall in the latter category.

It all boils down to physics and chemistry. A pound of fuel contains a certain quantity of chemical energy. Burning that fuel to convert the energy within creates positives and negatives. The positives are stored reserves of energy in the form of speed and altitude, and the negatives are wasted and useless heat.

All airplanes are compromises as energy converters. Mine has A/C. I have electively chosen to trade a cost, weight, drag, and engine power tap in exchange for being comfortable in the Arizona summer and having a happy wife.
My goal for my airplane was just a comfortable cruiser.

I’m not going to presuppose why someone else built their airplane the way they did. Having said that, if I were going to build a TDI 10 (something I considered), the defining goal of the project would be EFFICIENCY. Trying to get the ship from Point A to point B on the fewest fuel calories consumed. A passionate quest for that almighty SFC that blows the others away. That in my opinion is what justifies the extra time, money, and hassle, over simply hanging a Lycoming. Someone else’s goals may be entirely different.
Refining the holy efficiency quest goes back to the previous stored reserves of speed and altitude that we extract from our investment of fuel and wringing them out to the fullest return. Speed brakes, by design are an antithesis to that quest. They take the positive energy bought and paid for and dump it overboard trashing the SFC charts, and in my mind, the whole purpose of the conversion. I dont mean to be argumentative or disrespectful. I am actually in awe of what has been accomplished so far. Nevertheless, One schmoes’s opinion would be to look for a less wasteful solution.
Good luck and best wishes.

rocketman1988 12-22-2017 09:57 AM

Discussion
 
So in light of your post, how do you usually fly cross country in your -10?

I am not flying yet, so I am curious. Some guys, in search of that "efficiency" attempt to find the sweet spot between speed and fuel efficiency...others seem to open her up and let her run.

What is your technique?

Auburntsts 12-22-2017 10:09 AM

Quote:

Originally Posted by rocketman1988 (Post 1227231)
So in light of your post, how do you usually fly cross country in your -10?

I am not flying yet, so I am curious. Some guys, in search of that "efficiency" attempt to find the sweet spot between speed and fuel efficiency...others seem to open her up and let her run.

What is your technique?

Can't speak for Myron, but I fly between 8000 and 10000 (I don't have O2), WOT, leaned to 11.5 gph, 2350 RPM which usually nets me 160 KTS TAS. More often then not I'm also close to or at my GW of 2700lbs.


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